Patella Dislocation (Adult)

1. Clinical Overview

Summary

Acute patellar dislocation is a common traumatic knee injury characterized by lateral displacement of the patella from the trochlear groove of the femur. It represents the second most common cause of acute traumatic hemarthrosis in young adults after anterior cruciate ligament (ACL) injury. [1] The peak incidence occurs in adolescents and young adults aged 10-25 years, with an overall incidence of 5.8-29 per 100,000 population per year. [2]

The primary pathoanatomical lesion in acute patellar dislocation is rupture of the Medial Patellofemoral Ligament (MPFL), which provides approximately 50-60% of the restraint to lateral patellar translation in the first 0-30 degrees of knee flexion. [3] The MPFL arises from the medial femoral epicondyle (specifically Schottle's point) and inserts onto the superomedial pole of the patella.

Key Facts

Anatomical Stabilizers of the Patella:

1. Static Soft Tissue Restraints:

   • MPFL (Primary): Provides 50-60% of restraint to lateral translation at 0-30° flexion [3]
   • Medial patellomeniscal ligament (MPML)
   • Medial patellotibial ligament (MPTL)
   • Medial retinaculum

2. Static Bony Restraints:

   • Trochlear groove: Provides bony constraint at > 30° flexion
   • Trochlear depth and morphology critical for stability

3. Dynamic Muscular Restraints:

   • Vastus Medialis Obliquus (VMO): Provides dynamic medial stabilization
   • Overall quadriceps muscle balance

Critical Statistics:

• First-time dislocation recurrence: 15-44% in general population, up to 50-60% in adolescents [4]
• After second dislocation: Recurrence rate increases to 50-70% [5]
• Osteochondral fractures: Occur in 20-50% of acute dislocations [6]
• MPFL injury: Present in > 90% of acute patellar dislocations [7]
• Conservative management success: 50-70% for first-time dislocation without anatomical risk factors [8]

Clinical Pearls

"The J-Sign": With the patient seated and knee flexed to 90°, observe patellar tracking as they extend the knee. In the final 10-20° of extension, the patella may abruptly "jump" laterally out of the trochlear groove. This pathognomonic sign indicates patella alta, trochlear dysplasia, or MPFL insufficiency, and predicts recurrent instability.

"Fat Globules = Fracture": Aspiration of knee hemarthrosis revealing fat globules floating on the blood surface (lipohemarthrosis) is pathognomonic for intra-articular fracture, typically an osteochondral defect. This mandates immediate MRI or arthroscopy.

"Schottle's Point Tenderness": Maximum tenderness located at the medial femoral epicondyle, just anterior and distal to the adductor tubercle, indicates MPFL femoral avulsion—the most common site of rupture (50-70% of tears).

"The Relocation Injury": Most osteochondral damage occurs NOT during dislocation but during spontaneous reduction. As the patella relocates, the medial patellar facet impacts violently against the lateral femoral condyle, shearing off cartilage and subchondral bone.

"Redislocation Risk Stratification": First-time dislocators with ≥2 of the following have 70% recurrence risk: age less than 16 years, skeletal immaturity, contralateral instability, trochlear dysplasia, patella alta, or TT-TG distance > 20mm. [9]

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2. Epidemiology

Incidence and Prevalence

• Overall incidence: 5.8-29 per 100,000 population per year (varies by study methodology) [2]
• Peak age: 10-17 years (incidence up to 43 per 100,000) [10]
• Adult incidence: 5.8 per 100,000 per year [2]
• Lifetime risk: Approximately 0.5-1% of the population
• Bilateral instability: Occurs in 15-25% of patients with patellar dislocation [11]

Sex Distribution

• Female predominance: 2:1 female-to-male ratio [10]
• Higher rates in females attributed to:
  • Increased Q-angle (physiological genu valgum)
  • Greater ligamentous laxity
  • Different vastus medialis obliquus (VMO) activation patterns
  • Increased trochlear dysplasia prevalence

Mechanism of Injury

Low-Energy Mechanisms (Most Common - 70-80%):

• Twisting injury on planted foot
• Valgus stress with knee in flexion (0-30°)
• Sudden quadriceps contraction with external tibial rotation
• Change of direction during running/cutting sports
• Non-contact injury predominates

High-Energy Mechanisms (20-30%):

• Direct lateral-to-medial blow to the patella
• Dashboard injury
• High-velocity sports collision

Sport-Specific Risk:

• Soccer, basketball, gymnastics, dance highest risk
• 60% occur during athletic activity [10]

Anatomical Risk Factors ("The Terrible Tetrad")

1. Trochlear Dysplasia

• Prevalence: Present in 85-96% of recurrent dislocators vs. 3% in normal population [12]
• Definition: Abnormal morphology of the femoral trochlear groove
• Classified by Dejour system (A-D, see Investigations section)
• Pathomechanics: Reduced bony constraint allows lateral patellar translation
• Strongest independent predictor of recurrent instability [12]

2. Patella Alta (High-Riding Patella)

• Prevalence: 20-40% of patellar dislocators [13]
• Definition: Patella sits higher than normal relative to the trochlea
• Measurement: Insall-Salvati ratio > 1.2 (normal 0.8-1.2) [14]
• Pathomechanics: Patella engages trochlear groove late in flexion, reducing bony stability in extension (when most dislocations occur)
• Often requires distalization osteotomy if MPFL reconstruction alone fails

3. Increased TT-TG Distance

• Prevalence: TT-TG > 20mm in 30-50% of recurrent dislocators [15]
• Definition: Lateral offset of tibial tubercle relative to trochlear groove
• Normal values: less than 15mm
• Borderline: 15-20mm
• Pathological: > 20mm [15]
• Pathomechanics: Creates lateral "bowstring" force vector on patella through quadriceps mechanism
• Requires tibial tubercle medialization osteotomy if > 20mm

4. Generalized Ligamentous Laxity

• Prevalence: 30-50% of patellar dislocators [16]
• Assessment: Beighton score ≥4/9
• Associations: Ehlers-Danlos syndrome, Marfan syndrome, joint hypermobility syndrome
• Pathomechanics: Insufficient passive soft tissue restraint
• May require augmented MPFL reconstruction or additional procedures

Additional Risk Factors

• Patella morphology: Wiberg type III (convex medial facet)
• Excessive femoral anteversion: > 15°
• External tibial torsion: > 20°
• Genu valgum: Q-angle > 20° in females, > 15° in males
• VMO dysplasia/atrophy: Reduced dynamic stabilization
• Previous contralateral dislocation: 4-fold increased risk [11]
• Family history: 20-30% have affected first-degree relative [17]

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3. Pathophysiology

Biomechanics of Normal Patellar Stability

The patellofemoral joint functions as a cam mechanism that amplifies quadriceps force during knee extension. Patellar stability depends on the dynamic equilibrium between:

1. Centralizing forces (medial stabilizers, trochlear geometry)
2. Destabilizing forces (Q-angle, lateral retinaculum tension, valgus alignment)

Contact Mechanics:

• At full extension (0°): Minimal bony constraint, MPFL provides primary stability
• At 20-30° flexion: Patella enters trochlear groove, shared MPFL/bony stability
• At 30-90° flexion: Deep engagement in trochlea, bony constraint predominates
• At > 90° flexion: Patella rests on femoral condyles, inherently stable

Load Distribution:

• Patellofemoral contact pressure reaches 6-8x body weight during stair climbing
• Peak contact at 60° flexion (largest contact area)
• Higher pressures in dysplastic trochlea (concentrated loading)

The Medial Patellofemoral Ligament (MPFL)

Anatomy:

• Femoral attachment: Schottle's point (see Viva Vault section)
  • Located between medial epicondyle and adductor tubercle
  • 1mm anterior to posterior femoral cortex extension
  • 2.5mm distal to posterior origin line on lateral radiograph
• Patellar attachment: Superomedial pole (proximal 2/3 of medial border)
• Length: 53-63mm [18]
• Width: 3-30mm (highly variable)
• Thickness: 0.43mm average (thin structure, easily torn)

Biomechanical Function:

• Provides 50-60% of restraint to lateral translation at 0-20° flexion [3]
• Becomes slack beyond 30° flexion (trochlea takes over)
• Isometric point: Schottle's point allows minimal length change through flexion arc
• Force to failure: 208N average (much less than ACL at 2160N) [18]

Injury Patterns:

• Femoral avulsion (50-70%): Most common, best amenable to reconstruction
• Midsubstance tear (20-30%): Often with elongation/attenuation
• Patellar avulsion (10-20%): May include bony fragment
• Combined/multi-site (10%): Worse prognosis

Mechanism of Dislocation

Phase 1: Initiation (0-30° Flexion)

• Foot planted, tibia externally rotated
• Valgus stress applied to knee
• Quadriceps contracts, generating proximal patellar force
• Lateral vector exceeds MPFL restraint capacity
• MPFL ruptures (usually femoral attachment)
• Patella translates laterally over lateral femoral condyle

Phase 2: Dislocation (Patella Lateral to Trochlea)

• Patella rests on anterolateral aspect of lateral femoral condyle
• Medial retinaculum torn
• Hemarthrosis develops rapidly from disrupted medial geniculate vessels
• Patient typically falls, knee gives way

Phase 3: Spontaneous Reduction (Most Damaging)

• As knee extends or patient straightens leg
• Patella "snaps" back medially into trochlear groove
• Medial patellar facet impacts lateral femoral condyle with high force
• Shearing of osteochondral fragments from:
  • Medial patellar facet (more common)
  • Lateral femoral condyle
  • Both locations
• Generates lipohemarthrosis if subchondral bone involved

Osteochondral Injury

Incidence: 20-50% of acute dislocations [6]

Location:

• Medial patellar facet (60%): Typically inferomedial pole
• Lateral femoral condyle (30%): Weight-bearing surface
• Both (10%): Worst prognosis

Types (ICRS Classification):

• Grade I-II: Chondral softening/fissuring (no fragment)
• Grade III: Deep cartilage injury to subchondral bone
• Grade IV: Full-thickness osteochondral fragment (loose body)

Implications:

• Loose bodies cause mechanical symptoms (locking, catching)
• Exposed subchondral bone = early arthritis risk
• Large fragments (> 1cm²) amenable to fixation
• Small fragments typically removed arthroscopically

Bone Bruising Pattern

MRI reveals characteristic bone marrow edema:

• Lateral femoral condyle (90%): From direct patellar impact
• Medial patellar facet (85%): From impact during reduction
• Absence of bone bruising: Questions diagnosis of true dislocation

This pattern is pathognomonic for patellar dislocation and distinguishes it from other knee injuries.

Progression to Chronic Instability

Acute Phase (0-6 weeks):

• MPFL heals in elongated, attenuated position (if midsubstance tear)
• Or heals to wrong location (if avulsed)
• Results in incompetent restraint to lateral translation

Subacute Phase (6 weeks - 6 months):

• Patient develops apprehension, avoidance behaviors
• VMO atrophy from disuse
• Proprioceptive deficits
• Further episodes of subluxation/dislocation

Chronic Phase (> 6 months):

• Established pattern of recurrent instability
• Cartilage damage accumulates with each episode
• Early patellofemoral arthritis develops
• Functional limitation, inability to participate in sports

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4. Clinical Presentation

History

Chief Complaint:

• "My kneecap popped out of place"
• "My knee gave way and I felt something move"
• "I felt a pop and my knee swelled up immediately"

Mechanism Questions (Critical for Diagnosis):

• Position during injury: Foot planted? Knee bent or straight?
• Force direction: Twisting? Direct blow? Non-contact?
• Immediate sensation: Pop? Shift? Tearing?
• Self-reduction: Did patella relocate spontaneously, or was manual reduction required?
• Witness account: Did anyone see the patella displaced?

Post-Injury Course:

• Swelling onset: Within 1-2 hours suggests hemarthrosis (vs. 6-24 hours for ACL)
• Ability to weight-bear: Usually unable immediately after
• Current symptoms: Pain location, instability, mechanical symptoms

Previous History (Essential):

• Prior dislocations: Same knee? Other knee? How many times?
• Prior subluxations: "Near-miss" episodes of instability
• Childhood "growing pains": May indicate early patellofemoral symptoms
• Previous treatments: Physiotherapy? Surgery? Bracing?

Functional Impact:

• Sports participation: What sports? What level? Specific provocative movements?
• Daily activities: Stairs, getting up from chair, squatting
• Psychological impact: Fear of redislocation, activity avoidance

Risk Factor Screening:

• Hypermobility: Can you touch thumbs to forearm? Hyperextend knees/elbows?
• Family history: Relatives with "loose kneecaps"? Joint hypermobility syndromes?
• Knee alignment: Known knock-knees (valgus)?

Physical Examination

Inspection (Patient Standing - If Able):

• Genu valgum: Knees touch when feet apart (increased Q-angle)
• Patella position: "Squinting patellae" (face medially) or "grasshopper eyes" (face laterally)
• Patella alta: High-riding patella visible on lateral view
• Muscle bulk: VMO wasting (medial thigh just above patella)
• Effusion: Significant swelling visible

Inspection (Patient Supine):

• Deformity: Patella displaced laterally (if unreduced - rare presentation)
• Ecchymosis: Medial knee bruising (MPFL injury)
• Scars: Previous surgery

Palpation:

• Effusion: Ballottement test, sweep test for small effusions
• Tenderness:
  • "Medial epicondyle/adductor tubercle area (Schottle's point): MPFL femoral avulsion"
  • "Medial patellar border: MPFL patellar avulsion or retinaculum tear"
  • "Lateral femoral condyle: Bone bruise from impact"
  • "Joint line: Meniscal injury (less common)"
• Patellar position: Lateral displacement relative to trochlea
• Crepitus: Grinding suggests osteochondral injury

Range of Motion:

• Active: Patient may be unable to fully extend due to pain/effusion
• Passive: Gentle assessment; full ROM suggests no mechanical block
• Extension lag: Inability to actively extend last 10-15° suggests extensor mechanism disruption

Specialized Patellar Tests:

1. Patellar Apprehension Test (Fairbank's Test)

   • Technique: Knee flexed 20-30°, examiner pushes patella laterally
   • Positive: Patient apprehensive, grimaces, contracts quadriceps to resist, may grab examiner's hand
   • Sensitivity: 39-100% (variable)
   • Specificity: 75-88% [19]
   • Most specific test for patellar instability

2. J-Sign

   • Technique: Patient seated, actively extends knee from 90° to 0°
   • Positive: Patella tracks centrally until last 10-20° extension, then abruptly "jumps" laterally
   • Indicates: Patella alta or trochlear dysplasia (patella not captured by groove until late flexion)

3. Patellar Glide Test

   • Technique: Knee extended, relax quadriceps, push patella medially then laterally
   • Grading: Number of quadrants (normal patella width divided into 4)
   • Normal: 1-2 quadrants lateral, 0-1 quadrants medial
   • Instability: > 2-3 quadrants lateral translation
   • Hypermobility: > 3 quadrants combined medial + lateral

4. Patellar Tilt Test

   • Technique: Attempt to lift lateral patellar edge with knee extended
   • Positive: Lateral edge cannot be lifted above horizontal (tight lateral retinaculum)
   • Indicates: Lateral soft tissue contracture, may require lateral release

5. Bassett's Sign

   • Technique: Palpate medial femoral condyle/epicondyle area
   • Positive: Exquisite tenderness at MPFL femoral attachment
   • Confirms: MPFL injury site

6. Active Patellar Tracking Assessment

   • Technique: Observe patella during active straight leg raise
   • Abnormal: Lateral deviation during muscle contraction
   • Indicates: VMO insufficiency, lateral vector dominance

Beighton Score (Hypermobility Assessment):

• Thumb to forearm: 1 point each side
• Fifth finger > 90° hyperextension: 1 point each side
• Elbow hyperextension > 10°: 1 point each side
• Knee hyperextension > 10°: 1 point each side
• Palms flat on floor with knees straight: 1 point
• Total: 9 points maximum
• Positive: ≥4/9 suggests generalized ligamentous laxity

Neurovascular Examination:

• Pulses: Dorsalis pedis, posterior tibial (dislocation rarely causes vascular injury, but confirm)
• Sensation: Saphenous nerve distribution (medial leg/foot) - may be injured during surgical reconstruction
• Motor: Ankle dorsiflexion/plantarflexion

Ligament Stability Tests (Differentiate from ACL/Collateral Injury):

• Lachman test: Typically negative (rules out ACL)
• Valgus/varus stress: Typically negative (rules out collateral injury)
• McMurray test: Usually negative (meniscal injury less common)

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5. Investigations

Initial Radiographic Assessment

Plain Radiographs - Three Essential Views:

1. Anteroposterior (AP) View

• Purpose: Identify patellar fracture, femoral fracture
• Findings in dislocation: Usually normal
• Look for:
  • Loose bodies (osteochondral fragments)
  • Joint space narrowing (pre-existing arthritis)
  • Limb alignment (valgus/varus)

2. True Lateral View (30° Flexion)

• Most important view for patellar dislocation
• Measurements:

Insall-Salvati Ratio [14]

• Patellar tendon length (TL) ÷ Patellar length (PL)
• Normal: 0.8-1.2
• Patella alta: > 1.2
• Patella baja: less than 0.8
• Measured from inferior pole of patella to tibial tubercle

Caton-Deschamps Index (Alternative measure)

• Patellar articular surface length ÷ Distance from inferior articular surface to tibial plateau
• Normal: 0.6-1.3
• Patella alta: > 1.3
• More reliable than Insall-Salvati in some studies

Trochlear Dysplasia Signs:

• Crossing sign (Dejour): Trochlear floor crosses anterior femoral cortex line (normal trochlea is anterior to this line)
  • Sensitivity 95% for dysplasia [12]
• Supratrochlear spur: Bony prominence at proximal trochlea
  • Indicates Dejour type B or D dysplasia
• Trochlear depth: less than 3mm shallow (normal 4-7mm)
• Double contour sign: Two lines visible from asymmetric condyles

3. Skyline (Merchant/Sunrise) View

• Technique: 45° knee flexion, X-ray beam angled 30° from horizontal
• Purpose: Axial view of patellofemoral joint
• Findings:
  • "Patellar tilt: Lateral tilt > 20° abnormal"
  • "Patellar subluxation: Lateral displacement visible"
  • "Sulcus angle: > 145° suggests dysplasia (normal 130-145°)"
  • "Congruence angle: > 16° suggests maltracking"
  • "Osteochondral fragments: Visualized as loose bodies"
  • "Trochlear morphology: Flat or convex trochlea"

CT Scan Indications:

Not routinely performed acutely, but valuable for:

• TT-TG measurement: Gold standard assessment (see below)
• Trochlear dysplasia characterization: 3D reconstruction
• Surgical planning: Pre-operative mapping for osteotomy
• Chronic instability evaluation: Precise anatomical measurements

TT-TG Distance Measurement [15]

• Technique:
  • Axial CT slices through knee
  • Identify slice with largest trochlear cartilage prominence (trochlear groove)
  • Draw line perpendicular to posterior femoral condylar line through trochlear groove
  • Identify slice with tibial tubercle
  • Draw line perpendicular to posterior femoral condylar line through tibial tubercle
  • Measure distance between these two parallel lines
• Normal: less than 15mm
• Borderline: 15-20mm
• Abnormal: > 20mm (indicates need for tibial tubercle medialization)

MRI Evaluation

Indications:

• All first-time patellar dislocations: To assess MPFL, cartilage, bone bruising
• Suspected osteochondral fracture: Pre-operative planning
• Recurrent instability: Surgical planning

MRI Protocol:

• Sequences: T1, T2, PD fat-saturated, STIR
• Planes: Axial, sagittal, coronal
• Field strength: 1.5T or 3T

Key Findings:

MPFL Assessment

• Location of tear:
  • Femoral attachment (50-70%): "Empty socket" sign, fluid at Schottle's point
  • "Midsubstance (20-30%): Disrupted fibers, edema, hemorrhage"
  • "Patellar attachment (10-20%): Avulsion fragment may be visible"
• MPFL signal: High T2 signal indicates edema/tear
• MPFL remnant quality: Important for surgical planning
• Associated medial retinaculum injury: Usually present

Bone Bruising (Pathognomonic Pattern)

• Lateral femoral condyle (90%): High T2 signal in anterior/weight-bearing region
• Medial patellar facet (85%): High T2 signal
• Pattern specificity: This specific combination confirms patellar dislocation with > 95% certainty [20]

Osteochondral Injury

• Location: Medial patellar facet > lateral femoral condyle
• Size: Measure in mm² for surgical decision-making
• Fragment displacement: Attached vs. displaced (loose body)
• Subchondral bone involvement: Lipohemarthrosis visible
• ICRS grading: Grade I-IV cartilage injury
• Loose body location: Suprapatellar pouch, posterior compartment, medial/lateral gutter

Trochlear Dysplasia (Dejour Classification) [12]

Type A: Shallow trochlea

• Sulcus angle > 145° (normal 130-145°)
• Trochlear depth less than 3mm (normal 4-7mm)
• Crossing sign present
• Supratrochlear spur absent

Type B: Flat/convex trochlea

• Sulcus angle > 145°
• Trochlear floor flat or convex
• Crossing sign present
• Supratrochlear spur present

Type C: Asymmetric trochlea

• Hypoplastic medial condyle (lateral >medial)
• Asymmetric sulcus (shifted laterally)
• "Double contour sign" on lateral view

Type D: "Cliff" deformity

• Vertical link between femoral shaft and trochlea
• Deep supratrochlear spur
• "Cliff sign"
• abrupt transition from trochlea to femoral shaft
• Highest grade, worst prognosis

Severity: Type A (mild) < Type B < Type C < Type D (severe)

Additional Measurements

• Patellar height: Insall-Salvati, Caton-Deschamps (corroborate XR findings)
• TT-TG distance: Can be measured on MRI (axial images) [15]
• Patellar tilt: Lateral patellar tilt angle
• Trochlear depth: In mm
• Femoral anteversion: Requires special sequences
• Tibial torsion: Requires full leg imaging

Aspiration of Hemarthrosis (Diagnostic and Therapeutic)

Indications:

• Large, tense effusion limiting motion
• Diagnostic uncertainty
• Pain relief

Technique:

• Superolateral or superomedial approach
• Aseptic technique
• 18-gauge needle, 20-60mL syringe

Fluid Analysis:

• Blood: Confirms hemarthrosis (most patellar dislocations)
• Lipohemarthrosis (fat floating on blood): Pathognomonic for osteochondral fracture
  • Indicates immediate need for MRI/arthroscopy
• Straw-colored fluid: Unlikely to be acute dislocation
• Purulent fluid: Septic arthritis (rare differential)

Send for:

• Cell count and differential (if diagnostic uncertainty)
• Gram stain and culture (if infection suspected)

Arthroscopy (Diagnostic and Therapeutic)

Indications:

• Acute setting:
  • Suspected loose body with locking
  • Osteochondral fracture requiring fixation/removal
  • Diagnostic uncertainty despite imaging
• Chronic setting:
  • As part of MPFL reconstruction
  • Assessment and treatment of cartilage damage

Findings:

• MPFL injury: Usually cannot visualize fully (extra-articular), but may see medial capsular disruption
• Osteochondral fragments: Medial facet patella, lateral femoral condyle
• Cartilage damage: Grade with ICRS classification
• Bone exposure: Exposed subchondral bone from shearing injury
• Loose bodies: Multiple locations possible
• Trochlear morphology: Direct visualization of dysplasia

Therapeutic Interventions:

• Loose body removal: Grasper, basket
• Osteochondral fragment fixation: Bio-compression screws, pins (if > 1cm²)
• Debridement: Unstable cartilage flaps
• Lateral release: If tight lateral retinaculum (controversial)

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6. Acute Management

Emergency Department Management

Initial Assessment:

• ABCs: Ensure no other injuries in poly-trauma
• Neurovascular status: Palpate pulses, check sensation/motor function
• Confirm reduction: Most dislocations (70-80%) reduce spontaneously; if patella still lateral, urgent reduction required

Reduction Technique (If Not Spontaneously Reduced):

1. Analgesia:

   • IV opioids (morphine 0.1mg/kg)
   • Consider procedural sedation if severe pain/patient unable to relax

2. Position:

   • Patient supine, hip flexed 90°

3. Technique:

   • Extend the knee (this is key - opposite to hip dislocation)
   • Apply gentle medial pressure to lateral patella border
   • Avoid excessive force
   • Reduction usually occurs with palpable "clunk"

4. Post-reduction:

   • Reassess neurovascular status
   • Check for full passive ROM
   • Immediate X-rays (AP, lateral, skyline)

Red Flags Requiring Immediate Orthopedic Consultation:

• Unsuccessful reduction after 2 attempts
• Vertical dislocation (locked in intercondylar notch - extremely rare)
• Open dislocation
• Neurovascular compromise
• Concomitant femoral or tibial fracture
• True mechanical locking after reduction (suggests loose body)

Post-Reduction Management:

1. Immobilization:

   • Knee immobilizer or cylinder cast in full extension
   • Duration: 1-2 weeks for comfort, then wean as tolerated
   • Weight-bearing as tolerated (WBAT) with crutches

2. Ice and Elevation:

   • Ice 20 minutes every 2 hours for first 48-72 hours
   • Elevate leg when sitting/lying

3. Analgesia:

   • NSAIDs (ibuprofen 400mg TDS or naproxen 500mg BD)
   • Paracetamol 1g QDS
   • Short course opioids if severe pain (avoid prolonged use)

4. Aspiration:

   • Consider if tense effusion limiting motion
   • Diagnostic value (lipohemarthrosis indicates osteochondral fracture)

5. Imaging:

   • Plain X-rays: AP, lateral (30° flexion), skyline views
   • MRI: Arrange urgent/semi-urgent MRI (within 1-2 weeks) for all first-time dislocations to assess:
     • MPFL injury
     • Osteochondral fractures
     • Bone bruising pattern
     • Anatomical risk factors

6. Orthopedic Referral:

   • Urgent (same day): Locked knee, large osteochondral fragment visible on X-ray
   • Semi-urgent (1-2 weeks): All other first-time dislocations
   • Routine (4-6 weeks): Chronic instability without mechanical symptoms

Outpatient Follow-Up

Orthopedic Review (1-2 Weeks Post-Injury):

Assess:

• Clinical examination findings
• Review MRI results
• Risk stratification for recurrence
• Identify osteochondral injury requiring surgery

Decision Tree:

POST-REDUCTION ASSESSMENT
          ↓
   OSTEOCHONDRAL FRACTURE ON MRI?
     ┌─────────┴─────────┐
    YES                  NO
     ↓                   ↓
  FRAGMENT SIZE?    FIRST OR RECURRENT?
  ┌────┴────┐      ┌──────┴──────┐
less than 1cm²    > 1cm²   FIRST        RECURRENT
  ↓        ↓       ↓                ↓
REMOVE   FIX   CONSERVATIVE    SURGICAL RISK
(Scope)  (Scope)  TRIAL      STRATIFICATION
                    ↓                ↓
              REHAB 3-6mo    HIGH RISK  LOW RISK
                    ↓           ↓          ↓
              REASSESS     CONSIDER      TRIAL
              STABILITY    EARLY MPFL    CONSERVATIVE
                           RECONSTRUCTION

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7. Definitive Management

Conservative (Non-Operative) Management

Indications:

• First-time dislocation AND
• No large osteochondral loose body (or removed arthroscopically) AND
• less than 2 anatomical risk factors (low recurrence risk)

Goals:

• Allow MPFL to heal
• Restore quadriceps strength (especially VMO)
• Improve proprioception
• Return to sport with reduced recurrence risk

Rehabilitation Protocol:

Phase 1: Protection (0-2 Weeks)

• Brace/Immobilizer: Knee immobilizer or hinged brace locked in extension
• Weight-bearing: WBAT with crutches
• Exercises:
  • Quadriceps sets (isometric contraction)
  • Straight leg raises
  • Ankle pumps
  • Gentle passive ROM (avoid terminal extension apprehension)
• Goals: Reduce effusion, maintain quad activation, protect MPFL healing

Phase 2: Early Mobilization (2-6 Weeks)

• Brace: Unlock hinged brace, allow 0-90° ROM
• Weight-bearing: Wean crutches as tolerated
• Exercises:
  • "VMO strengthening (critical):"
    • Terminal knee extension with resistance
    • Wall squats (0-45°, feet externally rotated)
    • Short arc quads
  • "Closed-chain exercises: Leg press, mini-squats"
  • "Proprioception: Single-leg balance, wobble board"
  • Patellar mobilization (medial glides)
  • "Stretching: Hamstrings, ITB, hip flexors"
• Goals: ROM 0-120°, VMO hypertrophy, normalize gait

Phase 3: Progressive Strengthening (6-12 Weeks)

• Brace: Wean off brace
• Exercises:
  • "Progressive resistance training: Squats, lunges, step-ups"
  • "Eccentric quad control: Step-downs"
  • "Plyometrics (if athlete): Box jumps (low height initially)"
  • "Sport-specific drills: Cutting, pivoting (gradual progression)"
  • "Core and hip strengthening: Glute med work (single-leg stance)"
• Goals: Full ROM, 80-90% quad strength vs. contralateral, no apprehension

Phase 4: Return to Sport (3-6 Months)

• Criteria for return:
  • No effusion or pain
  • Full ROM
  • Quad strength > 90% of contralateral
  • Negative apprehension test
  • Sport-specific functional tests passed
  • Psychological readiness
• Bracing for sport: Patella stabilizing brace for 6-12 months
• Taping: McConnell taping (medial glide) for proprioception

Patella Taping (McConnell Technique):

• Medial glide component: Pull patella medially with rigid tape
• Medial tilt component: Lift lateral border
• Effect: Reduces pain, improves VMO recruitment, enhances proprioception
• Evidence: Moderate quality evidence for short-term pain reduction [21]

Bracing:

• Types: Patella stabilizing brace with lateral buttress or "C" or "J" pad
• Mechanism: Prevents lateral translation, provides proprioceptive feedback
• Evidence: Limited high-quality evidence; may reduce recurrence in adolescents [22]
• Duration: Typically 6-12 months for sport

Outcomes of Conservative Management:

• Success rate (no redislocation): 50-70% overall [8]
• Recurrence risk: 15-44% in general population [4]
• Recurrence risk in adolescents: 50-60% (higher if less than 16 years) [4]
• Redislocation timing: 70% occur within 2 years [4]
• Factors predicting success:
  • Age > 25 years
  • First dislocation
  • less than 2 anatomical risk factors
  • Good rehabilitation compliance
  • Non-athletic population

Surgical Management

Indications:

Absolute Indications:

• Large osteochondral fragment (> 1cm²) amenable to fixation
• Loose body causing mechanical locking
• Irreducible dislocation (rare)

Relative Indications:

• Recurrent dislocation (≥2 episodes)
• First dislocation with high-risk features:
  • Age less than 16 years with skeletal immaturity
  • ≥2 anatomical risk factors
  • Contralateral instability
  • High-level athlete with strict return-to-sport requirements
  • Patient preference after informed discussion
• Chronic symptomatic instability: Subluxations, apprehension limiting function

Surgical Options:

1. Arthroscopy for Osteochondral Injury

Indications:

• Loose osteochondral fragment
• Large unstable chondral flap
• Diagnostic uncertainty

Procedure:

• Standard arthroscopic portals (anterolateral, anteromedial)
• Thorough examination: Identify fragments, assess cartilage damage
• Loose body less than 1cm²: Remove with grasper
• Fragment > 1cm² with good bone: Fix with bio-compression screws or biodegradable pins
  • Perpendicular to fragment
  • Buried beneath cartilage
  • Stable fixation allowing early ROM
• Unstable chondral flap: Debride to stable margins
• Microfracture: If full-thickness defect less than 2cm² and no fixable fragment
  • Multiple perforations of subchondral bone
  • Stimulates fibrocartilage formation
  • Requires 6-8 weeks non-weight-bearing

Outcomes:

• Fragment fixation: 70-85% good-excellent results if acutely fixed [23]
• Loose body removal: Resolves mechanical symptoms in > 90%

2. MPFL Reconstruction (The Gold Standard for Recurrent Instability)

Rationale:

• MPFL is primary soft tissue restraint
• Direct repair has high failure rates (> 40%) [24]
• Reconstruction with graft provides robust restraint

Graft Options:

Surgical Technique (Hamstring Autograft):

1. Graft Harvest:

   • Anteromedial incision over pes anserinus
   • Identify gracilis and semitendinosus tendons
   • Harvest with tendon stripper
   • Prepare graft: 4-strand configuration, 7-8mm diameter, whip-stitch ends

2. Patellar Tunnel:

   • Medial longitudinal incision over medial patella border
   • Identify insertion site: Superomedial pole (proximal 2/3 of medial border)
   • Drill tunnel: 4.5mm drill bit, oblique trajectory, exit medial border
   • OR: Create socket (no trans-patellar tunnel - reduces fracture risk)

3. Femoral Tunnel - Schottle's Point (Critical Step):

   • Anatomical location:
     • 1.0mm anterior to posterior femoral cortex extension on lateral fluoroscopy
     • 2.5mm distal to posterior origin of medial femoral condyle
     • Proximal and posterior to medial femoral epicondyle
     • Anterior and distal to adductor tubercle
   • Technique:
     • Mini-open or fluoroscopic-guided
     • Protect saphenous nerve
     • Drill 4.5-5.0mm tunnel or socket
   • Critical importance: Non-anatomic femoral tunnel causes over-constraint or failure

4. Graft Passage and Fixation:

   • Pass graft through patellar tunnel/socket to femoral socket
   • Tensioning: Knee flexed 30-45° (critical - avoids over-constraint)
   • Femoral fixation: Interference screw, cortical button, or anchor
   • Patellar fixation: Interference screw, anchors, or sutures tied over bone bridge
   • Check ROM and patella tracking: Should glide smoothly through full arc

5. Closure:

   • Repair medial retinaculum
   • Subcutaneous and skin closure
   • Apply hinged knee brace locked in extension

Biomechanical Principles:

• Isometry: Graft length should change less than 2mm through ROM
  • Non-isometric graft → over-constraint or laxity
  • Schottle's point is most isometric location
• Tensioning: At 30-45° flexion prevents over-constraint in extension
• Graft strength: 4-strand hamstring provides 1800N vs. native MPFL 208N (8x stronger) [18]

Post-Operative Rehabilitation:

Phase 1 (0-2 Weeks):

• Brace locked in extension
• WBAT with crutches
• Quad sets, SLR, ankle pumps
• Cryotherapy

Phase 2 (2-6 Weeks):

• Unlock brace, 0-90° ROM
• Wean crutches
• Progress to full ROM by 6 weeks
• VMO strengthening
• Proprioception exercises

Phase 3 (6-12 Weeks):

• Wean brace
• Progressive resistance training
• Closed-chain exercises
• Light plyometrics

Phase 4 (3-6 Months):

• Sport-specific training
• Return to full activity 6-9 months (if criteria met)

Outcomes:

• Redislocation rate: 0-10% (most studies 5-7%) [25]
• Return to sport: 85-90% [25]
• Patient satisfaction: 80-90% good-excellent [25]
• Complications: See Complications section

3. Tibial Tubercle Osteotomy (TTO)

Indications:

• TT-TG distance > 20mm (lateral malalignment)
• Patella alta (adjunct to MPFL in selected cases)
• Patellofemoral arthritis with lateral overload (anteromedialization)
• Failed MPFL reconstruction with persistent lateral vector

Types:

Medialization (Elmslie-Trillat)

• Indication: Increased TT-TG (> 20mm)
• Technique:
  • Oblique osteotomy of tibial tubercle (distal-lateral to proximal-medial)
  • Shift tubercle medially 10-15mm
  • Fix with two 4.5mm cortical screws
  • "Goal: Reduce lateral bowstring force vector"
• Amount: Typically 10-15mm medial shift
• Consideration: Avoid > 15mm shift (risk of medial overload)

Anteriorization (Maquet)

• Indication: Patellofemoral arthritis with pain (unloads joint)
• Technique: Elevate tubercle anteriorly 10-15mm
• Effect: Reduces patellofemoral contact pressure by 30-50%
• Rarely used alone for instability

Anteromedialization (Fulkerson)

• Indication: Combined instability + arthritis
• Technique:
  • Oblique osteotomy (anterior-lateral to posterior-medial)
  • Shifts tubercle anteriorly AND medially
  • Combines benefits of Maquet + Elmslie-Trillat
• Most common TTO in modern practice
• Fixation: Two 4.5mm cortical screws

Distalization

• Indication: Patella alta (Insall-Salvati > 1.3)
• Technique:
  • Move tubercle distally 5-15mm
  • Brings patella into trochlear groove earlier in flexion
• Often combined: With MPFL reconstruction
• Fixation: Two screws or plate

Post-Operative Protocol:

• Weight-bearing: Non-weight-bearing (NWB) or touch weight-bearing (TWB) for 6 weeks
• ROM: Hinged brace, gentle ROM 0-90° (avoid quad contraction initially)
• Radiographs: Week 2, 6, 12 to confirm healing
• Full weight-bearing: After radiographic union (typically 6-8 weeks)
• Return to sport: 6-9 months

Outcomes:

• Success rate: 70-85% good-excellent when appropriately indicated [26]
• Complication rate: 15-30% (higher than isolated MPFL)
• Fracture through osteotomy: 1-3% (risk with early loading)
• Tibial tubercle nonunion: less than 5%

Combined MPFL + TTO:

• Indication: Recurrent instability + TT-TG > 20mm
• Evidence: Superior outcomes to isolated MPFL in high TT-TG patients [27]
• Staged vs. simultaneous: Both described; simultaneous more common

4. Trochleoplasty

Indications:

• Severe trochlear dysplasia (Dejour type B or D)
• Failed MPFL +/- TTO despite addressing soft tissue/alignment
• Young patients with high functional demands and dysplasia as primary pathology

Types:

Deepening Trochleoplasty (Dejour)

• Technique:
  • Arthrotomy, evert patella
  • Elevate thin cartilage layer from trochlea
  • Remove subchondral bone to deepen groove
  • Replace cartilage, fix with fibrin glue
• Goal: Create bony constraint where none existed

Recession Trochleoplasty (Bereiter)

• Technique: Recessed bone flap technique
• Less aggressive than Dejour

Outcomes:

• Redislocation rate: 0-5% (excellent stability) [28]
• Complications: 10-40% (osteoarthritis, stiffness, pain) [28]
• Long-term concerns: Accelerated arthritis in some studies
• Technical demand: Very high, performed in specialized centers only

Post-Operative:

• Protected weight-bearing: 6-8 weeks
• CPM: Continuous passive motion to prevent stiffness
• Prolonged rehab: 9-12 months to return to sport

Controversy:

• High complication rates limit widespread adoption
• Reserved for severe dysplasia with recurrent instability despite other procedures
• Some experts advocate early trochleoplasty in severe Dejour D; others prefer exhausting other options first

5. Lateral Retinacular Release (Largely Abandoned)

Historical Indication:

• Tight lateral retinaculum with patellar tilt
• "Lateral patellar compression syndrome"

Current Status:

• No longer performed in isolation for instability
• Evidence shows:
  • No benefit for instability [29]
  • May worsen medial instability by removing lateral restraint
  • High failure rates as sole procedure

Rare Current Uses:

• Adjunct to MPFL if severe lateral tilt persists after reconstruction
• Treatment of isolated lateral pain syndrome (debated)

Algorithmic Approach to Surgical Planning

RECURRENT PATELLAR INSTABILITY
              ↓
      ANATOMICAL ASSESSMENT
              ↓
   ┌──────────┼──────────┐
   ↓          ↓          ↓
MPFL Tear  TT-TG     Trochlear
           Distance  Dysplasia
   ↓          ↓          ↓
   │      less than 15mm    15-20mm  > 20mm    Type A/B  Type C/D
   │        ↓         ↓       ↓          ↓         ↓
   │        │    Borderline  │       Mild-Mod   Severe
   │        │         │      │          │         │
   └────────┴─────────┴──────┘          │         │
            ↓                            │         │
       MPFL RECONSTRUCTION               │         │
            +                            │         │
       (If TT-TG> 20mm)                  │         │
            ↓                            │         │
      TTO MEDIALIZATION                 │         │
            +                            │         │
       (If Patella Alta)                │         │
            ↓                            │         │
      TTO DISTALIZATION                 │         │
            +────────────────────────────┘         │
       (If Dejour C/D dysplasia)                  │
            ↓                                      │
      CONSIDER TROCHLEOPLASTY ←──────────────────┘
      (if severe, young, failed other procedures)

---

8. Prognosis

Natural History (Conservative Management)

After First-Time Dislocation:

• Overall recurrence rate: 15-44% (wide variation between studies) [4]
• Age-stratified recurrence:
  • less than 16 years: 50-60%
  • 16-25 years: 30-40%

  • 25 years: 10-20%

• Time to redislocation: 70% occur within 2 years [4]
• Redislocation mechanism: Often lower energy than initial dislocation

After Second Dislocation:

• Recurrence risk: 50-70% [5]
• Pattern: Establishes chronic recurrent instability
• Prognosis: Very high likelihood of continued episodes without surgery

Risk Factors for Recurrence (After Conservative Management):

• Skeletal immaturity: 6-fold increased risk [9]
• Age less than 16 years: 3-fold increased risk [9]
• Trochlear dysplasia: 3-fold increased risk [12]
• Patella alta: 2-fold increased risk [13]
• TT-TG > 20mm: 2-fold increased risk [15]
• Contralateral instability: 4-fold increased risk [11]
• Family history: 2-fold increased risk [17]

Predictive Models:

• Fithian Score: Age + anatomical factors → predicts recurrence risk
• ≥2 risk factors: 70% recurrence rate (strong indication for surgical consideration) [9]

Surgical Outcomes

MPFL Reconstruction

Redislocation Rate:

• Isolated MPFL: 5-10% redislocation rate (meta-analysis of 1400+ patients) [25]
• Best results: less than 5% in properly selected patients with appropriate anatomy (TT-TG less than 20mm, minimal dysplasia)
• Worse results: 10-20% if anatomical risk factors not addressed

Return to Sport:

• Overall: 85-90% return to sport [25]
• Same level: 70-80% return to pre-injury level
• Time frame: 6-9 months average
• Psychological barriers: Apprehension remains in 10-20%

Patient-Reported Outcomes:

• Kujala score: Improvement from 55-60 to 85-90 (scale 0-100) [25]
• Satisfaction: 80-90% satisfied or very satisfied
• Subjective instability: Resolves in 85-95%

Factors Predicting Success:

• TT-TG less than 20mm
• Anatomical femoral tunnel placement
• Appropriate graft tensioning
• Rehabilitation compliance

Factors Predicting Failure:

• Unaddressed anatomical abnormalities (alta, high TT-TG, dysplasia)
• Non-anatomic femoral tunnel (over-constraint or laxity)
• Severe trochlear dysplasia (Dejour D)

MPFL + Tibial Tubercle Osteotomy

Indications: TT-TG > 20mm

Outcomes:

• Redislocation rate: 2-8% (better than isolated MPFL in high TT-TG) [27]
• Return to sport: 75-85% (slightly lower than isolated MPFL due to bone healing)
• Satisfaction: 75-85%
• Complication rate: 15-30% (higher than isolated MPFL)

Success Factors:

• Appropriate medialization (10-15mm)
• Bone healing before return to activity
• Combined with MPFL for optimal stability

Trochleoplasty

Outcomes:

• Redislocation rate: 0-5% (excellent stability) [28]
• Complications: 10-40% (pain, stiffness, arthritis)
• Satisfaction: Variable (60-85%)
• Long-term arthritis: Concern in some studies, requires long-term follow-up

Risk-Benefit:

• Highly effective for stability
• Significant complication risk
• Reserved for severe dysplasia with failed other treatments

Long-Term Sequelae

Patellofemoral Osteoarthritis:

• Incidence after dislocation: 30-50% at 10-20 years [30]
• Risk factors:
  • Osteochondral injury at index dislocation (highest risk)
  • Recurrent dislocations (cumulative cartilage damage)
  • Trochlear dysplasia (abnormal contact mechanics)
  • Surgical intervention (controversial - may be protective vs. damage from instability)
• Onset: Typically 10-20 years after initial injury
• Severity: Variable - mild to severe requiring arthroplasty

Impact on Quality of Life:

• Chronic pain: 20-30% report ongoing anterior knee pain even after successful stabilization [30]
• Activity limitation: 15-25% permanently reduce activity level
• Psychological: Kinesiophobia (fear of movement/re-injury) in 20-30%

Prevention of Arthritis:

• Early anatomical restoration: May reduce long-term arthritis risk (debated)
• Osteochondral fragment fixation: Better outcomes than removal
• Avoid recurrent dislocations: Cumulative damage hypothesis

Comparative Effectiveness

Conservative vs. Surgical (First-Time Dislocation):

• Low-risk patients (less than 2 risk factors, age > 20): Conservative first-line (70% success)
• High-risk patients (≥2 risk factors, age less than 16): Consider early surgery (avoid multiple episodes)
• Debate ongoing: Some advocate early MPFL for all; others prefer trial of conservative management

MPFL Alone vs. MPFL + TTO:

• If TT-TG less than 15mm: MPFL alone sufficient (5-7% redislocation)
• If TT-TG 15-20mm: Debated; most do MPFL alone
• If TT-TG > 20mm: MPFL + TTO superior (2-5% vs. 15-20% redislocation) [27]

Timing of Surgery (After Recurrent Dislocation):

• Earlier intervention: May reduce cumulative cartilage damage
• Delayed intervention: Allows trial of conservative management, patient maturity
• Trend: Towards earlier surgical intervention in high-risk adolescents

---

9. Complications

Complications of the Injury Itself

Osteochondral Fracture

• Incidence: 20-50% of acute dislocations [6]
• Location: Medial patellar facet (60%), lateral femoral condyle (30%), both (10%)
• Consequence:
  • Loose bodies → mechanical symptoms (locking, catching)
  • Cartilage defect → early osteoarthritis
  • "If untreated: Progressive arthritis"
• Management: Fixation if large (> 1cm²), removal if small, debridement of unstable cartilage

Hemarthrosis

• Incidence: > 90% of acute dislocations
• Consequence: Pain, stiffness, quadriceps inhibition
• Management: Aspiration if tense, early mobilization to prevent adhesions

Chronic Recurrent Instability

• Incidence: 15-44% after conservative management [4]
• Consequence:
  • Activity limitation
  • Psychological impact (fear, avoidance)
  • Progressive cartilage damage with each episode
  • Eventual need for surgical stabilization
• Prevention: Identify and surgically treat high-risk patients early

Patellofemoral Osteoarthritis

• Incidence: 30-50% at 10-20 year follow-up [30]
• Risk factors: Osteochondral injury, recurrent dislocations, dysplasia
• Consequence: Chronic pain, functional limitation, potential need for arthroplasty
• Prevention: Early stabilization, avoid recurrent episodes, address osteochondral injuries acutely

Complications of MPFL Reconstruction

Redislocation

• Incidence: 5-10% [25]
• Causes:
  • Unaddressed anatomical factors (alta, high TT-TG, dysplasia)
  • Non-anatomic femoral tunnel placement
  • Graft failure (rupture, stretch-out)
  • Traumatic re-injury
• Management:
  • Identify cause (imaging for tunnel position, anatomical measurements)
  • Revision MPFL +/- TTO/distalization if anatomical factors present
  • Trochleoplasty if severe dysplasia

Patellar Over-Constraint (Medial Patellar Pain)

• Incidence: 5-15% [25]
• Causes:
  • Graft too tight (excessive tensioning in extension)
  • Non-isometric femoral tunnel (graft tightens in flexion)
  • Insufficient lateral release if severe lateral tightness (rare)
• Consequence:
  • Medial facet overload and pain
  • Accelerated medial compartment arthritis
  • Stiffness, loss of flexion
• Prevention:
  • Tension graft at 30-45° flexion
  • Anatomical femoral tunnel at Schottle's point
  • Check patella glide and tracking intraoperatively
• Management:
  • "Conservative: Activity modification, physiotherapy"
  • "Surgical: Graft release/revision if severe"

Patellar Fracture

• Incidence: 1-3% [25]
• Causes:
  • Drilling tunnels through patella (weakens bone)
  • Stress riser from tunnel
  • Trauma post-operatively
• Types:
  • Acute intraoperative fracture (drill too large, insufficient bone bridge)
  • Stress fracture post-operatively (weeks to months)
• Prevention:
  • Appropriate tunnel size (4.5mm maximum)
  • Sufficient bone bridge (> 1cm between tunnels)
  • Consider socket technique (no trans-patellar tunnel) - increasingly popular
• Management:
  • "Non-displaced: Immobilization, protected weight-bearing"
  • "Displaced: ORIF with tension band wiring"

Saphenous Nerve Injury

• Incidence: 5-20% (mostly temporary) [25]
• Location: Infrapatellar branch crosses surgical field
• Consequence:
  • Numbness over anteromedial proximal tibia (usually limited area)
  • Painful neuroma (rare)
• Prevention:
  • Careful dissection
  • Identify and protect nerve
  • Minimize retraction
• Management:
  • Most resolve spontaneously over 6-12 months
  • "Neuroma: Excision if symptomatic"

Stiffness (Loss of Motion)

• Incidence: 3-8% [25]
• Causes:
  • Over-constraint (graft too tight)
  • Arthrofibrosis
  • Inadequate rehabilitation
• Prevention:
  • Appropriate graft tensioning
  • Early ROM exercises
  • Aggressive physiotherapy
• Management:
  • Intensive physiotherapy
  • Manipulation under anesthesia if severe and persistent (rare)
  • Graft release if due to over-constraint

Graft Failure

• Incidence: 2-5% [25]
• Causes:
  • Traumatic re-injury
  • Fixation failure
  • Graft stretch-out over time
  • Biological incorporation failure
• Management: Revision MPFL reconstruction

Infection

• Incidence: less than 1% (rare)
• Presentation: Erythema, warmth, purulent drainage, fever
• Management: Antibiotics, irrigation and debridement if deep infection

Complications of Tibial Tubercle Osteotomy

Nonunion

• Incidence: 2-5% [26]
• Risk factors: Early weight-bearing, smoking, inadequate fixation
• Presentation: Persistent pain, motion at osteotomy site
• Management: Revision fixation with bone grafting

Fracture Through Osteotomy

• Incidence: 1-3% [26]
• Causes:
  • Premature weight-bearing
  • Trauma
  • Stress riser from screw holes
• Prevention: Strict non-weight-bearing 6 weeks, appropriate fixation
• Management: ORIF if displaced

Compartment Syndrome

• Incidence: less than 1% (rare but serious)
• Mechanism: Bleeding from osteotomy into anterior compartment
• Presentation: Severe pain out of proportion, tense leg, pain with passive stretch
• Management: Emergent fasciotomy

Tibial Tubercle Avulsion

• Incidence: less than 1%
• Causes: Inadequate fixation, premature quad contraction
• Management: Revision fixation

Over-Medialization

• Incidence: Variable (technique-dependent)
• Consequence: Medial compartment overload, medial pain
• Prevention: Limit medialization to 10-15mm
• Management: Revision lateralization if symptomatic

Complications of Trochleoplasty

Osteoarthritis

• Incidence: 10-30% at medium-term follow-up [28]
• Mechanism: Disruption of native cartilage, altered contact mechanics
• Concern: Long-term arthritis rates may be significant
• Debate: Whether trochleoplasty accelerates arthritis vs. prevents it by restoring stability

Stiffness

• Incidence: 10-20% [28]
• Causes: Extensive dissection, prolonged immobilization, arthrofibrosis
• Prevention: CPM, aggressive early ROM
• Management: Physiotherapy, manipulation under anesthesia if severe

Cartilage Damage

• Incidence: Variable
• Mechanism: Technical difficulty in preserving cartilage during bone reshaping
• Consequence: Accelerated arthritis

Persistent Pain

• Incidence: 15-25% [28]
• Management: Activity modification, analgesics; revision rare

---

10. Evidence & Guidelines

Landmark Studies

Fithian et al. 2004 [4]

• Title: "Epidemiology and Natural History of Acute Patellar Dislocation"
• Design: Large cohort study, systematic review
• Key Findings:
  • "Recurrence rate after first dislocation: 15-44%"
  • Higher recurrence in adolescents (up to 60%)
  • "Identified risk factors: age, anatomical abnormalities"
• Impact: Established natural history, informed surgical decision-making

Steiner et al. 2006 [3]

• Title: "MPFL Biomechanics and Force Distribution"
• Design: Cadaveric biomechanical study
• Key Findings:
  • MPFL provides 50-60% of restraint to lateral translation at 0-30° flexion
  • Isometric point identified (Schottle's point)
• Impact: Established anatomical basis for MPFL reconstruction technique

Dejour et al. 1994 [12]

• Title: "Factors of Patellar Instability: An Anatomic Radiographic Study"
• Design: Case-control study (objective dysplasia classification)
• Key Findings:
  • Trochlear dysplasia present in 85% of recurrent dislocators vs. 3% controls
  • Classification system (Dejour A-D)
  • Dysplasia strongest predictor of recurrence
• Impact: Established trochlear dysplasia as key risk factor, created classification system

Schöttle et al. 2007 [31]

• Title: "Radiographic Landmarks for Femoral Tunnel Placement in MPFL Reconstruction"
• Design: Cadaveric anatomical study
• Key Findings:
  • Defined "Schottle's point" radiographically
  • 1mm anterior to posterior cortex, 2.5mm distal to posterior condyle origin
  • Most isometric point for femoral tunnel
• Impact: Standardized surgical technique, improved reproducibility

Schneider et al. 2016 [25]

• Title: "Outcomes of MPFL Reconstruction - Meta-Analysis"
• Design: Systematic review and meta-analysis (40 studies, 1400+ patients)
• Key Findings:
  • Redislocation rate 5-10%
  • Return to sport 85-90%
  • Complication rate 15-20%
  • Patient satisfaction 80-90%
• Impact: Established MPFL reconstruction as gold standard

Lippacher et al. 2014 [15]

• Title: "TT-TG Distance and Surgical Decision-Making"
• Design: Cohort study with outcomes analysis
• Key Findings:
  • TT-TG > 20mm associated with higher failure of isolated MPFL
  • Combined MPFL + TTO superior outcomes when TT-TG > 20mm
• Impact: Defined threshold for adding TTO to MPFL

Systematic Reviews & Meta-Analyses

MPFL Reconstruction Techniques

• Conclusion: No superiority of any specific graft type (hamstring, quadriceps, allograft) [25]
• Conclusion: Anatomical femoral tunnel placement critical (Schottle's point)
• Conclusion: Single-bundle vs. double-bundle: no difference in outcomes

Conservative vs. Surgical for First-Time Dislocation

• Conclusion: No consensus
• Evidence: Conservative appropriate for low-risk patients (success 50-70%)
• Evidence: Surgery may be beneficial in high-risk patients (age less than 16, ≥2 risk factors)
• Ongoing debate: RCTs ongoing (JUPITER trial, etc.)

Tibial Tubercle Osteotomy

• Conclusion: Effective for TT-TG > 20mm when combined with MPFL [27]
• Conclusion: Higher complication rate than isolated MPFL (15-30% vs. 10-15%)
• Conclusion: Medialization by 10-15mm optimal (avoid over-medialization)

Trochleoplasty

• Conclusion: Highly effective for stability (redislocation 0-5%) [28]
• Concern: Significant complication rates (10-40%)
• Recommendation: Reserved for severe dysplasia with failed other procedures
• Long-term data: Limited; arthritis risk requires further study

Current Guidelines

British Elbow and Shoulder Society (BESS) / European Society for Sports Traumatology, Knee Surgery and Arthroscopy (ESSKA)

• Not specific patellar instability guidelines exist from major societies
• General recommendations from expert consensus:
  • "First-time dislocation: MRI for all patients"
  • "Conservative management: Appropriate for first-time, low-risk"
  • "Surgical indications: Recurrent dislocation (≥2), high-risk first-time (consider), large osteochondral fragment"
  • "MPFL reconstruction: Gold standard for recurrent instability"
  • "Address anatomical factors: TTO if TT-TG > 20mm, consider distalization if alta, trochleoplasty if severe dysplasia"

American Academy of Orthopaedic Surgeons (AAOS)

• No formal guideline specifically on patellar instability
• General principles align with expert consensus above

Ongoing Research & Controversies

Early Surgery for First-Time Dislocation?

• Debate: Should high-risk patients (age less than 16, anatomical factors) undergo immediate MPFL reconstruction?
• Proponents argue: Prevents recurrent episodes, cumulative cartilage damage
• Opponents argue: Many heal with conservative management; avoids surgery in 50-60%
• Current RCTs: JUPITER trial (Germany), other ongoing studies comparing conservative vs. early surgical

Socket vs. Tunnel Technique (Patellar Fixation)?

• Debate: Trans-patellar tunnel vs. socket without through-and-through tunnel
• Socket advantages: Lower patellar fracture risk
• Tunnel advantages: Traditional, robust fixation
• Current trend: Moving towards socket techniques

Trochleoplasty Timing?

• Debate: Should severe dysplasia undergo trochleoplasty upfront or only after failed MPFL +/- TTO?
• Early trochleoplasty proponents: Addresses root cause in Dejour D dysplasia
• Delayed trochleoplasty proponents: High complication risk; exhaust other options first
• No consensus: Varies by center and surgeon experience

Role of Lateral Release?

• Historical: Common adjunct to MPFL
• Current evidence: No benefit for instability; may worsen medial laxity [29]
• Current practice: Largely abandoned except rare cases of severe lateral tightness

---

11. Patient Explanation

What Is Patellar Dislocation?

Your kneecap (called the patella) normally sits in a groove on your thigh bone (femur) like a train on a track. When you bend and straighten your knee, the kneecap glides up and down in this groove. A patellar dislocation happens when the kneecap pops out of the groove, almost always to the outside (lateral direction).

What Causes It?

Most often, this happens during sports or activities when your foot is planted and your knee twists. It can happen from:

• A sudden change of direction while running
• Landing awkwardly from a jump
• A direct blow to the inside of the knee pushing the kneecap outward
• Sometimes it happens with minimal force if you have a shallow groove or loose ligaments

What Gets Damaged?

When the kneecap dislocates, the main ligament that holds it in place (called the MPFL - Medial Patellofemoral Ligament) tears. This ligament acts like a seatbelt preventing the kneecap from sliding outward.

Sometimes, when the kneecap pops back into place (which usually happens automatically), it can chip a piece of cartilage or bone off the kneecap or thigh bone. This creates a "loose body" that can get stuck in the joint.

Will It Happen Again?

This depends on several factors:

• Your age: Younger people (especially under 16) have a higher risk of it happening again (up to 50-60%)
• The shape of your knee bones: Some people have a shallow groove or a high-riding kneecap, which makes redislocation more likely
• If you've dislocated before: Each time it happens, the risk of it happening again increases

After the first dislocation, about 15-44% of people will have it happen again. After a second dislocation, the risk jumps to 50-70%.

How Is It Treated?

If it's the first time: Most people are treated without surgery:

• Knee brace for 1-2 weeks
• Crutches until you can walk comfortably
• Physical therapy focusing on strengthening the inside thigh muscle (VMO - vastus medialis obliquus)
• Gradual return to activities over 3-6 months
• About 50-70% of people do well without surgery

If it keeps happening (recurrent dislocation): Surgery is usually recommended to prevent ongoing problems. The most common surgery is called MPFL reconstruction:

• A tendon from your hamstring (or other source) is used to create a new "seatbelt" ligament
• This is attached to the kneecap and thigh bone to hold the kneecap in place
• Success rate is 90-95% (only 5-10% have another dislocation after surgery)
• Recovery takes about 6-9 months to return to sports

Additional procedures may be needed if:

• The groove is very shallow (trochleoplasty - reshape the groove)
• The kneecap sits too far outside (tibial tubercle osteotomy - move the attachment point of the kneecap tendon)
• The kneecap sits too high (distalization - move the tendon attachment down)

What About the Cartilage Damage?

If a piece of cartilage or bone broke off during the dislocation:

• Small pieces are usually removed through a small camera (arthroscopy)
• Large pieces (bigger than your thumbnail) may be screwed back into place
• This is important because loose pieces can cause the knee to lock or catch

Long-Term Outlook

Most people recover well, but there are some long-term concerns:

• Arthritis risk: 30-50% of people develop arthritis in the kneecap joint 10-20 years later, especially if there was cartilage damage
• Chronic pain: Some people have ongoing pain even after successful treatment
• Activity modification: Some people choose to avoid high-risk sports to prevent redislocation

What Can You Do to Help?

1. Strengthen your thigh muscles: The VMO (inside thigh muscle) is crucial for keeping the kneecap stable
2. Maintain flexibility: Tight muscles can pull the kneecap out of alignment
3. Wear a brace if recommended: Especially when returning to sports
4. Listen to your body: If your knee feels unstable, don't push through it
5. Follow your rehabilitation program: Compliance with physical therapy dramatically improves outcomes

Questions to Ask Your Doctor

• Do I have any bone shape abnormalities that increase my risk of redislocation?
• Should I have an MRI to check for cartilage damage?
• What is my personalized risk of this happening again?
• If I need surgery, what specific procedures would you recommend for my anatomy?
• When can I safely return to my sport or activity?

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12. Viva Vault (Examination Focus)

Core Knowledge Questions

Q1: Describe the anatomy of the MPFL.

Answer: The Medial Patellofemoral Ligament (MPFL) is the primary soft tissue restraint to lateral patellar displacement in early flexion.

Attachments:

• Femoral origin: Schottle's point - located at the medial femoral epicondyle, between the adductor tubercle and medial epicondyle, just anterior and distal to the adductor tubercle
• Patellar insertion: Superomedial pole of the patella, spanning the proximal two-thirds of the medial patellar border

Structure:

• Length: 53-63mm
• Width: 3-30mm (highly variable)
• Thickness: 0.43mm average (thin structure)
• Composed of two distinct bundles (superior and inferior) in some anatomical studies

Biomechanics:

• Provides 50-60% of restraint to lateral patellar translation at 0-30° of knee flexion
• Becomes slack at > 30° flexion as the patella engages the trochlear groove (bony constraint takes over)
• Isometric point at Schottle's point (minimal length change through flexion arc)

Blood supply: Branches from superior and inferior medial genicular arteries

Clinical relevance: Tears in > 90% of acute patellar dislocations; reconstruction restores primary restraint

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Q2: What is Schottle's point and how do you identify it?

Answer: Schottle's point is the radiographic landmark for the anatomical femoral attachment site of the MPFL, used to guide femoral tunnel placement in MPFL reconstruction.

Radiographic identification (on true lateral knee radiograph):

1. Extend the posterior femoral cortex as a line proximally
2. Identify the posterior origin of the medial femoral condyle (posterior point where condyle begins)
3. Schottle's point is:
   • 1.0mm anterior to the posterior cortex extension line
   • 2.5mm distal to the posterior origin line of the medial femoral condyle

Anatomical location:

• On the medial femoral condyle
• Between the medial epicondyle and adductor tubercle
• Proximal and posterior to the medial epicondyle
• Anterior and distal to the adductor tubercle

Clinical significance:

• Most isometric point: Graft length changes less than 2mm through full range of motion
• Avoids over-constraint: Non-anatomical tunnel placement causes over-tightening in flexion (anterior/distal tunnel) or extension (posterior/proximal tunnel)
• Reproducible: Allows standardized surgical technique across surgeons

Intraoperative identification:

• Fluoroscopic guidance using lateral view and Schottle's measurements
• Palpation: Firm ridge between soft adductor tubercle and medial epicondyle
• Arthroscopic transillumination in some techniques

Biomechanical importance: MPFL reconstruction using non-anatomic femoral tunnel has 3-4x higher failure rate compared to anatomic placement

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Q3: What is the TT-TG distance, how is it measured, and what are the implications?

Answer:

Definition: TT-TG (Tibial Tubercle-Trochlear Groove) distance is the lateral offset of the tibial tubercle relative to the trochlear groove, measured in millimeters. It quantifies the "bowstring effect" or lateral vector force that the quadriceps exerts on the patella.

Measurement technique (CT scan - gold standard):

1. Obtain axial CT slices through the knee
2. Identify the trochlear groove slice:
   • Find the slice showing the largest prominence of trochlear cartilage (deepest part of groove)
   • Draw a reference line perpendicular to the posterior femoral condylar line through the deepest point of the trochlear groove
3. Identify the tibial tubercle slice:
   • Find the slice showing the center of the tibial tubercle attachment
   • Draw a reference line perpendicular to the posterior femoral condylar line through the center of the tubercle
4. Measure: The distance between these two parallel lines is the TT-TG distance

Alternative measurement: Can be approximated on MRI using similar technique (axial sequences)

Normal values:

• Normal: less than 15mm
• Borderline: 15-20mm
• Pathological: > 20mm

Clinical implications:

TT-TG less than 15mm (Normal):

• Isolated MPFL reconstruction appropriate
• No need for tibial tubercle osteotomy

TT-TG 15-20mm (Borderline):

• Controversial zone
• Most surgeons perform isolated MPFL reconstruction
• Consider TTO if other high-risk features (dysplasia, young age)

TT-TG > 20mm (Pathological):

• Tibial tubercle medialization osteotomy indicated in addition to MPFL reconstruction
• Isolated MPFL has 15-20% failure rate vs. 2-5% for combined MPFL + TTO
• Medialization typically by 10-15mm (avoid over-medialization)

Pathophysiology: Increased TT-TG creates a laterally directed force vector on the patella because the extensor mechanism (quadriceps → patella → patellar tendon → tibial tubercle) forms a "bowstring" that pulls the patella laterally with each quadriceps contraction. This overwhelms even a reconstructed MPFL.

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Q4: Classify trochlear dysplasia. What are the radiological signs?

Answer:

Dejour Classification of Trochlear Dysplasia (Based on lateral radiograph and CT/MRI):

Type A: Shallow Trochlea

• Trochlear groove shallow but maintains concave shape
• Sulcus angle > 145° (normal 130-145°)
• Trochlear depth less than 3mm (normal 4-7mm)
• Crossing sign present
• Supratrochlear spur absent

Type B: Flat or Convex Trochlea

• Trochlear groove flat or convex (no groove)
• Sulcus angle > 145°
• Crossing sign present
• Supratrochlear spur present (differentiates from Type A)

Type C: Asymmetric Trochlea

• Lateral condyle higher than medial condyle
• Hypoplastic medial femoral condyle
• Asymmetric groove
• "Double contour sign" on lateral radiograph (two overlapping condyle lines due to asymmetry)

Type D: "Cliff" Sign (Vertical Link)

• Most severe form
• Vertical or near-vertical transition from femoral shaft to trochlear groove
• "Cliff sign": Abrupt step-off between trochlea and femoral shaft
• Deep supratrochlear spur
• Often combined with features of Type B

Severity: Type A (mildest) < Type B < Type C < Type D (most severe)

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Radiological Signs of Trochlear Dysplasia:

On lateral radiograph:

1. Crossing Sign (Most sensitive - 95%)

   • The trochlear floor crosses anterior to the line of the anterior femoral cortex
   • Normally, the trochlear groove is anterior to this line (does not cross)
   • Indicates shallow or flat trochlea

2. Supratrochlear Spur ("Trochlear Bump")

   • Bony prominence at the proximal end of the trochlea
   • Indicates Dejour Type B or D

3. Trochlear Depth less than 3mm

   • Measured as the perpendicular distance from the deepest point of the groove to a line connecting the anterior aspects of the condyles
   • Normal: 4-7mm

4. Double Contour Sign

   • Two distinct lines representing the anterior borders of medial and lateral condyles
   • Indicates asymmetry (Type C dysplasia)

On axial views (CT/MRI):

1. Sulcus angle > 145°

   • Angle formed by lines from the highest points of medial and lateral condyles to the deepest point of the groove
   • Normal: 130-145°

   • 145° indicates dysplasia

2. Flat or convex trochlea

   • Loss of concave shape
   • "Plateau" appearance

3. Lateral trochlear inclination less than 11°

   • Angle of lateral facet relative to horizontal
   • Low angle indicates flat lateral facet (poor lateral constraint)

Clinical significance:

• Trochlear dysplasia present in 85-96% of patients with recurrent patellar dislocation vs. 3% of normal population
• Strongest independent predictor of recurrent instability
• Severe dysplasia (Type D) may require trochleoplasty if MPFL ± TTO fails

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Q5: Why is direct repair of the MPFL not recommended compared to reconstruction?

Answer:

Evidence: Multiple studies demonstrate significantly higher failure rates with MPFL repair (suturing torn ends) compared to reconstruction (using tendon graft):

• Repair failure rate: 30-50%
• Reconstruction failure rate: 5-10%

Reasons for repair failure:

1. Tissue Quality:

   • MPFL is very thin (0.43mm average thickness) and structurally weak
   • After injury, the tissue is often attenuated, stretched, and of poor quality
   • Suturing poor-quality tissue provides inadequate strength

2. Healing in Elongated Position:

   • Even if the MPFL heals, it often heals in a lengthened position (if midsubstance tear)
   • Or heals to an incorrect anatomical location (if avulsed and scarred to surrounding tissue)
   • Results in incompetent restraint (too lax to prevent lateral translation)

3. Insufficient Strength:

   • Native MPFL force to failure: ~208N
   • After repair, strength is significantly reduced
   • Cannot withstand physiological forces during return to activity
   • 4-strand hamstring graft provides ~1800N (8-9x stronger)

4. Non-Anatomic Healing:

   • MPFL may heal to non-isometric position
   • Results in over-constraint in some positions (pain) or laxity in others (instability)

5. Biological Factors:

   • Blood supply to MPFL is limited
   • Healing potential poor compared to other ligaments (e.g., MCL)

Reconstruction Advantages:

• Uses robust tendon graft (gracilis, semitendinosus, quadriceps)
• Allows anatomical placement (Schottle's point)
• Isometric positioning prevents over-constraint
• Predictable tensioning at time of surgery
• Superior biomechanical strength
• Reproducible outcomes

Exceptions (where repair may be considered):

• Acute bony avulsion with large bone fragment
  • Fragment can be fixed with suture anchors or screws
  • Maintains native tissue and blood supply
  • Better outcomes than soft tissue repair
• Very acute presentation (less than 48 hours) with high-quality tissue (controversial, limited evidence)

Current standard of care: MPFL reconstruction is the gold standard for surgical treatment of recurrent patellar instability. Repair has been largely abandoned except for true bony avulsions.

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Advanced/Clinical Scenario Questions

Q6: A 15-year-old female basketball player presents with first-time patellar dislocation. MRI shows MPFL tear, no loose body, trochlear dysplasia Dejour Type B, patella alta (Insall-Salvati 1.35), TT-TG 18mm. Discuss your management.

Answer:

Initial Management:

• Confirm reduction (already achieved if presented after injury)
• Immobilization in knee brace, WBAT with crutches
• Physiotherapy referral for VMO strengthening and rehabilitation

Risk Stratification:

This patient has multiple high-risk features for recurrent instability:

1. Age 15 years (high recurrence risk 50-60% in adolescents)
2. Trochlear dysplasia Type B (85-96% of recurrent dislocators have dysplasia)
3. Patella alta (Insall-Salvati 1.35, normal less than 1.2)
4. Borderline TT-TG (18mm, borderline-high)
5. High-demand athlete (basketball)

Fithian risk score: ≥3 risk factors → ~70% chance of recurrence with conservative management

Treatment Options:

Option 1: Conservative Management (Trial)

• Rationale:
  • First-time dislocation
  • 30-40% may not redislocate even with risk factors
  • Avoids surgery in skeletal immature patient
  • No loose body requiring urgent surgery
• Protocol:
  • Structured rehabilitation for 3-6 months
  • VMO strengthening, proprioception training
  • Patella stabilizing brace for sports
  • Close follow-up
• Reassess: If redislocation occurs, proceed to surgery
• Risks: High redislocation risk; each episode causes cumulative cartilage damage

Option 2: Early Surgical Intervention (MPFL Reconstruction)

• Rationale:
  • High-risk patient (≥3 risk factors)
  • Prevent recurrent episodes and cumulative cartilage damage
  • Allow safe return to high-level sport
• Timing: After growth plate maturity or use physeal-sparing technique if skeletally immature
• Procedure:
  • MPFL reconstruction with hamstring autograft
  • "Address patella alta: Consider tibial tubercle distalization vs. isolated MPFL"
  • "TT-TG 18mm (borderline): Isolated MPFL likely sufficient; consider TTO if failure"
• Advantages: 90-95% success rate, return to sport 85-90%
• Risks: Surgical complications (5-15%), prolonged recovery (6-9 months)

Skeletal Maturity Consideration:

• If skeletally immature (open physes):
  • Risk of physeal injury with standard MPFL reconstruction
  • "Options:"
    1. Delay surgery until physeal closure (monitor with serial X-rays)
    2. Physeal-sparing MPFL reconstruction: Graft anchored with sutures to periosteum (avoids drilling across physis)
• If skeletally mature:
  • Standard MPFL reconstruction safe

Patella Alta Management:

• Insall-Salvati 1.35 is significantly high (normal less than 1.2)
• Decision:
  • Isolated MPFL reconstruction may suffice (some studies show success even with alta)
  • Consider tibial tubercle distalization if MPFL alone fails
  • Alternatively, combine MPFL + distalization as primary procedure (more invasive, longer recovery)

Recommended Approach: Given the patient's age and multiple risk factors:

1. Shared decision-making with patient and family:

   • Explain 60-70% recurrence risk with conservative management
   • Explain 5-10% redislocation risk with surgery
   • Discuss recovery timeline and return-to-sport expectations

2. My recommendation:

   • Trial of conservative management first (3-6 months) given first-time dislocation
   • Strict rehabilitation, bracing for sport
   • If redislocation occurs OR patient/family prefer proactive approach:
     • MPFL reconstruction (wait for skeletal maturity or use physeal-sparing technique)
     • Isolated MPFL first; add distalization if failure
   • Close follow-up every 3 months

3. Long-term:

   • Monitor for patellofemoral arthritis (30-50% risk)
   • Counsel on injury mechanisms to avoid

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Q7: A 25-year-old male presents with third patellar dislocation (same knee). Previous two episodes managed conservatively with physiotherapy. Discuss your surgical planning.

Answer:

Clinical Assessment:

History:

• Mechanism of previous and current dislocations (low vs. high energy)
• Functional limitation, sports/activity level
• Previous rehabilitation compliance
• Symptoms between episodes (subluxations, apprehension, pain)

Examination:

• Apprehension test
• J-sign
• Patellar tilt/glide assessment
• Beighton score (generalized laxity)
• VMO bulk

Investigations:

Imaging:

1. X-rays (AP, lateral, skyline):

   • Insall-Salvati ratio (patella alta?)
   • Trochlear dysplasia signs (crossing sign, supratrochlear spur)
   • Degenerative changes (early arthritis from recurrent dislocations)

2. CT scan:

   • TT-TG distance (most important measurement for surgical planning)
   • Trochlear dysplasia characterization
   • Femoral anteversion, tibial torsion if indicated

3. MRI:

   • MPFL status (chronic attenuation vs. acute re-tear)
   • Osteochondral lesions (cumulative damage from three episodes)
   • Cartilage assessment (early arthritis?)
   • Bone bruising (if recent dislocation)

Surgical Indications:

• Clear indication for surgery: Third dislocation, failed conservative management
• Goals: Restore stability, prevent further episodes, minimize long-term arthritis risk

Surgical Planning (Based on Anatomical Assessment):

Scenario 1: Normal Anatomy (TT-TG less than 15mm, Normal Trochlea, Normal Patellar Height)

• Procedure: Isolated MPFL reconstruction
• Rationale: MPFL insufficiency is sole pathology
• Expected outcome: 90-95% success rate

Scenario 2: Increased TT-TG (> 20mm)

• Procedure: MPFL reconstruction + Tibial tubercle medialization osteotomy
• Rationale: Isolated MPFL has 15-20% failure rate with high TT-TG; combined procedure reduces to 2-5%
• Technique:
  • Elmslie-Trillat or Fulkerson osteotomy
  • Medialize 10-15mm
  • Fix with two 4.5mm cortical screws
• Rehabilitation: Protected weight-bearing for 6 weeks (bone healing)

Scenario 3: Patella Alta (Insall-Salvati > 1.3)

• Procedure: MPFL reconstruction + Tibial tubercle distalization
• Rationale: Patella engages trochlea late in flexion; distalization improves capture
• Amount: Distal shift 10-15mm
• Combine: With medialization if TT-TG also elevated

Scenario 4: Severe Trochlear Dysplasia (Dejour Type D)

• Initial procedure: MPFL reconstruction ± TTO (based on TT-TG)
• If fails: Consider trochleoplasty as salvage
• Rationale: Trochleoplasty has high complication rates (10-40%); reserve for failures
• Referral: Tertiary center with expertise in trochleoplasty if indicated

Additional Considerations:

Osteochondral Lesions:

• If large loose body or fixable fragment identified on MRI:
  • Arthroscopy first to address (remove loose body or fix fragment)
  • Then proceed with MPFL ± TTO (can be staged or simultaneous)

Cartilage Damage:

• Assess at arthroscopy
• If full-thickness defects:
  • "Small (less than 2cm²): Microfracture"
  • "Large (> 2cm²): May require cartilage restoration procedure (osteochondral autograft, ACI) - staged after stabilization"

My Surgical Plan (Assuming Most Common Scenario: TT-TG 18mm, Mild Dysplasia, Normal Height):

1. Preoperative:

   • Optimize physiotherapy (VMO strengthening)
   • Patient education on realistic expectations
   • Consent: Risks (redislocation 5%, over-constraint 5%, infection less than 1%, nerve injury 5-10%, stiffness 5%)

2. Procedure:

   • MPFL reconstruction with gracilis autograft
   • Arthroscopy first to assess/address cartilage damage, remove loose bodies
   • Graft harvest: Gracilis tendon via anteromedial approach
   • Patellar fixation: Socket technique (avoid trans-patellar tunnel to reduce fracture risk), two suture anchors
   • Femoral tunnel: Schottle's point (fluoroscopic guidance)
   • Tensioning: 30-45° knee flexion
   • Check: Smooth patellar tracking, no over-constraint

3. Postoperative:

   • Hinged knee brace locked in extension
   • WBAT with crutches
   • Start ROM day 1-2 (unlock brace, gentle 0-90°)
   • Physiotherapy protocol:
     • Weeks 0-2: Quad sets, SLR, gentle ROM
     • Weeks 2-6: Progress ROM to full, VMO strengthening
     • Weeks 6-12: Progressive resistance, proprioception
     • Months 3-6: Sport-specific training
     • Months 6-9: Return to sport if criteria met
   • Follow-up: 2 weeks, 6 weeks, 3 months, 6 months, 1 year

4. If additional procedures needed:

   • TT-TG > 20 mm: Add medialization osteotomy (NWB 6 weeks)
   • Patella alta > 1.3: Consider distalization (discuss trade-offs)

Expected Outcome:

• Redislocation risk: 5-10%
• Return to sport: 85-90%
• Return to same level: 70-80%
• Satisfaction: 80-90%
• Timeline: 6-9 months to full sport

Long-term Monitoring:

• Risk of patellofemoral arthritis (30-50% at 10-20 years due to cumulative cartilage damage from three dislocations)
• Counsel on activity modification if symptoms develop

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Q8: What are the radiological signs of trochlear dysplasia on a lateral radiograph?

Answer:

On a true lateral knee radiograph (30° flexion), the key signs of trochlear dysplasia are:

1. Crossing Sign (Most Sensitive - 95%)

• The trochlear floor crosses anterior to the line formed by the anterior femoral cortex
• In a normal knee, the trochlear groove projects anterior to this line (does not cross)
• Indicates: Shallow or flat trochlear groove
• Present in: All types of dysplasia (A, B, C, D)

2. Supratrochlear Spur

• Bony prominence/bump at the proximal end of the trochlear groove
• Creates a "speed bump" at the entrance to the trochlea
• Indicates: Dejour Type B or D dysplasia
• Absent in: Type A and C

3. Trochlear Depth less than 3mm

• Measured from the deepest point of the groove perpendicular to a line connecting the most anterior points of the medial and lateral femoral condyles
• Normal: 4-7mm
• less than 3mm indicates shallow groove
• Indicates: Type A, B, or D dysplasia

4. Double Contour Sign

• Two distinct parallel lines visible, representing the anterior borders of the medial and lateral femoral condyles
• Occurs due to asymmetry between the two condyles (hypoplastic medial condyle)
• Indicates: Type C dysplasia specifically

Additional Measurement:

• Lateral trochlear inclination: Angle of the lateral facet can be measured but requires special views

Clinical Use: These signs identify patients at high risk of recurrent patellar instability and guide surgical decision-making (e.g., consideration of trochleoplasty in severe Type D dysplasia).

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