Summary

Acute patellar dislocation involves the lateral displacement of the patella from the trochlear groove of the femur. It is the most common acute knee disorder in adolescents (Peak age 15). The primary pathology is the rupture of the Medial Patellofemoral Ligament (MPFL), which acts as the check-rein against lateral translation. 90% of first-time dislocations will heal with conservative management, but recurrence rates are high (up to 50%) if anatomical risk factors exist ("The Big 4": Trochlear Dysplasia, Patella Alta, Increased TT-TG, Ligamentous Laxity). Surgical reconstruction of the MPFL is the gold standard for recurrent instability. [1,2,3]

Key Facts

• The MPFL: The primary restraint to lateral translation in the first 30 degrees of flexion. It attaches near the Adductor Tubercle (Schottle's Point) and the superomedial patella.
• Osteochondral Fractures: 40% of acute dislocations shear a fragment of cartilage/bone off the Medial Patellar Facet or Lateral Femoral Condyle as the patella relocates. Always look for loose bodies!
• Recurrence Risk: 15-44% after first-time dislocation. Increases to 70-80% after second dislocation.

Clinical Pearls

"The J-Sign": Ask the patient to sit on the edge of the bed and extend their knee from 90° to 0°. In the final 10° of extension, the patella abruptly "jumps" laterally out of the groove. This is a hallmark sign of Patella Alta or Trochlear Dysplasia.

"Fat Globules = Fracture": If you aspirate the hematoma and see fat globules swirling in the blood (Lipohemarthrosis), there is an underlying fracture (Osteochondral defect).

"Schottle's Point Tenderness": Max tenderness is usually at the femoral insertion of the MPFL (just anterior to the adductor tubercle), confirming the rupture site.

                  PATELLAR DISLOCATION
                         ↓
                  IS IT REDUCED?
           ┌─────────────┴─────────────┐
          NO                          YES
           ↓                           ↓
      REDUCE (ED)              OSTEOCHONDRAL #?
    (Extend Knee +           ┌─────────┴─────────┐
    Medial Pressure)       YES                  NO
                             ↓                   ↓
                        **SURGERY**         FIRST TIME?
                     (Fix/Remove Fragment) ┌─────┴──────┐
                                         YES         RECURRENT
                                          ↓             ↓
                                     CONSERVATIVE     SURGERY
                                     (Brace 2wks)   (MPFL Recon)

Indications

• First-time dislocation.
• No osteochondral loose body.
• No gross anatomical dysplasia.

Protocol

• Phase 1 (0-2 weeks): Knee Extension Splint/Brace. WBAT. Allow MPFL to heal.
• Phase 2 (2-6 weeks): ROM exercises. Strengthen VMO (Vastus Medialis).
• Phase 3 (3-6 months): Return to sport.
• Taping/Bracing: "J" taping helps proprioception.

1. Arthroscopy (Acute)

• Indication: Osteochondral loose body associated with acute dislocation.
• Action: Removal of loose body OR Fixation (Bio-compression screws) if large (>1cm²).

2. MPFL Reconstruction (The Workhorse)

• Indication: Recurrent instability. Failed conservative Rx.
• Graft: Gracilis or Semitendinosus autograft.
• Technique: Graft is docked on the patella (anchors/tunnels) and fixed to the femur at Schottle's Point with an interference screw.
• Goal: Restore the check-rein. Tensioned in 30° flexion (to avoid over-constraining).

3. Tibial Tubercle Osteotomy (TTO)

• Indication: TT-TG > 20mm or Patella Alta.
• Technique:
  • Fulkerson Osteotomy: Moves tubercle Anteriorly (unloads joint) and Medially (corrects TT-TG).
  • Distalization: Moves tubercle Down (corrects Alta).
• Fixation: 2 strong cortical screws.

4. Trochleoplasty

• Indication: Severe Trochlear Dysplasia (Dejour B/D - "Cliff" or "Bump").
• Technique: Deepening the bony groove beneath the cartilage. High risk, specialized procedure.

Fithian et al (Natural History)

• Recurrence risk after conservative management:
  • ~17% for standard patients.
  • ~50% if history of contralateral instability.

Reconstruction vs Repair

• Repair (Sewing the torn MPFL) has poor outcomes (high recurrence).
• Reconstruction (New graft) is superior and the gold standard.

Dejour's Metrics

• Defined the anatomical risk factors ("The menu à la carte"). Surgery should address the specific anatomical deficits (e.g., if TT-TG is high, do TTO; if not, do MPFL).

What happened?

Your kneecap (patella) sits in a groove on the thigh bone like a train on a track. A twisting force caused the train to jump the track to the outside. This tore the "seatbelt" ligament (MPFL) that keeps it safe.

Will it heal?

For a first injury, the ligament usually heals with rest and a brace. We focus on strengthening the inner thigh muscles (VMO) to help guide the kneecap.

What if it keeps happening?

If it happens again, the ligament is likely stretched out and useless. We need to perform surgery to build you a new ligament (MPFL Reconstruction) using a spare tendon from your hamstring.

Q1: Where is Schottle's Point? A: The radiographic landmark for the femoral insertion of the MPFL. Located 1mm anterior to the posterior femoral cortical line and 2.5mm distal to the posterior medial femoral condyle origin.

Q2: What is the significance of the TT-TG distance? A: Tibial Tubercle-Trochlear Groove distance. It measures the "lateral vector" or bowstring effect of the quadriceps. Normal is <15mm. >20mm is pathological and requires medialization osteotomy.

Q3: Name 3 radiological signs of Trochlear Dysplasia. A:

1. Crossing Sign: Trochlear floor crosses anterior condyles line on lateral view.
2. Supratrochlear Spur: A bump at the top of the trochlea.
3. Double Contour Sign: Medial condyle hypoplasia.

Q4: Why is direct repair of the MPFL generally not recommended? A: Direct repair (suturing) has high failure rates compared to reconstruction, likely because the tissue is attenuated/stretched. Reconstruction with a tendon graft provides a stronger, more predictable check-rein.

(End of Topic)