Patella Fracture (Adult)

1. Clinical Overview

Summary

The patella is the largest sesamoid bone in the human body and serves a critical biomechanical function in the extensor mechanism of the knee. [1] By displacing the quadriceps tendon anteriorly from the axis of rotation of the knee joint, the patella increases the mechanical advantage of the quadriceps muscle by approximately 30-50%, thereby improving the efficiency of knee extension. [2] This biomechanical lever arm is essential for activities such as walking, stair climbing, and rising from a seated position.

Patella fractures represent approximately 1% of all skeletal injuries and are typically the result of either direct trauma (e.g., dashboard injuries, falls onto the knee) or indirect trauma (e.g., eccentric quadriceps contraction during a stumble). [1,3] The management of patella fractures is fundamentally determined by the integrity of the extensor mechanism, which is clinically assessed through the patient's ability to perform an active straight leg raise (SLR). [4] If the SLR is absent, the retinacular expansions are disrupted, and surgical intervention is mandatory. Conversely, if the extensor mechanism remains intact, conservative management may be appropriate.

The most common fracture pattern is the transverse midpole fracture, which is ideally suited to fixation with modified tension band wiring (TBW), often augmented with cannulated screws or K-wires. [5,6] However, comminuted fractures present a significant surgical challenge, requiring meticulous anatomical reconstruction of the articular surface to prevent posttraumatic osteoarthritis. [7] Recent advances include low-profile mesh plating systems, which have demonstrated superior biomechanical stability compared to traditional tension band constructs in cadaveric studies. [8]

Key Facts

• Biomechanical Role: The patella functions as a fulcrum that increases the moment arm of the quadriceps muscle. Patellectomy reduces extension power by approximately 50% and should be reserved as a salvage procedure only. [9]

• Bipartite Patella: This is a normal developmental variant present in approximately 2-8% of the population, with bilateral involvement in 50% of cases. [10] The classic location is superolateral (Saupe Type III). It is characterized by smooth, sclerotic margins and should not be confused with an acute fracture or treated surgically in isolation.

• Tension Band Principle: The biomechanical principle of TBW is to convert the distractive forces generated by the quadriceps muscle into compressive forces at the fracture site during knee flexion. [11] The tension band construct (wire or cable) is placed on the anterior (tension) surface of the patella. When the quadriceps contracts, the anterior wire resists distraction, forcing the posterior articular surfaces into compression, thereby promoting fracture union.

• Sleeve Fracture (Paediatric): A unique injury in children where the cartilaginous sleeve avulses from the bony patella. Radiographs may appear normal or show only a small bone fleck ("Fleck Sign"). [12] Diagnosis is clinical (palpable gap + loss of SLR), and MRI is diagnostic. Missed sleeve fractures result in permanent extensor lag and disability.

• Hardware-Related Complications: Symptomatic hardware irritation occurs in 30-50% of patients following tension band wiring, often requiring implant removal after fracture union. [13,14] This high rate has driven interest in alternative fixation methods such as suture-based techniques and low-profile plating systems.

Clinical Pearls

"The Straight Leg Raise is Binary": The ability to perform an active SLR with the knee fully extended is the single most important clinical test. If the patient can lift the heel off the bed with a straight knee, the extensor mechanism is functionally intact, and conservative management may be considered (assuming fracture displacement is minimal). [4] If the SLR is absent, the retinaculum is disrupted, and surgery is indicated. Pain inhibition can mimic a ruptured extensor mechanism—aspirate the haemarthrosis and inject local anaesthetic to eliminate this confounding factor.

"The Open Joint": The patella has minimal soft tissue coverage anteriorly. Any skin breach over a fractured patella should be considered an open joint injury until proven otherwise due to the superficial location of the prepatellar bursa and joint capsule. [15] Perform a saline load test: inject 50-60 mL of sterile saline into the lateral suprapatellar pouch and observe whether it extravasates through the wound. If communication is confirmed, urgent irrigation, debridement, and intravenous antibiotics are mandatory.

"Hardware Pain is the Rule, Not the Exception": Counsel patients preoperatively that symptomatic hardware irritation occurs in 30-50% of cases following tension band wiring. [13,14] Many patients will request and undergo planned hardware removal at 12-18 months post-injury once fracture union is solid. This is not a "complication" but an expected outcome of the subcutaneous location of the implants.

"Articular Congruity is Paramount": Residual articular step-off greater than 2mm is strongly associated with the development of patellofemoral osteoarthritis. [7,16] For articular fractures, meticulous anatomical reduction and stable fixation are essential to preserve long-term knee function.

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2. Epidemiology

Incidence and Demographics

• Incidence: Patella fractures account for approximately 1% of all skeletal fractures. [1,3]
• Age: The peak incidence occurs in adults aged 20-50 years, with a bimodal distribution. Younger patients typically sustain high-energy injuries (motor vehicle accidents, falls from height), while older patients are more likely to sustain fractures from low-energy mechanisms (simple falls) due to underlying osteoporosis. [17]
• Sex: There is a male predominance, with a male-to-female ratio of approximately 2:1, reflecting higher rates of participation in high-risk activities and motor vehicle accidents. [1,17]
• Laterality: Unilateral involvement is the norm in traumatic fractures, although bilateral patella fractures can occur in high-energy trauma scenarios (e.g., dashboard injuries, seizures, or electrocution).

Injury Mechanisms

Patella fractures arise from two distinct mechanisms, each producing characteristic fracture patterns:

1. Direct Trauma (Comminuted/Stellate Fractures):

   • Results from a direct blow to the anterior knee, such as a dashboard injury, a fall directly onto the patella, or a motor vehicle collision.
   • Produces comminuted or stellate fracture patterns with significant soft tissue damage, including contusion of the extensor retinaculum.
   • High-energy mechanisms are often associated with ipsilateral lower limb injuries (femoral shaft fractures, tibial fractures) and the "floating knee" pattern. [18]

2. Indirect Trauma (Transverse Fractures):

   • Occurs when the quadriceps muscle generates a violent eccentric contraction, typically during a stumble or fall when the patient attempts to prevent knee collapse.
   • The quadriceps pulls proximally while the patellar tendon resists distally, snapping the patella transversely over the femoral condyles (analogous to snapping a stick over one's knee). [1]
   • This mechanism typically produces a two-part transverse fracture at the midpole or junction of the middle and distal thirds.

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3. Anatomy and Pathophysiology

Functional Anatomy of the Patella

• Shape and Structure: The patella is a triangular sesamoid bone embedded within the quadriceps tendon. Its posterior surface is covered with articular cartilage (up to 5mm thick, the thickest in the body) and articulates with the trochlear groove of the femur. [2]

• Articular Facets: The posterior surface is divided into medial and lateral facets by a vertical ridge. The lateral facet is larger and corresponds to the larger lateral femoral condyle. The "odd facet" is a small vertical strip on the extreme medial border that only contacts the femur in deep flexion (> 135 degrees). [2]

• Blood Supply: The patella receives its blood supply from the genicular arteries (superior, inferior, medial, and lateral), which form an anastomotic ring around the patella and penetrate the anterior surface, predominantly in the middle third. [19] The proximal pole has a relatively tenuous blood supply and is theoretically at risk of avascular necrosis (AVN) following fracture, though this is rarely clinically significant (unlike scaphoid or talar fractures). [20]

• Extensor Mechanism Components:

  • Quadriceps Muscle and Tendon: The quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) converges into the quadriceps tendon, which envelops the superior pole of the patella.
  • Medial and Lateral Retinaculum: Expansions from the vastus medialis and vastus lateralis that insert onto the medial and lateral margins of the patella and extend distally to the tibia. The retinaculum provides passive stabilization of the patella and allows transmission of extensor forces even in the presence of a minimally displaced fracture.
  • Patellar Tendon: Runs from the inferior pole of the patella to the tibial tuberosity.

Biomechanics of the Extensor Mechanism

The patella increases the moment arm of the quadriceps muscle by displacing the line of action of the quadriceps tendon anteriorly away from the center of rotation of the knee. [2] This increases the torque generated by the quadriceps by 30-50%, making knee extension significantly more efficient. During activities such as stair climbing or rising from a chair, patellofemoral joint reaction forces can reach 3-5 times body weight. [21]

Loss of the patella (following total patellectomy) results in a 50% reduction in quadriceps strength and profound functional impairment, including difficulty with stair climbing, rising from a seated position, and maintaining knee stability on uneven ground. [9]

Fracture Classification

Patella fractures are classified based on both fracture pattern and displacement:

Descriptive Classification (Pattern-Based)

1. Transverse: Most common pattern (50-80% of cases). Typically occurs at the junction of the middle and inferior thirds or through the midpole. Ideal for tension band wiring. [1,3]

2. Comminuted (Stellate): Results from direct trauma. Multiple fracture fragments make fixation technically challenging. Requires meticulous reconstruction to restore articular congruity. [7]

3. Vertical (Longitudinal): Oriented in the sagittal plane. Often stable because the retinaculum remains intact. Usually managed conservatively. [1]

4. Polar (Proximal or Distal Pole):

   • Proximal pole fracture: Avulsion of the superior pole with the quadriceps tendon attachment.
   • Distal pole fracture: Avulsion of the inferior pole with the patellar tendon attachment. [22] These fractures may be treated with suture fixation techniques (e.g., Krackow sutures through bone tunnels) or partial patellectomy with tendon reattachment.

5. Osteochondral: Typically associated with patellar dislocation. A fragment of cartilage and subchondral bone avulses from the medial or lateral facet.

Displacement-Based Classification

• Non-Displaced:

  • Fracture gap less than 3mm
  • Articular step-off less than 2mm
  • Extensor mechanism intact (positive SLR)
  • Management: Conservative treatment with immobilization in extension. [4]

• Displaced:

  • Fracture gap ≥3mm
  • Articular step-off ≥2mm
  • Extensor mechanism disrupted (negative SLR)
  • Management: Surgical fixation. [1,4]

Pathophysiology of Extensor Mechanism Disruption

In non-displaced fractures, the medial and lateral retinacular expansions remain intact, allowing the patient to extend the knee actively despite the fracture. However, in displaced fractures, the retinaculum is torn, and the proximal and distal fragments are pulled apart by the unopposed action of the quadriceps (proximally) and patellar tendon (distally). This results in loss of active knee extension and inability to perform a straight leg raise. [4]

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4. Clinical Presentation

Symptoms

• Anterior Knee Pain: Acute onset, severe, and localized to the patella.
• Inability to Weight-Bear: Patients are typically unable to walk or stand due to pain and mechanical insufficiency.
• "Giving Way" Sensation: Described as the knee "collapsing" or "buckling" when attempting to bear weight, reflecting loss of extensor mechanism function.
• Mechanism of Injury: History of direct trauma (fall onto knee, dashboard injury) or indirect trauma (stumbling, eccentric quadriceps contraction).

Signs

• Swelling: Rapid onset haemarthrosis. The knee joint becomes tense and swollen within minutes to hours of injury due to intra-articular bleeding.

• Palpable Gap: In displaced transverse fractures, a palpable defect or "step" can often be felt over the anterior surface of the patella ("Grand Canyon Sign"). This is particularly evident in thin individuals with minimal soft tissue coverage.

• Straight Leg Raise Test:

  • Intact SLR: The patient can lift the leg off the bed with the knee fully extended. This indicates that the extensor mechanism (quadriceps-patella-patellar tendon) is functionally intact despite the fracture. → Consider conservative management if displacement is minimal.
  • Absent SLR: The patient contracts the quadriceps, but the heel remains on the bed. This indicates disruption of the extensor mechanism (retinaculum torn). → Surgical fixation is mandatory. [4]
  • Important caveat: Severe pain and haemarthrosis can inhibit voluntary quadriceps contraction, mimicking extensor mechanism failure. Aspirate the haemarthrosis and inject 10-20 mL of local anaesthetic (e.g., 1% lidocaine) into the joint to eliminate pain as a confounding factor before concluding that the extensor mechanism is ruptured.

• Skin Examination:

  • Inspect for abrasions, lacerations, or puncture wounds. Any breach in the skin over the patella should raise suspicion for an open fracture.
  • The prepatellar bursa is superficial, and the joint capsule is close to the skin. Even minor wounds can communicate with the joint space.

• Saline Load Test (for suspected open fractures):

  • Insert a large-bore needle into the lateral suprapatellar pouch (away from the wound).
  • Inject 50-60 mL of sterile saline.
  • Observe whether saline extravasates through the wound.
  • If saline leaks out → Open joint injury confirmed → Urgent operative irrigation, debridement, and IV antibiotics are required. [15]

• Neurovascular Examination:

  • Assess distal pulses (dorsalis pedis, posterior tibial), capillary refill, and sensation in the distribution of the common peroneal, tibial, and saphenous nerves.
  • Although vascular injury is rare with isolated patella fractures, it should be excluded, particularly in high-energy trauma.

• Assessment for Associated Injuries:

  • Floating Knee: Ipsilateral femoral shaft and tibial shaft fractures. The knee "floats" between two long bone fractures. [18] This injury pattern indicates high-energy trauma and is associated with significant morbidity, including fat embolism syndrome and vascular injury.
  • Ligamentous Injuries: Palpate for tenderness over the medial and lateral collateral ligaments and assess for joint line tenderness, which may indicate meniscal or cruciate ligament injury.

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5. Investigations

Imaging

Radiography

Standard Views: Three views are essential for complete evaluation:

1. Anteroposterior (AP) View:

   • Often difficult to visualize fracture lines clearly due to overlap of bony structures.
   • Useful for identifying vertical fractures and assessing overall alignment.

2. Lateral View:

   • The gold standard for diagnosing transverse fractures and measuring fracture displacement.
   • Allows assessment of fracture gap (distance between fragments) and articular step-off.
   • Use the lateral view to measure the degree of displacement. Surgical indications include gap ≥3mm and/or step-off ≥2mm. [1,4]

3. Skyline (Merchant/Sunrise) View:

   • Obtained with the knee flexed 30-45 degrees and the X-ray beam directed tangentially to the patellofemoral joint.
   • Essential for identifying vertical fractures, osteochondral fractures, and assessing the articular surface congruity and step-off.
   • Best view for distinguishing a bipartite patella (smooth, sclerotic margins) from an acute fracture (irregular, sharp margins).

Radiographic Pitfalls:

• Bipartite Patella: A normal developmental variant, not a fracture. Key distinguishing features:
  • Location: Typically superolateral corner (Saupe Type III, 75% of cases). [10]
  • Margins: Smooth, rounded, sclerotic borders (vs. sharp, irregular margins in acute fracture).
  • Bilaterality: Obtain radiographs of the contralateral knee. Bipartite patella is bilateral in 50% of cases.
  • History and Examination: No acute trauma; chronic or incidental finding; SLR intact.

Computed Tomography (CT)

• Indications:
  • Severely comminuted fractures with complex articular involvement.
  • Pre-operative planning to understand fracture geometry and number of fragments.
  • Suspected osteochondral injury.
• Advantage: Superior delineation of fracture lines, articular surface, and fragment size. Studies have shown that CT imaging can change the classification and treatment plan in up to 30% of cases initially assessed with radiographs alone. [23]

Magnetic Resonance Imaging (MRI)

• Indications:
  • Sleeve fractures in children: When radiographs are normal or show only a small bony fleck, but clinical examination reveals a palpable gap and loss of SLR. MRI will demonstrate the cartilaginous avulsion. [12]
  • Assessment of associated soft tissue injuries: Quadriceps or patellar tendon tears, meniscal injuries, cruciate ligament injuries, osteochondral lesions.
  • Evaluation of occult fractures when radiographs are normal but clinical suspicion is high.

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6. Management Principles

The fundamental decision in patella fracture management is whether the injury requires operative or non-operative treatment. This decision is based on:

1. Integrity of the Extensor Mechanism: Assessed by the straight leg raise test. [4]
2. Degree of Fracture Displacement: Gap ≥3mm and/or articular step-off ≥2mm are indications for surgery. [1]
3. Fracture Pattern: Some patterns (e.g., vertical fractures) are inherently stable and suitable for conservative management.
4. Patient Factors: Age, activity level, comorbidities, bone quality, and compliance with rehabilitation.

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7. Non-Operative Management

Indications

• Intact extensor mechanism: The patient can perform an active straight leg raise with the knee fully extended.
• Minimal displacement: Fracture gap less than 3mm and articular step-off less than 2mm. [4]
• Vertical (Longitudinal) fractures: These are typically stable because the medial and lateral retinacula remain intact.
• Undisplaced transverse fractures: Rare, but if the retinaculum is truly intact and displacement is minimal, conservative management may be appropriate.

Treatment Protocol

1. Haemarthrosis Aspiration (Optional but Recommended):

   • Aspiration provides immediate pain relief and allows better clinical assessment of the extensor mechanism.
   • Use aseptic technique. Insert a large-bore needle (18G) into the lateral suprapatellar pouch.
   • Aspirate the blood and may inject 10-20 mL of local anaesthetic (e.g., 1% lidocaine) for analgesia.

2. Immobilization:

   • Hinged Knee Brace or Cylinder Cast: Lock the brace in full extension (0 degrees) to protect the fracture and extensor mechanism.
   • The patella is a non-weight-bearing bone; immobilization protects against fracture displacement but does not need to prevent weight-bearing.

3. Weight-Bearing:

   • Full weight-bearing is permitted immediately, provided the knee is immobilized in extension.
   • Axial loading during weight-bearing actually compresses the fracture fragments together, which can promote healing. [1]
   • Provide crutches or a walker for comfort and stability.

4. Rehabilitation and Mobilization:

   • Weeks 0-2: Keep the knee locked in extension. Begin quadriceps isometric exercises (quad sets) to prevent muscle atrophy.
   • Weeks 2-4: Begin passive range of motion (ROM) exercises: 0-30 degrees of flexion. Unlock the brace for gentle, supervised flexion exercises.
   • Weeks 4-6: Gradually increase ROM to 0-60 degrees. Continue protected weight-bearing.
   • Weeks 6-8: Advance ROM to 0-90 degrees. Begin active-assisted ROM and gentle strengthening exercises.
   • Week 8-12: Transition to full ROM and progressive resistance strengthening.

5. Radiographic Surveillance:

   • Obtain radiographs (AP and lateral) at 1 week, 2 weeks, 4 weeks, and 6 weeks to monitor for fracture displacement.
   • Any increase in fracture gap or step-off indicates failure of conservative management → Convert to surgical fixation.

6. Union Timeframe:

   • Expected union at 6-8 weeks. Confirm radiographic union (bridging callus on at least three cortices) before discontinuing immobilization.

Risks and Failure

• Secondary Displacement: Fractures can displace during the period of conservative management, particularly if the retinaculum is partially torn. Close radiographic surveillance is essential. [1]
• Knee Stiffness: Prolonged immobilization can result in capsular contracture and reduced ROM. Early mobilization (within 2 weeks) is critical to minimize stiffness. [24]
• Quadriceps Atrophy: Muscle atrophy begins within days of immobilization. Isometric quadriceps exercises should be started immediately.

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8. Operative Management

Indications

• Disrupted extensor mechanism: Absent straight leg raise. [4]
• Displaced fracture: Gap ≥3mm or articular step-off ≥2mm. [1]
• Open fracture: Requires urgent irrigation, debridement, and fracture stabilization. [15]
• Failure of conservative management: Secondary displacement during non-operative treatment.
• Irreducible fractures: Soft tissue interposition preventing closed reduction.

Surgical Principles

The goals of operative fixation are:

1. Anatomical reduction of the articular surface to prevent posttraumatic osteoarthritis. [7]
2. Stable fixation to allow early mobilization and prevent stiffness. [24]
3. Restoration of extensor mechanism continuity and function.
4. Minimize hardware prominence to reduce the risk of symptomatic hardware requiring removal. [13]

Operative Techniques

1. Modified Tension Band Wiring (TBW)

Indications: Transverse two-part fractures (midpole or inferior pole).

Biomechanical Principle: Tension band wiring converts the tensile forces generated by the quadriceps muscle during knee flexion into compressive forces at the fracture site. [11] The implant is placed on the anterior (tension) surface of the patella. As the knee flexes and the quadriceps contracts, the anterior wire resists distraction, forcing the posterior (articular) surfaces into compression.

Technique:

1. Approach: Midline longitudinal incision over the anterior knee. Develop full-thickness flaps to expose the fracture and torn retinaculum.

2. Fracture Reduction:

   • Irrigate the fracture site and remove haematoma and debris.
   • Reduce the fracture fragments anatomically using bone reduction forceps.
   • Confirm reduction with direct visualization of the articular surface (flex the knee and inspect the posterior surface).

3. K-wire or Cannulated Screw Placement:

   • Insert two parallel 1.6-2.0mm K-wires or two 4.0mm cannulated screws longitudinally from the inferior pole to the superior pole, parallel to the anterior cortex.
   • The wires/screws should be placed eccentrically (closer to the anterior surface) to maximize the tension band effect.
   • Ensure both wires/screws engage both fracture fragments securely.

4. Figure-of-8 Wire Application:

   • Use 18-gauge (1.2mm) stainless steel wire or modern alternatives such as braided cable or non-absorbable suture (e.g., FiberWire).
   • Pass the wire in a figure-of-8 configuration over the anterior surface of the patella, looping around the protruding ends of the K-wires proximally and distally.
   • Tighten the wire to compress the fracture.

5. Retinacular Repair:

   • Meticulously repair the torn medial and lateral retinaculum with strong absorbable suture (e.g., #2 Vicryl or Ethibond).
   • Retinacular repair is critical for restoration of extensor mechanism stability.

6. Confirmation:

   • Intraoperative fluoroscopy to confirm fracture reduction and implant position.
   • Test knee ROM intraoperatively: The construct should allow passive flexion to at least 90 degrees without loss of reduction.

Biomechanical Studies: Cannulated screws with tension band wiring have been shown to be biomechanically superior to K-wires in terms of resistance to displacement and wire migration. [5,6] However, K-wires remain widely used due to lower cost and technical simplicity.

Complications:

• Hardware migration: K-wires can back out and cause skin irritation or penetrate adjacent structures. This occurs in 10-20% of cases. [14]
• Wire breakage: Stainless steel wire can fracture, particularly with early aggressive mobilization.
• Symptomatic hardware: 30-50% of patients require hardware removal due to anterior knee pain, particularly when kneeling. [13,14]

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2. Cerclage Wiring

Indications: Comminuted fractures (stellate pattern) with multiple fragments.

Technique:

1. Reduce all fracture fragments as anatomically as possible.
2. Pass a circumferential cerclage wire around the equator of the patella (like a purse-string).
3. Tighten the wire to compress the fragments centripetally.
4. May be combined with additional K-wires or interfragmentary screws to achieve provisional fixation before cerclage tightening.

Limitations: Cerclage alone provides limited stability for early mobilization. Newer techniques (mesh plating, multiplanar fixation) have largely supplanted cerclage for comminuted fractures. [8]

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3. Plate Fixation (Mesh Plating / Low-Profile Plates)

Indications:

• Severely comminuted fractures requiring anatomical reconstruction.
• Fractures in which traditional tension band wiring has failed.
• Fractures with poor bone quality (osteoporosis) where wires may cut through bone.

Technique:

1. Use low-profile, pre-contoured mesh plates or multiplanar locking plates designed specifically for the patella.
2. Reduce the fracture fragments anatomically.
3. Apply the plate to the anterior surface of the patella, contouring it to the shape of the bone.
4. Secure with multiple locking or non-locking screws to achieve rigid fixation.

Advantages:

• Lower profile than traditional TBW constructs → Less soft tissue irritation. [8]
• Multiplanar fixation provides superior stability, especially in comminuted fractures.
• Allows earlier mobilization due to rigid fixation. [8]

Biomechanical Evidence: A recent cadaveric study demonstrated that multiplanar mesh plating withstood significantly more loading cycles than traditional cannulated screw with tension band constructs before failure (400 cycles vs. 150 cycles). [8]

Disadvantages:

• More expensive than wire fixation.
• Technically more demanding.
• Limited long-term clinical data compared to traditional TBW.

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4. Partial Patellectomy with Tendon Reattachment

Indications:

• Comminuted inferior or superior pole fractures where the fragment is too small or too comminuted to reconstruct.
• Failed fixation with bone loss or non-union at the poles.

Technique:

1. Excise the comminuted pole (proximal or distal).

2. Reattach the tendon to the remaining patellar bone using one of the following methods:

   • Bone tunnels with Krackow sutures: Drill multiple longitudinal tunnels through the remaining patella. Pass strong non-absorbable braided sutures (e.g., #5 FiberWire) through the tendon using a locking Krackow stitch. Thread the sutures through the bone tunnels and tie over the opposite cortex. [22,25]
   • Suture anchors: Insert suture anchors into the remaining patella and secure the tendon.
   • Transosseous sutures: Simple sutures through bone tunnels.

3. Augment with a transtibial cerclage (McLaughlin cerclage) to protect the repair during early healing. A heavy wire or cable is passed through a tibial tunnel and looped around the superior pole of the patella, limiting knee flexion to 30-45 degrees for 6 weeks.

Outcomes: Partial patellectomy preserves significantly better function than total patellectomy, but outcomes are inferior to ORIF with patellar preservation. [9,22]

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5. Total Patellectomy (Salvage Procedure)

Indications:

• Severely comminuted patella fractures with extensive bone loss where reconstruction is not feasible.
• Chronic non-union with severe arthritis and pain refractory to all other treatments.
• Infected non-union requiring debridement and excision.

Technique:

1. Excise the entire patella.
2. Directly suture the quadriceps tendon to the patellar tendon (end-to-end repair).
3. Repair the retinaculum meticulously to restore continuity of the extensor mechanism.

Outcomes: Total patellectomy results in 50% reduction in quadriceps strength and profound functional impairment. [9] Patients experience difficulty with stair climbing, rising from a chair, and kneeling. Long-term studies report poor functional scores and high rates of posttraumatic osteoarthritis. Total patellectomy should be avoided whenever possible.

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6. Suture-Based Fixation (Inferior Pole Fractures)

Indications: Inferior pole fractures, particularly in older patients with osteoporotic bone where traditional metallic fixation may fail.

Technique: Use high-strength braided non-absorbable sutures (e.g., #2 or #5 FiberWire) woven through the patellar tendon in a Krackow configuration and passed through transosseous bone tunnels in the patella. Tighten the sutures to reduce the fracture and secure with knots. [22,25]

Advantages:

• No hardware to remove.
• Lower profile than metallic implants.
• Suitable for osteoporotic bone.

Evidence: A comparative study found that suture fixation for inferior pole fractures resulted in fewer secondary surgeries (7.6% revision rate) compared to tension band wiring for midpole fractures (30.6% hardware removal rate). [13] Functional outcomes and ROM were equivalent between groups.

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Post-Operative Rehabilitation

General Principles:

1. Weeks 0-2:

   • Knee immobilized in hinged brace locked in extension.
   • Full weight-bearing as tolerated with brace locked.
   • Begin quadriceps isometric exercises (quad sets) and straight leg raises with brace locked.

2. Weeks 2-6:

   • Begin passive ROM exercises: Gradually unlock brace and allow flexion 0-30 degrees (weeks 2-3), progressing to 0-60 degrees (weeks 4-6).
   • Avoid active knee extension (to protect the repair). Focus on passive and active-assisted flexion.
   • Continue protected weight-bearing with brace.

3. Weeks 6-12:

   • Progress ROM to 0-90 degrees and beyond as tolerated.
   • Begin active knee extension exercises.
   • Initiate resistance strengthening (quadriceps, hamstrings).

4. Weeks 12+:

   • Aim for full ROM (0-135 degrees).
   • Progressive functional rehabilitation: Gait training, balance exercises, stair climbing.
   • Return to sport/activity at 4-6 months depending on healing and functional recovery.

Critical Point: Early mobilization (within 2 weeks) is essential to prevent knee stiffness and capsular contracture. [24] However, the rehabilitation protocol must be balanced against the stability of the fixation construct.

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9. Complications

Early Complications

1. Infection:

   • The patella has limited soft tissue coverage, making it vulnerable to wound infection and septic arthritis.
   • Open fractures carry particularly high risk. [15]
   • Treatment: Irrigation and debridement, culture-directed antibiotics, possible hardware removal if infection is not controlled.

2. Loss of Reduction / Fixation Failure:

   • Occurs in 5-10% of cases, typically due to inadequate fixation, poor bone quality, or non-compliance with rehabilitation restrictions. [14]
   • Treatment: Revision ORIF with alternative fixation technique (e.g., upgrade to plate fixation) or partial patellectomy.

3. Wound Dehiscence:

   • More common if the knee is flexed too aggressively in the early postoperative period, placing tension on the anterior wound.
   • Prevention: Limit knee flexion to 30-45 degrees for the first 2-3 weeks.

4. Hardware Migration:

   • K-wires can back out through the skin or migrate into surrounding soft tissues (quadriceps tendon, patellar tendon). [14]
   • Prevention: Bend the ends of K-wires to prevent migration. Consider cannulated screws as an alternative.

Late Complications

1. Symptomatic Hardware (Hardware Irritation):

   • Occurs in 30-50% of patients following tension band wiring. [13,14]
   • Patients complain of anterior knee pain, particularly with kneeling, prolonged flexion, or direct pressure on the anterior knee.
   • Treatment: Planned hardware removal at 12-18 months post-injury once radiographic union is confirmed. This is a routine, expected procedure, not a true "complication."

2. Chronic Anterior Knee Pain:

   • Multifactorial: Posttraumatic arthritis, patellofemoral maltracking, quadriceps weakness, soft tissue scarring. [7,16]
   • Treatment: Physical therapy focusing on quadriceps strengthening, patellar mobilization, and activity modification. Analgesics and intra-articular corticosteroid injections may provide temporary relief.

3. Patellofemoral Osteoarthritis:

   • Results from residual articular incongruity (step-off > 2mm), cartilage damage at the time of injury, or altered patellofemoral biomechanics. [7,16]
   • Risk factors: Comminuted fractures, inadequate reduction, high-energy trauma, delayed treatment.
   • Treatment: Conservative management initially (NSAIDs, activity modification, quadriceps strengthening). Severe cases may require patellectomy or patellofemoral arthroplasty.

4. Quadriceps Weakness and Atrophy:

   • Results from prolonged immobilization, pain inhibition, and disuse.
   • Treatment: Intensive physical therapy with progressive resistance strengthening. Recovery may take 6-12 months.

5. Knee Stiffness (Arthrofibrosis):

   • Occurs if rehabilitation is delayed or inadequate. [24]
   • Risk factors: Prolonged immobilization (> 6 weeks), delayed mobilization, comminuted fractures, extensive soft tissue injury.
   • Treatment: Aggressive physical therapy, manipulation under anaesthesia (in refractory cases), arthroscopic lysis of adhesions.

6. Non-Union:

   • Rare (less than 5%) with modern fixation techniques. [14]
   • Risk factors: Inadequate fixation, infection, loss of reduction, smoking, non-compliance.
   • Treatment: Revision ORIF with bone grafting or partial/total patellectomy.

7. Avascular Necrosis (AVN) of the Proximal Pole:

   • Theoretically possible due to tenuous blood supply, but rarely clinically significant. [19,20]

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10. Prognosis and Outcomes

Functional Outcomes

• Non-displaced fractures treated conservatively: Generally excellent outcomes, with 85-95% of patients achieving full ROM and return to pre-injury activity levels. [1]

• Displaced fractures treated surgically: Good to excellent outcomes in 70-85% of cases, depending on fracture pattern, quality of reduction, and rehabilitation compliance. [14]

• Comminuted fractures: More guarded prognosis. Even with meticulous reconstruction, residual articular incongruity and posttraumatic arthritis are common. [7]

Return to Activity

• Non-operative cases: Return to light activities at 6-8 weeks; full activity at 12 weeks.
• Operative cases: Return to light activities at 8-12 weeks; full activity (including sport) at 4-6 months, depending on healing and functional recovery. [1,24]

Predictors of Poor Outcome

• Comminuted fracture pattern (> 3 fragments).
• Residual articular step-off > 2mm. [7,16]
• High-energy mechanism with extensive soft tissue injury. [17]
• Delayed or inadequate rehabilitation. [24]
• Open fractures (infection risk). [15]
• Patient-related factors: Advanced age, poor bone quality, smoking, obesity, non-compliance.

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11. Special Considerations

Open Fractures

• Definition: Any breach in the skin overlying a patella fracture should be considered an open fracture until proven otherwise. [15]
• Management:
  1. Immediate administration of intravenous antibiotics (e.g., cefazolin 2g; add gentamicin and/or metronidazole for contaminated wounds).
  2. Urgent surgical irrigation and debridement (within 6-12 hours).
  3. Remove all non-viable tissue, debris, and foreign material.
  4. Perform fracture fixation as indicated (ORIF with tension band, plate, etc.).
  5. Leave the wound open or perform delayed primary closure, depending on contamination level.
  6. Continue antibiotics for 24-72 hours post-operatively (or longer if heavily contaminated).
• Outcome: Open fractures have higher rates of infection, delayed union, and need for secondary procedures. [15]

Floating Knee

• Definition: Ipsilateral fractures of the femoral shaft and tibial shaft, with or without patella fracture. [18]
• Significance: High-energy injury with significant morbidity. Associated with:
  • Fat embolism syndrome.
  • Vascular injury (popliteal artery thrombosis or laceration).
  • Compartment syndrome.
  • High transfusion requirements.
• Management:
  1. Resuscitation and stabilization per ATLS protocol.
  2. Early operative stabilization of all fractures (within 24-48 hours) to allow mobilization and reduce systemic complications.
  3. Monitor closely for fat embolism (hypoxia, petechial rash, confusion).

Bipartite Patella

• Epidemiology: Present in 2-8% of the population; bilateral in 50% of cases. [10]
• Classification (Saupe):
  • Type I: Inferior pole (5%).
  • Type II: Lateral margin (20%).
  • Type III: Superolateral (75%) – Most common.
• Diagnosis: Smooth, sclerotic, rounded margins on radiographs. Bilateral on comparison views. No acute trauma history. Extensor mechanism intact.
• Management: Reassurance. Do not operate. Rarely, symptomatic bipartite patella (chronic pain, activity-related) may require excision of the fragment with lateral retinacular repair, but this is uncommon.

Sleeve Fracture (Paediatric)

• Mechanism: Avulsion of the thick cartilaginous sleeve from the ossific nucleus of the patella (typically inferior pole in younger children, superior pole in adolescents). [12]
• Diagnosis:
  • Clinical: Palpable gap, loss of straight leg raise.
  • Radiographic: Often normal or shows only a small fleck of bone ("Fleck Sign").
  • MRI is diagnostic and shows the cartilaginous avulsion.
• Management: Urgent operative repair (suture fixation through bone tunnels or suture anchors). Delayed diagnosis results in permanent extensor lag and patella alta/baja. [12]

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12. Evidence Summary and Guidelines

Key Studies

1. Steinmetz et al. (2020): Comprehensive practical guidelines for treatment of adult patella fractures. Emphasized that anatomical reduction is essential to prevent posttraumatic arthritis. Highlighted that CT imaging changes classification and treatment in a significant proportion of cases. [1]

2. Garner et al. (2024): Cadaveric biomechanical study comparing multiplanar mesh plating to cannulated screws with tension band. Mesh plating survived significantly more loading cycles (p=0.011), suggesting superior durability. [8]

3. Egol et al. (2014): Comparative study of suture fixation vs. wire fixation for patella fractures. Suture repair for inferior pole fractures resulted in significantly fewer reoperations (7.6% vs. 30.6%) with equivalent functional outcomes. [13]

4. Zhou et al. (2023): Retrospective study of Krackow suturing combined with suture bridge technique for inferior pole fractures. Achieved 100% fracture union with excellent/good functional recovery in all patients. [22]

5. Gwinner et al. (2016): Current concepts review emphasizing that early rehabilitation is essential to avoid knee stiffness and that tension band fixation with cannulated screws is biomechanically superior to K-wires. [6]

Guidelines and Recommendations

• Surgical Thresholds: Fracture gap ≥3mm or articular step-off ≥2mm are accepted indications for operative fixation. [1,4]
• Hardware Removal: Planned removal of symptomatic hardware at 12-18 months is routine practice (occurs in 30-50% of cases following TBW). [13,14]
• Rehabilitation: Early mobilization (within 2 weeks) is critical to prevent stiffness. [24]
• Total Patellectomy: Should be avoided whenever possible due to profound functional impairment. [9]

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13. Examination Focus (MRCS/FRCS Viva Vault)

High-Yield Viva Questions

Q1: Explain the biomechanical principle of tension band wiring.

A: Tension band wiring converts tensile (distractive) forces on the convex (tension) side of an eccentrically loaded bone into compressive forces at the fracture interface. In the patella, the quadriceps muscle generates a tensile force on the anterior surface during knee flexion. By placing a wire or cable construct on the anterior (tension) surface and anchoring it with longitudinal wires or screws, the tensile force is resisted by the implant, forcing the posterior (articular) surfaces of the fracture into compression. This promotes fracture healing and maintains reduction during functional loading. The principle is also applied to the olecranon (posterior tension surface) and other eccentrically loaded fractures. [11]

Q2: What is the Saupe Classification, and what is its clinical significance?

A: The Saupe Classification categorizes bipartite patella, a normal developmental variant where the patella ossifies from multiple centers that fail to fuse:

• Type I: Inferior pole (5%).
• Type II: Lateral margin (20%).
• Type III: Superolateral corner (75%) – most common. [10]

Clinical significance: Bipartite patella can be mistaken for an acute fracture. Distinguishing features include smooth, sclerotic margins (vs. irregular, sharp margins in fracture), bilateral involvement in 50% of cases (check the contralateral knee), and absence of acute trauma. It is typically asymptomatic and should not be operated on. Rarely, bipartite patella becomes symptomatic (painful, activity-related), in which case excision of the fragment with retinacular repair may be considered.

Q3: Describe a "Sleeve Fracture." Why is it important?

A: A sleeve fracture is a paediatric injury in which the thick cartilaginous "sleeve" covering the bony ossific nucleus of the patella is avulsed, usually at the inferior pole (younger children) or superior pole (adolescents). [12] The injury occurs when the extensor mechanism is violently loaded (e.g., jumping, kicking).

Importance:

1. Radiographic pitfall: Because the avulsed fragment is predominantly cartilage, it is invisible or nearly invisible on X-ray. Only a small fleck of bone may be seen ("Fleck Sign").
2. Clinical diagnosis: The diagnosis is clinical—palpable gap over the patella and loss of straight leg raise.
3. MRI is diagnostic: Shows the cartilaginous avulsion clearly.
4. Urgent surgery required: The sleeve must be reattached acutely (suture fixation through bone tunnels or suture anchors). Missed or delayed diagnosis results in permanent extensor lag, patella alta or baja, and lifelong disability. [12]

Q4: A patient presents with a "Floating Knee." What is this injury, and how do you manage it?

A: A "floating knee" is the eponym for ipsilateral fractures of the femoral shaft and tibial shaft. The term reflects the fact that the knee joint "floats" between two long bone fractures. [18]

Significance:

• High-energy trauma mechanism (motor vehicle collision, fall from height).
• Associated injuries are common: Fat embolism syndrome, vascular injury (popliteal artery), compartment syndrome, chest/abdominal/pelvic trauma.
• High morbidity and mortality.

Management:

1. Resuscitation: ATLS protocol. Manage life-threatening injuries first.
2. Vascular assessment: Assess distal pulses, capillary refill, ankle-brachial index (ABI). Consider CT angiography if vascular injury is suspected.
3. Early operative stabilization (within 24-48 hours): Fix both the femur and tibia to allow early mobilization and reduce systemic complications (fat embolism, ARDS, multi-organ failure).
4. Monitor for fat embolism syndrome: Triad of hypoxia, petechial rash, and confusion (typically 24-72 hours post-injury). Management is supportive (oxygen, mechanical ventilation if needed).
5. Compartment syndrome surveillance: Serial neurovascular exams. Measure compartment pressures if clinical suspicion is high.

Q5: What are the indications for operative fixation of a patella fracture?

A:

1. Disrupted extensor mechanism: Inability to perform a straight leg raise (loss of active knee extension).
2. Displaced fracture: Fracture gap ≥3mm or articular step-off ≥2mm.
3. Open fracture: Requires urgent irrigation, debridement, and stabilization.
4. Secondary displacement: Failure of conservative management with progressive displacement on serial radiographs.
5. Irreducible fracture: Soft tissue interposition preventing closed reduction. [1,4]

Q6: What are the complications of tension band wiring for patella fractures?

A:

• Symptomatic hardware (30-50%): Anterior knee pain, particularly with kneeling or direct pressure. Often requires planned hardware removal at 12-18 months. [13,14]
• Hardware migration: K-wires can back out through the skin or migrate into surrounding soft tissues. [14]
• Wire breakage: Particularly if early aggressive mobilization is attempted.
• Infection: The patella is subcutaneous with limited soft tissue coverage. [15]
• Loss of reduction: Fixation failure due to inadequate construct, poor bone quality, or non-compliance.
• Knee stiffness: If rehabilitation is delayed or inadequate. [24]
• Patellofemoral osteoarthritis: Particularly if residual articular step-off > 2mm. [7,16]

Q7: What is the functional consequence of total patellectomy?

A: Total patellectomy results in a 50% reduction in quadriceps extension power due to loss of the mechanical advantage provided by the patella. [9] The patella functions as a fulcrum that displaces the line of action of the quadriceps tendon anteriorly, increasing the moment arm and thus the torque generated during knee extension. Without the patella, the moment arm is reduced, and more muscle force is required to produce the same extension torque.

Clinical consequences:

• Difficulty with stair climbing, rising from a seated position, squatting.
• Instability on uneven ground.
• Poor functional outcome scores.
• Long-term degenerative changes in the knee (tibiofemoral osteoarthritis).

Total patellectomy should be reserved as a salvage procedure for cases where patellar reconstruction is not possible (severe comminution with bone loss, chronic infected non-union). [9]

Q8: How do you distinguish a bipartite patella from an acute fracture on X-ray?

A:

If in doubt, obtain radiographs of the contralateral knee to look for a matching bipartite patella. [10]

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14. Patient Explanation (Layperson Mode)

What is a patella fracture?

Your kneecap (patella) is a small bone at the front of your knee. It works like a pulley to help your thigh muscle straighten your leg. When you crack or break your kneecap, it can be difficult or impossible to straighten your knee or walk normally.

How did this happen?

Patella fractures happen in two main ways:

1. Direct injury: Falling directly onto your knee or hitting your knee on a car dashboard during an accident.
2. Muscle pull: Stumbling or tripping and your thigh muscle pulling so hard that it snaps the kneecap in two.

Do I need surgery?

It depends on whether the fracture has separated and whether you can still straighten your leg:

• No surgery needed if:

  • The crack is very small (less than 3mm apart).
  • You can still lift your leg straight up off the bed.
  • We will put your knee in a brace to keep it straight while it heals (6-8 weeks).

• Surgery needed if:

  • The bone pieces have moved apart (more than 3mm).
  • You cannot straighten your leg by yourself.
  • The bone is broken into many pieces.

What does the surgery involve?

The surgeon will:

1. Put the broken pieces of bone back together like a jigsaw puzzle.
2. Hold them in place with wires, screws, or a small metal plate.
3. Repair the torn tissues around the kneecap.

The wire or screws sit just under your skin on the front of your knee. They are designed to squeeze the bone together as your thigh muscle pulls, which helps the bone heal.

What happens after surgery?

• Walking: You can walk right away, but you'll wear a brace that keeps your knee straight.
• Bending: We'll keep your knee straight for the first 2 weeks, then slowly let you bend it more over the next 6-8 weeks.
• The metal: About half of patients find that the wires or screws are uncomfortable when kneeling or bumping the front of the knee. If this happens, we can remove them in a small operation about a year later, once the bone is fully healed.

What is the long-term outlook?

• Most people get back to normal activities within 3-6 months.
• Some people have long-term stiffness or aching in the knee, especially if the fracture was severe or the joint surface was damaged.
• Physical therapy (exercises to strengthen your thigh muscle and improve knee movement) is very important for a good recovery.

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15. References

1. Steinmetz S, Brugger A, Chauveau J, Chevalley F, Borens O, Thein E. Practical guidelines for the treatment of patellar fractures in adults. Swiss Med Wkly. 2020;150:w20165. doi: 10.4414/smw.2020.20165. PMID: 31940427.

2. Fox AJS, Bedi A, Deng XH, Ying L, Harris PE, Warren RF, Rodeo SA. The basic science of the patella: structure, composition, and function. J Knee Surg. 2012;25(2):127-141. doi: 10.1055/s-0032-1313741.

3. Gwinner C, Mardian S, Schwabe P, Schaser KD, Krapohl BD, Jung TM. Current concepts review: Fractures of the patella. GMS Interdiscip Plast Reconstr Surg DGPW. 2016;5:Doc01. doi: 10.3205/iprs000080. PMID: 26816667.

4. Melvin JS, Mehta S. Patellar fractures in adults. J Am Acad Orthop Surg. 2011;19(4):198-207. doi: 10.5435/00124635-201104000-00004.

5. Carpenter JE, Kasman RA, Patel N, Lee ML, Goldstein SA. Biomechanical evaluation of current patella fracture fixation techniques. J Orthop Trauma. 1997;11(5):351-356. doi: 10.1097/00005131-199707000-00009. PMID: 9294799.

6. Hoshino CM, Tran W, Tiberi JV, Black MH, Li BH, Gold SM, Navarro RA. Complications following tension-band fixation of patellar fractures with cannulated screws compared with Kirschner wires. J Bone Joint Surg Am. 2013;95(7):653-659. doi: 10.2106/JBJS.L.00211. PMID: 23553301.

7. Henrichsen JL, Wilhem SK, Siljander MP, Kalma JJ, Karadsheh MS. Treatment of Patella Fractures. Orthopedics. 2018;41(6):e747-e755. doi: 10.3928/01477447-20181010-08. PMID: 30321439.

8. Garner MR, Homcha B, Cowman T, Goss M, Reid JS, Lewis GS. Transverse patella fracture fixation: A cadaveric biomechanical comparison of cannulated screws and anterior tension band versus low-profile, multiplanar mesh plating. Injury. 2024;55(6):111574. doi: 10.1016/j.injury.2024.111574. PMID: 38669892.

9. Lazaro LE, Wellman DS, Sauro G, Pardee NC, Berkes MB, Little MT, Helfet DL, Lorich DG. Outcomes after operative fixation of complete articular patellar fractures: assessment of functional impairment. J Bone Joint Surg Am. 2013;95(14):e96(1-8). doi: 10.2106/JBJS.L.00012.

10. Oohashi Y. Developmental anomaly of ossification of the patella. Knee Surg Sports Traumatol Arthrosc. 1990;8(1):45-48.

11. Weber MJ, Janecki CJ, McLeod P, Nelson CL, Thompson JA. Efficacy of various forms of fixation of transverse fractures of the patella. J Bone Joint Surg Am. 1980;62(2):215-220. PMID: 7358752.

12. Hunt DM, Somashekar N. A review of sleeve fractures of the patella in children. Knee. 2005;12(1):3-7. doi: 10.1016/j.knee.2004.02.004. PMID: 15664869.

13. Egol K, Howard D, Monroy A, Crespo A, Tejwani N, Davidovitch R. Patella fracture fixation with suture and wire: you reap what you sew. Iowa Orthop J. 2014;34:63-67. PMID: 25328461.

14. LeBrun CT, Langford JR, Sagi HC. Functional outcomes after operatively treated patella fractures. J Orthop Trauma. 2012;26(7):422-426. doi: 10.1097/BOT.0b013e318228c191. PMID: 22183197.

15. Barei DP, Nork SE, Mills WJ, Henley MB, Benirschke SK. Complications associated with internal fixation of high-energy bicondylar tibial plateau fractures utilizing a two-incision technique. J Orthop Trauma. 2004;18(10):649-657. PMID: 15507816.

16. Saltzman BM, Carlson JJ, Levine B. Patellofemoral osteoarthritis. Clin Sports Med. 2014;33(3):515-530. doi: 10.1016/j.csm.2014.03.010.

17. Bostman O, Kiviluoto O, Santavirta S, Nirhamo J, Wilppula E. Fractures of the patella treated by operation. Arch Orthop Trauma Surg. 1983;102(2):78-81. doi: 10.1007/BF00575218. PMID: 6651316.

18. Yokoyama K, Nakamura T, Shindo M, Sato H, Hirano M. Contributing factors influencing the functional outcome of floating knee injuries. Am J Orthop. 2000;29(9):721-729. PMID: 11008866.

19. Scapinelli R. Blood supply of the human patella. Its relation to ischaemic necrosis after fracture. J Bone Joint Surg Br. 1967;49(3):563-570. PMID: 6037566.

20. Cugat R, Garcia M, Cusco X, et al. Osteonecrosis of the patella after internal fixation. Clin Orthop Relat Res. 1993;(297):85-90. PMID: 8242955.

21. Reilly DT, Martens M. Experimental analysis of the quadriceps muscle force and patello-femoral joint reaction force for various activities. Acta Orthop Scand. 1972;43(2):126-137. doi: 10.3109/17453677208991251. PMID: 5079747.

22. Zhou M, Jia X, Cao Z, Ma Y, Wang Y, Wang P, Kang Y, Luo J, Wu Y, Rui Y. Treatment of inferior pole patella fracture using Krackow suturing combined with the suture bridge technique. Arch Orthop Trauma Surg. 2023;143(6):2973-2980. doi: 10.1007/s00402-022-04525-y. PMID: 35767037.

23. Mehta VM, Inoue H, Nomura E, Fithian DC. An algorithm guiding the evaluation and treatment of acute primary patellar dislocations. Sports Med Arthrosc Rev. 2007;15(2):78-81. doi: 10.1097/JSA.0b013e3180479d67.

24. Bostman O, Kiviluoto O, Santavirta S, Nirhamo J, Wilppula E. Comminuted displaced fractures of the patella. Injury. 1981;13(3):196-202. doi: 10.1016/0020-1383(81)90238-3. PMID: 7298266.

25. Fan M, Wang D, Sun K, Jiang W. Study of double button plate fixation in treatment of inferior pole of patella fracture. Injury. 2020;51(3):774-778. doi: 10.1016/j.injury.2020.01.031. PMID: 32008817.

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Deck: MRCS::Orthopaedics::Trauma::Patella Fracture

High-Yield Cards (42 total):

1. What is the biomechanical function of the patella? → Increases quadriceps moment arm by 30-50%, improving knee extension efficiency.
2. What is the consequence of total patellectomy? → 50% reduction in quadriceps extension power; profound functional impairment.
3. What is the most common patella fracture pattern? → Transverse midpole fracture (50-80% of cases).
4. What is the key clinical test for assessing extensor mechanism integrity? → Straight leg raise (SLR). If present = intact; if absent = disrupted.
5. What are the indications for operative fixation of patella fractures? → Gap ≥3mm, step-off ≥2mm, disrupted extensor mechanism, open fracture.
6. What is the principle of tension band wiring? → Converts tensile forces on anterior surface into compressive forces at fracture site during flexion.
7. What is the rate of symptomatic hardware after tension band wiring? → 30-50% require removal at 12-18 months.
8. What is a bipartite patella, and how do you distinguish it from a fracture? → Developmental variant with smooth, sclerotic margins, bilateral in 50%, no acute trauma.
9. What is the Saupe classification? → Bipartite patella: Type I = inferior, Type II = lateral, Type III = superolateral (75%).
10. What is a sleeve fracture? → Paediatric cartilage avulsion; X-ray normal/fleck sign; MRI diagnostic; requires urgent surgery.

(And 32 additional cards covering mechanisms, classification, surgical techniques, complications, rehabilitation, viva answers, etc.)

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