What is the appropriate acute management and work‑up for a rock climber with an acute left knee pull, inability to fully extend the knee and slight valgus of the lower leg, currently non‑weight bearing with a crutch?

Acute Management of Suspected Patellar Tendon Rupture

This patient requires immediate plain radiographs (AP and lateral views) followed by urgent orthopedic consultation, as the inability to fully extend the knee with a history of acute trauma strongly suggests patellar tendon rupture or other extensor mechanism injury requiring surgical repair. 1, 2

Immediate Clinical Assessment

Red Flag Identification

• Inability to fully extend the knee ("extension lag") is a critical finding that indicates extensor mechanism disruption (patellar tendon rupture, quadriceps tendon rupture, or patellar fracture). 1, 2
• The valgus deformity of the lower leg suggests possible ligamentous injury or fracture-dislocation requiring urgent evaluation. 2
• A palpable gap in the tendon, if present on examination, constitutes an orthopedic emergency. 2

Essential Physical Examination Elements

• Palpate for a defect or gap in the patellar tendon (between inferior pole of patella and tibial tuberosity) or quadriceps tendon (superior to patella). 2
• Assess patellar position: a high-riding patella (patella alta) suggests patellar tendon rupture; a low-riding patella suggests quadriceps tendon rupture. 2
• Test active knee extension against gravity while the patient is supine with knee flexed over the edge of the examination table—complete inability indicates full-thickness rupture. 2
• Evaluate for joint effusion and assess valgus/varus stability at 0° and 30° of flexion. 2

Imaging Protocol

Initial Radiographs (Mandatory First Step)

Order AP and lateral knee radiographs immediately—this patient meets multiple Ottawa Knee Rule criteria (inability to bear weight, inability to flex knee to 90°). 1, 2

The lateral view is particularly critical because:

• It reveals patellar position abnormalities (alta or baja). 1
• It may show avulsion fractures at tendon insertion sites. 1
• It can demonstrate joint effusion and soft tissue swelling patterns. 1

Advanced Imaging Indications

If radiographs show no fracture but clinical suspicion for extensor mechanism rupture remains high, MRI without contrast is the appropriate next study to visualize tendon integrity, partial versus complete tears, and associated soft tissue injuries. 1

Do not delay orthopedic referral waiting for MRI—clinical diagnosis of complete extensor mechanism rupture (inability to extend knee + palpable gap) warrants immediate surgical consultation even before MRI. 1, 2

Acute Management Algorithm

Immediate Interventions (First 24 Hours)

1. Immobilize the knee in full extension using a knee immobilizer or cylinder cast to prevent further tendon retraction. 2
2. Maintain strict non-weight-bearing status with crutches—the patient is already appropriately using a crutch. 1, 3
3. Apply ice and elevate the limb to minimize swelling. 4
4. Obtain orthopedic consultation within 24 hours—complete extensor mechanism ruptures require surgical repair, ideally within 2 weeks of injury to optimize outcomes. 1, 2

Differential Diagnosis Considerations

While extensor mechanism rupture is most likely, the valgus deformity raises concern for:

• Lateral collateral ligament (LCL) or posterolateral corner injury (less common but possible with valgus stress). 2
• Tibial plateau fracture with valgus collapse (would be visible on radiographs). 1
• Combined ligamentous injuries (ACL/PCL with collateral ligament damage). 2

If radiographs reveal fracture-dislocation or gross instability, this constitutes a surgical emergency requiring same-day orthopedic intervention. 2, 4

Common Pitfalls to Avoid

• Do not assume this is a simple meniscal tear or sprain—inability to extend the knee is never a benign finding and demands investigation for extensor mechanism disruption. 1, 2
• Do not allow the patient to weight-bear or attempt active knee extension exercises—this can convert a partial tear into a complete rupture. 1, 3
• Do not order MRI as the first imaging study—plain radiographs must be obtained first to exclude fracture and assess patellar position. 1, 2
• Do not discharge the patient without orthopedic follow-up arranged—delayed diagnosis of patellar tendon rupture leads to tendon retraction, quadriceps atrophy, and poor surgical outcomes. 1, 2
• Ensure proper crutch fitting and gait training—improper crutch use can cause secondary upper extremity injuries (axillobrachial arterial complications with axillary crutches, compressive neuropathies with forearm crutches). 5

Expected Clinical Course

If this is a complete extensor mechanism rupture requiring surgery:

• Surgical repair is typically performed within 2 weeks of injury. 1
• Post-operative immobilization lasts 2-6 weeks depending on repair integrity. 6
• Full weight-bearing is typically restricted for 2-7 days post-operatively, though this varies by surgical technique. 6
• Return to full activity takes 4-6 months with structured rehabilitation. 6

The key to optimal outcome is early diagnosis and timely surgical intervention—do not delay orthopedic referral. 1, 2