Adolescent Anterior Knee Pain With Buckling: Instability or Something Else?
A 16-year-old female club soccer player presents with 4 weeks of vague anterior knee pain that worsens with running and stair descent. She denies a single traumatic event but recalls one episode of buckling while planting to cut 10 days ago; there was no swelling, and she finished practice. She grew 6 cm in the past year. Examination shows no effusion, tenderness over the medial patellar facet, a positive patellar apprehension sign at 30 degrees of flexion, a positive J-sign, a Q-angle of 18 degrees, and tight hamstrings. Single-leg squat shows dynamic valgus; triple-hop symmetry is 85%. She wants to play in a tournament in 3 weeks. Radiographs have not yet been obtained.
1. What is the most likely diagnosis, and which findings argue against osteochondritis dissecans (OCD) or a physeal injury?
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The most likely diagnosis is patellar instability with maltracking and patellofemoral pain, not a fixed structural lesion.
- For instability/maltracking: apprehension at 30 degrees, J-sign, dynamic valgus, medial facet tenderness, and a buckling episode without effusion. The buckling likely reflects quadriceps inhibition rather than a true dislocation.
- Against OCD: OCD usually produces a recurrent effusion, focal tenderness over the medial femoral condyle, locking, or a history of insidious deep pain. This patient has no effusion or locking, and her pain is activity-related and diffuse.
- Against physeal injury: traction apophysitis causes well-localized tenderness at the tibial tubercle or inferior pole, pain with jumping, and no apprehension or J-sign. Her growth spurt is relevant, but the examination points elsewhere.
The absence of swelling and the positive apprehension/J-sign make patellar instability the leading problem. A full-resolution examination after strengthening is still needed.
2. What imaging, if any, should be obtained now, and what would change your decision to order MRI?
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Obtain plain radiographs now: weight-bearing AP, lateral, and skyline views. These assess patellar height, trochlear dysplasia, loose bodies, physeal status, and degenerative changes, and they are inexpensive and low-risk.
MRI is not routine for a first buckling episode without effusion, locking, or a loose body on radiographs. Order MRI if any of the following occur:
- recurrent dislocation or a true giving-way event with hemarthrosis;
- mechanical symptoms such as locking or catching;
- a loose body or osteochondral fragment seen on radiographs;
- failure to improve after 6-8 weeks of appropriate nonoperative care;
- inability to return to sport because of persistent pain or instability.
In this case, clinical examination and radiographs guide initial care; MRI would be overtesting unless a red flag appears.
3. She wants to play in a tournament in 3 weeks. What is your return-to-play plan and objective criteria?
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Tell her that 3 weeks is a short timeline and that clearance depends on criteria, not on the calendar.
Initial phase: relative rest from cutting, pivoting, and deep knee flexion; avoid complete rest. Begin quadriceps, gluteus medius, and hip external rotator strengthening; landing and single-leg squat retraining; optional patellar bracing or taping for comfort.
Return-to-play criteria before tournament play:
- no pain with daily activities or running;
- quadriceps strength at least 90% of the uninvolved side;
- triple-hop and single-leg hop limb symmetry at least 90%;
- controlled single-leg squat without dynamic valgus;
- no apprehension with sport-specific cutting drills.
If she does not meet these criteria, delay tournament play. Do not use a corticosteroid injection to mask symptoms; it does not correct maltracking and may increase tendon risk.