Knee Valgus Collapse on Landing in a Basketball Guard
A 22-year-old female Division I basketball guard has had recurrent right anterior knee pain for two seasons, worst with rebounding and landing. She has no effusion, full knee range of motion, and pain with patellar compression at 30° of flexion. Slow-motion video of a two-foot rebound landing shows both knees crossing medial to the great toes, right knee valgus of about 18°, and a loud landing with minimal hip and knee flexion. Weight-bearing ankle dorsiflexion is 8° on the right and 20° on the left; hip abduction strength is 18% lower on the right; single-leg squat shows 20° of contralateral pelvic drop. She wants to complete the season without missing games. The team has two practices and one game per week and no access to a motion lab.
1. Explain the mechanism linking her landing mechanics to patellofemoral pain, using moment arms, the dynamic Q angle, and muscle demand.
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At landing, the ground reaction force acts upward through the foot. If the knee is in valgus, the force line passes medial to the knee joint center, creating a frontal-plane moment arm. The knee extensors and hip abductors must counteract that moment: the quadriceps generate a large patellofemoral joint reaction force, while the gluteus medius and external rotators work eccentrically to control femoral adduction and internal rotation. Valgus also increases the dynamic Q angle, which laterally displaces the patella and raises stress on the lateral facet. The observed 18° valgus and the loud landing with little hip and knee flexion mean the force is absorbed over a short time and small range, increasing peak force. The combination of a larger frontal-plane moment arm, a higher Q angle, and a stiff landing explains why her pain is worst with rebounding. The absence of effusion argues against intra-articular pathology, but patellar compression pain supports a patellofemoral source.
2. Explain how the ankle and hip findings interact with the knee, and list the assessments you would add.
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Limited ankle dorsiflexion (8° versus 20°) restricts how far the tibia can advance over the foot. To achieve the knee flexion needed to absorb force, she likely compensates by moving the knee inward and landing more flat-footed, which increases valgus. Reduced hip abduction strength (18% deficit) limits her ability to resist that valgus. The contralateral pelvic drop during single-leg squat shows the same hip abductor problem in a controlled task. The two findings interact: stiff ankles push the demand up the chain, and weak hips cannot control it. Assessments to add: weight-bearing lunge test for dorsiflexion, hip abduction and external rotation strength with a hand-held dynamometer, single-leg squat and drop-jump kinematics using frontal plane projection angle from video, and landing force symmetry if a force plate is available. Treating only the knee would miss the proximal and distal drivers.
3. Design a four-week in-season program and describe how you would monitor whether her landing mechanics change.
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In-season, keep volume low and frequency high: two 15-minute sessions per week plus brief pre-practice activation. Weeks 1–2: ankle dorsiflexion mobility (weight-bearing lunge, 3 × 30 s), gluteus medius strengthening (side-lying clamshell, lateral band walk, 2 × 12), and landing technique with an external focus cue such as 'land quietly' or 'spread the floor' rather than 'don't let your knees cave.' Weeks 3–4: add drop landings from a 20–30 cm box, then rebound jumps, progressing from two legs to one leg only if the knee stays over the foot. Monitor with a frontal plane projection angle from a phone video at each session and with pain during and 24 hours after. If pain exceeds 3/10 or she develops an effusion, reduce jump volume. The rationale is to change the frontal-plane moment arm and improve force absorption, not just to strengthen muscles in isolation.