Patellar mobility and lower limb kinematics during functional activities in individuals with and without patellar tendinopathy

STUDY DESIGN: Case-control. OBJECTIVE: To examine whether patients with patellar tendinopathy (PT) display greater patellar mobility and different lower body kinematics than patients without PT. BACKGROUND: PT is a common overuse condition of the patellar tendon that can cause pain and impair function. Subjects with overuse knee problems display different hip and knee functional mechanics, specifically valgus collapse. Patellar hypermobility has not been specifically studied as a possible risk factor for PT. METHODS: 11 patients with PT and 11 controls without PT, age 18 to 40, were studied. Using a patellofemoral arthrometer (PFA), maximal lateral and medial patellar displacement was measured. 3-D motion analysis was performed to determine lower extremity joint motions during single-leg step down and drop vertical jump tests. RESULTS: Patients with PT had significantly increased lateral patellar mobility compared to controls (12.21 ± 3.33 mm vs. 9.19 ± 1.92 mm, P = .017). PT patients showed significantly greater peak hip adduction with both drop vertical jump (2.7° ± 6.3° vs. −5.6° ± 4.2°; P = .003) and step down (17.0° ± 3.8° vs. 12.5° ± 4.4°, P = .024). PT patients demonstrated increased peak ankle external rotation with drop vertical jump (−21.1° ± 5.9° vs. −14.8° ± 5.5°, P = .023) and step down (−15.6° ± 5.5° vs. −9.0° ± 6.0°, P = .017). CONCLUSIONS: Patients with PT exhibit increased lateral patellar mobility, hip adduction, and ankle external rotation. The effects of increased patellar mobility deserve further study in the development, management, and prevention of PT.