STUDY DESIGN: Controlled laboratory study using a cross-sectional design. OBJECTIVES: To evaluate knee joint dynamics in elite volleyball players with and without a history of patellar tendinopathy, focusing on mechanical energy absorption and generation. We hypothesized that tendinopathy would be associated with
reduced net joint work and net joint power. BACKGROUND: Patellar tendinopathy is a common, debilitating injury affecting competitive volleyball players. METHODS: Thirteen elite male players with and without a history of patellar tendinopathy (mean ± SD age, 27 ± 7 years) performed maximum-effort volleyball approach jumps. Sagittal plane knee joint kinematics, kinetics, and energetics were quantified in the lead limb, using data obtained from a force platform and an 8-camera motion analysis system. Vertical ground reaction forces and pelvis vertical velocity at takeoff were examined. Independent sample t tests were used to evaluate group differences (α = .05). RESULTS: The tendinopathy group, compared to controls, demonstrated significant reductions (approximately 30%) in net joint work and net joint power during the eccentric phase of the jump, with no differences in the concentric phase. Positive to-negative net joint work and net joint power ratios were significantly higher in the tendinopathy group, which had a net joint work ratio of 1.00 (95% CI: 0.77, 1.24) versus 0.76 (95% CI: 0.64, 0.88) for controls, and a net joint power ratio of 1.62 (95% CI: 1.15, 2.10) versus 1.00 (95% CI: 0.80, 1.21) for controls. There were no significant differences in net joint moment, angular velocity, or range of motion. Peak vertical ground reaction forces were lower for the tendinopathy group, while average vertical ground reaction forces and pelvis vertical velocity were similar. CONCLUSION: Patellar tendinopathy is associated with differences in sagittal plane mechanical energy absorption at the knee during maximum-effort volleyball approach jumps. Net joint work and net joint power may help define underlying mechanisms, adaptive effects, or rehabilitative strategies for individuals with patellar tendinopathy.

J Orthop Sports Phys Ther 2010;40(9):568-576, Epub 27 May 2010. doi:10.2519/jospt.2010.3313

KEY WORDS: biomechanics, eccentric, energetics, joint kinetics, tendon

Objective:To quantify patellofemoral joint reaction forces and stress while squatting with and without an external load.

Background: Although squatting exercises in the rehabilitation setting are often executed to a relatively shallow depth in order to avoid the higher joint forces associated with increased knee flexion, objective criteria for ranges of motion have not been established.

Methods and Measures: Fifteen healthy adults performed single-repetition squats to 90° of knee flexion without an external load and with an external load (35% of the subject’s body weight [BW]). Anthropometric data, three-dimensional kinematics, and ground reaction forces were used to calculate knee extensor moments (inverse dynamics approach), while a biomechanical model of the patellofemoral joint was used to quantify the patellofemoral joint reaction forces and patellofemoral joint stress. Data were analyzed during the eccentric (0–90°) and concentric (90–0°) phases of the squat maneuver.

Results: In both conditions, knee extensor moments, patellofemoral joint reaction forces, and patellofemoral joint stress increased significantly with greater knee flexion angles (P < 0.05). Peak patellofemoral joint force and stress was observed at 90° of knee flexion. Patellofemoral joint stress at 45°, 60°, 75°, and 90° of knee flexion during the eccentric phase, and at 75° and 90° during the concentric phase, was significantly greater in the loaded trials versus the unloaded trials.

Conclusion: The data indicate that during squatting, patellofemoral joint stress increases as the knee flexion angle increases, and that the addition of external resistance further increases patellofemoral joint stress. These findings suggest that in order to limit patellofemoral joint stress during squatting activities, clinicians should consider limiting terminal joint flexion angles and resistance loads.

J Orthop Sports Phys Ther. 2002; 32(4):141–148.

Key Words: biomechanics, knee, patellofemoral joint reaction force, patellofemoral joint stress