The biomechanics of sit-to-stand and physical performance in patellofemoral osteoarthritis

Osteoarthritis (OA) of the knee is common in Western society. OA of the patellofemoral (PF) compartment of the knee is prevalent in adults greater than 55 years of age. Isolated radiographic PFOA is present in 13.6-24% of females and 11-15.4% of males with knee pain. Biomechanical factors such as tibiofemoral alignment and high joint stress are associated with the development and progression of PFOA. PF joint stress is high when the quadriceps contracts with the knee in a position of extreme flexion, such as rising from sitting. The purposes of this study were to determine (1) the triplanar biomechanics of the hips and knees during sit-to-stand (STS) for persons with PFOA versus age- and gender-matched control subjects, (2) the impact of PFOA on physical performance, perceived functional status, and pain, and (3) the relationship between knee kinematics during STS and physical performance. The biomechanics of STS was examined using a video-based motion analysis system and two force plates. Physical performance was measured with the Timed Up and Go (TUG) and Fifty-Foot Walk (FFW) tests. Perceived functional status, pain, and stiffness were measured using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) questionnaire. Knee pain was measured with a Visual Analog Scale (VAS) following STS, TUG, and FFW. Persons with PFOA required a significantly longer time to perform STS and the TUG as compared to healthy controls. The PFOA group demonstrated greater hip flexion and knee abduction versus the control group. The hip and knee moments were significantly different with the PFOA group demonstrating greater hip extension, hip abduction, hip external rotation, knee extension, and knee adduction moments. Persons with PFOA were found to have significantly less perceived physical function, greater stiffness, and greater pain. Pain following STS, TUG, and FFW were all greater in the PFOA group. No significant association was found between any knee angle and time to perform the TUG or the FFW. These results indicate that dynamic malalignment of the TF joint is present during STS in persons with PFOA. This may contribute to the increased pain and decreased function in persons with PFOA.