Biomechanical Analysis of the Effects of Knee Savers on Knee Joint Loading During High Knee-Flexion Tasks

Occupational activities that require high knee flexion, such as kneeling and squatting, are associated with a higher prevalence of knee osteoarthritis (OA). It is generally accepted that excessive contact pressures in the joint may cause degeneration of healthy knee joints. Ailments in the patellofemoral (PF) joint were a common cause for knee pain in clinical observations. Knee savers have been used in sports and occupational activities to protect the knee joints during tasks involving high knee flexion. The biomechanics of the effects of knee savers on musculoskeletal loading have not been investigated. The purpose of the current study was two-fold: first was to develop a biomechanical model that accounts for the effects of the interface contact forces between thigh and shank, or between thigh-shank and knee savers; and second was to evaluate, using the biomechanical modeling, the effects of knee savers on musculoskeletal loading in the knee joint in high knee-flexion tasks. Five healthy male subjects (age $20.6\pm 1.96$ years, body mass $87.74\pm 9.98$ kg, height $1.81\pm 0.08$ m) participated in the study. The subjects started from a standing posture, squatted down to a working posture, and returned to the standing posture, while subjects' heels remained on the ground during the tasks. The tasks were repeated without and with knee savers. The musculoskeletal loadings in the knees were calculated using inverse dynamic modeling. Our results indicated that the wearing of knee savers in the high knee-flexion tasks helped to reduce the contact forces in the PF joint by about 20%. Our findings suggest that wearing knee savers may help reduce the risks of the knee OA for workers who are frequently required to perform high knee-flexion tasks for extended time.