Interpreting joint moments and powers in gait

Gait analysis is becoming an increasingly important tool to provide a quantitative description of a patient's gait deviations. It is not only used to diagnose walking disorders but also for treatment selection and evaluation. While spatiotemporal, kinematic, and EMG parameters are commonly used to describe movement and muscle activity, kinetic measures are less often evaluated, even though they give insight into the moments and powers that drive human walking. As such, kinetic parameters are able to connect abnormal movement to underlying muscle malfunction and bony malalignment. This chapter focuses on the role of joint moments and powers of the lower extremities in clinical gait analysis. After a brief introduction of normal kinetic patterns, the clinical interpretation of abnormal joint moments and powers is described. Next, typical deviations in lower limb kinetics are illustrated for several patient populations, including stroke, cerebral palsy, Duchenne muscular dystrophy, anterior cruciate ligament (ACL) injury, and osteoarthritis (OA), and for patients walking with prostheses or orthotics. This section also illustrates the clinical usefulness of specific kinetic parameters in these patient populations, including their sensitivity to treatment and ability to predict treatment outcome. The chapter illustrates that the role of kinetics within clinical gait analysis deserves more attention, and potential applications should be further pursued.