Effects of arthrodeses on walking: kinemati and kinetic studies of subtalar and knee arthrodesis.

We studied the effects of subtalar (n=2) or knee (n=2) arthrodesis on the gait of four subjects with particular attention to the temporal and sagittal plane kinematic and kinetic characteristics. Each subject had a painless arthrodesis and no other gait limitation. To compensate for their disability the subtalar arthrodesis subjects showed altered angular displacement patterns at the ipsilateral ankle, knee and hip joints, and greater than normal resultant joint moments at the knee and hip in late stance. A symmetric gait was achieved by mimicking ipsilateral movements with the opposite limb. Compensations for subtalar joint arthrodesis were shown to differ from those for a unilateral arthrodesed ankle joint. To compensate for knee arthrodesis, subjects showed an increased range of movement at both the ankle and hip joints, and excessive resultant joint moments generated at the hip joint. Little variability was seen in the kinematics of the hip joint, suggesting that its role in locomotion (maintenance of progression) was rigidly defined. Variation from normal patterns were also seen in the kinematics of the contralateral limb, primarily in a 'vaulting' response. The results of this study indicate that contrary to the effects of unilateral ankle or subtalar arthrodesis, the locomotor system is unable to compensate effectively for the complete loss of movement at one knee joint, and an inefficient asymmetric gait is produced. The magnitude of the resultant joint moments at the ipsilateral hip joint, combined with the lack of kinematic flexibility may predispose this joint to subsequent degeneration.