Ankle, knee, and hip moments during standing with and without joint contractures: Simulation study for functional electrical stimulation

Joint contractures have been one of the contraindications for use of functional electrical stimulation for standing in paraplegic patients. A simulation study using a three-segment link mechanical model of the human body was performed to calculate the muscle moments at the ankles, knees, and hips during standing with and without having joint contractures. The knee and hip angles were varied in 5° increments, whereas the ankle angles were varied in 1° increments. It was assumed that energy efficient posture was obtained with the least sum of the squared moments of the ankles, knees, and hips joints by the muscles. Ankles at 5° of dorsiflexion, knees at 0°, and hips at 15° of extension resulted in the most energy efficient posture without joint contractures. The muscle moments increased with the increase in angle of contractures. The joint contractures at ankle angles ≥6° of plantar flexion, knee angles ≥20° of flexion, and/or hip angles ≥20° of flexion produce a potentially unstable posture. These findings suggest that some degree of joint contractures can be tolerated in paraplegic patients using functional electrical stimulation for standing.