[Muscle Biomechanics in Total Ankle Replacement]

The purpose of this orthopaedic-biomechanical study was to evaluate the muscle function in total ankle replacement (TAR) patients 1 year after surgery. Ten patients underwent a combined clinical and muscle biomechanical assessment prior to implantation and at the 1-year follow-up. Pain score, American Orthopaedic Foot and Ankle Society (AOFAS) ankle score, ankle range of motion (ROM), and calf circumference difference between the affected leg and contralateral healthy leg were assessed. Biomechanically, isometric maximal voluntary torque for ankle dorsiflexion and plantar flexion was measured simultaneously with surface electromyography of four lower leg muscles. At follow-up, a significant improvement of the pain score (from 6.7 to 0.8 points), AOFAS ankle score (from 35.6 to 92.3 points), and ROM could be shown. Not significantly, the mean calf circumference difference between legs decreased from 2.2 to 1.4 cm. However, a significant increase was seen in the mean dorsiflexion (from 17.0 to 25.8 Nm) and plantar flexion torque (15.7 to 24.6 Nm) of the TAR-treated ankle. The mean EMG frequency content of the affected lower leg at TAR follow-up was lower than in the muscles of the contralateral healthy side. In contrast, the mean EMG intensity at TAR follow-up in side-comparison was statistically the same for all muscles. Ankle OA patients have better muscle function with TAR than under the arthritic condition, but they do not reach the normal level of the contralateral healthy leg 1 year after surgery.