Active Weight Bearing Tibio-talar Motion and Meniscal Translation in the S.T.A.R Prosthesis-A Radiographic Comparative Study of the S.T.A.R. Toward the Opposite Normal Ankle Joint

Abstract

Background: The kinematics of meniscal bearing artificial ankle joints is not well documented after the implantation of the prosthesis. Purpose of the study To investigate the active weight-bearing tibio-talar motion and the translation of the meniscus radiographically after mean 36 months in patients with unilateral traumatic ankle osteoarthritis. Methods: Straight lateral radiographic views under image intensification of the replaced ankle and the opposite normal ankle were performed during active weight-bearing. The tibio-talar motion of both ankles, as well as the translation/rotation of the meniscus in the replaced ankles was measured. Results: The total range of motion in normal ankles was mean 59° (33.7–68.7). The motion in the replaced ankles was mean 37.2° (16.7–53.3), p<0.02. Normal extension was mean 24° (3.7–37.7). Replaced ankle extension was mean 14.7° (2-26.7), p<0.02. Normal plantarflexion was mean 31° (19.7–51), in replaced ankles plantar flexion was mean 22.3° (12.3–34), p<0.02. The translation of the meniscus was 0.7 mm (-1.5 to 1.2). This could also be calculated to be a rotation of 3.9°. The translation of the meniscus is most probably a combination of gliding and rotation. Conclusions: The active weight-bearing motion of the replaced ankle is about 2/3 of the normal ankle motion. Functionally this is a satisfactory result. After 36 months the translation of the meniscus is rather small suggestion that the replaced ankle has reached a steady state of conformity.