In-vivo kinematics evaluation of total ankle replacement through dynamic radiostereometric analysis: a prospective study

Introduction Nowadays, total ankle replacement (TAR) kinematics has undergone many changes, and critical issues that led to the improvement of prosthetic designs have been highlighted. The dynamic model-based radiostereometric analysis (dMBRSA) allows to study in vivo, under load, and with active muscular action, the biomechanical behavior of the prosthetic components. The study aims to perform clinical and kinematical evaluations of people with TAR. Methods A cohort of 18 patients (13 male and 5 female) with a mean age of 61.1±10.1 suffering from ankle osteoarthritis were enrolled in this study. The patients riceved an ankle prosthesis (7 right and 11 left) with a mobile insert (Exactech Vantage) and anterior access. The clinical evaluation was carried out through the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Score before the surgery and 9 months after surgery. Kinematical data were obtained in vivo through dMBRSA 9 months after surgery during two motor tasks: from plantar flexion to maximum dorsal flexion (lunge); stand on foot and the rise on tiptoes (rise on toes). For each patient kinematical data were calculated (Grood and Suntay decomposition): Internal-External (IE) rotations, Anterior-Posterior (AP) translations, and Varus-Valgus (VV) rotations of the Tibial component with respect to the Talus component during ankle flexion. Results In the kinematical results obtained 9 months after surgery, the “lunge” task showed an anterior translation of the tibia of 11.6 mm, while VV and IE rotations were less than 2 mm during the dorsi-flexion movement. In the “rise on toes” task, the tibial component showed a 14.0° anterior traslation, while VV and IE rotations were similar to the first motor task (Table). Concerning the clinical evaluation, after surgery the AOFAS significantly improved from 33.7±13.7 to 85.9±8.3 (p<0.001). Discussion and Conclusion The evaluation of joint range of motion with dMBRSA allowed to describe and quantify the movements of tibial component with respect to the talus component, excluding other joints contribution, in people with TAR two common ankle movements. In addition, there was an improvement of clinical outcomes in people after the TAR.