Background: The popularity of total ankle replacement as a treatment for end-stage arthritis continues to grow. The purpose of this study was to assess changes in ankle kinetics and kinematics from a preoperative time point through two years postoperatively in patients who had received either a fixed-bearing or a mobile-bearing implant.
Methods: Ninety patients who received a primary total ankle replacement (forty-nine mobile-bearing and forty-one fixed-bearing) were examined. Three-dimensional joint mechanics and ground reaction forces were measured during level walking preoperatively and one and two years postoperatively. Patient-reported and functional outcomes were also collected. Data were analyzed with use of a 3 × 2 repeated-measures analysis of variance (ANOVA) to determine significant differences between implant types and across time (α = 0.05).
Results: No significant difference was observed in the ankle motion or step time between implant types or across time. However, there was a greater increase in the peak plantar flexion moment and the Short Form-36 (SF-36) total score across time in the fixed-bearing group than in the mobile-bearing group. Conversely, visual analog scale (VAS) pain scores exhibited greater improvement in the mobile-bearing group than in the fixed-bearing group. Independent of implant type, a significant improvement was observed in walking speed, results of the functional tests, spatiotemporal variables, patient-reported outcomes, and vertical ground reaction forces. Independent of time, the fixed-bearing group demonstrated a significant increase in both the weight-acceptance and the propulsion ground reaction forces compared with the mobile-bearing group. The mobile-bearing group completed the Sit-to-Stand test significantly faster.
Conclusions: All of the observed changes suggest improved or maintenance of function following total ankle replacement. In general, the group with a fixed-bearing implant demonstrated improvements in ankle moment and ground reaction forces, while the mobile-bearing-implant group demonstrated improvements in patient-reported pain outcome. There were few significant changes between the two implant types.
Level of Evidence: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.
1Department of Orthopaedic Surgery (R.M.Q., T.L.S., S.B.A., J.K.D., M.E.E., and J.A.N.) and Michael W. Krzyzewski Human Performance Research Laboratory (R.M.Q., T.L.S., and R.J.B.), Duke University Medical Center, Box 3435, Durham, NC 27710. E-mail address for R.M. Queen: firstname.lastname@example.org