Stemmed Ankle Implants Showed Less Initial Tibial Micromotion in Cadaver Study

Early mechanical failure is a concern after total ankle replacement. In a cadaveric study, investigators implanted one ankle in each of 10 matched pairs with either a stemmed or low-profile tibial component. A robotic gait simulator reproduced walking, while imaging-based methods measured movement at the bone-implant interface during stance. The specimens came from donors with a mean age of 48 years (±11); the study was classified as Therapeutic Level IV evidence.

Compared with stemmed components, low-profile components had 150 µm greater average peak micromotion (95% CI, 98 to 203; p<0.001) and 30 µm greater mean micromotion (95% CI, 9 to 52; p<0.001). Peak movement in low-profile implants was typically posterior, whereas it occurred near the stem tip in stemmed implants. The authors interpreted the pattern as consistent with rocking of low-profile components and greater compression of stemmed components into bone.

The results provide a biomechanical explanation for a possible link between low-profile fixation and early mechanical failure, but they do not demonstrate that one design reduces failures in patients. The experiment used cadaveric specimens and measured time-zero micromotion under simulated gait; clinical outcomes and longer-term fixation were not assessed.