Hindfoot Motion Following STAR Total Ankle Arthroplasty: A Multisegment Foot Model Gait Study

Background: One of the rationales for total ankle arthroplasty (TAA) is that it may retard the changes of hypermobility and accelerated arthritis in the hindfoot after ankle arthrodesis. Until recently, it has not been possible to quantify or even objectively demonstrate biomechanical findings to substantiate the theory that postsurgical biomechanical changes in the ankle produce changes in the kinematics of the hindfoot. Standard gait analysis has treated the foot as a single biomechanical unit. This study was undertaken to describe the hindfoot motion following Scandinavian Total Ankle Replacement (STAR) TAA by using multisegment foot model gait analysis. Methods: Forty-six patients with a mean age of 66 years underwent a 3D gait analysis following TAR. Mean interval between surgery and gait analysis was 4.9 years (range 2 to 9). The contralateral limb was used as control for each patient. Temporospatial variables and kinematic parameters were studied. Results: Temporospatial results showed statistically significant differences. Stance time on the affected side was 61.1% +/- 2.2% of the gait cycle compared to 63.2% +/- 2.1% for the unaffected side. Step length was 55.6 cm +/- 10 on the affected side compared to 53.9 cm +/- 10 for the unaffected side. Kinematics results were statistically significant: Ankle range of motion (ROM) on the arthroplasty side was 16.8 +/- 4.5 degrees compared to 23.6 +/- 5.0 on the unaffected side. Sagittal plane ROM was 12.7 +/- 4.2 degrees on the arthroplasty side and 17.3 +/- 3.5 degrees on the unaffected side. Coronal plane ROM was 4.7 +/- 2.4 degrees on the arthroplasty side and 7.5 +/- 2.4 degrees on the unaffected side. Transverse plane ROM on the arthroplasty side was 4.1 +/- 1.5 degrees and 4.9 +/- 1.6 on the unaffected side. Conclusion: This study showed that, in addition to previously documented diminution in sagittal plane motion and gait velocity, some of the residual abnormalities of gait following TAR were comprised of differences in hindfoot function. These results relate to the growing recognition of the importance of understanding hindfoot mechanics apart from those of the tibiotalar joint.