Range of Motion Following Total Ankle Replacement and Subtalar Fusion Through Lateral Versus Anterior Approach. Biomechanics Analysis

Abstract

Category: Ankle Arthritis Introduction/Purpose: A gait analysis of patients who underwent simultaneous total ankle replacement (TAR) and subtalar fusion allows to assess the ankle range of motion (ROM) with precision. In healthy subjects or in patients who underwent isolated TAR this is not possible because it is influenced by the subtalar ROM and it is not possible to analyse the two joints separately. Excluding the role of the subtalar joint, it is possible to analyse the consequences of different prosthetic designs and different surgical approaches on joint kinematics. The aim was to evaluate and compare with a gait analysis the effects of two different TAR designs on the functionality of the tibiotalar joint by exploiting the exclusion of the subtalar effect determined by the subtalar fusion simultaneously performed. Methods: Minimum follow-up was 12 months. 16 patients underwent a fix-bearing TAR through lateral approach (Zimmer Trabecular Metal Total Ankle), 7 patients underwent a mobile-bearing TAR through anterior approach (Hintegra). A six-camera motion capture system was used to measure foot static posture and foot segment kinematics. Rotations in the sagittal, frontal, and transverse planes between shank and the whole foot, shank and calcaneus, calcaneus and midfoot, midfoot and metatarsus, and calcaneus and metatarsus were calculated. Sagittal and transverse plane rotations of the first matatarso-phalangeal joint, medial longitudinal arch deformation, transverse plane angle between first and second metatarsal bone and between second and fifth metatarsal bone, and sagittal plane orientation of the first and second metatarsal bone with respect to the ground were also calculated. The following spatio-temporal parameters were calculated: stance time, swing time, stride length, normalized stride length, cycle time, cadence, walking speed, and normalized walking speed. Results: On average, the lateral approach group walked at a faster speed and with a longer stride length than the anterior approach group. However, spatio-temporal parameters in both groups were generally lower than the control values. No major differences were detected between the two groups in terms of ROM in any foot joint, with the exception of the frontal-plane motion of the midfoot with respect to the calcaneus (midtarsal joint) which was larger in the anterior approach group. Conclusion: patients with TAR through lateral approach seem to walk at a faster speed and with a longer stride length than patients with TAR through anterior approach; the midtarsal joint ROM was larger in the anterior approach group and this could mean that mobile bearing TARs through an anterior approach could lead to an overload of the midtarsal joint with respect to fixed-bearing TARs through a lateral approach. However, further studies with larger samples of patients are needed to confirm these results.