Abstract
CATEGORY: Ankle Arthritis, Basic Sciences/Biologics INTRODUCTION/PURPOSE: Adjacent joint disease often occurs after many orthopaedic surgical interventions. Specifically in the foot and ankle, subtalar arthritis has been demonstrated as a long term sequelae after ankle arthrodesis. The purpose of this study was to evaluate real time qualitative and quantitative motion differences in the hindfoot and midfoot during simulated gait, both before and after ankle fusion in a cadaveric model. Data recorded from each cadaveric trial is used in conjunction with a CT scan of each specimen, allowing creation of a three-dimensional, real time, anatomic model of motion of the foot and ankle. METHODS: Three human cadaveric specimens (lower leg and foot) were obtained and prepared for testing. Taking care to preserve the ligamentous and tendinous attachments, radiopaque fiducial makers were placed in each bone (tibia, fibula, talus, calcaneus, navicular, all cuneiforms, 1st metatarsal). CT scan of each specimen was then performed, and used to develop a three dimensional anatomic model of the specimen. Each specimen was then mounted into a custom built apparatus, and load was applied to the construct using a follower load model. Each specimen was taken through two full cycles of the simulated stance phase. Kinematic data of the individual bones/joints were measured in real time, using optoelectronic targets, and saved for later comparison. Next, tibiotalar fusion was performed on each of the previously tested specimens using an anterior plate and screw construct. The specimens were again cycled in the same fashion and data was recorded in the same manner. RESULTS: Tibiotalar fusion successfully eliminated motion between the talus and tibia, directly altering the normal kinematics of the foot ankle complex. Quantitatively, the motion at the subtalar and talonavicular joints increased only slightly with fusion. However, this represents a relative increased motion demand at each joint that exceeds what was observed in the non-fusion condition. Qualitatively, the motion curves for the talocalcaneal and talonavicular joints were altered when compared to the non-fusion state (Figure 1). The qualitative change in motion revealed a relative linkage of motion between the subtalar and talonavicular joints and this was consistently observed across all specimens. CONCLUSION: Simulated ankle fusion via an anterior plate and screw construct directly alters the kinematics of the downstream (talocalcaneal and talonavicular) joints. Real time observation demonstrates a relative linkage of the motion occurring in the subtalar and talonavicular joints. This linkage resulted in alteration from the observed physiologic motion that occurred in these joints during the non-fusion condition. These findings may provide insight into the etiology of adjacent segment disease seen in the subtalar and talonavicular joints after ankle fusion.