Abstract
Category:
Hindfoot; Basic Sciences/Biologics
Introduction/Purpose:
Talonavicular and subtalar joint arthrodeses are frequently performed in isolation. While these procedures generally produce good results, patients often experience reduced range of motion (ROM) and adjacent hindfoot arthritis. Several studies have shown that the arthrodesis of a single hindfoot joint considerably limits the motion of the adjacent unfused joints during simplified loading scenarios, but the effect on kinematics during dynamic activity is unknown. This study sought to assess the changes in subtalar and talonavicular kinematics after isolated talonavicular and subtalar arthrodesis, respectively, during simulations of stance and to quantify the motion of the unfused joint after the first hindfoot arthrodesis. We hypothesized that isolated arthrodesis of the subtalar and talonavicular joints would significantly alter kinematics and reduce the remaining unfused joint's ROM.
Methods:
Fourteen mid-tibia specimens were used. A validated robotic gait simulator of the stance phase of gait was used. An eight-camera motion-capture system tracked reflective markers on the talus, calcaneus, and navicular. Two testing conditions were simulated for each specimen: intact condition and after isolated subtalar or talonavicular arthrodesis. Each specimen was randomized into two groups of seven, either receiving an isolated subtalar (STIso) or talonavicular arthrodesis (TNIso). The subtalar and talonavicular arthrodeses were performed using 7.0-mm and 5.5-mm partially-threaded screws, respectively. The difference in subtalar and talonavicular joint kinematics between the intact and arthrodesis conditions was calculated using bootstrapped bias-corrected 95% confidence intervals of the joint kinematics. Significant differences (P< 0.05) were defined as areas where the intervals of the intact and arthrodesis conditions did not overlap. ROM for each joint was calculated by subtracting minimum from maximum joint motion, and the difference between conditions was analyzed using paired t-tests.
Results:
The TNiso demonstrated significant changes in the subtalar kinematics. After the TNiso, mean subtalar plantarflexion decreased during late stance from 3.2º to 0.1º (P< 0.05). Mean subtalar inversion decreased in both early and late stance from 1.2° to 0.3° and 7.5° to 2.7°, respectively. Conversely, subtalar inversion increased during mid-stance from 1.7° to 2.8° after arthrodesis. In the axial plane, mean subtalar adduction decreased in the early and late stances from 1.6° to 0.4° and 4.8° to 0.4°, respectively. The subtalar ROM was significantly reduced in the sagittal and coronal planes by 40%(P=0.009) and 46%(P=0.002), respectively. No significant differences in talonavicular kinematics were observed after isolated subtalar arthrodesis; however, the absolute ROM was significantly reduced by 61%(P=0.007) and 50%(P=0.003) in the coronal and axial planes, respectively.
Conclusion:
Our study showed that both types of isolated hindfoot arthrodesis decreased the ROM of the remaining unfused hindfoot joint. However, we only observed significant changes in subtalar kinematics following isolated talonavicular arthrodesis. Conversely, isolated subtalar joint fusion did not significantly affect talonavicular kinematics, confirming previous findings that have identified the talonavicular joint as the key hindfoot joint. Isolated subtalar fusion may represent a viable treatment option, as it may have a lesser impact on the overall hindfoot function. However, isolated talonavicular arthrodesis should be avoided when possible since the procedure significantly affects the kinematics of the unfused subtalar joint.
