Morphologic assessment of peritalar compensation in patients with advanced varus ankle osteoarthritis

OBJECTIVE: Varus ankle malalignment is observed in most ankle osteoarthritis patients with approximately half of these patients presenting with peritalar compensation, where the subtalar joint is aligned valgus to compensate for a varus tibiotalar joint. This study developed a 3D weight-bearing computed tomography-based multi-bone statistical shape model to quantify morphologic and alignment differences between compensated and non-compensated presentations of advanced varus ankle osteoarthritis. MATERIALS AND METHODS: Our assessment included 70 individuals, 44 diagnosed with advanced varus ankle osteoarthritis, and 26 asymptomatic controls. Each participant underwent weight-bearing computed tomography. Semi-automatic segmentations produced patient-specific 3D bone reconstructions of the distal tibia, distal fibula, talus, calcaneus, navicular, and cuboid. A multi-bone statistical shape model was created using each of the 3D bone reconstructions. Joint space distance, coverage area, and congruence index were measured at equivalent anatomic locations within articular coverage obtained from the statistical shape model. RESULTS: Eleven principal component analysis modes retained 85.8% variance. Significant differences existed in mode 1 (medial malleolus and talar dome morphology, fibular positioning; 26.6% variance, p < 0.001 for all comparisons) and mode 3 (talar head morphology, midtarsal joint orientation; 10.8% variance, p < 0.05). Morphometric analysis showed 67.5% combined shape-alignment differences in non-compensated versus controls, predominantly affecting peritalar structures. CONCLUSION: Patients with non-compensated varus ankle osteoarthritis demonstrate decreased medial tibiotalar joint space, increased talofibular joint space, and increased peritalar joint coverage compared to compensated and asymptomatic ankles. These differences are driven primarily by alignment variation in non-compensated ankles. Complexity between these two clinical presentations should be taken into consideration with rehabilitation efforts and surgical planning.