Changes in the Subtalar Joint Alignment after Supramalleolar Osteotomy for Varus Ankle Arthritis

Category: Ankle; Hindfoot Introduction/Purpose: The subtalar joint may compensate for tibio-talar deformity, but what would happen to the joint after the deformity was corrected is not well known. Supramalleolar osteotomy (SMOT) is an effective procedure for the treatment of varus deformity of ankle arthritis. The objective of this study was to investigate the subtalar joint alignment pre and postoperatively following SMOT, and the factors which influenced the alignment of the subtalar joint. Methods: Thirty-one patients with varus ankle arthritis (Takakura stage 2, 3a and 3b) who were treated using SMOT were retrospectively reviewed. The subtalar and ankle joint alignment was measured on weightbearing radiograph and weightbearing computerized tomography (WBCT). Results: The foot ankle offset (FAO), tibial articular surface angle (TAS), tibio-talar surface angle (TTS), subtalar vertical angle (SVA) and subtalar inclination angle (SIA) were significantly corrected (P<0.05). There were 19 cases with the subtalar joints shifted medially after surgery (ΔSIA=-4.27±3.23°), and the other 12 cases with the subtalar joints moved to the lateral side (ΔSIA=2.79±1.68°). The shift of subtalar joint (ΔSIA) showed an inverse correlation with the preoperative FAO (P<0.001, r=-0.621). Conclusion: The shift of subtalar joint after SMOT could maintain the neutral position of the hindfoot and showed a negative correlation with the preoperative FAO. The ΔSIA was greater in the severer preoperative hindfoot deformity. Figure 1 The varus deformation of the ankle joint was corrected by the supramalleolar osteotomy, and the increased SIA after surgery resulted in the stenosis of the lateral joint space. (A and C, preoperative; B and D, postoperative, the pre and postoperatively SIA were 3 degrees and 10 degrees; the pre and postoperatively FAO were -5.77% and -1.89%). Abbreviations: TAS, tibia articular surface angle; SIA, subtalar inclination ankle; FAO, foot ankle offset.