Distance Mapping of the Ankle Joint Before and After Corrective Anterolateral Arthroscopic Subtalar Arthrodesis (ALAPSTA)

Abstract

Category: Hindfoot; Arthroscopy Introduction/Purpose: Supramalleolar osteotomies have been proposed as surgical option to realign the ankle joint in case of altered intra-articular loading. Little is known about the changes occurring at the tibiotalar joint after inframalleolar procedures, such as the corrective arthroscopic anterolateral subtalar arthrodesis (ALAPSTA). We set out to investigate changes in terms of joint interaction between the articular surfaces at the tibiotalar joint after corrective anterolateral arthroscopic subtalar arthrodesis (ALAPSTA) to treat Progressive Collapsing Foot Deformity (PCFD) with sinus tarsi impingement and subtalar joint degeneration. We hypothesized that ALAPSTA would improve hindfoot malalignment and that the distances between articular surfaces at the ankle would change significantly. Methods: In this retrospective study, we evaluated a consecutive series of 33 feet from 33 patients (mean age 60 years, SD 16.2; 16 right and 17 left) diagnosed with PCFD undergone ALAPSTA and reassessed at a mean follow-up of 7 months (range, 2 to 50). Weightbearing computed-tomography (WBCT) images were retrieved and the Foot and Ankle Offset (FAO) was calculated to assess the hindfoot alignment. Distance Mapping (DM) at the ankle joint (divided in 9 regions) allowed to assess changes in terms of joint interaction at this level between pre and postoperative images. Results: Hindfoot alignment significantly improved with a pre-operative FAO at 10.7 points (SD 4.7) and a post-operative FAO at 4.8 (SD 4.9) (p < 0.001). The mean improvement was 5.6 points. We found a significant increase in mean distances occurring posterolaterally at the ankle (from 4.5 mm (SD 1.2) to 5.4 mm (SD 1.5), p< 0.001) along with a significant decrease occurring anteromedially (from 9.1 mm (SD 1.2) to 8.3 mm (SD 1.4), p< 0.001). Conclusion: In this series, ALAPSTA was effective at correcting hindfoot malalignment in PCFD. After the procedure, the interaction at the ankle joint significantly changed with a reduction of anteromedial distance and an increase of posterolateral distance. Inframalleolar procedures seem to alter significantly the interaction between the tibia and the talus at the ankle. Further studies are warranted to ascertain whether changes in distances between surfaces correspond to changes in intra-articular pressures.