Progressive First Metatarsal Shortening Is Observed Following Dermal Allograft Interpositional Arthroplasty in Hallux Rigidus: Short Report

Background: The main goal of this study was to evaluate postoperative changes in the length of the first metatarsal (M1) and the proximal phalanx of the hallux (P1) after acellular dermal allograft interpositional arthroplasty (ADA-IPA). We hypothesized that there would be a shortening of the first ray at the first metatarsal, the proximal phalanx, or both. Methods: In this retrospective study, we assessed patients who underwent ADA-IPA between 2019 and 2022. On standing anteroposterior (AP) foot radiographs, we measured first metatarsal (M1), second metatarsal (M2), proximal phalanx (P1), and the entire hallux (HX) lengths. M1/M2 and P1/HX ratios were calculated. The first metatarsophalangeal joint space was calculated. All measurements were recorded preoperatively, at 6 weeks postoperatively, and at final follow-up. Results: The pilot study included 11 patients. At final follow-up, we found shortening of M1 and P1 in comparison to the preoperative length, as evidenced by lower M1/M2 (82.6 ± 2.3 vs 75.4 ± 5.1; P = .001) and P1/HX ratios (53.4 ± 2.3 vs 48.9 ± 7.9; P = .001). Follow-up length was negatively correlated with M1/M2 (r = −0.76, P = .003). Conclusion: ADA-IPA might be associated with shortening of both first metatarsal and proximal phalanx, with the former showing progressive shortening.