Does First Metatarsal Pronation Correct Itself With Metatarsal-Sesamoid Reduction?

Background In the past few years, great importance has been given to coronal plane deformity and to pronation of the first metatarsal (M1) in hallux valgus. We believe that tensioning of the medial metatarsal-sesamoid ligament (MMSL) as a consequence of M1 medial displacement in relation to the sesamoids might be the main cause of M1 pronation. This study aimed to retrospectively evaluate if M1 pronation is corrected after an adequate M1 head reduction over the sesamoids, using the Minimally Invasive Chevron–Akin (MICA) technique. Material and Methods We retrospectively reviewed a series of consecutive patients with symptomatic hallux valgus deformity, who underwent surgical treatment with the MICA technique between November 2021 and July 2022. Patients’ radiographic weight-bearing images were retrospectively evaluated for pre- and postoperative pronation and metatarsal-sesamoid relative positioning. M1 pronation was assessed and classified as described by Okuda et al. Pronation was considered to exist in types R and I, ie, every time there was not an angular shape of the M1 head. Satisfactory sesamoid reduction was considered when the lateral sesamoid was, at least, 50% covered by the metatarsal. Results Ninety-one feet (67 patients) met the inclusion criteria. The mean age at the time of surgery was 57.9 years. Most patients underwent unilateral surgery [right foot, 24 (35.8%); left foot, 19 (28.4%)] with 24 patients (35.8%) undergoing bilateral surgery. Eighty-four feet (92.3%) had preoperative pronation. Among these, 54 feet (64.3%) had satisfactory positioning of the head over the sesamoids postoperatively and 30 feet (35.7%) did not. Of the 54 feet with satisfactory positioning, 51 (94.4%) did not show postoperative metatarsal pronation, while 3 (5.6%) did (P < .0001). Of the 30 feet with unsatisfactory reduction of the M1 head, 28 (93.3%) had postoperative pronation and 2 (6.7%) had no pronation (P < .0001). Conclusion According to our study, first metatarsal pronation is predominantly self-corrected when a satisfactory reduction of the head of M1 over the sesamoids is achieved, using the MICA technique. We hypothesize that pronation might be due to MMSL tensioning however further basic science and clinical studies using weight-bearing computed tomography and biomechanical evaluation are needed to confirm our findings. Level of Evidence: Level IV