Does a 1st Metatarsophalangeal Fusion in a Patient with Pes Planus Improve the Pes Planus Deformity? A Retrospective Case Series

CATEGORY: Midfoot/Forefoot; Bunion INTRODUCTION/PURPOSE: A pes planus deformity is a pathology relating to the loss of normality of the complex interaction of the bones and joints of the foot resulting in a flattening of the medial longitudinal arch with or without abduction of the midfoot. The distal aspect of the medial longitudinal arch can be a feature of the deformity. The fusion of the 1st metatarsophalangeal joint (MTPJ) is a common operation. In patients with concomitant pes planus deformity, it is unknown if reducing and stabilising the distal aspect of the medial ray through a 1st MTPJ fusion can subsequently improve the pes planus deformity. We sought to analyse the pes planus deformity pre and post 1st MTPJ fusion with the null hypothesis that there was no difference. METHODS: We identified patients who had undergone 1st MTPJ fusion using our electronic database from January 2011 to October 2021. To meet the inclusion criteria, cases required pre- and post-operative weightbearing plain radiographs, with a Meary's angle of >4 degrees on pre-operative imaging. Routine pes planus measurements were undertaken by 2 independent observers. Pre- and post-operative measurements were tested for significant change using Wilcoxon Signed Rank Test or Paired T-Test depending on the normality testing of the data. Routine demographic data was also collected. Data was analysed using IBM SPSS v.27. RESULTS: Following radiographic analysis, 25 feet fitted the inclusion criteria. The mean patient age was 63 years. There was no pre-operative correlation between Meary's angle and the hallux valgus angle (Kendall's tau p=.441). Pre-operatively, Meary's line broke at the talo-navicular and navicular-cuneiform joints in 12 cases each; the remaining case broke at the tarsal-metatarsal joint. A statistically significant improvement between the pre- and post-operative measurements was identified in Meary's angle, calcaneal pitch angle, talo-navicular coverage angle, intermetatarsal angle and talo-navicular angle (see table). Significant changes were also noted in the medial cuneiform height (mean increase of 2.74mm; p=.022). A post-operative Meary's angle of <4°was only achieved in 4/25 (16%) of cases. Of the remaining 21 cases, the point at which Meary's line broke moved proximally one joint in 4 and distally one joint in 3 cases; it remained at the same joint in 14 cases. CONCLUSION: Our results suggest that 1st MTPJ fusion improves axial alignment of the foot as well as reducing Meary's angle by a statistically significant amount, although diagnostic criteria for pes planus remained in most cases.