Does a 1st metatarsophalangeal fusion in a patient with pes planus improve the pes planus deformity? A retrospective case series

J. Chapman, N. Dalal, H. Jenkinson, L. Mason

¹Liverpool University Hospitals NHS Foundation Trust, Liverpool Trauma and Orthopaedics Service, Liverpool, United Kingdom,

²University of Liverpool, School of Medicine, Liverpool, United Kingdom

Introduction: Fusion of the 1^st metatarsophalangeal joint (MTPJ) is the most common orthopaedic operation in the treatment of 1^st MTPJ arthritis. In patients with concomitant pes planus deformity, what is unknown is if stabilising the distal aspect of the medial ray improves the pes planus deformity.

Primary objective: Our primary objective was the analyse the pes planus deformity pre and post 1^st MTPJ fusion with the nul hypothesis that there was no difference.

Methods: We identified patients who underwent 1^st MTPJ fusion using our electronic database from January 2011 to October 2021. Inclusion criteria were pre- and post-operative weightbearing plain radiographs, with a Meary’s angle of >4 degrees on pre-operative radiographs. Routine pes planus measurements were undertaken. Pre- and post-operative measurements were tested for significant change using Wilcoxon Signed Rank or Paired T-Tests. Data was analysed using IBM SPSS v.27.

Results: 26 feet were identified. The mean patient age was 62 years (range=38–76). There was no pre-operative correlation between Meary’s angle (MA) and the hallux valgus angle (HVA) (p=.923). A significant improvement between the pre- and post-operative measurements was identified in MA (mean reduction=3.69°; range: 13.47-0.05, p<.001), medial cuneiform height (mean increase=2.48mm; range: -8.26-3.7, p=.035), talo-navicular coverage angle (mean decrease=2.23°; range -6.94-13.14, p=.03), talar 1^stmetatarsal angle (mean decrease=3.64°, range -5.71-20.12, p=.021) and intermetatarsal angle (mean decrease=4.17°, range -4.2-15.32, p<.001). As expected, the HVA was also significantly decreased post-operatively. Talo-navicular angle (p=.819), medial cuneiform 1^st metatarsal angle (p=.594) and calcaneal pitch angle (p=.120) were not significantly changed. A post-operative MA of <4° was only achieved in 5/26 (19%) of cases.

Conclusions: Our results suggest that 1^st MTPJ fusion improves axial alignment of the foot as well as reducing MA by a significant amount, although diagnostic criteria for pes planus remained in many cases.

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