Dorsiflexion angles following first MTP arthrodesis in adult pes planus: A Retrospective radiographic cohort study.

Abstract

Background: First metatarsophalangeal (MTP) joint arthrodesis is a well-established treatment for hallux rigidus, but the influence of pes planus on postoperative sagittal-plane alignment remains unclear.

Purpose: To determine whether radiographic pes planus influences postoperative hallux dorsiflexion angle following first MTP arthrodesis.

Study design: Retrospective radiographic cohort study.

Methods: Patients aged 18-90 years undergoing primary first MTP arthrodesis from 2006-2021 at a single academic institution were reviewed. Weight-bearing radiographs obtained ≥12 weeks postoperatively were evaluated by three independent orthopedic residency-trained reviewers. Dorsiflexion angle, Meary's angle, and calcaneal pitch were measured and averaged for analysis. Pes planus was defined as Meary's angle >4° or calcaneal pitch ≤19°. Linear mixed-effects regression with a patient-level random intercept accounted for bilateral procedures.

Results: A total of 112 operative feet from 102 patients were included; 93 (83%) met criteria for pes planus. Mean dorsiflexion angle was 23.49° ± 8.59° with pes planus versus 24.61° ± 7.92° without. After adjustment for age, sex, and BMI, pes planus was not independently associated with dorsiflexion angle (β=-0.62°, 95% CI -4.69° to 3.46°, p=.765). Calcaneal pitch was lower with pes planus (18.51° ± 5.84° vs 24.14° ± 3.42°, p<.001). A significant pes planus-calcaneal pitch interaction was identified (β=1.24, 95% CI 0.06-2.41, p=.039). Complication rates did not differ between groups.

Conclusions: Pes planus did not independently influence postoperative dorsiflexion angle. However, calcaneal pitch modified this relationship, suggesting hindfoot alignment should be considered during preoperative planning.