Assessing Transverse Arch Plantar Angle in Surgical Intervention for Progressive Collapsing Foot Deformity

Category: Midfoot/Forefoot; Hindfoot Introduction/Purpose: The transverse tarsal arch (TTA) is perpendicular to the medial longitudinal arch (MLA) and enhances the intrinsic stiffness of the longitudinal curvature. Given the importance of TTA/MLA, a collapse of this complex may indicate a point of TA/MLA uncoupling, resulting in a decreased foot stiffness and a gradual flattening observed in Progressive Collapsing Foot Deformity (PCFD). A recently described angle, the transverse arch plantar (TAP) angle, was found to be significantly increased in PCFD compared to controls, indicating a transverse as well as longitudinal collapse. The objective of this study is to assess the TAP angle in patients who underwent surgical treatment for PCFD and to determine whether surgical intervention has the potential to enhance or alter the transverse arch. Methods: This retrospective cohort, single-center study received institutional review board approval. Patients presenting with symptomatic PCFD who underwent weight-bearing CT (WBCT) assessment at our institution were included in this study. All patients included underwent a PCFD surgical correction. Exclusion criteria comprised individuals under 18 years old, those with a history of prior foot surgery, individuals with tarsal coalition, inflammatory diseases, or neuropathic pain. Demographic data, including sex, age, body mass index (BMI), surgery date, date of WBCT, and the number of procedures performed to correct PCFD, were collected. As previously described in the literature, the TAP angle was measured as the angle between the most plantar side of the first, second, and fifth tarsometatarsal joints. The foot and ankle offset (FAO) was also measured (Figure 1). The normality of all quantitative variables was assessed using the Shapiro-Wilk test, and the measurements were compared using a Student t-test or Wilcoxon test. Results: The sample comprised 26 patients, of which 20 are female. The mean age was 47 years, the mean BMI was 34.1, and the average time between surgery and weight-bearing CT (WBCT) was 108 days (Table 1). The mean number of interventions during the surgical procedure was 4.9 (min. 2; max. 8). The pre-operative TAP mean angle was 113.6º (SD 7.1º; CI 95% 110.7º-116.5º), while the post-operative TAP mean angle was 106.0º (SD 7.3º; CI 95% 103.1º-109.0º), and the difference is statistically significant (p=0.0001). Additionally, the pre-operative mean FAO was 9.4% (SD 3.3%; CI 95% 8.0%-10.7%), and the post-operative mean FAO mean was 1.9% (SD 2.8%; CI 95% 0.8%-3.0%), with a statistically significant difference as well (p=0.0001) (Table 2). Conclusion: This study indicates that surgical correction of PCFD significantly reduced the collapse of the TAP angle by 6.7% postoperatively (p=0.0001). Considering the critical role of TA/MLA coupling in maintaining intrinsic foot stiffness, targeting this specific collapse for correction may be a key objective for the success of surgical interventions. Additional research investigating functional outcomes is essential to assess the correlation between TAP angle correction and patients' reported outcome (PROMs) as well as their overall satisfaction.