Morphological Characteristics of the Intrinsic Foot Muscles in Individuals With Flat Foot: A Systematic Review and Meta-Analysis.

Background: The purpose of this meta-analysis was to discern the changes in morphological characteristics of the intrinsic foot muscles, including changes in the cross-sectional area (CSA) and thickness of the abductor hallucis (AbH), flexor hallucis brevis (FHB), flexor digitorum brevis (FDB), and abductor digiti minimi (AbDM) in individuals with flat foot (FF).

Methods: We conducted our literature search in the PubMed, Web of Science, and Scopus electronic databases. We included English-language case-control and cross-sectional studies comparing the morphological features of the intrinsic foot muscles in adults with and without FF. The methodological quality of the five studies that met the inclusion criteria was assessed with an adapted version of the Newcastle-Ottawa Scale for cross-sectional studies. The mean difference (MD) with corresponding 95% confidence intervals (CIs) was used to quantify the effects between adults with and without FF.

Results: The study included five studies, one of which was classified as high quality, while the remaining studies were classified as moderate quality. The CSA of the FHB (MD = -0.41, 95% CI = -0.61, -0.22; p < 0.001, I2:59%) and AbDM (MD = -0.21, 95% CI = -0.32, -0.11; p< 0.001; I2=1%) and the thickness of the AbDM (MD = -1.43, 95% CI = -1.81, -1.05; p< 0.001; I2=1%) were lower in individuals with FF than in the control group. However, the CSA of the AbH and FDB, and the thickness of the AbH, FHB, and FDB exhibited no significant differences between the FF and control groups.

Conclusion: The results of our study indicate that individuals with FF exhibited significant atrophy of the FHB and AbDM muscles. However, the morphology of the AbH and FDB muscles did not appear to influence foot posture, based on the five studies that were considered.