Altered tibialis anterior tendon mechanics in hallux valgus: a shear-wave elastography study integrating distal insertion patterns.

Abstract

Background: While distal tibialis anterior tendon (TAT) insertion variants have been associated with hallux valgus, the in vivo mechanical behavior of the tendon has not been adequately investigated. This study aimed to evaluate tibialis anterior tendon stiffness using shear-wave elastography (SWE) in patients with hallux valgus and healthy controls, to examine its relationship with radiographic deformity parameters, distal insertion patterns, and body mass index, and to assess measurement reliability.

Methods: In this prospective case-control study, 105 patients with radiographically confirmed hallux valgus and 98 age- and gender-matched healthy controls were enrolled. Tibialis anterior tendon elasticity was measured using shear-wave elastography on the index side. Hallux valgus angle (HVA) and intermetatarsal angle (IMA) were obtained from weight-bearing foot radiographs. Distal TAT insertion types were evaluated ultrasonographically. Correlations between tendon elasticity and radiographic parameters and body mass index were analyzed. Intra- and inter-observer reliability were assessed using intraclass correlation coefficients (ICC), standard error of measurement (SEM), minimal detectable change (MDC), and Bland-Altman analysis.

Results: Tibialis anterior tendon elasticity was significantly lower in the hallux valgus group compared with controls (11.07 ± 3.61 vs. 12.71 ± 3.86 kPa; p = 0.004; Cohen's d = - 0.44). In correlation analyses, tendon elasticity showed a weak, non-significant association with hallux valgus angle in the hallux valgus group (r = 0.19, p = 0.065) and no significant association with intermetatarsal angle in this subgroup (r = 0.12, p = 0.243). When all participants were analyzed together, a weak but statistically significant positive correlation was observed between tendon elasticity and intermetatarsal angle (r = 0.20, p = 0.006), whereas no significant correlation was found with hallux valgus angle (r = - 0.10, p = 0.194). Distal insertion analysis demonstrated that Type 5 was the most prevalent insertion pattern (75.7%) and was associated with markedly lower tendon elasticity (10.84 ± 3.25 kPa) compared with Types 1-3 (16.43-17.29 kPa). No significant association was identified between body mass index and tendon elasticity in the hallux valgus group (r = - 0.17, p = 0.087) or in the overall cohort (r = - 0.12, p = 0.113). Measurement reliability was excellent, with intra-observer and inter-observer ICC values of 0.93 and 0.91, respectively, and low measurement error (SEM < 1 kPa).

Conclusions: Hallux valgus was associated with lower tibialis anterior tendon elasticity on shear-wave elastography; however, tendon elasticity showed only weak or non-significant correlations with radiographic deformity severity. Therefore, TAT stiffness should not be interpreted as a primary determinant of first metatarsal varus or hallux valgus severity. Rather, it may represent a secondary soft-tissue adaptation or an accompanying biomechanical feature. Future studies focusing on tendons with a more direct functional role in first-ray stabilization, including the peroneus longus and flexor tendons, may provide further insight into the dynamic pathomechanics of hallux valgus.