Hallux Alignment and Flexor Hallucis Brevis Morphology Are Independently Associated With Jump-Landing Stability in Adolescent Athletes.

The functional impact of hallux valgus (HV) on dynamic postural stability in adolescent athletes remains unclear. We investigated whether hallux alignment and intrinsic foot muscle morphology are associated with dynamic postural stability during a jump-landing task. This study included 185 adolescent athletes (mean age, 13.6 years). Participants with perceived ankle instability (Cumberland Ankle Instability Tool score ≤ 25 in either ankle) were excluded. Weight-bearing radiographs were used to measure the HV angle (HVA), hallux interphalangeal angle (HIA), and skeletal maturity. Ultrasonography was used to quantify the cross-sectional area (CSA) of intrinsic foot muscles, including the flexor hallucis brevis (FHB). The Dynamic Postural Stability Index (DPSI) was assessed during a single-leg jump-landing task. Associations were examined using linear mixed-effects models, accounting for within-participant correlation across limbs. HV and interphalangeal HV were present in approximately 33% and 86% of feet, respectively. In the multivariable model, greater combined hallux deformity (HVA + HIA) and open physes were independently associated with higher DPSI values, indicating poorer stability. Conversely, larger FHB CSA and higher body mass index (BMI) were associated with lower DPSI values, indicating better stability (all p < 0.05). Neither limb side nor the interaction between limb side and hallux alignment was significant. These findings suggest that hallux alignment, FHB morphology, and skeletal maturity are associated with jump-landing stability in adolescent athletes, without evidence of limb-dependent effects. Static hallux alignment and intrinsic foot muscle morphology provide clinically relevant information for evaluating dynamic stability in this population.