Association between running gait biomechanics and femoral neck bone stress injuries in female runners.

Background: Femoral neck stress fractures are prevalent injuries among young female runners, yet biomechanical and strength features have not been well-described in adolescents and young adults.

Objective: To compare running gait biomechanics and strength measures of female runners diagnosed with a femoral neck bone stress injury (BSI) to healthy female runner controls.

Design: Retrospective case-control study.

Setting: Outpatient sports medicine department.

Patients: There were 18 female runners with a history of femoral neck BSI (age: 20.3 ± 1.0 years, BMI: 19.8 ± 0.6 kg/m²) and 18 healthy female runners without femoral neck BSI (age: 18.3 ± 0.7 years, BMI: 21.5 ± 0.6 kg/m²).

Methods: Participants underwent instrumented running gait analyses with 2-dimensional videos, and standardized handheld dynamometry hip strength measures.

Main outcome measures: Primary outcomes included spatiotemporal, kinematic, and kinetic running gait biomechanics, and tri-planar hip muscle strength. Non-parametric Mann-Whitney U tests were used to compare participant demographics. Linear regressions were used to compare strength and continuous gait outcomes, and logistic regressions were used to compare categorical gait outcomes between groups, covarying for age and body mass index (α = .05).

Results: A higher proportion of those with a history of femoral neck BSI demonstrated limb midline cross-over (Adjusted Probability [Adj.]: 65.0% vs. 38.5 %; p = .04), contralateral pelvic drop (Adj.: 99.0% vs. 52.9%; p = .02), medial knee displacement (Adj.: 67.0% vs. 37.9%; p = .03), and pronation at midstance (Adj.: 86.5% vs. 41.2%; p = .02) compared to those without a history of BSI. Those with a history of femoral neck BSI had lower hip abduction strength on dynamometry testing (1.64 ± 0.30 Nm/kg vs. 1.99 ± 0.66 Nm/kg; p = .01).

Conclusions: Female runners with a history of femoral neck BSI demonstrated characteristic coronal plane gait and hip abductor strength deficits, suggesting an association between impaired lower limb proximal and distal biomechanics during femoral neck BSI recovery.