Weight‐Bearing Lunge Test in Young Patients With Haemophilia and Limited Joint Damage: Reliability and Functional Associations for Ankle Assessment

INTRODUCTION: Performance-based measures are essential for detecting early musculoskeletal functional limitations in patients with haemophilia (PwH). The Weight-Bearing Lunge Test (WBLT) assesses ankle dorsiflexion mobility, but its psychometric properties in PwH remain unclear. AIM: To determine the test-retest reliability and construct validity of the WBLT in young PwH and limited joint damage, and to examine its associations with ankle-specific clinical and imaging measures. METHODS: This prospective cross-sectional study included 24 PwH (mean age: 15.6 ± 4.7 years). Ankle dorsiflexion was assessed using the WBLT and tibial inclination angle with Goniometer PRO. Test-retest reliability was evaluated in 20 participants. Joint health was assessed using the HJHS and HEAD-US. Reliability was analysed using ICC (2,1), and construct validity using Spearman correlations. RESULTS: The WBLT demonstrated excellent test-retest reliability (ICC = 0.96-0.99). Moderate correlations were found between WBLT Right and HJHS Total Score (r = -0.493, p = 0.014), HJHS Right Ankle Score (r = -0.621, p = 0.001), and HEAD-US Right Ankle Score (r = -0.481, p = 0.017). WBLT Left correlated with GPRO Left (r = -0.587, p = 0.006) and HEAD-US Left Ankle Score (r = -0.456, p = 0.025). No significant correlations were found with HEAD-US Total or GPRO Right. CONCLUSION: The WBLT showed excellent test-retest reliability and meaningful associations with ankle-related clinical and imaging findings in young PwH and limited joint damage. These findings suggest that the WBLT may provide a simple, functional, and objective measure of ankle dorsiflexion mobility.