Investigating the relationship between hip joint kinematics and patient-reported measures during squatting tasks & reliability of clinical methods of squatting assessment in females with acetabular dysplasia

Background: Acetabular dysplasia (AD), a classification of non-arthritic hip pain, commonly affects females and leads to long-term morbidity if untreated. Purposes: To investigate hip kinematics during squatting tasks in females with AD, explore relationships between kinematics and patient-reported outcome measures, and analyze feasibility and reliability of methods for assessing squat performance. Methods: To assess kinematic variability and relationships between variables, 23 females with AD and 28 controls participated. Three-dimensional kinematic data was collected in one session using motion capture. Participants completed outcomes related to pain, hip-specific function, and activity level. Independent t-tests were used to examine differences in maximal hip adduction between groups. A within-subject repeated measures ANOVA was used to investigate hip adduction differences across multiple positions by task. Spearman rank-ordered correlation coefficients were used to evaluate the relationship between maximal hip adduction and each outcome measure. To assess feasibility and reliability of two-dimensional video analysis, 8 females with AD participated. Small knee bend and deep squat performances from the Hip and Lower Limb Movement Screen were recorded and then scored by two investigators. Feasibility was investigated in domains of process and science. Inter-rater reliability was assessed by comparing two raters’ scores using Cohen’s kappa (κ). Results: There were no significant differences between groups in the amount of maximal hip adduction measured during a single (p = .52) or double-leg (p = .35) squat. The amount of adduction did differ significantly across positions during both tasks in females with AD. No significant relationships were found between outcome scores and maximal hip adduction on a single (p =.06 to .70) or double-leg (p =.48 to .85) squat. Two-dimensional video analysis was feasible for this population. Inter-rater reliability was higher for assessing a single-leg (κ = .33 to 1.00) than for a double-leg (κ = .25 to .75) squat. Conclusion: Variability in hip kinematics observed in females with AD suggests that focusing on functional performance may be better than a single kinematic factor when working with this population. While two-dimensional video analysis of both tasks was feasible, assessing a single-leg squat during evaluation is recommended to save time and minimize symptom-provoking activities.