Altered Joint Forces Found in Symptomatic Dysplastic Hips in Women During Sport-Specific Activities.

Background: Many patients with developmental dysplasia of the hip (DDH) are young and highly active but often become limited by activity-induced pain. Characterizing how the abnormal bony geometry of DDH affects hip joint loading and multiplanar kinematics during sport-specific motions relevant to active patients may provide insight into injury mechanisms and inform optimal treatment options. Purpose/Hypothesis: The purpose of this study was to determine how hip joint loading and kinematics are altered in DDH during 2 common sport activities: running and multidirectional hop-cutting. It was hypothesized that superior and medial joint-reaction forces (JRFs) would be elevated during running and that medial JRFs would be elevated during hop-cutting when compared with controls. Study Design: Controlled laboratory study. Methods: Using patient-specific musculoskeletal modeling, both running and hop-cutting motions were analyzed for female patients with symptomatic DDH (DDH group) and female controls without hip disorders who were enrolled from October 2017 to August 2022. Hip joint angles, JRFs, and muscle forces were compared between the groups using 1-dimensional statistical parametric mapping. Results: Overall, 19 women in the DDH group and 19 female controls were included in the running analysis, and 13 women in the DDH group and 10 female controls were included in the hop-cutting analysis. During the running motion, medial hip JRFs and gluteal muscle forces were significantly elevated in the DDH group, while rectus femoris muscle forces were reduced. During the hop-cutting motion, medial hip JRFs, gluteus minimus, and gluteus medius muscle forces were elevated, while gluteus maximus forces were reduced in the DDH group. There were no significant group differences in hip joint angles for either activity. Conclusion: The lack of kinematic differences between women with symptomatic DDH and controls suggests that the JRF differences between groups stemmed from the abnormal joint geometry in the DDH group. These activities may have greater damaging potential than previously studied lower impact activities such as walking. Clinical Relevance: Better understanding of how loading varies from activity to activity can help patients with DDH, and clinicians understand the mechanistic causes of DDH-related hip pain and damage and plan appropriate intervention strategies.