Generalized Joint Hypermobility Is Associated with Type-A Hip Dysplasia in Patients Undergoing Periacetabular Osteotomy

Background: Joint hypermobility may be associated with developmental dysplasia of the hip (DDH), but no definite conclusion has been reached. On the basis of long-term clinical observations, we hypothesized that joint hypermobility was associated with the occurrence, imaging findings, and clinical symptoms of DDH. Methods: We conducted a case-control study that included 175 Chinese Han patients between 13 and 45 years of age with Hartofilakidis type-A hip dysplasia. All of these patients underwent periacetabular osteotomy (PAO) between November 2021 and February 2023. An additional 76 individuals of comparable age and sex but without hip dysplasia were selected from the general population to serve as healthy controls. The Beighton 9-point scoring system was used to evaluate joint hypermobility, and a score of ≥4 was defined as generalized joint hypermobility. Standing anteroposterior pelvic radiographs were reviewed. For patients with DDH, the lateral center-edge angle, Tönnis angle, Sharp angle, lateralization of the femoral head, and patient-reported outcomes (iHOT-12, HHS, and WOMAC) were also collected to determine the radiographic severity or clinical symptoms of DDH. Results: Patients with DDH had an elevated prevalence of generalized joint hypermobility compared with that in the healthy population (27% versus 12%; p = 0.009). Among patients with DDH, those with concomitant generalized joint hypermobility had lower lateral center-edge angles (3.55° versus 9.36°; p = 0.012), greater lateralization of the femoral head (13.78 versus 12.17 mm; p = 0.020), greater standardized lateralization of the femoral head (0.64 versus 0.54; p = 0.009), and lower iHOT-12 scores (35.22 versus 40.96; p = 0.009) than did those without concomitant generalized joint hypermobility. Further multivariable linear regression analysis revealed that higher Beighton scores and younger age were predictive of more severe hip dysplasia. However, the Beighton score was not found to be independently associated with patient-reported outcomes according to multivariable linear regression analysis. Conclusions: The prevalence of generalized joint hypermobility was greater in patients with DDH than in healthy controls. A higher degree of joint hypermobility was also correlated with more severe hip dysplasia. These results suggest that joint laxity, in addition to bone or cartilage factors, is an important factor related to DDH. Level of Evidence: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.