What happens to the gluteus medius in young and middle-aged patients with hip dysplasia?

Background Much research has focused on quantifying the bony characteristics of patients with developmental dysplasia of the hip (DDH). Far less attention, however, has been paid to muscle abnormalities around the hip such as those in the gluteus medius (GM). Methods We retrospectively examined clinical and imaging data, such as the age of onset and computed tomography (CT) findings, in 108 consecutive hips. Subjects for the control group were selected from our radiology database. Two readers independently evaluated the length (LGM), cross-sectional area (CSA), width (WGM), and thickness (TGM) of the GM and arm of GM (AGM) and angle of the GM activation (AOA) and bony parameters including the acetabulum-head index (AHI), lateral central edge angle (LCEA), acetabular index (AI), femoral offset (FO), and height of the rotation centre of femoral head (HCFH) among all cases using the imaging data. Results The patient group included 108 hips. The AGM, LGM, CSA, and TGM were lower in the DDH patients, while AOA was higher. However, there was no significant difference in the WGM between the two groups. Multiple linear regression analysis showed that AGM and AOA were independent factors affecting LCEA. The following regression equation was used: Y ( LCEA ) = 5.377 * X 1 ( AGM ) − 0.310 * X 2 ( AOA ) − 11.331. The mechanical characteristics of the GM and many bony parameters were significantly correlated (the AGM and AHI, LCEA, AI, FO, but not HCFH; AOA and AHI, LCEA, AI, but not FO or HCFH). The CSA was positively correlated with only HCFH. The rest were not statistical significance linear correlation. The multivariate regression results showed that the age of onset was positively correlated with AGM ( r = 0.467). The regression equation used was Y = 9.0 * X (age of onset) − 11.4. Conclusion We found difference in the morphological and mechanical characteristics of the GM between hips with DDH and hips of normal morphology. Of note, the mechanical characteristics of the GM were influenced by bony parameters in patients with DDH.