The relationship between gluteus medius and minimus muscle volumes and hip development in developmental dysplasia of the hip.

BACKGROUND:Several studies in adult hips have revealed the role of the gluteus medius (Gmed) and gluteus minimus (Gmin) muscles in maintaining the stability and centripetal force of the hip joint. Hip centripetality in developmental dysplasia of the hip (DDH) patients contributes to subsequent healthy hip development later in life. The purpose of this study is to investigate the relationship between Gmed and Gmin volume and centripetality of the hip in infant DDH patients. METHODS:We retrospectively enrolled 41 unilateral DDH patients (4 males, 37 females) who were treated by closed reduction from 2006 to 2016 and underwent magnetic resonance imaging at around 2 years old. Gmed, and Gmin volume was measured in magnetic resonance imaging. We defined both Gmin and Gmed together as hip abductor gluteus muscles (GMs; Gmed + Gmin). The muscle volume ratio of the affected side was calculated by dividing the GMs volume of the affected side by the contralateral side. Relationships between center-head distance discrepancy (CHDD) at 2 years old, and at 4-6 years old and GMs volume ratio were investigated by Pearson's correlation coefficient within the same patients. RESULTS:Mean age of closed reduction was 0.8 years old and mean age at MRI was 2.2 years old with a mean follow-up period of 3.7 years. Mean GMs volume in the affected side, contralateral side, and muscle volume ratio were 25.3 cm3, 27.0 cm3, and 0.94, respectively. GMs volumes were significantly higher in the contralateral side (p < 0.001). GMs volume ratio at 2 years old significantly correlated with CHDD at 4-6 years old (p < 0.05). CONCLUSION:GMs volume at 2 years old was found to be associated with later hip afferents. Promoting the healthy development of GMs by properly maintaining the infant's natural hip movement is important for the healthy hip development. LEVEL OF EVIDENCE:Level III.