Popliteal angle as an indicator for successful closed reduction of developmental dysplasia of the hip.

PURPOSE To evaluate the use of the popliteal angle as an indicator for successful closed reduction of developmental dysplasia of the hip (DDH) in children with delayed presentation. METHODS 29 patients aged 6 to 18 months underwent successful closed reduction for unilateral DDH under general anaesthesia. Using a graduated goniometer, the popliteal angle was measured with the hip abducted within the safe zone (to avoid redislocation and injury to the femoral capital epiphysis) before and after reduction and after 6 weeks of spica casting. RESULTS The mean popliteal angles before and after reduction and after 6 weeks of spica casting were 5.1, 37.5, and 17.9 degrees, respectively (p<0.0001, paired t test). Because of discomfort, the spica casts were altered in 3 patients (2 at week 1 and one at week 3). CONCLUSION Reduction of the hip in DDH results in an increased popliteal angle of >20 degree. This may be used to indicate the diagnosis and safe closed reduction.