Table 1 Zhao’s criteria for GMC classification

Level 1 (GMC I)

GMC with mild manifestations, including less than 15° abduction contracture when hip and knee are both at 90° flexion, or less than 20° if hip or knee has no flexion. Weakly positive for Ober’s sign and frog squatting sign. No obvious limp gait shown when the lateral inclination of pelvis is less than 10° on the anterior–posterior radiograph

Level 2 (GMC II)

GMC with moderate manifestations, including 15° to 60° abduction contracture when hip and knee are at the 90° flexion position, or abduction less than 10° if hip and knee are at the extension position. Clearly positive for Ober’s sign and frog-leg squatting sign. Obvious limp gait is shown when the lateral inclination of pelvis on the anterior–posterior radiograph is from 10° to 20°

Level 3 (GMC III)

GMC with severe manifestations, including over 60° of abduction deformity when hip and knee joints are at 90° flexion, or no abduction if hip and knee joints are at the extension position. Strongly positive for Ober’s sign and frog squatting sign. Extremely obvious limp gait is shown when the lateral inclination of pelvis is over 20° on the anterior–posterior radiograph