MRI evaluation of hip muscles for unilateral developmental dysplasia of the hip and T2-mapping quantitative analysis

Abstract

Objective To explore the magnetic resonance imaging (MRI) features of hip muscles for unilateral developmental dysplasia of the hip by measuring the area of hip flexor muscles with MRI and to assess the development tendency of T2-mapping technology in muscle lesions by quantitative analysis of T2 relaxation time. Methods Forty-nine children of unilateral DDH (dislocation group) and eight children of normal hips (control group) aged under 3 years without any treatment were included. All patients underwent routine MRI and T2-mapping sequence. The dislocation group was divided into three types according to Dunn's classification standard. MRI assessment and T2 relaxation time measuring of iliopsoas, rectus femoris, tensor fasia lata and sartorius were performed, muscles of dislocated hip compared with normal contralateral hip and ratios of dislocated and health sides calculated. The difference between different degree of dislocation and the correlation to ratios of area or T2 relaxation time with degree of dislocation, correlation to ratios of area with T2 relaxation time were analyzed. Results Area of hip muscles and T2 relaxation time in dislocated side was less than contralateral side. The area ratios of iliopsoas were significantly different among four groups. Area ratios of tensor fascia lata showed significant difference only in type 3 as compared with other types, ratios of rectus femoris showed in any pairwise comparisons except the comparisons between normal group with type 1 and type 1 with type 2. No significance was detected in sartorius muscle (P=0.115). While T2 relaxation time ratios of four muscles were significantly different among the groups. The area ratios of iliopsoas, tensor fascia lata and rectus femoris were negatively correlated with the dislocation degrees (r values of -0.89, -0.56, -0.69, P<0.05). However, no significance correlation was detected in sartorius muscle. In addition, T2 relaxation time ratios of four muscles were negatively correlated with the degrees of dislocation (r values of -0.85, -0.74, -0.80, -0.53, P<0.05). The area ratios of iliopsoas, tensor fascia lata and rectus femoris were positively correlated with their T2 relaxation time ratios (r values of 0.74, 0.52, 0.64, P<0.05) and no significance correlation was detected in sartorius. Conclusions Muscle contracture is present in dislocated hips as compared with contralateral hips. It aggravates the development of the hip dislocation to some extent and affects the treatment and prognosis. Imaging and clinical physicians should attach importance to it. T2 relaxation time shows an obvious difference before the change of muscle morphology. Thus T2-mapping technique can elucidate potential pathological changes earlier as compared with conventional MRI. Thus it has potential clinical application value of early diagnosis and timely treatment. Key words: Hip dislocation, developmental; Magnetic resonance imaging; Relaxation time