Fate of the psoas muscle after open reduction for developmental dislocation of the hip (DDH)

We evaluated the anatomic and functional consequences of psoas lengthening during operative intervention for developmental dislocation of the hip (DDH ). Possible anatomic changes were assessed by magnetic resonance imaging (M RI), and functional assessment included strength determination by an isokin etic dynamometer and gait analysis. Six girls and one boy, ranging in age f rom 15 to 20 months, had operative reduction of a unilateral DDH. One close d and six open reductions (three anteromedial and three anterolateral appro aches) were performed. Follow-up ranged from 4 years 0 months to 9 years 2 months. The cross-sectional area determined by MRI of the lengthened psoas muscles was markedly reduced for all of the six open-reduction patients (th ree moderate and three severe). Atrophy of the iliacus muscle also was appa rent by MRI in five of the six open-reduction patients. Maximum flexion tor que, as determined by the isokinetic dynamometer, was diminished on the DDH side for the three patients whose hips were reduced open through the anter omedial approach. Average hip-flexion torque over the entire range of motio n was decreased for both anteromedial and anterolateral groups on the opera ted-on side. Lengthening of the psoas tendon during open reduction of a DDH is associated with considerable atrophy of the psoas muscle.