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 (MRI), and functional assessment included strength determination by an isokinetic dynamometer and gait analysis. Six girls and one boy, ranging in age from 15 to 20 months, had operative reduction of a unilateral DDH. One closed and six open reductions (three anteromedial and three anterolateral approaches) 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 (three moderate and three severe). Atrophy of the iliacus muscle also was apparent by MRI in five of the six open-reduction patients. Maximum flexion torque, as determined by the isokinetic dynamometer, was diminished on the DDH side for the three patients whose hips were reduced open through the anteromedial approach. Average hip-flexion torque over the entire range of motion was decreased for both anteromedial and anterolateral groups on the operated-on side. Lengthening of the psoas tendon during open reduction of a DDH is associated with considerable atrophy of the psoas muscle.