X-RAY TRANSPARENCY INTERPOSITIONS AFTER REDUCTION OF TRAUMATIC DISLOCATIONS OF THE HIP IN CHILDREN

Traumatic dislocations of the hip are much less frequent in children t han in adults. If some complications are well known (avascular necrosi s of the femoral head, recurrent dislocation), the lateralization of t he head by x-ray transparency interposition is less appreciated. We re port 4 cases of x-ray transparency interposition in 15 reductions of i ncomplete traumatic dislocation of the hip. These 4 dislocations were posterior in non-pathological hips, three on the left side and one on the right. Our reductions have been easy and the hips remained stable. However, the post-reduction roentgenogram shows the same unusual enla rged joint space corresponding to the lateralization of the femoral he ad. Four arthrotomies were performed, tracing a cartilaginous fragment free or fixed to the articular capsule into the femoral joint. We hav e found a concentric reduction of the hip in 4 cases and enlargement f rom 1 to 3 mm of the joint space of the hip. After several years, arti cular function of the four hips is normal, nevertheless, they have sho wn a coxa valga with a femoral elongation to 10 mm, a coxa magna with an articular space wider than 1 mm, 2 very good concentric reductions of the hip. The lateralization of the head after reduction had to be d etected as soon as the first radiographic control because it can cause immediate instability or arthrosis of the hip. Because of the cartila ginous or capsular composition and the size of the interposition, an a rthrotomy is performed in front of a radiological enlarging of the spa ce joint, or a loss of parallelism of osteochondral acetabulum bone. C omputerized tomography and MRI can reveal the nature, the place of the included fragment, as well as the surgical approach. An arthrogram is not absolutely indispensible. Surgical exploration should avoid degen erative arthrosis after a lateralisation left untreated.