Osteochondral impaction of the femoral head associated with hip dislocation: CT study in 35 patients.

Chondral and osteochondral impactions are insults to articular cartilage and subchondral bone of the femoral head during hip dislocation. To evaluate the frequency and sites of femoral head impaction, we reviewed CT scans of 35 patients with hip dislocation (32 posterior and three anterior). Osteochondral impaction fractures were present in 20 (63%) of the 32 patients with posterior hip dislocation and in all three patients with anterior dislocation. In patients with posterior dislocation, the impaction occurred anteriorly in an arc between the 11-o'clock and 1-o'clock positions in all seven cases (100%) of right-sided dislocation and in eight (61%) of 13 cases of left-sided dislocation. Twelve (60%) of the 20 patients with femoral head impaction fracture underwent surgery; osteochondral impaction was substantiated in all 12. In those with anterior dislocation, osteochondral impaction occurred at the posterolateral aspect of the femoral head in an arc between the 4-o'clock and 5-o'clock positions. A high rate of osteochondral impaction after hip dislocation was detected in this series. Observing the site of femoral head impaction allows determination of the type of original dislocation. Alternatively, when the type of original dislocation is known, the site of femoral head impaction can be predicted.