A comparison of twenty-six paralytic dislocations of the hip with seventy-five severely paralyzed hips which did not dislocate reveals the fact that no definite type of paralysis was responsible for the dislocation, but that dislocation was most frequent in hips with strong flexors, adductors, and internal rotators and weak extensors, abductors, and external rotators. Of the above muscle groups the abductors appeared to be the most important in maintaining the stability of the hip as we had no cases in which dislocation occurred in the presence of good abductors.
A study of the x-rays of these cases revealed the fact that in paralytic hips which had dislocated the acetabulum was poor and severe coxa valga was usually present. However, it is to be emphasized that these deformities were probably the result of the paralysis and dislocation rather than the cause, as we do not believe that there were any congenital abnormalities in these cases.
We were impressed by the fact that nearly all of the hips which dislocated presented a definite deformity. As any severely paralyzed hip is liable to dislocate, we believe that the prevention of deformities is especially important in these cases. We were further impressed by the fact that the deformities were not always the direct result of muscle imbalance, but in many cases seemed to have been the result of habitual posture. Consequently, we believe that patients with severely paralyzed hips should spend much of their time with the hips in a position of extension and abduction and external rotation.
Operative treatment should be considered in those cases in which conservative treatment has failed or in which there is no reasonable hope that conservative treatment (that is, correction of deformities and maintenance of abduction) will lead to a cure. Contra-indications to operation are such poor general condition that the operation would be unusually dangerous, and such extensive paralysis that even with a stable hip it would not be possible for the patient to walk on crutches and braces. The operation recommended is the shelf operation and we believe that an accurate placing of the shelf is more important than its size, as we have found small shelves just as efficient as large ones.