[Innominate osteotomy (Salter) related to the correction of the acetabular abnormality and the prediction of the acetabular angle after operation (author's transl)].

: The purpose of this paper is to know how to correct the maldirection of the acetabulum. The author devised a new system for the measurement of the degree of the forward rotation of the acetabulum. The acetabular improvement after the osteotomy is classified into two types, namely the primary and secondary improvement. The primary improvement is seen immediately after the osteotomy and the secondary improvement follows gradually. The effective factors for each of them were analyzed. The primary improvement is influenced mostly by the lateral inclination of the distal fragment. The secondary improvement was intimately correlated to the forward rotation of the acetabulum at the operation. The development of the acetabulum after operation can therefore be predicted from the post-operative X-ray film. In the case of the residual subluxation of the hip, there is about 10 degrees of acetabular elevation (frontalization), so the acetabulum should be rotated forward by more than 10 degrees in this operation.