Abstract
We have performed bipolar hip arthroplasty, combining acetabuloplasty with the use of the femoral head, for patients with hip dysplasia. Clinical and X-P evaluations were made in 34 joints of 30 cases of secondary osteoarthritis caused by CDH or hip dysplasia. The age at operation ranged from 39 to 69 years, an average of 53. The Osteonics Omnifit cementless stem with bipolar head was used in all cases. Evaluations were made at 3 years after operation, using the criteria of the Japanese Orthopaedic Association. The average preoperative score of 48 was increased to 85 postoperatively. The roentgenographical evaluations were of the outer head migration postoperatively, the medial acetabular width at the operation, and the original acetabular coverage angle of the outer head.
The results were as follows: Migration of the outer head of more than 3mm was seen with 15 joints (44%) . But such migration affected no clinical results except decrease of flexion range. The preoperative acetabular medial wall width was 16.7mm and the postoperative 7.9mm; accordingly, the intraoperative acetabular wall reaming was 8.8mm on an average. The average original acetabular coverage angle of the outer head was 890. The cases with insufficiency of medial acetabular reaming or original acetabular coverage of the outer head showed greater upward or lateral migration, and an average of llmm of medial displacement and 8mm of distal displacement were seen in them. To prevent outer head migration, both adequate reaming of the thickened acetabulum and fitting of the outer head in an anatomical position are very important.
