Plasmacup--special design. Aspects of the dysplastic acetabulum.

In Japan, the main reason for osteoarthritis of the hip joint is caused by dysplastic deformities. The implantation technique of cementless press-fit cup with multi-screw fixation and acetabular bone graft to reconstruct the true acetabular center is described. In addition, special design aspects of the BiCONTACT-N stem were optimized for these patients. Between January 1997 and December 1999, 29 patients (33 hips) received a BiCONTACT-N/Plasmacup-M total hip replacement. There were 28 women and one man. Average age at the time of THA of 64 (range 51-76) years. Average time of follow-up was 41 (range 25-59) months. According to the Crowe classification, 18 hips where classified as type 1 (less than 50% subluxation of the femoral head from the acetabulum), nine type 2 (50-75% subluxation), five type 3 (75-100% subluxation), and one type 4 (complete dislocation). At time of follow-up, there was no loosening of the acetabular implant or collapse of the acetabular bone graft. In the radiographic examination, 80% of the femoral implants showed spot welds in the transitional zone of the coated and uncoated area, and 96% sclerotic lines in the coated area. At the uncoated surface, radiolucent lines were seen in 12% and a cortical hypertrophy in 24%. No stress shielding could be observed. Stem subsidence was measured with an average value of 0.32 (range 0-1.6) mm. No patient complained about thigh pain, and no intraoperative complications were observed. Postoperative complications were two anterior dislocations due to cup malposition and excessive lumbar hypnosis. Three deep-venous thromboses where found with venography and treated with warfarin therapy. The limited experience indicates that BiCONTACT-N stem design in combination with the Plasmacup multihole implant is appropriate for the treatment of dysplastic hip deformities in Japanese patients. However, a long-term follow-up study is needed.