Abstract
Bone preserving hip arthroplasty devices are appealingfor use in young patients because their high-demand activities and extended lifetimes makes the prospect of multiple revisions a reality. Therefore prostheses which ensure a straightforward revision with a low complication rate and good clinical outcome are favourable for young and active patients.
Modern hip resurfacing serves these conditions and shows very good mid-term and now longer term (10 and 13 years) results especially in osteoarthritis. With other diagnoses like avascular necrosis, deformities of the femoral head in m. Perthes or slipped femoral epiphysis (SUFE), or in large bone cysts and erosive arthritis the bone stock of the femoral head gives insufficient support to the femoral component. In these conditions the alternative to a resurfacing procedure had been a stemmed total hip arthroplasty (THA).
The Birmingham Mid Head Resection device (BMHR; Smith&Nephew Orthopaedics) is an alternative to resurfacing and to a stemmed THA. The BMHR device consists of an uncemented short stem made of titanium alloy and a large diameter cobalt-chrome head. The stem does not enter the femoral canal thus facilitating future revisions. The metal-on-metal bearing is the same as in resurfacing. The instrumentation allows switching from a planned BHR to the BMHR. The BMHR uses the unique anatomy of the head neck junction to prepare internally a cone that matches the frustoconical section of the BMHR stem. Thus a cement free press fit can be achieved. This maintains anatomical load transmission and avoids osteopenia of the proximal fenur.
Since 2006 we have performed 662 BMHR implantations. The indications were osteoarthritis in about 70%, dysplasia in 20%, AVN 5,5%, posttraumatic OA in 3%, SUFE and m. Perthes in 1%. Complications occured in 3,2%. Fractures of the femoral neck occured in 8 patients, 4 of them caused by technical errors in the beginning, 3 because of higher risk indication. All revisions were performed successfully and the cup was retained. Low grade infections in 2 cases with one stage revision and 3 unstable cups needed to be reinserted. All revisions were successful. One early dislocation was treated by closed reduction, another remained unstable and was treated by THA. In conclusion we continue to use the BMHR to bridge the gap between resurfacing and stemmed THA because the complications we experienced are not inevitable and had become very rare with our growing experience.
