|FDA Approved in USUpdated 11/9/09|
The BHR, Birmingham Hip Resurfacing, offers younger, active patients more ROM, no restrictions of activities and almost no possiblity of dislocations as many of the older THR hip devices.
Derek McMinn and Ronan Treacy at the Royal Orthopaedic & Nuffield Hospitals, Birmingham, UK, have more than 9 years experience with metal on metal hip resurfacing devices. Hip Resurfacing offers a patient a bone conserving operation since the femur head does not have to be removed, just reshaped to accept the cap of the BHR. Should a revision be required at some time in the future, there is still an intact healthy femur allowing for a ‘primary’ hip without the normal complications associated with revision.
Hip resurfacing has been shown to eliminate the problems of proximal femoral stress shielding and osteolysis caused by plastic wear debris associated with traditional plastic/metal THR hips. Hip resurfacing eliminates the problems of hip dislocation and significantly reduces the problem of leg lengthening.
For patients with defects of the acetabulum, the BHR offers the Dysplasia Cup. These are available in 6 sizes from 46mm to 66mm in 4mm increments. The Dysplasia Cups are available in 6 sizes from 46mm to 66mm in 4mm increments. The cup has 2 superolateral threaded lugs which allow for a unique screw fixation to ensure solid cup fixation in the deficient acetabulum. Structural bone grafting is not required.
BHR BHR with Dysplasia Cup
The BHR* is produced using the investment casting process from high carbon cobalt chrome in the As Cast micro-structural condition.
Wear studies have shown that Cobalt Chrome in its As Cast form has superior wear resistance to other forms of the alloy. 10, 11, 12
Heat treating, which includes hot isostatic pressing (HIP), solution heat treatment (HT), wrought forging or sintering modifies the microstructure, reducing the block carbides in both quantity and quality. This directly affects the wear resistance of the metal, as shown in diagram A. 13, 14, 15
The importance of carbide structure has been demonstrated in independent testing with other devices. A recent publication highlighted the difference in the wear rates of heat treated and As Cast products. The cumulative linear wear rate data showed substantially more wear with the heat treated metallurgy when compared to the As Cast devices. 16Clinical Evidence
The BIRMINGHAM HIP* Resurfacing (BHR*) has demonstrated exceptional clinical results worldwide. High survival rates of 98% or better were achieved in clinical centres around the world. 1,2,3,4,5
In addition, the recently published Australian Orthopaedic Association National Joint Replacement Registry reports BHR as having the lowest revisions per 100 observed ‘component’ years when comparing all resurfacing implants used in the country. 6
Other clinical studies have focused on predictive measurements to project long-term survivorship of the resurfaced femoral head. Researchers at the University of Oxford, England used roentgen stereophotogrammetric analysis (RSA) to measure the stability of the femoral head. At 24 months, the total three-dimensional migration of the head was not statistically significant at 0.2mm.
Previous studies have shown that implants that loosen quickly have rapid early migration. According to the authors, these results suggest the BHR femoral component is an inherently stable device predicting a good long-term performance. 7,8
It is widely accepted that the Bone Mineral Density (BMD) of the proximal femur generally decreases after cementless THA using standard designs of femoral components. However, BMD studies conducted at Osaka University, Japan reported the post-operative BMD in the proximal femur was significantly greater in patients treated with the BHR system compared to the conventional system. The patients treated with the BHR system demonstrated preservation of the BMD in Gruen zone 1 and an increase in zone 7.
These results suggest that transfer of load to the proximal femur was more normal after surface replacement with the BHR system. These findings also show the BHR system preserves the bone stock of the proximal femur after surgery. 9Information from Smith & Nephew WebsiteLink http://www.hipresurfacing.com/surgeonarticle.asp?sect=5