What is new in hip resurfacing?
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Articular Surface Replacement of the hip joint is being performed for over eight years now in India with very good results in young active patients requiring bone conserving replacement of the hip joint.
Resurfacing of the hip joint is only advisable when the shape of femoral head and strength of the bone can support the prosthesis. Healthy active patients in their third or fourth decade who will benefit from a conservative arthroplasty but have poor bone quality in the proximal half of the head of femur are ideally suited for the new prosthesis called Birmingham Mid Head Resection prosthesis (BMHR). With this prosthesis, the fixation of the femoral component depends less on the bone of the femoral head but more on the stem in the healthy part of the head and neck. The femoral medullary cavity is not opened as in the case of modular BHR with a long stem.
Prosthesis:
The BMHR uses the same socket (hydroxyapatite-coated metal uncemented cup) and bearing(metal on metal) as the BHR. The modular head component fits onto a hydroxyapatite proximal porous coated cobalt chrome stem. It is an uncemented short stemmed prosthesis. It was invented by Prof. Dereck Mc.Minn a year ago and is performed by very few surgeons the world over. In India it is being done only at the Asian Regional Center for Hip Resurfacing in Chennai.
Dynamics:
The head of femur is resected just above the head and neck junction. The following dotted line C indicates the level of resection at the head for a Birmingham Mid Head Modular Resection prosthesis. Lines A and B represent the conventional hip resection levels for Total hip replacement and neck sparing total hip replacement, respectively. The resection level for resurfacing is more proximal to line C.
Indications:
The specific type of arthroplasty for a given patient depends on the volume of necrotic segment, patient demographics and activity demands.
1. Extensive avascular necrosis of the femoral head.
2. Developmental dysplasia with shortened head-neck segment.
3. Large cysts of the femoral head.
4. Involution of the head of femur due to severe arthritis.
Advantages:
The BMHR prosthesis due to metal on metal bearing does not wear easily. Patients who have poor residual viable bone can still have the benefits of a near natural hip by using this prosthesis. The BMHR stem offers the advantage of a more physiological proximal loading than the BHR.
References:
Avascular Necrosis in the young Patient: A Triology of Arthroplasty Options. By Derek J.W. McMinn, FRCS; Joseph Daniel, FRCS: Chandra Pradhan 2005.
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