Question:My fairly new hip replacement came loose and dislocated. I never had a clue it was coming. The surgeon said it was the result of bone loss. Shouldn't I have felt something before it happened? What did I miss here?
Answer:Anytime a rigid implant such as a total hip replacement (THR) is put into a bone, there can be bone loss. Bone is a living tissue that needs physical stress to keep it strong and active. Moving about on two legs usually gives it just the right amount of stress needed to stay healthy.
When a piece of metal such as the femoral stem component of the THR is put inside the bone, there's a mismatch of materials, load, and strength. The body reacts to this in a protective fashion. Any time two materials are joined, the stiffer material bears most of the load. The result is loss of bone density where the stiffer implant takes over.
X-rays don't show early changes in bone density. In fact, the bone can lose up to 30 per cent of its density before it can be seen on X-ray. Newer DEXA scanning is more sensitive but isn't used routinely. Future medical practice may suggest the need to use DEXA to assess implant condition after total hip replacement.
New drugs to help strengthen bone after THR may be another strategy to combat the loss of bone density. Meanwhile, researchers continue to make changes in the implants to help prevent bone resorption.A. H. Glassman, MD, MS, et al. New Femoral Designs. In Clinical Orthopaedics and Related Research. December 2006. No. 453. Pp. 64-74.
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