In a total hip replacement, also called total hip arthroplasty, both the thigh bone (femur) and the socket are replaced with implant prostheses. Specifically, a metal stem is inserted into your thighbone. Attached to the neck of the stem is a hip ball, just over an inch in diameter. The hip ball fits into a liner. Together, the ball and liner create the new joint. The liner is inserted into a metal shell that in turn is anchored to your pelvis. But there are a number of different approaches a surgeon can take, depending on her analysis of your particular case.
Because of the advances in the last thirty years, several types of implant materials have also been found useful in hip replacement procedures. Each material has its own advantages and disadvantages, but it is ultimately up to your surgeon which type of implant to use.
Beyond the different types of materials, a surgeon must also decide whether to anchor the hip implant to the bone using cement fixation or something called “bone ingrowth.” For bone ingrowth, the surface of the prostheses simulates the bone with a special granular surface into which the bone grows, thereby locking the implant into place. Cement fixation holds the implant in the bone by acting as a filler between the bone and the implant. It is made of a substance that is mixed at the operation and hardens into a durable, long lasting polymer.
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You may also want to consult with your doctor about the design of the implant. Modular systems offer the ability to interface different sizes of femoral heads to fit over the stem; angles, sizes, and lengths of the implant are made to fit your anatomy. The advantage of a modular system is that it gives the patient more flexibility.
Hip Implant Materials
The main issue that doctors and patients confront when choosing implant material revolves around the wear debris that is released into your body from any of the implant materials. Even the materials with the most wear debris (metal ball and polyethylene liners) show up only after many years (10-15). Nevertheless, it is important to educate yourself about the various options for hip replacement surgery. Be sure to ask your surgeon whether he or she uses metal-on-polyethylene, metal-on-metal, ceramic-on-polyethylene or ceramic-on-ceramic implants – and why.
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For younger patients, a total hip replacement may not be the best solution for their hip pain because it can mean difficult and numerous revisions later in life. Hip resurfacing, however, leaves more of the bone in place, giving these patients more time before a total hip replacement becomes necessary.
If you are a candidate for hip replacement surgery, fixation, modularity, and implant materials are all topics that factor into making the right decision. Ultimately your doctor should explain to you which procedure and materials are best for you.
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