Sunday, January 9, 2011

Discussion on the pros and cons of various types of hip replacement materials

 Reprinted from

In an effort to ease the pain and suffering of osteoporosis, osteoarthritis, and other conditions that degenerate the hip, doctors and inventors have been trying for many years to perfect artificial hips. Early attempts used materials such as ivory and metal with limited success. Nowadays, more advanced materials offer patients much better results, but hip replacement surgery is still far from perfect. This is well illustrated by the recent DePuy hip replacement recall. Although the ASR XL Acetabular and the ASR Hip Resurfacing System were constructed from modern metals, the devices have injured many recipients. In fact, the very design that made the implants durable also contributed to them failing in 1 out of 8 patients. A brief look at the most common materials used in hip replacements today shows that not only metal on metal, but all varieties of replacement hips, have pros and cons.

Ceramic on Ceramic: Ceramic hip prostheses were developed principally to address the issue of excessive wear found in plastic and metal hip implants. Ceramic is a smooth, hard material but it can be prone to breakage and so-called “catastrophic failure.” Some patients may also experience loud squeaking from a ceramic implant.

Metal-on-plastic: This combination is one of the most widely used in hip replacement procedures. A typical design features a plastic liner that fits into the socket portion of the hip joint and a metal stem and ball that is set inside the femur (leg) bone. The main concern with this type of implant is that wear produces particles that may irritate and damage tissue and bone. The use of advanced plastics such as polyethylene reduces wear but decreases tensile strength.

Metal-on-Metal: Metal on metal implants are extremely strong and durable and allow many recipients to enjoy an active lifestyle. The downside, however, is that these devices are prone to releasing toxic metal fragments that can cause tumor-like soft tissue reactions and damage bone, nerves, and sinew around the implant.

This is one of the major problems with the recalled DePuy ASR devices. The ASRs rely on bone ingrowth to secure the implants, which can be disrupted by metal debris. Some experts have also detected a design flaw with the ASRs. They argue that because the devices are difficult to implant properly, they tend to sit at an angle, which produces a chisel-like effect that can release excessive metal debris.

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