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Adding a New Dimension to Study Hip Joint Implants

Hip joint replacements these days are faring well, but they still don't last long enough. Researchers are designing new joint surfaces to combat wear and tear. Lab tests must be done to see if the changed designs show less wear.

Researchers can measure wear and tear on implant surfaces using new technology. Two- and three-dimensional digital X-ray findings are entered into a computer for analysis. In 2-D, X-rays can't see everything. Sometimes the edges of the implant (where problems occur) aren't shown. 3-D studies can overcome this problem, but more X-rays are usually needed. The angle of the extra X-rays makes the view of poor quality.

Researchers at the University of Chicago Hospitals compared 2-D and 3-D computer analysis of joint implant wear. Wear rates were measured every year for an average of eight years. The research team found that the 3-D analysis finds 10 percent more wear. But there's one major drawback with 3-D analysis. Repeating the test to verify the findings is much harder using this method.

The position of the hip cup (the acetabulum) after it is implanted in the bone can affect the amount of wear occurring in the implant. In this study, the angle and tilt of the cup, called acetabular anteversion, was linked by 3-D analysis to wear that doesn't show up in 2-D studies.

References: John M. Martell, MD, et al. Comparison of Two and Three-Dimensional Computerized Polyethylene Wear Analysis after Total Hip Arthroplasty. In The Journal of Bone and Joint Surgery. June 2003. Vol. 85-A. No. 6. Pp. 1111-1117.

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