Some hip replacements wear out faster than others. In fact, the same joint implant used in a group of adults will vary in its wear pattern.
Researchers aren’t sure why this happens. It might be the patient’s weight, and therefore, the load on the joint. It could be activity level that affects the rate of wear. This study looked at these two factors in patients with hip replacements on both sides, which is called bilateral total hip arthroplasty.
A small group of patients with the same type of arthroplasty was studied. Each patient had the same operation, cup design, and replacement parts in both hips. No one with a limp was allowed in the study to prevent uneven wear patterns in one hip.
The authors of this study thought that by matching all replacement parts, they would reduce the differences in wear on the implant. They measured the first hip replaced and compared it to the second hip arthroplasty.
As it turned out, the difference in wear rates between the first hip and the second was drastic. In most cases, there was up to a 75 percent difference in the wear between the two implants. With all things considered, identical implants in the same patient with the same activity levels showed marked differences in wear.
The authors conclude that wear and tear on hip arthroplasties depends on more than a patient’s weight and activity. At least 40 percent of the differences in wear rate come from other factors that include patient age, joint angle, and bone slivers or metal particles caught between the implant and the joint surface. Doctors can’t assume that identical hip replacements will have the same result. This is true even for patients having bilateral hip arthroplasties.