The Multifactorial Nature of Polyethylene Wear in Vivo*

In the 1980s, the focus of the joint-replacement industry was on fixation of the implants, and progress has been made both with devices that are inserted with cement and with those that are inserted without cement. As has always been the case in the history of joint replacement, each advance has unmasked another limitation. More durable fixation allows for more frequent, more intense, and more variable use of the joint, and the indications for the procedure have gradually been expanded to include younger and more active patients. With greater anticipated longevity for both patients and devices, there are justified concerns about long-term skeletal remodeling, but this has not yet been demonstrated to be a widespread clinical problem. The current problem is osteolysis, which most commonly occurs in association with polyethylene wear particles. The clinical assessment of the performance of a bearing couple has traditionally been based on radiographic studies. With this approach, which presumably measures a change in the thickness of the polyethylene, there is a tendency to attribute the change in thickness to variables inherent to the polyethylene bearing. This is especially true when issues related to the manufacturing and sterilization of polyethylene have been put in the spotlight by both science and industry. We must be cautious about this tendency. As polyethylene wear is a focal issue in joint replacement, it is essential that we appreciate the complexities of studying such wear in vivo. The October 1997 issue of The Journal contained an article by Livingston et al. entitled, “Complications of Total Hip Arthroplasty Associated with the Use of an Acetabular Component with a Hylamer Liner.”18 While we share the authors' concern about the in vivo performance of Hylamer, we wish to point out that there were differences in their comparison groups, in addition to the difference …