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Arthroscopic-assisted reconstruction of the anterior cruciate ligament.

THE DESTRUCTIVE EFFECTS of wear and wear debris have challenged the existence of joint replacement. Charnley's initial use of polytetrafluoroethylene (Teflon) resulted in severe destructive granulomas from the Teflon debris. Highdensity polyethylene at this time continues to be the most used of all substitute bearing materials, but problems with it have now begun to emerge. Many now think that osteolysis is as much related to wear debris as it is to cement fragmentation. The term "cement disease" is considered a misnomer; it should be particle disease. Attempts are being made to improve the high-density polyethylene as a joint surface material, changing the physical structure by altering its molecular chains. This new material seems to have superior properties when creep, oxidation, fracture, pitting, delamination, and wear are tested in the laboratory. It is unknown if this material will decrease the amount of wear debris when it is used clinically in patients. Titanium alloy should not be used as an articular surface in joint replacement. Titanium alloy loses its polished surface when articulating against polyethylene and generates particulate debris that produces osteolysis, thus making it ill-suited as a bearing surface for joint replacement. A new process of nitrogen ion bombardment of titanium is being developed and used, but its clinical usefulness is unknown. Ceramic on ceramic-bearing components also appears to generate considerable particulate debris, and caution must be exercised before this combination is used. Ceramic heads, articulating with polyethylene, have been shown to have superior wear characteristics and thus generate less particulate debris. Time will tell whether the incidence of lysis is affected by ceramic on polyethylene, thus justifying the expense of the ceramic heads. In addition to the materials chosen, the size of the femoral head is important in joint replacement. The 28-mm head, or midrange head prosthesis, seems to be the best compromise when linear wear and volumetric wear are considered. This head size, though, must be placed in proportion to the patient and the amount of polyethylene in the bearing. RICHARD B. WELCH, MD GARY LEVENGOOD, MD San Francisco, California REFERENCES