Prosthetic design and outcome in total hip arthroplasty.

Abstract

To The Editor: I read with great interest “Total Hip Arthroplasty with Use of the Metasul Metal-on-Metal Articulation” (82-A: 789-798, June 2000), by Dorr et al. The authors are to be commended for their very thorough report on a new hip prosthesis and for underscoring the problems associated with the introduction of a new joint prosthesis into clinical practice. The report, however, still leaves some important questions unanswered. The paper describes the results with a new cup (the Weber cup) that has a metallic articulating surface. This cup was paired with an “old” cementless femoral prosthesis with the proprietary name Anatomic Porous Replacement-II (APR-II). There are two designs of the APR femoral prosthesis (APR-I and APR-II), which are characterized by the different forms and coatings of their stems. These two designs were originally used with proprietary polyethylene cups and demonstrated different clinical results in five reports on the APR prosthesis, all coauthored by Dr. Dorr, that are registered in the Medline database. This information is, however, not revealed in the present paper. Will the authors explain the omission? Use of the APR-I stem in conjunction with a polyethylene cup was associated with loosening, mainly of the femoral stem, which had a rate of revision of 16%1. Thus, the results for this APR-I prosthesis were much worse than those reported for other “standard” polyethylene-on-metal hip prostheses2. On the other hand, use of the APR-II stem in conjunction with a polyethylene cup was associated with a rate of femoral loosening of only 0.8% and was not associated with acetabular loosening or osteolysis3. These results, which the authors do not mention, were better than the results reported in the present paper, in which the combination of the APR-II stem and the Weber cup was associated with a …