Commentary & Perspective on
"Survival and Polyethylene Wear of Porous-Coated Acetabular Components in Patients Less Than Fifty Years Old. Results at Nine to Fourteen Years"
By James D. Crowther, MD, and Paul F. Lachiewicz, MD
and on
"The Need to Account for Patient Activity When Evaluating the Results of Total Hip Arthroplasty Survivorship Analysis"
By Frederick J. Dorey, PhD, and Harlan C. Amstutz, MD

Commentary & Perspective by
William H. Harris, MD*,
Orthopaedic Biomechanics Laboratory, Massachusetts General Hospital, Boston, MA

The article by Crowther and Lachiewicz serves as an excellent review of the results of the use of the Harris-Galante I acetabular component in "younger" patients at a mean follow-up of eleven years. Positive outcomes were the excellence of fixation and the high survival rate (98%). Of serious concern is the high prevalence of pelvic lysis (23%) and the need for reoperation (bone-grafting and liner exchange) in two patients because of asymptomatic pelvic lysis. It is clear that the rate of lysis in this cohort will increase with time.

In an Editorial in the same issue of The Journal, Drs. Dorey and Amstutz made the compelling point that one major omission in the report by Crowther and Lachiewicz is the absence of quantification of patient activity levels.

Schmalzried et al. have quantified the wide variation in patients' activity levels, providing specific data to support the hypothesis that wear is a factor of use, not time¹. With lysis being most directly related to generation of particulate debris (although not completely so) and with the generation of debris being most directly related to usage (although not completely so), the comments by Dorey and Amstutz are germane and important.

They also pointed out the difficulties in answering their own challenge to establish a formal method of evaluating patient activity, particularly the difficulty of collecting relevant data to establish summary scores that would reflect the relative contributions of all aspects of activities to wear.

Two considerations are relevant to improvement in the survival of total hip arthroplasty in the future. The first involves the further development of simpler and more universally applicable means of quantifying patient activity. It would also be of substantial interest and perhaps of substantial value to be able to differentiate between the relative contributions of gait and stair-climbing to prosthetic wear. One can only hope that rapidly developing current technology will create an easier and more widely applicable solution to the problem of quantification of patient activity.

Second, the wear rates of the traditional type of ultra-high molecular weight polyethylene may prove to be less germane in the future, with the rather wide adoption of improved articulating surfaces, such as more highly crosslinked polyethylenes, ceramic-on-polyethylene articulations, ceramic-on-ceramic articulations, and metal-on-metal articulations. It would appear likely that the wear rates observed during the past four decades when conventional polyethylene was the predominant bearing surface will be markedly reduced going forward into the twenty-first century.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. The author received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Zimmer, Sulzer Orthopaedics). In addition, a commercial entity (Zimmer, Sulzer Orthopaedics) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

Reference

1. Schmalzried TP, Shepard EF, Dorey FJ, Jackson WO, dela Rosa M, Fa'vae F, McKellop HA, McClung CD, Martell J, Moreland JR, Amstutz HC. The John Charnley Award. Wear is a function of use, not time. Clin Orthop. 2000;381:36-46.