Commentary & Perspective

Commentary & Perspective on
"The Use of a Constrained Acetabular Component to Treat Instability After Total Hip Arthroplasty"
by M. Wade Shrader, MD, et al.

Commentary & Perspective by
John J. Callaghan, MD*,
Department of Orthopaedic Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa

Shrader et al. have evaluated the use of a particular constrained acetabular liner to treat patients in whom other surgical procedures have failed to correct recurrent instability after failed primary total hip replacement or who had absent or grossly deficient soft-tissue attachments at the time of revision hip surgery. The Howmedica bipolar constrained acetabular liner was used in all cases.

After a relatively short follow-up period (average, 3.2 years clinically and 2.9 years radiographically), the authors reported no failures of the constrained device. However, they did report loosening of the acetabular component that required revision in four hips, and they noted a combined prevalence of progressive acetabular radiolucencies in ten of 110 arthroplasties.

The strength of the present study is that unlike other studies, including our own¹, most of these hips (seventy-nine of 110), had had at least one previous procedure to correct a hip instability that occurred following total hip arthroplasty. In eleven hips, the liners were cemented into pre-existing, well-fixed metal shells; in the remaining hips, the liners were snap-fit into new, matching shells. The large, Mayo Clinic Hip Registry also allowed the authors to put into perspective how infrequently this approach was used in comparison with other treatment modalities at their institution. The weakness of the article is the relatively short-term follow-up.

I believe that several important clinical points can be gleaned from this article that will be of help to practicing orthopaedic surgeons. The authors demonstrate that at their institution, the use of this liner prevented recurrent dislocation following reoperation for dislocation better than any other treatment option². However, as with many other things in medicine and life, there is no "free lunch." At just 3.2 years of follow-up (average), four acetabular components were revised for loosening; radiolucent lines were seen around the acetabular component in a total of fifteen hips (including the four revised for loosening), and progression of acetabular radiolucent lines was seen in ten of those hips. Six components also demonstrated observable polyethylene wear. Hence, this approach should not be "the first-line treatment" for recurrent dislocation following total hip replacement, especially if other, remediable causes, such as gross component malposition, are thought to be the cause of the instability.

In addition, the authors demonstrated success with cementing the constrained liner into a secure shell if the technique include the following: roughening the liner surface and roughening the metal shell if it is polished and has no holes, containing the liner³ within the shell, and providing an adequate cement mantle between the liner and shell. While this approach recently has been questioned by other authors⁴; our own data corroborate this approach¹. Finally, the authors used postoperative bracing for sixteen hips and a hip-spica cast for five hips. I concur with this approach. Until ingrowth occurs, the surgeon must protect the hip from excessive sheer stress on the acetabular shell-bone interfaces. For this reason, I use as many screws as I can to gain acetabular bone purchase and I use bracing for most patients for six weeks following this surgery. Because our studies with this component demonstrated less loosening than that encountered in the present study¹, even with our extended 10-year follow-up, these technical points may be pertinent.

In summary, the authors provide further evidence to support the use of constrained acetabular liners in complex cases of hip instability following total hip replacement. Their findings concerning aseptic loosening at the acetabular shell-bone interface provide evidence that these devices should not be used indiscriminately. One must also remember that, in this paper, a single tripolar type of constrained liner was used and other types of constrained liners may not have the same success.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Goetz DD, Capello WN, Callaghan JJ, Brown TD, Johnston RC. Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular component: a retrospective analysis of fifty-six cases. J Bone Joint Surg Am. 1998;80:502-9.
2. Alberton GM, High WA, Morrey BF. Dislocation after revision total hip arthroplasty: an analysis of risk factors and treatment options. J Bone Joint Surg Am. 2002;84:1788-92.
3. Haft GF, Heiner AD, Dorr LD, Brown TD, Callaghan JJ. A Biomechanical Analysis of Polyethylene Liner Cementation Into a Fixed Metal Acetabular Shell. J Bone Joint Surg Am. 2003;85:1100-10.
4. Shapiro GS, Weiland DE, Markel DC, Padgett DE, Sculco TP, Pellicci PM. The use of a constrained acetabular component for recurrent dislocation. J Arthroplasty. 2003;18:250-8.