The Journal of Bone and Joint Surgery

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Commentary & Perspective

Commentary & Perspective on
"Patellar Resurfacing in Total Knee Arthroplasty: A Meta-Analysis"
by Emilios E. Pakos, MD, et al.

Commentary & Perspective by
Robert B. Bourne, MD, FRCSC, MD*,
London Health Sciences Centre, London, Ontario, Canada

Whether or not to resurface the patella at the time of total knee arthroplasty remains controversial. Historic data have been of limited value, as many early implants were not designed for patellar resurfacing. More recently, several randomized controlled trials have compared total knee arthroplasty, with and without patellar resurfacing, with conflicting results. The authors of this manuscript have suggested that many of these studies were underpowered and unable to detect differences between the two treatment groups. As a consequence, a meta-analysis was performed of these randomized clinical trials to obtain a larger group of patients and answer three questions: (1) Is reoperation less frequently needed when the patella is resurfaced?; (2) How commonly is postoperative anterior knee pain associated with each method of treatment?; (3) What is the mean improvement in the knee score associated with each type of treatment?

To perform this study, the authors searched MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials for randomized trials comparing total knee arthroplasties performed with and without patellar resurfacing. The last search was performed in November 2004. Ten independent randomized trials (described in twelve papers) were included in the overall meta-analysis with a cumulative sample size of 1223 involved knees. When all studies were combined, the frequency of reoperations in the patellar resurfacing group was 0.48 times lower (95% confidence interval, 0.30 to 0.75 times lower) than that in the nonresurfacing group. Five of the reports provided relevant data on anterior knee pain and, in this group of patients, the meta-analysis revealed that postoperative anterior knee pain was 0.40 times lower (95% confidence interval, 0.19 to 0.85 times lower) in the resurfacing arm. Only four studies provided adequate summary knee score data necessary for quantitative analysis. The data showed no significant difference between the patellar resurfaced group and the nonresurfaced comparison group, but the authors believe that these data should be interpreted with caution.

The authors are to be congratulated for attempting to perform a meta-analysis to determine the role of patellar resurfacing during total knee arthroplasty. They correctly point out that the available data were limited (1223 involved knees), that only five reports provided details on postoperative anterior knee pain, and that only four reports provided data for a quantitative analysis of changes in various knee scores postoperatively. Additional problems not reported in this manuscript include whether or not the data from the studies are generalizable to all other knee-replacement designs. For instance, the majority of the total knee replacement designs assessed in the meta-analysis featured non-anatomic patellofemoral joints. It is perhaps not surprising that an unresurfaced patella articulating against a non-anatomic femoral component might be expected to produce more anterior knee pain. It would have been interesting to have data from a comparison of implants that had anatomic "patella-friendly" designs with implants that had non-anatomic designs. The use of reoperation as a primary outcome measure in a meta-analysis of resurfaced and nonresurfaced patellae also must be viewed with caution. Anterior knee pain is common following total knee replacement both with and without patellar resurfacing. In a patient with a nonresurfaced patella and anterior knee pain, the surgeon and patient have a surgical treatment option, namely, a secondary operation to resurface the patella. In a patient with a resurfaced patella and anterior knee pain, no such option exists. There is obviously a bias toward a secondary reoperation in patients in which the patella has not been resurfaced.

At the time of total knee arthroplasty, surgeons usually fall into one of three camps: some always resurface the patella, others never resurface the patella, and the remainder selectively resurface the patella depending on the patient's symptoms and the appearance of the patellofemoral joint at the time of surgery. A randomized clinical trial really only addresses the first two situations, namely, those who always resurface the patella or those who never resurface the patella. As a consequence, this meta-analysis does not really address the outcomes following selective resurfacing of the patella during total knee replacement.

In summary, the authors are to be congratulated for performing this meta-analysis to determine whether or not the patella should be resurfaced during total knee replacement. Unfortunately, a meta-analysis is only as good as the data available for assessment. In this regard, the sample size of available patients remains small and includes total knee replacement designs, which were not optimally designed to reproduce normal patellofemoral mechanics. As a consequence, it remains very difficult to generalize the results of both this study and the studies published previously in the literature. In an ideal world, we would have design-specific outcomes (i.e., reoperation rates, anterior knee pain rates, and change in knee scores, all of which would be implant-specific). While randomized clinical trials are the gold standard to provide such data, this information might be difficult to obtain. Post-market surveillance as provided by a national joint replacement registry might be able to provide supplemental data in this regard.

*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.