Commentary and Perspective on
"Patellar Resurfacing in Total Knee Arthroplasty.
A Prospective, Randomized, Double-Blind Study
with Five to Seven Years of Follow-up"
By Robert L. Barrack, MD et al.

Commentary and Perspective by Thomas S. Thornhill, MD*,
Brigham and Women's Hospital, Boston, Massachusetts

The debate of whether to resurface or not to resurface the patella during total knee arthroplasty has been influenced by patients' functional needs, component designs, and surgical techniques. Early hinge and even modular designs ignored the patellofemoral articulation, but with limited motion and low patient demand, the results were satisfactory. With increasing patient activity and demand, necessary design changes were driven by the high rate of patellofemoral failure. Addition of a femoral trochlear flange was followed by the use of a polyethylene button to resurface the patellar articulation. Patients with rheumatoid arthritis were more susceptible to patellofemoral failure when the patella was not resurfaced, which resulted in the decision of most surgeons in the United States to resurface the patella in all cases.

In the 1980s, however, there were a significant number of patellofemoral failures that were related to both technical and design issues. With patients now achieving greater flexion, the forces on the patellofemoral joint substantially increased. The advent of intramedullary and extramedullary instrumentation greatly facilitated correct bony cuts, but instrumentation could not adequately address the need for soft-tissue balancing to ensure clinical success at the patellofemoral articulation. Static soft-tissue balancing (assessed by the "no-thumbs test" and the "medial contact test") required the surgeon's judgment and experience. An excessively internally rotated tibial component necessitated an internally rotated femoral component, which invariably caused patellofemoral malalignment. Moreover, use of metal-backed patellae with a thin layer of polyethylene and poor locking mechanisms led to a large number of early patellofemoral failures. Frequently, an isolated patellar revision for patellofemoral failure led to a poor result. Boyd et al. determined that there was little difference between resurfacing or not resurfacing the patella with regard to the failure rates¹.

With these data in hand, surgeons made individual choices about whether or not to resurface the patella. Regional differences in the choice of treatment reflected surgeons' experience and the influence of their peers. There were also component differences that influenced the choice; some femoral trochlear designs were more "friendly" to the nonresurfaced patella.

The present study is a good one in that it takes a relevant clinical problem, applies a prospective, randomized study design, and interprets the data without apparent bias. There is input from multiple surgeons, and the authors address most of the clinically important factors. While they showed no difference in the groups randomized to treatment with or without patellar resurfacing, there was a marked difference in the revision rate between the two groups. Seven of the original sixty knees with nonresurfaced patellae (11.7%) subsequently required resurfacing because of anterior knee pain. None of the resurfaced knees required revision even though nine patients reported postoperative anterior knee pain. Interestingly, the authors found no correlation between patellar chondromalacia, obesity, or preoperative anterior knee pain and postoperative knee scores or postoperative anterior knee pain in either treatment group. The revisions in the nonresurfaced group were performed because of anterior knee pain. While the rating of anterior knee pain in the resurfaced knees was similar, none of those knees was revised. Doesn't this constitute a significant clinical difference between the two groups?

The overall incidence of anterior knee pain in both treatment groups is unexpectedly high, particularly given the fact that the average range of motion at final follow-up was only 101°. Perhaps this is a function of the method used to assess anterior knee pain, or perhaps it is a function of the femoral component design. It is important to note that patients without patellar resurfacing underwent a patellaplasty with excision of osteophytes and drilling of areas of eburnated bone. This, in addition to the soft-tissue meniscus that forms after this procedure, may have protected many of these nonresurfaced patellae.

I currently resurface all patellae during total knee arthroplasty. After switching from the use of metal-backed patellae to a three-fixation lug, all-polyethylene biconvex or oval dome patella with a deepened femoral trochlear groove, we have had no patellar failures in our series^2,3. The technical lessons that we have learned include the importance of restoring patellar height, preserving a minimum of 12 mm of native patellar bone, and achieving the correct orientation of the resection line (inferior resection at the infrapatellar tubercle, superior resection at the junction of the quadriceps tendon, and medial-lateral resection at the chondro-osseous junction).

How are readers to interpret the results presented by Barrack et al.? Does the failure to show differences between treatment methods in this small group of patients indicate that differences do not exist? While the available study group consisted of eighty-six patients (118 knees), only sixty-seven patients (93 knees) were available for the five-year minimum follow-up. This left only forty-seven knees in the patellar resurfacing group and forty-six knees in the nonresurfaced group. Would the low incidence of patellofemoral failure be seen in this small study group? Should the patients lost to follow-up be considered failures? Does the high incidence of anterior knee pain in both groups suggest that this is a component-specific problem? If the surgeon/reader is having success with his or her current treatment of the patellofemoral joint, should he or she change it on the basis of these data? I think not. It is, however, well-conceived prospective, randomized, clinically relevant studies like the present one that will give us these important answers, and for this the authors should be applauded.

*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. Depuy-Johnson and Johnson, Stryker-Howmedica, Smith and Nephew, and Synthes paid or directed, or agreed to pay or direct, benefits to a research fund (Foundation 50103) for the department with which the author is affiliated or associated.

References

1. Boyd AD Jr, Ewald FC, Thomas WH, Poss R, Sledge CB. Long-term complications after total knee arthroplasty with or without resurfacing of the patella. J Bone Joint Surg Am. 1993;75:674-81.
2. Schai PA, Thornhill TS, Scott RD. Total knee arthroplasty with the PFC system. Results at a minimum of ten years and survivorship analysis. J Bone Joint Surg Br. 1998;80:850-8.
3. Schai PA, Scott RD, Thornhill TS. Total knee arthroplasty with posterior cruciate retention in patients with rheumatoid arthritis. Clin Orthop. 1999;367:96-106.