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Resurfacing of the Patella in Total Knee Arthroplasty. A Prospective, Randomized, Double-Blind Study*

ROBERT L. BARRACK, M.D., MICHAEL W. WOLFE, M.D., NEW ORLEANS, DOUGLAS A. WALDMAN, M.D., ALEXANDRIA, MATKO MILICIC, M.D., ALEXANDER J. BERTOT, B.S. and LEANN MYERS, PH.D.¶, NEW ORLEANS, LOUISIANA

Investigation performed at the Tulane University School of Medicine, New Orleans, and the Veterans Administration Medical Centers, Alexandria and New Orleans

	Abstract

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During a two-year period, eighty-nine patients who were scheduled to have a total knee arthroplasty for the treatment of degenerative osteoarthrosis were randomly assigned to one of two groups: resurfacing of the patella or retention of the patella. All patients received the same posterior cruciate-sparing prosthesis, and all operations were performed by, or under the direct supervision of, one of us. Three patients died in the early postoperative period. The remaining eighty-six patients (118 knees; fifty-eight that had had resurfacing of the patella and sixty that had not) formed the study group. They were followed for a mean of thirty months (range, twenty-four to forty-four months). Evaluation was performed with use of the clinical scoring system of The Knee Society, a patient-satisfaction questionnaire, specific questions regarding patellofemoral symptoms and function, and radiographs. All clinical evaluations were performed by the same research nurse, without the involvement of a physician, in a blinded manner (neither the nurse nor the patient had knowledge of whether the patella had been resurfaced). Preoperatively, the mean Knee Society score, on a scale ranging from 0 to 200 points, was 89.7 points (range, 33 to 132 points); postoperatively, this score improved to a mean of 172.7 points (range, 98 to 200 points). With the numbers available for study, we could detect no significant difference between the knees that had had patellar resurfacing and those that had not with regard to the over-all score (p = 0.63), the subscore for pain (p = 0.56), or the subscore for function (p = 0.77). We also could detect no difference between the treatment groups, with the numbers available, with regard to patient satisfaction or the responses to questions involving the function of the patellofemoral joint, including the ability to exit from an automobile, to rise from a chair, and to climb stairs. Thirty-two patients had bilateral total knee replacement with resurfacing of the patella in one knee and retention of the patella in the other. These patients expressed no clear preference for either knee. Eight (13 per cent) of the sixty knees that had not had resurfacing were painful anteriorly compared with four (7 per cent) of the fifty-eight that had; this was not a significant difference (p = 0.38), with the numbers available. The anterior pain that was noted postoperatively was predominantly of new onset; it had not been observed preoperatively in three of the four knees that had had resurfacing or in four of the eight that had not. No additional treatment options were offered to the patients who had anterior pain in the knee after resurfacing. However, six (10 per cent) of the sixty knees that had not had resurfacing had it subsequently, because of anterior pain in the knee, after the twelfth postoperative month (range, fifteen to thirty-nine months). The pain decreased in four of these knees. Thus, total knee arthroplasty with retention of the patella yielded clinical results that were comparable with those after total knee arthroplasty with patellar resurfacing, but it was associated with a 10 per cent prevalence of the need for subsequent resurfacing. The prevalence of anterior pain after total knee arthroplasty was not influenced by whether or not the patella had been resurfaced. The postoperative clinical scores, the postoperative development of anterior pain, and the need for subsequent resurfacing were not predicted by the presence of preoperative anterior pain, obesity, or the grade of chondromalacia observed intraoperatively. Because of the short duration of follow-up, these results should be considered preliminary. Additional follow-up is planned.

	Introduction

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Resurfacing of the patella was not a feature of many early designs of total knee prostheses. The occurrence of postoperative patellofemoral pain, particularly in patients who had rheumatoid arthritis, resulted in the incorporation of patellofemoral resurfacing into most subsequent designs^9,15,30. With the advent of modern condylar components, resurfacing of the patella became a standard part of total knee arthroplasty²⁰. However, complications related to the patella emerged as the major cause of reoperations after total knee arthroplasty. The reported rates of these complications, which have included postoperative anterior pain in the knee, subluxation, dislocation, patellar fracture, rupture of the quadriceps tendon or the patellar ligament, and patellar clunk, have ranged from 4 per cent (sixteen of 396 knees) to 50 per cent (twenty-six of fifty-two knees)^{4,11,16,27,29}. Because many of these patellofemoral complications seemed to be more common after the patella had been resurfaced, so-called selective resurfacing was suggested as a means of lowering the prevalence of complications after total knee arthroplasty^13,21,29. The recommended criteria for resurfacing of the patella have varied widely, depending on the results observed by various investigators. The proposed indications for resurfacing have included obesity, preoperative anterior pain in the knee, moderate or severe chondromalacia, patellar tilt or deformity, and patellar height¹³. However, the indications remain somewhat controversial. In one study, postoperative anterior pain in the knee was reported as being more common in obese patients when the patella had not been resurfaced²⁹; in another study published in the same year, however, such pain was reported as being more common in obese patients when the patella had been resurfaced³⁴.

Almost all studies of resurfacing of the patella have been retrospective and non-randomized, and none have involved blinded examiners or patients, to our knowledge. We undertook a randomized, prospective, blinded study to investigate the indications for resurfacing of the patella in total knee arthroplasty.

	Materials and Methods

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All patients who were to have a total knee arthroplasty at one of three university-affiliated teaching hospitals between January 1992 and December 1993 were included in the study. The indication for the operation was degenerative osteoarthrosis that was severe enough to warrant total knee arthroplasty after an adequate trial of non-operative therapy. The criteria for exclusion included a previous tibial osteotomy or operation involving the extensor mechanism, a history of septic osteoarthrosis or osteomyelitis, a severe medical disability that limited the ability to walk, disabling disease involving other joints of the lower extremities, inflammatory arthropathy, and severe deformity (varus angulation, valgus angulation, or flexion contracture of more than 15 degrees).

One hundred and thirty-seven patients were evaluated for inclusion in the study. Forty patients (fifty-four knees) met one criterion for exclusion and were not offered enrollment in the study. Patients who had a severe deformity received a posterior cruciate-substituting, posterior-stabilized component and also were not included. Ninety-seven patients who met the criteria for inclusion were asked to participate in the study, and eighty-nine (92 per cent of all eligible patients; 121 knees) agreed. Three patients died in the early postoperative period. These deaths, which were secondary to two motor-vehicle accidents and a myocardial infarction, were unrelated to the operation. This left 118 knees in eighty-six patients for analysis.

Participation in the study was entirely voluntary. All patients were provided with an explanation of the purpose of the study and an opportunity to ask questions. They were assured that non-participation or withdrawal would not jeopardize their care. The study protocol, including the consent forms, was approved by the institutional review boards of all three hospitals. A detailed informed-consent form was signed by each patient, and all information was kept confidential. The patients agreed to be blinded with regard to which procedure they had had in order to reduce bias in their responses on the follow-up questionnaires.

All patients received the same posterior cruciate-sparing prosthesis (Miller-Galante II; Zimmer, Warsaw, Indiana) (Figs. 1-A and 1-B). All operations were performed by, or under the direct supervision of, one of us (R. L. B., D. A. W., or M. M.).

View larger version (139K): [in this window] [in a new window]   Figs. 1-A and 1-B: Photographs of the Miller-Galante-II prosthesis. Fig. 1-A: Anteroposterior view.

View larger version (133K): [in this window] [in a new window]   Fig. 1-B: Lateral view.

All procedures were performed with a uniform approach and technique. The operative technique included external rotation of the femoral component, lateralization of the femoral and tibial components, and medialization of the patellar component. Lateralization and medialization are defined as placement of the component to the lateral or medial edge of the cut surface of the bone, respectively. Generally, this means that the component is centered one to three millimeters lateral or medial to the midline of the cut surface in the medial-lateral dimension. All components were inserted with cement, and all patellar components were all-polyethylene (non-metal-backed). We sought to reproduce accurately the preoperative thickness of the patella, as measured by calipers, with use of the resurfacing technique.

Intraoperative photographs of the articular surface of the patella were made, and the degree of chondromalacia was graded according to the criteria of Outerbridge²⁸. If the patella subluxated during passive range-of-motion testing (the so-called no-thumbs technique¹²), a lateral retinacular release was performed with use of an inside-out technique and an attempt to preserve the superior lateral geniculate artery. When resurfacing was not performed, a so-called patelloplasty was carried out, including removal of osteophytes, smoothing of fibrillated cartilage, and drilling of eburnated bone.

All patients were managed with the same perioperative regimen, including administration of antibiotics and prophylaxis against venous thrombosis. Physical therapy was conducted in a uniform fashion for all patients at each institution, according to a protocol provided to the therapists. This consisted of weight-bearing as tolerated and active flexion conducted twice daily under the supervision of the therapist and commencing on the first postoperative day.

Evaluations were conducted preoperatively; at six, twelve, and twenty-four months; and annually thereafter. All physical examinations were performed in the orthopaedic clinics by a trained nurse clinician, and radiographs again were made. At all preoperative and postoperative visits, a clinical score was determined with use of The Knee Society scale²⁰, which ranges from 0 to 200 points. These scores were ascertained for each knee in a double-blind fashion—that is, neither the patient nor the examiner was aware of whether the patella had been resurfaced.

To explore the relationship between the patient's weight and the clinical result, the percentage by which the patient's weight exceeded the maximum allowed for a so-called large frame by the 1983 Metropolitan Life Insurance Company weight-for-height tables²⁶ was calculated. Analysis of covariance was performed to assess the relationship of The Knee Society clinical score to obesity and to the presence or absence of resurfacing, which were used as independent variables. The preoperative score was used as a covariant to adjust for any preoperative differences among the subjects.

Patient satisfaction was assessed with use of detailed questionnaires that all patients completed preoperatively and at each follow-up visit. The instruments used included visual-analog scales pertaining to pain and function and an assessment of patient satisfaction. Questionnaire items concerned how the knee symptoms interfered with activities of daily living, work, and recreation. The ability to climb stairs, to rise from a chair, and to exit from an automobile were of particular interest in this study population, and these items were assessed specifically, as was the presence or absence of anterior knee pain, as a means of identifying symptoms related to the patella. If anterior pain in the knee was present, it was graded by the patient on a 1-to-10-point scale, with 1 point indicating slight pain and 10 points, severe pain.

Preoperatively, a full-length (hip, knee, and ankle) anteroposterior radiograph with the patient standing and lateral and axial (sunrise) radiographs were made. An anteroposterior radiograph, made with the patient standing, as well as lateral and axial radiographs, were evaluated at one-year intervals postoperatively. The radiographs were analyzed by investigators other than the surgeons. On the anteroposterior radiograph, the anatomical axis was measured with use of the longitudinal axes of the femur and the tibia as references. On the lateral radiograph, the Insall-Salvati index¹⁹ was used to calculate the patellar height by dividing the length of the patellar ligament by the diagonal length of the patella. On the axial radiograph, patellar tilt and subluxation were measured as described previously by Gomes et al.¹⁴.

The data were analyzed and the descriptive statistics (means and standard deviations) were calculated with Microsoft Excel (version 5.0; Redmond, Washington). All other analyses were performed with the BMDP statistical package (Berkeley, California)¹⁰. Continuous variables were analyzed with analysis of covariance, with adjustment for the preoperative status. Because the data were negatively skewed and were not amenable to normalizing transformations, the results of the analysis of covariance were confirmed with Kruskal-Wallis tests. Categorical variables were analyzed with logistic regression or Pearson chi-square tests. Data for the thirty-two patients who had had a bilateral procedure were analyzed both parametrically, with repeated-measures analysis of variance, and non-parametrically, with the Wilcoxon signed-rank test and the sign test. Categorical data, such as the prevalence of anterior pain in the knee, were compared with use of the chi-square test or the Fisher exact test, with the level of significance set at alpha = 0.05.

	Results

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Demographic Data
The study group consisted of 118 knees in eighty-six patients. Fifty-eight knees had resurfacing of the patella and sixty did not. The demographic data for the two groups of patients were similar. Of the twenty-six patients who had a unilateral total knee arthroplasty with resurfacing of the patella, twenty-two were men and four were women; of the twenty-eight who had a unilateral procedure without resurfacing, twenty-six were men and two were women; and of the thirty-two who had a bilateral procedure, twenty were men and twelve were women. The high percentage of male patients is attributable to the inclusion of patients seen at Veterans Administration Medical Centers, who are predominantly male. In those patients, thirty-eight knees had resurfacing of the patella and thirty-one did not. The mean age of the patients who had resurfacing was 65.3 years (range, twenty-seven to eighty-two years) compared with 67.1 years (range, thirty to eighty-seven years) for those who did not; this difference was not significant (p = 0.57). The mean duration of follow-up was thirty months (range, twenty-four to forty-four months); only one surviving patient was lost to follow-up.

Operative Data
The mean duration of the operation was 128 minutes (range, 110 to 139 minutes) for the knees that had resurfacing of the patella compared with 115 minutes (range, 104 to 131 minutes) for those that did not; this difference was significant (p = 0.04, Student t test). The mean estimated loss of blood was 226 milliliters (range, 190 to 300 milliliters) for the procedures that included resurfacing compared with 200 milliliters (range, 180 to 250 milliliters) for those that did not; with the numbers available, this difference was not significant (p = 0.33, Student t test).

Lateral retinacular release was performed in eighteen (31 per cent) of the fifty-eight knees that had resurfacing and in eleven (18 per cent) of the sixty that did not; this difference represented a trend, but, with the numbers available, it was not significant (p = 0.11; chi-square test).

Patellar thickness was restored accurately in the knees that had resurfacing; the mean thickness was 24.4 millimeters (range, twenty-two to twenty-eight millimeters) preoperatively compared with 23.4 millimeters (range, twenty-one to twenty-six millimeters) postoperatively.

The patellae were examined intraoperatively to determine the degree of chondromalacia. Seven patellae that had grade-IV chondromalacia²⁸ were left non-resurfaced. An analysis of the results according to the grade of chondromalacia (Table I) revealed that the highest over-all mean score was for the knees that had not had resurfacing and had grade-I or grade-IV chondromalacia; however, the over-all score (p = 0.32) as well as the subscores for pain (p = 0.26) and function (p = 0.27) were not found to be significantly different than those for knees with the other grades.

Complications
There were no acute infections within twenty-four months. One patient had a late hematogenous infection, which necessitated a revision at thirty-three months. Thus, the over-all rate of infection was 0.8 per cent (one of 118 knees).

Six knees that had not had resurfacing subsequently were resurfaced, all because of anterior pain, after twelve months (range, fifteen to thirty-nine months). The abnormality at the time of resurfacing was similar in all six knees and consisted of tightness of the lateral retinacular structures and progression of the chondromalacia. The Knee Society clinical score before the revision was deemed the final follow-up score and was incorporated into the data and the analysis. There were no complications associated with these six revisions, and all resulted in a decrease in pain. Before resurfacing, all six patients had rated the pain as at least 8 of a possible 10 points. After resurfacing, five of the six continued to have some pain, but all rated the severity as less than 5 points (Table II). These results must be considered preliminary, however, as the mean duration of follow-up for these patients was only one year (range, six to eighteen months).

Clinical Results

The Knee Society Clinical Score
According to the scale of The Knee Society, the mean preoperative clinical score for the study cohort as a whole was 89.7 points (range, 33 to 132 points). The mean score for pain was 46.6 points (range, 0 to 78 points), and the mean score for function was 41.4 points (range, 0 to 60 points) (Table III). At the latest follow-up evaluation, the over-all score had improved to a mean of 172.7 points (range, 98 to 200 points); that for pain, to 90.4 points (range, 53 to 100 points); and that for function, to 82.3 points (range, -20 to 100 points). The mean preoperative clinical score for the knees that had had resurfacing was 88.0 points (range, 33 to 118 points) compared with 174.5 points (range, 98 to 199 points) postoperatively. The mean preoperative clinical score for the knees that had not had resurfacing was 91.4 points (range, 48 to 132 points) compared with 170.9 points (range, 108 to 200 points) postoperatively.

The preoperative and postoperative clinical scores were not highly correlated (Pearson product-moment correlation coefficient, 0.20), reflecting independence of the responses before and after the operation. In other words, the patients did not necessarily respond similarly preoperatively and postoperatively, and severely affected patients did not necessarily report worse results postoperatively.

Patient Satisfaction and Questions Related to Patellofemoral Symptoms and Function
In both groups, the scores related to function of the patellofemoral joint improved, from a mean of 2.5 to 3.4 points (on a scale ranging from 0 ["impossible"] to 10 points ["no problem"]) preoperatively to a mean of 7.7 to 8.9 points postoperatively (Table IV).

With the numbers available, we could detect no significant difference between the two groups of patients with regard to the ability to exit from an automobile (p = 0.64), to rise from a chair (p = 0.79), or to climb stairs (p = 0.81) postoperatively. The ratings of the degree of difficulty for these activities were virtually identical for the two groups (Table IV).

Anterior Pain in the Knee
Anterior pain in the knee was used as the criterion for pain related to the patellofemoral joint. Forty-nine (42 per cent) of the 118 knees had had anterior pain preoperatively, and forty-five (92 per cent) had relief of this symptom after the operation. As expected, the knees that had had such pain had also had lower pain scores preoperatively (mean, 38.4 points; range, -42 to 70 points) compared with those that had not had anterior pain (mean, 52.2 points; range, 25 to 78 points; p < 0.001); however, this difference was not reflected in the function scores (a mean of 40.7 points and a range of -20 to 60 points compared with a mean of 41.9 points and a range of 5 to 90 points; p = 0.71). With the numbers available, the postoperative clinical scores (a mean of 173 points and a range of 98 to 199 points compared with a mean of 174 points and a range of 98 to 200 points) could not be shown to be significantly different between the patients who had had preoperative anterior pain and those who had not had such pain (p = 0.81).

Only one (4 per cent) of the twenty-six knees that had had anterior pain before resurfacing had pain after the operation compared with three (9 per cent) of the thirty-four knees that had not had anterior pain before resurfacing. Thus, a total of four (7 per cent) of the fifty-eight knees that had had resurfacing had postoperative anterior pain. Three (13 per cent) of the twenty-three knees that had had anterior pain before an arthroplasty without resurfacing had pain after the operation compared with five (14 per cent) of the thirty-seven that had not had such pain before an arthroplasty without resurfacing. Thus, a total of eight (13 per cent) of the sixty knees that had not had resurfacing had anterior pain postoperatively.

With the numbers available, we could detect no significant difference with regard to the prevalence of postoperative anterior pain when the knees that had had resurfacing and those that had not were compared (p = 0.24, chi-square test). Although the sample was small, analysis of covariance of the twelve patients who had had anterior pain showed no differences attributable to the method of treatment (p = 0.38). This result was confirmed with the Kruskal-Wallis test (p = 0.22). Therefore, it cannot be stated that resurfacing or non-resurfacing is related to postoperative anterior pain in the knee. Such pain was not significantly related either to preoperative anterior pain or to the method of treatment, according to logistic regression analysis (p = 0.24).

Six of the eight knees that had anterior pain after an arthroplasty without resurfacing subsequently had patellar resurfacing because of the pain. This represents a rate of revision of 10 per cent for the sixty knees that had not had resurfacing in this study. None of the fifty-eight knees that had had resurfacing had a revision because of pain, but four (7 per cent) had anterior pain that was rated 4 points or more on a scale of 1 to 10 points (Table II). There were no patellar fractures, dislocations, or loose patellar components in the patients who had a resurfaced patella.

Obesity
The mean weight of the eighty-six patients exceeded the maximum allowable weight by a mean of 15.3 kilograms (18 per cent; range, -17 to 113 per cent). With the numbers available, there was no difference, with regard to the mean percentage of excess weight, between the patients who had anterior pain in the knee postoperatively and those who did not (18 per cent for both groups; p = 0.45).

We could detect no significant differences, in the prevalences of anterior pain in the knee, that were attributable to whether or not the patella had been resurfaced or to obesity, and there was no interaction between these factors (p = 0.30). These results were confirmed with stratified Kruskal-Wallis tests (p = 0.25).

To compare the findings of the present study with historical data, the patients were grouped according to the categories established by Stern and Insall³⁴ (80 to 120 per cent, 121 to 149 per cent, 150 to 174 per cent, or 175 per cent or more of ideal weight). The patients in the first weight-group were compared with all other patients—that is, those who were not obese were compared with those who were—because of the small numbers in the two highest weight-groups. With the numbers available, no significant difference was detected between the mean Knee Society clinical scores of the obese and non-obese patients (p = 0.46; Table V). When the mean score for the obese patients who had had resurfacing was compared with that for the obese patients who had not had resurfacing, again, with the numbers available, no significant difference was seen (p = 0.32). To test the hypothesis that overweight patients would have a worse result with retention of the patella, the mean knee score for the obese patients who had not had resurfacing was compared with the score for the non-obese patients who had not had resurfacing; again, no difference was seen (p = 0.45).

Chondromalacia Patellae
For the knees that had not had resurfacing, with the numbers available we could detect no relationship between the grade of chondromalacia and postoperative pain (p = 0.32), postoperative function (p = 0.26), or the over-all postoperative clinical score (p = 0.27), as demonstrated with analysis of covariance with the preoperative score as the covariant and the grade of chondromalacia as the grouping variable. The grade of chondromalacia was not a significant predictor of postoperative anterior pain in the knee, as shown with logistic regression analysis (p = 0.35). None of the patellae that had not been resurfaced and had grade-IV chondromalacia needed a revision.

Radiographic Findings
The knees that had resurfacing of the patella had significantly less patellar tilt postoperatively than those that did not have resurfacing (p < 0.001). However, the knees that had anterior pain did not have a considerably higher prevalence or severity of patellar tilt preoperatively or postoperatively.

Twenty-six knees were in 0 to 5 degrees of valgus, eighty-seven were in more than 5 degrees of valgus (mean, 6.5 degrees; range, 5 to 8 degrees), and five were in varus alignment (mean, 3.4 degrees; range, 1 to 5 degrees). When the clinical scores for the knees that had had resurfacing and for those that had not were analyzed according to over-all anteroposterior alignment, no substantial differences were found. Neither the mean clinical score for the knees that were in more than 5 degrees of valgus nor that for the five that were in varus alignment could be shown to be significantly different from the clinical score for the study cohort as a whole, with the numbers available (p = 0.48).

The mean Insall-Salvati ratios for the knees that had had resurfacing and those that had not were 1.1 (range, 0.81 to 1.4) and 1.2 (range, 0.85 to 1.5), respectively. This difference was not found to be significant, and there was no association between the Insall-Salvati ratio and the clinical score (p = 0.69).

We could detect no difference between the knees that did and did not have anterior pain postoperatively with regard to radiographic measurements of changes in the joint line, the anterior or posterior offset of the tibial component relative to the center of the tibia (the distance from the neutral axis), the distance between the inferior pole of the patella and the tibial prosthesis, or centralization of the tibial component on the cut surface of the tibia. The tibial component that was used came in eight sizes and was placed in a uniform manner, as had been agreed on prospectively before the start of the study. Thus, there was an extremely small variation between groups with regard to the placement of the tibial component. On the average, there was less than a millimeter of difference, in the anteroposterior and lateral planes, between the center of the tibial component and the neutral axis of the tibia.

Patients Who Had a Bilateral Procedure
Of the thirty-two patients who had had a bilateral procedure, thirty (94 per cent) were satisfied with the knee that had not had resurfacing and thirty-one (97 per cent) were satisfied with the knee that had had resurfacing; with the numbers available, this difference could not be shown to be significant (p = 0.55, chi-square test). When these thirty-two patients were asked to compare the knees, eleven (34 per cent) said that they preferred the resurfaced side, twelve (38 per cent) said that they preferred the non-resurfaced side, and nine (28 per cent) had no preference. For the patients who expressed a preference, the mean difference in the score for satisfaction was 2.6 points on a scale ranging from 1 point ("a little") to 10 points ("a lot").

	Discussion

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The present study is one of a small number of randomized, prospective trials of which we are aware that compared the results of resurfacing of the patella with those of retention of the patella³. With the numbers available for study, no significant differences were seen, between the knees that had had resurfacing and those that had not, with regard to The Knee Society score for pain (p = 0.56) or function (p = 0.77) or the assessment of patellofemoral function (p > 0.64). The patients who had had a bilateral procedure with resurfacing of one side but not the other did not express a clear preference for either side.

Obesity, the grade of patellar chondromalacia, and preoperative anterior pain in the knee did not predict either a lower knee score or postoperative anterior pain. These three factors commonly have been cited as key in the decision whether to resurface the patella when the so-called selective resurfacing approach is used.

Picetti et al. reported the results of 100 total knee arthroplasties performed without resurfacing of the patella in a series that included all classes of patellar disease²⁹. On the basis of increased postoperative anterior pain in the knees of patients who had rheumatoid arthritis and in those of larger patients, Picetti et al. recommended resurfacing of the patella for all patients who had rheumatoid arthritis, a height of more than 160 centimeters (five feet and three inches), a weight of more than sixty kilograms (132 pounds), anterior pain in the knee preoperatively, and grade-IV chondromalacia. It should be noted that these guidelines would leave very few patients (only those who are very small and have osteoarthrosis, relatively well preserved patellar articular cartilage, and no anterior pain in the knee) with a non-resurfaced patella. Only one patient in our study population fit this profile in its entirety. Stern and Insall, in a study of total knee arthroplasty in obese patients, used parameters of weight that were more relevant to our patient population³⁴. They reported a twofold rate of patellofemoral symptoms in patients who were at least 150 per cent of their ideal weight. However, this cannot be considered support for retaining the patella in obese patients, as this alternative was not studied.

Chondromalacia of the patella, as assessed at the time of total knee arthroplasty, has been used as a reason to resurface the patella. In the largest retrospective series of which we are aware, Boyd et al. compared the results, at a mean of 6.5 years postoperatively, for 396 knees that had had resurfacing of the patella and 495 knees that had not had resurfacing⁴. Their patients had had selective resurfacing on the basis of the appearance of the patella at the time of the operation. Those authors recommended resurfacing of the patella both for patients who have degenerative osteoarthrosis and for those who have inflammatory arthritis, despite the fact that, in their study, the rate of patellar complications in osteoarthrotic knees was 4 per cent after resurfacing compared with 6 per cent after arthroplasty without resurfacing. The same 6 per cent prevalence of patellofemoral pain was found by Sneppen et al., in a prospective study of 100 knees that had had an arthroplasty with use of an Insall-Burstein total condylar prosthesis³². The present study confirms that only a small percentage of patients will have anterior pain after either resurfacing or retention of the patella. The prevalence of anterior pain in our study was consistent with the rates reported previously^3,7,8.

Importantly, there are fewer treatment options available for patients who have already had resurfacing of the patella. Berry and Rand found that isolated revision of the patellar component is fraught with complications². Fourteen (39 per cent) of thirty-six such revisions in their study were associated with major complications that compromised the result.

In 1986, Soudry et al. reported on twenty-seven knees in twenty-four patients that had been treated with total knee arthroplasty without resurfacing of the patella³³. Twenty-two knees (81 per cent) had patellofemoral chondromalacia that was classified as none or moderate. Although twenty-four knees (89 per cent) had a good or excellent result according to the knee score of The Hospital for Special Surgery, those authors concluded that the results were unsatisfactory because one-third of the patients could not lead with the involved knee in stair-climbing. Soudry et al. recommended that resurfacing of the patella be omitted only in patients who have relatively normal patellar cartilage and are overweight and thus at higher risk for a patellar fracture³³. We did not find any relationship between the ability to climb stairs, to rise from a chair, or to exit from an automobile and the grade of chondromalacia of the patella. In fact, the knees that had grade-IV chondromalacia and had not had resurfacing had a mean over-all score of 187.4 points, and none subsequently needed resurfacing.

Preoperative anterior pain in the knee seems to be a logical reason to resurface the patella, particularly as resurfacing relieved such pain in forty-five (92 per cent) of forty-nine knees that had had that symptom in the present study. Although previously published information has suggested that anterior pain in the knee is a reason for resurfacing^12,29, we found that the presence of such pain preoperatively did not predict its occurrence postoperatively. Moreover, the postoperative pain was usually of new onset. The likelihood that a patient will have new-onset postoperative anterior pain in the knee does not seem to be affected by whether or not the patella was resurfaced.

The function of the patellofemoral joint frequently has been cited as an important parameter in the evaluation of the outcome of total knee arthroplasty. Stair-climbing ability is the most common specific activity used to assess such function. Cameron retrospectively studied patients who had had a total knee arthroplasty; sixty-eight had had resurfacing of the patella and forty-three had had a patelloplasty only⁷. The patients who had not had resurfacing were considered to have had inferior results because fewer of them could climb stairs normally. Patellofemoral pain was experienced by 8 per cent of the patients who had had resurfacing compared with 18 per cent of those who had not, a difference that was not significant. As in the study by Soudry et al.³³, this apparent deficit in stair-climbing ability was cited as a reason to recommend routine resurfacing of the patella. Differences in stair-climbing ability and in other activities stressing the patellofemoral articulation were not seen by Braakman et al.⁵, who reported the results for 219 patients who had had a total knee arthroplasty performed with use of a Miller-Galante-I implant (Zimmer), the predecessor of the implant used in the present study. At a mean of 3.5 years, 151 patients who had had resurfacing of the patella were compared with sixty-eight who had had a patelloplasty only. No differences were observed with regard to range of motion, pain, stability, walking distance, stair-climbing, patellofemoral complications, or revision.

As far as we know, the thirty-two patients who had a bilateral total knee arthroplasty with resurfacing of one patella and retention of the other in the present study represent the largest such group reported on to date. The size of this group offers an opportunity to evaluate the two techniques in a controlled fashion. We found no clear preference for one knee by these patients, who were carefully blinded with regard to which knee had had resurfacing of the patella. Levitsky et al. reported the results for seventy-nine knees (sixty-six patients) that had not had resurfacing of the patella, a decision that had been made intraoperatively²². Of thirteen patients who had also had an arthroplasty with resurfacing in the contralateral knee, only six preferred the resurfaced side. This finding is similar to the observation in the present study, although presumably only the less diseased patella was retained in the patients evaluated by Levitsky et al. Fifteen (19 per cent) of the seventy-nine knees that did not have resurfacing in that study were mildly painful anteriorly after a mean duration of follow-up of 7.5 years. Those authors concluded that selective non-resurfacing may be appropriate for younger, active patients, although this remains speculative as their study included no subgroup of such patients.

Enis et al. reported on a series of twenty-five patients who had had bilateral total knee arthroplasty with resurfacing of the right patella but not the left¹¹. Lateral retinacular release was performed more frequently when resurfacing of the patella was done, as was the case in the present study. When asked which knee "felt better," ten patients chose the resurfaced side but twelve thought that there was no difference between sides. Shoji et al. also reported no difference between sides in patients who had had a bilateral total knee arthroplasty with resurfacing on one side but not the other³¹. This finding is similar to that in the present study. Keblish et al. reported on thirty patients who had had a bilateral total knee arthroplasty with use of a Low-Contact Stress implant (LCS; DePuy, Warsaw, Indiana), with resurfacing of only one patella²¹. Those authors also found no differences between the two sides and concluded that retention of the patellar articular surface is an acceptable option.

There are few prospective, randomized studies available for comparison with the present study. Bourne et al. recently reported the results of such a study in which 100 consecutive patients who had a total knee replacement with insertion of an Anatomic Modular Knee implant (AMK; DePuy) were randomized to treatment with either resurfacing or retention of the patella³. Two (4 per cent) of the fifty patients who had not had resurfacing needed it subsequently because of anterior pain. The patients who had not had resurfacing had significantly less pain (p < 0.03) at the two-year follow-up evaluation. Those authors suggested that, while longer follow-up is needed, surgeons should remain open-minded with regard to whether or not the patella should be resurfaced.

The current study demonstrates that prospective, randomized trials with high rates of enrollment and follow-up are feasible for patients who have a total joint arthroplasty. The main strength of this type of study lies in its prospective design. Data collected prospectively are more accurate than those obtained in a retrospective study that relies on recalled information. For example, had the current study been retrospective, we may not have learned that anterior pain in the knee was often of postoperative onset, both in patients who had had resurfacing and in those who had not. Consequently, we may not have discovered that preoperative anterior pain is an unreliable predictor of the postoperative result. Also, patient histories were recorded and examinations were conducted by an independent observer, not by the surgeon. A recent study by McGrory et al. confirmed that, after a total knee arthroplasty, knee scores based on interviews with physicians were significantly higher (p < 0.05) than those based on responses that patients had given independently of the physician (p < 0.0001)²³. This may account for the scores in the present study being somewhat lower than those reported in some retrospective studies of total knee arthroplasty. Furthermore, Brinker et al. reported a mean Knee Society clinical score of 180.2 points for 200 knees among asymptomatic older individuals (mean age, 59.6 years)⁶. If the mean postoperative knee score of 173 points is normalized with use of this rating for asymptomatic controls, a score of 96 per cent (173 of 180 points) is obtained, verifying the excellent clinical results attained by the study group as a whole.

With a mean duration of follow-up of thirty months, the results of the present study must be considered preliminary. It is possible that additional patellofemoral complications will develop in both study groups with the passage of time. For example, Healy et al., in a study of the results of 211 total knee arthroplasties that included fourteen that were performed without resurfacing of the patella, found that anterior pain developed in only two knees that had not had resurfacing but at a median of sixty-three months¹⁶. Intermediate-term results also were reported by Abraham et al., in a retrospective evaluation of 100 knees in eighty-four patients who were followed for a minimum of five years¹. This study of well matched groups revealed no significant differences, with the numbers available, with regard to pain with walking, function, or range of motion between the knees that had had resurfacing of the patella and those that had not. It is not clear why patients have anterior pain in the knee after total knee arthroplasty. Such pain appears to occur at approximately equal rates in patients who have had resurfacing and in those who have not. A number of studies have shown that virtually all currently available designs of total knee implants alter patellar tracking to some degree^17,18,24,25, therefore altering the stresses on the extensor mechanism. It also may be that a few patients have subtle anatomical variations and that the standard orientation of the components cannot accommodate for these differences well.

Recently developed total knee designs represent an attempt to improve the patellofemoral articulation with a deeper, more anatomical groove that should yield more normal kinematics. A higher degree of support and conformity may result in a corresponding decrease in patellofemoral contact stresses. The prevalence of postoperative patellofemoral symptoms theoretically should decrease; however, this has not been proved clinically.

Retention of the patella appears to be a reasonable option, but patients must be willing to accept the considerable risk that a reoperation might be necessary in order to resurface the patella. They also should know that such a reoperation is likely to decrease symptoms substantially. Conversely, patients who have resurfacing must contend with the risk of postoperative anterior pain in the knee for which there may not be an adequate solution. Therefore, the decision regarding whether to resurface the patella during a total knee arthroplasty remains problematic. Importantly, the present study demonstrated no evidence that the weight of the patient, the grade of chondromalacia, or the presence of anterior pain in the knee should be considered when deciding whether to resurface the patella.

NOTE: The authors gratefully acknowledge the valuable contribution of Deborah B. Dahan, R.N., who performed all clinical evaluations related to this study.

	Footnotes

 
*Although none of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article, benefits have been or will be received but are directed solely to a research fund, foundation, educational institution, or other non-profit organization with which one or more of the authors are associated. Funds were received in total or partial support of the research or clinical study presented in this article. The funding source was a grant from the Zimmer Corporation, Warsaw, Indiana.

Department of Orthopaedic Surgery, SL-32, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, Louisiana 70112. E-mail address: rbarrac@tmcpop.tmc.tulane.edu (Dr. Barrack).

Orthopaedic Surgery Section, Surgical Service, Veterans Administration Medical Center, 3351 Masonic Drive, Alexandria, Louisiana 71301.

Orthopaedic Surgery Section, Surgical Service, Veterans Administration Medical Center, 1601 Perdido Street, New Orleans, Louisiana 70148.

¶Department of Biostatistics and Epidemiology, Tulane University School of Public Health and Tropical Medicine, 1501 Canal Street, New Orleans, Louisiana 70112.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

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