The etiology of anterior knee pain after total knee arthroplasty often is unclear. We prospectively followed 80 patients (139 knees) with rheumatoid arthritis who had total knee arthroplasties without patellar resurfacing from January 1998 to June 2000. We used binary logistic regression to evaluate the predictive value of preoperative anterior knee pain and the state of patellar articular cartilage on postoperative anterior knee pain. We compared the preoperative and postoperative knee and function scores for patients with and without anterior knee pain. The mean followup was 5.8 years (range, 5-7 years). Ninety one percent of the knees (127 of 139 knees) had The Knee Society scores greater than 80. Anterior knee pain developed in 12 of 139 knees (8.5%). Patients who had anterior knee pain had lower knee and function scores compared with patients without anterior knee pain. Two patients had secondary patellar resurfacing. Preoperative anterior knee pain and the state of patellar articular cartilage did not predict postoperative anterior knee pain. Kaplan-Meier survivorship analysis with anterior knee pain as the end point revealed an 88.3% survivorship at 6.5 years postoperatively. Total knee arthroplasty without patellar resurfacing produced satisfactory results in patients with rheumatoid arthritis.
Level of Evidence: Level IV Therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence. Resurfacing the patella as a part of a total knee arthroplasty (TKA) is controversial, and the results of the available prospective randomized trials are inconclusive.3,6,8,15,22,23,32 Some studies show that patients with unresurfaced patellae6,8,15 perform as well as patients with resurfaced patellae,23 although others show that patients with a native patella have a 10% reoperation rate and a greater incidence of anterior knee pain.3,4,7,13,22,29,32,36,42
Patellar replacement traditionally has been recommended for patients with inflammatory arthritis41 because of the fear that antigens in the retained articular cartilage may provide stimulus for persistent synovial inflammation and might perpetuate the immune- mediated inflammatory disease.39 Routine patellar resurfacing also is performed for patients with rheumatoid arthritis (RA) to avoid postoperative patellofemoral pain.34 Many patients with RA, especially those with severely degenerated knees,5 are sedentary and are receiving preoperative steroids, which contribute to relative osteopenia.10 The patella often is small, osteopenic, and at risk for fracture if resurfaced.23 The etiology of anterior knee pain after a TKA is unclear, and surgeons can expect approximately 10% of patients to have anterior knee pain after TKA.2,17,18,37 One study showed an association between preoperative patellofem- oral symptoms, Class IV patellar articular cartilage, and postoperative patellar pain.33 However, other studies showed that preoperative anterior knee pain does not predict postoperative anterior knee pain, and that there is no correlation between the degree of patellar articular cartilage seen intraoperatively and the degree of pain or quality of results postoperatively.3,40
We asked whether preoperative anterior knee pain and the state of patellar articular cartilage predicted postoperative anterior knee pain in patients with RA who had TKAs without patellar resurfacing. We also asked whether the knee scores in patients with postoperative anterior knee pain differed from those in patients without anterior knee pain.
MATERIALS AND METHODS
We prospectively evaluated 145 TKAs without patellar resurfacing in 85 consecutive patients with RA refractory to nonoperative treatment from January 1998 to June 2000. During this period, it was the practice of the surgeon (SB) not to resurface the patella regardless of the diagnosis and state of the articular cartilage. We excluded patients with a history of surgery on the extensor mechanism and three patients (four knees) who required use of constrained prostheses. The two patients lost to followup also were excluded. This left 80 patients (139 knees) for evaluation.
Forty-nine patients had bilateral TKAs. There were 56 women and 22 men with an average age of 55.6 ± 12 years (range, 31-79 years). The mean body mass index (BMI) was 24.1 (range, 20-29), and the average duration of followup was 5.8 years (range, 5-7 years). Patients with unilateral arthroplas- ties were classified as Group A, patients with bilateral arthroplasties with the other joints requiring arthroplasty were classified as Group B, and patients with multiple arthritis, medical comorbidities, and diminished physiologic reserves were classified as Group C. At the time of the index TKA, 20 of 80 patients (25%) were in Group A, 49 of 80 patients (61%) were in Group B, and 11 of 80 patients (14%) were in Group C according to Knee Society classification.21 Written and informed consents were obtained from all patients, and the study was approved by the institutional review board.
Patients who had bilateral TKAs were operated on sequentially under one anesthetic. We used regional anesthesia (spinal and/or epidural) in 63 patients and general anesthesia in 17 patients. Patients received antibiotic prophylaxis with intravenous cefazolin (2 g every 1.5 hours before inflation of the tourniquet followed by 1 g every 8 hours for 3 days) and antithrombotic prophylaxis with subcutaneous enoxaparin (40 mg from the night before surgery and continued until 10 days postoperatively).
We performed the surgeries with tourniquet control using a midline skin incision and a medial parapatellar approach. The posterior cruciate ligament was sacrificed. We used extramedullary alignment jigs for the tibia and intramedullary alignment jigs for the femur. The patella was not replaced regardless of the state of the articular cartilage, which was recorded intraoperatively. The patellar cartilage was graded, using the Outerbridge classification,31 by the senior author (SB) as Class I if the articular surface appeared normal (Fig 1), Class II if the patellar cartilage was abnormal or fibrillated (Fig 2), Class III if there was chondromalacia and as much as 25% bone exposure (Fig 3), and Class IV if greater than 25% of the bone was exposed or eburnated (Fig 4). The patellar cartilage was graded as Class II in 47 knees, Class III in 61 knees, and Class IV in 31 knees. We measured preoperative patellar thickness and performed a patelloplasty that included soft tissue release from the lateral patella, division of the patellofemoral ligament, patellar rim cautery to provide partial denervation, and osteophyte removal. In addition, we removed 2 to 4 mm of the articular surface and resurfaced the medial and lateral facets.
Soft tissue procedures to realign the knee included lateral retinacular release in five patients (six knees) and lateral gutter débridement in five patients (seven knees). Sixteen patients (28 knees) required extensive posterior capsulotomies, and two patients (four knees) required a 5-mm additional distal femoral cut to correct the severe preoperative flexion deformity (40°). We performed medial capsular sleeve dissection in 10 patients (17 knees), including three patients (five knees) requiring extensive dissection and stripping of the superficial medial collateral ligament to correct the preoperative varus deformity (35°). We performed limited medial dissection and release of the iliotibial band from Gerdy's tubercle in 14 patients (19 knees) with valgus deformities. We made a tibial cut at a right angle to the long axis of the tibia. We used posterior-stabilized NexGen® (Zimmer, Warsaw, Poland) prostheses in all patients. The femoral component had a lateral flange and a deep trochlear groove to accommodate the patella. The center of the tibial prosthesis was aligned with the medial ⅓ of the tibial tuberosity to ensure rotational alignment. The distal femur was cut in 5° valgus. The external rotation of the femoral component was determined using a jig referencing the posterior condyles, which had an inbuilt external rotation of 3°. The external rotation was confirmed using the cut tibial surface and the transepicondylar axis as the reference. No thumb technique26 was used to assess the adequacy of patellar tracking and the need for lateral retinacular release. The tibial and femoral components were cemented, and pulsatile lavage was used before cementing the implants.
The postoperative regimen included knee immobilization for 2 days, gravity-assisted regaining of flexion from the third postoperative day, and walking with support from the fourth postoperative day. All patients used support while walking for 3 months postoperatively.
Followup included examinations at 1, 3, and 6 months, and then at yearly intervals. Patients were evaluated clinically by two orthopaedic surgeons (EKK, RM) not involved in the arthroplas- ties. Preoperative and postoperative clinical evaluations were performed according to The Knee Society recommendations.21
Preoperatively, patients were questioned about the location of knee pain to identify those with anterior knee pain. These patients were evaluated postoperatively to determine the persistence of anterior knee pain. We documented the knee and function scores of patients with and without anterior knee pain, and in patients with different grades of chondromalacia preoperatively and postoperatively. The postoperative knee and function scores in patients with preoperative anterior knee pain were compared with scores of patients without preoperative anterior knee pain.
The senior author (SB) evaluated the preoperative and followup postoperative radiographs, including anteroposterior (AP) views with the patient standing, supine lateral views, and skyline patellar views. The overall limb alignment, prosthesis position, and location of radiolucent lines at the bone-cement interface were analyzed according to The Knee Society guidelines.14 We used skyline patellar-view radiographs to determine patellar tilt, subluxation, or dislocation. Patellar alignment was classified as Type I (normal) (Fig 5), Type II (shifted), Type III (tilted) (Fig 6), or Type IV (shifted and tilted) (Fig 7).30
We used descriptive statistics to summarize the data and binary logistic regression to evaluate the predictive value of pre- operative anterior knee pain and the state of patellar articular cartilage on postoperative anterior knee pain. We compared pre- operative and postoperative knee and function scores in patients with and without anterior knee pain and in patients with different grades of patellar chondromalacia using the independent samples t test and one-way analysis of variance (ANOVA), respectively. A p value less than 0.05 was considered significant. We performed a Kaplan-Meier survivorship analysis with the occur- rence of anterior knee pain as the end point using a worst-case scenario analysis. Both patients lost to followup were included in the analysis. Analyses were performed using SPSS 10 statistical software (SPSS, Inc, Chicago, IL).
The preoperative state of patellar articular cartilage and presence of preoperative anterior knee pain did not predict postoperative anterior knee pain. Postoperative anterior knee pain occurred in 12 of 139 knees (8.5%). None of the patients with Type IV articular cartilage preoperatively had anterior knee pain develop postoperatively. There were no differences in the postoperative Knee Society pain and function scores among patients with different grades of chondromalacia. Preoperatively, 47 of the 139 knees had anterior knee pain. The patellar cartilage was Class II in 17 knees, Class III in 19 knees, and Class IV in 11 knees. Only two patients continued to have anterior knee pain after arthroplasty. Both patients had Type II patellar articular cartilage preoperatively. Patients with preoperative anterior knee pain did not have increased Knee Society pain and function scores postoperatively. Ten patients (10 knees) had new onset of anterior knee pain. Two of these patients had pain severe enough to warrant repeat surgery. Revision patellar resurfacing was performed in two patients; one after 28 months and one after 34 months. Both patients had a lateral release with patellar resurfacing to realign the prosthetic patella. Intraoperatively, there was reformation of the synovial lining around the patella and extensor tendon, joint effusion, and partial remodeling of the patella. There was no bony erosion or component mal- rotation. Preoperatively, both knees had Class III patellar articular cartilage. Both patients had only partial improvement after the second surgery and continued to have moderate anterior knee pain on stair climbing.
Patients with postoperative anterior knee pain had lower (p < 0.001) postoperative knee and function scores than patients without anterior knee pain (Table 1). Overall, the postoperative knee and function scores and arc of flexion improved (Table 2). Ninety-one percent (127 of 139 knees) obtained Knee Society scores greater than 80. Using anterior knee pain as the end point, a worst-case scenario Kaplan-Meier survivorship analysis showed 88.3% (95% confidence interval, 85.25-91.45) survival at 6.5 years followup.
We evaluated the clinical and radiographic results of TKAs without resurfacing the patella in patients with RA. One surgeon (SB) operated on all patients using similar posterior-stabilized prostheses with anatomic femoral components that minimized surgeon- and implant-related bias.
We acknowledge the limitations of our study, including lack of a control group. Also, the operating surgeon (SB) performed the intraoperative grading of the patellar cartilage and the radiographic evaluation, therefore, the possibility of bias cannot be excluded. Our results are representative only of Asian patients with RA, low BMI, with severe deformities, smaller patellae, and limited demands. It may not be applicable to the Caucasian population and more active patients with osteoarthritis. We had no validated way to assess anterior knee pain, and therefore our approach is subjective and likely prone to interobserver variability. We had no way of ensuring whether the anterior knee pain arose from the patellofemoral joint or from other parts of the knee..
Picetti et al reported a strong association between pre- operative patellar symptoms, a Class IV patellar surface, and postoperative pain.33 Other studies have shown these factors may not be predictive of postoperative anterior knee pain.3,15 Only two of our patients with preoperative anterior knee pain continued to have the symptoms postoperatively. The rest of the patients had new onset of anterior knee pain. The state of the patellar articular cartilage was not predictive of the preoperative and postoperative occurrence of anterior knee pain. All nine knees with preoperative Class IV articular cartilage were pain- free at the latest followup. Our results suggest preoperative patellar symptoms and Class IV articular cartilage are not predictive of postoperative knee pain, and may not be reasons to resurface the patella.
Authors of numerous studies have recommended routine patellar resurfacing for patients with RA.6,27,33,34,39 Patellar replacement traditionally has been recommended for all patients with inflammatory arthritis41 because of the fear that antigens in the retained articular cartilage may provide a stimulus for persistent synovial inflammation, which might perpetuate the immune-mediated inflammatory disease.39 However, many of the patients with RA are sedentary and are receiving preoperative steroids, which contributes to relative osteopenia.10 In patients with RA, the patella is often small, osteopenic, and at risk of fracture if resurfaced.23 The mean patellar thickness in patients in our series was only 23 mm. Patients with RA generally are more satisfied with TKAs than patients with osteoarthritis regardless of patella resurfacing.35 Fern et al reported patellar resurfacing may be avoided in 80% of the knees with a patellar height of 15 mm or greater in patients with RA having TKAs.16 Few studies have shown no differences in functional results between patients with or without patellar resurfacing and that the unresurfaced patellae perform as well as resurfaced patellae.1,6,9,15,23 Patellar complications occur in 4% to 45% of patients after patellar resurfacing,7,11-13,33 including patellar fracture, anterior knee pain, disruption of extensor mechanism, osteonecrosis, aseptic loosening, instability and dislocation, overstuffing of the patellofemoral joint, patellar polyethylene wear, and patellar clunk syndrome. We did not perform patellar resur- facing because we thought the small patellae in our patient population combined with relative osteopenia would increase the risk of patellar fracture.
To remove the antigenic stimulus from the articular cartilage, we shaved 2 to 4 mm of patellar surface including the articular cartilage.40 Reshaping the medial and lateral facets, meticulous attention to the surgical technique, and the use of an anatomic femoral component helped intraoperative patellar tracking and minimized the need for lateral retinacular release. Only 5% of the knees required lateral release. Three were performed in valgus knees as a part of the exposure. This is important because patellar rim cautery, performed as part of a patelloplasty when combined with a lateral retinacular release, may additionally devascularize the patella and predispose the knee to avascular necrosis.23 Patelloplasty with reshaping of the patellar facets improves the patellofemoral congruency and may help in better patellar remodeling.23 Shoji et al did not advise routine resurfacing of patellae without gross deformity in patients with RA.38
Ninety-one percent of the knees (127 of 139 patients) had Knee Society scores greater than 80. Similar results were reported in other studies.13,23,27,38 Brinker et al9 reported an average Knee Society clinical score of 180.2 points for 200 knees of asymptomatic older patients (average age, 59.6 years). The average clinical knee score of our patients (160.2 points) was lower. This may be attributable to the polyarticular involvement in some patients, which contributed to lower function scores.
There is no consensus concerning the terminology, etiology, and treatment of anterior knee pain.10 Anterior knee pain after a TKA may be caused by several factors, including internal malrotation of components,20 overstuffing the knee, component size mismatch, patellofemoral incongruity, and articulation of the patella at greater degrees of flexion.10 Patellofemoral pain was reported in 5% to 45% of patients, but these studies were retrospective, and implants that were poorly designed to deal with the patellofemoral joint were used.11,19,28 The incidence of anterior knee pain occurred in less than 14% of patients with unresurfaced patellae and in 8% of patients with resurfaced patellae.3,6,24,25 We found similar occurrences of anterior knee pain.
A potential disadvantage of not resurfacing the patella is the possibility for eventually requiring subsequent re- surfacing. Patellar resurfacing was required in two knees (2.6%). Intraoperative findings included recurrent synovitis involving the extensor tendon and partial remodeling of the patella. There was no erosion of the patella. Resurfacing only partially improved the patients' symptoms. Patients with anterior knee pain with an unresurfaced patella are at substantial risk of recurrent anterior knee pain despite resurfacing.3
We found satisfactory midterm results of TKAs without patellar resurfacing in patients with severely degenerated knees and RA. The incidence of anterior knee pain was approximately 8.5%, and the need for secondary resurfacing was low. Patelloplasty with reshaping of the articular facets is useful. Preoperative anterior knee pain and the state of the patellar articular cartilage are not predictive of postoperative knee pain. Patellar resurfacing usually is not needed in patients with RA. Longer followup is needed, and patients must be counseled regarding the possible need for secondary resurfacing when the patella is retained.
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