Abstract: The purpose of the present study was to determine the long-term results of a series of 150 consecutive primary posterior stabilized modular knee arthroplasties that had been performed in 118 patients with use of a circumferential tibial insert capture as described in a previous report, published in 1997. The patients were evaluated with use of a patient-administered questionnaire; Knee Society clinical, functional, and radiographic scoring systems; and Kaplan-Meier survivorship analysis. A good to excellent result was confirmed in seventy-six (90%) of the eighty-four patients (105 knees) with a mean duration of follow-up of twelve years (range, ten to thirteen years). At twelve years, the survival rate was 94.6% ± 4.0% with failure for any reason as the end point and 98.3% ± 2.4% with mechanical failure as the end point. Revision surgery was performed in five knees because of infection (two knees), dislocation (one knee), and substantial polyethylene wear with femoral osteolysis (two knees). We concluded that, while fixation failure is rare, polyethylene wear and osteolysis are emerging as important causes of failure.
Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.
1 Department of Orthopaedic Surgery, Ranawat Orthopaedics Center, Lenox Hill Hospital, 130 East 77th Street, 11th Floor Black Hall, New York, NY 10021
The posterior stabilized press-fit condylar modular total knee prosthesis (PFC; Johnson and Johnson, Raynham, Massachusetts) was introduced for general use in 1989. The design features addressed shortcomings of the precursor total condylar prosthesis with regard to range of motion1-6, posterior cruciate ligament substitution7, patellofemoral contact stresses7-9, and modular constrained tibial polyethylene inserts, resulting in improved relief of pain, improved range of motion, improved function, and a lower prevalence of patellofemoral problems8.
The safety and efficacy of this cemented prosthesis was reported in 19978 after four to six years of follow-up in a cohort of 150 consecutive knees in 118 patients. We followed these patients in a prospective manner to assess fixation durability, performance, instability, and polyethylene wear. The purpose of the present review was to determine the long-term results in this same cohort after an average duration of followup of twelve years.
One hundred and fifty consecutive primary total knee arthroplasties were performed with cement in 118 patients by a single surgeon (C.S.R.) with use of the press-fit condylar modular total knee system (PFC; Johnson and Johnson) of the posterior cruciate-substituting design. The surgeon was a designer of this implant system. All patients received a cemented all-polyethylene resurfacing patellar component, and none of the patients underwent bilateral knee arthroplasty during a single operation. The surgical technique was uniform and has been previously reported8,10,11. Institutional review board approval was obtained for the present study.
Two blinded, independent observers (V.J.R. and J.A.R.) assessed the clinical and radiographic results at the time of the latest follow-up. All data were collected prospectively at followup visits scheduled for one year, five years, eight to ten years, ten to thirteen years, and more than fifteen years postoperatively. Patients who were unable to attend a follow-up visit were contacted by telephone and mail, and follow-up radiographs were made at local facilities. Living patients were traced by means of Social Security death index database services that were available online (www.ancestry.com). Clinical and functional results were assessed according to the Knee Society scoring system12. In addition, the patients were evaluated with use of a questionnaire involving a visual analog scale ranging from 0 to 10 (see Appendix). The questionnaire evaluated the intensity, location, and frequency of pain; function in terms of stair-climbing, walking distance, participation in recreational sports; the overall sense of well-being; and the level of satisfaction.
Standing anteroposterior, lateral, and skyline patellar radiographs were made preoperatively and at all follow-up intervals. Radiolucent lines were evaluated according to the zones established by the Knee Society13. In addition, the radiographs were assessed for the presence of osteolysis and implant loosening. Osteolysis was deemed to be present in periprosthetic bone when radiographs demonstrated a radiolucency measuring >1 cm in diameter, without osseous trabeculae, that had been absent on previous radiographs.
The data were analyzed with use of SPSS statistical software (version 10.0 for Windows; SPSS, Chicago, Illinois). Descriptive statistics and independent-samples t tests (nonparametric) were used to analyze the results, with the level of significance set at p < 0.05. Kaplan-Meier survivorship analysis14,15, with revision or a recommendation for revision for any reason and mechanical failure as the end points, was performed. All patients and all knees were included, and the data are presented in terms of best-case and worst-case scenarios16. In the best-case scenario, patients who had been lost to follow-up were considered to have had a successful outcome. In the worst-case scenario, patients who had been lost to follow-up were considered to have had a failure. Patients who died were not considered to have had a failure if they had not complained about the knees before death.
Of the 118 patients (150 knees), twenty patients (thirty knees) died and fourteen patients (fifteen knees) were lost to follow-up. Clinical and radiographic follow-up was thus available for eighty-four patients (105 knees) with a mean duration of follow-up of twelve years (range, ten to thirteen years). The preoperative diagnosis in this cohort of eighty-four patients was osteoarthritis in seventy-seven patients (ninety-four knees), rheumatoid arthritis in four patients (eight knees), and osteonecrosis in three patients (three knees).
Knee Society Score
The mean Knee Society functional score at the time of the latest follow-up for the eighty-four patients (105 knees) was 73 points (range, 50 to 100 points), and the mean clinical score was 88 points (range, 50 to 100 points). The overall clinical result was excellent for seventy-nine knees (75%) in sixty-three patients (75%), good for fifteen knees (14%) in thirteen patients (15%), fair for six knees (6%) in four patients (5%), and poor for five knees (5%) in four patients (5%). Hence, a good or excellent result was attained in ninety-four knees (90%) in seventy-six patients (90%).
Among the 105 knees, ninety (86%) had no pain, eleven (10%) had minor anterior pain, and four (4%) had moderate pain. Sixty-eight (81%) of the eighty-four patients were able to ascend or descend stairs in a reciprocal fashion without support.
Overall, eighty patients (95%) were fully satisfied and four (5%) were only partially satisfied because of pain during walking. Fifty-one (61%) of the eighty-four patients were participating in recreational sports such as walking 1 to 3 mi (1.6 to 4.8 km) per day, golf, doubles tennis, swimming (thirty minutes per day), or stationary bicycling (thirty minutes per day) at the time of the latest follow-up.
Range of Motion
The mean range of motion at the time of the latest follow-up was 108° (range, 60° to 135°). Eleven knees (10%) had <90° of motion, twenty-two knees (21%) had 91° to 110°, and seventy-two knees (69%) had >110°. Five knees had a flexion contracture of 5°.
There were no instances of patellar fracture, patellar dislocation, patellar component loosening, or patellar clunk syndrome. Mild anterior knee pain was present in eight patients (eleven knees; 10%). No patient had persisting delayed-onset disabling anterior knee pain as described in the previous report8.
The mean duration of radiographic follow-up of the overall cohort of survivors was twelve years (range, ten to thirteen years). Fifty-two (50%) of the 105 knees had an incomplete radiolucent line around the tibial component (twenty-six knees; 25%), the femoral component (fifteen knees; 14%), or both components (eleven knees; 10%). None of the knees had radiolucent lines in more than two contiguous zones. Two knees had progressive radiolucent lines around the tibial component in zones 1 and 2. Both of these knees also had expansive medial femoral condylar osteolysis (Figs. 1 and 2) and subsequently underwent revision. No other knee had radiographic evidence of loosening of any component.
Five knees were revised in five patients. Two knees were revised because of infection, and one was revised because of dislocation, as reported earlier8. Two additional knees were revised at six and eight years because of femoral osteolysis. Both of the knees had had failure of the locking mechanism of the polyethylene insert due to fracture of the locking tab. The top side of the polyethylene liners had delamination and yellow discoloration due to oxidation. Burnished tibial baseplates and the absence of manufacturer markings on the insert suggested so-called backside polyethylene wear. Both knees had well-fixed femoral and tibial components at the time of revision. The femoral components were removed because of extensive bone loss under the components. After removal of the components, the metaphyseal bone was reconstructed with bone graft and wedges. Press Fit Condylar TC-3 implants (Johnson and Johnson) were then inserted to achieve knee stability in flexion.
With revision or recommended revision for any reason as the end point, the twelve-year survival rate for the entire cohort was 94.6% ± 4.0% in the best-case scenario and 84.9% ± 5.9% in the worst-case scenario (Fig. 3). With mechanical failure as the end point, the twelve-year survival rate was 98.3% ± 2.4% in the best-case scenario and 88.3% ± 5.3% in the worst-case scenario (Fig. 4). Forty-five knees in thirty-five patients were at risk after twelve years of follow-up. As none of the knees had radiographic evidence of loosening at the time of the last review, the radiographic survival rate was the same as the clinical survival rate.
The present report on the mean twelve-year survival of the cemented press-fit condylar modular total knee prosthesis with a posterior cruciate-substituting design confirms the durability of this device. The twelve-year survival rate for the entire cohort of 118 patients (150 knees) was predicted to be 98.3% ± 2.4% with mechanical failure as the end point and was comparable with the reported results of posterior cruciate ligament-retaining15,17-19, sacrificing6,20,21, and substituting16 fixed-bearing designs. We employed a patient-assessment questionnaire to attain better objective insight into the quality of the results. Fifty-one (61%) of the eighty-four surviving patients were participating in recreational sports, and eighty (95%) of the eighty-four patients were fully satisfied with the overall result.
Since the publication of the early results for this cohort of patients in 19978, two arthroplasties failed because of osteolysis of the medial femoral condyle and polyethylene-induced reactive synovitis. The locking mechanism in both of these implants was incompetent22 as a result of breakage of the anterior locking tab, causing gross motion of the tibial polyethylene insert inside the metal baseplate. The articular surfaces had wear patterns that were suggestive of pitting and delamination23. In addition, the underside of the polyethylene inserts had evidence of backside polyethylene wear24. Problems related to polyethylene wear and erosive osteolysis have been reported in association with cementless25-27 and cemented modular total knee implants with posterior cruciate-retaining19 and substituting28 designs and are a cause for concern. We hypothesize that the factors responsible for this process may be a combination of oxidation of the polyethylene, leading to increased wear at the primary bearing surface, and failure of the locking mechanism due to oxidation, resulting in increased motion between the insert and the baseplate. Increased polyethylene wear may cause florid synovitis similar to chronic rheumatoid synovitis11 and secondary ligamentous laxity. The experience gained in association with these two cases has led us to recommend polyethylene liner exchange when persistent symptomatic synovitis related to osteolysis is present in the absence of tibial baseplate burnishing. However, in the presence of tibial baseplate burnishing, revision of the tibial component may be necessary as polyethylene liner exchange predisposes to accelerated wear and early failure. Additionally, recent successor total knee designs have been modified with better locking mechanisms, improved polyethylene sterilization with use of gamma irradiation in an oxygen-free environment to reduce oxidation risks, and a chromium-cobalt alloy tibial baseplate with a polished top surface.
The patient-assessment questionnaire is available with the electronic versions of this article, on our web site at jbjs.org (go to the article citation and click on “Supplementary Material”) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM). ▪
The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They 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 authors are affiliated or associated.
* Original Publication
* Ranawat CS, Luessenhop CP, Rodriguez JA. The press-fit condylar modular total knee system. Four-to-six-year results with a posterior-cruciate-substituting design. J Bone Joint Surg Am. 1997;79:342-8.
Investigation performed at the Department of Orthopaedic Surgery, Ranawat Orthopaedics Center, Lenox Hill Hospital, New York, NY
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