Functional analysis for the entire cohort at the time of the last physical examination revealed improved ROM from a mean preoperative flexion contracture of 5.8° (range, 0°-20°) to a mean of 0.6° (range, 0°-15°) extension at the time of the most recent clinical followup (mean, 8.9 years; range, 1.1-13.2 years). The mean preoperative flexion of 107.6° (range, 75°-140°) improved to a mean of 116.2° (range, 85°-130°) postoperatively. HSS knee scores for patients who had a complete evaluation at a minimum 10-years postoperatively improved from a mean of 47.7 (range, 23-78) preoperatively to a mean of 85.4 (range, 33-100). Five knees in five patients had a score less than 70, or patients reported the inability to walk on the self-reported evaluation; all five cited arthritis in another joint as a factor limiting their ability to ambulate. Two of these five patients also had a major comorbidity, including disseminated cancer in one and peripheral arterial disease in another, as limiting their ambulatory capacity. The remaining three patients had manipulation under anesthesia after the index arthroplasty for poor postoperative ROM. At the most recent followup, two of these patients had full extension and flexion to 110° and 130°, respectively. The remaining patient had multiple patellar realignment procedures before the index arthroplasty, and at her most recent followup, she had a 10° flexion contracture and additional flexion to 85°.
Complications occurred in 24 of the entire cohort of 161 patients (14.9%). Two complications occurred intraoperatively, including one laceration of the medial collateral ligament, which was repaired primarily and treated with a hinged knee brace for 6 weeks, and one fracture of the medial femoral condyle, which was treated with screw fixation at the time of surgery. Seven knees (3.9%) had manipulation under anesthesia for poor ROM. A deep venous thrombosis was diagnosed in four knees (2.2%), and a hematoma developed in three knees (1.7%); all were treated nonoperatively. Two patients (1.2%) experienced a postoperative ileus and a gastrointestinal ulcer respectively, which both eventually resolved. Six knees (3.4%) underwent reoperation during the followup period; the components were retained in three of six knees. The three component revisions included one two-stage exchange for a deep infection, one revision for stiffness, and one supracondylar femur fracture treated with a modular tumor endoprosthesis (the components were well-fixed intraoperatively). The three remaining reoperations included one irrigation and débridement for an early postoperative infection, one periprosthetic femur fracture treated with a retrograde intramedullary nail, and one arthroscopic arthrolysis for postoperative stiffness; all three components were retained. There were no reoperations or specific complications related to the patellofemoral joint or to wear of the bearing surface.
Nonprogressive radiolucencies were identified on radiographs in association with 21 of the 63 tibial components (33.3%) and eight of the femoral components (12.7%). The majority of radiolucencies surrounding the tibial and femoral components were seen in Zones 1 and 4, respectively. No components were radiographically loose and osteolysis was not identified in any patient. The mean Insall ratio was 0.79 (SD, 0.14; range, 0.6-1.2), and the mean valgus angle was 3.58° (SD, 2.05°; range, 0°-6°). The mean patellar tilt was 0.85° (range, 0°-4°), and the mean lateral displacement was 1.34 mm (range, 0-4 mm).
The contemporary prosthesis used in our study was developed to improve implant survival, wear behavior, and address problems associated with earlier implants, including high rates of patellofemoral maltracking and loosening. The purposes of this study were to determine the outcomes of primary TKA using this implant with a focus on identifying patellofemoral and wear-related complications (including osteolysis), overall survivorship, and clinical outcomes. We previously reported results for a larger cohort of patients at a minimum of 5 years  (that included the subset of patients described in this report) and wanted to ensure that durable results were obtained at a minimum of 10 years.
Our study has several limitations. First, eight patients (nine knees) were lost to followup. Assuming all nine knees in these eight patients lost to followup failed owing to aseptic loosening, the worst-case scenario analysis revealed 10-year implant survivorship rates of 92% and 95% using revision for any reason and for aseptic loosening, respectively, as end points. Six of the eight patients (seven of nine knees) were seen within 3 years of the time of this investigation and at that time none of these patients had undergone a reoperation or revision, and none had experienced a complication. Second, we did not have minimum 10-year followup radiographs for all 179 knees, and it is possible radiographic findings (such as osteolysis) may have been identified and thus underestimated in our study. We have made the assumption in our survival analysis that these implants were not loose, malfunctioning, or in need of revision. Further, not all patients were seen physically by one of the authors at a minimum of 10 years, with 70 of the 113 patients living far enough from our offices that a telephone questionnaire and/or physical examination by another physician was used for the analysis, and based on the lack of a complete physical examination, a complete HSS knee score could not be calculated at a minimum of 10 years for all patients included in this study. Finally, outcomes such as ROM measurements and the radiographic analysis did not have multiple observers and may be subject to interobserver variability.
There are few long-term studies available to document the longevity of contemporary cruciate-retaining total knee implants (Table 1) [3, 4, 7, 14, 41, 43, 52]. Our results compare favorably with those of prior studies with 98% and 100% survivorship rates with revision for any reason and aseptic loosening as end points at 10 years. The system described in this series is unique in that it incorporates the use of a four-pegged tibial design. Potential advantages of this design include preservation of proximal tibial bone, ease of preparation and component insertion, and the potential for reduced stress shielding of the proximal tibia by avoiding fixation deep in the tibial metaphysis [5, 11, 29, 32, 51]. Although the use of polymethylmethacrylate precoating has been associated with problems when used for a cemented femoral stem of a THA [36, 48], in this series aseptic loosening of precoated tibial and femoral components was not seen. A cement gun was used in all cases and proper pressurization and meticulous cementation technique may be additional factors in achieving durable long-term implant fixation .
Functional results after TKA in our series were comparable to results in other long-term studies of contemporary cruciate-retaining implants (Table 1).
There were no reoperations or revisions owing to issues related to the patellofemoral articulation in this series. This is in contrast to previous experience with first-generation implants, especially those with a metal-backed patella and a nonanatomic femoral trochlea, which had a higher incidence of component loosening, patellofemoral maltracking, and surface abrasion of a well-fixed femoral component secondary to wear-through of the metal-backed patella . The all-polyethylene, three-pegged patellar component, used in conjunction with a deeper femoral trochlea and improved understanding of femoral and tibial component rotation, provided reliable long-term survival.
In our series, there were no complications attributable to wear or failure of the modular insert and osteolysis was not identified among the portion of the cohort who had radiographs at a minimum of 10 years. Although the orthopaedic literature is mixed regarding the wear-related effects of cruciate retention versus substitution [10, 12, 17, 23, 27, 31, 33, 34, 47, 49], two studies identified osteolysis and wear problems associated with a posterior stabilized design [15, 37]. In addition to shape, the properties of the polyethylene constitute one of the critical variables affecting wear of the tibial insert. The devices used in our series incorporated net-molded UHMWPE, a material that reportedly has superior wear characteristics [6, 19].
We report the longer-term outcomes of a series of patients who underwent cruciate-retaining cemented TKA using a third-generation design with four short pegs for tibial fixation. At a minimum 10-year followup, this implant continues to provide reliable clinical function with a low risk of revision or reoperation.
We acknowledge Peggy Arp, Reggie Barden, Laura Quigley, and Nicholas Ting for assistance with preparation of this manuscript.
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