All-polyethylene Patellar Component Research Articles

Metal-Backed Patella Implants in Knee Arthroplasty: Can the Past Predict the Future?

BackgroundThere is a renewed interest in uncemented total knee arthroplasty to potentially provide longer durability, including the use of newer design metal-backed patellae (MBPs). The purpose of this study was to review survivorship with failure mode and time to failure of an earlier version MBP at up to 10-30 years of follow-up that may influence the desirability of using these components today. MethodsA retrospective review was performed of patients that had uncemented total knee arthroplasty with an uncemented MBP. All-cause revision rates were obtained from chart reviews and telephone discussions with patients and family members of deceased patients. Kaplan–Meier plots were used to determine the implant survivorship. Outcome scores were compared between revised and nonrevised patients. ResultsThe 97 knees that had an end point of an aseptic revision or last known contact with implant survivorship averaged 15 years (range, 0-32 years). There were 40 knees that underwent revision that included 37 patella component failures (38.1%). All patellar failures had polyethylene wear or fracture. None were revised due to loosening. Survivorship was 97.9% at 5 years, 88.7% at 10 years, and 53.0% at 20 years. Median time to failure was 11 years. ConclusionLoosening is not a failure mode with this MBP. There were 75% of the failures occurring after 10 years. Use of contemporary MBP with improved but still thin polyethylene warrants guarded optimism when used in younger patients where longer survivorship than with a cemented all-polyethylene patellar component is the goal.

What's New in Adult Reconstructive Knee Surgery.

What's New in Adult Reconstructive Knee Surgery.

Factors Affecting the Risk of Aseptic Patellar Complications in Primary TKA Performed with Cemented All-Polyethylene Patellar Resurfacing.

Patellar complications are a consequential cause of failure of primary total knee arthroplasty (TKA). The purpose of this study was to evaluate the association of demographic and patient factors with the long-term risk of patellar complications as a function of time in a very large cohort of primary TKAs performed with patellar resurfacing. We identified 27,192 primary TKAs utilizing cemented all-polyethylene patellar components that were performed at a single institution from 1977 through 2015. We evaluated the risk of any aseptic patellar complication and any aseptic patellar reoperation or revision, subanalyzed risks of reoperation or revision for loosening, maltracking/instability, and wear, and evaluated the risk of clinical diagnosis of patellar fracture and clunk/crepitus. The mean age at TKA was 68 years (range, 18 to 99 years); 57% of the patients were female. The mean body mass index (BMI) was 32 kg/m2. The primary diagnosis was osteoarthritis in 83%, and 70% of the TKAs were posterior-stabilized. Median follow-up was 7 years (range, 2 to 40 years). Risk factors for each outcome were evaluated with Cox regression models. Nine hundred and seventy-seven knees with all-polyethylene patellae developed patellar complications. Survivorship free from any aseptic patellar complication was 93.3% at 20 years. Twenty-year survivorship free from any aseptic patellar reoperation was 97.3% and free from any aseptic patellar revision was 97.4%. Fifteen-year survivorship for the same end points for procedures performed from 2000 to 2015 was 95.7%, 99.2% and 99.3% respectively, representing substantial improvements compared with implants placed before 2000. Univariate analysis demonstrated that male sex (hazard ratio [HR], 1.4), an age of <65 years (HR, 1.3), and a BMI of ≥30 kg/m2 (HR, 1.2) were associated with increased risk of patellar complications (all p ≤0.01). Posterior-stabilized designs were associated with fewer patellar reoperations and revisions overall (HR, 0.4 and 0.4; p < 0.001) but higher risk of patellar clunk/crepitus (HR, 14.1; p < 0.001). The 20-year survivorship free from any aseptic patellar complication in this series of cemented all-polyethylene patellae was 93%. Important risk factors for any aseptic patellar complication were male sex, an age of <65 years, a BMI of ≥30 kg/m2, and a patella implanted before 2000. Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Biomechanical Study of Patellar Component Fixation with Varying Degrees of Bone Loss

BackgroundThe decision as to whether or not to resurface the patella in revision total knee arthroplasty (TKA) is affected by the amount of patellar bone stock remaining; however, the impact of the cancellous bone status on patellar component fixation has not been studied. Therefore, we conducted a biomechanical study of patellar component fixation with varying degrees of cancellous bone loss. MethodsSixty pairs of cadaveric patellae were randomly assigned between 3 groups and prepared in similar manner to a TKA with the standard 3-hole configuration. A control patella and an experimental patella were designated in each pair. To simulate bone loss in the experimental patellae, 1, 2, and 3 of the standard drill holes were uniformly enlarged to 12 mm in group 1, group 2, and group 3, respectively. Afterward, an all-polyethylene patellar component was cemented to each patella, as done intraoperatively. Patellar components were then sheared off using a materials testing system. The resulting mean offset yield force was analyzed within each group using paired t-tests. ResultsThe mean offset yield force for the control patellae was greater than the experimental patellae in group 1. In groups 2 and 3, the experimental patellae produced a greater mean offset yield force than the control patellae. Comparison within each group did not demonstrate a statistically significant difference. ConclusionBone loss with enlargement of the patellar fixation holes, as is frequently seen in revision TKA, with holes up to 12 mm, does not significantly decrease patellar component fixation shear strength in this biomechanical cadaveric study.

Significant Functional Improvement at 2 Years After Isolated Patellofemoral Arthroplasty With an Onlay Trochlear Implant, But Low Mental Health Scores Predispose to Dissatisfaction

IntroductionWe reviewed the clinical and radiographic outcomes of a consecutive series of patients who underwent patellofemoral arthroplasty (PFA) using a modern onlay-style trochlear design and all-polyethylene patellar component. An additional goal of the study was to elucidate, for the first time, the extent to which patients were satisfied with their implant and whether expectations were met after undergoing PFA. Methods and MaterialsWe identified a consecutive series of 70 knees (53 patients) treated with primary isolated PFA between October 2007 and May 2012. For our clinical outcomes analysis, we included patients with a minimum follow-up of 2 years and available preoperative original Knee Society scores. ResultsAt an average 4.9 years of follow-up, the mean range of motion and Knee Society Knee and Function scores improved significantly, and less than 4% of patients required revision arthroplasty. There was no radiographic evidence of component loosening or wear. Despite these improvements, new Knee Society scores indicated that fewer than two-thirds of patients were satisfied or had their expectations met. Dissatisfied patients and those whose expectations were not met had significantly lower Mental Health scores according to the Short Form–36 following PFA. ConclusionsDespite the clinical and radiographic success of this implant, patient satisfaction remained low, which may be partially explained by poor mental health.

Paper 105: Changes in Patellar Alignment After Total Knee Arthroplasty

Although the results of total knee arthroplasty continue to improve, problems related to the patellofemoral joint remain significant. This study examined the factors affecting patellar alignment after total knee arthroplasty and subsequent changes during a postoperative period of 5.3 years. Fifty-five knees in 39 patients were retrospectively evaluated by radiography for postoperative patellar alignment. This study included four men and 35 women with a mean follow-up time of 5.3 years (range: 2.5 to 8.4). All procedures utilized identical surgical technique; through a midline skin incision and medial parapatellar arthrotomy, the patella was fully everted. We adjusted the rotation of the femoral component until it was parallel to the surgical epicondylar axis. Using the posterior femoral condyles as references, we inserted the femoral components with 3° to 5° of external rotation to the posterior condylar axis according to preoperative CT scans. Tibial components were set using the medial third of the tibial tuberosity as a reference. All patellae were resurfaced with three-peg offset-dome all-polyethylene patellar component. Patellar alignment was assessed by measuring the lateral tilt and lateral displacement in skyline views taken with the knees at approximately 60° of flexion. Patellar alignment was evaluated one month after surgery, and at final follow-up. Changes in patellar lateral tilt angle and lateral displacement in the postoperative period were calculated using data obtained one month after surgery and at final follow-up. We did not observe severe malalignment of the femorotibial joint, patellar bone fracture, prosthesis failure, or any other clinical complications after TKA in any cases. The mean patellar lateral tilt angle was -0.7° (range: −13.7 to 7.0°) one month after surgery and −0.4° (range: −11.4 to 11.6°) at final follow-up. The mean patellar lateral displacement was 1.1mm (−2.7 to 6.6mm) one month after surgery and 0.9mm (−3.7 to 5.8mm) at final follow-up. We observed a negative correlation between the patellar resection angle and lateral tilt one month after surgery (p<0.0001) and between the patellar resection angle and patellar lateral displacement one month after surgery (p=0.0003). Lateral retinacular release was required for thirteen knees. In these cases, the resection angle was significantly smaller than that seen in knees without lateral retinacular release (p=0.0012). These results demonstrate that a smaller resection angle correlated with an increased frequency of lateral retinacular release. The change in patellar lateral tilt angle after 5.3 years was 0.3° (range: −7.2 to 7.0°), while the change in patellar lateral displacement was −0.3 mm (range: −5.2 to 3.7 mm). These changes did not significantly correlate with patellar alignment at any time point, resection angle, resection thickness, lateral retinacular release, or clinical results. The postoperative femorotibial alignment, however, exhibited a statistically significant correlation with the changes in lateral tilt angle (p=0.020). A more varus postoperative alignment correlated with increased lateral tilt of the patella in the postoperative period. We observed a satisfactory patellar alignment after a postoperative period of 5.3 years. The patellar resection angle had a significant effect on postoperative patellar alignment. Our findings suggest that leaving a thicker patellar remnant on the medial side can decrease postoperative lateral tilt and the resulting need for lateral retinacular release. Postoperative changes in patellar alignment were very small; none of the knees demonstrated complications of the patellofemoral joints. In this study, we observed the tendency that a postoperative varus alignment leads to patellar lateral tilt. Surgeons should pay scrupulous attention to femorotibial alignment during total knee arthroplasty to decrease patellofemoral complications and femorotibial problems.

Paper 110: Patellar Cut Obliquity in the Sagittal Plane May Be Predictive of Peri-prosthetic Patella Fracture in Cemented Total Knee Arthroplasty

Patellar cut geometry has been proposed to influence patellar fracture after total knee arthroplasty (TKA). To our knowledge, there are no large studies in current literature directly examining the association of patella fractures to the integrity of the patellar cut. This paper examines the thickness and obliquity of the bony patellar resection in 74 patella fractures occurring in cemented all-polyethylene patellar components. We retrospectively reviewed 5,073 TKAs performed between 10/4/88 to 8/31/2004 by a single surgeon. Within this period, 74 peri-prosthetic patella fractures in 68 patients were identified and compared to a matched control group. Post-operative radiographic assessments of all patellae included merchant and lateral views of the patellae. Thickness of the remaining patellar bone was measured using both merchant and lateral radiographs. Patellar cut tilt was evaluated on lateral and merchant views using 10mm thickness measurements from the midpoint on each view. Geometric and statistical analysis was conducted. With greater sagittal obliquity angles, patellae were 1.196 times more likely to experience a fracture than our controls. Patella fracture after TKA may be due to trauma or a stress fracture around the construct. Bone removal for the fixation lugs can weaken the patella, causing fracture through the stress risers. This effect may be magnified with a more generous or oblique cut. Improvement in surgical technique to retain a more level cut could theoretically help prevent the problem.

Bilateral Patellar Component Shear Failure of Highly Cross-Linked Polyethylene Components: Report of a Case and Laboratory Analysis of Failure Mechanisms

A case of bilateral patellar component failure due to fatigue fracture of the all-polyethylene fixation pegs in a highly cross-linked ultra–high-molecular-weight polyethylene design is presented. To recreate this failure mode, a novel test method was developed to investigate the effects of peg orientation and cement technique on patella fatigue strength under cyclic compression and shear loading. Patellar peg orientation had a minor effect on shear strength, whereas lack of cement in the backside patellar groove had a substantial effect. The shear fatigue strength exceeded in vivo force estimates when the patellar groove was fully cemented. The test results and retrieval analysis suggest that high activity level and inadequate cement fixation of the patellar component may contribute to all-polyethylene patellar component peg fractures.

Fracture of Highly Cross-linked All-Polyethylene Patella after Total Knee Arthroplasty

Recent advances in polyethylene fabrication have led to the introduction of highly cross-linked polyethylene tibial and patellar components for use in total knee arthroplasty (TKA) with the goal of reducing wear-related osteolysis. However, some reports suggest decreased mechanical strength as a result of the additional thermal and sterilization treatments in the manufacturing of implants. Complications related to the patella are among the most common causes of failure in TKA, but patellar component fracture is rare. The authors report a case of a highly cross-linked all-polyethylene patellar component that failed as a result of fracture in vivo in a patient 3 years after TKA.

Cemented Rotating-Platform Total Knee Replacement

We previously evaluated 119 consecutive total knee arthroplasties performed by a single surgeon in eighty-six patients with use of the cemented LCS (low contact stress) mobile-bearing, rotating-platform system and an all-polyethylene patellar component. The average age of the patients at the time of surgery was seventy years. The patients were contacted as part of their routine follow-up and were asked to participate in this study. The purpose of the present study was to report the updated results at a minimum follow-up of twenty years. Twenty patients (twenty-six knees) were living, and one was lost to follow-up. Three knees required a reoperation (two for periprosthetic fractures and one for infection). No component was revised as a part of the reoperations. No knee required revision since the fifteen-year follow-up evaluation. Osteolysis was present in six knees compared with only three knees at the time of the fifteen-year follow-up. One knee had radiographic signs of femoral component loosening, which was associated with osteolysis. It occurred after the fifteen-year follow-up study. The average range of motion was from 1 degrees of extension to 105 degrees of flexion. The average clinical and functional Knee Society scores were 43 and 49 points, respectively, at the preoperative evaluation and 89 and 67 points at the time of the final follow-up. We concluded that the cemented LCS rotating-platform knee performed well, with durable clinical and radiographic results at a minimum follow-up of twenty years. However, the prevalence of osteolysis continues to increase with a longer duration of follow-up in these patients.

Predicting Patellar Failure After Total Knee Arthroplasty

We identified patient and surgeon factors associated with patellar component failure in a series of 8530 TKAs performed in 5640 patients using the same posterior cruciate ligament-retaining TKA with all-polyethylene patellar components between January 1983 and December 2003. Patellar failure was defined as loosening, fracture, or patellar revision. All infections were excluded. Statistical analysis using Kaplan-Meier and Cox regression was used to determine the risk of patellar failure. Followup averaged 7.0 years (range, 2-22 years). Patellar component loosening occurred in 4.8% of TKAs (409 knees). Patellar fracture was identified in 5.2% of TKA (444 knees). Twenty-five patellae were revised (0.3%). TKA performed with a lateral release and patients with a body mass index of greater than 30 kg/m(2) were at the greatest risk of patellar loosening and fracture, respectively. Male gender, preoperative varus alignment of greater than 5 degrees , and large patellar component size also predicted a higher risk of patellar fracture. Medial patellar component position, tibial component thickness of greater than 12 mm, preoperative valgus alignment of 10 degrees or more, and preoperative flexion of 100 degrees or more predicted patellar loosening. An awareness of these factors that predict patellar failure after TKA may help determine the relative indications for TKA and influence surgical technique, especially when using this prosthesis. Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Isolated All-polyethylene Patellar Revisions for Metal-backed Patellar Failure

The outcome of isolated patellar component revisions after metal-backed patellar failure is variable with satisfactory results reported from 78% to 100%. To supplement information in the literature we determined the failure rate and the functional outcome based on the Knee Society clinical and roentgenographic evaluation systems of isolated patellar component revisions after metal-backed patellar component failure. We retrospectively reviewed 27 patients with 28 isolated patellar component revisions for metal-backed patellar component failure performed between 1988 and 2005. Twenty-five knees in 24 patients were available for review with a minimum followup of 24 months (mean, 90 months; range, 24-210 months). All knees were revised with a cemented all-polyethylene patellar component and all tibial polyethylene components were routinely exchanged. One failure (4%) occurred 122.6 months after the isolated patellar component revision secondary to femoral and tibial component loosening. The average Knee Society knee score improved from 73 to 89 points, whereas the average Knee Society function score improved from 56 to 65. Our data confirm those in the literature suggesting a successful outcome can be achieved with an isolated patellar component revision for metal-backed patellar component failure. Level IV, retrospective case series. See the Guidelines for Authors for a complete description of levels of evidence.

The Effect of Drill Hole Size on the Fixation Strength of a Cemented Prosthetic Patellar Button

This study used a cadaver model to analyze the fixation strength of 3 different patellar resurfacing preparations using an all-polyethylene patellar component. One of 3 drill hole sizes was randomly selected and used to prepare the patella. The entire construct was cemented, mounted to a servohydraulic testing machine, cycled between 0 and 50 N, and then tested to failure. Mean forces obtained prior to failure were 258.5, 293, and 353.1 N for the chamfer, 4.5-mm, and 9.5-mm drill holes, respectively. There was a statistically significant difference in strength to failure between the 9.5-mm and chamfer drill hole sizes. These findings may help to reduce patellar implant failures.

Fixation strength comparison of onlay and inset patellar implants

Patellar implant fixation continues to be one of the most troublesome areas in total knee arthroplasty (TKA). It has been reported that patellofemoral complications in TKA are responsible for almost half of all re-operations. The literature review revealed the rate of primary all-polyethylene patellar implant loosening ranging 1%–4.2% [Berend ME, Ritter MA, Keating EM, Faris PM, Crites BM. The failure of all-polyethylene patellar components in total knee replacement. Clin Orthop 2001;388:105–11, Chew JT, Stewart NJ, Hanssen AD, Luo ZP, Rand JA, An KN. Differences in patellar tracking and knee kinematics among three different total knee designs. Clin Orthop 1997;345:87–98, Barrack RL, Wolfe MW, Waldman DA, et al. Patellar resurfacing in total knee arthroplasty: a five to seven year follow-up of prospective, randomized, double-blind study. Proceedings of Sixty-Seventh Annual Meeting of the American Academy of Orthopaedic Surgeons 2000. p. 547]. The loosening rates for metal-backed or following patellar component revisions were considerably higher [Chew JT, Stewart NJ, Hanssen AD, Luo ZP, Rand JA, An KN. Differences in patellar tracking and knee kinematics among three different total knee designs. Clin Orthop 1997;345:87–98, Jordan LR, Sorrells RB, Jordan LC, Olivo JL. The long-term results of a metal-backed mobile bearing patella. Clin Orthop 2005;436:111–8, Berger RA, Lyon, JH, Jacobs JJ, Barden RM, Berkson EM, Sheinkop MB, et al. Problems with cementless total knee arthroplasty at 11 years followup. Clin Orthop 2001;392:196–207, Ritter MA, Pierce MJ, Zhou H, Meding JB, Faris PM, Keating EM. Patellar complications (total knee arthroplasty). Effect of lateral release and thickness. Clin Orthop 1999;367:149–57] Onlay and inset patellar components with variable fixation surface geometry are currently available for clinical use. The purpose of this study was to quantify the shear disassociation strength for both onlay and inset patellar fixation techniques. The variation in host material was minimized by the use of synthetic patellae, which has been previously validated in implant fixation studies. The testing revealed that inset patellar fixation resistance to shear disassociation was 25% higher than onlay patellae ( p = 0.0002).

Isolated Revision of Failed Metal-Backed Patellar Components: Outcome With Minimum 4-Year Follow-Up

Several reports document high failure rates of metal-backed patellar components, but few report the outcome of revising these components to all-polyethylene, cemented implants. At a mean 87.2-month follow-up, we describe a series of 36 patients (40 knees) who underwent isolated metal-backed patellar revision to a cemented, all-polyethylene patellar component. After the patellar revision, 5 patients (6 knees) underwent additional surgery, but no patellar components required revision. The additional surgeries were performed at an average of 77.6 months after patellar revision and included 3 tibial insert exchanges for polyethylene wear, 2 revisions of femoral and tibial components for osteolysis, and 1 realignment procedure for recurrent subluxation of the patella. We conclude that revision of a failed metal-backed patellar component to a cemented, all-polyethylene patella is a durable, successful procedure.

Cemented Rotating-Platform Total Knee Replacement

We previously evaluated 119 consecutive total knee arthroplasties that were performed in eighty-six patients with use of the cemented LCS (low contact stress) rotating-platform system with an all-polyethylene patellar component. The average age of the patients at the time of surgery was seventy years (range, thirty-seven to eighty-eight years). The purpose of this study was to report the updated results at a minimum follow-up of fifteen years. Thirty-seven patients (fifty-three knees) were living, and no patient was lost to follow-up. No knee was revised because of loosening, osteolysis, or wear. Three knees required a reoperation (two for periprosthetic fractures and one for infection). No component was revised as a part of the reoperations. Osteolysis was present in three knees. No knee had radiographic signs of component loosening, and there were no dislocated bearings. The average range of motion was from 1 degrees of extension to 105 degrees of flexion. The average clinical and functional Knee Society scores were 43 and 49, respectively, at the preoperative evaluation and 85 and 58 at the time of the final follow-up. We concluded that the cemented LCS rotating-platform knee performed well, with durable clinical and radiographic results at a minimum follow-up of fifteen years.

CEMENTED ROTATING-PLATFORM TOTAL KNEE REPLACEMENT

Abstract: We previously evaluated 119 consecutive total knee arthroplasties that were performed in eighty-six patients with use of the cemented LCS (low contact stress) rotating-platform system with an all-polyethylene patellar component. The average age of the patients at the time of surgery was seventy years (range, thirty-seven to eighty-eight years). The purpose of this study was to report the updated results at a minimum follow-up of fifteen years. Thirty-seven patients (fifty-three knees) were living, and no patient was lost to follow-up. No knee was revised because of loosening, osteolysis, or wear. Three knees required a reoperation (two for periprosthetic fractures and one for infection). No component was revised as a part of the reoperations. Osteolysis was present in three knees. No knee had radiographic signs of component loosening, and there were no dislocated bearings. The average range of motion was from 1° of extension to 105° of flexion. The average clinical and functional Knee Society scores were 43 and 49, respectively, at the preoperative evaluation and 85 and 58 at the time of the final follow-up. We concluded that the cemented LCS rotating-platform knee performed well, with durable clinical and radiographic results at a minimum follow-up of fifteen years. Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

Mechanical properties and fatigue performance of crosslinked polyethylene in total knee applications

Abstract There has been increasing concern about the structural fatigue resistance of crosslinked ultra-high molecular weight polyethylene (UHMWPE) components due to deterioration of certain mechanical properties. However, due to the lack of clear correlation between specific mechanical properties and clinical performance, these concerns remain theoretical. To mimic clinical use and thus evaluate the potential risks and benefits of various crosslinked polyethylene materials for knee and hip bearing applications, two clinically relevant, worst-case scenarios were simulated on functional devices. In the first scenario, cemented all-polyethylene patellar components were tested under simulated stair-climbing conditions with femoral component rotational malalignment. In the second scenario, thin, metal-backed, polyethylene acetabular liners were tested in a hip joint simulator under rim-loading conditions. To compare the mechanical properties of these materials, various types of crosslinked UHMWPE were prepared according to published process descriptions of commercial materials. These materials were then subjected to standardized tensile strength testing. The results indicated that material performance was more significantly affected by the postirradiation thermal treatment history than by the total dose of irradiation. Remelting following irradiation led to catastrophic fractures of the pegs of the rotationally malaligned patellar components and the rim-loaded liners. The ultimate tensile strength appeared to be the key mechanical property that correlated with the structural fatigue performance of crosslinked polyethylene materials, whereas tensile elongation within the 250 to 400% range had no effect on structural integrity.

Excisional arthroplasty for patellar loosening in total knee arthroplasty

Four thousand two hundred eighty-seven cases of Anatomic Graduated Components total knee replacements with a cemented, single-peg, all-polyethylene patellar component were performed at our institution over the past 15 years. One hundred eighty cases of patellar component loosening were found. Eleven knees (0.3%) in 11 patients required isolated patellar component reoperation. In all cases, the patellar component was excised and not reimplanted. The average follow-up for the 11 patients was 2.2 years. Five had a complete minimum follow-up of 2 years following reoperation. Pain and function were improved. Complications included infection in 3 knees and extensor lag in 1 knee. Because of the complication rate associated with isolated patellar component excision caused by a loose patellar component, we recommend surgical removal of the patellar component only in cases of severe pain and/or prominence of the component.

Factors affecting the durability of primary total knee prostheses.

Failure of total knee arthroplasty is problematic. The purpose of this study was to evaluate the factors that influence the durability of a primary total knee prosthesis. A survivorship analysis of 11,606 primary total knee arthroplasties carried out between January 1, 1978, and December 31, 2000, was performed. An analysis of patient and implant-related factors affecting survivorship was done with use of a multivariate Cox model. The survivorship was 91% (95% confidence interval, 90% to 91%) at ten years (2943 knees), 84% (95% confidence interval, 82% to 86%) at fifteen years (595 knees), and 78% (95% confidence interval, 74% to 81%) at twenty years (104 knees) following the surgery. Prosthetic survivorship at ten years was 83% for patients fifty-five years of age or less compared with 94% for those older than seventy years of age (p < 0.0001), 90% for those with a diagnosis of osteoarthritis compared with 95% for those with inflammatory arthritis (p < 0.005), and 91% for those with retention of the posterior cruciate ligament compared with 76% for those with substitution of the posterior cruciate ligament (a posterior stabilized prosthesis) (p < 0.0001). Survivorship at ten years was 92% for nonmodular metal-backed tibial components, 90% for modular metal-backed tibial components, and 97% for all-polyethylene tibial components (p < 0.0001). Survivorship at ten years was 92% for prostheses fixed with cement compared with 61% for those fixed without cement (p < 0.0001). Significant risk factors for failure of total knee arthroplasty were the type of implant, age and gender of the patient, diagnosis, type of fixation, and design of the patellar component. In the ideal situation-treatment of a woman over the age of seventy years who has inflammatory arthritis with a nonmodular, metal-backed tibial component, cement fixation, an all-polyethylene patellar component, and retention of the posterior cruciate ligament-the ten-year survivorship of the prosthesis was estimated to be 98% (95% confidence interval, 97% to 99%).