All-polyethylene tibia (APT) components composed the majority of early total knee arthroplasty (TKA) designs. However, early failures from aseptic loosening and increased versatility offered by metal-backed components led to a gradual decrease in the use of APT,1 despite improved outcomes with modern polyethylene.2 Metal-backed components offer the addition of cones or sleeves, augments, stem extensions, and the opportunity for exchange of the polyethylene liner after final implantation of the tibial baseplate during the index arthroplasty, or at a later date during revision (eg, for acute infection).1 Unfortunately, they have also brought about new problems, including backside wear, increased difficulty in performing an isolated tibia revision,1,3,4 and increased costs ranging from 20% to 50% more per implant.1,5
The evolution of bundled payment initiatives by the Centers for Medicare & Medicaid Services (CMS) has resulted in several programs designed to reduce the cost of care and maintain high-quality patient outcomes.6 The Comprehensive Care for Joint Replacement (CJR) model is one such initiative that establishes a target price for the 90-day episode of care. Costs exceeding the target price result in financial losses for the hospital, whereas cost of care below the target provides the opportunity for gainsharing.6,7 This has moved health care centers to establish perioperative protocols and preoperative optimization programs for patients undergoing TKA.8–11 Importantly, within these bundled reimbursement programs, surgeons maintain the ability to control intraoperative costs, which has received significantly less attention in recent literature relative to pre- and postoperative initiatives.
As continued emphasis is placed on decreasing the cost of care, it is possible that use of an APT in appropriately selected patients could provide equivalent outcomes while significantly reducing costs within a bundled reimbursement model. The authors hypothesized that at a single center participating in CJR, selective use of an APT would contribute to equivalent 90-day quality outcome metrics while decreasing the direct hospital costs, thereby leaving an increased opportunity for gain-sharing.
Materials and Methods
Following institutional review board approval, the authors retrospectively reviewed primary TKAs performed by 2 surgeons (D.E.A., S.S.W.) on Medicare patients from July 2015 to December 2017. The investigating institution was a tertiary care academic center participating in the CJR bundle, and 2 authors selectively performed TKA with APTs during the study period. The APTs were used at each surgeon's discretion after shared decision making with patients who were at least 60 years old, had lower activity levels, and were of lower body weight (cutoff body mass index [BMI] <40 kg/m2). Patients were excluded if they had revision TKA, unicompartmental arthroplasty, or cementless designs, or if tibial stem extensions were required. Only the 3 most commonly used implants (Klassic, Total Joint Orthopedics; Sigma, DePuy; and Triathlon, Stryker) were evaluated, and other implant types were excluded. All 3 of these implant types were used as both APT and metal-backed components.
Patient demographic data, including age, sex, BMI, and American Society of Anesthesiologists (ASA) score, were collected, in addition to implant type, surgery duration, length of stay (LOS), hospital disposition to skilled nursing facility (SNF) or rehabilitation facility vs home, and 90-day emergency department (ED) visit or readmission. Direct surgical and total direct hospital costs were collected from an internal accounting database (EPSi), which prospectively tracks expenses at various phases of care (surgical, radiology, intensive services, pharmacy, cardiology, respiratory, physical and occupational therapy, laboratory, transfusion, medical surgical supplies, and other direct costs). These outcome metrics were selected specifically because they are commonly used by the CMS for hospital performance evaluations.
Patients were then stratified by APTs vs metal-backed tibial components. Cohorts were compared for surgery duration (minutes), LOS, home discharge disposition, and 90-day hospital returns. Furthermore, surgical costs and total direct hospital costs were evaluated by normalizing the cost relative to the mean cost of a metal-backed component. Significant findings on univariable analysis were then evaluated in multivariable linear regression analysis controlling for age, BMI, ASA score (categorized as 1, 2 vs 3, 4), surgeon, and implant type. Statistical analysis was performed with JMP Pro, version 14.0.0 (SAS Institute Inc). Continuous data were presented as median (lower quartile, upper quartile), and analysis was performed with a Wilcoxon rank-sum test. Categorical data were presented as count (percent) and were analyzed with a chi-square test. Multivariable models are presented as beta coefficient with 95% CIs. P<.05 is considered statistically significant unless otherwise noted.
A total of 188 primary TKAs in Medicare patients met the inclusion criteria (92 APT, 96 metal-backed) for analysis (Figure 1). The cohort had a mean age of 71 years and mean BMI of 30.8 kg/m2, and 108 (57.4%) patients were female. Demographic data by tibial component design are presented in Table 1. Patients receiving APT components were significantly older (P<.001) and had a lower BMI (P<.001), but there was no difference in sex or ASA score between groups.
Distribution of patients by implant and tibial design. Abbreviations: APT, all-polyethylene tibial; TJO, Total Joint Orthopedics; TKA, total knee arthroplasty.
Demographic Data for Tibial Component Design
Perioperatively, operative time was significantly less for APTs (mean, 13 minutes); however, there was no significant difference in postoperative LOS, discharge disposition, 90-day readmission, or 90-day ED visits between groups (Table 2). Direct surgery costs were significantly lower by an average of 12.6% (P<.001), and total hospital cost for the admission demonstrated an average of 6.2% savings with APT components (P<.001) (Figure 2). In a multivariable linear regression model, surgical costs remained significantly greater for metal-backed components ($448.65; 95% CI, $326.88 to $570.43; P<.001), and operative time was significantly prolonged (0.049; 95% CI, 0.002 to 0.096, P=.041), whereas total hospital costs did not reach statistical significance ($137.4; 95% CI, $−163.49 to $438.31; P=.369).
Perioperative Outcomes by Tibial Component Design
Surgical and total hospital cost of care for metal-backed and all-polyethylene tibial (APT) components. Data are presented as mean values normalized to metal-backed components (ie, cost/average metal-backed cost), with 95% CIs.
This study agrees with prior authors who have shown equivalent outcomes for patients with APTs relative to metal-backed components. In a matched pair analysis of APTs vs metal-backed components, Najibi et al12 found no difference in outcomes for patients older than 59 years at a minimum of 2-year follow-up. In a prospective study by Gioe et al,2 they found 99.4% survivorship with APT components at 14.3 years, which was better than that of metal-backed designs. Even in younger patients, prior authors have shown excellent survivorship and performance at 5 years without evidence of osteolysis or aseptic loosening.13 Although in vitro biomechanical studies have suggested uneven distribution of stress in the cancellous bone below cemented APT components,14 which may lead to failure and implant migration,15 this has not been supported in the clinical literature. Although numerous APT implants have demonstrated clinical success, this is not universal. Faris et al16 described their 10-year outcomes of the Anatomic Graduated Component all-polyethylene tibia and noted only 90% 3-year and 68% 10-year survival. Despite successful outcomes with other APT implants, this highlights the importance of implant surveillance and design scrutinization.
In addition to the overall equivalent survival and patient-reported outcomes offered by an APT component, other distinct advantages include easier isolated tibial revision by cutting through the polyethylene stem1 and lack of backside wear.3,4,17 Additionally, to the current authors' knowledge, there has not been the reported debonding of the cement-implant interface for APTs as with other metal-backed components.18 The current study found a significant decrease in operative time for APT components, which was unanticipated. The authors postulate that this is due to proceeding with closure immediately following implantation of the components, rather than waiting for cement to cure with metal-backed components, and subsequently exchanging the trial liner with the final after rechecking flexion and extension gaps. Despite these advantages, in addition to the decreased cost, APTs represented a maximum yearly utilization of 1.5% of all TKAs from 2003 to 2008, according to the Hospital Purchasing Database.1 Through implementation of a perioperative clinical pathway that incorporated an implant standardization program based on patient age, weight, activity level, bone stock, and general health, the Lahey clinic was able to increase their utilization of APTs by 14% in lower-demand patients and maintain patient outcomes.5
Recent literature has predominantly focused on metal-backed components, and APTs have not been widely investigated since the early 2000s. However, in a bundled reimbursement initiative, which is currently the focus of the CMS, the use of APTs merits a renewed discussion. The current study shows that during participation in CJR, Medicare patients undergoing TKA cost the hospital significantly less if they were treated with an APT relative to a metal-backed component while achieving equivalent 90-day quality outcome metrics. Importantly, in the current study, this applied not to 1 specific implant, but across 3 different manufacturers, adding to the likely generalizability of the findings.
There are several important limitations to this study worth noting. First, as a retrospective review, the cohort was of limited size partially because only 2 surgeons, who selectively use APTs, were included. Despite the limited sample size, the authors were still able to achieve statistical significance both in univariable and multivariable regression models. Total hospital costs for the admission did not reach significance in the multivariable model, and the authors believe this was likely due to the sample size limitation. Additionally, this study was an analysis of direct hospital costs, rather than the entire 90-day episode-of-care costs. This was performed due to the current structure of bundled reimbursements, where a single target price is provided for the episode of care. Therefore, if a decrease in operating costs can be achieved, there is an increased opportunity for gainsharing. To show that this significantly affects 90-day episode-of-care costs would require a significantly larger cohort, and likely a multicenter study, which is beyond the scope of the current project. Finally, the outcomes were limited to 90-day quality outcome metrics commonly considered by the CMS, and equivalent outcomes cannot be extrapolated over the long term. Fortunately, prior authors have shown equivalent long-term survivorship, as previously noted.
Ultimately, the primary driver for intra-operative decisions should be patient outcomes. As shown in this and prior studies, patient outcomes appear to be equivalent with APTs and metal-backed components. Secondarily, an important consideration should be cost of care, which the CMS has made the responsibility of the modern arthroplasty surgeon. Therefore, based on these results, as well as the findings of prior authors, the authors think that APTs should be considered in appropriately selected patients to achieve optimal outcomes at a lower cost—the true focus of what value-based care is striving to accomplish.
- Gioe TJ, Maheshwari AV. The all-polyethylene tibial component in primary total knee arthroplasty. J Bone Joint Surg Am. 2010;92(2):478–487. doi:10.2106/JBJS.I.00842 [CrossRef] PMID:20124081
- Gioe TJ, Sinner P, Mehle S, Ma W, Killeen KK. Excellent survival of all-polyethylene tibial components in a community joint registry. Clin Orthop Relat Res. 2007;464(464):88–92. doi:10.1097/BLO.0b013e31812f7879 [CrossRef] PMID:17589363
- Rao AR, Engh GA, Collier MB, Lounici S. Tibial interface wear in retrieved total knee components and correlations with modular insert motion. J Bone Joint Surg Am. 2002;84(10):1849–1855. doi:10.2106/00004623-200210000-00017 [CrossRef] PMID:12377918
- Parks NL, Engh GA, Topoleski LD, Emperado J. The Coventry Award. Modular tibial insert micromotion: a concern with contemporary knee implants. Clin Orthop Relat Res. 1998;356:10–15. doi:10.1097/00003086-199811000-00003 [CrossRef] PMID:9917661
- Healy WL, Iorio R, Ko J, Appleby D, Lemos DW. Impact of cost reduction programs on short-term patient outcome and hospital cost of total knee arthroplasty. J Bone Joint Surg Am. 2002;84(3):348–353. doi:10.2106/00004623-200203000-00003 [CrossRef] PMID:11886902
- Anoushiravani AA, Iorio R. Alternative payment models: from bundled payments for care improvement and comprehensive care for joint replacement to the future?Semin Arthroplasty.2016;27(3):151–162. doi:10.1053/j.sart.2016.10.002 [CrossRef]
- Cram P, Ravi B, Vaughan-Sarrazin MS, Lu X, Li Y, Hawker G. What drives variation in episode-of-care payments for primary TKA? An analysis of medicare administrative data. Clin Orthop Relat Res. 2015;473(11):3337–3347. doi:10.1007/s11999-015-4445-0 [CrossRef] PMID:26239239
- Jiranek W. Modifiable risk factors in total joint arthroplasty. J Arthroplasty. 2016;31(8):1619. doi:10.1016/j.arth.2016.06.017 [CrossRef] PMID:27449557
- Ryan SP, Goltz DE, Howell CB, et al. Predicting costs exceeding bundled payment targets for total joint arthroplasty. J Arthroplasty. 2019;34(3):412–417. doi:10.1016/j.arth.2018.11.012 [CrossRef] PMID:30518476
- Ryan SP, Howell CB, Wellman SS, et al. Preoperative optimization checklists within the comprehensive care for joint replacement bundle have not decreased hospital returns for total knee arthroplasty. J Arthroplasty. 2019;34(7S):S108–S113. doi:10.1016/j.arth.2018.12.010 [CrossRef] PMID:30611521
- Schroer WC, Diesfeld PJ, LeMarr AR, Morton DJ, Reedy ME. Modifiable risk factors in primary joint arthroplasty increase 90-day cost of care. J Arthroplasty. 2018;33(9):2740–2744. doi:10.1016/j.arth.2018.04.018 [CrossRef] PMID:29807789
- Najibi S, Iorio R, Surdam JW, Whang W, Appleby D, Healy WL. All-polyethylene and metal-backed tibial components in total knee arthroplasty: a matched pair analysis of functional outcome. J Arthroplasty. 2003;18(7) (suppl 1):9–15. doi:10.1016/S0883-5403(03)00304-8 [CrossRef] PMID:14560404
- Ranawat AS, Mohanty SS, Goldsmith SE, Rasquinha VJ, Rodriguez JA, Ranawat CS. Experience with an all-polyethylene total knee arthroplasty in younger, active patients with follow-up from 2 to 11 years. J Arthroplasty. 2005;20(7)(suppl 3):7–11. doi:10.1016/j.arth.2005.04.027 [CrossRef] PMID:16213996
- Brihault J, Navacchia A, Pianigiani S, et al. All-polyethylene tibial components generate higher stress and micromotions than metal-backed tibial components in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2016;24(8):2550–2559. doi:10.1007/s00167-015-3630-8 [CrossRef] PMID:25957612
- Taylor M, Tanner KE, Freeman MA. Finite element analysis of the implanted proximal tibia: a relationship between the initial cancellous bone stresses and implant migration. J Biomech. 1998;31(4):303–310. doi:10.1016/S0021-9290(98)00022-0 [CrossRef] PMID:9672083
- Faris PM, Ritter MA, Keating EM, Meding JB, Harty LD. The AGC all-polyethylene tibial component: a ten-year clinical evaluation. J Bone Joint Surg Am. 2003;85(3):489–493. doi:10.2106/00004623-200303000-00014 [CrossRef] PMID:12637436
- Herschmiller T, Bradley KE, Wellman SS, Attarian DE. Early to midterm clinical and radiographic survivorship of the all-polyethylene versus modular metal-backed tibia component in primary total knee replacement. J Surg Orthop Adv. 2019;28(2):108–114. PMID:31411955
- Cerquiglini A, Henckel J, Hothi H, et al. Analysis of the attune tibial tray backside: a comparative retrieval study. Bone Joint Res. 2019;8(3):136–145. doi:10.1302/2046-3758.83.BJJ-2018-0102.R2 [CrossRef] PMID:30997039
Demographic Data for Tibial Component Design
|Characteristic||APT (n=92)||Metal-backed (n=96)||P|
|Age, median (lower quartile, upper quartile), y||73 (69, 77)||69 (66, 71)||<.001a|
|Female, No. (%)||55 (59.8)||53 (55.2)||.526|
|Body mass index, median (lower quartile, upper quartile), kg/m2||29.4 (26.1, 32.1)||32.5 (29.1, 35.9)||<.001a|
|American Society of Anesthesiologists score 1 or 2, No. (%)||38 (41.3)||36 (37.5)||.594|
Perioperative Outcomes by Tibial Component Design
|Outcome||APT (n=92)||Metal-backed (n=96)||P|
|Home discharge, No. (%)||70 (76.1)||83 (86.5)||.068|
|90-day ED visit, No. (%)||9 (9.8)||12 (12.5)||.554|
|90-day readmission, No. (%)||6 (6.5)||5 (5.2)||.701|
|Operative time, median (lower quartile, upper quartile), h||1.6 (1.4, 1.8)||1.8 (1.6, 2.0)||<.001a|
|Postoperative LOS, median (lower quartile, upper quartile), h||43.0 (24.0, 49.8)||42.0 (23.3, 47.0)||.273|