All-Polyethylene Tibial Components: An Analysis of Long-Term Outcomes and Infection

Accepted Manuscript All Polyethylene Tibial Components: An Analysis of Long-Term Outcomes and Infection Matthew T. Houdek, M.D., Eric R. Wagner, M.D., Cody C. Wyles, B.S., Chad D. Watts, M.D., Joseph R. Cass, M.D., Robert T. Trousdale, M.D. PII:

S0883-5403(16)00015-2

DOI:

10.1016/j.arth.2015.12.048

Reference:

YARTH 54890

To appear in:

The Journal of Arthroplasty

Received Date: 4 November 2015 Revised Date:

17 December 2015

Accepted Date: 29 December 2015

Please cite this article as: Houdek MT, Wagner ER, Wyles CC, Watts CD, Cass JR, Trousdale RT, All Polyethylene Tibial Components: An Analysis of Long-Term Outcomes and Infection, The Journal of Arthroplasty (2016), doi: 10.1016/j.arth.2015.12.048. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Title:

All Polyethylene Tibial Components: An Analysis of Long-Term Outcomes and Infection

Authors:

Matthew T. Houdek, M.D. *

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[email protected] Eric R. Wagner, M.D.* [email protected]

[email protected]

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Chad D. Watts, M.D.*

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Cody C. Wyles, B.S.€

[email protected] Joseph R. Cass, M.D.*

[email protected]

Robert T. Trousdale, M.D.* §

Affiliations:

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[email protected] * Mayo Clinic, Department of Orthopedic Surgery

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200 First St. SW, Rochester, MN 55905 € Mayo Graduate School of Medical Eduction

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200 First St. SW, Rochester, MN 55905 § Corresponding Author

Correspondence:

Robert T. Trousdale, M.D. Mayo Clinic, Department of Orthopedic Surgery 200 First St. SW, Rochester, MN 55905 Telephone Number: 507-284-2511 [email protected]

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COI:

No conflicts of interest are declared by any author on this study.

Source of funding:

No disclosures of funding were received for this work from NIH,

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Wellcome Trust, or HHMI.

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Purpose: There is debate regarding tibial component modularity and composition in total knee

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arthroplasty (TKA). Biomechanical studies have suggested improved stress distribution in metal-

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backed tibias; however these results have not translated clinically. The purpose of this study was

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to analyze the outcomes of all-polyethylene components and to compare the results to those with

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metal-backed components.

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Methods: We reviewed 31,939 patients undergoing a primary TKA over a 43-year period (1970-

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2013).

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components. The metal-backed and all-polyethylene groups had comparable demographics with

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respect to gender, age and BMI. Mean follow-up was 7 years.

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There were 28,224 (88%) metal-backed and 3,715 (12%) all-polyethylene tibial

Results: The mean survival for all primary TKA's at the 5-, 10-, 20- and 30-year time points was

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95%, 89%, 73% and 57%, respectively. All-polyethylene tibial components were found to have

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a significantly improved (P<0.0001) survivorship when compared to their metal-backed

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counterparts. All-polyethylene tibial components were also found to have a significantly lower

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rate of infection, instability, tibial component loosening, and periprosthetic fracture. The all-

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polyethylene group had improved survival rates in all age groups, except in patients 85 years old

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or greater, where there was no significant difference. All-polyethylene tibial components had

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improved survival for all BMI groups except in the morbidly obese (BMI ≥40) where there was

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no significant difference.

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Conclusion: All-polyethylene tibial components had significantly improved implant survival,

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reduced rates of postoperative infection, fracture and tibial component loosening. All-

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polyethylene should be considered for the majority of patients, regardless of age and BMI.

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Keywords: total knee arthroplasty; all-polyethylene tibia; metal backed; outcome

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Introduction Total knee arthroplasty (TKA) has been used to successfully treat advanced knee

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degenerative joint disease [1]. Many developed countries are spending billions of dollars per

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year on this procedure [1-4]. In the changing health-care marketplace, the demand for high-

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volume procedures, such as the TKA, has encouraged a search for innovative, cost-effective

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strategies to optimize initial and long-term costs while maintaining reproducible outcomes [1-4].

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As one of the original condylar tibial component designs, the all-polyethylene tibias have

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been demonstrated to produce excellent outcomes, with long-term survivorship over 90% [5-9].

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Despite the highly successful initial clinical outcomes, biomechanical studies performed in the

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1980s questioned the implants durability [10-13]. Furthermore, in 2003 Faris et al. published on

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the results of ACG all polyethylene tibial components and showed the disastrous results of a flat-

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on-flat designed all polyethylene tibia [14]. The combination of the biomechanical studies and

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the results of the ACG study led surgeons to begin to favor metal-backed tibial designs [10-14].

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Although the components were more expensive, it was thought this cost would be offset by the

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biomechanical and technical advantages of modularity [15-17].

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In recent years, multiple studies have shown equivalent or improved long-term

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survivorship of all-polyethylene tibial components compared to their metal-backed counterparts

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[4, 6, 15-21]. Recently our institution published on the influence of various tibial component

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designs and their impact on long-term TKA survivorship [16]. The results of this study showed

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all-polyethylene tibial components had improved survival related to aseptic failure compared to

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metal-backed components [16]. The purpose of this study was to expand on these findings to

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delineate differences between outcomes and survival in all-polyethylene and metal-backed tibial

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components. Specifically this study is different since we focused on; (1) rates of infection, (2)

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tibial component failure subgrouped by body mass index (BMI) and age groups, and (3) rates of

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reoperation and postoperative complications.

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Materials and Methods After obtaining approval from our Institutional Review Board, we performed a review of

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all patients undergoing a primary total knee arthroplasty using our institution’s total joint

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database. This registry prospectively follows patients either in clinic or they are contacted by the

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telephone and/or letter at two and five years, and then every five years thereafter.

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Revision surgery was defined as a surgical procedure where a component of the TKA

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was removed and/or exchanged. Reoperation was defined as a surgical procedure occurring on

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the TKA where components were not removed or exchanged. It is possible that a patient could

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have a reoperation or revision surgery which was not performed at our institution, and therefore

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has not been recorded by the joints registry at our institution.

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superficial (above the fascia) or deep (below the fascia). The diagnosis of a deep infection was

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also based on the definition of a periprosthetic joint infection as established by the

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Musculoskeletal Infection Society [22]. Complications are captured in the registry if they are

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recorded in the patients’ medical record, as such complications can be missed if there is not

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adequate documentation. In an attempt to match the patient cohorts for the overall survival

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analysis, they were subgrouped based on BMI and age at the time of surgery. Complications

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analyzed were noted in the patients’ clinical registry record included infection, periprosthetic

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fracture, flexion contracture, tibial and femoral component loosening, osteolysis and component

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fracture were analyzed.

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Infection was defined as

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Patients undergoing unicompartmental procedures, revisions of prior arthroplasty

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procedures or undergoing a TKA for an oncological diagnosis were excluded. Over a forty-three

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year period (1970-2013), 31,939 patients were included in this analysis, including 28,224 (88%)

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metal-backed and 3,715 (12%) all-polyethylene tibial components (Table 1). The metal-backed

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group was 57% (n=16,099) female, with a mean age of 67 years (range 13-101 years) and mean

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BMI of 31.6 (range 14.1-72.7). There were 48% (n=13,477) cruciate retaining (CR) metal-

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backed implants. The all-polyethylene group was 57% female (n=2,117), with a mean age of 71

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years (range 21-99 years) and mean BMI of 31.1 (range 16.2-59.5). In the all-polyethylene

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group, 28% (n=1,058) were CR designed knees. The most common preoperative diagnosis was

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degenerative joint disease in the metal-backed (n=23,691, 74%) and all-polyethylene (n=3,334,

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90%) groups. The mean follow-up over this period was 7 years (range 1-40 years). Patients in

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the all-polyethylene group were older (71 years vs. 67 years, P<0.0001), had a lower BMI (31.1

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vs. 31.6, P<0.0001), more likely to have a diagnosis of osteoarthritis (87% vs. 81%, P<0.0001)

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and had more cruciate substituting (CS) designed knees (72% vs. 52%, P<0.0001). There was

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no significant difference in gender composition of the cohorts (P=1.0).

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Statistical Analysis

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Kaplan-Meier survival method was used to make survival estimates, with comparisons

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between the metal-backed and all-polyethylene components performed using the log-rank test.

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Proportional hazard regression analysis was performed to assess the association of clinically

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interesting covariates with the risk of implant failure, reinfection, and reoperation. Continuous

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variables were compared using unpaired Student T-tests and categorical variables were

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compared with the Fisher Exact tests and Odds Ratios. All statistic calculations were made using

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JMP version 10 (Statistical Analysis Software, Cary, NC) with statistical significance set at a P-

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value <0.05.

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Source of Funding

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No external source of funding was used for this study.

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Results

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Revision Surgery

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Over the course of the study, 2,973 knees (9.3%) were revised for any reason at a mean

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of 7 years (range 1 week to 35 years) postoperatively. The overall revision-free survival for all

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primary TKA’s at the 5-, 10-, 20- and 30-year time points were 95%, 89%, 73% and 57%,

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respectively. The use of a metal-backed tibial component was associated with a significantly

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increased risk of revision (HR 3.41, P<0.0001) (Table 2). All-polyethylene tibial components

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had significantly improved survivorship compared to metal-backed components across all-time

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points (p<0.0001), including 5-, 10-, 20- and 30-year survival of 98% vs 94%, 96% vs 88%, 91%

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vs 72%, and 83% vs 55%, respectively (Figure 1).

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In comparing CS to CR designs, there was a significantly greater risk of revision surgery

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(HR 3.28, P<0.0001) for metal backed CS tibias compared to all-polyethylene CS tibias.

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Likewise metal-backed CR designs had significantly increased risk of revision (HR 3.01,

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P<0.0001) compared to all-polyethylene CR tibial components.

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Aseptic Revision

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After removing the patients who were revised for prosthetic joint infections, a

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significantly increased risk of revision for mechanical failure was maintained in the metal-

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backed tibial components (HR 3.80, P<0.0001). All-polyethylene tibial components had

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significantly improved survivorship free of revision for mechanical failure compared to metal-

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backed components across all-time points (p<0.0001), with 5-, 10-, 20- and 30-year survival of

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99% vs 96%, 97% vs 90%, 92% vs 74%, and 86% vs 59%, respectively (Figure 1). Subgroup

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analysis was performed of the aseptic revision-free survival of all-polyethylene and metal backed

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tibial components based on age, dividing the patients into every age group every 10 years. The

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all-polyethylene tibial components showed improved survival across all age groups, except in

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patients 85 years or older where there was no difference in outcomes (Table 3). Likewise, all-

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polyethylene tibial components had significantly improved revision free survivorship across all

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BMI’s when subdivided into commonly used cutoffs for BMI, except for patients with morbid

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obesity (BMI ≥40), where there was no difference in revision-free survival (Table 3).

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An isolated polyethylene exchange was performed in 166 (5.7%) of the metal-backed

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tibia revisions. Indications for this revision included instability (n=60), wear of the polyethylene

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(n= 99), or to improve motion (n=7). None of these patients required a further revision surgery.

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Infection

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Eight hundred fifty-eight (2.7%) patients were diagnosed with a postoperative infection

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(superficial or deep) at a mean 3 years (range 3 days to 29 years) postoperative. The overall

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infection-free survival following primary TKA at the 5-, 10-, 20- and 30-year time points were

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98%, 97%, 95% and 93%. This cohort consisted of 803 metal-backed (2.5%) and 55 all-

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polyethylene (0.2%) components. The use of a metal-backed tibial component was associated

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with a significantly increased risk of postoperative infection (HR 1.60, P<0.0003).

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polyethylene tibial components had improved infection-free survivorship compared to metal-

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backed components across all-time points, with 5-, 10-, 20- and 30-year infection free survival of

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99% vs. 97%, 98% vs. 97%, 98% vs. 95%, and 96% vs. 93%, respectively (p=0.0007) (Figure

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1). Furthermore, patients with an all-polyethylene tibial component had a reduced incidence of

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both deep infection (OR 0.46, P<0.0001) and superficial infection (OR 0.62, P=0.04). In

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All-

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comparing the patients with an infection of an all-polyethylene or metal-backed tibia, there was

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no difference in the mean BMI (32.2 vs. 32.6, P=0.71), percentage of male patients (49% vs.

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48%, P=1.0) or preoperative diagnosis (Table 4).

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tibial component were significantly older than patients with a metal-backed tibial component (71

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years vs. 64 years, P=0.0001). Likewise there were significantly more CS implants in the all-

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polyethylene group compared to the metal-backed group (73% vs. 49%, P=0.0007). Although

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there were more patients with CS implants in the all-polyethylene group, in the all-polyethylene

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group having a CS implant did not increase the risk of infection (HR 1.34, P=0.32).

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Patients with an infected all-polyethylene

With infection as an end point, besides the composition of the tibial component, cruciate

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substituting (CS) implants, male sex, obesity (BMI ≥30), younger age (≤64 years), and a

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preoperative diagnosis of rheumatoid or post-traumatic arthritis significantly increased the risk of

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infection (Table 5).

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Reoperation

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Over the course of the study, 4,297 patients (13.4%) underwent a reoperation for any

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reason at a mean 5-years (range day of primary surgery to 35 years) postoperative. The overall

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reoperation-free survival following primary TKA at the 5-, 10-, 20- and 30-year time points were

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91%, 85%, 68% and 51%. This cohort consisted of 4,806 metal-backed (15%) and 211 all-

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polyethylene (6%) components. The use of a metal-backed tibial component was associated with

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an increased risk of reoperation (HR 1.84, P<0.0001). All-polyethylene tibial components had

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significantly improved survivorship compared to metal-backed components across all-time

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points (p<0.0001), including 5-, 10-, 20- and 30-year reoperation free survival of 94% vs. 91%,

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92% vs. 84%, 86% vs.64%, and 76% vs. 50%, respectively (Figure 1).

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Complications

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Postoperative complications occurred in 8,647 (27%) patients. Overall there was no

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difference in the risk of a postoperative complication between the all-polyethylene and metal

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backed tibia groups (HR 0.96, P=0.31).

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complications it was found that patients with an all-polyethylene tibial component were less

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likely to have isolated tibial component loosening (OR 0.08, P<0.0001), femoral component

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loosening (OR 0.18, P0.0002), tibial osteolysis (OR 0.03, P<0.0001), femoral osteolysis (OR

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0.06, P=0.0007), femoral periprosthetic fracture (OR 0.58, P=0.005) and tibial component

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fracture (OR 0.12, P=0.001). However, the all-polyethylene tibial components were more likely

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to have a postoperative flexion contracture (OR 1.64, P<0.0001) compared to patients with metal

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backed tibias (Table 6).

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Discussion

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There remains debate with regards to the optimal composition and the indication for

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different tibial components in TKA. Metal-backed components have been the primary

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component used over the last couple decades due to its modularity, improved in vitro

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biomechanical outcomes, and superior results when compared to a poorly designed all-

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polyethylene tibial component [10, 11, 13, 14, 23]. Alternatively, studies have suggested

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improved overall survivorship with all-polyethylene tibial components compared to metal-

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backed counterparts [4, 16]. The purpose of this study was to examine the component survival,

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rates of infection, complications, and reoperations between all-polyethylene tibial components

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and metal-backed components from one large institutions total joints registry. The results of this

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study show that all-polyethylene tibial components outperform their metal-backed counterparts

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in terms of overall survival, risk of infection and required fewer reoperations.

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There are several limitations to our study. The data were examined retrospectively and

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were limited to the information contained in the total joints registry and medical record;

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however, the prospective registry data helps to reduce recall and selection bias of the study.

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With only 12% of the population in this study having an all-polyethylene tibial component, there

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is obvious selection bias. The senior author uses an all-polyethylene tibia component for nearly

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all his patients and reserves a metal-backed component for patients with severely osteopenic

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bone or where the bone of the proximal tibia has been previously compromised. Likewise

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activity level was not assessed in this study, which could have played an important factor in

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choosing an all-polyethylene tibial component, leading to selection bias. This study is limited to

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a single institution with multiple surgeons performing the operation. However a vast majority of

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the surgeons performing the procedure were adult reconstruction trained subspecialty surgeons.

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The sample does include implants that are no longer available for use in the United States but at

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all points both metal-backed and all polyethylene components were available.

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Revision-free survival was improved in all-polyethylene components compared to metal-

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backed components due to septic and aseptic etiologies. This expands on the results previously

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published by our institution in an attempt to further understand the improved survivorship of all-

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polyethylene tibial components [16]. It has been proposed that all-polyethylene tibial

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components should be reserved for older and non-obese patients [6, 8, 9, 12]. The results of this

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study do not support this notion, with the all-polyethylene components having improved or

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equivalent survivorship across all BMIs and ages when subgrouped according to commonly used

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cutoffs.

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To date only one study has clinically demonstrated improved survivorship of metal-

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backed components compared to all-polyethylene components [14]. This was found in a poorly

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designed flat all-polyethylene tibial component which increased peripheral-edge loading, leading

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to failure [14]. In addition to the improved survivorship of all-polyethylene tibial components, it

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has been shown that cost of an all-polyethylene tibial component is less than metal-backed

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designs, highlighted by a projected annual $39 million dollar savings to the National Health

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Systems of England and Wales if only half of the TKAs used in their system were all-

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polyethylene [15, 19, 24].

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The use of all-polyethylene tibial components in obese patients is a subject of

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controversy [6, 8, 9, 12]. . In patients with a BMI less than 37.5, Toman and colleagues found

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no difference in survival of all-polyethylene tibial components compared to metal-backed

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components [6]. Likewise, in an analysis of only all-polyethylene tibial components, Dalury et

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al. found all-polyethylene tibial components could be successfully used in obese patients [25]. In

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our analysis, subgroup analysis using commonly used BMI cutoffs, there was improved

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survivorship across all BMIs using all-polyethylene components, except in the morbidly obese

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where there was no significant difference in survival.

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Likewise, although all-polyethylene tibial components have historically been

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recommended for elderly patients, the results of this study demonstrates that their use can be

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expanded to younger patients [5, 8, 12]. Ranawat and colleagues found that all-polyethylene

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tibial components can be successfully used in patients less than 60, however this study did not

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have a comparison group [5]. Survivorship of all-polyethylene tibial components was improved

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compared to metal-backed components in our study across all age groups, except in patients 85

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or older, where there was no difference in outcomes.

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One of the theoretical advantages of a modular metal-backed component is the ability to

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perform isolated exchanges of the polyethylene component, however this form of revision made

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up a small percentage (5.7%) of patients undergoing a revision surgery. Although this was

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successful for these patients, we feel this theoretical advantage should not be a primary factor for

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using a metal-backed tibial component. Infection is the most common indication for revision TKA in the United States [26].

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Treatment of prosthetic joint infections (PJI) require substantial resources, and are typically

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associated with relatively poor patient outcomes in single- and two-stage revision procedures

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compared to the results of revision TKA for aseptic failure [26-35]. The finding that all-

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polyethylene tibial components have a lower risk of postoperative infection compared to metal-

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backed components has been recently reported in the Swedish Knee Arthroplasty Register

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(SKAR) [20]. However, the authors felt this finding was limited due to the ability to capture

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infections that did not lead to a revision arthroplasty [20].

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Unlike the SKAR, our data includes patients with postoperative infections treated

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nonoperatively with antibiotics or irrigation and debridement only, in addition to those treated

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with revision surgery. In further breaking down potential confounding factors to this finding, we

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found no difference in previously established risk factors for PJI between these two groups,

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including male gender, BMI, and diagnosis of rheumatoid arthritis [36-38]. We did find a

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difference in the number of patients with CS versus CR knees however, with the all polyethylene

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group having a significantly greater number of CS knees. In further subgroup analysis of our

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data, CS knees were at increased risk for infection. However this seems to be negated in patients

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with all polyethylene tibial designs, as there was a reduced risk for infection overall, even with

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the greater number of CS knees. Likewise there was no difference in the number of patients with

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either a wound dehiscence or delayed wound healing, both risk factors for a postoperative

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infection [36-38].

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As the infection rate was lower without any obvious confounding variable,

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the results show that TKA with all-polyethylene tibial components is less prone to infection

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compared to TKA with metal-backed components. Although the mechanism for this increased

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risk in metal-backed components is not well understood, one possible explanation could be

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related to particulate metal and polyethylene debris that accumulates in metal-backed

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components. This may cause a relative synovitis, effusion, hyperemia and an impaired immune

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response, making the knee a “prosthesis at risk” for the development of PJI [39, 40].

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Complications were common following a TKA in our study, with 1 in 4 patients having a

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postoperative complication. Besides infection, patients in the metal-backed tibia group were

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more likely to have a postoperative complication related to the tibial and femoral component,

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including fracture, osteolysis, and loosening. A known complication for metal-backed modular

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knee implants is back-side wear of the polyethylene insert due to micromotion at this interface,

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leading to osteolysis [41-45]. In studies comparing all-polyethylene and metal-backed tibial

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designs, back-side wear leading to osteolysis and loosening has been proposed as one of the

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factors that leads to poorer outcomes with the metal-backed designs [46]. We found a higher rate

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of postoperative flexion contractures in patients with all-polyethylene tibial components. We feel

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this is an inherent disadvantage to the implant, as once the implant size is selected and cemented;

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the surgeon is unable to easily change the size of the polyethylene component.

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Overall the results of this study show all-polyethylene components were associated with a

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lower rate of revision for infection and mechanical failure, and reoperation. We feel the all-

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polyethylene tibial component provides a durable, long-term option for primary total knee

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arthroplasty and should be considered in the majority of patients undergoing this procedure.

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Medicare beneficiaries, 1991-2010. JAMA, 2012. 308(12): p. 1227-36.

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Cram, P., et al., Total knee arthroplasty volume, utilization, and outcomes among

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Voigt, J. and M. Mosier, Cemented all-polyethylene and metal-backed polyethylene tibial components used for primary total knee arthroplasty: a systematic review of the literature

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Dalury, D.F., et al., Midterm results of all-polyethylene tibial components in primary

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Bartel, D.L., V.L. Bicknell, and T.M. Wright, The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint

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Rodriguez, J.A., et al., Metal-backed and all-polyethylene tibial components in total knee

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M AN U

SC

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replacement. Clinical orthopaedics and related research, 2001(392): p. 174-83.

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AC C

384

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Table 1: Comparison of Patients in Metal Backed to All-Polyethylene Tibial Component Groups All-Polyethylene

Metal-Backed

P Value

Number of Patients

3,715

28,224

Number of Females

2,117 (57%)

16,099 (57%)

Number Males

1,598 (43%)

12,125 (43%)

Mean Age at Surgery (Years)

71 (range 21-99)

67 (range 13-101)

<0.0001

Mean Body Mass Index (kg/m2)

31.1 (range 16.2-59.5)

31.6 (range 14.1-72.7)

<0.0001

Cruciate Substituting Implant

2,657 (72%)

14,747 (52%)

Cruciate Retaining Implant

1,058 (28%)

Diagnosis of Osteoarthritis

3,228 (87%)

Diagnosis of Rheumatoid Arthritis

232 (6%)

3,440 (12%)

<0.0001

Posttraumatic Arthritis

221 (6%)

1,764 (6%)

0.49

SC

<0.0001

13,477 (48%)

22,795 (81%)

M AN U

TE D EP AC C

RI PT

1.0

<0.0001

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Table 2: Comparison of Outcomes of Metal Backed to All-Polyethylene Tibial Components HR (95% CI)

P Value

Aseptic Failure

3.80 (2.91-5.08)

<0.0001

Revision Total Knee Arthroplasty

3.41 (2.72-4.34)

<0.0001

Reoperation

1.84 (1.61-2.13)

<0.0001

Postoperative Infection

1.60 (1.22-2.12)

Postoperative Complications

0.96 (0.89-1.03)

RI PT

Outcome

0.0003

AC C

EP

TE D

M AN U

SC

0.31

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Table 3: Component Survivorship Based on Age and BMI No. at 5-Year 10-Year 20-Year Age (Years) risk Survivorship* Survivorship* Survivorship*

30-Year P Survivorship* Value

≤45 45 811

94% (+/- 4) 87% (+/- 1)

86% (+/- 7) 76% (+/- 2)

80% (+/- 8) 48% (+/- 3)

70% (+/- 12) 35% (+/- 3)

0.01

182 2,262

99% (+/- 1) 91% (+/- 1)

99% (+/- 1) 81% (+/- 1)

90% (+/- 6) 60% (+/- 2)

82% (+/- 9) 44% (+/- 5)

<0.0001

603 6,551

99% (+/- 1) 93% (+/- 1)

95% (+/- 2) 84% (+/- 1)

86% (+/- 4) 64% (+/- 2)

78% (+/- 7) 52% (+/- 3)

<0.0001

1,386 11,610

98% (+/- 1) 96% (+/- 1)

96% (+/- 1) 91% (+/- 1)

94% (+/- 1) 80% (+/- 1)

94% (+/- 1) 76% (+/- 1)

<0.0001

1,309 6,289

99% (+/- 1) 96% (+/- 1)

99% (+/- 1) 94% (+/- 1)

99% (+/- 1) 90% (+/- 4)

-

<0.0001

190 693

99% (+/- 1) 98% (+/- 1)

99% (+/- 1) 96% (+/- 1)

-

-

0.16

461 2,594

98% (+/- 1) 96% (+/- 1)

97% (+/- 1) 92% (+/- 1)

97% (+/- 1) 77% (+/- 2)

-

0.005

1,152 6,680

99% (+/- 1) 96% (+/- 1)

98% (+/- 1) 92% (+/- 1)

97% (+/- 1) 75% (+/- 2)

-

<0.0001

97% (+/- 1) 93% (+/- 1)

97% (+/- 1) 80% (+/- 1)

-

0.0002

-

<0.0001

-

0.20

RI PT

All Polyethylene Metal Backed 45-54 All Polyethylene Metal Backed

All Polyethylene Metal Backed ≥85 All Polyethylene Metal Backed Body Mass Index <25 All Polyethylene Metal Backed All Polyethylene Metal Backed 30-35

1,021 6,142

98% (+/- 1) 96% (+/- 1)

AC C

All Polyethylene Metal Backed

EP

25-30

TE D

75-84

M AN U

All Polyethylene Metal Backed 65-74 All Polyethylene Metal Backed

SC

55-64

35-40 All Polyethylene 508 99% (+/- 1) 98% (+/- 1) 96% (+/- 2) Metal Backed 3,004 95% (+/- 1) 90% (+/- 1) 69% (+/- 3) >40 All Polyethylene 243 96% (+/- 1) 93% (+/- 3) Metal Backed 2,074 93% (+/- 1) 90% (+/- 1) 79% (+/- 4) *Values are given as the Kaplan-Meier survival estimate (+/- Standard Error)

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Table 4: Comparison of Patients with an Infection following TKA based on Tibial Component Metal Backed Tibia (n=803)

P Value

Mean Age (Years)

71

64

0.0001

Mean Body Mass Index (BMI)

32.2

32.6

0.71

% Male

49%

48%

1.0

Cruciate Substituting Implant

40 (73%)

393 (49%)

0.0007

Diagnosis of Degenerative Joint Disease

46 (84%)

584 (73%)

0.08

Diagnosis of Rheumatoid Arthritis

5 (9%)

153 (19%)

0.07

Diagnosis of Post-traumatic Arthritis

4 (7%)

89 (11%)

0.50

Time to Infection

3.7 years

5 years

0.07

AC C

EP

TE D

M AN U

SC

RI PT

All Polyethylene (n=55)

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Table 5: Analysis of Risk Factors for Postoperative Infection: Preoperative Factor

Hazard Ratio (95% CI)

P Value

Tibial Component Metal Backed

1.60 (1.23-2.13)

All-Polyethylene

0.62 (0.46-0.81)

Cruciate Retaining Implant

0.82 (0.71-0.94)

Cruciate Substituting Implant

1.21 (1.05-1.39)

RI PT

0.0003

Gender Male

1.31(1.14-1.49)

Female

0.76 (0.66-0.87)

SC

0.005

M AN U

<0.0001

Age

2.32 (1.76-2.99)

<0.0001

45-54 years

1.35 (1.08-1.67)

0.008

55-64 years

1.12 (0.95-1.30)

0.14

65-74 years

0.81 (0.70-0.93)

0.003

TE D

≤45 years

75-84 years ≥85 years

EP

Body Mass Index

0.80 (0.67-0.95)

0.01

0.93 (0.55-1.46)

0.79

Non-obese (BMI <30)

0.82 (0.69-0.96)

Obese (BMI ≥30)

1.21 (1.03-1.46)

Morbid Obesity (BMI ≥40)

0.01 <0.0001

Degenerative Joint Disease (DJD)

0.54 (0.46-0.63)

<0.0001

Rheumatoid Arthritis

1.44 (1.20-1.71)

<0.0001

Post-Traumatic Arthritis

2.11 (1.69-2.60)

<0.0001

AC C

1.95 (1.56-2.42)

Reason for Total Knee

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Table 6: Comparison of Postoperative Complications between All-Polyethylene and Metal Backed Tibial Components All-Polyethylene (n=3,715)

Metal-Backed (n=28,224)

Odds Ratio (95% CI)

P value

Infection

55 (1.4%)

803 (2.8%)

0.51 (0.39-0.67)

<0.0001

Superficial Infection

22 (0.6%)

267 (0.9%)

0.62 (0.40-0.96)

0.04

Deep Infection

35 (0.9%)

571 (2.0%)

0.46 (0.32-0.64)

<0.0001

Tibial Component Loosening

7 (0.02%)

669 (2.4%)

0.08 (0.03-0.16)

<0.0001

Femoral Component Loosening

4 (0.01%)

166 (0.6%)

0.18 (0.06-0.49)

0.0002

Tibial Component Fracture

2 (0.05%)

118 (0.4%)

0.12 (0.03-0.51)

0.001

Tibial Osteolysis

1 (0.02%)

210 (0.7%)

0.03 (0.005-0.25)

<0.0001

Femoral Osteolysis

1 (0.02%)

110 (0.4%)

0.06 (0.009-0.49)

0.0007

172 (4.6%)

806 (2.8%)

1.64 (1.39-1.95)

<0.0001

Femoral Periprosthetic Fracture

31 (0.8%)

398 (1.4%)

0.58 (0.40-0.84)

0.005

Hematoma

60 (1.6%)

559 (1.9%)

0.81 (0.62-1.06)

0.14

21 (0.5%)

142 (0.5%)

1.12 (0.71-1.78)

0.70

Delayed Wound Healing

59 (1.6%)

394 (1.4%)

1.13 (0.86-1.50)

0.38

DVT/PE

83 (2.2%)

507 (1.8%)

1.24 (0.98-1.57)

0.07

Tibial Periprosthetic Fracture

13 (0.3%)

151 (0.5%)

0.65 (0.36-1.14)

0.17

SC

M AN U

TE D

AC C

Wound Dehiscence

EP

Flexion Contracture

RI PT

Complication

AC C

EP

TE D

M AN U

SC

RI PT

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