AbstractA systematic review was conducted to evaluate the clinical performance of the Vanguard® Complete Knee System (Biomet, Warsaw, IN). A total of 15 data sources were identified, which included published and unpublished clinical studies and National Joint Registry (NJR) annual reports. The performance parameters of interest were implant survivorship and clinical patient outcomes.
A comparison of implant survivorship between the Vanguard® Knee and various baselines of total knee arthroplasty (TKA) shows that the performance of the Vanguard® Knee, with various fixation options, is comparable to that of overall TKA and competitive TKA products.1–15 The analysis of patient clinical outcomes, American Knee Society Score (AKSS), shows that the majority of patients who received the Vanguard® Knee achieved good to excellent function with demonstrated survivorship of 97.7% at 5 years in over 16,000 knees.1–15
IntroductionThe proven clinical heritage of the AGC,® Maxim,® and Ascent™ Total Knee Systems16–18 and the combined state-of-the-art design features have allowed Biomet to produce the most comprehensive total knee replacement system on the market. Introduced in 2003, the Vanguard® Complete Knee System offers the flexibility to change from a cruciate retaining (CR) to a posterior stabilized (PS) within a single system, while also featuring optimal congruency in the coronal plane resulting in 1:1 conformity and allowing complete interchangeability between femoral and tibial components.
Device DescriptionThe Vanguard® Complete Knee System consists of four main components: femoral component, tibial tray, tibial bearing and patellar component. For the purpose of this systematic review, both fixed and mobile bearing Vanguard® Knee designs are included.
Vanguard® Knee Fixed Bearing Construct Design (Figure 1):
1. Anatomically specific, cobalt chrome femoral component
• Available in 10 sizes from 55 to 80 mm, inaverage 2.4 mm increments M/L and average 2.3 mm increments A/P, with both CR and PS options, available for either cemented or cementless fixation.
2. Tibial tray • Available as either a titanium alloy baseplate
(with modular stems for cemented or cementless fixation) or cobalt chrome alloy baseplate (with fixed I-beam or cruciate fin for cemented fixation).
• Availablein9sizeswithconsistent4mmM/Lincrements from 59 to 91 mm.
3. ArCom® Direct Compression Molded (DCM) Ultra High Molecular Weight Polyethylene (UHMWPE) tibial bearing
• AvailableinthreeCRoptions:CR,CRLippedand Anterior Stabilized (AS); and two PS options: PS and PS+, with up to 6 sizes per type and up to 8 thicknesses per size.
• The CR and PS femoral components featurecomplete size interchangeability with their respective primary bearings, with the exception of the AS bearing.
A Systematic Review on Performance of the Vanguard® Complete Knee System
Author: Jing Xie, Ph.D.
June 30, 2011
Fig. 1Vanguard® PS Fixed Bearing Construct
2•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
4. Dome-shaped ArCom® UHMWPE patellar component
• Available in multiple diameters, thicknessesand peg configurations.
Table 1. Fixed and Mobile Bearing Vanguard® Knees Included in the Study
Vanguard® Knees1–15
Number of Cases Analyzed
Percentage
Fixed Bearing 13848 84%
Fixed Bearing Monobloc*
1848 11%
Mobile Bearing* (Deep Dish,
Vanguard® ROCC and Vanguard®
Highflex RP)
862 5%
TOTAL 16558 100%
*have NOT been cleared or approved in the US by the FDA
Materials and Methods
Dataset Identification and Appraisal Datasets relevant to the Vanguard® System were searched from three sources: published literature, clinical experience and clinical investigation. Clinical experience includes data from post-market clinical studies and NJR data and annual reports. Any clinical investigations such as regulated pre-market clinical studies were also searched. Only datasets available in English were included.
A set of potential datasets were identified which contained data on the Vanguard® Knee. Each dataset was appraised based on suitability for contribution to the assessment of performance of the Vanguard® Knee. Specifically, data suitability was examined based on:
1. Whether the dataset was generated from a patient population where the Vanguard® Knee was the treatment intention AND
2. Whether the dataset contained information on implant survivorship and AKSS which could be used to assess the performance of the Vanguard® Knee
Additionally, contribution assessment included an evaluation of the study design in the data collection (e.g. randomized controlled, consecutive case series, etc.), specific measures collected (e.g. revision, AKSS, length of follow-up and poolability). This assessment helps determine how each dataset was utilized in assessing safety and performance of the Vanguard® Complete Knee System. Appendix 1 summarizes the datasets chosen to be included in this review and the corresponding suitability and contribution assessment.
Fig. 2Vanguard® CR Rotating Platform Construct
Vanguard® Knee Rotating Platform Construct Design (Figure 2):
1. Anatomically specific, cobalt chrome femoral component
• Available in 10 sizes from 55 to 80 mm, inaverage 2.4 mm increments M/L and average 2.3 mm increments A/P, available for cemented fixation only.
2. Central cone tibial tray • Central tibial tray design offered in cobalt
chrome alloy with three surface finishes: Interlok® finish on the fixation surface, polished planar articulating surface and the bore has a satin finish.
• Available in9different sizeswithconsistent4mm M/L increments from 59 to 91 mm. The 59, 63 and 67 mm trays feature a 35 mm long tapered stem with 4 ribs, while the remaining sizes feature 40 mm long tapered stem with 4 ribs.
3. ArCom® Direct Compression Molded (DCM) Ultra High Molecular Weight Polyethylene (UHMWPE) tibial bearing
• Vanguard® Rotating Platform deep-dish bearings are offered in nine symmetrical sizes that correspond to femoral component sizes.
• Bearings articulate with any size tibial tray;however, bearing overhang will occur with significant bearing/tray mismatch.
4. Dome-shaped ArCom® UHMWPE patellar component
• Available in multiple diameters, thicknessesand peg configurations.
3•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
For implant survivorship analysis, revisions for any reasons will be included. When data is available at the case level, it will be used for overall data pooling. If the data was available in summary form only, data pooling was performed whenever possible employing statistical method by Sutton et al 19; otherwise it will be reported as is.
III. Patient Clinical Outcomes - AKSSThe AKSS, developed by The Hospital for Special Surgery, consists of a functional measurement and a composite measure of knee pain, stability and range of motion. The maximum function score is 100 which can be obtained by a patient who can walk an unlimited distance and can go up and down stairs normally. The maximum composite is also 100 which can be obtained from a knee that is well aligned with no pain, can achieve 125° of motion and negligible anteroposterior and mediolateral instability. This tool is used to evaluate patient satisfaction post TKA. The endpoint considered for this analysis was the sum of the function and composite measures, thus a maximum of 200 points would be allowed at any one assessment.
BaselinesTo establish the comparative performance of the Vanguard® Knee, implant survivorship will be further compared to that of baseline as reported in NJR annual reports and included the following variants within TKA:
1. TKA product family per NJRs
2. Pooled competitive TKA products
Data Analysis
I. DemographicsOverall gender was collected in all subsets and summarized in Table 2. The gender distribution is similar to that reported in various NJRs.
Table 2. Gender Distribution1–15
Male Female
All Vanguard® Knees
42% (5535/13140)*
58% (7605/13140)*
AOANJRR 43% 57%
SKAR** 42% 58%
UKNJR 43% 57%
NZNJR 48% 52%
*based on datasets reporting gender**based on graphic information reported 2009
II. Implant SurvivorshipImplant survivorship was analyzed using three methods:
1. Raw Revision RateRaw Revision Rate was used to calculate the unadjusted percentage of implants known to have failed. This rate does not take into consideration implant survival time for all cases, including those that did not fail. This factor is critical for accurate device performance evaluation.
2. Cumulative Survival Rate – Kaplan-Meier CurveCumulative Survival Rate uses implant survival time to calculate an estimate on the fraction of implants survived over a certain period of time. However, this calculation, when derived from several datasets cannot be standardized due to variation in the length of follow-up.
3. Revision per 100 Observed Component Year (OCY)The formula for this calculation is:
Number of Revisions for any reason X 100Total Number of Observed Component Year
Where Total Number of Observed Component Year = ∑n
i =1 individual years from implantation
This method allows for comparison among datasets where the calculation has been adjusted for the two main factors influencing the value of individual cohorts: number of cases and number of days in the follow-up period. Revision per 100 OCY was introduced to orthopedic research in Australian National Joint Registry and has been adopted by the New Zealand National Joint Registry and the European Arthroplasty Register as a standard method of reporting revision rates.
4•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
Results
Implant SurvivorshipImplant survivorship analysis was performed using a total of 13 datasets. The results on Raw Revision Rate and Revision per 100 Observed Component Years are presented in Table 3. Sensitivity analysis was conducted to assess how each dataset’s contribution impacts the results from data pooling as shown in Table 4.
Table 3. Raw Revision Rate and Revision per 100 OCY – Vanguard® Knee1–10,12,14–15
Total No. of Cases Analyzed
Total No. of Revisions
Raw Revision Rate
Total No. of Cases Reported
Survival Time
Total No. of Revisions
Reported Survival Time
Total No. of Component Year
Revision per 100 OCY (95% CI)
13877 1320.95
(0.79, 1.11)13757 130 24193
0.54 (0.45, 0.64)
Table 4. Sensitivity Analysis of Each Contributing Dataset1–10,12,14–15
Dataset ExcludedNumber of Cases
ExcludedRevision Excluded
OCY ExcludedRaw Revision Rate Percent
Revision per 100 OCY
1 70 0 150.8138 0.96 (0.79, 1.12) 0.55 (0.46, 0.65)
4 43 0 31.46663 0.95 (0.79, 1.12) 0.55 (0.46, 0.65)
6 600 10 2131.85 0.92 (0.75, 1.09) 0.55 (0.46, 0.66)
7 265 0 248.32 0.97 (0.80, 1.14) 0.55 (0.46, 0.65)
9 294 0 348.2 0.97 (0.80, 1.14) 0.55 (0.46, 0.66)
10 81 1 82.28057 0.95 (0.78, 1.12) 0.54 (0.45, 0.64)
11 357 6 1768.022 0.93 (0.77, 1.10) 0.56 (0.47, 070)
12 1101 8 2769.767 0.97 (0.80, 1.15) 0.58 (0.48, 0.69)
14 6659 40 10417.29 1.27 (1.01, 1.54) 0.67 (0.54, 0.82)
15 4009 58 5786 0.75 (0.57, 0.93) 0.40 (0.32, 0.50)
17 120 2 NA 0.94 (0.78, 1.10) NA
20 237 4 312 0.94 (0.77, 1.10) 0.54 (0.45, 0.64)
21 41 3 147.3305 0.93 (0.77, 1.10) 0.54 (0.45, 0.64)
5•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
Kaplan-Meier survival analyses were conducted for each of the 10 datasets which had: 1) Case level data or poolable summarized and 2) A minimum of 1 year survival data. The Vanguard® Knee demonstrated excellent survival with this data, demonstrating an overall survivorship of 97.7% at 5 years (Table 5).1,3–5,7–10,13,15 Kaplan-Meier survival analysis for each dataset performed equally well as shown in Table 6.1,3–5,7–10,13,15
Table 5. Kaplan-Meier Survival Analysis – Pooled Survivorship (95% CI)1,3–5,7–10,13,15
No. of Cases
Year 1 Year 3 Year 5
16201 99.5 (99, 100) 98.7 (97.9, 99.5) 97.7 (95.8, 99.7)
Table 6. Kaplan-Meier Survival Analysis – Individual Datasets Survivorship (95% CI)1,3–5,7–10,13,15
Dataset Year 1 Year 3 Year 5
VGDS6 99.7 (98.7, 99.9) 98.8 (97.6, 99.4) 97.2 (94.3, 98.6)
VGDS11 99.2 (97.4, 99.7) 98.5 (96.5, 99.4) 98.2 (96.0, 99.2)
VGDS12 99.5 (98.9, 99.8) 99.1 (98.1, 99.6)
VGDS14 99.7 (99.5, 99.8) 98.6 (98.0, 99.0)
VGDS21 97.6 (83.9, 99.7) 94.7 (80.3, 98.7)
VGDS1 100
VGDS9 100
VGDS7 100
AOANJRR 98.8 (98.2, 99.3) 97.2 (95.5, 98.2)
AOANJRR 99.4 (97.6, 99.8) 97.8 (95.2, 99.0)
AOANJRR 98.8 (97.9, 99.4) 97.2 (95.6, 98.2)
AOANJRR 99.7 (98.1, 100)
Danish NJR
95.6 (94.4, 96.8)
Figure 3 illustrates the distribution of the cumulative survival rates based on datasets with case-level details, a total of 9511 cases. This survival curve further confirms the excellent survival for the Vanguard® Knee.1,3–5,7–9,13–15
Fig. 3Vanguard® Knee Cumulative Survival Rate Distribution
10
Follow up Time
95% Confidence LimitsCensoredS
urvi
val P
rob
abili
ty
2 3 4 50.0
0.2
0.4
0.6
0.8
1.0
6•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
The Swedish and Danish Registries have also reported Vanguard® Knee performance in comparison to the AGC® Knee. Since the parameters used for performance reporting in these registries are different and cannot be pooled with other Vanguard® Knee datasets, they are reported as is in Table 7.
Table 7. Risk of Revision11,13
NJR Condition Reference Vanguard® Knees Risk of Revision 95% CI
Swedish OA/TKA AGC® 924 1.63 0.98, 2.71
Swedish RA/TKA AGC® 49 2.58 0.56, 11.84
Danish ALL AGC® V2 2071 1.10 0.82, 1.48
Comparison to BaselinesA comparison between implant survivorship of the Vanguard® Knee and baselines was also conducted. Baseline is defined as results from the meta analysis, overall Vanguard® Knee raw revision rate and revision per 100 OCY, and Kaplan-Meir survivorship, with pooled survivorship and 95% CI. Raw revision rate, revision per 100 OCY and Kaplan-Meier survival were first compared to the TKA product family reported in various NJRs. All three implant survivorship parameters of the Vanguard® Knee were comparable to the baselines of TKA product families1–15 as illustrated in Tables 8 and 9.
Implant survivorship of the Vanguard® Knee was then compared to that of various competitive TKA products reported in NJRs.1–15 This comparison is detailed in Tables 10 and 11.
Table 8. Comparison to NJR Data – TKA Product Family1–15
Revision per 100 OCY (95% CI)
All Vanguard® Knees
NZNJR (11 yrs)
ALL TKA
AOANJRR 2010
ALL TKA
AOANJRR 2010
Cemented TKA
AOANJRR 2010
Hybrid TKA
AOANJRR 2010
Cementless TKA
0.54 (0.45, 0.64)
0.53 (0.50, 0.56)
0.75 (0.75, 0.79)
0.75 (0.73, 0.78)
0.73 (0.70, 0.77)
0.86 (0.82, 0.90)
N = 13757 N = 45969 N = 231409 N = 118484 N = 57614 N= 55311
Raw Revision Rate in % (95% CI)
All Vanguard® Knees
NZNJR (11 yrs)
ALL TKA
AOANJRR 2010
ALL TKA
AOANJRR 2010
Cemented TKA
AOANJRR 2010
Hybrid TKA
AOANJRR 2010
Cementless TKA
0.95 (0.79, 1.11)
2.23 (2.1, 2.37)
2.86 (2.79, 2.93)
2.7 (2.6, 2.8)
3.0 (2.85, 3.14)
3.16 (3.01, 3.31)
N = 13877 N = 45969 N = 231409 N = 118484 N = 57614 N= 55311
7•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
Table 9. Revision Rate Comparison to NJR Data – TKA Product Family1–15
CPR – Cumulative Percent Revision Rate (1-Survivorship)
(95% CI) N Total
CPR at 1 yr in Percent
CPR at 3 yrs in Percent
CPR at 5 yrs in Percent
All Vanguard® Knees 16201 0.5 (0.00, 1) 1.3 (0.4, 2.1) 2.3 (0.3, 4.2)
AOANJRR TKA 231409 0.8 (0.2, 1.4) 2.2 (0.74, 3.61) 2.9 (0.94, 4.81)
UKNJR TKA 39970 – 2.0 (2.0, 2.1) 2.8 (2.7, 3.0)
SKAR TKA* Unknown 0.6 2.4 2.6
Danish NJR TKA – Cementless*
49169
2.5 5.0 7.0
Danish NJR TKA – Cemented* 1.5 3.5 4.5
Danish NJR TKA – Hybrid* 1.0 3.0 4.0
*based on graphic information
Table 10. Comparison to NJR Data – Competitors’ Products*1–15
All Vanguard® Knees
NexGen® Knees Genesis II® KneesP.F.C. Sigma®
KneesTriathlon™ Knees
Revision per 100 OCY (95%CI)
0.54 (0.45, 0.64)
0.53 (0.5, 0.56)
0.79 (0.74, 0.84)
0.66 (0.61, 0.71)
0.61 (0.52, 0.72)
N 13757 53448 36070 31728 16434
Raw Revision Rate (95% CI)
0.95 (0.79, 1.11)
1.96 (1.85, 2.08)
2.72 (2.55, 2.89)
2.26 (2.09, 2.42)
0.95 (0.8, 1.1)
N 13877 53448 36070 31728 16434
*based on Australian and New Zealand NJR latest reports
Table 11. Revision Rate Comparison to NJR Data – Competitors’ Products*1–15
CPR – Cumulative Percent Revision (1-Survivorship)
N TotalCPR at 1 yr in
Percent (95% CI)CPR at 3 yrs in
Percent (95% CI)CPR at 5 yrs in
Percent (95% CI)
All Vanguard® Knees 16201 0.5 (0.00, 0.01) 1.3 (0.5, 2.1) 2.3 (0.3, 4.2)
Genesis II® Knees 36070 1.14 (0.84, 1.44) 2.83 (1.75, 3.92) 3.44 (1.95, 4.92)
NexGen® Knees 53448 0.65 (0.24, 1.06) 1.8 (0.93, 2.68) 2.39 (1.06, 3.72)
P.F.C. Sigma® Knees 31728 0.9 (0.22, 1.58) 1.89 (1.17, 2.6) 2.56 (1.55, 3.56)
Triathlon™ Knees 16434 0.8 (0.67, 0.92) 1.53 (0.73, 2.34) Insufficient follow-up
*based on Australian and UK NJR latest reports
8•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
Patient OutcomesThe AKSS, including both objective and function scores were collected in 6 of the datasets used in analysis. Statistically significant improvement in AKSS was found preoperatively to 1-year follow-up.2–7 Summarized AKSS statistics from pooled datasets can be found in Figures 4 and 5.
DiscussionThe performance of the Vanguard® Knee was evaluated based on implant survivorship and AKSS. Clinical data was gathered from a variety of clinical datasets, including both clinical studies and national joint registries. This approach ensures a comprehensive review of the Vanguard® Complete Knee System. The analysis shows that the survivorship of the Vanguard® Knee, based on all three parameters, is well within that of overall results of TKA with various bearing configurations and fixations (baselines).1–15 Patients who have received the Vanguard® Knee demonstrated improved clinical outcomes from preoperative to 1-year follow-up based on the AKSS.2–7
ConclusionThis review demonstrates that the Vanguard® Complete Knee System demonstrated consistent and excellent clinical performance based on worldwide clinical data, with the majority of patients achieving good to excellent function with demonstrated survivorship of 97.7% at 5 years.1–15
Fig. 4Fixed Bearing - Mean AKS Scores2–7
Fig. 5Mobile Bearing - Mean AKS Scores2–7
Preop 6 m 1 y 2 y 3 y 5 y
AKS - Objective Score
AKS - Function Score
0
20
40
60
80
100
Preop 6 m 1 y 2 y 3 y
AKS - Objective Score
AKS - Function Score
0
20
40
60
80
100
9•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
Appendix 1
Data Suitability Criteria
Criteria Description Suitability Grading
Appropriate Device
Was the data generated from the device in question? D1 Actual device D2 Comparable device D3 Other device
Appropriate Indications
Was the device used for the same intended use (e.g., methods of deployment, application, etc.)? A1 Same use A2 Minor deviation A3 Major deviation
Appropriate Patient Group
Was the data generated from a patient group that is representative of the intended treatment population (e.g., age, sex, etc.) and clinical condition (i.e., disease, including state and severity)?
P1 Applicable P2 Limited P3 Different population
Type of Data Will the data address safety or performance of the device in question? T1 Safety T2 Performance T3 Both T4 Neither
Criteria of Data Contribution
Criteria Description Contribution Grading
Data source type Type of studies from which the data is collected. T1 RCT T2 Cohort T3 Case-control T4 Case series
Outcome measures
Does the dataset include implant survivorship and/or AKS? O1 Survivorship O2 AKS O3 Both
Follow-up Is the duration of follow-up long enough to assess the treatment effects and identify complications?
F1 Yes F2 No
Poolability Can the data be pooled with other datasets? P1 Yes P2 No
10•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
Data Sources Available as of June 2011
Data Source (Internal ID)
Data Source Description (Location)
Study Type No. of Cases Fixed Mobile Suitability Contribution
1Prospective Comparison of MIS/Usual Technique for Vanguard® (Japan)
Post-market Study
70 CR, PS D1,A1,P1,T1 T4,O1,F1,P1
4Regenerex® Tibial Tray Multi-Center data Collection (US)
Post-market Study
43 PS, CR D1,A1,P1,T3 T2,O3,F1,P1
6Prospective Study on Vanguard® MIS Approach (US)
Post-market Study
600 PS D1,A1,P1,T3 T2,O3,F1,P1
7Prospective Comparative Study on Vanguard® (Korea)
Post-market Study
265 PS Highflex RP D1,A1,P1,T3 T1,O3,F1,P1
9
Prospective Controlled Study on Vanguard® Deep Dish Rotating Platform IDE (US, Germany, Austria and Finland)
Pre-market Study
300 CR DDRP D1,A1,P1,T3 T1,O3,F1,P1
10
Prospective Randomized Controlled Study on Vanguard® Deep Dish Rotating Platform (UK)
Post-market Study
81 CR DDRP D1,A1,P1,T3 T1,O3,F1,P1
11Prospective Study on Vanguard® Total Knee System (CR and PS) (US)
Post-market Study
357 CR, PS D1,A1,P1,T3 T2,O3,F1,P1
12Prospective Study on Vanguard® (UK)
Post-market Study
1104 CR, PS D1,A1,P1,T1 T2,O1,F1,P1
14The England and Wales National Joint Registry (UKNJR)
Registry Raw Data
6659 CR, PSDDRP, VG ROCC
D1,T1 T4,O1,F1,P1
15Australian National Joint Registry (AOANJRR)
2010 Annual Report
4009 ALL ALL D1,T1 T4,O1,F1,P1
16Swedish Knee Arthroplasty Register (SKAR)
2010 Annual Report
973 ALL ALL D1,T1 T4,O1,F1,P2
17Prospective Controlled Study on Vanguard® Deep Dish Rotating Platform (France)
Post-market Study
120 DDRP D1,A1,P1,T3 T2,O1,F1,P1
19 Danish Knee Register 2010 Registry Data 2681 CR D1,T1 T4,O1,F1,P1
20New Zealand National Joint Registry 10 year Report
Registry Report 237 CR D1,T1 T4,O1,F1,P1
21
Prospective Study on Vanguard® Deep Dish Rotating Platform Knee (IDE Feasibility US)
Pre-market Study
41 DDRP D1,A1,P1,T3 T2,O3,F1,P1
11•ASystematicReviewonPerformanceoftheVanguard® Complete Knee System
References
1. Biomet Comparison of MIS/Usual Technique for Vanguard (DS1)
2. Biomet Regenerex Tibial Tray Multi-center Data Collection (DS4)
3. Schroer Vanguard MIS Approach (DS6)
4. Biomet Korea Vanguard Study (DS7)
5. Biomet Vanguard DDRP IDE Study (DS9)
6. Biomet UK Vanguard DDRP Study (DS10)
7. Biomet Vanguard Study (DS11)
8. Biomet UK Vanguard Study (DS12)
9. The New England and Wales National Joint Registry Data Extract (DS14)
10. Australian National Joint Registry Annual Report 2010 (DS15)
11. Swedish Knee Arthroplasty Annual Report 2010 (DS16)
12. Biomet France Vanguard Study (DS17)
13. Danish Knee Registry 2010 (DS19, DS22)
14. New Zealand National Joint Registry 10 years
15. Biomet Vanguard DDRP IDE Feasibility (DS21)
16. Ritter, M. The Anatomical Graduated Component Total Knee Replacement: A Long-Term Evaluation with 20-year Survival Analysis. The Journal of Bone and Joint Surgery. 91-B(6):745–49, 2009.
17. Lombardi, A. et al. An Algorithm for the Posterior Cruciate Ligament In Total Knee Arthroplasty. Clinical Orthopaedics and Related Research. 392:75-87, 2001.
18. Bassett, R. Results of 1,000 Performance Knees Cementless Versus Cemented Fixation. The Journal of Arthroplasty. 13(4):409-13, 1998.
19. Sutton A. et al. Methods for Meta-Analysis in Medical Research. John Wiley and Sons. March 2002.
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