A systematic review of clinical outcomes and survivorship after total knee arthroplasty with a contemporary modular knee system.

The Journal of Arthroplasty xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org

A Systematic Review of Clinical Outcomes and Survivorship After Total Knee Arthroplasty With a Contemporary Modular Knee System Colin D. J. Hopley, MEng, MBA MPH a, David F. Dalury, MD b a b

DePuy International Ltd., Leeds, United Kingdom St. Joseph Medical Center, Baltimore, Maryland

a r t i c l e

i n f o

Article history: Received 26 December 2012 Accepted 14 January 2014 Available online xxxx Keywords: total knee arthroplasty systematic review SIGMA knee modular knee system survivorship

a b s t r a c t A systematic review appraising the clinical performance and safety of the primary SIGMA modular knee system (DePuy-Synthes, Warsaw, Ind.) found 5 registry reports and 53 journal publications reporting survivorship or postoperative increase in Knee Society scores on 241 632 primary SIGMA knee arthroplasties. Pooled data from national joint registries and clinical studies on primary SIGMA knee survivorship were comparable. Both were higher than for all other knees in 5 national joint registries up to 5 years. Compared with pooled data from 2 independent systematic reviews of primary non-SIGMA knees, the SIGMA system provided comparable postoperative changes in Knee Society knee score and a nonsignificant trend of higher postoperative changes in Knee Society function score. This finding suggests that this knee system provides excellent durable results. © 2014 Elsevier Inc. All rights reserved.

The SIGMA Knee Replacement System (DePuy-Synthes, Warsaw, Ind.), hereinafter termed the SIGMA knee, is a family of total knee arthroplasty (TKA) prostheses with a variety of configurations that accommodate several surgical philosophies and patient needs. Introduced in 1996, it is the product of the evolutionary development of TKA encompassing the Total Condylar Knee, The Insall Burstein Knee, and the original P.F.C Modular Knee System. The SIGMA knee includes fixed-bearing (FB), mobile-bearing (MB), cruciate-retaining (CR), cruciate-sacrificing, and posterior-stabilized (PS) prostheses, with high-flexion designs available with the FBs and MBs [1–4]. Within the system, the implants have a number of common design features, and many of the components are shared across the system [5–7]. On the femoral side, all the prostheses have the same multi-radius sagittal curve, coronal cross-section of the condyles, and patella flange [2,5,8]. The same tibial components can be used with the FB, CR, and PS designs [8]. Similarly, the MB tibial tray is the same for all configurations of the MB SIGMA knee implants [8]. The CR and PS-rotating-platform (RP) configurations of the SIGMA knee system use the same CR and PS femoral components as the FB-CR and PS configurations, respectively. Furthermore, much of the instrumentation and surgical technique is standardized [5,9]. As a class, the SIGMA knee is 1 of the most widely used knee implants world-wide, and the amount of its follow-up data in journal

The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.01.012. Reprint requests: David F. Dalury, MD, c/o Elaine P. Henze, BJ, ELS, Medical Editor, Department of Orthopaedic Surgery, The Johns Hopkins University/Johns Hopkins Bayview Medical Center, 4940 Eastern Ave., #A672, Baltimore, MD 21224-2780.

publications and registry data is substantial [10–12]. Given its high levels of use, there is inevitable interest in the clinical performance of the system. The purpose of this study was 2-fold: 1) to conduct a systematic review and meta-analysis of the clinical and safety evidence on the SIGMA knee, with subgroup analyses of the clinical performance of the FB, CR, PS, cruciate-sacrificing, and RP configurations; and 2) to compare this analysis with published evidence on TKA as a class since 1996 (when the SIGMA knee was introduced), including data available in national joint registries, and with contemporary cohorts of TKAs available in systematic reviews of TKA as a class. Materials and Methods No institutional review board approval was necessary for this study because it predominantly involved national registries and no personal identifiers were used. Study Selection Publications reporting preoperative and postoperative KS scores or survivorship with all configurations of the primary SIGMA knee were eligible for inclusion in the review. All study designs were included, and no limits were put on the number of knees. The minimum length of study follow-up was 6 months. National joint registry datasets on survivorship of TKA were eligible for inclusion as a comparison only if the data on the SIGMA knee system could be separated. To compare clinical outcomes, systematic reviews of TKA that reviewed KS scores for primary TKA with non-SIGMA, or non-P.F.C Modular knees (the predecessor to the SIGMA knee) were included only if the mean

0883-5403/0000-0000$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2014.01.012

Please cite this article as: Hopley CDJ, Dalury DF, A Systematic Review of Clinical Outcomes and Survivorship After Total Knee Arthroplasty With a Contemporary Modular Knee System, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.01.012

2

C.D.J. Hopley, D.F. Dalury / The Journal of Arthroplasty xxx (2014) xxx–xxx

preoperative and postoperative KS knee and function scores for these knees were reported separately. SIGMA Studies and Patients A search was done for articles published since 1995 in any language, reporting preoperative and postoperative Knee Society (KS) knee or function scores, or implant survivorship with the primary SIGMA knee in all configurations. The online databases EMBASE and Medline were searched using a strategy including the terms knee, arthroplasty, SIGMA, posterior stabilized, cruciate retaining, fixed bearing, mobile bearing, rotating platform, and high flexion. In addition, the bibliographies of identified studies and national registry reports were reviewed. As a comparator for survivorship, national registry reports were searched for survivorship datasets on contemporary cohorts of non-SIGMA knees implanted since 1996. The search identified 93 peer-reviewed journal publications on TKA with the primary SIGMA knee. Of those 93, 53 (8003 SIGMA knees) were eligible for inclusion in the review. Survivorship and preoperative and postoperative KS scores were reported in 11 papers, 38 papers reported preoperative and postoperative KS scores only, and 4 reported survivorship only. The remaining 40 publications were excluded because they did not report the outcomes of interest or were not on primary TKA. In total, the included peer-reviewed publications reported on 75 groups of patients treated with the SIGMA knee. Among these groups, 30 were from 16 level I randomized controlled trials in 17 publications [1,2,4–7,13–23]. Another 26 groups were from 15 level II and III prospective and retrospective controlled studies [3,8,9,24–36]. The remaining 19 groups were from 18 level IV case series [37–54]. One study reported on a cohort of SIGMA PS knees and on a cohort SIGMA RP-PS knees [51]. However, there were different time periods and different follow-ups (5 and 2 years). Therefore, these data were classified as level IV. Six publications reported on 3 studies at different time points [17,22,28,32,44,55]. Two separately reported survivorship and KS scores in the same patients [25,56]. In all of the eligible SIGMA knee studies, the mean age of patients was more than 70 years in 25 groups, 60 to 70 years in 45 groups, less than 60 years in 2 groups, and not reported in 3 groups. The diagnosis was osteoarthritis (OA) in more than 90% of patients in 56 groups, less than 90% in 9 groups, and not reported in 10 groups. The female proportion of patients was more than 60% in 54 groups and less than 60% in 14 groups; gender was not reported in 7 groups. Loss to followup was 14% in 4 groups [25,39,43,56], 20% in 1 group [31], less than 10% in 60 groups, and not reported in 11 groups. The baseline patient characteristics were considered to be generally similar in all the SIGMA knee groups and typical for TKA. In the 9 groups in which a diagnosis of OA occurred in less than 90% of patients, the diagnosis was OA in less than 80% in only 1 group [35]. In 10 groups, more than 50% of patients were male; 2 of those groups had more than 95% male patients [2]. Preoperative and postoperative KS knee scores were available for 72 groups of SIGMA knees from 46 studies (7741 knees). Preoperative and postoperative KS function scores were available on 60 groups of SIGMA knee patients from 39 studies (6001 knees). The follow-up on KS knee and function scores ranged from 3 months to 13 years. Survivorship was reported on 19 groups of patients in 15 peerreviewed journal articles (4025 knees) [6,17,19,29,35,38,40,41,44, 46,48,52,54–56]. There were also 5 national joint registry reports (from Sweden, Denmark, UK, Australia, and New Zealand) that contained survivorship datasets on 28 groups of SIGMA knee patients (233 843 knees) [10–12,57,58]. Among the SIGMA knees included in the national joint registries of England, Wales, and New Zealand are 214 knees in 3 studies reporting postoperative KS scores [4,14,21]. Avoiding double counting of these knees, the total dataset analyzed covered 241 632 SIGMA knees followed in national joint registries or journal articles.

Comparators To compare clinical outcomes, a search was made for contemporaneous systematic reviews of TKA as a class, presenting preoperative and postoperative KS scores reported in journal articles on TKA with designs other than the SIGMA knee. We identified 2 reviews, the Agency for Healthcare Research and Quality (AHRQ) [59] and Ontario Reviews [60]. These reviews included TKA studies, each containing more than 100 patients, published between 1995 and 2005. In the reviews, there were 36 studies reporting preoperative and postoperative KS scores with non-SIGMA knees. These contained 48 groups (11 036 knees) with preoperative and postoperative KS knee scores and 48 groups (10 880 knees) with preoperative and postoperative KS function scores. The patient baseline characteristics in the AHRQ and Ontario groups were generally similar to those in the SIGMA knee studies and also typical of primary TKA patients. The mean patient age was more than 75 years in 9 groups, 60 to 70 years in 39 groups, and less than 40 years in 2 groups. The diagnosis was OA in more than 90% of patients in 29 groups, 70% to 90% of patients in 13 groups, and not reported in 1 group. In the 6 groups with fewer than 70% of patients with OA, only 46% of patients were diagnosed with OA in 1 group and 35% in another. In 4 groups, rheumatoid arthritis was the diagnosis in all patients. Patient gender was more than 60% female in 31 groups, less than 60% female in 14 groups, and not reported in 5 groups. Fewer than 50% of patients were female in 3 groups; in 2 of those groups, more than 95% of the patients were male. Of the national registries reports in 2012, 5 from the UK, Sweden, Denmark, New Zealand, and Australia included survivorship analyses by prosthesis type for knees implanted from 1996 to 2009 and included datasets on primary non-SIGMA knees that could be used as the comparator [10–12,58]. Additionally, survivorship data on all knees captured on the Norwegian Arthroplasty Registry between 1997 and 2007 has been published by Robertsson et al [61]. To our knowledge, there are no SIGMA knees in this dataset and therefore it was also considered to be a suitable comparator for survivorship. Consequently, the data from these 6 sources were pooled as a single generalizable dataset on the survivorship of contemporary knee arthroplasty. In total, the non-SIGMA knee survivorship data consisted of 158 separate datasets on 678 756 TKAs. Database Development Original copies of all the publications eligible in the review were obtained, including the non-SIGMA knee studies identified in the eligible systematic reviews selected as the comparator for clinical outcomes. Data were extracted by 2 independent reviewers using standard blank data tables, and any differences were resolved by discussion. Outcomes data extracted were the preoperative and postoperative KS scores, survivorship, and cumulative revision rate. When studies measured KS scores at more than 1 time point, data were extracted for each follow-up. Where reported, the standard deviations (SDs), range, and confidence intervals (CIs) of the preoperative and postoperative KS scores were also extracted for statistical analysis. To allow for assessment of study quality and interstudy variability, patient demographic data, number of patients, and loss to follow-up were also extracted, and studies were classified according to study design. Where cumulative revision rate was reported, it was converted into survivorship by calculating 100 − cumulative revision rate (%). Statistical Methods Survivorship and clinical outcomes reported on SIGMA knees and on non-SIGMA knees were pooled separately using random effects meta-analysis (Appendix). This method calculates a weighted average



3

Results

between the SIGMA knee studies and the non-SIGMA knee (AHRQ and Ontario) review papers. In addition, no differences were found in any of the subgroups or time-stratified analyses. In all the SIGMA knee and non-SIGMA knee review papers, the preoperative KS knee and function scores were very similar: weighted mean 43 (range, 24– 62) and 41 (range, 21–69) for the KS knee scores, respectively, and weighted mean 45 (range, 24–60) and 45 (range, 28–64) for the KS function scores, respectively (Tables 1 and 2). The mean postoperative change in the KS knee score was the same in the SIGMA knee and non-SIGMA knee review studies: 47.7 (95% CI, 45.1–50.2) and 46.1 (95% CI, 43.5–48.6), respectively (Tables 1 and 2). The postoperative change in KS function was higher on average in the SIGMA knee studies than in the non-SIGMA review studies: 37.4 (95% CI, 33.6– 41.2) and 31.4 (95% CI, 27.2–35.6), respectively; however, the difference was not significant. In the SIGMA knee studies, the mean postoperative KS knee score was greater than 90 (rated as excellent) in 42 groups and between 80 and 90 (rated as good) in 26 groups. The mean postoperative KS function score in the SIGMA knee studies was greater than 90 in 18 groups, between 80 and 90 in 22 groups, and between 70 and 80 (rated as fair) in 12 groups. When the studies were grouped by length of mean follow-up, the pooled postoperative change in KS knee scores was higher on average at all time points in the SIGMA knee studies, except in those with a mean 6- to 7-years’ follow-up, but the differences were not significant (Figs. 1 and 2, Tables 1 and 2). In studies with 1 and 2–3 years of mean follow-up, the difference in mean change in score was small (b1 KS knee score point). In the groups with 4 to 5 years of follow-up, the pooled postoperative change in KS knee scores was 50.8 (95% CI, 43.8– 57.7) in the SIGMA knee studies and 43.9 (95% CI, 37.4–50.4) in the non-SIGMA knee review studies. In the groups with 6–7 years of follow-up, the pooled increase in KS knee score was 43.5 (95% CI, 30.7–56.3) in the SIGMA knee studies and 46.9 (95% CI, 39.6–54.3) in the non-SIGMA knee review studies. The postoperative change in KS function was also higher on average at all time points in the SIGMA knee studies, except for those with 4–5 years mean follow-up, but, again, none of these differences were significant. The mean postoperative changes in KS function were 38.7 (95% CI, 33.4–43.9), 37.1 (95% CI, 30.0–44.3), and 33.0 (95% CI, 24.6–41.5) in SIGMA knee studies with 1, 2–3, and 6–7 years of mean follow-up, respectively. In the non-SIGMA knee review studies with the same respective average follow-up, the postoperative increases in KS function were 30.4 (95% CI, 17.7–43.2), 30.8 (95% CI, 21.3–40.4), and 29.5 (95% CI, 15.7–43.2), respectively. There were no significant differences in the postoperative change in KS knee scores with any of the individual configurations of the SIGMA knee compared with each other or with the non-SIGMA knees review studies (Table 3). On average, the non-SIGMA knee review studies had a pooled postoperative change in KS knee score similar to those of the SIGMA FB, PS, and CR knee studies with a less than 1 KS knee score point difference between the 3 groups. This postoperative change in KS knee score was 3–4 KS knee score points higher, on average, in the subgroup of SIGMA RP knee studies, but not significantly so. The pooled preoperative KS knee scores were similar, ranging from 41 to 43. On average, the postoperative changes in KS function were similar in the SIGMA CR and the non-SIGMA review studies. These were lower, on average, than the average postoperative change in KS function in the SIGMA PS and RP subgroups, which were 5–10 KS function score points higher. The difference in the postoperative change in KS function in the SIGMA RP subgroup may potentially be significantly higher than in the non-SIGMA review studies, but not when compared with the SIGMA PS and CR knee studies.

Clinical Outcomes: Postoperative Increase Knee Society Scores

Survivorship

No differences were found in the overall preoperative KS scores, the postoperative KS scores, or the postoperative change in KS scores

In the meta-analysis of peer-reviewed literature only, the pooled survivorship of SIGMA knee was 98.4% at 5 years and 97% at 13 years

of the outcomes using the inverse of the variance of the outcome reported in each study as the weighting using the Dersimonian and Laird method [62]. The change in postoperative KS knee and function scores from baseline reported in each eligible publication on the SIGMA knee and from the systematic reviews of TKA as a class was separately meta-analyzed and compared. The postoperative change in KS scores from baseline was calculated for each study, and the variance of the change in KS score was estimated by combining the SDs of the baseline and postoperative KS scores in each study [63]. Where data on the SD of KS scores were missing, the variance was estimated from the range or interquartile range, if reported. For those studies not reporting KS score SDs, pooled values of the SD of baseline and postoperative KS scores were estimated from those that did. Pooled values of the postoperative change in KS scores were estimated for all studies and for studies grouped by mean length of follow-up. Some studies reported KS scores at more than 1 follow-up; the results from those studies at each respective follow-up were included in the pooling by mean length of follow-up. However, to avoid double-counting KS scores, only the postoperative change in KS score at the shortest follow-up was included in the pooling across all studies. Additionally, subgroup analyses were made of the KS scores results on SIGMA FB PS, SIGMA FB CR, and SIGMA RP knees. In the time-stratified analysis, independence of data was assumed, and an adjustment of the CIs of the postoperative change in KS scores was made for multiplicity using the Bonferroni method [64]. In each analysis, a weighted mean of the preoperative and postoperative KS scores was calculated using the same weighting for each study as used in the meta-analyses of postoperative increase in KS scores, the variance of the change in score. Because the weighting was not based on the variance of the preoperative or postoperative KS score respectively, a CI was not estimated, and only the ranges of the mean reported preoperative and postoperative KS scores were calculated. SIGMA knee survivorship datasets were grouped by source, with registry data meta-analyzed separately from data from the peerreviewed literature to minimize performance bias. Pooled survivorship for SIGMA knees was calculated at 2, 3, 4, 5, 6, 7, 8, 9, 10, and 13 years. At each time point, the variance of survivorship from the studies reporting at that time point was estimated using Greenwood’s formula [65]. To do so, it was necessary to estimate the number of patients at risk of revision in each study at each time point. As studies rarely report the number at risk at each follow-up, to simulate patient attrition, it was assumed that the number of patients at risk of revision reduced 5% per year in each study. The 95% CIs of survivorship were assumed to be asymmetric and were estimated using the method described by Kalbfleisch and Prentice [66]. To represent the performance of the class of TKA, datasets of non-SIGMA knee survivorship at 3, 5, 7, and 10 years identified from national joint registry reports were pooled using the same method. In the analysis of KS scores and survivorship, assumptions and estimates were used in calculating the variance of outcomes. Therefore, it was not thought appropriate to give exact P values for any difference found. To assess whether any differences between the KS scores and survivorship reported with the SIGMA knee and the comparison groups were statistically significant, the CIs were compared. If the CIs did not coincide, the difference was considered to potentially be statistically significant, with a P value less than 0.05. Potentially significant differences in the survivorship analyses were tested with sensitivity analyses by increasing the assumed attrition from 5% to 10% per year of follow-up.


4

Studya Arif et al [37] Ballantyne et al [24] Ballantyne [24] Clayton et al [55] Goldstein et al [42] Gupta et al [3] Gupta et al [3] Hall et al [27] Hanusch et al [4]b Hanusch et al [4] b Harrington et al [5] Harrington et al [5] Hepinstall et al [43]b Hossain et al [14] Jawed et al [15] Jawed et al [15] Juosponis et al [16] Juosponis et al [16] Kim et al [20] b Martin-Hernandez et al [31] Martin-Hernandez et al [31] Pagnano et al [22] Pagnano et al [22] Pagnano et al [22] KS score pooled outcome, 1-year follow-up Choi et al [1] Choi et al [1] Clayton et al [55] Geiger et al [26] Gioe et al [2]b Gioe et al [2]b Harrington et al [5] Harrington et al [5] Hasegawa et al [13] Hasegawa et al [13] Hossain et al [14] Indelli et al [45] Jawed et al [15] Jawed et al [15] Kim et al [19] Kim et al [19] Kim et al [20]b Lang et al [30] Lang et al [30] Luring et al [9] Luring et al [9]

KS Knee Score

KS Function Score

Study Design Level

Number of Knees

Number of Knees Clinical Follow-Up

Number Lost to Follow-Up (%)

Mean Follow-Up, Years

Mean Age, Years

Female, %

OA Diagnosis, %

SIGMA Configuration

Preoperative

Postoperative

Change

Preoperative

Postoperative

Change

IV II II IV IV III III II I I I I IV I I I I I I II I I I I

18 395 28 212 500 50 50 50 60 60 72 68 117 40 50 50 35 35 96 20 20 80 80 80

18 395 28 161 500 50 50 50 55 50 72 68 100 40 50 50 35 35 92 20 20 80 80 80

0 (0) 0 (0) 0 (0) 8 (3.8) NR (NR) 0 (0) 0 (0) 0 (0) 4 (6.7) 4 (6.7) NR (NR) NR (NR) 17 (14.5) 0 (0) NR (NR) NR (NR) 0 (0) 0 (0) 4 (4.2) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0)

1.3 0.5 0.5 1.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.3 0.3 1.0 1.0 1.0 1.0 1.0 1.0

69.0 68.0 68.0 67.0 66.0 67.0 68.5 72.6 69.4 70.0 63.3 63.7 68.0 68.9 64.5 64.5 72.0 71.0 69.5 75.0 75.0 67.0 67.0 67.0

90 49 49 47 NR 78 78 NR 40 60 69 59 60 55 80 80 86 86 89 65 65 70 70 70

NR 92 92 88 NR 100 100 NR 100 100 88 85 100 NR 88 88 100 100 100 100 100 100 100 100

RP CR FB CR FB CS FB CR RP CR RP-F PS RP PS CR FB CR RP CR FB RP RP-F PS FB PS FB PS RPF PS FB PS FB PS RP CR FB PS RP-F PS All poly PS FB PS RP PS

28 25 25 31 57 57 57 43 37 43 45 45 56 48 56 56 40 36 28 41 40 44 46 42 43

91 84 83 90 95 94 95 83 85 84 89 89 95 67 80 80 91 89 94 86 88 92 92 92 88

63 58 57 59 38 37 38 40 48 41 45 44 39 18 24 24 51 53 66 45 48 48 46 50 45

26 48 54 50 55 44 45 59 48 36 37 45 44 43 49 52 51 46

82 83 96 93 68 77 76 91 68 90 89 85 81 91 89 89 89 85

56 0.0 0.0 35 41 43 13 33 32 32 20 54 52 40 37 48 40 37 38 39

I I IV II I I I I I I I IV I I I I I III III III III

85 85 203 30 191 191 72 68 25 25 40 30 50 50 100 100 96 15 109 20 20

85 85 161 30 136 176 72 68 25 25 40 30 50 50 100 100 92 15 109 20 20

4 (4.7) 4 (4.7) 0 (0) 0 (0) 1 (0.5) 1 (0.5) NR (NR) NR (NR) 0 (0) 0 (0) NR (NR) 0 (0) NR (NR) NR (NR) 0 (0) 0 (0) 4 (4.2) 0 (0) 0 (0) 0 (0) 0 (0)

2.0 2.0 3.0 2.0 3.5 3.5 2.0 2.0 3.3 3.3 2.0 2.0 3.3 3.3 2.3 2.3 2.6 2.0 2.0 2.0 2.0

70.1 71.1 67.0 70.1 72.6 71.8 63.3 63.7 73.0 73.0 68.9 69.0 64.5 64.5 67.6 67.6 69.5 NR NR 67.0 69.0

96 93 47 90 4 2 69 59 88 88 55 73 80 80 85 85 89 NR NR 70 70

100 100 89 100 96 98 88 85 100 100 NR 100 88 88 100 100 100 NR NR 100 100

RP PS RP-F PS FB CR FB CR All poly PS RP PS FB RP RP PS FB PS FB PS FB PS FB PS RPF PS RP CR RP CR RP CR FB CR&CS FB PS RP CR FB CR

37 36 31 35 49 50 45 45 26 24 48 43 56 56 29 28 28 38 30 62 61

95 94 88 85 90 88 93 91 97 98 69 89 87 88 93 94 94 86 89 83 87

58 58 57 50 42 38 49 47 71 74 20 46 31 31 64 66 66 48 60 22 31

38 36 48 48 45 47 42 46 48 42 25 26 45 49 43 -

92 91 79 77 55 63 83 84 68 76 85 84 86 71 77 92 90

54 55 31 29 10 17 41 38 20 34 60 58 41 22 34 0 0



Table 1 Reported KS Scores for SIGMA Knee Studies.

II II III III III I I IV IV IV II II

20 20 30 30 28 27 27 312 162 105 41 41

20 20 30 30 28 23 25 298 162 100 41 41

0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 1.5 (5.6) 1.5 (5.6) 0 (0) NR (NR) 5 (4.8) NR (NR) NR (NR)

2.6 2.6 2.0 2.0 2.0 2.0 2.0 2.9 2.6 2.5 2.2 2.2

74.3 74.3 75.3 73.3 71.6 67.7 67.2 75.0 68.0 NR 67.5 70.5

60 60 83 83 79 48 40 66 42 75 93 78

100 100 100 100 93 100 100 NR 97 94 90 80

FB PS FB CR FB PS FB PS RP PS FB RP All Poly CR RP PS RP CR RP-F FB PS

44 43 52 51 41 58 54 38 42 53 53 54 43

90 90 85 90 93 89 88 79 96 95 96 95 89

46 47 33 39 53 31 34 53 54 42 42 40 47

55 55 50 50 44 54 51 42 60 50 51 45

83 83 94 96 86 79 81 90 82 96 95 82

28 28 44 45 42 25 30 48 22 46 44 37

IV IV IV I I I I I IV IV III III I I IV

179 203 205 80 80 80 184 184 53 125 26 26 150 150 30

142 161 175 75 75 76 174 174 52 109 26 26 150 150 24

22 (12.3) 0 (0) 14 (6.8) 1 (1.3) 1 (1.3) 1 (1.3) 10 (5.4) 10 (5.4) 1 (1.9) 8 (6.4) 0 (0) 0 (0) 0 (0) 0 (0) 1 (3.3)

3.8 5.0 5.7 5.0 5.0 5.0 5.6 5.6 4.2 4.5 3.8 3.8 5.0 5.0 5.0

64.0 67.0 69.0 67.0 67.0 67.0 67.0 67.0 66.0 68.5 74.0 74.0 70.0 68.0 73.0

65 47 58 69 70 70 64 64 73 64.4 65 65 68 60 62

88 89 NR 100 100 100 99 99 100 NR 96 96 NR NR 100

RPF PS FB CR FB CR All poly PS FB PS RP PS FB CR RP CR RPF PS RPF PS FB & MB RP PS FB PS RPF PS FB CR

41 31 57 29 28 36 54 56 49 41 40 48 42

95 89 92 91 90 96 95 96 96 92 93 91 93

54 58 35 62 62 60 41 40 47 51 53 43 51

59 48 53 54 51 24 25 55 59 50 48 47 45 59 48

90 80 70 77 69 86 83 91 91 96 95 85 86 69 83

31 32 17 23 19 62 58 35 32 46 47 38 41 10 35

II II IV IV III III I I IV IV IV

384 602 284 318 30 30 52 52 133 135 166

384 602 222 147/211 27 27 48 44 118 135 155

- (14.9) - (14.9) 4 (1.4) 14 (4.4) 6 (20.0) 3 (10.0) 2 (3.8) 4 (7.7) 12 (9.0) NR (NR) 5 (3.0)

7.3 7.3 7.3 8.5 6.0 6.0 7.1 7.1 6.5 6.0 7.5

68.6 68.6 80.0 68.0 76.0 76.0 69.8 72.0 64.8 68.0 70.0

0 100 58 49 85 85 77 60 73 NR 62

96 96 97 90 100 100 90 90 95 96 88

FB CR & CS FB CR & CS FB CR FB CR FB PS FB PS FB PS RP PS RP PS FB PS FB CR & PS

51 54 50 33 47 47 41 41 27 43 45 45

89 87 95 84 94 84 92 92 96 95 84 88

37 33 45 51 47 37 51 51 69 52 39 43

52 44 50 48 50 55 43 44 51 42 38 46

76 67 100 64 80 80 78 81 83 95 73 79

25 24 50 16 30 25 35 37 32 53 35 33

III III IV

174 174 138

174 174 106

- (5.8) - (4.7) 8 (5.8)

10.9 13.2 10.0

57.0 57.0 68.4

63 61 56

100 100 97

RP FB RP PS

28 29 44 29

90 91 94 90

62 62 50 62

25 24 39 25

83 86 90 85

58 62 51 60



Maruyama et al [8] Maruyama et al [8] Matsumoto et al [32] Matsumoto et al [32] Minoda et al [33] Munro et al [21]b Munro et al [21]b Pomeroy et al [50]b Ranawat et al [51] Signorelli et al [52] Suh et al [36] Suh et al [36] KS score pooled outcome, 2- to 3-year follow-up Bauman et al [39]b Clayton et al [55] Cossetto and Gouda [40] Kalisvaart et al [17] Kalisvaart et al [17] Kalisvaart et al [17] Kim et al [6]b Kim et al [6]b Maniar et al [47] Meftah et al [49]b Ranawat et al [34] Ranawat et al [34] Shemshaki et al [23] Shemshaki et al [23] von Schewelov et al [53] KS score pooled outcome, 4- to 5-year follow-up Dalury et al [25] Dalury et al [25] Dalury et al [41] Hunter et al [44] Ishida et al [28]b Ishida et al [28]b Ladermann et al [7] Ladermann et al [7] Maniar et al [46] Ranawat et al [51] Zaki et al [54] KS score pooled outcome, 6- to 7-year follow-up Kim et al [29] Kim et al [29] Meftah et al [48]b KS score pooled outcome, 10- to 13-year follow-up

Dash indicates the study did not report this outcome. CS, cruciate sacrificing; CR, cruciate retaining; FB, fixed bearing; NR, not reported; OA, osteoarthritis PS, posterior stabilized; and RP, rotating platform. a Some studies reported outcomes at more than one time point, which were included in the analysis of KS scores at each follow-up. For the overall scores analysis, only the data from the shortest follow-up were included to avoid double-counting. b Demographic data relate to the follow-up, rather than the overall, cohort.

5

6

KS Knee Score

KS Function Score

Mean Age, years

Female, %

OA Diagnosis, %

Preoperative

Postoperative

Change

Preoperative

Postoperative

Change

1 1 1 1 0.5 0.5 1 1 1 0.5 0.5 1 1 1

72 72 68 66 70 69 69 75 69 67 70 70 70 69

70 70 46 55 62 62 53 80 81 71 67 52 60 62

NR 100 100 100 79 81 100 100 0 83 91 94 91 92

41 37 41 45 53 55 23 28 21 52 51 47 39 50 42

85 82 82 90 89 87 79 89 90 90 90 88 77 95 87

44 45 41 45 36 32 56 61 69 38 39 41 38 45 45

45 41 44 46 43 47 42 53 40 46 47 41 49 41 44

71 70 71 75 63 60 63 70 70 74 75 74 86 94 75

26 29 27 29 20 13 21 17 30 28 28 33 37 53 30

50 48 300 43 268 276 32 93 276 329 4891 251 109

2 2 3 3 2 3 2 2 3 3 3 2 4

72 68 75 69 70 66 69 69 71 70 70 69 69

70 46 80 81 63 55 69 69 79 52 NR 62 85

100 100 100 0 100 88 80 80 100 94 91 100 95

37 41 28 21 35 50 41 29 47 39 40 37 37

81 87 89 85 68 89 90 82 88 79 89 79 84

44 46 61 64 33 49 49 53 41 40 49 42 47

41 44 53 40 41 52 41 38 46 41 49 46 44 45

67 76 70 70 69 91 80 79 72 76 89 81 64 76

26 32 17 30 28 39 39 41 26 35 40 35 20 31

100 103 97 241

5 4 4 5

67 69 69 65

NR 4 4 58

61 92 92 100

33 38 35 42

84 84 85 92

51 46 50 50

29 56 57 52

52 74 72 90

23 18 15 38

AHRQ [59] and Ontario [60] Review Studies

Number of Knees

Number of Knees Clinical Follow Up

Bert et al, 2001 Bourne et al, 1995 Bourne et al, 1995 Brander et al, 2003 Cohen et al, 1997 Cohen et al, 1997 Deshmukh et al, 2002 Elke et al, 1995 Elke et al, 1995 Matsueda and Gustilo, 2000 Matsueda and Gustilo, 2000 Meding et al, 2003 Meding et al, 2003 Mokriset al, 1997 KS score pooled outcome, 1-year mean follow-up Bourne et al, 1995 Bourne et al, 1995 Elke et al, 1995 Elke et al, 1995 Heck et al, 1998 Hube et al, 2002 Jenny and Jenny, 1998 Jenny and Jenny, 1998 Konig et al, 1998 Meding et al, 2003 Meding et al, 2003 Rand and Gustilo, 1996 Yang et al, 2001 KS score pooled outcome, 2- to 3-year mean follow-up Bullens et al, 2001 Gioe and Bowman, 2000 Gioe and Bowman, 2000 Harwin, 1998

264 50 50 149 172 100 180 415 61 169 167 329 4891 126

90 50 48 149 172 100 130 300 43 169 167 329 4891 105

50 50 415 61 330 297 32 93 398 329 4891 277 109

126 111 102 241

Mean Follow-up Years



Table 2 KS Scores of Non-SIGMA Knees in AHRQ and Ontario Reviews.

109 103 329 4891 126 121 121 102

109 95 329 4891 105 118 118 102

5 5 5 5 4 5 6 5

65 70 70 70 69 70 70 67

58 NR 52 NR 62 62 62 77

0 100 94 91 92 96 96 76

32 52 47 39 50 52 52 49 43

86 92 87 75 97 94 94 77 87

54 40 40 36 47 42 42 28 44

28 50 41 49 41 42 42 43 42

68 75 73 84 88 70 70 64 78

40 25 32 35 47 28 28 21 35

198 500 36 415 61 100 329 4891 145 31 125

198 500 36 300 43 92 329 4891 78 9 110

7 6 6 7 7 7.5 7 7 6 6 6

69 68 68 75 69 69 70 70 69 76 72

63 68 68 80 81 85 52 NR 59 NR 53

80 89 89 100 0 100 94 91 93 90 95

29 51 54 28 21 41 47 39 30 34 33 37

76 90 91 87 77 94 80 75 85 87 82 84

47 39 37 51 56 53 33 36 55 53 49 47

31 0 0 53 40 48 41 49 50 64 45 46

75 0 0 66 65 79 70 80 79 79 74 75

44

13 25 31 29 31 29 15 29 29

163 61 59 539 110 56 186 41

107 55 51 306 25 47 186 41

10 10 10 10 10 8 9 9

67 54 65 63 84 71 65 65

74 50 51 NR 69 NR 89 89

75 76 82 46 100 100 100 100

33 33 32 42 40 44 68 67 45

91 88 92 82 86 91 91 90 89

58 55 60 40 46 47 23 23 44

44 52 45 37 39 45 61 58 55

82 66 72 68 51 75 89 87 83

38 14 27 31 12 30 28 29 28

254 124 108 145 168

116 98 60 104 66

17 14 14 13 16

68 62 61 52 65

65 51 85 88 61

100 100 35 0 65

39 31 28 0 33 33

90 91 89 0 88 89

51 60 61

44 28 30 28 49 34

58 85 69 55 51 65

14 57 39 27 2 31

Dash indicates the study did not report this outcome. AHRQ, Agency for Healthcare Research and Quality; NR, not reported; OA, osteoarthritis.

55 57



Harwin, 1998 Healy et al, 2002 Meding et al, 2003 Meding et al, 2003 Mokris et al, 1997 Mont et al, 1999 Mont et al, 1999 RintaKiikka et al, 1996 KS score pooled outcome, 4- to 5-year mean follow-up Bankes et al, 2003 Brown et al, 2001 Brown et al, 2001 Elke et al, 1995 Elke et al, 1995 Indelli et al, 2002 Meding et al, 2003 Meding et al, 2003 O’Rourke et al, 2002 O’Rourke et al, 2002 Sansone et al, 2004 KS score pooled outcome, 6- to 7-year mean follow-up Cloutier et al, 2001 Duffy et al, 1998 Duffy et al, 1998 Ewald et al, 1999 Joshi et al, 2003 Healy et al, 2002 Shih et al, 2004 Shih et al, 2004 KS score pooled outcome, 8- to 10-year mean follow-up Gill and Joshi, 2001 Goldberg and Kraay, 2004 Miyasaka et al, 1997 Rodriguez et al, 1996 Sextro et al, 2001 KS score pooled outcome, 13- to 17-year mean follow-up

7

8


Fig. 1. Postoperative increase in KS knee scores of SIGMA and non-SIGMA (AHRQ and Ontario) knees.

(Table 4, Fig. 3). Several studies reported very high survivorship (99.4%–100%) at 6 and 7 years [35,41,46,54]. At 6, 7, and 8 years, the pooled survivorship of the SIGMA knee in the peer-reviewed literature was 99.3%, 99.2%, and 99.3%, respectively. The meta-analysis of knee registry data (233 843 knees) from Sweden [11], Australia [57], Denmark [57], New Zealand [58], and the UK [12] reported survivorship for the SIGMA knee of 97.5% and 95.7% at 5 and 10 years’ follow-up, respectively. This difference in the pooled SIGMA knee survivorship from knee registry data and the peer-reviewed literature was not significant at any time point, as denoted by the CIs estimated for these datasets (Table 4). The meta-analyzed survivorship of the SIGMA knee from the peer-reviewed literature and national joint registries was higher on average at 3, 5, 7, and 10 years than that reported for the class of contemporary knee systems in 5 national joint registries implanted over the same period between 1997 and

2009 (Fig. 3). This difference was significant only for the SIGMA knee survivorship from the peer-reviewed literature at 7 years (P b 0.05). For the SIGMA knee survivorship from national joint registries, the difference was significant at 3 and 5 years (P b 0.05). At 5 years, the pooled survivorship of SIGMA knees from national joint registries was 97.5% (95% CI, 97.64–97.37), and the pooled survivorship of nonSIGMA knees was 97.3% (95% CI, 97.36–97.26). At 7 years, the pooled survivorship of SIGMA knees from national joint registries was also significantly different than that of non-SIGMA knees: 97.7% (95% CI, 97.98–97.45) and 97.1% (95% CI, 97.24–97.04), respectively. However, the pooled survivorship at 7 years for SIGMA and non-SIGMA knees was based on data from only the UK [12], Swedish [11], and New Zealand [58] national joint registries and was higher than the pooled survivorship at 5 years for the SIGMA knee group. The difference at 3, 5, and 7 years was also significant when the assumed rate of patient

Fig. 2. Postoperative increase in KS function scores of SIGMA and non-SIGMA (AHRQ and Ontario) knees.



9

Table 3 Pooled KS Scores from Subgroup Analyses by Configuration of the Primary SIGMA Knee System. KS Knee Score

KS Function Score

SIGMA Configuration

Groups/Kneesa

Preoperative

Postoperative

Change (95% CI)

Groups/Kneesa

Preoperative

Postoperative

Change (95% CI)

All Sigma studies Sigma FB PS Sigma FB CR Sigma RP AHRQ Ontario

72/7368 20/1142 12/1686 33/3120 48/11036

42.9 43.23 40.5 42.2 40.8

90.4 89.2 87.3 92.6 86.9

47.7 (45.1–50.2) 45.9 (42.7–49.2) 46.7 (41.1–52.4) 50.5 (46.7–54.3) 46.1 (43.5–48.6)

68/5663 17/1118 7/778 29/2478 48/10880

45.1 45.5 46.8 44.2 44.6

82.5 82.0 77.3 86.0 76.0

37.4 36.5 30.5 41.8 31.4

(33.6–41.2) (29.7–43.1) (12.5–48.4) (37.3–46.3) (27.2–35.6)

AHRQ, Agency for Healthcare Research Quality; CI, confidence interval; CR, cruciate retaining; FB, fixed bearing; PS, posterior stabilized; RP, rotating platform. a Number of knees is the number of knees with clinical follow-up.

attrition was increased from 5% to 10% (P b 0.05). At 10 years, the pooled survivorship of the SIGMA knees was higher on average than that for the non-SIGMA knee, but the difference was not significant: 95.7% (95% CI, 96.01–95.38) and 95.5 (95% CI, 95.56– 95.38), respectively. Discussion The clinical effectiveness and safety of the primary SIGMA knee system are supported by a very large body of evidence, and this review pools data on all configurations in the system. The SIGMA knee can be considered to be a relatively homogenous group because of the commonality of the implant designs, sharing of components across the system, and standard surgical technique. Furthermore, in all the randomized controlled studies in which 1 SIGMA knee design is compared with another, the results are similar. This consistency of results was also apparent in our review of the wider body of studies of all SIGMA knee studies. By using data on SIGMA and non-SIGMA knees from several high quality sources, it has been possible to perform a notable comparison with some very large numbers of approximately matched patients. Good or excellent clinical outcomes ratings using KS scores were largely reported across all the SIGMA knee studies. KS knee scores were rated as good or excellent in all but 1 publication [14]. Mean KS function scores rated as good or excellent were reported in 40 of 59 groups, and scores were rated as fair in 12 groups. Postoperative increases in KS knee scores reported with the SIGMA knee were comparable to those reported for TKA in general in the non-SIGMA knees, and there were no significant differences in any of the comparisons. Postoperative increases in KS function scores with the SIGMA knee compared well with those for knees in general; there was a trend for a higher increase in postoperative KS function across all the studies and at all time points up to 13 years in the time-stratified analysis. This result was significant only for the SIGMA knee studies reporting at 10– 13 years; a small group of 2 studies [36,48] in which the baseline KS knee and function scores were particularly low compared with the baseline scores in the other studies. Subgroup analysis showed that the postoperative change in KS function was higher in the SIGMA PS and RP knee studies than in the SIGMA CR knee and the non-SIGMA knee review studies. The difference in postoperative change in KS function among the SIGMA PS, CR, and RP knee subgroups was not significant. It was significant when comparing the SIGMA RP knee subgroup and the non-SIGMA knee review studies. This finding should be treated with caution as in 5 of the 29 groups in SIGMA RP knee KS function dataset the preoperative function was 25–26 [6,19,29,37]. It could be considered to be low and a potential source of bias because the pooled preoperative KS function was estimated to be approximately 45 in the whole set of SIGMA knee studies and in the non-SIGMA review studies. In addition, this difference in the postoperative change in KS function with the SIGMA RP knee may not last beyond 1–2 years follow-up. In controlled studies with up to 2 years follow-up, higher range of motion and KS function have been

reported with the SIGMA RP than with the SIGMA FB knee [31]. However, controlled studies with longer follow-up have found no difference in outcomes between these knees [5]. By pooling data on SIGMA and non-SIGMA knees from 6 joint registries, it has been possible to create 2 very large datasets of knees for comparison. The modular design allows for the SIGMA knee to be used in most patients, and because all available datasets on all patients have been included, it is likely to be representative of general TKA populations, similar to the comparator. This ability to use the SIGMA Knee across the knee replacement case mix, and the scale of the samples, may reduce the risk of confounding and has enabled some very precise estimates of performance. The data support the idea that the primary SIGMA knee system is a versatile and durable system that provides results comparable to those reported with other devices. In the general TKA populations, the outcome of the SIGMA knee, represented by the pooled registry survivorship, was similar to that of the single surgeon series (P N 0.05) and was 96% and at 10 years. Compared with the survivorship of non-SIGMA knees reported by national joint registries, it appears that the pooled registry survivorship of the SIGMA knee is significantly higher at 3, 5, and 7 years (P b 0.05). However, the difference was small, only 0.3% at 5 years, potentially representing a 7% difference in the risk of revision with the SIGMA knee. This small difference remained significant even in the sensitivity analysis when the assumed annual patient attrition rate was changed from 5% to 10%. At this relatively short follow-up, it is not clear whether this difference is potentially clinically important. It may become apparent with time as more knees in the national joint registry datasets achieve a longer follow-up of 10 years and more. At 7 years, the pooled survivorship of the SIGMA knee from national joint registries was estimated to be higher than that at 5 years. The 5-year estimate pools data from all 5 of the national joint registers identified, whereas the 7-year estimate pools data from just the UK [12], Swedish [11], and New Zealand [58] registries, which generally report higher survivorship than the Australian [10] and Danish [57] knee registries. Although the finding at 7 years of statistically higher survivorship with the SIGMA knee is based only on 3 registries, it does support the finding at 5 years. However, the ability to quantify the absolute difference in the risk of revision at 7 years with SIGMA knees compared to the class is limited, this analysis being 1 of just 3 of the 5 registries. Long-term survivorship data beyond 10 years on the SIGMA knee are now beginning to emerge, and survivorship of 94% and 98% at 13 years has been reported by Kim et al [29]. In our study, our goal was to identify all the survivorship and KS score data on the primary SIGMA knee system and compare its performance with generalizable data on TKA as a class. Although SIGMA knee studies include several level I randomized controlled trials, only 4 compared the SIGMA knee with other knee designs, and meta-analysis of this small amount of data would not meet our objective. Because data from level I studies were pooled together with observational data from level II, III, and IV studies, this review should be classified as a comparison of pooled observational data and hence subject to the limitations of this type of data. Without random allocation of patients to SIGMA knees or non-SIGMA knees, there is a


10


Table 4 Survivorship of the SIGMA Knee System.

Study SIGMA peer-reviewed data Asif and Choon [38] Clayton et al [55] Cossetto and Gouda [40] Dalury et al [41] Dalury et al [56] Hunter et al [44] Kalisvaart et al [17] Kalisvaart et al [17] Kalisvaart et al [17] Kim et al [6] Kim et al [6] Kim et al [19] Kim et al [29] Kim et al [29] Maniar et al [46] Meftha et al [48] Reay et al [35] Signorelli et al [52] Zaki et al [54] Pooled survivorship (%)

SIGMA Bearing CR & CS FB CR CR 96% CR 81% CR, 19% CS CR FB PS all poly FB PS RP PS FB CR RP CR RP PS FB MB RP PS RP PS FB RP CR 94% CR, 6% PS

SIGMA national joint registry data Australia NJRR, 11 FB cemented Australia NJRR, 11 MB cemented Australia NJRR, 11 AMK cementless Australia NJRR, 11 MB cementless Australia NJRR, 11 MB hybrid Australia NJRR, 11 FB hybrid Denmark DKAR, 60 All-poly CR cemented Denmark DKAR, 60 CR hybrid Denmark DKAR, 60 All-poly CR hybrid Denmark DKAR, 60 All-poly CR uncemented Denmark DKAR, 60 RP CR cemented Denmark DKAR, 60 RP PS cemented Denmark DKAR, 60 CR cemented Denmark DKAR, 60 CR hybrid Denmark DKAR, 60 CR Denmark DKAR, 60 PS Denmark DKAR, 60 RP CR hybrid Denmark DKAR, 60 RP CR uncemented Denmark DKAR, 60 PS cemented Denmark DKAR, 60 RP PS cemented New Zealand NZJR, 61 Cemented Sweden SKAR, 12 FB Sweden SKAR, 12 MB UK NJR, 10 FB CR cemented UK NJR, 10 RP CR cemented UK NJR, 10 FB PS cemented UK NJR, 10 RP PS cemented UK NJR, 10 CR hybrid Pooled survivorship Upper 95% CI Lower 95% CI TKA registry survivorship (non-SIGMA) 1996–2011 Upper 95% CI Lower 95% CI

Number of Knees 87 212 175 284 1316 318 80 80 80 174 174 112 174 174 118 138 63 100 166 4025

12,715 5,321 1,663 2,503 4,406 7,028 537 706 301 749 695 1897 2854 78 40 29 532 219 459 539 8,030 25,432 968 99,824 5,946 44,202 4,594 1,576 233,774

Survivorship (%) at Follow-Up Years: 2

3

5

98.6

97.8

100.0

99.6

97.0 98.9 99.6

6

7

8

99.6

99.6

9

10

11

13

94.0

99.6

95.6 97.7 98.7 97.4 98.7

98.7 97.4 98.7

98.7 97.4 98.7 94.0 93.0 98.1 93.7 98.0

98.5 100.0 99.0 99.4 99.4

98.8 98.3 95.8

98.27 98.7 97.69

677,583

98.5 100.0

97.7 100.0

100.0 97.7 100.0

97.7 100.0

97.7 100.0

97.7 100.0

97.7

99.4 99.1

99.4 98.5

99.4 99.3

99.4 99.2

99.3

97.7

97.0

98.0 97.6 98.4 95.8 95.9 97.9

98.3 97.8 94.4 98.9 98.1 98.6 97.7 99.2 98.22 98.33 98.10 98.04

97.4 96.7 97.6 94.5 94.6 97.2 98.9 97.3 97.4 97.3 96.8 93.5 96.4 97.8 100.0 99.9 96.4 94.3 94.1 91.9 97.9 97.4 93.1 98.5 97.4 98.1 96.9 98.8 97.51 97.64 97.37 97.31

98.08 97.99

97.36 97.26

95.3 96

93.8 95.4 98.9 95.4 95.2 94.2 93.7 93.5 93.0

97.6 97.1

97.3 97.0

97.2 96.9

97.1 96.8

96.9 96.7

96.96 97.16 96.75

96.86 97.07 96.64

95.70 96.01 95.38 95.47

97.0

95.3

95.4

98.2 97.8

97.33 97.77 96.79

98.8 97.73 97.98 97.45 97.14 97.24 97.04

96.30 96.82 95.70

95.56 95.38

AMK, anatomic modular knee; CI, confidence interval; CS, cruciate sacrificing; CR, cruciate retaining; DKAR, Danish Knee Arthroplasty Register; FB, fixed bearing; MB, mobile bearing; NJRR National Joint Registry Report; NJR, National Joint Registry; NZJR, New Zealand Joint Registry; OA, osteoarthritis PS, posterior stabilized; and RP, rotating platform; SKAR, Swedish Knee Arthroplasty Register; TKA, total knee arthroplasty.

possibility that some confounding factors may have influenced the findings. It was not possible to control for sources of confounding such as differences in patient selection, application of clinical outcome measures, rehabilitation protocols, surgeon experience, and thresholds for revision. In addition, in the survivorship comparison, the primary SIGMA knee system was compared with all other systems collectively as 1 group, in which the results of good performing systems have been pooled with those of poorer performing ones. There are other modular knee systems available with similar features and characteristics, which may introduce

some bias against them. However, the results do seem to indicate that the SIGMA knee is 1 of the better performing knee systems. Including all systems collectively does ensure that the survivorship comparison group is representative of knee arthroplasty patients. The primary SIGMA knee system has options designed for a broad spectrum of patient needs. Consequently, we believe that the patients treated with all configurations of the SIGMA knee in registries are also a representative sample, which may help mitigate some of the potential patient selection bias in the analysis. It should also be highlighted that although national joint



11

Fig. 3. Survivorship of SIGMA knees and the class of TKA.

registry data are more generalizable than data from peer-reviewed publications by single surgeons, it is still subject to these limitations and may not be fully generalizable. In particular, surgeon performance bias may be present, depending on whether devices are used in high-volume or smaller, more general surgical centers. The inclusion of learning curves in registry data can be an additional confounding factor. However, joint registry data remain a rich and valuable source of information. In the analysis of KS scores, the accuracy of the pooled estimates of the postoperative increase in KS scores and their CIs may be impaired by missing data. An estimate of the SD of preoperative and postoperative KS scores was used for 15% of the treatment groups in the analysis. Patient baseline demographics and baseline KS scores were, in general, similar across the studies, although in a small number of studies there was considerable variation in baseline characteristics. The pooled preoperative KS knee and function scores in the SIGMA knee and non-SIGMA knee studies were within 2 KS points of each other. Furthermore, analysis of the preoperative increase in KS scores may have partially mitigated any differences in baseline KS scores, and registry and peer-reviewed journal survivorship were meta-analyzed separately to avoid performance bias. The interstudy variation was accounted for using random effects approaches, a substantial factor in the nonstatistical significance of most of the results. In the analysis of clinical outcomes, a statistical difference was observed in only 1 of the comparisons. The pooled postoperative increase in KS knee and function scores were fairly similar in all the analyses. In contrast, considering the number of studies and knees, the CIs of postoperative increases in KS scores were relatively broad, and in most cases, they were larger than the difference in the means of the postoperative increases in KS score between any 2 groups. The size of the estimated CIs was largely the result of the variation in the postoperative increase reported in each study and could mean that any treatment effects were not apparent because of this variability. This variability in the postoperative change in KS scores may expose the weakness of our approach. However, among the randomized clinical studies identified in this review, only 2 found any differences in clinical or patient outcomes [14,20], which may indicate that within individual studies it may also be difficult to eliminate variability that may be affecting our review. Additionally, there may be ceiling effects

with current outcomes instruments [13]. To detect treatment effects may require well powered randomized controlled studies, with highly controlled patient selection and clinical conditions and the use of more sensitive outcomes instruments. Our study also does not address the performance of the primary SIGMA knee system in revision, an important factor in clinical decision making about which system to use. Revision TKA is a substantially different indication to primary TKA. Patients are more heterogeneous, and surgeons and knee systems need to be able to address considerable technical challenges, such as substantial bone loss. Although no definitive conclusions can be drawn about the performance of the primary SIGMA knee compared with the class of TKA, the results do give confidence that good clinical outcomes can be achieved with the SIGMA knee and that the risk of revision is as low or lower than that of the class of TKA, regardless of surgeon experience. Conclusion There is a large body of clinical outcomes and survivorship evidence from clinical studies and joint registries on the primary SIGMA knee system (241632 knees). Clinical outcomes with the SIGMA knee, measured using KS scores, compared well with those of the contemporary class of TKA. There was a nonsignificant trend for better function, which was higher on average at all time points up to 13 years than those reported for the non-SIGMA knee (AHRQ and Ontario) systematic reviews of TKA. At 3 and 5 years in 5 national joint registry reports, at 7 years in 3 national joint registry reports, and at 7 years in the peer-reviewed literature, representing use of the SIGMA knee by specialist surgeons and in general practice, the pooled survivorship of the SIGMA knee appears to be higher than that of the generalizable survivorship data on primary non-SIGMA knees. Additionally, the emerging long-term data (10–13 years follow-up) on the SIGMA knee suggest that this knee system provides excellent durable outcomes. Acknowledgments The review was carried out as an academic exercise by the authors; 1 is an employee of DePuy International, Ltd. and the other received


12


funding for this work. Both authors have received payments in excess of $10 000 from DePuy International, Ltd. or DePuy Inc. One author received specific funding for this work. The authors wish to thank Jack Williams of Aston University (Birmingham, England) and Alice Colligan of the University of Leeds (Leeds, England) for their assistance with data extraction, and John Leopold of DePuy, Inc (Warsaw, Indiana) for guidance on the statistical methods. Appendix A. Technical Note on Statistical Methods

VarðSt Þ ¼

i¼1

Dt Nt ðN t −Dt Þ

pooledsKSS

j¼1

2

ð1Þ

where h is the number of time intervals in follow-up (eg, years), N is the number of patients at risk of revision at each time interval t, and D is the number of failures during the time interval [67]. At each interval, Dt was calculated by multiplying Nt by the difference in survivorship between the year in question and the survivorship at the previous year. In many survivorship studies, only the number of patients entered into the study and the average length of follow-up were included. To account for patient attrition when estimating the variance of survivorship, it was assumed that the number of patients at risk of revision in each study (Nt in Equation 1) decreased by 5% with each year after surgery. A sensitivity analysis was also performed, assuming a 10% decrease in the number at risk with each year after surgery. This approach was applied at 3, 5, and 7 years for the UK National Joint Registry Data; at 3, 5, and 10 years for the Australian National Joint Registry Report data; at 2, 3, 5, 6, 7, 8, 9, and 10 years for the data from the New Zealand and Swedish national joint registries; and at 5 and 10 years for the Danish Knee Arthroplasty Registry data. When survivorship of 100% was reported, it was not possible to calculate Greenwood’s formula because there were 0 failures. For these datasets, the variance of survivorship was estimated to be 1/D 2, the number estimated to be in the sample, accounting for attrition by applying a fixed percentage reduction in patients followed, at the first year the 100% survivorship was reported. When pooling KS scores, the postoperative increase for each study was calculated as the difference in the KS score at baseline and after surgery. To estimate the variance of the change in KS score, the variance/SDs of preoperative and postoperative KS scores were extracted directly from the papers or estimated from the range or interquartile range when reported. When the range was reported, the SD was estimated to be the range divided by 6 for studies with more than 70 knees, and the range divided by 4 for studies with less than 70 knees. When no such information was available, the pooled SD of KS scores from studies that do report it was used, calculated with Equation 2 (15): vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi u i uX 2 u nj −1 sj u u j¼1 ¼u u X u i t nj −1

SchangeKSS

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi v u u npre −1 s2pre þ npost −1 s2post u ¼t npre −1 þ npost −1

varchangekKSS ¼ s

Results for SIGMA knee treatment groups were pooled across all eligible studies and compared indirectly with the best available published evidence on non-SIGMA TKA prostheses. SIGMA knee survivorship data and postoperative change in KS scores were meta-analyzed using weighted averages in a random effects model. Studies were weighted using the inverse variance method, where the weight of the study in the pooled estimate is equal to 1 divided by the variance of the survivorship reported by the study [67]. The variance of survivorship in each study was calculated using Greenwood’s formula (Equation 1): h X

The variance of the change in KS scores was then estimated from the preoperative and postoperative SDs of KS scores, Spre and Spost, by applying Equations 3 and 4:

ð2Þ

changeKSS

1 1 þ n1 n2

ð3Þ

ð4Þ

where SchangeKSS is the SD of the change in KS score and varchangeKSS is the variance in KS score [67]. Between-study variation was accounted for using the Dersimonian and Laird method [67], which assumes that treatment effects in the studies have a fixed mean and are normally distributed with a fixed variance. This variance is calculated using Equation 5: 2

τ ¼

Q −ðk−1Þ 2

∑wtj −

∑wti ∑wti

!

ð5Þ

where Q = the heterogeneity statistic, w = the sum of the weights, and k = the number of studies. The heterogeneity statistic Q was the weighted average of the difference in survivorship (or change in KS score) reported in each study and the pooled survivorship (or change in KS score) across the studies using the inverse variance method. The random effects study weighting was “the reciprocal of the sum of the between and within study variances” [67]. The pooled survivorship of the SIGMA knee from studies and national joint registries was estimated at 2, 3, 5, 6, 7, 8, 9, 10, 11, and 13 years. At each time interval, data were included from SIGMA knee data sets that reported results at that time; where survivorship data could be extracted for the preceding time points, they were also used in the meta-analysis at those time points. Asymmetric estimates of the 95% upper and lower confidence limits of the survivorship were also calculated using the method described by Kalbfleisch and Prentice [66]. Survivorship data were calculated using the Kaplan Meier method, as used in the clinical papers, or the Life Table Method, as used in the Swedish Registry [67]. Cumulative revision rates were converted to survivorship by the following simple calculation: survivorship% ¼ 100 − cumulative revision rateð% Þ: When pooling the postoperative change in KS knee and function, results in SIGMA papers were grouped according to average length of follow-up. Scores were also pooled across all studies and in subgroups of papers with the CR, PS, and RP configurations and compared with non-SIGMA knee postoperative scores published in systematic reviews of TKA, grouped and analyzed using the same method. Although some studies reported KS scores at multiple time points, in the analysis stratified for time, it was assumed that the KS scores at different time points were independent. To account for the independence of KS scores at different time points, Bonferroni adjustment for multiplicity was used for KS scores, resulting in individual 99% CIs on the basis of 5 comparisons in each analysis [68]. Because variances were based on estimates of sample size and SDs, rather than calculating P values for differences, any differences were considered to be potentially significant if the 95% CIs of the survivorship or postoperative change in KS scores with SIGMA knees did not coincide with those of the comparison groups.



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Physical activity after total knee arthroplasty: A critical review.

Cementless total knee arthroplasty: a review.

Bicruciate-retaining total knee arthroplasty: a review.

Does malalignment affect patient reported outcomes following total knee arthroplasty: a systematic review of the literature.

Pain catastrophizing as a risk factor for chronic pain after total knee arthroplasty: a systematic review.

Causes and Clinical Outcomes of Revision Total Knee Arthroplasty.

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Comparison of robot surgery modular and total knee arthroplasty kinematics.

Instability after total knee arthroplasty.

Stiffness after total knee arthroplasty.

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Patients' expectations about total knee arthroplasty outcomes.

[Rare cause of knee pain after total knee arthroplasty].

Monoblock versus modular polyethylene insert in uncemented total knee arthroplasty.

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Mortality After Total Knee and Total Hip Arthroplasty in a Large Integrated Health Care System.

Comparison of clinical outcomes between total knee arthroplasty and unicompartmental knee arthroplasty for osteoarthritis of the knee: a retrospective analysis of preoperative and postoperative results.

PAIN FOLLOWING TOTAL KNEE ARTHROPLASTY - A SYSTEMATIC APPROACH.