Does Computer Assisted Navigation Improve ...

The Journal of Arthroplasty xxx (2015) xxx–xxx

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Does Computer Assisted Navigation Improve Functional Outcomes and Implant Survivability after Total Knee Arthroplasty? Timothy D. Roberts, MBChB a, Mark G. Clatworthy, MBChB, FRACS a, Chris M. Frampton, BSc, PhD b, Simon W. Young, MBChB, FRACS c a b c

Department of Orthopaedic Surgery, Middlemore Hospital, Auckland, New Zealand Christchurch Clinical School, University of Otago, Christchurch, New Zealand Department of Orthopaedic Surgery, North Shore Hospital, Auckland, New Zealand

a r t i c l e

i n f o

Article history: Received 27 September 2014 Accepted 8 December 2014 Available online xxxx Keywords: total knee arthroplasty computer-assisted surgery navigated total knee Oxford Knee Score revision rate joint registry

a b s t r a c t The objective of this study was to determine whether computer assisted navigation in total knee arthroplasty (TKA) improves functional outcomes and implant survivability using data from a large national database. We analysed 9054 primary TKA procedures performed between 2006 and 2012 from the New Zealand National Joint Registry. Functional outcomes were assessed using Oxford Knee Questionnaires at six months and five years. On multivariate analysis, there was no significant difference in mean Oxford Knee Scores between the navigated and non-navigated groups at six months (39.0 vs 38.1, P = 0.54) or five years (42.2 vs 42.0, P = 0.76). At current follow-up, there was no difference in revision rates between navigated and non-navigated TKA (0.46 vs 0.43 revisions 100 component years, P = 0.8). © 2015 Elsevier Inc. All rights reserved.

The rationale for the introduction of computer-assisted navigation systems for TKA surgery is to improve the alignment and allow components to be implanted more accurately and reliably than conventional mechanical alignment systems [1]. Using infrared technology to track the spatial positioning of patient anatomy and surgical equipment, computer-assisted navigation systems provide real-time information to guide bony cuts and allow the surgeon to evaluate these cuts after they have been performed. It has been suggested that this will especially aid lower volume surgeons to accurately implant components [2]. Even in major arthroplasty centres, conventional surgical techniques have been shown to result in high incidence of TKA malalignment [3–6]. Computer-assisted navigation in total knee arthroplasty improves accuracy of component positioning and overall limb alignment in TKA, potentially improving long term durability of the implants [7–10]. A meta-analysis of 21 randomised controlled trials involving 2541 patients demonstrated a significantly lower risk of coronal and sagittal malalignment for both femoral and tibial components in navigated TKA [7,8,11]. A recent meta-analysis of level one randomised controlled trials also found better functional outcomes as defined by Knee Society Scores at

three month and 12–32 month follow-up in TKAs performed with computer-assisted navigation [10]. However the three month functional outcome data was obtained from only four papers with a total of 218 patients. The 12–32 month functional outcome data was obtained from five papers with a total of 477 patients included in analysis. The remainder of published literature addressing functional outcomes is plagued by small sample sizes and low levels of evidence [12,13]. As navigation in TKAs is still a relatively new technology, there are few studies comparing survivorship to conventional instrumentation [14]. It is therefore yet to be determined whether the improved alignment associated with navigation leads to a reduction in the revision rate of TKA. The aim of this present study was to use a large cohort of patients from an established nationwide joint registry to address whether imageless computer-assisted navigation resulted in improved functional outcome scores and survivorship in TKA. We also focused analysis on TKA for patients under the age of 65 years as they represent a subgroup with higher functional demands and would benefit the most from improved implant survival.

One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2014.12.036. Reprint requests: Timothy Roberts, MBChB, Private Bag 93311, Middlemore Hospital, Auckland, New Zealand.

This study utilised data collected by the New Zealand National Joint Registry from 2006–2012, beginning 2006 when the first computer assisted navigation component was implanted. Details of this registry have been published previously [15]. In brief The National Joint Registry was set up in 1999 to collect data from all primary and revision hip and knee arthroplasty performed in New Zealand. Regular audit has

Methods

http://dx.doi.org/10.1016/j.arth.2014.12.036 0883-5403/© 2015 Elsevier Inc. All rights reserved.

Please cite this article as: Roberts TD, et al, Does Computer Assisted Navigation Improve Functional Outcomes and Implant Survivability after Total Knee Arthroplasty?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2014.12.036

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T.D. Roberts et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx

demonstrated a capture rate consistently greater than 95% [15–17]. National ethics committee permission was obtained and all patients signed a written consent to be included in the registry database. Study Sample Patients undergoing primary TKA for a diagnosis of osteoarthritis from 2006–2012 were identified and included in the study. Revision TKA cases were excluded. Conversions of unicompartmental knee arthroplasty to TKA were also excluded. Of the 5454 TKAs that were performed with imageless computer-assisted navigation that fit these inclusion criteria, 3329 (61%) used Stryker’s Triathlon Knee Replacement System (Stryket, Kalamazoo, MI). A variety of other implants were used in the remaining 2125 (39%) navigated TKAs and for the most part these represented the output of a small number of high volume surgeons. For example DePuy Synthes PFC Sigma was the next most common implant on the registry with 751 knees installed. Of these, 555 (74%) were implanted by a single surgeon. Of the 9205 Triathlon knees in the registry, over 36% were implanted using navigation whilst less than 20% of PFC Sigma knees used navigation. In order to reduce potential bias we elected to focus this investigation on the Triathlon system only. This meant that 9054 TKAs were included in the study of which 3329 were implanted using computer assisted analysis to compare with 5725 that were implanted using conventional instruments. Outcome Assessment The main outcomes were the functional outcome scores at six months and five years post-surgery, and the rates of revision recorded by the joint registry. Functional data was recorded from the results of Oxford Knee Questionnaires (OKQ). These questionnaires were sent out at the six month mark following TKA to a randomly selected sample of 28% of patients on the joint registry. The OKQ contains 12 questions related to pain and function, with answers ranked from 0–4. The maximum score is 48 and minimum score is zero. The OKQ is joint specific and validated confirming the reliability of the questionnaire [18]. At five years post-operatively, those that registered six month OKQ scores were sent a further OKQ to record the functional score five years postoperation. Revisions for TKAs are recorded in the joint registry and this data was used to obtain the revision rates for both the navigated and conventional groups. Operative time was collected as a secondary outcome from the registry data. Demographic and Peri-Operative Characteristics The patient characteristics potentially influencing outcomes and therefore, collected included age, gender and American Society of Anaesthesiologists (ASA) scores. Surgical variables collected included whether the TKA was performed in a public or private hospital, theatre ventilation (conventional or laminar flow), surgical approach (medial parapatellar, lateral or minimally invasive), implant type (cruciate retaining or posterior stabilised), bearing (fixed or mobile), cementation, and whether the patellar was resurfaced. In addition, surgeon experience was categorised into level of training (basic trainee, advanced trainee and consultant) and the total number of TKAs previously performed. Statistics Univariate comparisons were undertaken comparing demographic and surgical characteristics between navigated and non-navigated procedures using Chi-square and independent t-tests as appropriate. Outcome measures, revision rate and six month and five year OKQ were compared between navigated and non-navigated groups using a logrank and independent t-tests respectively. Demographic and surgical measures identified from the univariate analyses as potentially

confounding the comparisons between the navigated and nonnavigated groups were included in multivariate analyses to identify the independent influence of the navigated procedure on outcomes. For comparing revision rates a multivariate Cox proportional hazards regression model was used and for the Oxford scores a general linear model was utilised. A two-tailed P value b0.05 was taken to indicate statistical significance. Results Of the 9054 primary Triathlon TKAs included in the study, 3329 were implanted using navigation and 5725 using conventional alignment systems. One hundred surgeons were involved in the study of which 53 performed at least one computer-assisted navigated TKA. The average number of navigated knees performed by each of these surgeons was 65. Of the 53 surgeons, 24 had performed less than 10 navigated knees and 12 had performed more than 50. The 12 surgeons who performed the majority of the navigated knees also performed conventional knees, although 76% of the surgeries they did were navigated. Of all the TKAs performed by the 12 highest volume non-navigated surgeons, 87% of these were done with conventional alignment systems. There was a significant difference in age between the navigated and nonnavigated groups with a mean age of 68.7 years and 68.1 years respectively (P = 0.005) (Table 1). There was no significant difference in gender or ASA scores between the navigated and non-navigated groups. In the navigated group 52.1% of the participants were male compared with 50.3% in the non-navigated group (P = 0.096) and the mean ASA scores were 2.12 and 2.14 respectively (P = 0.194). Regarding the surgical variables, there were differences between the navigated and non-navigated groups in terms of whether the surgery was done in the public setting (45.8% vs 53.6% P b 0.001), whether the theatre ventilation used laminar flow (81.5% vs 58.9% P b 0.001), whether the procedure utilised a medial parapatellar approach (98.6% vs 97.6% P b 0.001), whether the implant was cruciate retaining (76.3% vs 86.1% P b 0.001) or used a fixed bearing type (97.0% vs 99.8% P b 0.001) and whether the patellar was resurfaced (42.5% vs 36.5% P b 0.001). From the data available there was no clear explanation apparent as to why there were differences between the two groups regarding these surgical variables. On average, each navigated TKA procedure took almost twelve minutes longer to complete (91.2 min vs 79.6 min, P b 0.001) (Table 2a). Mortality in the navigated group was not significantly different to the conventional group at 30 days (0.12% vs 0.18% P = 0.53) and at six months (0.30% vs 0.40% P = 0.44) (Table 2a). On univariate analysis the navigated group had a higher six month OKQ score compared with the conventional group (39.0 vs 38.1 P = 0.006) (Table 2a).

Table 1 Breakdown of Patient Factors and Surgical Variables between Navigated and NonNavigated Groups.

Age Mean (sd) Number b65 years Gender — Male ASA Score 1 2 3 4 Public Setting Lamina Flow Approach Medial Cruciate Retaining Bearing Fixed Cemented Patella Resurfaced

Navigated

Non-Navigated

(N = 3329)

(N = 5725)

P Value

68.7 (9.4) 1103 (33.1%) 1735 (52.1%)

68.1 (9.1) 1993 (34.8%) 2880 (50.3%)

0.005

450 (13.6%) 2008 (60.7%) 838 (25.3%) 12 (0.4%) 1516 (45.8%) 2701 (81.5%) 3127 (98.6%) 2540 (76.3%) 3220 (99.8%) 3329 (100%) 1416 (42.5%)

621 (11.0%) 3619 (64.2%) 1378 (24.4%) 21 (0.4%) 3022 (53.6%) 3357 (58.9%) 5311 (97.6%) 4927 (86.1%) 5685 (97.0%) 5725 (100%) 2088 (36.5%)

0.096 0.194

b0.001 b0.001 b0.001 b0.001 b0.001 1.00 b0.001

Please cite this article as: Roberts TD, et al, Does Computer Assisted Navigation Improve Functional Outcomes and Implant Survivability after Total Knee Arthroplasty?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2014.12.036

T.D. Roberts et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx

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Table 2a Univariate Analysis of Outcomes Comparing Navigated and Conventional Total Knee Arthroplasty.

Mean Oxford Scores 6 months 6 months (age b65 years) 5 years 5 years (age b65 years) Implant Survival Number of Revisionsa Revision Rate Number of Revisions (b65 years)a Revision Rate (b65 years) Mortality 30 Day 6 Month Duration of Surgery Mean a b

Navigated

Non-Navigated

(N = 3329)

(N = 5727)

39.0 39.1 42.1 43.5

38.1 38.1 42.0 42.5

43 0.46b 24 0.79b

73 0.43b 29 0.47b

4 (0.12%) 9 (0.30%)

10 (0.18%) 21 (0.40%)

91.2 min

79.6 min

P Value 0.006 0.073 0.764 0.412

0.819 0.088

Fig. 1. Mean Oxford Scores at six months with regard to the number of TKAs implanted by the surgeon.

0.53 0.44 b0.001

After 5 years. Per 100 component years.

important surgeon controlled factor in TKA [20]. The goal of navigated TKA is to improve alignment, and this has been shown to improve coronal and sagittal alignment [7]. The expectation is that as a result clinical outcomes in terms of functionality and revision rates will be improved

However on multivariate analysis, adjusting for the aforementioned variables there was no statistically significant difference in OKQ scores at six months (P = 0.54, Table 2b). There was no difference in six month OKQ scores in patients younger than 65 years of age who underwent computer-assisted navigated versus conventional TKA (39.15 vs 38.12 P = 0.078) (Table 2a). Lower six month OKQ scores were associated with lower volume surgeons compared to higher volume surgeons, although the use of navigation did not improve functional outcomes in either the low or high volume surgeons (Fig. 1). There was no significant difference in OKQ at five years between the computer-assisted navigated and conventional system groups (42.2 vs 42.0, P = 0.764). In the under 65 year old subgroup, there was also no significant difference in five year OKQ scores (43.5 vs 42.5 P = 0.412, Table 2a). At current follow-up, with a mean follow-up of 2.9 years there was no significant difference found in the revision rate per 100 component years between the navigated and conventional groups (0.46 vs 0.43 P = 0.819) (Fig. 2a). The multivariate Cox regression confirmed this non-significant result with a hazard ratio for navigated compared to conventional procedures of 1.12 (P = 0.589). The reasons given for revision from the joint registry are shown (Appendix 1). In the under 65 year old subgroup, there was a trend for navigated knees to have a higher revision rate per 100 component years although again this did not reach statistical significance (0.79 vs 0.47 P = 0.088, Fig. 2b). Discussion The alignment of the knee following total knee arthroplasty (TKA) is thought to influence implant survivorship [19]. In terms of failure rates, it has been claimed that coronal alignment in particular is the most Table 2b Multivariate Analysis of Outcomes Comparing Navigated and Conventional Total Knee Arthroplasty. Navigated

Non-Navigated P Value

Oxford Scores — Mean 6 months 6 months (Adjusted)a Revision Hazard Ratiob Hazard Ratio (Adjusted)c a b c

39.0 35.6

38.1 35.4

1.05 (95% CI 0.72 to 1.52) 0.85 (95% CI 0.58 to 1.26)

0.006 0.54 0.82 0.42

Adjusted for gender, theatre (public/private), age, ASA and surgeon experience. Hazard ratio N1.0 indicates a greater revision rate in the navigated group. Adjusted for age, ASA, surgeon experience and patellar resurfacing.

Fig. 2. (A) Kaplan–Meier revision-free survival curves for navigated and conventional total knee arthroplasty. (B) Kaplan–Meier revision-free survival curves for navigated and conventional total knee arthroplasty in patients under 65 years old at time of surgery.

Please cite this article as: Roberts TD, et al, Does Computer Assisted Navigation Improve Functional Outcomes and Implant Survivability after Total Knee Arthroplasty?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2014.12.036

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T.D. Roberts et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx

and will justify the greater cost of navigation. This reflects the traditional view that the most important factor in preventing aseptic failure of TKA is satisfactory postoperative alignment [19]. Our study did not support this view, with no difference in medium-term implant survivorship seen between groups overall or in the under 65 age group. A recent retrospective study looking at the effect of postoperative mechanical axis alignment on the fifteen year survival of implants following TKA found no difference in outcomes between TKAs with a postoperative mechanical axis of 0° ± 3° and those that had a postoperative mechanical axis outside this range [21]. In the patients younger than 65 years included in the study, there was a trend for the navigated knees to have poorer five year survival. Given that navigation has been shown to improve coronal and sagittal alignment, these results would suggest that improving alignment in these planes alone does not result in better TKA durability. A range of factors and variables rather than the operative alignment alone are likely to influence the longterm revision rates of TKA. Improved alignment with computer navigation has also been associated with improved functional outcomes [22]. Accurate coronal alignment with navigation may improve the accuracy of soft tissue balancing in TKA, by consistently and reliably obtaining rectangular flexion and extension gaps leading to improved kinematics [23]. However the literature to date has not consistently demonstrated better functional outcomes with navigated TKA [14]. This study represents the largest data cohort yet reported comparing navigated and conventional TKA with functional outcome scores. Multivariate analysis demonstrated no difference in functionality with navigated TKA at six months or five years. The importance of TKA component rotational positioning in the axial plane with regards to functional outcomes and revision has been well demonstrated previously [24,25]. Extensor mechanism maltracking as a result of rotational malpositioning is associated with significant anterior knee, poorer functional outcomes and further surgery following TKA. It is important to note that there is no current evidence in the literature to suggest that navigation leads to improved axial rotational alignment of components [7,8,11]. Additionally, we were unable to demonstrate that navigation led to improved functional outcomes in lower volume surgeons compared to higher volume surgeons using conventional TKA. This is despite proponents expecting navigation to especially aid lower volume surgeons to accurately implant components [2]. We found a trend for improved OKQ scores in higher volume surgeons compared to lower volume surgeons, however this was irrespective of the implantation technique. Disadvantages of navigated TKA include longer operating time and higher cost. We found that mean duration of surgery was 12 minutes longer in the navigated TKAs, consistent with the findings from previous studies [10]. Costs are influenced by a range of variables including region, volume of procedures performed and implant types. Based on Medicare reimbursement for TKA in 2006 it has been estimated that navigated TKA costs approximately $1500 (US) more per procedure compared to conventional systems, although this data is now somewhat dated [26]. Using a decision-analysis model, Novak et al (2007) concluded that a cost saving might be achieved if navigated TKA was to cost less than $629 US more than conventional systems, although this study’s conclusion was based on revision rates over a 15 year period with the assumption that coronal malalignment outside of a mechanical axis of 0° ± 3° was associated with higher revision rates [26]. Other benefits suggested by proponents of navigation such as the potential for reduced blood loss and lower risks of fat or marrow embolism were not specifically explored in this study [27,28]. However, we found no difference in mortality between the navigated and conventional groups at 30 days suggesting that any differences in these perioperative factors are not significant enough to influence patient survival. Certain limitations of the present study must be noted. Firstly, only those TKAs that were performed using the Triathlon system were included. We focused our analysis on this implant to reduce bias as it was by far the most common navigation system used, however this

limits the generalisability of our results to other navigation systems. Secondly, revision rates have only been examined over midterm follow-up as navigation was only introduced widely in the late 2000s. Consequently the long-term survival of navigated TKA compared to conventional TKA has yet to be assessed. An element of bias may also be present in the selection of which knees were navigated and non-navigated as some surgeons in the registry performed both navigated and nonnavigated knees. In some instances, cases that were anticipated to be more difficult may have been selected preferentially for navigation. In conclusion, the present study involved a comprehensive analysis of 9054 TKA procedures and failed to demonstrate improved functional outcomes for computer-assisted navigation compared to conventional systems. At midterm follow-up, the anticipated improvements in implant alignment with navigation have yet to demonstrate any benefit to implant survivorship. Appendix 1. Primary Reasons for Revision Comparing Navigated and Conventional Total Knee Arthroplasty

Deep Infection Pain Loosening Femoral Component Loosening Tibial Component Unlisted

Navigated

Non-Navigated

(N = 43)

(N = 73)

16 (37.2%) 10 (23.3%) 2 (4.7%) 0 (0%) 15 (34.9%)

27 (37.0%) 26 (35.6%) 3 (4.1%) 3 (4.1%) 14 (19.2%)

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Please cite this article as: Roberts TD, et al, Does Computer Assisted Navigation Improve Functional Outcomes and Implant Survivability after Total Knee Arthroplasty?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2014.12.036