The Journal of Arthroplasty xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty Eddie H. Huang, MD a, Steven N. Copp, MD b, William D. Bugbee, MD b a b
University of Texas Health Science Center, Houston, Texas Division of Orthopaedic Surgery, Scripps Clinic, La Jolla, California
a r t i c l e
i n f o
Article history: Received 18 September 2013 Accepted 15 May 2015 Available online xxxx Keywords: total knee arthroplasty navigation computer-assisted surgery alignment replacement
a b s t r a c t Restoration of mechanical axis in total knee arthroplasty (TKA) is correlated with improved implant survivorship. We assessed the accuracy and required surgical time using a hand-held accelerometer-based navigation system for TKA. Data collected on 53 patients included assembly, resection, and tourniquet times. Implant alignment and mechanical axis were measured on radiographs. Femoral alignment was 0.29o ± 2.2o varus. Tibial alignment was 0.09o ± 1.4o valgus. Postoperative mechanical axis was 0.2o ± 2.1o varus. Malalignment rates for the femur, tibia, and axis were 13%, 3.8%, and 17%, respectively. Average time for pinning and navigating was 3.6 minutes for the femur and 2.6 minutes for the tibia; mean tourniquet time was 62 minutes. This navigation system accurately reestablished mechanical axis without increasing surgical time. © 2015 Elsevier Inc. All rights reserved.
One of the primary technical goals of total knee arthroplasty (TKA) is to restore the mechanical axis of the lower extremity. Despite Parratte’s work, variance beyond ±3° has been established as the surrogate for ‘inadequate alignment’, even though no firm limit has been defined clinically [1]. Failure to achieve acceptable femoral and tibial component alignment and consequent limb alignment, particularly in the coronal plane (varus/valgus), has been shown to compromise the long-term survival of TKA [2,3]. Specifically, malalignment of greater than 3° leads to off-axis loading, polyethylene wear, implant loosening, and increases the rate of revision by up to 24% [4–6]. Conventional mechanical alignment guides are currently the most commonly used method for performing the distal femoral and proximal tibial resection. However, significant errors in mechanical axis alignment of greater than 3° have been reported, ranging from 22% to 35% of TKAs [7,8]. The development of computer-assisted navigation systems (CAS) as an alternative to conventional instrumentation was meant to improve the accuracy of component positioning. Studies demonstrate that CAS has reduced the frequency of component malalignment to between 3% and 19% [9]. However, the use of CAS is associated with increased costs and longer procedure times. As a result the use of CAS has been estimated to be no more than 3% of TKA procedures. More recently, patient specific instrumentation (PSI) was developed in an attempt to increase surgical efficiency and to improve 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.2015.05.055. Reprint requests: William D. Bugbee, MD, Division of Orthopaedic Surgery, Scripps Clinic, 10666 North Torrey Pines Road, MS116, La Jolla, CA, 92037.
accuracy. Limited studies have demonstrated mixed results with a rate of alignment outliers from 9% to 20% [10,11]. The increased cost and requirement of preoperative cross-sectional imaging (MRI or CT) and fabrication of cutting guides have limited the adoption of this technology. New devices or techniques that can improve surgical accuracy compared to conventional mechanical instrumentation without disruptions in surgical efficiency or significantly increased costs may be of benefit. Handheld accelerometer-based navigation systems have been developed in an attempt to improve accuracy without compromising surgical efficiency or logistics. The purpose of this study was to evaluate the accuracy of a handheld navigation device used for distal femoral and proximal tibial bone resections in TKA. In this pilot study, our aim was to determine the (1) surgical time and (2) accuracy of alignment. We hypothesized that this device, in comparison to data in the literature, would require minimal additional surgical time and would be more accurate than conventional mechanical instruments.
Methods and Materials This was an institutional review board-approved prospective, single-arm study of patients undergoing an elective primary TKA using a handheld navigation system for distal femoral and tibial resection and positioning. Exclusion criteria included ipsilateral deformity/ below knee amputation, previous TKA or osteotomy, and hip pathology limiting range of motion. Fifty-six consecutive TKA utilizing the handheld navigation system were performed by 1 of 2 senior surgeons at one institution from October 2012 to July 2013. Three patients were excluded because of inadequate postoperative radiographs. The remaining 53 patients comprised the study population. The average age was 65
http://dx.doi.org/10.1016/j.arth.2015.05.055 0883-5403/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
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E.H. Huang et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
years (range, 40–82 years), 58% were female, and the average BMI was 30. The KneeAlign navigation system (OrthAlign, Aliso Viejo, CA) is 510(K) FDA-cleared palm-sized navigation unit intended for use in TKA to assist the surgeon with coronal (varus/valgus) and sagittal (posterior slope) component positioning. The navigation system is a handheld, accelerometer-based surgical navigation system consisting of a display console and reference sensor mounted on a jig. Details of the device and navigation have been previously described [12,13]. The tibial device has two primary components that are articulated relative to one another on an extramedullary style tibial jig (Fig. 1). The fixed component is pinned to the bone, while the mobile component guides the cutting block. During the procedure, the unit is attached to the mobile component of the tibial jig, with the reference sensor attached to the fixed component of the tibial jig in order for the system to compensate for movement of the leg. The femoral jig also has two primary components that articulate with each other (Fig. 2). The fixed component is stabilized to the distal femur, while the mobile component guides the cutting block with the reference sensor. The femoral jig is seated on the distal femoral condyle, centered with reference to the deepest point of the intercondylar notch and fixed to the distal femur with three 3.2 mm threaded pins. The initial cutting block position is registered, followed by the hip center of rotation through a series of motions. The coronal and sagittal planes can then be adjusted at the surgeon’s discretion. The resection depth is not navigated but set by sliding the cutting block a measured distance relative to the femoral condyle as in conventional instrumentation systems. Intraoperative data collection included navigation time (time between the device being handed to the surgeon and the cutting block being fixed to the bone) and tourniquet time. The target femoral coronal resection angle was 0° mechanical varus/valgus alignment. The target tibial coronal resection angle was 0° varus/valgus alignment. The target tibial slope was 3° posterior slope. The overall desired mechanical axis of the limb was 0° varus/valgus in all patients. Full length (51”) anteroposterior hip to ankle and mediolateral radiographs were obtained on all patients at the first postoperative visit and reviewed utilizing a standardized protocol. Radiographic measurements for femoral component, tibial component, and mechanical alignment were performed by an independent outside musculoskeletal radiologist and by an orthopedic surgeon. By convention, all varus alignment measurements were
Fig. 2. KneeAlign navigation system femoral jig and assembly consisting of the fixed component stabilized to the distal femur and the mobile component, which guides the cutting block with the reference sensor.
assigned a negative value; valgus alignment measurements were assigned a positive value. Slope measurements were negative for anterior slope and positive for posterior slope. Interobserver reliability between the independent radiologist and the orthopedic surgeon was assessed by calculating Pearson correlation coefficients and interobserver correlation coefficients for all radiologic measurements. Means (including 95% confidence intervals) and frequencies were computed to summarize navigation time, tourniquet time, and radiographic results. Results The average time for navigating and pinning the femoral cutting block was 3.6 minutes (95% confidence interval, 3.2–4.0). The average time for navigating and pinning the tibial cutting block was 2.6 minutes (95% confidence interval, 2.3–3.9). The average tourniquet time was 62 minutes (95% confidence interval, 58–67). All correlation coefficients were above 85%, indicating a strong reliability between the independent radiologist and orthopedic surgeon for all radiographic measurements. Therefore, the measurements of both readers were averaged and used to calculate the means and frequency of outliers. The mean femoral coronal alignment was 0.8° ± 2.2° varus (range, 6.5° varus–3.8° valgus); 13% of the femoral components were placed in greater than 3° of coronal malalignment (Fig. 3). The mean tibial coronal alignment was 0.09° ± 1.4° varus (range, 3.5° varus–3.5° valgus); 3.8% of tibial components were placed in greater than 3° of coronal malalignment. The mean tibial slope was 3.3° ± 1.8° (range, 2.5°–7.0° flexion); 5.7% of tibial components were placed in greater than ± 3° of targeted tibial posterior slope (Fig. 4).The mean mechanical axis was 0.2° ± 2.1° valgus (range, 5.3° varus–5.3° valgus); 17% of knees had greater than 3° of coronal malalignment (Fig. 5). Discussion
Fig. 1. KneeAlign navigation system tibial jig and assembly consisting of the fixed component pinned to the bone and the mobile component that guides the cutting block.
The purpose of this pilot study was to evaluate a novel, handheld accelerometer-based navigation device, KneeAlign, for use in TKA. We sought to determine if this device would lead to accurate femoral and
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
E.H. Huang et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
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Fig. 3. Femur coronal alignment distribution showing 13% of the femoral components placed in greater than 3° of coronal malalignment.
tibial bone resections. For tibial component position, the device was excellent, demonstrating an accuracy of 96.2% for coronal alignment of the tibial component with only 3.8% being outside of ±3° and an accuracy of 94.3% for sagittal alignment (tibial slope) with only 5.7% outside of ±3°. The accuracy for femoral component positioning and overall mechanical axis was slightly less accurate. The femoral component resection accuracy was 87% with 13% outside of ± 3°. The overall accuracy of the mechanical axis was 83% with 17% outside of ±3°.
Fig. 5. Mechanical axis distribution showing 17% of knees with greater than 3° of coronal malalignment.
This KneeAlign device demonstrated significantly better accuracy than that reported in multiple studies utilizing conventional mechanical alignment jigs for TKA resections [4,14–19]. Cates compared the accuracy of intramedullary versus extramedullary femoral alignment systems in a series of 200 consecutive TKA and found that 28% of the extramedullary group and 14.4% of the intramedullary group were outside the acceptable range of ± 3° [14]. Engh also compared intramedullary and extramedullary femoral alignment systems in 72 consecutive TKA and found a 12.5% rate of intramedullary and a 31.2% rate of extramedullary of malalignment [16]. Dennis in a study of 120 TKA found a rate of acceptable tibial alignment in 88% in the extramedullary group and 72% of the intramedullary group [15]. Reed et al. also compared tibial component positioning in extramedullary and intramedullary instrumentation. They found a “correct” tibial alignment in 65% in the extramedullary group and in 85% of the intramedullary group [17]. Teter found that with extramedullary alignment, 92% of the cuts were ±4° of ideal, whereas 94% of the cuts with intramedullary alignment were ±4° ideal [19]. Jeffery evaluated the accuracy of intramedullary alignment guides in 115 patients with TKA and measured an accuracy of 68% [4] (Table 1). Ritter, in a review of 6070 TKAs noted an accuracy of 91.6% of their femoral components within the acceptable range of ± 3° and overall neutral mechanical alignment ±3° in 71% of TKAs [18]. Together these studies suggest a relatively high Table 1 Studies of Extramedullary and Intramedullary Comparison.
Fig. 4. Tibia coronal alignment distribution showing 3.8% of tibial components placed in greater than ± 3° of target position.
Author
Number of Subjects
Extramedullary
Intramedullary
Cates Engh Dennis Reed Teter Jeffery
200 72 120 135 352 115
28% 31.2% 12% 35% 8% —
14.4% 12.5% 28% 15% 6% 32%
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
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Table 2 Studies Reporting Alignment within ±3°: CAS vs. Conventional Surgery. Author
Number of Subjects
CAS
Mason Blakeney Hand-held
3437 108 53
91% 81% 91.6%
Conventional 68.2% 63% —
rate of outliers with the use of either intramedullary or extramedullary alignment jig and have prompted attempts to improve the accuracy of TKA technique with respect to implant and mechanical alignment. Navigation during computer assisted surgery (CAS) has also been extensively studied and compared to conventional instrumentation with respect to accuracy. Numerous studies have found increased accuracy in femoral, tibial, and mechanical alignment but with a significant increase in procedure time [8]. This increased procedure time is one of several reasons why CAS has failed to be utilized in more than 3% of the TKAs in the United States despite the improved accuracy [20] (Table 2). In terms of accuracy, Mason conducted a meta-analysis of 29 studies evaluating CAS in TKA and found CAS had a malalignment outlier ±3° frequency of 9% compared with a conventional outlier frequency of 31.8% [9]. Blakeney compared the ability of intramedullary guides, extramedullary guides, and CAS to restore the mechanical axis in 108 patients and found CAS had an accuracy of 81% compared to 64% and 62% accuracy with intramedullary and extramedullary guides, respectively. The results of our study are consistent with the values of tibial component alignment previously presented in the literature; however the results are slightly less accurate in terms of mechanical axis and femoral component alignment. The KneeAlign handheld navigation device has previously been studied by Nam. In a prospective study by Nam of 39 TKAs performed by one surgeon, 93.8% of TKA had a mechanical axis of ±3°, 96% of tibial components were within ±2° of goal, and 95.8% of femoral components were within ± 2° [13]. While the accuracy of the KneeAlign device is promising, further investigation of the effects on implant would be worthwhile to pursue in future studies given that no studies have demonstrated improved clinical outcome regarding accuracy of mechanical alignment. One study has made preliminary investigations of this issue, demonstrating that a postoperative mechanical axis of 0° ± 3° did not improve the 15-year implant survival rate in their study involving 398 TKAs [1]. While it is challenging to compare the procedure times in this study to historical reports during CAS or conventional navigation in TKA, the relatively short navigation time using the KneeAlign device suggests the “ease of use” of usability of this device during TKA. While the “ease of use” or usability of an instrumentation system is difficult due to its subjective nature, procedure time may be a useful objective measure to consider. Blakeney compared the accuracy and operative times between conventional and CAS navigated TKA. CAS required significantly more time (107 minutes) compared with extramedullary (83 minutes) or intramedullary (80 minutes) guides [8]. The mean tourniquet time in this study was generally consistent with the time reported by Nam using the same handheld navigation system; Nam reported in 160 patients a mean tourniquet time of 48.1 ± 10.2 minutes versus 54.1 ± 10.5 minutes in the CAS cohort. [12] In the present study, we reported that the KneeAlign required less than 4 minutes to navigate the femoral cut and less than 3 minutes to navigate the tibial cut. While the utility and extrapolation of this data are limited, these times support the anecdotal claims regarding ease of use of the device and suggest that the KneeAlign may offer a promising advantage over CAS for TKA. The investigation of using the KneeAlign in the navigation for alignment during TKAs involved the consideration of a several issues. First, while this was a single-arm prospective case series of patients without a randomized control group (either CAS or conventional guides), the study provided feasibility data for the device and indicated that the
device was suitable for quick and reliable navigation during TKA. The use of historical controls provides reasonable context for the performance of the device; however, additional studies with appropriate controls are needed for direct comparison. Additionally, one could also argue that computed tomography (CT) would be more accurate in measuring component positioning. However, the reliability of hip-to-ankle radiographs has been demonstrated as an accurate metric for evaluating limb alignment [21]. The excellent interobserver reliability observed here suggests there was sufficient precision and accuracy in the radiographic measurements used during this study and was chosen as the preferred method given that radiographs are part of this institutions routine postoperative care and CT would subject patients to increased radiation and costs. Our study is encouraging and validates the use of a handheld accelerometer-based navigation system. In our hands, this handheld accelerator-based navigation system demonstrated a high rate of alignment accuracy over, which is historically higher than conventional guides and approached that of a number of other CAS devices. The use of two surgeons on different levels of the learning curve may have led to a higher number of outliers during femoral and mechanical axis measurements and alignment; however, the reliability and ease of use of this device for both surgeons may offer an advantage for both early and seasoned surgeons. Utilizing the KneeAlign device may also offer several advantages including the very limited time for navigation (~3–4 minutes), the ease of attachment of the system to conventional alignment jigs, the lack of additional complications and/or fracture, and a lower cost in comparison to CAS devices which require advanced imaging and optical cameras and/or computer console devices. Although this handheld navigation system demonstrates improved accuracy of the femoral component to rival CAS devices, there is still room for improvement and surgical techniques require the ongoing pursuit of improved accuracy and efficiency within the operative theater. Thus, we are encouraged to pursue further randomized testing and algorithm optimization to improve femoral component accuracy with the KneeAlign device.
Acknowledgments Funding for conducting the research project was supported by OrthoAlign (Aliso Viejo, CA). The authors would also like to thank Julie McCauley, MPHc for her help with preparation of this manuscript and Andrea Pallante-Kichura, PhD for technical writing assistance.
References 1. Parratte S, Pagnano MW, Trousdale RT, et al. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am 2010;92(12):2143. 2. Berend ME, Ritter MA, Meding JB, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res 2004;428:26. 3. Mulhall KJ, Ghomrawi HM, Scully S, et al. Current etiologies and modes of failure in total knee arthroplasty revision. Clin Orthop Relat Res 2006;446:45. 4. Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg (Br) 1991;73(5):709. 5. Srivastava A, Lee GY, Steklov N, et al. Effect of tibial component varus on wear in total knee arthroplasty. Knee 2012;19(5):560. 6. Wasielewski RC, Galante JO, Leighty RM, et al. Wear patterns on retrieved polyethylene tibial inserts and their relationship to technical considerations during total knee arthroplasty. Clin Orthop Relat Res 1994;299:31. 7. Anderson KC, Buehler KC, Markel DC. Computer assisted navigation in total knee arthroplasty: comparison with conventional methods. J Arthroplasty 2005; 20(7 Suppl. 3):132. 8. Blakeney WG, Khan RJ, Wall SJ. Computer-assisted techniques versus conventional guides for component alignment in total knee arthroplasty: a randomized controlled trial. J Bone Joint Surg Am 2011;93(15):1377. 9. Mason JB, Fehring TK, Estok R, et al. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22(8):1097. 10. Lustig S, Scholes CJ, Oussedik SI, et al. Unsatisfactory accuracy as determined by computer navigation of VISIONAIRE patient-specific instrumentation for total knee arthroplasty. J Arthroplasty 2013;28(3):469.
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
E.H. Huang et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx 11. Ng VY, DeClaire JH, Berend KR, et al. Improved accuracy of alignment with patientspecific positioning guides compared with manual instrumentation in TKA. Clin Orthop Relat Res 2012;470(1):99. 12. Nam D, Cross M, Deshmane P, et al. Radiographic results of an accelerometer-based, handheld surgical navigation system for the tibial resection in total knee arthroplasty. Orthopedics 2011;34(10):e615. 13. Nam D, Nawabi DH, Cross MB, et al. Accelerometer-based computer navigation for performing the distal femoral resection in total knee arthroplasty. J Arthroplasty 2012;27(9):1717. 14. Cates HE, Ritter MA, Keating EM, et al. Intramedullary versus extramedullary femoral alignment systems in total knee replacement. Clin Orthop Relat Res 1993;286:32. 15. Dennis DA, Channer M, Susman MH, et al. Intramedullary versus extramedullary tibial alignment systems in total knee arthroplasty. J Arthroplasty 1993;8(1):43. 16. Engh GA, Petersen TL. Comparative experience with intramedullary and extramedullary alignment in total knee arthroplasty. J Arthroplasty 1990;5(1):1.
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17. Reed MR, Bliss W, Sher JL, et al. Extramedullary or intramedullary tibial alignment guides: a randomised, prospective trial of radiological alignment. J Bone Joint Surg (Br) 2002;84(6):858. 18. Ritter MA, Davis KE, Meding JB, et al. The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am 2011;93(17):1588. 19. Teter KE, Bregman D, Colwell Jr CW. Accuracy of intramedullary versus extramedullary tibial alignment cutting systems in total knee arthroplasty. Clin Orthop Relat Res 1995;321:106. 20. Flint JM, Samir, Washington Health Policy Fellows. From Pong to CAOS: a short history of computers in orthopaedics. AAOS Now. AAOS; 2007 [http://wwwaaosorg/news/ bulletin/sep07/reimbursement3asp]. 21. Skytta ET, Haapamaki V, Koivikko M, et al. Reliability of the hip-to-ankle radiograph in determining the knee and implant alignment after total knee arthroplasty. Acta Orthop Belg 2011;77(3):329.
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty Eddie H. Huang, MD a, Steven N. Copp, MD b, William D. Bugbee, MD b a b
University of Texas Health Science Center, Houston, Texas Division of Orthopaedic Surgery, Scripps Clinic, La Jolla, California
a r t i c l e
i n f o
Article history: Received 18 September 2013 Accepted 15 May 2015 Available online xxxx Keywords: total knee arthroplasty navigation computer-assisted surgery alignment replacement
a b s t r a c t Restoration of mechanical axis in total knee arthroplasty (TKA) is correlated with improved implant survivorship. We assessed the accuracy and required surgical time using a hand-held accelerometer-based navigation system for TKA. Data collected on 53 patients included assembly, resection, and tourniquet times. Implant alignment and mechanical axis were measured on radiographs. Femoral alignment was 0.29o ± 2.2o varus. Tibial alignment was 0.09o ± 1.4o valgus. Postoperative mechanical axis was 0.2o ± 2.1o varus. Malalignment rates for the femur, tibia, and axis were 13%, 3.8%, and 17%, respectively. Average time for pinning and navigating was 3.6 minutes for the femur and 2.6 minutes for the tibia; mean tourniquet time was 62 minutes. This navigation system accurately reestablished mechanical axis without increasing surgical time. © 2015 Elsevier Inc. All rights reserved.
One of the primary technical goals of total knee arthroplasty (TKA) is to restore the mechanical axis of the lower extremity. Despite Parratte’s work, variance beyond ±3° has been established as the surrogate for ‘inadequate alignment’, even though no firm limit has been defined clinically [1]. Failure to achieve acceptable femoral and tibial component alignment and consequent limb alignment, particularly in the coronal plane (varus/valgus), has been shown to compromise the long-term survival of TKA [2,3]. Specifically, malalignment of greater than 3° leads to off-axis loading, polyethylene wear, implant loosening, and increases the rate of revision by up to 24% [4–6]. Conventional mechanical alignment guides are currently the most commonly used method for performing the distal femoral and proximal tibial resection. However, significant errors in mechanical axis alignment of greater than 3° have been reported, ranging from 22% to 35% of TKAs [7,8]. The development of computer-assisted navigation systems (CAS) as an alternative to conventional instrumentation was meant to improve the accuracy of component positioning. Studies demonstrate that CAS has reduced the frequency of component malalignment to between 3% and 19% [9]. However, the use of CAS is associated with increased costs and longer procedure times. As a result the use of CAS has been estimated to be no more than 3% of TKA procedures. More recently, patient specific instrumentation (PSI) was developed in an attempt to increase surgical efficiency and to improve 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.2015.05.055. Reprint requests: William D. Bugbee, MD, Division of Orthopaedic Surgery, Scripps Clinic, 10666 North Torrey Pines Road, MS116, La Jolla, CA, 92037.
accuracy. Limited studies have demonstrated mixed results with a rate of alignment outliers from 9% to 20% [10,11]. The increased cost and requirement of preoperative cross-sectional imaging (MRI or CT) and fabrication of cutting guides have limited the adoption of this technology. New devices or techniques that can improve surgical accuracy compared to conventional mechanical instrumentation without disruptions in surgical efficiency or significantly increased costs may be of benefit. Handheld accelerometer-based navigation systems have been developed in an attempt to improve accuracy without compromising surgical efficiency or logistics. The purpose of this study was to evaluate the accuracy of a handheld navigation device used for distal femoral and proximal tibial bone resections in TKA. In this pilot study, our aim was to determine the (1) surgical time and (2) accuracy of alignment. We hypothesized that this device, in comparison to data in the literature, would require minimal additional surgical time and would be more accurate than conventional mechanical instruments.
Methods and Materials This was an institutional review board-approved prospective, single-arm study of patients undergoing an elective primary TKA using a handheld navigation system for distal femoral and tibial resection and positioning. Exclusion criteria included ipsilateral deformity/ below knee amputation, previous TKA or osteotomy, and hip pathology limiting range of motion. Fifty-six consecutive TKA utilizing the handheld navigation system were performed by 1 of 2 senior surgeons at one institution from October 2012 to July 2013. Three patients were excluded because of inadequate postoperative radiographs. The remaining 53 patients comprised the study population. The average age was 65
http://dx.doi.org/10.1016/j.arth.2015.05.055 0883-5403/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
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E.H. Huang et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
years (range, 40–82 years), 58% were female, and the average BMI was 30. The KneeAlign navigation system (OrthAlign, Aliso Viejo, CA) is 510(K) FDA-cleared palm-sized navigation unit intended for use in TKA to assist the surgeon with coronal (varus/valgus) and sagittal (posterior slope) component positioning. The navigation system is a handheld, accelerometer-based surgical navigation system consisting of a display console and reference sensor mounted on a jig. Details of the device and navigation have been previously described [12,13]. The tibial device has two primary components that are articulated relative to one another on an extramedullary style tibial jig (Fig. 1). The fixed component is pinned to the bone, while the mobile component guides the cutting block. During the procedure, the unit is attached to the mobile component of the tibial jig, with the reference sensor attached to the fixed component of the tibial jig in order for the system to compensate for movement of the leg. The femoral jig also has two primary components that articulate with each other (Fig. 2). The fixed component is stabilized to the distal femur, while the mobile component guides the cutting block with the reference sensor. The femoral jig is seated on the distal femoral condyle, centered with reference to the deepest point of the intercondylar notch and fixed to the distal femur with three 3.2 mm threaded pins. The initial cutting block position is registered, followed by the hip center of rotation through a series of motions. The coronal and sagittal planes can then be adjusted at the surgeon’s discretion. The resection depth is not navigated but set by sliding the cutting block a measured distance relative to the femoral condyle as in conventional instrumentation systems. Intraoperative data collection included navigation time (time between the device being handed to the surgeon and the cutting block being fixed to the bone) and tourniquet time. The target femoral coronal resection angle was 0° mechanical varus/valgus alignment. The target tibial coronal resection angle was 0° varus/valgus alignment. The target tibial slope was 3° posterior slope. The overall desired mechanical axis of the limb was 0° varus/valgus in all patients. Full length (51”) anteroposterior hip to ankle and mediolateral radiographs were obtained on all patients at the first postoperative visit and reviewed utilizing a standardized protocol. Radiographic measurements for femoral component, tibial component, and mechanical alignment were performed by an independent outside musculoskeletal radiologist and by an orthopedic surgeon. By convention, all varus alignment measurements were
Fig. 2. KneeAlign navigation system femoral jig and assembly consisting of the fixed component stabilized to the distal femur and the mobile component, which guides the cutting block with the reference sensor.
assigned a negative value; valgus alignment measurements were assigned a positive value. Slope measurements were negative for anterior slope and positive for posterior slope. Interobserver reliability between the independent radiologist and the orthopedic surgeon was assessed by calculating Pearson correlation coefficients and interobserver correlation coefficients for all radiologic measurements. Means (including 95% confidence intervals) and frequencies were computed to summarize navigation time, tourniquet time, and radiographic results. Results The average time for navigating and pinning the femoral cutting block was 3.6 minutes (95% confidence interval, 3.2–4.0). The average time for navigating and pinning the tibial cutting block was 2.6 minutes (95% confidence interval, 2.3–3.9). The average tourniquet time was 62 minutes (95% confidence interval, 58–67). All correlation coefficients were above 85%, indicating a strong reliability between the independent radiologist and orthopedic surgeon for all radiographic measurements. Therefore, the measurements of both readers were averaged and used to calculate the means and frequency of outliers. The mean femoral coronal alignment was 0.8° ± 2.2° varus (range, 6.5° varus–3.8° valgus); 13% of the femoral components were placed in greater than 3° of coronal malalignment (Fig. 3). The mean tibial coronal alignment was 0.09° ± 1.4° varus (range, 3.5° varus–3.5° valgus); 3.8% of tibial components were placed in greater than 3° of coronal malalignment. The mean tibial slope was 3.3° ± 1.8° (range, 2.5°–7.0° flexion); 5.7% of tibial components were placed in greater than ± 3° of targeted tibial posterior slope (Fig. 4).The mean mechanical axis was 0.2° ± 2.1° valgus (range, 5.3° varus–5.3° valgus); 17% of knees had greater than 3° of coronal malalignment (Fig. 5). Discussion
Fig. 1. KneeAlign navigation system tibial jig and assembly consisting of the fixed component pinned to the bone and the mobile component that guides the cutting block.
The purpose of this pilot study was to evaluate a novel, handheld accelerometer-based navigation device, KneeAlign, for use in TKA. We sought to determine if this device would lead to accurate femoral and
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
E.H. Huang et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
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Fig. 3. Femur coronal alignment distribution showing 13% of the femoral components placed in greater than 3° of coronal malalignment.
tibial bone resections. For tibial component position, the device was excellent, demonstrating an accuracy of 96.2% for coronal alignment of the tibial component with only 3.8% being outside of ±3° and an accuracy of 94.3% for sagittal alignment (tibial slope) with only 5.7% outside of ±3°. The accuracy for femoral component positioning and overall mechanical axis was slightly less accurate. The femoral component resection accuracy was 87% with 13% outside of ± 3°. The overall accuracy of the mechanical axis was 83% with 17% outside of ±3°.
Fig. 5. Mechanical axis distribution showing 17% of knees with greater than 3° of coronal malalignment.
This KneeAlign device demonstrated significantly better accuracy than that reported in multiple studies utilizing conventional mechanical alignment jigs for TKA resections [4,14–19]. Cates compared the accuracy of intramedullary versus extramedullary femoral alignment systems in a series of 200 consecutive TKA and found that 28% of the extramedullary group and 14.4% of the intramedullary group were outside the acceptable range of ± 3° [14]. Engh also compared intramedullary and extramedullary femoral alignment systems in 72 consecutive TKA and found a 12.5% rate of intramedullary and a 31.2% rate of extramedullary of malalignment [16]. Dennis in a study of 120 TKA found a rate of acceptable tibial alignment in 88% in the extramedullary group and 72% of the intramedullary group [15]. Reed et al. also compared tibial component positioning in extramedullary and intramedullary instrumentation. They found a “correct” tibial alignment in 65% in the extramedullary group and in 85% of the intramedullary group [17]. Teter found that with extramedullary alignment, 92% of the cuts were ±4° of ideal, whereas 94% of the cuts with intramedullary alignment were ±4° ideal [19]. Jeffery evaluated the accuracy of intramedullary alignment guides in 115 patients with TKA and measured an accuracy of 68% [4] (Table 1). Ritter, in a review of 6070 TKAs noted an accuracy of 91.6% of their femoral components within the acceptable range of ± 3° and overall neutral mechanical alignment ±3° in 71% of TKAs [18]. Together these studies suggest a relatively high Table 1 Studies of Extramedullary and Intramedullary Comparison.
Fig. 4. Tibia coronal alignment distribution showing 3.8% of tibial components placed in greater than ± 3° of target position.
Author
Number of Subjects
Extramedullary
Intramedullary
Cates Engh Dennis Reed Teter Jeffery
200 72 120 135 352 115
28% 31.2% 12% 35% 8% —
14.4% 12.5% 28% 15% 6% 32%
Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
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E.H. Huang et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Table 2 Studies Reporting Alignment within ±3°: CAS vs. Conventional Surgery. Author
Number of Subjects
CAS
Mason Blakeney Hand-held
3437 108 53
91% 81% 91.6%
Conventional 68.2% 63% —
rate of outliers with the use of either intramedullary or extramedullary alignment jig and have prompted attempts to improve the accuracy of TKA technique with respect to implant and mechanical alignment. Navigation during computer assisted surgery (CAS) has also been extensively studied and compared to conventional instrumentation with respect to accuracy. Numerous studies have found increased accuracy in femoral, tibial, and mechanical alignment but with a significant increase in procedure time [8]. This increased procedure time is one of several reasons why CAS has failed to be utilized in more than 3% of the TKAs in the United States despite the improved accuracy [20] (Table 2). In terms of accuracy, Mason conducted a meta-analysis of 29 studies evaluating CAS in TKA and found CAS had a malalignment outlier ±3° frequency of 9% compared with a conventional outlier frequency of 31.8% [9]. Blakeney compared the ability of intramedullary guides, extramedullary guides, and CAS to restore the mechanical axis in 108 patients and found CAS had an accuracy of 81% compared to 64% and 62% accuracy with intramedullary and extramedullary guides, respectively. The results of our study are consistent with the values of tibial component alignment previously presented in the literature; however the results are slightly less accurate in terms of mechanical axis and femoral component alignment. The KneeAlign handheld navigation device has previously been studied by Nam. In a prospective study by Nam of 39 TKAs performed by one surgeon, 93.8% of TKA had a mechanical axis of ±3°, 96% of tibial components were within ±2° of goal, and 95.8% of femoral components were within ± 2° [13]. While the accuracy of the KneeAlign device is promising, further investigation of the effects on implant would be worthwhile to pursue in future studies given that no studies have demonstrated improved clinical outcome regarding accuracy of mechanical alignment. One study has made preliminary investigations of this issue, demonstrating that a postoperative mechanical axis of 0° ± 3° did not improve the 15-year implant survival rate in their study involving 398 TKAs [1]. While it is challenging to compare the procedure times in this study to historical reports during CAS or conventional navigation in TKA, the relatively short navigation time using the KneeAlign device suggests the “ease of use” of usability of this device during TKA. While the “ease of use” or usability of an instrumentation system is difficult due to its subjective nature, procedure time may be a useful objective measure to consider. Blakeney compared the accuracy and operative times between conventional and CAS navigated TKA. CAS required significantly more time (107 minutes) compared with extramedullary (83 minutes) or intramedullary (80 minutes) guides [8]. The mean tourniquet time in this study was generally consistent with the time reported by Nam using the same handheld navigation system; Nam reported in 160 patients a mean tourniquet time of 48.1 ± 10.2 minutes versus 54.1 ± 10.5 minutes in the CAS cohort. [12] In the present study, we reported that the KneeAlign required less than 4 minutes to navigate the femoral cut and less than 3 minutes to navigate the tibial cut. While the utility and extrapolation of this data are limited, these times support the anecdotal claims regarding ease of use of the device and suggest that the KneeAlign may offer a promising advantage over CAS for TKA. The investigation of using the KneeAlign in the navigation for alignment during TKAs involved the consideration of a several issues. First, while this was a single-arm prospective case series of patients without a randomized control group (either CAS or conventional guides), the study provided feasibility data for the device and indicated that the
device was suitable for quick and reliable navigation during TKA. The use of historical controls provides reasonable context for the performance of the device; however, additional studies with appropriate controls are needed for direct comparison. Additionally, one could also argue that computed tomography (CT) would be more accurate in measuring component positioning. However, the reliability of hip-to-ankle radiographs has been demonstrated as an accurate metric for evaluating limb alignment [21]. The excellent interobserver reliability observed here suggests there was sufficient precision and accuracy in the radiographic measurements used during this study and was chosen as the preferred method given that radiographs are part of this institutions routine postoperative care and CT would subject patients to increased radiation and costs. Our study is encouraging and validates the use of a handheld accelerometer-based navigation system. In our hands, this handheld accelerator-based navigation system demonstrated a high rate of alignment accuracy over, which is historically higher than conventional guides and approached that of a number of other CAS devices. The use of two surgeons on different levels of the learning curve may have led to a higher number of outliers during femoral and mechanical axis measurements and alignment; however, the reliability and ease of use of this device for both surgeons may offer an advantage for both early and seasoned surgeons. Utilizing the KneeAlign device may also offer several advantages including the very limited time for navigation (~3–4 minutes), the ease of attachment of the system to conventional alignment jigs, the lack of additional complications and/or fracture, and a lower cost in comparison to CAS devices which require advanced imaging and optical cameras and/or computer console devices. Although this handheld navigation system demonstrates improved accuracy of the femoral component to rival CAS devices, there is still room for improvement and surgical techniques require the ongoing pursuit of improved accuracy and efficiency within the operative theater. Thus, we are encouraged to pursue further randomized testing and algorithm optimization to improve femoral component accuracy with the KneeAlign device.
Acknowledgments Funding for conducting the research project was supported by OrthoAlign (Aliso Viejo, CA). The authors would also like to thank Julie McCauley, MPHc for her help with preparation of this manuscript and Andrea Pallante-Kichura, PhD for technical writing assistance.
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Please cite this article as: Huang EH, et al, Accuracy of A Handheld Accelerometer-Based Navigation System for Femoral and Tibial Resection in Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.055
