Special Focus Section
171
Does the Use of Navigation in Total Knee Arthroplasty Affect Outcomes? Adrian W. Clayton, DO1 Jeffrey J. Cherian, DO1 Samik Banerjee, MS (Orth), MRCS (Glasg)1 Bhaveen H. Kapadia, MD1 Julio J. Jauregui, MD1 Steven F. Harwin, MD2 Michael A. Mont, MD1 1 Center for Joint Preservation and Replacement, Rubin Institute for
Advanced Orthopedics, Baltimore, Maryland 2 Department of Orthopaedic Surgery, Beth Israel Medical Center, New York, New York
Address for correspondence Michael A. Mont, MD, Center for Joint Preservation and Replacement, Rubin Institute for Advanced Orthopedics, 2401 West Belvedere Avenue, Baltimore, MD 21215 (e-mail: [email protected]).
Abstract
Keywords
► computer-assisted ► total knee arthroplasty ► navigation
Numerous studies have demonstrated that deviation from the mechanical axis of more than 3 degrees can lead to increased complications and decreased patient satisfaction. The stimulus for navigation of total knee arthroplasty (TKA) was born out of the need for more precise and reliable component alignment. Proponents believe that navigated TKA has the theoretical benefits of improved implant survivorship, better functional outcomes, and greater patient satisfaction. Several studies have shown that intraoperative use of navigation results in superior component positioning when compared with conventional TKA. However, because of concerns about higher institutional costs, intraoperative difficulties, steep learning curves, and potential tracker pin complications, navigation TKA has not gained wide popularity. Moreover, to fully evaluate the use of navigation in TKA, we believe that larger prospective randomized studies are required to clearly define outcomes, as well as economic implications.
Proper component alignment in total knee arthroplasty (TKA) is considered to be a critical factor in determining the longterm functional and survivorship outcomes.1,2 It has been estimated that 10% or greater of TKAs have marked (> 3 degrees) errors in mechanical alignment.3 Many authors believe that optimal alignment may decrease mechanical and shear stresses placed on the bearing surfaces, as well as the bone/prosthesis interfaces.4–6 In addition, it is believed that appropriate alignment assists in balancing the forces conveyed through the soft-tissue envelope, which is essential for proper joint function.5 Studies have supported this assertion by demonstrating that deviation from the mechanical axis of more than 3 degrees can lead to decreased implant survivorship, increased wear, poor functional outcomes, and early failures leading to component loosening.4,6–12 Therefore, the driving stimulus for navigated TKA was the need for more precise and reliable component alignment. Computer navigation aids surgeons in achieving more accu-
rate postoperative alignment through more precise bony cuts and ligamentous balancing.13,14 This consistency has the potential benefits of increased implant longevity, improved functional outcomes, and greater patient satisfaction.15 The purpose of this review was to summarize the recent evidence concerning the use of navigation in TKA. We specifically focused on the following: (1) history and technology; (2) survivorship; (3) alignment/functional outcomes; (4) economics; and (5) the future outlook on the use of this technology.
received February 19, 2014 accepted March 16, 2014 published online April 24, 2014
Copyright © 2014 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
History and Technology Computer-assisted navigation was originally used for insertion of pedicle screws,16 but in 1997 the first published case was performed in a TKA.17 The software and hardware of these systems have been constantly improving from its inception.18 Previously used bulky systems have been
DOI http://dx.doi.org/ 10.1055/s-0034-1374814. ISSN 1538-8506.
Downloaded by: NYU. Copyrighted material.
J Knee Surg 2014;27:171–176.
Does the Use of Navigation in Total Knee Arthroplasty Affect Outcomes? engineered into smaller components, even to the point where there are hand-held options available today. These navigation systems aid in constructing a three-dimensional model of the patient’s knee intraoperatively, and correlate the position of the surgeon’s instruments to the model. Various navigated surgical systems are currently available for use during knee arthroplasty. Image-guided systems use intraoperative (fluoroscopy assisted) or preoperative anatomic data points (obtained by computed tomographic scan) to construct the threedimensional knee models. In these systems, the position of the knee is recorded intraoperatively by reflective markers drilled into the tibia and femur. Additional markers are tactically placed on surgical instruments, which are tracked with the previous markers in the bone, providing a computer-assisted guide for cutting jig placement. The emitter and navigation computer receives information from infrared cameras which track the movement of the markers, allowing the computer to guide the surgeon’s placement of cutting jigs in the most accurate position. This may potentially reduce the incidence of intraoperative errors in bone cuts during TKA. Conversely, imageless systems utilize a database of knee CT scans to match a three-dimensional knee model based on anatomic registration points obtained intraoperatively by the surgeon. The knee position and cutting jig placement are then recorded, and are positioned as directed by the image-guided systems.19 Customized patient instrumentation builds a model of the knee based on preoperative CT or magnetic resonance imaging scans. Some systems produce cutting guides that are placed directly onto the patient intraoperatively, whereas others allow placement of guide pins in the bone onto which conventional cutting blocks are placed. These updates in this one system have demonstrated shorter operating room times, while maintaining accurate component positioning.19
Results The radiographic consistency of the mechanical axis using navigation TKA has been well documented in the literature.20–26 A meta-analysis by Rebal et al evaluated 1,713 knees (869 computer assisted; 844 control cohort) from 21 studies to determine whether computer navigation provided superior short-term outcomes compared with conventional TKA.27 The authors found that navigated TKAs were significantly more likely to obtain coronal alignments within 3 degrees of the mechanical axis compared with conventional TKAs (87.1 vs. 73.7%, p < 0.01). In addition, they reported that the patients who underwent TKA using navigation had significantly greater increases in their Knee Society scores at 3-month (68.5 vs. 58.1 points; p < 0.03) and 12-month (53.1 vs. 45.8 points; p < 0.01) mean follow-ups. Similarly, another meta-analysis by Thienpont et al examined if there were improvements in knee alignment in TKA with the use of navigation compared with conventional methods in 28,763 patients from 10 meta-analyses.28 The authors found that for overall mechanical alignment of > 2 degrees, there was lower likelihood of mechanical axis outliers with the use of computer navigation when compared with conventional techniThe Journal of Knee Surgery
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ques (effects measured; odds and risk ratio ¼ 0.21–0.76). A recent study by Johnson et al15 compared the use of navigation to conventional TKA methods in 54 patients who underwent sequential bilateral TKA. They did not find significant differences with regards to mean tibiofemoral (p ¼ 0.115), mechanical (p ¼ 0.802), proximal tibial angle (p ¼ 0.303), distal femoral angle (p ¼ 0.555), femoral component flexion (p ¼ 0.781), or posterior tibial slope (p ¼ 0.843). Despite these results, there were less mechanical axes outliers in the navigation group with regards to tibiofemoral angle, mechanical axis, and proximal tibial angle. However, several studies have refuted the potentially superior mechanical alignment of navigation systems.15,29–32 Kim et al, examined 160 patients (320 knees) using computerassisted TKA compared with conventional techniques on alignment and functional outcomes. The authors demonstrated that there were no significant differences in alignment (implant position, prevalence of outlier) and mean postoperative functional outcomes (Knee Society scores, 83 vs. 81 points; range of motion [ROM], 123 vs. 126 degrees; and Hospital for Special Surgery scores, 89 vs. 91 points) at a mean 3.4-year follow-up (p > 0.05).30 Despite the majority of research verifying that navigation TKA has fewer outliers with regards to the mechanical axis, clinical results have not demonstrated equal success.30,33–38 A recent systematic review by Burnett and Barrack evaluated this technology.33 The authors found that navigation resulted in improved coronal alignment when compared with conventional techniques, however, they observed little to no evidence supporting improvements in functional outcomes. Similarly, Johnson et al evaluated alignment and functional outcomes in 54 patients who underwent bilateral sequential TKA utilizing navigation in one knee and traditional instrumentation in the other.15 The authors reported that there was a significant reduction in radiographic outliers for the computer-assisted TKA cohort compared with tradition methods with regards to mechanical axis (6.1 vs. 20.4%, p ¼ 0.037) and tibial component alignment (0 vs. 7.5%, p ¼ 0.042). However, the authors were unable to demonstrate any improvements in KSS and ROM with the use of computer-assisted TKA (p > 0.05) at a mean follow-up of 2.5 years. These findings were confirmed by several Level 1 studies that have found no differences in patient outcomes when navigated TKA was compared with conventional performed procedures (►Table 1).34–38
Potential Pitfalls of Computer Navigation Navigation systems that rely on anatomic registration points to construct the three-dimensional model of the patient’s knee do have zones, which if marked incorrectly may lead to component malposition. Amanatullah et al found that registration errors were the most commonly associated with the distal femoral epicondyles, with both intraobserver and interobserver variability.39 These types of registration errors can lead to malrotation of the femoral component, as well as result in balancing and tracking issues. Navigation systems that use reflective markers drilled into the femur and tibia are at the potential risk of tracker pin movement when placed in patients
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Table 1 Level 1 studies of functional outcomes with navigation TKA Author
Year 53
Mean follow-up (y)
Brief summary of functional results
2014
5
No difference in KSS, high-activity arthroplasty scores
Lützner et al54
2013
2 and 5
No difference in KSS, Knee Score, Functional score, VAS scale
Kim et al36
2012
10.8
No difference in KSS, WOMAC scores
2012
5
No difference in KSS, WOMAC scores
2009
Minimum 2
No difference in HSS, WOMAC scores
Allen et al
Harvie et al
34
Seon et al38
who have osteoporotic bone. In addition, Lee et al found that in patients who had osteoporotic bone there was a higher likelihood of tibia valgus component positioning.40 Fractures have also been reported with navigation pin tracker sites and must be taken in account when using these systems.41,42 Software and hardware accuracy are factors not controlled by the surgeon that can also determine the accuracy of navigated TKA. However, there are some instances in which navigation systems may provide a useful tool and may be more successful than other methods. Patients who have retained hardware and severe extra-articular deformities can be treated successfully with navigation TKA.43–50 Navigation systems have also been used to achieve soft tissue balance in TKA. Joseph et al, found that navigation provided a superior mediolateral extension gap, however, no differences were found in the flexion gap or in achieving equal flexion and extension gaps when compared with conventional methods.51
et al examined the relationship between component alignment and survivorship in 398 TKAs.52 The authors found no differences in Kaplan–Meier 15-year survivorship estimates between the prostheses placed within 3 degrees of varus or valgus to the prosthesis aligned outside of this range. Studies such as these have raised questions of the importance of alignment within 3 degrees of the mechanical axis, which would ultimately render navigation in TKA less useful. However, proponents believe that improvements in implant survivorship over long-term follow-up will outweigh the initial increased costs of navigated TKA. Much of the costs of this technology may decrease with time, which may lead to more affordable navigation systems. These systems may become more popular in the future leading to more surgeons being trained on them, which may decrease the learning curve associated with navigation TKA. However, it is vital to understand that conventional TKA has a proven track record of 20-year plus survivorship that is working against the transition to navigated TKA.
Cost Analyses The institutional costs of navigation TKA are often not justified with regards to clinical results based on the majority of literature available. Novak et al, performed a decision-analysis model to estimate the cost effectiveness of navigation TKA.41 They found that there was cost savings for navigation TKA, if the additional cost per operation was below $629.41 This model, however, included a predicted favorable clinical outcome with precision mechanical alignment that is produced with navigation TKA. All of these systems may increase the cost of the operation with regards to installation and maintenance, as well as advanced imaging that is required by some of the systems. The machines and software are expensive, however, the increase in manpower for set up and additional steps leading to longer operating room times also add to the health care cost. These may be the reasons that despite radiographic evidence of improved limb alignment, less than 5% of surgeons in the United States currently use navigated TKA.42
Conclusion Appropriate component alignment in TKA is considered to be an important factor in determining long-term outcomes. Many reports have demonstrated that deviation from the mechanical axis of more than 3 degrees can lead to decreased implant survivorship, increased wear, and poor functional outcomes. Studies have shown that navigated TKA can reduce the number of radiographic outliers when compared with traditional techniques. Nevertheless, only a few reports have shown that navigation can result in improved functional outcomes after TKA. In addition, high startup costs, steep learning curves, increased operative times, and bulky equipment needs are believed to have prevented widespread popularity of these systems. Moreover, to fully evaluate the use of navigation in TKA, the authors believe that larger prospective randomized studies are required to clearly define outcomes, as well as any potential economic benefits.
Future Outlook TKA performed with navigation is believed to result in superior radiographic alignment outliers when compared with conventional instrumentation, however, functional benefits are still questionable. More recently, a study by Parratte
References 1 Barrett WP, Mason JB, Moskal JT, Dalury DF, Oliashirazi A, Fisher
DA. Comparison of radiographic alignment of imageless computerassisted surgery vs conventional instrumentation in primary total knee arthroplasty. J Arthroplasty 2011;26(8):1273–1284, e1 The Journal of Knee Surgery
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Abbreviations: HSS, Hospital for Special Surgery score; KSS, Knee Society score; TKA, total knee arthroplasty; VAS, visual analog scale; WOMAC, Western Ontario and McMaster Universities osteoarthritis index.
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comparison of alignment using patient specific guides, computer navigation and conventional instrumentation in total knee arthroplasty. Knee 2013; November 14 (Epub ahead of print) Schmitt J, Hauk C, Kienapfel H, et al. Navigation of total knee arthroplasty: rotation of components and clinical results in a prospectively randomized study. BMC Musculoskelet Disord 2011;12:16 Soares LF, Nunes TA, de Andrade MA, Neyret P, Badet R. The effect of computerized navigation on component alignment in total knee arthroplasty. Acta Orthop Traumatol Turc 2013;47(1):8–13 Rebal BA, Babatunde OM, Lee JH, Geller JA, Patrick DA Jr, Macaulay W. Imageless computer navigation in total knee arthroplasty provides superior short term functional outcomes: a meta-analysis. J Arthroplasty 2013; October 17 (Epub ahead of print) Thienpont E, Fennema P, Price A. Can technology improve alignment during knee arthroplasty. Knee 2013;20(Suppl 1):S21–S28 Choi WC, Lee S, An JH, Kim D, Seong SC, Lee MC. Plain radiograph fails to reflect the alignment and advantages of navigation in total knee arthroplasty. J Arthroplasty 2011;26(5):756–764 Kim YH, Kim JS, Choi Y, Kwon OR. Computer-assisted surgical navigation does not improve the alignment and orientation of the components in total knee arthroplasty. J Bone Joint Surg Am 2009; 91(1):14–19 Nunley RM, Ellison BS, Ruh EL, et al. Are patient-specific cutting blocks cost-effective for total knee arthroplasty? Clin Orthop Relat Res 2012;470(3):889–894 Barrack RL, Ruh EL, Williams BM, Ford AD, Foreman K, Nunley RM. Patient specific cutting blocks are currently of no proven value. J Bone Joint Surg Br 2012;94(11, Suppl A):95–99 Burnett RS, Barrack RL. Computer-assisted total knee arthroplasty is currently of no proven clinical benefit: a systematic review. Clin Orthop Relat Res 2013;471(1):264–276 Harvie P, Sloan K, Beaver RJ. Computer navigation vs conventional total knee arthroplasty: five-year functional results of a prospective randomized trial. J Arthroplasty 2012;27(5):667–672, e1 Hoffart HE, Langenstein E, Vasak N. A prospective study comparing the functional outcome of computer-assisted and conventional total knee replacement. J Bone Joint Surg Br 2012;94(2):194–199 Kim YH, Park JW, Kim JS. Computer-navigated versus conventional total knee arthroplasty a prospective randomized trial. J Bone Joint Surg Am 2012;94(22):2017–2024 O’Connor MI, Brodersen MP, Feinglass NG, Leone BJ, Crook JE, Switzer BE. Fat emboli in total knee arthroplasty: a prospective randomized study of computer-assisted navigation vs standard surgical technique. J Arthroplasty 2010;25(7):1034–1040 Seon JK, Park SJ, Lee KB, Li G, Kozanek M, Song EK. Functional comparison of total knee arthroplasty performed with and without a navigation system. Int Orthop 2009;33(4):987–990 Amanatullah DF, Di Cesare PE, Meere PA, Pereira GC. Identification of the landmark registration safe zones during total knee arthroplasty using an imageless navigation system. J Arthroplasty 2013; 28(6):938–942 Lee DH, Padhy D, Lee SH, Nha KW, Park JH, Han SB. Osteoporosis affects component positioning in computer navigation-assisted total knee arthroplasty. Knee 2012;19(3):203–207 Jung HJ, Jung YB, Song KS, Park SJ, Lee JS. Fractures associated with computer-navigated total knee arthroplasty. A report of two cases. J Bone Joint Surg Am 2007;89(10):2280–2284 Ossendorf C, Fuchs B, Koch P. Femoral stress fracture after computer navigated total knee arthroplasty. Knee 2006;13(5): 397–399 Bottros J, Klika AK, Lee HH, Polousky J, Barsoum WK. The use of navigation in total knee arthroplasty for patients with extraarticular deformity. J Arthroplasty 2008;23(1):74–78 Catani F, Digennaro V, Ensini A, Leardini A, Giannini S. Navigationassisted total knee arthroplasty in knees with osteoarthritis due to
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extra-articular deformity. Knee Surg Sports Traumatol Arthrosc 2012;20(3):546–551 Chou WY, Ko JY, Wang CJ, Wang FS, Wu RW, Wong T. Navigationassisted total knee arthroplasty for a knee with malunion of the distal femur. J Arthroplasty 2008;23(8):e13–e19 Hernandez-Vaquero D, Suarez-Vazquez A, Iglesias-Fernandez S. Computer-assisted navigation in total knee arthroplasty without femoral hardware removal. Acta Chir Orthop Traumatol Cech 2012;79(4):331–24 Kim KK, Heo YM, Won YY, Lee WS. Navigation-assisted total knee arthroplasty for the knee retaining femoral intramedullary nail, and distal femoral plate and screws. Clin Orthop Surg 2011;3(1):77–80 Kuo CC, Bosque J, Meehan JP, Jamali AA. Computer-assisted navigation of total knee arthroplasty for osteoarthritis in a patient with severe posttraumatic femoral deformity. J Arthroplasty 2011; 26(6):e17–e20 Liu Z, Pan X, Zhang X. Total knee arthroplasty using navigation system for severe osteoarthritis with extra-articular deformity. Eur J Orthop Surg Traumatol 2013;23(1):93–96
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The Journal of Knee Surgery
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171
Does the Use of Navigation in Total Knee Arthroplasty Affect Outcomes? Adrian W. Clayton, DO1 Jeffrey J. Cherian, DO1 Samik Banerjee, MS (Orth), MRCS (Glasg)1 Bhaveen H. Kapadia, MD1 Julio J. Jauregui, MD1 Steven F. Harwin, MD2 Michael A. Mont, MD1 1 Center for Joint Preservation and Replacement, Rubin Institute for
Advanced Orthopedics, Baltimore, Maryland 2 Department of Orthopaedic Surgery, Beth Israel Medical Center, New York, New York
Address for correspondence Michael A. Mont, MD, Center for Joint Preservation and Replacement, Rubin Institute for Advanced Orthopedics, 2401 West Belvedere Avenue, Baltimore, MD 21215 (e-mail: [email protected]).
Abstract
Keywords
► computer-assisted ► total knee arthroplasty ► navigation
Numerous studies have demonstrated that deviation from the mechanical axis of more than 3 degrees can lead to increased complications and decreased patient satisfaction. The stimulus for navigation of total knee arthroplasty (TKA) was born out of the need for more precise and reliable component alignment. Proponents believe that navigated TKA has the theoretical benefits of improved implant survivorship, better functional outcomes, and greater patient satisfaction. Several studies have shown that intraoperative use of navigation results in superior component positioning when compared with conventional TKA. However, because of concerns about higher institutional costs, intraoperative difficulties, steep learning curves, and potential tracker pin complications, navigation TKA has not gained wide popularity. Moreover, to fully evaluate the use of navigation in TKA, we believe that larger prospective randomized studies are required to clearly define outcomes, as well as economic implications.
Proper component alignment in total knee arthroplasty (TKA) is considered to be a critical factor in determining the longterm functional and survivorship outcomes.1,2 It has been estimated that 10% or greater of TKAs have marked (> 3 degrees) errors in mechanical alignment.3 Many authors believe that optimal alignment may decrease mechanical and shear stresses placed on the bearing surfaces, as well as the bone/prosthesis interfaces.4–6 In addition, it is believed that appropriate alignment assists in balancing the forces conveyed through the soft-tissue envelope, which is essential for proper joint function.5 Studies have supported this assertion by demonstrating that deviation from the mechanical axis of more than 3 degrees can lead to decreased implant survivorship, increased wear, poor functional outcomes, and early failures leading to component loosening.4,6–12 Therefore, the driving stimulus for navigated TKA was the need for more precise and reliable component alignment. Computer navigation aids surgeons in achieving more accu-
rate postoperative alignment through more precise bony cuts and ligamentous balancing.13,14 This consistency has the potential benefits of increased implant longevity, improved functional outcomes, and greater patient satisfaction.15 The purpose of this review was to summarize the recent evidence concerning the use of navigation in TKA. We specifically focused on the following: (1) history and technology; (2) survivorship; (3) alignment/functional outcomes; (4) economics; and (5) the future outlook on the use of this technology.
received February 19, 2014 accepted March 16, 2014 published online April 24, 2014
Copyright © 2014 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
History and Technology Computer-assisted navigation was originally used for insertion of pedicle screws,16 but in 1997 the first published case was performed in a TKA.17 The software and hardware of these systems have been constantly improving from its inception.18 Previously used bulky systems have been
DOI http://dx.doi.org/ 10.1055/s-0034-1374814. ISSN 1538-8506.
Downloaded by: NYU. Copyrighted material.
J Knee Surg 2014;27:171–176.
Does the Use of Navigation in Total Knee Arthroplasty Affect Outcomes? engineered into smaller components, even to the point where there are hand-held options available today. These navigation systems aid in constructing a three-dimensional model of the patient’s knee intraoperatively, and correlate the position of the surgeon’s instruments to the model. Various navigated surgical systems are currently available for use during knee arthroplasty. Image-guided systems use intraoperative (fluoroscopy assisted) or preoperative anatomic data points (obtained by computed tomographic scan) to construct the threedimensional knee models. In these systems, the position of the knee is recorded intraoperatively by reflective markers drilled into the tibia and femur. Additional markers are tactically placed on surgical instruments, which are tracked with the previous markers in the bone, providing a computer-assisted guide for cutting jig placement. The emitter and navigation computer receives information from infrared cameras which track the movement of the markers, allowing the computer to guide the surgeon’s placement of cutting jigs in the most accurate position. This may potentially reduce the incidence of intraoperative errors in bone cuts during TKA. Conversely, imageless systems utilize a database of knee CT scans to match a three-dimensional knee model based on anatomic registration points obtained intraoperatively by the surgeon. The knee position and cutting jig placement are then recorded, and are positioned as directed by the image-guided systems.19 Customized patient instrumentation builds a model of the knee based on preoperative CT or magnetic resonance imaging scans. Some systems produce cutting guides that are placed directly onto the patient intraoperatively, whereas others allow placement of guide pins in the bone onto which conventional cutting blocks are placed. These updates in this one system have demonstrated shorter operating room times, while maintaining accurate component positioning.19
Results The radiographic consistency of the mechanical axis using navigation TKA has been well documented in the literature.20–26 A meta-analysis by Rebal et al evaluated 1,713 knees (869 computer assisted; 844 control cohort) from 21 studies to determine whether computer navigation provided superior short-term outcomes compared with conventional TKA.27 The authors found that navigated TKAs were significantly more likely to obtain coronal alignments within 3 degrees of the mechanical axis compared with conventional TKAs (87.1 vs. 73.7%, p < 0.01). In addition, they reported that the patients who underwent TKA using navigation had significantly greater increases in their Knee Society scores at 3-month (68.5 vs. 58.1 points; p < 0.03) and 12-month (53.1 vs. 45.8 points; p < 0.01) mean follow-ups. Similarly, another meta-analysis by Thienpont et al examined if there were improvements in knee alignment in TKA with the use of navigation compared with conventional methods in 28,763 patients from 10 meta-analyses.28 The authors found that for overall mechanical alignment of > 2 degrees, there was lower likelihood of mechanical axis outliers with the use of computer navigation when compared with conventional techniThe Journal of Knee Surgery
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ques (effects measured; odds and risk ratio ¼ 0.21–0.76). A recent study by Johnson et al15 compared the use of navigation to conventional TKA methods in 54 patients who underwent sequential bilateral TKA. They did not find significant differences with regards to mean tibiofemoral (p ¼ 0.115), mechanical (p ¼ 0.802), proximal tibial angle (p ¼ 0.303), distal femoral angle (p ¼ 0.555), femoral component flexion (p ¼ 0.781), or posterior tibial slope (p ¼ 0.843). Despite these results, there were less mechanical axes outliers in the navigation group with regards to tibiofemoral angle, mechanical axis, and proximal tibial angle. However, several studies have refuted the potentially superior mechanical alignment of navigation systems.15,29–32 Kim et al, examined 160 patients (320 knees) using computerassisted TKA compared with conventional techniques on alignment and functional outcomes. The authors demonstrated that there were no significant differences in alignment (implant position, prevalence of outlier) and mean postoperative functional outcomes (Knee Society scores, 83 vs. 81 points; range of motion [ROM], 123 vs. 126 degrees; and Hospital for Special Surgery scores, 89 vs. 91 points) at a mean 3.4-year follow-up (p > 0.05).30 Despite the majority of research verifying that navigation TKA has fewer outliers with regards to the mechanical axis, clinical results have not demonstrated equal success.30,33–38 A recent systematic review by Burnett and Barrack evaluated this technology.33 The authors found that navigation resulted in improved coronal alignment when compared with conventional techniques, however, they observed little to no evidence supporting improvements in functional outcomes. Similarly, Johnson et al evaluated alignment and functional outcomes in 54 patients who underwent bilateral sequential TKA utilizing navigation in one knee and traditional instrumentation in the other.15 The authors reported that there was a significant reduction in radiographic outliers for the computer-assisted TKA cohort compared with tradition methods with regards to mechanical axis (6.1 vs. 20.4%, p ¼ 0.037) and tibial component alignment (0 vs. 7.5%, p ¼ 0.042). However, the authors were unable to demonstrate any improvements in KSS and ROM with the use of computer-assisted TKA (p > 0.05) at a mean follow-up of 2.5 years. These findings were confirmed by several Level 1 studies that have found no differences in patient outcomes when navigated TKA was compared with conventional performed procedures (►Table 1).34–38
Potential Pitfalls of Computer Navigation Navigation systems that rely on anatomic registration points to construct the three-dimensional model of the patient’s knee do have zones, which if marked incorrectly may lead to component malposition. Amanatullah et al found that registration errors were the most commonly associated with the distal femoral epicondyles, with both intraobserver and interobserver variability.39 These types of registration errors can lead to malrotation of the femoral component, as well as result in balancing and tracking issues. Navigation systems that use reflective markers drilled into the femur and tibia are at the potential risk of tracker pin movement when placed in patients
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Table 1 Level 1 studies of functional outcomes with navigation TKA Author
Year 53
Mean follow-up (y)
Brief summary of functional results
2014
5
No difference in KSS, high-activity arthroplasty scores
Lützner et al54
2013
2 and 5
No difference in KSS, Knee Score, Functional score, VAS scale
Kim et al36
2012
10.8
No difference in KSS, WOMAC scores
2012
5
No difference in KSS, WOMAC scores
2009
Minimum 2
No difference in HSS, WOMAC scores
Allen et al
Harvie et al
34
Seon et al38
who have osteoporotic bone. In addition, Lee et al found that in patients who had osteoporotic bone there was a higher likelihood of tibia valgus component positioning.40 Fractures have also been reported with navigation pin tracker sites and must be taken in account when using these systems.41,42 Software and hardware accuracy are factors not controlled by the surgeon that can also determine the accuracy of navigated TKA. However, there are some instances in which navigation systems may provide a useful tool and may be more successful than other methods. Patients who have retained hardware and severe extra-articular deformities can be treated successfully with navigation TKA.43–50 Navigation systems have also been used to achieve soft tissue balance in TKA. Joseph et al, found that navigation provided a superior mediolateral extension gap, however, no differences were found in the flexion gap or in achieving equal flexion and extension gaps when compared with conventional methods.51
et al examined the relationship between component alignment and survivorship in 398 TKAs.52 The authors found no differences in Kaplan–Meier 15-year survivorship estimates between the prostheses placed within 3 degrees of varus or valgus to the prosthesis aligned outside of this range. Studies such as these have raised questions of the importance of alignment within 3 degrees of the mechanical axis, which would ultimately render navigation in TKA less useful. However, proponents believe that improvements in implant survivorship over long-term follow-up will outweigh the initial increased costs of navigated TKA. Much of the costs of this technology may decrease with time, which may lead to more affordable navigation systems. These systems may become more popular in the future leading to more surgeons being trained on them, which may decrease the learning curve associated with navigation TKA. However, it is vital to understand that conventional TKA has a proven track record of 20-year plus survivorship that is working against the transition to navigated TKA.
Cost Analyses The institutional costs of navigation TKA are often not justified with regards to clinical results based on the majority of literature available. Novak et al, performed a decision-analysis model to estimate the cost effectiveness of navigation TKA.41 They found that there was cost savings for navigation TKA, if the additional cost per operation was below $629.41 This model, however, included a predicted favorable clinical outcome with precision mechanical alignment that is produced with navigation TKA. All of these systems may increase the cost of the operation with regards to installation and maintenance, as well as advanced imaging that is required by some of the systems. The machines and software are expensive, however, the increase in manpower for set up and additional steps leading to longer operating room times also add to the health care cost. These may be the reasons that despite radiographic evidence of improved limb alignment, less than 5% of surgeons in the United States currently use navigated TKA.42
Conclusion Appropriate component alignment in TKA is considered to be an important factor in determining long-term outcomes. Many reports have demonstrated that deviation from the mechanical axis of more than 3 degrees can lead to decreased implant survivorship, increased wear, and poor functional outcomes. Studies have shown that navigated TKA can reduce the number of radiographic outliers when compared with traditional techniques. Nevertheless, only a few reports have shown that navigation can result in improved functional outcomes after TKA. In addition, high startup costs, steep learning curves, increased operative times, and bulky equipment needs are believed to have prevented widespread popularity of these systems. Moreover, to fully evaluate the use of navigation in TKA, the authors believe that larger prospective randomized studies are required to clearly define outcomes, as well as any potential economic benefits.
Future Outlook TKA performed with navigation is believed to result in superior radiographic alignment outliers when compared with conventional instrumentation, however, functional benefits are still questionable. More recently, a study by Parratte
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Abbreviations: HSS, Hospital for Special Surgery score; KSS, Knee Society score; TKA, total knee arthroplasty; VAS, visual analog scale; WOMAC, Western Ontario and McMaster Universities osteoarthritis index.
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