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Cadaveric results of an accelerometer based, extramedullary navigation system for the tibial resection in total knee arthroplasty
The Knee 19 (2012) 617–621
Contents lists available at SciVerse ScienceDirect
The Knee
Cadaveric results of an accelerometer based, extramedullary navigation system for the tibial resection in total knee arthroplasty Denis Nam ⁎, Christopher J. Dy, Michael B. Cross, Michael N. Kang, David J. Mayman Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, United States
a r t i c l e
i n f o
Article history: Received 27 April 2011 Received in revised form 15 September 2011 Accepted 18 September 2011 Keywords: Osteoarthritis Total knee arthroplasty Computer navigation Tibial resection Posterior slope
a b s t r a c t Introduction: In total knee arthroplasty, the accuracy and precision of the tibial resection must be improved. The purpose of this study was to determine the accuracy and time associated with the use of an accelerometer based, extramedullary surgical navigation system for performing the tibial resection. Materials and methods: Four orthopedic surgeons performed a tibial resection utilizing the KneeAlign™ system, each on five separate, cadaveric tibiae. Each surgeon was assigned a preoperative “target” of varus/ valgus alignment and posterior slope prior to each resection. The alignment of each resection was measured using both plain radiographs and computed tomography, along with the time required to use the device. Results: Regarding coronal alignment, the mean absolute difference between the preoperative “target” and tibial resection alignment was 0.77° ± 0.64° using plain radiograph, and 0.68° ± 0.46° using CT scan measurements. Regarding the posterior slope, the mean absolute difference between the preoperative “target” and the tibial resection was 1.06° ± 0.59° using plain radiograph, and 0.70° ± 0.47° using CT scan measurements. The time to use the KneeAlign™ for the fifth specimen was less than 300 s for all four orthopedic surgeons in this study. Discussion: This cadaveric study demonstrates that the KneeAlign™ system is able to accurately align the tibial resection in both the coronal and sagittal planes. Level of evidence: Cadaveric study. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Although total knee arthroplasty (TKA) has proven to be a successful procedure in the management of degenerative joint disease, inaccurate tibial and femoral component positioning still occurs. Mason et al., in a meta-analysis, demonstrated that 31.8% of total knee arthroplasties are placed in greater than 3° of mechanical axis malalignment using conventional alignment and resection techniques [1]. The accuracy and precision of the tibial resection are crucial, as tibial component malalignment has been associated with an increased risk of implant failure. Berend et al. demonstrated that tibial varus alignment of N3° increased the odds of tibial component failure by approximately 17 times [2]. Controversy remains regarding the efficacy and accuracy of using tibial intramedullary (IM) versus extramedullary (EM) alignment guides to achieve a tibial resection that is 90° to the mechanical axis of the tibia in the coronal plane [3–14]. However, it remains clear that neither tibial intramedullary or extramedullary alignment guides have been shown to be highly accurate. In a prospective, randomized control trial comparing IM and EM tibial alignment guides in 135 knees, Reed et
⁎ Corresponding author. Tel.: + 1 917 596 0620; fax: + 1 212 606 1477. E-mail address: [email protected] (D. Nam). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.09.008
al. demonstrated only 65% accuracy with the use of EM guides, versus 85% with the use of IM guides, in obtaining a tibial component alignment 90° ± 2° to the mechanical axis [5]. In addition, few studies have addressed the accuracy of tibial component alignment in the sagittal plane with the use of conventional techniques. Han et al. utilized an intramedullary rod extending to the distal metaphysis of the tibia for alignment of the tibial cutting block, with a goal of 0° slope, and demonstrated no incidence of anterior slope, and a mean posterior slope of 1.6°± 1.2° in 31 total knee replacements measured on postoperative computed tomography scans [15]. However, IM alignment guides may increase the risk of fat emboli syndrome and pulmonary complications following TKA, without conclusively leading to superior alignment when compared to EM alignment guides [11,16]. The goal of obtaining more accurate component positioning in total knee arthroplasty has led to the development of computerassisted surgical (CAS) techniques. However, computer assisted surgery has not been widely embraced, despite numerous comparative studies demonstrating statistically significant improvements in both the overall mechanical alignment and tibial component positioning with the use of CAS techniques. Concerns over increased operative times, cost, and the learning curve associated with using computerassisted surgery has limited its widespread acceptance, as evidenced by the fact that less than 3% of total knee replacements in the United States are performed using CAS [16].
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The KneeAlign™ device (OrthAlign Inc., Aliso Viejo, CA) is a FDAapproved, accelerometer based, extramedullary surgical navigation system for performing the tibial resection in total knee arthroplasty. This device works similarly to conventional extramedullary systems, and does not require the use of a large-console for registration and alignment feedback as is required in most CAS systems. The objective of this study was to determine the accuracy and time associated with the use of this surgical navigation system in obtaining a specific “target” alignment angle of the tibial resection relative to the mechanical axis of the tibia, in both the coronal and sagittal planes. 2. Materials and methods This study was a cadaveric study to assess the accuracy of an accelerometer based, extramedullary navigation system for performing the tibial resection in total knee arthroplasty. Prior to initiation of the study, IRB approval for the appropriate use of cadaveric specimens was obtained from both participating institutions. Ten cadaveric specimens (20 hip-to-toe lower extremities), with a mean age of 56 years (range: 25–77 years), and BMI of 23.9 kg/m2 (range: 18–36 kg/m2), were included in this study. Four orthopedic surgeons from two separate Accreditation Council for Graduate Medical Education (ACGME)-approved fellowship programs were instructed to perform a tibial resection utilizing the KneeAlign™ system. Each surgeon performed a tibial resection on five separate specimens. Prior to each resection, the surgeon was assigned a randomly generated “target” of tibial varus/valgus and posterior slope (in degrees), which they attempted to create with their tibial resection. The “targets” ranged from 1° of valgus to 4° of varus in the coronal plane, and from 2° to 5° of posterior slope in the sagittal plane. For each procedure, the time from which the surgeon was handed the KneeAlign™ device, to the point immediately prior to cutting the tibia, was recorded (in seconds). The KneeAlign™ system is an accelerometer based surgical navigation system (Fig. 1), which consists of a KneeAlign™ display console (Fig. 2), reference sensor, and an extramedullary tibial jig to which the display console is attached. The KneeAlign™ display console and reference sensor each contain triaxial accelerometers and communicate wirelessly with one another. The KneeAlign™ tibial jig has two primary components that are articulated relative to one
Fig. 1. Image of the KneeAlign™ system (OrthAlign Inc., Aliso Viejo, CA). The 2 × 4 × 2 in. display console attaches to the front of an extramedullary tibial jig, and provides real-time feedback of both the posterior slope, and varus–valgus alignment of the tibial cutting block. Alignment of the tibial cutting block is calculated by using the differential between the outputs of the accelerometers between the mobile and fixed components of the KneeAlign™ jig.
Fig. 2. Image showing the face of the KneeAlign™ display console, which provides the surgeon with real-time feedback as to the alignment of the tibial cutting block, prior to performing the tibial resection (Image provided by OrthAlign Inc., Aliso Viejo, CA).
another. The fixed component is pinned to the tibia, while the mobile component guides the tibial cutting block. During the procedure, the KneeAlign™ display console is attached to the mobile component to guide the angle of the cutting block, and the reference sensor is attached to the fixed component to compensate for movement of the tibia. The coronal mechanical axis is defined by a line joining the proximal mechanical axis point (the footprint of the anterior cruciate ligament) and the distal mechanical axis point. The first step in using the KneeAlign™ is to pin the fixed component of the system to the tibia. The fixed component is a rod that has a removal proximal aiming arm that aligns it with the footprint of the anterior cruciate ligament (Fig. 1). Two headless pins are used to secure the proximal aspect of the fixed component to the proximal tibia. Distally, the rod is secured to the tibia using a spring that wraps around the distal tibia. The proximal mechanical axis point is then registered by the KneeAlign™ device. The functions of the fixed component are to 1) act as a reference for the proximal mechanical axis point and 2) to account for tibial movement while aligning the tibial cutting block (which is attached to the mobile component). Next, the medial and lateral malleoli are registered utilizing the mobile component of the KneeAlign™ tibial jig, and the distal mechanical axis point is defined by the center of the plafond, which is approximated by weighted interpolation between the apexes of the medial and lateral malleoli. The mobile component articulates proximally with the fixed component. Once registration is complete, the system is able to establish the orientation of the mobile component and tibial cutting block relative to the tibia by using the differential between the outputs of the accelerometers between the mobile and fixed components of the KneeAlign™ jig. The KneeAlign™ display
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console then provides dynamic numerical measurements of the alignment of the cutting block relative to the mechanical axis in both the coronal and sagittal planes. The surgeon is able to select the desired resection angles prior to locking the cutting block into place. The varus/valgus angle and posterior slope of the tibial resection were measured utilizing anteroposterior (AP) and lateral knee radiographs. The angle between the tibial anatomic axis, and a line across the surface of the tibial resection formed the varus/valgus alignment of the tibial resection in the coronal plane. For convention, the difference between the measured angle and 90° was recorded, with negative values representing valgus alignment (i.e. −0.5° represents a tibial component in 0.5° of valgus relative to the anatomic axis). Measurement of the posterior slope on lateral knee radiographs was performed as described by Hernigou et al. utilizing a trigonometric formula to account for lower extremity rotation [17]. For convention, the difference between the measured angle and 90° was recorded as the posterior slope, with a negative value representing an anterior slope of the tibial resection. In addition, computed tomography (CT) scans from the knee through the ankle were performed for all cadaveric specimens following each tibial resection. The proximal mechanical axis point was marked on an axial image at the level of the tibial resection, and was defined as the intersection point between two lines drawn through the middle of the tibial resection in both the medial–lateral and anterior–posterior directions. The center of the talus was also marked separately in the sagittal and coronal planes, and a line connecting the proximal mechanical axis point to the center of the talus was taken to be the mechanical axis of the tibia in each, respective plane (Fig. 3). The varus/valgus alignment and the posterior slope were then measured relative to the mechanical axis of the tibia in the coronal and sagittal planes, respectively (Fig. 4). 3. Statistical methods The percent of tibial resections within 2° of the preoperative “target” in both the coronal and sagittal planes was calculated for both the radiographic and CT analysis. The mean absolute difference and standard deviation between the tibial resection alignment and the preoperative “target” was also determined, along with 99% confidence intervals from the plain radiographic measurements. All data was collected and analyzed utilizing Microsoft Excel software (Microsoft Corporation, Redmond, WA). 4. Results After analyzing the varus/valgus alignment of the tibial resections, 95% was found to be within 2° of the preoperative “target” using both plain radiograph and CT scan measurements. Only one tibial resection measured outside this 2° window (2.4° on plain radiograph, and 2.2° on CT scan from the preoperative “target”). The mean absolute difference between the preoperative “target” and tibial resection alignment angle was 0.77° ± 0.64° using plain radiograph measurements, and 0.68° ± 0.46° using CT scan measurements (Table 1). The 99% confidence interval of the mean absolute difference using the plain radiograph measurements was between 0.40° and 1.13°. Similarly, 95% of the tibial resections were found to have a posterior slope within 2° of the preoperative “target” for both plain radiograph and CT scan measurements, with only one tibial resection measuring greater than 2° from the preoperative goal (2.3° on plain radiograph and CT scan). The mean absolute difference between the preoperative “target” for posterior slope, and the tibial resection alignment, was 1.06° ± 0.59° using plain radiograph measurements, and 0.70° ± 0.47° using CT scan measurements. The 99% confidence of the mean absolute difference using the plain radiograph measurements was between 0.72° and 1.41°. Regarding the time required to use the KneeAlign™ system, each surgeon was able to use the system in less than 500 s for the first specimen. As familiarity with the device increased, each surgeon was able to use the system in less than 300 s for the fifth and final specimen. Using a two-tailed, Student's paired t-Test, the mean absolute difference for varus/valgus for the first specimens was 0.33° ± 0.29° versus 0.66° ± 0.35° for the fifth specimens (p = 0.35), and posterior slope was 0.63° ± 0.76° for the first specimens versus 1.17° ± 0.49° for the fifth specimens (p = 0.23). Therefore, the mean absolute difference between the “targeted” and actual alignment angles, obtained using plain radiographs, was not significantly different for the first specimens when compared to the fifth specimens.
Fig. 3. Computed tomography images demonstrating measurement of a) the proximal mechanical axis point on an axial image, and the center of the talus on both b) sagittal and c) coronal images for definition of the mechanical axis in both planes.
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Fig. 4. Computed tomography images demonstrating the mechanical axis in a) the sagittal plane along with measurement of b) the posterior slope (3.7° in this specimen: “target” was 3° of posterior slope), and the mechanical axis in c) the coronal plane along with measurement of d) the varus/valgus alignment (1.4° of varus in this specimen: “target” was 2° of varus).
5. Discussion The purpose of this cadaveric study was to assess the accuracy and precision of the KneeAlign™ system, by not only asking surgeons to obtain a varus/valgus alignment perpendicular to the mechanical axis in the coronal plane, and posterior slope of 3° (as are the goals of most posterior cruciate substituting knee replacement systems), but also asking them to obtain resection alignments outside of these
Table 1 Table summarizing the mean absolute difference between the preoperative “target” and the tibial resection alignment angle in both the coronal and sagittal planes, as measured using plain radiography and computed tomography. Mean absolute difference between preoperative “target” and postoperative alignment
Plain radiographs
Computed tomography
Varus/valgus Posterior slope
0.77° ± 0.64° 1.06° ± 0.59°
0.68° ± 0.46° 0.70° ± 0.47°
“normal” values. This study demonstrates the KneeAlign™ system to be highly accurate in aligning the tibial resection in both the coronal and sagittal planes. In addition, the time to use the device was for the fifth specimen was less than 300 s for all four orthopedic surgeons in this study. Tibial component alignment in total knee arthroplasty is dictated by the orientation of the tibial resection, and thus the accuracy and precision of the tibial cut is crucial. Both intramedullary and extramedullary tibial alignment guides are available to assist surgeons intraoperatively, however neither method has proven to be highly accurate [11,13,3,18]. Dennis et al. analyzed 60 cases in which an EM guide was used for the tibial resection, versus 60 cases performed with an IM guide, and found that only 88% of the tibial components in the EM group were aligned within 2° of perpendicular to the mechanical axis in the coronal plane, and only 72% in the IM group [11]. In addition, IM guides have become less favorable due to the increased risk of pulmonary complications, in addition to the difficulty of use in patients with tibial bowing, prior fractures, or anatomic deformities
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[16]. Therefore, controversy still remains over the safety and accuracy of intramedullary versus extramedullary alignment guides for performing the tibial resection in total knee arthroplasty. While CAS techniques have been shown to improve the accuracy and precision of overall mechanical and component alignment in total knee arthroplasty, concerns over the increased cost, increased operative time, and high learning curve associated with its use has prevented its widespread acceptance [1,16,19]. However, reported advantages of CAS techniques are the immediate, intraoperative feedback provided, and the reduction in outliers in obese patients or patients with extra-articular deformities, in whom conventional IM or EM techniques may be inadequate [20]. Manzotti et al., in a review of 38 TKAs implanted using a CAS system, found 89.4% of tibial components to be aligned within 2° of perpendicular to the mechanical axis in the coronal plane, and 100% of components aligned within 4° of the targeted value in the sagittal plane [21]. In addition, Pang et al., in a review of 35 TKAs implanted using a CAS system, found the mean postoperative coronal alignment to be 0.5° ± 1.8°, and sagittal alignment to be 1.7° ± 1.9° (goal 0°) [19]. The KneeAlign™ system is an accelerometer based, extramedullary surgical navigation system for performing the tibial resection in TKA, which attempts to combine the noted benefits of CAS techniques, with the ease of use of conventional, extramedullary alignment systems. The KneeAlign™ system provides immediate, intraoperative feedback of the tibial cutting block's alignment relative to the mechanical axis in both the coronal and sagittal planes, without requiring large consoles typically associated with most CAS systems. The intraoperative readings provided by the KneeAlign™ display console are highly accurate, as 95% of the tibial resections were within 2° of the preoperative “target” for both coronal and sagittal alignment, as measured on both plain radiographs and CT scans. As noted above, the mean absolute difference between the preoperative “target” and the postoperative alignment angle was 0.68° ± 0.46° for varus/valgus alignment, and 0.70° ± 0.47° for posterior slope, using CT scan measurements. While the KneeAlign™ device was shown to be highly accurate both on plain radiographs and CT scans, it is felt that CT scan measurements are a better indicator of the true accuracy of the system, as the mechanical axis in both the coronal and sagittal planes were directly measured. This cadaveric study demonstrates that the KneeAlign™ system is able to obtain an accurate level of alignment in both the coronal and sagittal planes, without having to violate the intramedullary canal. One concern with the implementation of any new technological device is the time associated with utilizing the device, along with inaccuracies that may occur during the acclimation process. In this study, the time to use the KneeAlign™ system by the fifth and final specimen was less than 300 s for all four orthopedic surgeons, with one surgeon successfully using the device in less than 150 s. In addition, the accuracy in achieving the “target” alignment was not significantly different between the first and fifth specimens, thus indicating that although initially it may require more time to use the device, this does not result in malalignment of the tibial resection. Based on this cadaveric study, the KneeAlign™ system achieves a high degree of accuracy of the tibial resection in both the coronal and sagittal planes. However, while the results of this study are encouraging, it does possess several limitations. First, this is a cadaveric study, and the clinical results of the KneeAlign™ system need to be assessed. In addition, there was no control group in this study, and thus the increased
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effectiveness among the four surgeons when using the KneeAlign™ system versus a conventional IM or EM alignment guide must also be studied. However, based on this cadaveric study, the KneeAlign™ system achieves a high degree of accuracy of the tibial resection in total knee arthroplasty, while maintaining the familiarity of conventional, EM alignment systems. Conflict of interest statement One of the authors of this study (DJM) has stock options in OrthAlign Incorporation (Aliso Viejo, California, U.S.A.). References [1] Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty Dec 2007;22(8):1097–106. [2] Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res Nov 2004(428):26–34. [3] Simmons Jr ED, Sullivan JA, Rackemann S, Scott RD. The accuracy of tibial intramedullary alignment devices in total knee arthroplasty. J Arthroplasty Mar 1991;6(1):45–50. [4] Rottman SJ, Dvorkin M, Gold D. Extramedullary versus intramedullary tibial alignment guides for total knee arthroplasty. Orthopedics Dec 2005;28(12):1445–8. [5] Reed MR, Bliss W, Sher JL, Emmerson KP, Jones SM, Partington PF. Extramedullary or intramedullary tibial alignment guides: a randomised, prospective trial of radiological alignment. J Bone Joint Surg Br Aug 2002;84(6):858–60. [6] Mihalko WM, Krackow KA. Differences between extramedullary, intramedullary, and computer-aided surgery tibial alignment techniques for total knee arthroplasty. J Knee Surg Jan 2006;19(1):33–6. [7] Maestro A, Harwin SF, Sandoval MG, Vaquero DH, Murcia A. Influence of intramedullary versus extramedullary alignment guides on final total knee arthroplasty component position: a radiographic analysis. J Arthroplasty Aug 1998;13(5):552–8. [8] Jenny JY. Influence of intramedullary versus extramedullary alignment: guides on final total knee arthroplasty component position by antonio maestro et al. (pp 552–558). J Arthroplasty Oct 1999;14(7):898–9. [9] Ishii Y, Ohmori G, Bechtold JE, Gustilo RB. Extramedullary versus intramedullary alignment guides in total knee arthroplasty. Clin Orthop Relat Res Sep 1995(318):167–75. [10] Coull R, Bankes MJ, Rossouw DJ. Evaluation of tibial component angles in 79 consecutive total knee arthroplasties. Knee 1999;6:235–7. [11] Dennis DA, Channer M, Susman MH, Stringer EA. Intramedullary versus extramedullary tibial alignment systems in total knee arthroplasty. J Arthroplasty Feb 1993;8(1):43–7. [12] Anand S, Harrison JW, Buch KA. Extramedullary or intramedullary tibial alignment guides: a randomised, prospective trial of radiological alignment. J Bone Joint Surg Br Sep 2003;85(7):1084 author reply 1084. [13] Brys DA, Lombardi Jr AV, Mallory TH, Vaughn BK. A comparison of intramedullary and extramedullary alignment systems for tibial component placement in total knee arthroplasty. Clin Orthop Relat Res Feb 1991(263):175–9. [14] Belvedere C, Ensini A, Leardini A, Bianchi L, Catani F, Giannini S. Alignment of resection planes in total knee replacement obtained with the conventional technique, as assessed by a modern computer-based navigation system. Int J Med Robot Jun 2007;3(2):117–24. [15] Han HS, Kang SB, Jo CH, Kim SH, Lee JH. The accuracy of intramedullary tibial guide of sagittal alignment of PCL-substituting total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc Oct 2010;18(10):1334–8. [16] Canale ST, Beaty JH. Campbell's operative orthopaedics. Eleventh ed. Philadelphia, PA: Elsevier Inc.; 2008. [17] Hernigou P, Deschamps G. Posterior slope of the tibial implant and the outcome of unicompartmental knee arthroplasty. J Bone Joint Surg Am Mar 2004;86-A(3): 506–11. [18] Confalonieri N, Manzotti A, Pullen C, Ragone V. Computer-assisted technique versus intramedullary and extramedullary alignment systems in total knee replacement: a radiological comparison. Acta Orthop Belg Dec 2005;71(6):703–9. [19] Pang CH, Chan WL, Yen CH, Cheng SC, Woo SB, Choi ST, et al. Comparison of total knee arthroplasty using computer-assisted navigation versus conventional guiding systems: a prospective study. J Orthop Surg (Hong Kong) Aug 2009;17(2):170–3. [20] Mullaji A, Shetty GM. Computer-assisted total knee arthroplasty for arthritis with extra-articular deformity. J Arthroplasty Dec 2009;24(8):1164,9.e1. [21] Manzotti A, Pullen C, Confalonieri N. Computer-assisted alignment system for tibial component placement in total knee replacement: a radiological study. Chir Organi Mov Jan 2008;91(1):7–11.
Contents lists available at SciVerse ScienceDirect
The Knee
Cadaveric results of an accelerometer based, extramedullary navigation system for the tibial resection in total knee arthroplasty Denis Nam ⁎, Christopher J. Dy, Michael B. Cross, Michael N. Kang, David J. Mayman Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, United States
a r t i c l e
i n f o
Article history: Received 27 April 2011 Received in revised form 15 September 2011 Accepted 18 September 2011 Keywords: Osteoarthritis Total knee arthroplasty Computer navigation Tibial resection Posterior slope
a b s t r a c t Introduction: In total knee arthroplasty, the accuracy and precision of the tibial resection must be improved. The purpose of this study was to determine the accuracy and time associated with the use of an accelerometer based, extramedullary surgical navigation system for performing the tibial resection. Materials and methods: Four orthopedic surgeons performed a tibial resection utilizing the KneeAlign™ system, each on five separate, cadaveric tibiae. Each surgeon was assigned a preoperative “target” of varus/ valgus alignment and posterior slope prior to each resection. The alignment of each resection was measured using both plain radiographs and computed tomography, along with the time required to use the device. Results: Regarding coronal alignment, the mean absolute difference between the preoperative “target” and tibial resection alignment was 0.77° ± 0.64° using plain radiograph, and 0.68° ± 0.46° using CT scan measurements. Regarding the posterior slope, the mean absolute difference between the preoperative “target” and the tibial resection was 1.06° ± 0.59° using plain radiograph, and 0.70° ± 0.47° using CT scan measurements. The time to use the KneeAlign™ for the fifth specimen was less than 300 s for all four orthopedic surgeons in this study. Discussion: This cadaveric study demonstrates that the KneeAlign™ system is able to accurately align the tibial resection in both the coronal and sagittal planes. Level of evidence: Cadaveric study. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Although total knee arthroplasty (TKA) has proven to be a successful procedure in the management of degenerative joint disease, inaccurate tibial and femoral component positioning still occurs. Mason et al., in a meta-analysis, demonstrated that 31.8% of total knee arthroplasties are placed in greater than 3° of mechanical axis malalignment using conventional alignment and resection techniques [1]. The accuracy and precision of the tibial resection are crucial, as tibial component malalignment has been associated with an increased risk of implant failure. Berend et al. demonstrated that tibial varus alignment of N3° increased the odds of tibial component failure by approximately 17 times [2]. Controversy remains regarding the efficacy and accuracy of using tibial intramedullary (IM) versus extramedullary (EM) alignment guides to achieve a tibial resection that is 90° to the mechanical axis of the tibia in the coronal plane [3–14]. However, it remains clear that neither tibial intramedullary or extramedullary alignment guides have been shown to be highly accurate. In a prospective, randomized control trial comparing IM and EM tibial alignment guides in 135 knees, Reed et
⁎ Corresponding author. Tel.: + 1 917 596 0620; fax: + 1 212 606 1477. E-mail address: [email protected] (D. Nam). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.09.008
al. demonstrated only 65% accuracy with the use of EM guides, versus 85% with the use of IM guides, in obtaining a tibial component alignment 90° ± 2° to the mechanical axis [5]. In addition, few studies have addressed the accuracy of tibial component alignment in the sagittal plane with the use of conventional techniques. Han et al. utilized an intramedullary rod extending to the distal metaphysis of the tibia for alignment of the tibial cutting block, with a goal of 0° slope, and demonstrated no incidence of anterior slope, and a mean posterior slope of 1.6°± 1.2° in 31 total knee replacements measured on postoperative computed tomography scans [15]. However, IM alignment guides may increase the risk of fat emboli syndrome and pulmonary complications following TKA, without conclusively leading to superior alignment when compared to EM alignment guides [11,16]. The goal of obtaining more accurate component positioning in total knee arthroplasty has led to the development of computerassisted surgical (CAS) techniques. However, computer assisted surgery has not been widely embraced, despite numerous comparative studies demonstrating statistically significant improvements in both the overall mechanical alignment and tibial component positioning with the use of CAS techniques. Concerns over increased operative times, cost, and the learning curve associated with using computerassisted surgery has limited its widespread acceptance, as evidenced by the fact that less than 3% of total knee replacements in the United States are performed using CAS [16].
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The KneeAlign™ device (OrthAlign Inc., Aliso Viejo, CA) is a FDAapproved, accelerometer based, extramedullary surgical navigation system for performing the tibial resection in total knee arthroplasty. This device works similarly to conventional extramedullary systems, and does not require the use of a large-console for registration and alignment feedback as is required in most CAS systems. The objective of this study was to determine the accuracy and time associated with the use of this surgical navigation system in obtaining a specific “target” alignment angle of the tibial resection relative to the mechanical axis of the tibia, in both the coronal and sagittal planes. 2. Materials and methods This study was a cadaveric study to assess the accuracy of an accelerometer based, extramedullary navigation system for performing the tibial resection in total knee arthroplasty. Prior to initiation of the study, IRB approval for the appropriate use of cadaveric specimens was obtained from both participating institutions. Ten cadaveric specimens (20 hip-to-toe lower extremities), with a mean age of 56 years (range: 25–77 years), and BMI of 23.9 kg/m2 (range: 18–36 kg/m2), were included in this study. Four orthopedic surgeons from two separate Accreditation Council for Graduate Medical Education (ACGME)-approved fellowship programs were instructed to perform a tibial resection utilizing the KneeAlign™ system. Each surgeon performed a tibial resection on five separate specimens. Prior to each resection, the surgeon was assigned a randomly generated “target” of tibial varus/valgus and posterior slope (in degrees), which they attempted to create with their tibial resection. The “targets” ranged from 1° of valgus to 4° of varus in the coronal plane, and from 2° to 5° of posterior slope in the sagittal plane. For each procedure, the time from which the surgeon was handed the KneeAlign™ device, to the point immediately prior to cutting the tibia, was recorded (in seconds). The KneeAlign™ system is an accelerometer based surgical navigation system (Fig. 1), which consists of a KneeAlign™ display console (Fig. 2), reference sensor, and an extramedullary tibial jig to which the display console is attached. The KneeAlign™ display console and reference sensor each contain triaxial accelerometers and communicate wirelessly with one another. The KneeAlign™ tibial jig has two primary components that are articulated relative to one
Fig. 1. Image of the KneeAlign™ system (OrthAlign Inc., Aliso Viejo, CA). The 2 × 4 × 2 in. display console attaches to the front of an extramedullary tibial jig, and provides real-time feedback of both the posterior slope, and varus–valgus alignment of the tibial cutting block. Alignment of the tibial cutting block is calculated by using the differential between the outputs of the accelerometers between the mobile and fixed components of the KneeAlign™ jig.
Fig. 2. Image showing the face of the KneeAlign™ display console, which provides the surgeon with real-time feedback as to the alignment of the tibial cutting block, prior to performing the tibial resection (Image provided by OrthAlign Inc., Aliso Viejo, CA).
another. The fixed component is pinned to the tibia, while the mobile component guides the tibial cutting block. During the procedure, the KneeAlign™ display console is attached to the mobile component to guide the angle of the cutting block, and the reference sensor is attached to the fixed component to compensate for movement of the tibia. The coronal mechanical axis is defined by a line joining the proximal mechanical axis point (the footprint of the anterior cruciate ligament) and the distal mechanical axis point. The first step in using the KneeAlign™ is to pin the fixed component of the system to the tibia. The fixed component is a rod that has a removal proximal aiming arm that aligns it with the footprint of the anterior cruciate ligament (Fig. 1). Two headless pins are used to secure the proximal aspect of the fixed component to the proximal tibia. Distally, the rod is secured to the tibia using a spring that wraps around the distal tibia. The proximal mechanical axis point is then registered by the KneeAlign™ device. The functions of the fixed component are to 1) act as a reference for the proximal mechanical axis point and 2) to account for tibial movement while aligning the tibial cutting block (which is attached to the mobile component). Next, the medial and lateral malleoli are registered utilizing the mobile component of the KneeAlign™ tibial jig, and the distal mechanical axis point is defined by the center of the plafond, which is approximated by weighted interpolation between the apexes of the medial and lateral malleoli. The mobile component articulates proximally with the fixed component. Once registration is complete, the system is able to establish the orientation of the mobile component and tibial cutting block relative to the tibia by using the differential between the outputs of the accelerometers between the mobile and fixed components of the KneeAlign™ jig. The KneeAlign™ display
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console then provides dynamic numerical measurements of the alignment of the cutting block relative to the mechanical axis in both the coronal and sagittal planes. The surgeon is able to select the desired resection angles prior to locking the cutting block into place. The varus/valgus angle and posterior slope of the tibial resection were measured utilizing anteroposterior (AP) and lateral knee radiographs. The angle between the tibial anatomic axis, and a line across the surface of the tibial resection formed the varus/valgus alignment of the tibial resection in the coronal plane. For convention, the difference between the measured angle and 90° was recorded, with negative values representing valgus alignment (i.e. −0.5° represents a tibial component in 0.5° of valgus relative to the anatomic axis). Measurement of the posterior slope on lateral knee radiographs was performed as described by Hernigou et al. utilizing a trigonometric formula to account for lower extremity rotation [17]. For convention, the difference between the measured angle and 90° was recorded as the posterior slope, with a negative value representing an anterior slope of the tibial resection. In addition, computed tomography (CT) scans from the knee through the ankle were performed for all cadaveric specimens following each tibial resection. The proximal mechanical axis point was marked on an axial image at the level of the tibial resection, and was defined as the intersection point between two lines drawn through the middle of the tibial resection in both the medial–lateral and anterior–posterior directions. The center of the talus was also marked separately in the sagittal and coronal planes, and a line connecting the proximal mechanical axis point to the center of the talus was taken to be the mechanical axis of the tibia in each, respective plane (Fig. 3). The varus/valgus alignment and the posterior slope were then measured relative to the mechanical axis of the tibia in the coronal and sagittal planes, respectively (Fig. 4). 3. Statistical methods The percent of tibial resections within 2° of the preoperative “target” in both the coronal and sagittal planes was calculated for both the radiographic and CT analysis. The mean absolute difference and standard deviation between the tibial resection alignment and the preoperative “target” was also determined, along with 99% confidence intervals from the plain radiographic measurements. All data was collected and analyzed utilizing Microsoft Excel software (Microsoft Corporation, Redmond, WA). 4. Results After analyzing the varus/valgus alignment of the tibial resections, 95% was found to be within 2° of the preoperative “target” using both plain radiograph and CT scan measurements. Only one tibial resection measured outside this 2° window (2.4° on plain radiograph, and 2.2° on CT scan from the preoperative “target”). The mean absolute difference between the preoperative “target” and tibial resection alignment angle was 0.77° ± 0.64° using plain radiograph measurements, and 0.68° ± 0.46° using CT scan measurements (Table 1). The 99% confidence interval of the mean absolute difference using the plain radiograph measurements was between 0.40° and 1.13°. Similarly, 95% of the tibial resections were found to have a posterior slope within 2° of the preoperative “target” for both plain radiograph and CT scan measurements, with only one tibial resection measuring greater than 2° from the preoperative goal (2.3° on plain radiograph and CT scan). The mean absolute difference between the preoperative “target” for posterior slope, and the tibial resection alignment, was 1.06° ± 0.59° using plain radiograph measurements, and 0.70° ± 0.47° using CT scan measurements. The 99% confidence of the mean absolute difference using the plain radiograph measurements was between 0.72° and 1.41°. Regarding the time required to use the KneeAlign™ system, each surgeon was able to use the system in less than 500 s for the first specimen. As familiarity with the device increased, each surgeon was able to use the system in less than 300 s for the fifth and final specimen. Using a two-tailed, Student's paired t-Test, the mean absolute difference for varus/valgus for the first specimens was 0.33° ± 0.29° versus 0.66° ± 0.35° for the fifth specimens (p = 0.35), and posterior slope was 0.63° ± 0.76° for the first specimens versus 1.17° ± 0.49° for the fifth specimens (p = 0.23). Therefore, the mean absolute difference between the “targeted” and actual alignment angles, obtained using plain radiographs, was not significantly different for the first specimens when compared to the fifth specimens.
Fig. 3. Computed tomography images demonstrating measurement of a) the proximal mechanical axis point on an axial image, and the center of the talus on both b) sagittal and c) coronal images for definition of the mechanical axis in both planes.
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Fig. 4. Computed tomography images demonstrating the mechanical axis in a) the sagittal plane along with measurement of b) the posterior slope (3.7° in this specimen: “target” was 3° of posterior slope), and the mechanical axis in c) the coronal plane along with measurement of d) the varus/valgus alignment (1.4° of varus in this specimen: “target” was 2° of varus).
5. Discussion The purpose of this cadaveric study was to assess the accuracy and precision of the KneeAlign™ system, by not only asking surgeons to obtain a varus/valgus alignment perpendicular to the mechanical axis in the coronal plane, and posterior slope of 3° (as are the goals of most posterior cruciate substituting knee replacement systems), but also asking them to obtain resection alignments outside of these
Table 1 Table summarizing the mean absolute difference between the preoperative “target” and the tibial resection alignment angle in both the coronal and sagittal planes, as measured using plain radiography and computed tomography. Mean absolute difference between preoperative “target” and postoperative alignment
Plain radiographs
Computed tomography
Varus/valgus Posterior slope
0.77° ± 0.64° 1.06° ± 0.59°
0.68° ± 0.46° 0.70° ± 0.47°
“normal” values. This study demonstrates the KneeAlign™ system to be highly accurate in aligning the tibial resection in both the coronal and sagittal planes. In addition, the time to use the device was for the fifth specimen was less than 300 s for all four orthopedic surgeons in this study. Tibial component alignment in total knee arthroplasty is dictated by the orientation of the tibial resection, and thus the accuracy and precision of the tibial cut is crucial. Both intramedullary and extramedullary tibial alignment guides are available to assist surgeons intraoperatively, however neither method has proven to be highly accurate [11,13,3,18]. Dennis et al. analyzed 60 cases in which an EM guide was used for the tibial resection, versus 60 cases performed with an IM guide, and found that only 88% of the tibial components in the EM group were aligned within 2° of perpendicular to the mechanical axis in the coronal plane, and only 72% in the IM group [11]. In addition, IM guides have become less favorable due to the increased risk of pulmonary complications, in addition to the difficulty of use in patients with tibial bowing, prior fractures, or anatomic deformities
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[16]. Therefore, controversy still remains over the safety and accuracy of intramedullary versus extramedullary alignment guides for performing the tibial resection in total knee arthroplasty. While CAS techniques have been shown to improve the accuracy and precision of overall mechanical and component alignment in total knee arthroplasty, concerns over the increased cost, increased operative time, and high learning curve associated with its use has prevented its widespread acceptance [1,16,19]. However, reported advantages of CAS techniques are the immediate, intraoperative feedback provided, and the reduction in outliers in obese patients or patients with extra-articular deformities, in whom conventional IM or EM techniques may be inadequate [20]. Manzotti et al., in a review of 38 TKAs implanted using a CAS system, found 89.4% of tibial components to be aligned within 2° of perpendicular to the mechanical axis in the coronal plane, and 100% of components aligned within 4° of the targeted value in the sagittal plane [21]. In addition, Pang et al., in a review of 35 TKAs implanted using a CAS system, found the mean postoperative coronal alignment to be 0.5° ± 1.8°, and sagittal alignment to be 1.7° ± 1.9° (goal 0°) [19]. The KneeAlign™ system is an accelerometer based, extramedullary surgical navigation system for performing the tibial resection in TKA, which attempts to combine the noted benefits of CAS techniques, with the ease of use of conventional, extramedullary alignment systems. The KneeAlign™ system provides immediate, intraoperative feedback of the tibial cutting block's alignment relative to the mechanical axis in both the coronal and sagittal planes, without requiring large consoles typically associated with most CAS systems. The intraoperative readings provided by the KneeAlign™ display console are highly accurate, as 95% of the tibial resections were within 2° of the preoperative “target” for both coronal and sagittal alignment, as measured on both plain radiographs and CT scans. As noted above, the mean absolute difference between the preoperative “target” and the postoperative alignment angle was 0.68° ± 0.46° for varus/valgus alignment, and 0.70° ± 0.47° for posterior slope, using CT scan measurements. While the KneeAlign™ device was shown to be highly accurate both on plain radiographs and CT scans, it is felt that CT scan measurements are a better indicator of the true accuracy of the system, as the mechanical axis in both the coronal and sagittal planes were directly measured. This cadaveric study demonstrates that the KneeAlign™ system is able to obtain an accurate level of alignment in both the coronal and sagittal planes, without having to violate the intramedullary canal. One concern with the implementation of any new technological device is the time associated with utilizing the device, along with inaccuracies that may occur during the acclimation process. In this study, the time to use the KneeAlign™ system by the fifth and final specimen was less than 300 s for all four orthopedic surgeons, with one surgeon successfully using the device in less than 150 s. In addition, the accuracy in achieving the “target” alignment was not significantly different between the first and fifth specimens, thus indicating that although initially it may require more time to use the device, this does not result in malalignment of the tibial resection. Based on this cadaveric study, the KneeAlign™ system achieves a high degree of accuracy of the tibial resection in both the coronal and sagittal planes. However, while the results of this study are encouraging, it does possess several limitations. First, this is a cadaveric study, and the clinical results of the KneeAlign™ system need to be assessed. In addition, there was no control group in this study, and thus the increased
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effectiveness among the four surgeons when using the KneeAlign™ system versus a conventional IM or EM alignment guide must also be studied. However, based on this cadaveric study, the KneeAlign™ system achieves a high degree of accuracy of the tibial resection in total knee arthroplasty, while maintaining the familiarity of conventional, EM alignment systems. Conflict of interest statement One of the authors of this study (DJM) has stock options in OrthAlign Incorporation (Aliso Viejo, California, U.S.A.). References [1] Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty Dec 2007;22(8):1097–106. [2] Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res Nov 2004(428):26–34. [3] Simmons Jr ED, Sullivan JA, Rackemann S, Scott RD. The accuracy of tibial intramedullary alignment devices in total knee arthroplasty. J Arthroplasty Mar 1991;6(1):45–50. [4] Rottman SJ, Dvorkin M, Gold D. Extramedullary versus intramedullary tibial alignment guides for total knee arthroplasty. Orthopedics Dec 2005;28(12):1445–8. [5] Reed MR, Bliss W, Sher JL, Emmerson KP, Jones SM, Partington PF. Extramedullary or intramedullary tibial alignment guides: a randomised, prospective trial of radiological alignment. J Bone Joint Surg Br Aug 2002;84(6):858–60. [6] Mihalko WM, Krackow KA. Differences between extramedullary, intramedullary, and computer-aided surgery tibial alignment techniques for total knee arthroplasty. J Knee Surg Jan 2006;19(1):33–6. [7] Maestro A, Harwin SF, Sandoval MG, Vaquero DH, Murcia A. Influence of intramedullary versus extramedullary alignment guides on final total knee arthroplasty component position: a radiographic analysis. J Arthroplasty Aug 1998;13(5):552–8. [8] Jenny JY. Influence of intramedullary versus extramedullary alignment: guides on final total knee arthroplasty component position by antonio maestro et al. (pp 552–558). J Arthroplasty Oct 1999;14(7):898–9. [9] Ishii Y, Ohmori G, Bechtold JE, Gustilo RB. Extramedullary versus intramedullary alignment guides in total knee arthroplasty. Clin Orthop Relat Res Sep 1995(318):167–75. [10] Coull R, Bankes MJ, Rossouw DJ. Evaluation of tibial component angles in 79 consecutive total knee arthroplasties. Knee 1999;6:235–7. [11] Dennis DA, Channer M, Susman MH, Stringer EA. Intramedullary versus extramedullary tibial alignment systems in total knee arthroplasty. J Arthroplasty Feb 1993;8(1):43–7. [12] Anand S, Harrison JW, Buch KA. Extramedullary or intramedullary tibial alignment guides: a randomised, prospective trial of radiological alignment. J Bone Joint Surg Br Sep 2003;85(7):1084 author reply 1084. [13] Brys DA, Lombardi Jr AV, Mallory TH, Vaughn BK. A comparison of intramedullary and extramedullary alignment systems for tibial component placement in total knee arthroplasty. Clin Orthop Relat Res Feb 1991(263):175–9. [14] Belvedere C, Ensini A, Leardini A, Bianchi L, Catani F, Giannini S. Alignment of resection planes in total knee replacement obtained with the conventional technique, as assessed by a modern computer-based navigation system. Int J Med Robot Jun 2007;3(2):117–24. [15] Han HS, Kang SB, Jo CH, Kim SH, Lee JH. The accuracy of intramedullary tibial guide of sagittal alignment of PCL-substituting total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc Oct 2010;18(10):1334–8. [16] Canale ST, Beaty JH. Campbell's operative orthopaedics. Eleventh ed. Philadelphia, PA: Elsevier Inc.; 2008. [17] Hernigou P, Deschamps G. Posterior slope of the tibial implant and the outcome of unicompartmental knee arthroplasty. J Bone Joint Surg Am Mar 2004;86-A(3): 506–11. [18] Confalonieri N, Manzotti A, Pullen C, Ragone V. Computer-assisted technique versus intramedullary and extramedullary alignment systems in total knee replacement: a radiological comparison. Acta Orthop Belg Dec 2005;71(6):703–9. [19] Pang CH, Chan WL, Yen CH, Cheng SC, Woo SB, Choi ST, et al. Comparison of total knee arthroplasty using computer-assisted navigation versus conventional guiding systems: a prospective study. J Orthop Surg (Hong Kong) Aug 2009;17(2):170–3. [20] Mullaji A, Shetty GM. Computer-assisted total knee arthroplasty for arthritis with extra-articular deformity. J Arthroplasty Dec 2009;24(8):1164,9.e1. [21] Manzotti A, Pullen C, Confalonieri N. Computer-assisted alignment system for tibial component placement in total knee replacement: a radiological study. Chir Organi Mov Jan 2008;91(1):7–11.