The Journal of Arthroplasty 29 (2014) 1138–1142
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
A Multi-Planar CT-Based Comparative Analysis of Patient-Specific Cutting Guides With Conventional Instrumentation in Total Knee Arthroplasty Kanniraj Marimuthu, MBBS, MS (Ortho), DNB (Ortho) a, Darren B. Chen, MBBS FRACS (Ortho) b, Ian A. Harris, MBBS FRACS (Ortho) c, Emma Wheatley, BAppSc (MRS) d, Carl J. Bryant, MBBS, DDR, FRANZCR d, Samuel J. MacDessi, MBBS FRACS (Ortho) b a b c d
Fellow in Knee Reconstructive Surgery, Sydney Knee Specialists, NSW, Australia Sydney Knee Specialists, St George Private Hospital, Sydney, NSW, Australia South Western Sydney Clinical School, University of New South Wales, Australia Bryant Radiology, St George Private Hospital, Sydney, NSW, Australia
a r t i c l e
i n f o
Article history: Received 26 September 2013 Accepted 13 December 2013 Keywords: knee total knee arthroplasty patient specific alignment rotation computed tomography
a b s t r a c t Patient specific guides (PSGs) are postulated to improve the alignment of components in total knee arthroplasty. Three hundred consecutive total knee arthroplasties performed with either conventional (CON) (n = 185) or Visionaire PSG (n = 115) were evaluated with a CT protocol for coronal limb alignment, coronal and sagittal alignment of individual components and femoral component rotation. There was no statistically significant difference between the two groups in any of the above parameters. In addition, no difference was found in total operative time. PSGs do not offer any benefit over conventional guides in terms improving the coronal alignment of the limb or alignment of individual components. © 2014 Elsevier Inc. All rights reserved.
Near anatomical alignment of prosthetic components in the coronal, sagittal and rotational axes is one of the important factors that determine the success of total knee arthroplasty (TKA) [1–3]. Malposition of components may result in suboptimal outcomes in terms of pain, decreased range of motion, symptomatic instability, and early component loosening [4–7]. In conventional TKA, fixed anatomic landmarks and the medullary canal of femur and tibia are used as guides for proper implant positioning. Patient-specific cutting guides (PSGs) are a relatively recent technology where three dimensional templates of the patient’s knees are created using either computed tomography (CT) or magnetic resonance (MR) image sections. PSGs are designed based on these templates using rapid prototyping technology, with inputs from the surgeon on size and position of components [8]. Several trials have compared the alignment of components in conventional and PSG TKA based on plain radiographic images and reported either equal or improved alignment of components with PSG technology [9–12]. Rotational alignment of the femoral component has not been adequately analyzed. Rotational malalignment may lead The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2013.12.019. Reprint requests: Samuel J. MacDessi, MBBS FRACS (Ortho), Sydney Knee Specialists, Suite 8, 19 Kensington St Kogarah NSW 2217, Australia. http://dx.doi.org/10.1016/j.arth.2013.12.019 0883-5403/© 2014 Elsevier Inc. All rights reserved.
to poor patellar tracking, flexion instability, unexplained pain and stiffness [4,6,7,13]. Plain radiographs do not permit precise assessment of rotational alignment of the components. In addition, limb rotation at the time of radiographic assessment has been shown to have a significant effect on the measured anatomic alignment and mechanical angles [14]. The CT Perth Protocol is a low dose CT imaging sequence that allows accurate assessment of sagittal, coronal and rotational alignment of the TKA components [15]. A retrospective analysis of all patients who underwent a TKA using PSGs was undertaken and compared to a cohort of patients who underwent a TKA using conventional techniques during the same period. Our hypothesis is that PSG for TKA will result in better alignment of components than conventional methods. Materials and Methods A retrospective analysis of alignment of TKA components was undertaken based on post-operative CT imaging to compare conventional TKA with PSG TKA. All patients who underwent primary total knee arthroplasty in our practice using the Legion Total Knee Prosthesis (Smith and Nephew, Memphis, TN) between February 2012 and June 2013 with either conventional intramedullary cutting guides (CONs) or patient specific guides (Visionaire, Smith & Nephew, Memphis, Tenn.) were reviewed for the study after approval from the
K. Marimuthu et al. / The Journal of Arthroplasty 29 (2014) 1138–1142
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ethics committee. A total of 300 patients underwent TKA during this period, 185 with conventional instrumentation and 115 with PSG. All patients were assessed for suitability to undergo a PSG TKA. Reasons for patients not proceeding to a PSG TKA were contraindications to MRI such as the presence of cardiac or cerebral implants, claustrophobia and lack of time available before the intended date of surgery. Pre-Operative Planning Patients in both PSG and CON groups had pre-operative long leg weight bearing radiographs (LLRs) for surgical planning. The preoperative hip–knee angle (HKA) was recorded, based on the angle subtended by the coronal femoral mechanical axis (CFMA) with the coronal tibial mechanical axis (CTMA). Patients in PSG group underwent MR and plain x-ray imaging in accordance with the Visionaire protocol and the images were forwarded to Smith & Nephew for manufacturing of the PSG. Preoperative computer based planning software was programmed for perpendicular resections in the coronal plane to the mechanical axis of the distal femur and proximal tibia. In the sagittal plane, a neutral femoral flexion angle was planned along with 3° of posterior tibial slope. Femoral component rotation was set parallel to the surgical transepicondylar axis. Surgical Technique All the surgeries were performed using a standardized surgical technique by one of the two authors (SJM or DBC) under spinal anaesthesia with sedation. A medial parapatellar arthrotomy was used for exposure and a high thigh tourniquet was inflated until the distal femoral resection was completed. In both groups, the distal femoral resection was performed first followed by proximal tibial resection. In the CON group, intra-medullary guides were used both for preparation of the femur and tibia and femoral rotation was set relative to the surgical transepicondylar axis. In PSG group, the guides were used for distal femoral and proximal tibial resections as well as for setting rotation of the femoral component. In both groups, tibial component rotation was aligned parallel to the line connecting the center of PCL footprint to the junction of medial and middle thirds of tibial tuberosity. Patellar resurfacing and a partial lateral facetectomy were performed in all cases. The components were cemented after mediolateral ligament balancing.
Fig. 1. Femoral flexion measured as the angle between sagittal mechanical femoral axis (SFMA) and a line along the posterior flange of the femoral component.
(SFMA) and a line along the posterior flange of the femoral component (Fig. 1). Tibial slope was measured between the sagittal mechanical tibial axis (STMA) and a line level with the proximal aspect of the tibial component (Fig. 2). In the sagittal plane, our aim was to achieve neutral flexion of the femoral component and 3° of posterior slope of the tibial component. The angle between the surgical epicondylar axis (line connecting the lateral femoral epicondyle to medial epicondylar sulcus) and a line through the posterior flange of the knee arthroplasty was the femoral component rotational alignment (Fig. 3). Femoral rotational alignment was considered neutral when parallel to the surgical transepicondylar
Radiographic Analysis All patients underwent a post-operative helical CT scan as per the Perth Protocol using a low dose radiation of 2–3 mSv. The coronal and sagittal alignment of femoral and tibial components, as well as the femoral component rotation, was measured in all patients by one of the authors (EW). To ensure reliability, the measurements were done by a second author (KM) in 20 randomly selected scans. Outcome Measures The HKA, or coronal alignment of the limb was measured as the angle between the CFMA and CTMA. HKA was considered satisfactory if it deviated 3° or less from neutral alignment. Coronal femoral alignment was the angle between CFMA and a line through the inferior aspect of the femoral component of the knee arthroplasty, measured on the medial aspect. Tibial coronal alignment was the angle between CTMA and a line level through the proximal aspect of the tibial component of the knee arthroplasty, measured medially. Individual component positioning was considered satisfactory if the deviation from neutral was 2° or less. Sagittal femoral alignment was measured as the angle between the sagittal mechanical femoral axis
Fig. 2. Tibial slope measured between sagittal mechanical tibial axis (STMA) and a line level with the proximal aspect of the tibial component.
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Coronal Alignment On analysis of the coronal alignment, the mean HKA was − 0.02° (SD 2.5°) and 0.11° (SD 2.4°) in CON and PSG groups respectively. There was no statistically significant difference between the groups (Table 2). In addition, no statistically significant difference was observed between the two groups in terms of the proportion of outliers, using both 2° and 3° as cut-off values. No statistically significant difference was observed between CON and PSG groups in coronal alignment of individual components (Table 2). Mean femoral coronal alignment measured 89.6° (SD1.8°) in the CON group and 89.6° (SD 1.8°) in the PSG group (P = 0.82). Mean tibial coronal alignment measured 90.4° (SD 1.6°) in the CON group versus 90.5° (SD 1.5°) in the PSG group (P = 0.84). 80.5% of the subjects had a femoral component alignment within 2° of neutral (90°) in the CON group compared to 81.6% in the PSG group (P = 0.82). 89.7% of the subjects had a tibial alignment within 2° of neutral in the CON group compared to 89.6% in the PSG group (P = 0.96). Sagittal Alignment
Fig. 3. Femoral rotation is the angle between the line connecting the lateral femoral epicondyle to medial epicondylar sulcus (surgical epicondylar axis) and a line through the posterior flange of the femoral component. External rotation of the component with respect to surgical epicondylar axis was marked as positive values while internal rotation of the component was marked negative.
axis. Varus and internal rotation were considered as negative values whilst valgus and external rotation were considered as positive values.
No statistically significant difference was observed between CON and PSG groups when assessing mean femoral component alignment in the sagittal plane (P = 0.50, 1.2° vs. 1.3°). The proportion of outliers (greater than 2°) was 17.3% in the CON group and 18.4% in the PSG group (P = 0.81) (Table 3). Mean tibial slope was not statistically significantly different between groups (P = 0.68, 4.2° ± 2.2° vs 4.1° ± 2.5°). The proportion of outliers (greater than 2°) was 35.3% in the CON group and 39.1% in the PSG group (P = 0.51). Rotational Alignment
Statistical Analysis Continuous variables were analyzed using Student’s t-test and ANOVA for differences in means. Pearson’s chi squared test was used for difference in proportions between groups for dichotomous variables. Statistical significance level was set at a p value of less than 0.05.
Mean femoral component rotation recorded 0.1° (SD 2.0°) of internal rotation in CON group and 0.2° (SD 2.2°) of internal rotation in PSG group. The proportion of outliers (greater than 2°) was 20.1% and 24.4% in the CON and PSG groups respectively. There was no statistically significant difference between the two groups in terms of mean rotation and proportion of outliers (P values 0.60 and 0.39, respectively).
Results Discussion Characteristics of study subjects in both the groups are presented in Table 1. The groups were similar in terms of age, BMI and pre-operative HKA. No statistically significant difference was observed between the two groups in terms of tourniquet time and operative time. On analysis of inter-observer variability, the mean absolute difference in angle measurements (pooling all angles measured) was 1.10° (SD 1.1) and the mean difference between observers was less than 1.6° for each individual angle. The difference between the observers was 2° or less in 91% of angles measured. This lies within the standard inter-observer variability error reported in literature on any given TKA radiograph [16].
Table 1 Patient Demographics.
Character Age in years BMI Pre op HKA Operative time in minutes Tourniquet time in minutes
Conventional Group PSG Visionaire Group Mean (SD) Mean (SD) P Value 67.6 30.6 −4.3 75.0 13.1
(9.7) (5.4) (6.9) (10.6) (8.3)
68.3 (8.8) 30.8 (8.6) −3.6 (8.4) 72.5(13.9) 13.5 (8.8)
0.47 0.83 0.49 0.13 0.73
Evidence supports the proposition that proper component alignment is important for a successful outcome in total knee arthroplasty surgery [1–5]. Rotational malalignment of components has been shown to be a common cause of unexplained pain, reduced range of motion and symptomatic instability following TKA [4–6]. Plain radiographs are unable to analyze the rotational alignment of components and hence a majority of studies on alignment of components do not discuss rotational alignment in detail. Analysis of rotational alignment of components requires postoperative CT or MRI scanning and the metallic components cause artefacts in both these modalities [17,18]. MRI is more costly than CT and is best suited for analysis of zirconium than cobalt chromium components. Rotation of tibial component measurement is less reproducible using MRI and depends on the geometric method used to quantify rotation [18]. In addition to enabling measurement of rotational alignment, CT scans are more accurate that plain radiographs for measurement of coronal and sagittal alignment as rotation of the limb and flexion of the knee affects the plain radiographic measurement of coronal and sagittal alignment [14,19]. Patient-specific customized cutting guides based on pre-operative MR or CT imaging are aimed at improving the alignment of components over conventional methods. They are reported to reduce the operating time and the inventory required in the operating room [20]. The
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Table 2 Coronal Alignment of Components. Femoro-Tibial Axis Parameter Mean (SD) Range (Min to Max) Confidence Interval 95% P value Outliers (greater than 3°) Outliers (%) P Value Outliers (greater than 2°) Outliers (%) P Value
Femoral Coronal Angle
Tibial Coronal Angle
CON
VIS
CON
VIS
CON
VIS
−0.02 (2.5) −6 to 7 −0.4 to 0.3
0.11 (2.4) −5 to 5 −0.3 to 0.6
89. 6 (1.8) 86 to 95 89.3 to 89.8
89.6(1.8) 86 to 93 89.3 to 89.9
90.4(1.6) 85 to 96 90.2 to 90.7
90.5 (1.5) 87 to 95 90.2 to 90.7
0.65 16.8
0.82 13.9
4.3
0.51 28.1
0.84 3.5
2.7
3.5
0.73 35.7
19.5
0.17
0.70 18.4
10.3
10.4
0.82
drawbacks of this new technology include higher costs and time required for manufacturing of cutting guides which is usually between 3 and 6 weeks [21,22]. Current evidence on patient specific guides is limited and most only analyze coronal plane alignment, involve small cohorts of patients and results are inconsistent [20,21,23,24]. Several studies have examined the coronal alignment of components in TKA using PSG and conventional methods. Our definition of HKA outliers as values that deviate from neutral by more than 3° is based on the fact that this alignment range has been shown to correlate with functional outcome [25] and long term survival of the prosthesis [26]. For coronal and sagittal alignment of individual components though, there has been no clear consensus on cut off values. Most studies assessing alignment use either 3° or 2° as cut off values, and as such, both values were used as outcome measures in determining the success of each technique for individual component positioning [27–29]. In a prospective randomized controlled trial, Chareancholvanich et al compared coronal alignment using CT scanogram in TKA using conventional and patient specific guides (Zimmer PSI, Warsaw, IN). Both groups were statistically similar with regard to overall HKA and coronal femoral component alignment. Tibial component coronal alignment was significantly closer to neutral in PSG group. Outliers for femoral component coronal alignment were significantly lower in the PSG group [23]. Ng et al compared the coronal alignment of 569 TKAs using PSG (Biomet, Signature, Warsaw, IN) with 155 TKAs using conventional instrumentation based on long leg radiographs. The mean HKA value was similar in both groups but the number of outliers using a 3 0 cut off was significantly lower in the PSG group. No statistically significant difference was observed between the groups in terms of femoral and tibial coronal alignment outliers but the mean angles were closer to neutral in the PSG group [11]. Sagittal alignment of the femoral and tibial components has been analyzed in only a few studies. Vundelinckx et al evaluated coronal and sagittal plane alignment, short term functional outcomes, patient
0.96
satisfaction and blood loss in Visionaire PSG and conventional TKA patients in a prospective study design. The PSG group had significantly better tibial slope alignment than the conventional group and there was no difference in coronal alignment between the two groups. They also documented that the PSG group had more patients who could not achieve full extension and suggested an increased distal resection of the femur to avoid this. No difference between the two groups was found in terms of functional outcomes, patient satisfaction, blood loss or hospital stay [10]. There is a paucity of data assessing rotational alignment in TKA. Heyse et al compared femoral component rotation in CON and PSG TKA (Visionaire) using MR imaging. Coronal and sagittal alignment was not recorded. There were significantly more outliers (over 3°, P = 0.003) in the conventional group (22.9%) than in the PSI group (2.2%)[20]. Victor et al compared the alignment of components using conventional methods with patient specific guides from four different manufacturers, which differed with each other in terms of the imaging modality used, nature of the guide (pinning guide/cutting guide), the programmed sagittal plane alignment of components (femoral flexion and tibial slope) and hence was not homogenous. There were only 16 knees in each of the four PSG groups. Intra-operative navigation was used as a control in PSG group and when the measured value exceeded the target alignment in any plane and any direction by more than 3°, the use of the PSG was abandoned and the cuts were made following the surgical navigation system. PSGs did not improve the alignment of components or reduce the number of outliers in any plane. The PSG group had more outliers in tibial coronal and sagittal planes than conventional group. When comparing the PSG subgroups amongst themselves, the Visionaire group had a statistically significant, higher number of femoral coronal outliers and fewer femoral sagittal outliers than the other guides analyzed. The percentage of knees with components aligned within 3° of neutral in all the three planes was highest in Signature PSG subgroup followed by PSI subgroup and least in the Trumatch (DePuy Inc.,Warsaw, IN, USA) subgroup [24].
Table 3 Sagittal and Rotational Alignment of Components. Femoral Flexion Parameter Mean (SD) Range (Min to Max) Confidence Interval 95% P value Outliers (greater than 3°) % Outliers % Cases Normal P value Outliers (greater than 2°) % Outliers % Cases Normal P value
Tibial Slope
Femoral Rotation
CON
VIS
CON
VIS
CON
VIS
1.2 (1.6) −3 to 6 0.9 to 1.4
1.3 (1.9) −4 to 9 0.9 to 1.6
4.2 (2.2) −1 to 11 3.9 to 4.5
4.1 (2.5) −3 to 10 3.7 to 4.6
−0.1 (2.0) −6 to 6 −0.4 to 0.2
−0.2 (2.2) −5 to 6 −0.6 to 0.2
0.50 8.1 91.9
0.68 10.5 89.5
13.0 87.0
0.48 17.3 82.7
19.1 80.9
8.4 91.6
0.16 18.4 81.6
0.81
0.60
35.3 64.7
0.29 39.1 60.9
0.51
12.2 87.8
20.1 79.9
24.4 75.6 0.39
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Our study found no significant difference between conventional instrumentation and patient specific guides in coronal, sagittal or rotational alignment of individual components. In addition, the numbers of outliers, using both 3° and 2° as cut off were not found to be different between groups. The proposed benefit of this technology is that it may improve implant alignment, especially with femoral rotational positioning, where determination of the transepicondylar axis would theoretically be more precise with MR based guides than manual intra-operative assessment. However, the PSG group did not improve alignment compared to CON. These findings using the Visionaire system conflict with the results of Vundelinckx et al on sagittal positioning and with those of Heyse et al on rotational positioning. A limitation of this study is that it is a retrospective comparative analysis and hence selection bias cannot be excluded. However, we feel this study has significant merit in that it includes analysis of alignment in all the three planes using CT scans. This assessment cannot be made with plain radiographs. In addition, this study has a relatively large number of patients in each group as compared to previously published studies. The data from this study suggest that patient specific cutting guides using the Visionaire system do not offer any advantage over the conventional cutting guides in terms of alignment of components in coronal, sagittal or rotational planes. References 1. Benjamin J. Component alignment in total knee arthroplasty. Instr Course Lect 2006;55:405. 2. Lotke PA, Ecker ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am 1977;59:77. 3. Longstaff LM, Sloan K, Stamp N, et al. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty 2009;24:570. 4. Barrack RL, Schrader T, Bertot AJ, et al. Component rotation and anterior knee pain after total knee arthroplasty. Clin Orthop Relat Res 2001;46–55. 5. Sikorski JM. Alignment in total knee replacement. J Bone Joint Surg Br 2008; 90:1121. 6. Bong MR, Di Cesare PE. Stiffness after total knee arthroplasty. J Am Acad Orthop Surg 2004;12:164. 7. Lützner J, Krummenauer F, Günther K-P, et al. Rotational alignment of the tibial component in total knee arthroplasty is better at the medial third of tibial tuberosity than at the medial border. BMC Musculoskelet Disord 2010;11:57. 8. Krishnan SP, Dawood A, Richards R, et al. A review of rapid prototyped surgical guides for patient-specific total knee replacement. J Bone Joint Surg Br 2012;94:1457.
9. Nunley RM, Ellison BS, Zhu J, et al. Do patient-specific guides improve coronal alignment in total knee arthroplasty? Clin Orthop Relat Res 2012;470:895. 10. Vundelinckx BJ, Bruckers L, De Mulder K, et al. Functional and radio- graphic shortterm outcome evaluation of the visionaire system, a patient-matched instrumentation system for total knee arthroplasty. J Arthroplasty 2013. http://dx.doi. org/10.1016/j.arth.2012.09.010. 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;470:99. 12. Bali K, Walker P, Bruce W. Custom-fit total knee arthroplasty: our initial experience in 32 knees. J Arthroplasty 2012;27:1149. 13. Bell SW, Young P, Drury C, et al. Component rotational alignment in unexplained painful primary total knee arthroplasty. Knee 2012. http://dx. doi.org/10.1016/j.knee.2012.09.011. 14. Radtke K, Becher C, Noll Y, et al. Effect of limb rotation on radiographic alignment in total knee arthroplasties. Arch Orthop Trauma Surg 2010;130:451. 15. Chauhan SK, Clark GW, Lloyd S, et al. Computer-assisted total knee replacement. A controlled cadaver study using a multi-parameter quantitative CT assessment of alignment (the Perth CT Protocol). J Bone Joint Surg Br 2004;86:818. 16. Lonner JH, Laird MT, Stuchin SA. Effect of rotation and knee flexion on radiographic alignment in total knee arthroplasties. Clin Orthop Relat Res 1996;102–106. 17. Jazrawi LM, Birdzell L, Kummer FJ, et al. The accuracy of computed tomography for determining femoral and tibial total knee arthroplasty component rotation. J Arthroplasty 2000;15:761. 18. Heyse TJ, Chong LR, Davis J, et al. MRI analysis for rotation of total knee components. Knee 2012;19:571. 19. Kannan A, Hawdon G, McMahon SJ. Effect of flexion and rotation on measures of coronal alignment after TKA. J Knee Surg 2012;25:407. 20. Noble Jr JW, Moore CA, Liu N. The value of patient-matched instrumentation in total knee arthroplasty. J Arthroplasty 2012;27:153. 21. Nunley RM, Ellison BS, Ruh EL, et al. Are patient-specific cutting blocks costeffective for total knee arthroplasty? Clin Orthop Relat Res 2012;470:889. 22. Slover JD, Rubash HE, Malchau H, et al. Cost-effectiveness analysis of custom total knee cutting blocks. J Arthroplasty 2012;27:180. 23. Chareancholvanich K, Narkbunnam R, Pornrattanamaneewong C. A prospective randomised controlled study of patient-specific cutting guides compared with conventional instrumentation in total knee replacement. Bone Joint J 2013;95-B:354. 24. Victor J, Dujardin J, Vandenneucker H, et al. Patient-specific guides do not improve accuracy in total knee arthroplasty: a prospective randomized controlled trial. Clin Orthop Relat Res 2013. http://dx.doi.org/10.1007/s11999-013-2997-4. 25. Huang NFR, Dowsey MM, Ee E, et al. Coronal alignment correlates with outcome after total knee arthroplasty: five-year follow-up of a randomized controlled trial. J Arthroplasty 2012;27:1737. 26. Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg Br 1991;73:709. 27. Fu Y, Wang M, Liu Y, et al. Alignment outcomes in navigated total knee arthroplasty: a meta-analysis. Knee Surg Sports Traumatol Arthrosc 2012;20:1075. 28. Mason JB, Fehring TK, Estok R, et al. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22:1097. 29. Conteduca F, Iorio R, Mazza D, et al. Are MRI-based, patient matched cutting jigs as accurate as the tibial guides? Int Orthop 2012;36:1589.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
A Multi-Planar CT-Based Comparative Analysis of Patient-Specific Cutting Guides With Conventional Instrumentation in Total Knee Arthroplasty Kanniraj Marimuthu, MBBS, MS (Ortho), DNB (Ortho) a, Darren B. Chen, MBBS FRACS (Ortho) b, Ian A. Harris, MBBS FRACS (Ortho) c, Emma Wheatley, BAppSc (MRS) d, Carl J. Bryant, MBBS, DDR, FRANZCR d, Samuel J. MacDessi, MBBS FRACS (Ortho) b a b c d
Fellow in Knee Reconstructive Surgery, Sydney Knee Specialists, NSW, Australia Sydney Knee Specialists, St George Private Hospital, Sydney, NSW, Australia South Western Sydney Clinical School, University of New South Wales, Australia Bryant Radiology, St George Private Hospital, Sydney, NSW, Australia
a r t i c l e
i n f o
Article history: Received 26 September 2013 Accepted 13 December 2013 Keywords: knee total knee arthroplasty patient specific alignment rotation computed tomography
a b s t r a c t Patient specific guides (PSGs) are postulated to improve the alignment of components in total knee arthroplasty. Three hundred consecutive total knee arthroplasties performed with either conventional (CON) (n = 185) or Visionaire PSG (n = 115) were evaluated with a CT protocol for coronal limb alignment, coronal and sagittal alignment of individual components and femoral component rotation. There was no statistically significant difference between the two groups in any of the above parameters. In addition, no difference was found in total operative time. PSGs do not offer any benefit over conventional guides in terms improving the coronal alignment of the limb or alignment of individual components. © 2014 Elsevier Inc. All rights reserved.
Near anatomical alignment of prosthetic components in the coronal, sagittal and rotational axes is one of the important factors that determine the success of total knee arthroplasty (TKA) [1–3]. Malposition of components may result in suboptimal outcomes in terms of pain, decreased range of motion, symptomatic instability, and early component loosening [4–7]. In conventional TKA, fixed anatomic landmarks and the medullary canal of femur and tibia are used as guides for proper implant positioning. Patient-specific cutting guides (PSGs) are a relatively recent technology where three dimensional templates of the patient’s knees are created using either computed tomography (CT) or magnetic resonance (MR) image sections. PSGs are designed based on these templates using rapid prototyping technology, with inputs from the surgeon on size and position of components [8]. Several trials have compared the alignment of components in conventional and PSG TKA based on plain radiographic images and reported either equal or improved alignment of components with PSG technology [9–12]. Rotational alignment of the femoral component has not been adequately analyzed. Rotational malalignment may lead The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2013.12.019. Reprint requests: Samuel J. MacDessi, MBBS FRACS (Ortho), Sydney Knee Specialists, Suite 8, 19 Kensington St Kogarah NSW 2217, Australia. http://dx.doi.org/10.1016/j.arth.2013.12.019 0883-5403/© 2014 Elsevier Inc. All rights reserved.
to poor patellar tracking, flexion instability, unexplained pain and stiffness [4,6,7,13]. Plain radiographs do not permit precise assessment of rotational alignment of the components. In addition, limb rotation at the time of radiographic assessment has been shown to have a significant effect on the measured anatomic alignment and mechanical angles [14]. The CT Perth Protocol is a low dose CT imaging sequence that allows accurate assessment of sagittal, coronal and rotational alignment of the TKA components [15]. A retrospective analysis of all patients who underwent a TKA using PSGs was undertaken and compared to a cohort of patients who underwent a TKA using conventional techniques during the same period. Our hypothesis is that PSG for TKA will result in better alignment of components than conventional methods. Materials and Methods A retrospective analysis of alignment of TKA components was undertaken based on post-operative CT imaging to compare conventional TKA with PSG TKA. All patients who underwent primary total knee arthroplasty in our practice using the Legion Total Knee Prosthesis (Smith and Nephew, Memphis, TN) between February 2012 and June 2013 with either conventional intramedullary cutting guides (CONs) or patient specific guides (Visionaire, Smith & Nephew, Memphis, Tenn.) were reviewed for the study after approval from the
K. Marimuthu et al. / The Journal of Arthroplasty 29 (2014) 1138–1142
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ethics committee. A total of 300 patients underwent TKA during this period, 185 with conventional instrumentation and 115 with PSG. All patients were assessed for suitability to undergo a PSG TKA. Reasons for patients not proceeding to a PSG TKA were contraindications to MRI such as the presence of cardiac or cerebral implants, claustrophobia and lack of time available before the intended date of surgery. Pre-Operative Planning Patients in both PSG and CON groups had pre-operative long leg weight bearing radiographs (LLRs) for surgical planning. The preoperative hip–knee angle (HKA) was recorded, based on the angle subtended by the coronal femoral mechanical axis (CFMA) with the coronal tibial mechanical axis (CTMA). Patients in PSG group underwent MR and plain x-ray imaging in accordance with the Visionaire protocol and the images were forwarded to Smith & Nephew for manufacturing of the PSG. Preoperative computer based planning software was programmed for perpendicular resections in the coronal plane to the mechanical axis of the distal femur and proximal tibia. In the sagittal plane, a neutral femoral flexion angle was planned along with 3° of posterior tibial slope. Femoral component rotation was set parallel to the surgical transepicondylar axis. Surgical Technique All the surgeries were performed using a standardized surgical technique by one of the two authors (SJM or DBC) under spinal anaesthesia with sedation. A medial parapatellar arthrotomy was used for exposure and a high thigh tourniquet was inflated until the distal femoral resection was completed. In both groups, the distal femoral resection was performed first followed by proximal tibial resection. In the CON group, intra-medullary guides were used both for preparation of the femur and tibia and femoral rotation was set relative to the surgical transepicondylar axis. In PSG group, the guides were used for distal femoral and proximal tibial resections as well as for setting rotation of the femoral component. In both groups, tibial component rotation was aligned parallel to the line connecting the center of PCL footprint to the junction of medial and middle thirds of tibial tuberosity. Patellar resurfacing and a partial lateral facetectomy were performed in all cases. The components were cemented after mediolateral ligament balancing.
Fig. 1. Femoral flexion measured as the angle between sagittal mechanical femoral axis (SFMA) and a line along the posterior flange of the femoral component.
(SFMA) and a line along the posterior flange of the femoral component (Fig. 1). Tibial slope was measured between the sagittal mechanical tibial axis (STMA) and a line level with the proximal aspect of the tibial component (Fig. 2). In the sagittal plane, our aim was to achieve neutral flexion of the femoral component and 3° of posterior slope of the tibial component. The angle between the surgical epicondylar axis (line connecting the lateral femoral epicondyle to medial epicondylar sulcus) and a line through the posterior flange of the knee arthroplasty was the femoral component rotational alignment (Fig. 3). Femoral rotational alignment was considered neutral when parallel to the surgical transepicondylar
Radiographic Analysis All patients underwent a post-operative helical CT scan as per the Perth Protocol using a low dose radiation of 2–3 mSv. The coronal and sagittal alignment of femoral and tibial components, as well as the femoral component rotation, was measured in all patients by one of the authors (EW). To ensure reliability, the measurements were done by a second author (KM) in 20 randomly selected scans. Outcome Measures The HKA, or coronal alignment of the limb was measured as the angle between the CFMA and CTMA. HKA was considered satisfactory if it deviated 3° or less from neutral alignment. Coronal femoral alignment was the angle between CFMA and a line through the inferior aspect of the femoral component of the knee arthroplasty, measured on the medial aspect. Tibial coronal alignment was the angle between CTMA and a line level through the proximal aspect of the tibial component of the knee arthroplasty, measured medially. Individual component positioning was considered satisfactory if the deviation from neutral was 2° or less. Sagittal femoral alignment was measured as the angle between the sagittal mechanical femoral axis
Fig. 2. Tibial slope measured between sagittal mechanical tibial axis (STMA) and a line level with the proximal aspect of the tibial component.
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Coronal Alignment On analysis of the coronal alignment, the mean HKA was − 0.02° (SD 2.5°) and 0.11° (SD 2.4°) in CON and PSG groups respectively. There was no statistically significant difference between the groups (Table 2). In addition, no statistically significant difference was observed between the two groups in terms of the proportion of outliers, using both 2° and 3° as cut-off values. No statistically significant difference was observed between CON and PSG groups in coronal alignment of individual components (Table 2). Mean femoral coronal alignment measured 89.6° (SD1.8°) in the CON group and 89.6° (SD 1.8°) in the PSG group (P = 0.82). Mean tibial coronal alignment measured 90.4° (SD 1.6°) in the CON group versus 90.5° (SD 1.5°) in the PSG group (P = 0.84). 80.5% of the subjects had a femoral component alignment within 2° of neutral (90°) in the CON group compared to 81.6% in the PSG group (P = 0.82). 89.7% of the subjects had a tibial alignment within 2° of neutral in the CON group compared to 89.6% in the PSG group (P = 0.96). Sagittal Alignment
Fig. 3. Femoral rotation is the angle between the line connecting the lateral femoral epicondyle to medial epicondylar sulcus (surgical epicondylar axis) and a line through the posterior flange of the femoral component. External rotation of the component with respect to surgical epicondylar axis was marked as positive values while internal rotation of the component was marked negative.
axis. Varus and internal rotation were considered as negative values whilst valgus and external rotation were considered as positive values.
No statistically significant difference was observed between CON and PSG groups when assessing mean femoral component alignment in the sagittal plane (P = 0.50, 1.2° vs. 1.3°). The proportion of outliers (greater than 2°) was 17.3% in the CON group and 18.4% in the PSG group (P = 0.81) (Table 3). Mean tibial slope was not statistically significantly different between groups (P = 0.68, 4.2° ± 2.2° vs 4.1° ± 2.5°). The proportion of outliers (greater than 2°) was 35.3% in the CON group and 39.1% in the PSG group (P = 0.51). Rotational Alignment
Statistical Analysis Continuous variables were analyzed using Student’s t-test and ANOVA for differences in means. Pearson’s chi squared test was used for difference in proportions between groups for dichotomous variables. Statistical significance level was set at a p value of less than 0.05.
Mean femoral component rotation recorded 0.1° (SD 2.0°) of internal rotation in CON group and 0.2° (SD 2.2°) of internal rotation in PSG group. The proportion of outliers (greater than 2°) was 20.1% and 24.4% in the CON and PSG groups respectively. There was no statistically significant difference between the two groups in terms of mean rotation and proportion of outliers (P values 0.60 and 0.39, respectively).
Results Discussion Characteristics of study subjects in both the groups are presented in Table 1. The groups were similar in terms of age, BMI and pre-operative HKA. No statistically significant difference was observed between the two groups in terms of tourniquet time and operative time. On analysis of inter-observer variability, the mean absolute difference in angle measurements (pooling all angles measured) was 1.10° (SD 1.1) and the mean difference between observers was less than 1.6° for each individual angle. The difference between the observers was 2° or less in 91% of angles measured. This lies within the standard inter-observer variability error reported in literature on any given TKA radiograph [16].
Table 1 Patient Demographics.
Character Age in years BMI Pre op HKA Operative time in minutes Tourniquet time in minutes
Conventional Group PSG Visionaire Group Mean (SD) Mean (SD) P Value 67.6 30.6 −4.3 75.0 13.1
(9.7) (5.4) (6.9) (10.6) (8.3)
68.3 (8.8) 30.8 (8.6) −3.6 (8.4) 72.5(13.9) 13.5 (8.8)
0.47 0.83 0.49 0.13 0.73
Evidence supports the proposition that proper component alignment is important for a successful outcome in total knee arthroplasty surgery [1–5]. Rotational malalignment of components has been shown to be a common cause of unexplained pain, reduced range of motion and symptomatic instability following TKA [4–6]. Plain radiographs are unable to analyze the rotational alignment of components and hence a majority of studies on alignment of components do not discuss rotational alignment in detail. Analysis of rotational alignment of components requires postoperative CT or MRI scanning and the metallic components cause artefacts in both these modalities [17,18]. MRI is more costly than CT and is best suited for analysis of zirconium than cobalt chromium components. Rotation of tibial component measurement is less reproducible using MRI and depends on the geometric method used to quantify rotation [18]. In addition to enabling measurement of rotational alignment, CT scans are more accurate that plain radiographs for measurement of coronal and sagittal alignment as rotation of the limb and flexion of the knee affects the plain radiographic measurement of coronal and sagittal alignment [14,19]. Patient-specific customized cutting guides based on pre-operative MR or CT imaging are aimed at improving the alignment of components over conventional methods. They are reported to reduce the operating time and the inventory required in the operating room [20]. The
K. Marimuthu et al. / The Journal of Arthroplasty 29 (2014) 1138–1142
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Table 2 Coronal Alignment of Components. Femoro-Tibial Axis Parameter Mean (SD) Range (Min to Max) Confidence Interval 95% P value Outliers (greater than 3°) Outliers (%) P Value Outliers (greater than 2°) Outliers (%) P Value
Femoral Coronal Angle
Tibial Coronal Angle
CON
VIS
CON
VIS
CON
VIS
−0.02 (2.5) −6 to 7 −0.4 to 0.3
0.11 (2.4) −5 to 5 −0.3 to 0.6
89. 6 (1.8) 86 to 95 89.3 to 89.8
89.6(1.8) 86 to 93 89.3 to 89.9
90.4(1.6) 85 to 96 90.2 to 90.7
90.5 (1.5) 87 to 95 90.2 to 90.7
0.65 16.8
0.82 13.9
4.3
0.51 28.1
0.84 3.5
2.7
3.5
0.73 35.7
19.5
0.17
0.70 18.4
10.3
10.4
0.82
drawbacks of this new technology include higher costs and time required for manufacturing of cutting guides which is usually between 3 and 6 weeks [21,22]. Current evidence on patient specific guides is limited and most only analyze coronal plane alignment, involve small cohorts of patients and results are inconsistent [20,21,23,24]. Several studies have examined the coronal alignment of components in TKA using PSG and conventional methods. Our definition of HKA outliers as values that deviate from neutral by more than 3° is based on the fact that this alignment range has been shown to correlate with functional outcome [25] and long term survival of the prosthesis [26]. For coronal and sagittal alignment of individual components though, there has been no clear consensus on cut off values. Most studies assessing alignment use either 3° or 2° as cut off values, and as such, both values were used as outcome measures in determining the success of each technique for individual component positioning [27–29]. In a prospective randomized controlled trial, Chareancholvanich et al compared coronal alignment using CT scanogram in TKA using conventional and patient specific guides (Zimmer PSI, Warsaw, IN). Both groups were statistically similar with regard to overall HKA and coronal femoral component alignment. Tibial component coronal alignment was significantly closer to neutral in PSG group. Outliers for femoral component coronal alignment were significantly lower in the PSG group [23]. Ng et al compared the coronal alignment of 569 TKAs using PSG (Biomet, Signature, Warsaw, IN) with 155 TKAs using conventional instrumentation based on long leg radiographs. The mean HKA value was similar in both groups but the number of outliers using a 3 0 cut off was significantly lower in the PSG group. No statistically significant difference was observed between the groups in terms of femoral and tibial coronal alignment outliers but the mean angles were closer to neutral in the PSG group [11]. Sagittal alignment of the femoral and tibial components has been analyzed in only a few studies. Vundelinckx et al evaluated coronal and sagittal plane alignment, short term functional outcomes, patient
0.96
satisfaction and blood loss in Visionaire PSG and conventional TKA patients in a prospective study design. The PSG group had significantly better tibial slope alignment than the conventional group and there was no difference in coronal alignment between the two groups. They also documented that the PSG group had more patients who could not achieve full extension and suggested an increased distal resection of the femur to avoid this. No difference between the two groups was found in terms of functional outcomes, patient satisfaction, blood loss or hospital stay [10]. There is a paucity of data assessing rotational alignment in TKA. Heyse et al compared femoral component rotation in CON and PSG TKA (Visionaire) using MR imaging. Coronal and sagittal alignment was not recorded. There were significantly more outliers (over 3°, P = 0.003) in the conventional group (22.9%) than in the PSI group (2.2%)[20]. Victor et al compared the alignment of components using conventional methods with patient specific guides from four different manufacturers, which differed with each other in terms of the imaging modality used, nature of the guide (pinning guide/cutting guide), the programmed sagittal plane alignment of components (femoral flexion and tibial slope) and hence was not homogenous. There were only 16 knees in each of the four PSG groups. Intra-operative navigation was used as a control in PSG group and when the measured value exceeded the target alignment in any plane and any direction by more than 3°, the use of the PSG was abandoned and the cuts were made following the surgical navigation system. PSGs did not improve the alignment of components or reduce the number of outliers in any plane. The PSG group had more outliers in tibial coronal and sagittal planes than conventional group. When comparing the PSG subgroups amongst themselves, the Visionaire group had a statistically significant, higher number of femoral coronal outliers and fewer femoral sagittal outliers than the other guides analyzed. The percentage of knees with components aligned within 3° of neutral in all the three planes was highest in Signature PSG subgroup followed by PSI subgroup and least in the Trumatch (DePuy Inc.,Warsaw, IN, USA) subgroup [24].
Table 3 Sagittal and Rotational Alignment of Components. Femoral Flexion Parameter Mean (SD) Range (Min to Max) Confidence Interval 95% P value Outliers (greater than 3°) % Outliers % Cases Normal P value Outliers (greater than 2°) % Outliers % Cases Normal P value
Tibial Slope
Femoral Rotation
CON
VIS
CON
VIS
CON
VIS
1.2 (1.6) −3 to 6 0.9 to 1.4
1.3 (1.9) −4 to 9 0.9 to 1.6
4.2 (2.2) −1 to 11 3.9 to 4.5
4.1 (2.5) −3 to 10 3.7 to 4.6
−0.1 (2.0) −6 to 6 −0.4 to 0.2
−0.2 (2.2) −5 to 6 −0.6 to 0.2
0.50 8.1 91.9
0.68 10.5 89.5
13.0 87.0
0.48 17.3 82.7
19.1 80.9
8.4 91.6
0.16 18.4 81.6
0.81
0.60
35.3 64.7
0.29 39.1 60.9
0.51
12.2 87.8
20.1 79.9
24.4 75.6 0.39
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Our study found no significant difference between conventional instrumentation and patient specific guides in coronal, sagittal or rotational alignment of individual components. In addition, the numbers of outliers, using both 3° and 2° as cut off were not found to be different between groups. The proposed benefit of this technology is that it may improve implant alignment, especially with femoral rotational positioning, where determination of the transepicondylar axis would theoretically be more precise with MR based guides than manual intra-operative assessment. However, the PSG group did not improve alignment compared to CON. These findings using the Visionaire system conflict with the results of Vundelinckx et al on sagittal positioning and with those of Heyse et al on rotational positioning. A limitation of this study is that it is a retrospective comparative analysis and hence selection bias cannot be excluded. However, we feel this study has significant merit in that it includes analysis of alignment in all the three planes using CT scans. This assessment cannot be made with plain radiographs. In addition, this study has a relatively large number of patients in each group as compared to previously published studies. The data from this study suggest that patient specific cutting guides using the Visionaire system do not offer any advantage over the conventional cutting guides in terms of alignment of components in coronal, sagittal or rotational planes. References 1. Benjamin J. Component alignment in total knee arthroplasty. Instr Course Lect 2006;55:405. 2. Lotke PA, Ecker ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am 1977;59:77. 3. Longstaff LM, Sloan K, Stamp N, et al. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty 2009;24:570. 4. Barrack RL, Schrader T, Bertot AJ, et al. Component rotation and anterior knee pain after total knee arthroplasty. Clin Orthop Relat Res 2001;46–55. 5. Sikorski JM. Alignment in total knee replacement. J Bone Joint Surg Br 2008; 90:1121. 6. Bong MR, Di Cesare PE. Stiffness after total knee arthroplasty. J Am Acad Orthop Surg 2004;12:164. 7. Lützner J, Krummenauer F, Günther K-P, et al. Rotational alignment of the tibial component in total knee arthroplasty is better at the medial third of tibial tuberosity than at the medial border. BMC Musculoskelet Disord 2010;11:57. 8. Krishnan SP, Dawood A, Richards R, et al. A review of rapid prototyped surgical guides for patient-specific total knee replacement. J Bone Joint Surg Br 2012;94:1457.
9. Nunley RM, Ellison BS, Zhu J, et al. Do patient-specific guides improve coronal alignment in total knee arthroplasty? Clin Orthop Relat Res 2012;470:895. 10. Vundelinckx BJ, Bruckers L, De Mulder K, et al. Functional and radio- graphic shortterm outcome evaluation of the visionaire system, a patient-matched instrumentation system for total knee arthroplasty. J Arthroplasty 2013. http://dx.doi. org/10.1016/j.arth.2012.09.010. 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;470:99. 12. Bali K, Walker P, Bruce W. Custom-fit total knee arthroplasty: our initial experience in 32 knees. J Arthroplasty 2012;27:1149. 13. Bell SW, Young P, Drury C, et al. Component rotational alignment in unexplained painful primary total knee arthroplasty. Knee 2012. http://dx. doi.org/10.1016/j.knee.2012.09.011. 14. Radtke K, Becher C, Noll Y, et al. Effect of limb rotation on radiographic alignment in total knee arthroplasties. Arch Orthop Trauma Surg 2010;130:451. 15. Chauhan SK, Clark GW, Lloyd S, et al. Computer-assisted total knee replacement. A controlled cadaver study using a multi-parameter quantitative CT assessment of alignment (the Perth CT Protocol). J Bone Joint Surg Br 2004;86:818. 16. Lonner JH, Laird MT, Stuchin SA. Effect of rotation and knee flexion on radiographic alignment in total knee arthroplasties. Clin Orthop Relat Res 1996;102–106. 17. Jazrawi LM, Birdzell L, Kummer FJ, et al. The accuracy of computed tomography for determining femoral and tibial total knee arthroplasty component rotation. J Arthroplasty 2000;15:761. 18. Heyse TJ, Chong LR, Davis J, et al. MRI analysis for rotation of total knee components. Knee 2012;19:571. 19. Kannan A, Hawdon G, McMahon SJ. Effect of flexion and rotation on measures of coronal alignment after TKA. J Knee Surg 2012;25:407. 20. Noble Jr JW, Moore CA, Liu N. The value of patient-matched instrumentation in total knee arthroplasty. J Arthroplasty 2012;27:153. 21. Nunley RM, Ellison BS, Ruh EL, et al. Are patient-specific cutting blocks costeffective for total knee arthroplasty? Clin Orthop Relat Res 2012;470:889. 22. Slover JD, Rubash HE, Malchau H, et al. Cost-effectiveness analysis of custom total knee cutting blocks. J Arthroplasty 2012;27:180. 23. Chareancholvanich K, Narkbunnam R, Pornrattanamaneewong C. A prospective randomised controlled study of patient-specific cutting guides compared with conventional instrumentation in total knee replacement. Bone Joint J 2013;95-B:354. 24. Victor J, Dujardin J, Vandenneucker H, et al. Patient-specific guides do not improve accuracy in total knee arthroplasty: a prospective randomized controlled trial. Clin Orthop Relat Res 2013. http://dx.doi.org/10.1007/s11999-013-2997-4. 25. Huang NFR, Dowsey MM, Ee E, et al. Coronal alignment correlates with outcome after total knee arthroplasty: five-year follow-up of a randomized controlled trial. J Arthroplasty 2012;27:1737. 26. Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg Br 1991;73:709. 27. Fu Y, Wang M, Liu Y, et al. Alignment outcomes in navigated total knee arthroplasty: a meta-analysis. Knee Surg Sports Traumatol Arthrosc 2012;20:1075. 28. Mason JB, Fehring TK, Estok R, et al. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22:1097. 29. Conteduca F, Iorio R, Mazza D, et al. Are MRI-based, patient matched cutting jigs as accurate as the tibial guides? Int Orthop 2012;36:1589.
