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The use of navigation to achieve soft tissue balance in total knee arthroplasty — A randomised clinical study
The Knee 20 (2013) 401–406
Contents lists available at ScienceDirect
The Knee
The use of navigation to achieve soft tissue balance in total knee arthroplasty — A randomised clinical study J. Joseph a, P.M.S. Simpson a, S.L. Whitehouse a, H.W. English b,⁎, W.J. Donnelly b a b
Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia Brisbane Orthopaedic Specialist Services, Holy Spirit Northside Hospital, Brisbane, Queensland, Australia
a r t i c l e
i n f o
Article history: Received 14 February 2013 Received in revised form 14 May 2013 Accepted 23 June 2013 Keywords: Navigation Arthroplasty Tissue balance Surgery Total knee replacement
a b s t r a c t Background: Achieving soft tissue balance is an operative goal in total knee arthroplasty. This randomised, prospective study compared computer navigation to conventional techniques in achieving soft tissue balance. Methods: Forty one consecutive knee arthroplasties were randomised to either a non-navigated or navigated group. In the non-navigated group, balancing was carried out using surgeon judgement. In the navigated group, balancing was carried out using navigation software. In both groups, the navigation software was used as a measuring tool. Results: Balancing of the mediolateral extension gap was superior in the navigation group (p = 0.001). No significant difference was found between the two groups in balancing the mediolateral flexion gap or in achieving equal flexion and extension gaps. Conclusions: Computer navigation offered little advantage over experienced surgeon judgement in achieving soft tissue balance in knee replacement. However, the method employed in the navigated group did provide a reproducible and objective assessment of flexion and extension gaps and may therefore benefit surgeons in training. Level of evidence: Level I, RCT. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
1. Introduction It is widely accepted in orthopaedic practice that, during total knee arthroplasty, the surgeon should aim to achieve a balance in flexion and extension gaps and aim for rectangular gaps (i.e. balanced medial and lateral sides) [1–3]. This achievement of balance is thought to improve the outcome of total knee arthroplasty. Abnormal polyethylene wear patterns are thought to be associated with knee arthroplasties that are not equally balanced [4]. Adequate soft tissue balance has also been postulated to improve proprioception post knee arthroplasty [5]. Clinically apparent instability following knee arthroplasty can be due to flexion and extension gap mismatch [6]. There are a number of options available to the surgeon in terms of assessing or measuring whether balance has been achieved. In the opinion of the authors, it is felt that the majority of surgeons assess balance by means of ‘feel’. Other options include utilising tensiometers or spacer blocks; computer navigation is a possible further option as a tool to assess gap balance. Using navigation as an aid to soft tissue release in knee arthroplasty has been reported [7]. ⁎ Corresponding author at: Brisbane Orthopaedic Specialist Services, Holy Spirit Northside Hospital, 627 Rode Road, Chermside, Queensland 4032, Australia. Tel.: +61 1300 436 454; fax: +61 7 3256 4634. E-mail address: [email protected] (H.W. English).
A number of studies show the accuracy of computer navigation systems in terms of component positioning and overall limb alignment is reliable [8–10]. The short, medium and long-term benefits of this accuracy in terms of patient satisfaction and outcome are as yet not fully known. In the current literature, there is only one published study [11] that has reported on soft-tissue balancing in navigated knee arthroplasty. This study involved a single group of 30 patients undergoing unilateral knee arthroplasty. For measurements of joint space gaps, this study showed a good correlation between measurements obtained from a tensiometer and those obtained from the imageless navigation software. The validity of an imageless navigation software system as a measuring tool in terms of component position and alignment [12] and in terms of joint gap measurement [11] has been demonstrated. In this prospective, randomised, patient blinded study, the accuracy of ligament balancing in two groups of patients was compared. In one group, the non-navigated group, balancing was undertaken by using the surgeon's ‘feel’. In the other group, the navigated group, balancing was undertaken utilising imageless computer navigation to guide the surgeon. In both groups, the computer navigation software was used as a measuring tool to record gap measurements. Our aim was to show whether the use of computer navigation conferred greater accuracy in soft tissue balancing compared to a non-navigated technique.
0968-0160/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.knee.2013.06.007
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J. Joseph et al. / The Knee 20 (2013) 401–406
2. Materials and methods Power analysis indicated that with 80% power, 5% significance level and a standardised difference of 1.0 [13], a minimum of 17 patients were needed in each group. To ensure this minimum requirement was met, we aimed for 20 knees per group. Forty consecutive patients listed for primary knee arthroplasty (41 knee arthroplasties) were prospectively recruited by the operating surgeon into this study between October 2008 and May 2009 when the recruitment goal was reached. Ethical approval was obtained from our institution's ethics committee. Patients were provided with information sheets and gave informed consent to enter this study at the time of being listed for the procedure. No patients refused consent for this study. Randomisation was performed by a statistician (SLW) using the Sampsize program [14] with a block size of 4 and allocation ratio of 1:1, and stored in theatre by means of envelopes allocating patients to either a non-navigated or navigated group. Envelopes were opened sequentially in theatre prior to the incision being made. Patients were blinded as to whether they had been allocated to the navigated or non-navigated group. Patients with both varus and valgus coronal plane deformities were included. There were no exclusion criteria. 2.1. Surgical technique All patients received a Triathlon posterior stabilised, fixed bearing total knee replacement (Stryker Orthopaedics, Mahwah, NJ) inserted via a standardised medial para-patellar approach. This involved initial dissection of the medial collateral ligament (MCL) fibres sufficient to expose the mid-equatorial point of the tibial surface. Stryker navigation femoral and tibial trackers were placed in all patients in both groups. The trackers were attached to bone via 3 mm diameter Ortholock drill pins (Stryker Orthopaedics, Mahwah, NJ). The Stryker Image Free navigation system (version 4.0) was used to register the femoral and tibial landmarks in all patients. In the non-navigated group, the navigation software was used purely as a measuring tool whereas in the navigated group it was used to facilitate the acquisition of accurate bony cuts, to modify implant position and guide soft tissue release. A Stryker tensiometer (Stryker Orthopaedics, Mahwah, NJ) was utilised to provide a known fixed tension force across the joint in order to measure the gaps at 90° flexion and full extension. Actual gap readings were taken from the measurements recorded by the navigation software and recorded by an unscrubbed theatre assistant. In all cases, the surgeon aimed to cut the proximal tibia with a posterior slope of 0°. The surgeon aimed to remove 9 mm of proximal tibial bone from the non-affected side of the tibial plateau. All procedures were undertaken by the senior authors (HWE and WJD) who are experienced surgeons in both non-navigated and navigated total knee arthroplasty. All procedures were carried out under tourniquet inflated at 350 mm Hg. 2.1.1. Surgical technique non-navigated group The tibia was cut first in all cases using extra-medullary referencing. The distal femoral cut was then made using intra-medullary referencing. Standard techniques were used to size and finish off the femur using a 4 in 1 femoral cutting block. Following the removal of all osteophytes, a trial reduction was performed and soft tissue releases were undertaken based upon a subjective assessment of balance by the surgeon. Further releases were made after assessment of the mediolateral gaps and the flexion and extension gaps. This was done with the trial components in situ. The surgeon applied a manual varus/valgus strain through a full passive range of motion and assessed for inequality in gaps by ‘feel’. Once the surgeon was happy that he had achieved a balanced arthroplasty, the joint gaps were recorded at 90° flexion and at full extension, without the trial components in place and with the patella reduced. No further modifications could be made by the surgeon following
this. All measurements were carried out with a fixed tension of 135 N (Newton) provided by the tensiometer across the joint. 2.1.2. Surgical technique for navigated group The tibia was cut first in all cases. This cut was verified following completion and was modified if necessary to ensure it fell perpendicular to the mechanical axis +/− 2°. Following this, an initial measurement of the gaps at 90° flexion and full extension was undertaken with the tensiometer in situ. The Stryker version 4.0 software was able to calculate the size of the femoral component after registration of the epicondyles and registration of the bony morphology of the anterior and posterior femoral condyles. Based on the initial gap measurements, the surgeon had a number of options to equilibrate the flexion and extension gaps. These included downsizing the femoral prosthesis or modifying the position of the femoral prosthesis in the anteroposterior or proximodistal planes. The software used algorithms that took a mean value of the registered femoral transepicondylar axis and the registered femoral anteroposterior axis (Whiteside's line) to determine axial rotation of the femur. The surgeon aimed for the femoral bony cut to have a value of 0° +/− 2° external rotation based on the software measurement. After the femoral cuts, the gaps at 135 N were measured again. The surgeon then made further soft tissue releases as necessary to try and equalise the mediolateral gaps to within 2 mm of each other. Final gap measurements (without the trial components in place) were recorded once again at 135 N of tension. 135 N was chosen as the tension force as it was felt that this level of tension produced sufficient strain to overcome any laxity in the soft tissues to allow reliable measurement of gaps, and is similar to forces used in other studies [15]. In both groups of patients, the initial and final coronal plane alignment in 0° extension and initial and final on-table range of movement (ROM) were recorded intra-operatively. These values were measured by the navigation software after registration of the mechanical axis and bony surfaces. The values reflected the coronal plane deformity from the mechanical axis not the coronal plane deformity as given by the tibiofemoral anatomical axis angle. Also the accuracy of the bony cuts in terms of coronal plane alignment in the femur and tibia and femoral rotation were also recorded in both groups. Pre-operative patient demographics and measurements are shown in Table 1. In the non-navigated group there were 21 patients (21 knee replacements. In the navigated group there were 19 patients (20 knee replacements). Gender and age distribution was similar for both groups. The spectrum of deformity, in terms of the coronal and sagittal planes, was similar in both groups as was the pre-operative ROM. 2.2. Tensiometer The Stryker tensiometer (Fig. 1) used in this study consisted of two metal plates that sat on the cut surfaces of the tibia and femur. The surgeon was able to exert a known distraction force (135 N in this study) via a torque driver which was attached to the body of
Table 1 Baseline pre-operative demographics for each group.
n, knees (patients) Gender, male/female Mean age (range) Deformity (°) varus: n, mean (range) valgus: n, mean (range) FFD: mean (range) Median range of motion (°) range (IQR) FFD — fixed flexion deformity. IQR — inter-quartile range.
Non-navigated
Navigated
21 (21 patients) 11/10 65.5 (53–85)
20 (19 patients) 5/14 67.6 (52–86)
16, 6.5 (0.5–14.5) 5, 4.2 (1.0–8.5) 3.6 (9.5–20.0) 123.5 106–138 (7.8)
14, 6.1 (1.0–12.0) 6, 3.6 (1.0–6.0) 4.6 (−9.0–21.5) 121.8 111–136 (12.8)
J. Joseph et al. / The Knee 20 (2013) 401–406
Fig. 1. Stryker tensiometer.
the tensiometer to distract the two plates. The distance between the two plates was measured by the navigation software as the joint gap. The software showed the gap on the medial side and the lateral side of the joint. The tensiometer had a scale which measured the distance (in millimetres) between the two plates. As shown in the previously quoted study [11], the value shown on the tensiometer scale correlated well with that shown on the navigation monitor screen. The tensiometer also had a further scale to show angular deviation (in degrees) of the upper plate relative to the lower plate i.e. varus/valgus imbalance. The tensiometer measurements were not recorded in this study. The tensiometer was used solely as an instrument to provide a known, constant tension across the joint in order to facilitate joint gap measurements by the navigation software. It was found that recording the gaps from the monitor screen, whilst maintaining a constant joint distraction force with the tensiometer was easier practically and more ‘user friendly’ than recording the gaps from the tensiometer scale. In addition, it was found recording the imbalance between medial and lateral sides as a distance in millimetres, as opposed to an angular value in degrees read from the tensiometer scale, to be more practical and intuitive. The torque produced by the tensiometer was calibrated in the laboratory using a tensile tester (Instron 5848 Microtester) to verify the tension force produced was 135 N.
403
Fig. 3. Box and whisker plot of differences between the two groups in achieving a balanced extension gap.
(the primary endpoint) and range of movement data was not normally distributed and so non-parametric methods were employed for analysis. Medians and interquartile ranges (IQR) are presented. The Mann–Whitney U test and Levene's test for homogeneity of variance were used to determine significance of differences in gap measurements between the non-navigated and navigated groups. Data for accuracy of bony cuts and final overall limb alignment was found to be normally distributed. The Student's t-test was used to establish if differences in mean values for bony cut accuracy and final alignment between the non-navigated and navigated groups were significant. Means and standard deviations are presented. Levene's test for homogeneity of variance was used to determine if variances for bony cut accuracy and final limb alignment between the two groups were significantly different. Adjustment for multiple testing was made using Bonferroni's method at each level.
3. Results
The results were analysed using SPSS for Windows (V18, SPSS Inc., Chicago, II). Normality testing indicated that the gap measurement
All 41 cases (40 patients) were included in the final analysis, as data collection at surgery was complete. With regard to comparing gap measurements, the results showed a statistically significant difference (Figs. 2 & 3) between the non-navigated and navigated groups in obtaining a balanced mediolateral extension gap in both median and variability (Mann–Whitney U-test p = 0.013, Levene's test for homogeneity of variance p = 0.001) (Table 2). The mediolateral extension gap was more accurately balanced in the navigated group. There was no statistically significant difference (Figs. 4 & 5) between the two groups for balancing the mediolateral flexion gap (p = 0.56 M-W, p = 0.16 Levene's test). There was also no statistically significant
Fig. 2. Histogram of differences between the two groups in achieving a balanced extension gap.
Fig. 4. Histogram of differences between the two groups in achieving a balanced flexion gap.
2.3. Statistical analysis
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Fig. 5. Box and whisker plot of differences between the two groups in achieving a balanced flexion gap.
Fig. 7. Box and whisker plot of differences between the two groups in achieving equal flexion and extension gaps.
difference (Figs. 6 & 7) between the two groups in obtaining equal flexion and extension gaps (p = 0.77 M-W, p = 0.48 Levene's test). With regard to comparing accuracy of bony cuts between the two groups, the results showed statistically significant greater accuracy in the navigated group for all bony cuts with regards to variability (Levene's test: distal femur p = 0.005, proximal tibia p = 0.018, femoral rotation p = 0.002) (Table 3). However, there was no statistically significant difference in the mean values between both groups (Student's t-test: distal femur p = 1.0, proximal tibia p = 0.19, femoral rotation p = 0.62). Final overall limb alignment was statistically less variable (Figs. 8 & 9) in the navigated group (Levene's test: p = 0.023) although no difference was found in mean values between the two groups (Student's t-test: p = 0.10) (Table 4). No significant difference was found between the two groups in terms of extent of final range of movement or change in range of movement (Table 5).
significantly better in the navigated group. In the navigated group, the coronal plane final alignment was accurate to within 1°. The joint tension force produced by the tensiometer was quantifiable and reproducible. It was also found that quantifying the flexion and extension gaps and the coronal plane imbalance using the navigation software readily facilitated the surgeon to carry out further soft tissue release or modify the component position in order to optimise the gaps. Having the measurements displayed on the monitor screen and also the change in subsequent measurements following soft tissue release and/or component position modification allowed practical and intuitive balancing procedures to be performed. This study demonstrated no advantage of computer navigation in improving on-table final ROM. The use of navigation for data recording in both groups minimised measurement bias and the use of the tensionometer reduced the variability in the stresses applied. In their study of 30 patients, Matsumoto et al. [11] achieved a mean joint component gap imbalance of 8.8 mm with the patella everted and 5.4 mm imbalance with the patella reduced, with flexion gaps being larger in both cases. They also reported a coronal plane ligament imbalance toward varus. Griffin et al. [16] measured flexion and extension gaps directly with a ruler during total knee arthroplasty procedures. In their study, they used lamina spreaders, placed medially and laterally, after bony cuts and soft tissue releases to produce a maximal manual tension across the joint and then measured the flexion and extension gaps. They reported perfect balance with equal, rectangular flexion and extension gaps in 8 out of 104 (7.7%) total knee arthroplasties.
4. Discussion This study showed significantly more accurate balancing of the mediolateral extension gap using the navigation system to guide the surgeon when compared to balancing by ‘feel’ alone. The surgeon could use the software to accurately alter the femoral component position either proximally or distally and also be guided as to the degree of necessary soft tissue release. There was no statistically significant difference between the two groups in balancing the mediolateral flexion gap or in achieving equal flexion and extension gaps. In this study, balancing of gaps in both groups was accurate to within 1–2 mm. The accuracy of the bony cuts and the final overall limb alignment was
Table 2 Table showing differences between the two groups for gap balancing. Non-navigated Navigated p-Value p-Value (Mann–Whitney) (Levene's)
Fig. 6. Histogram of differences between the two groups in achieving equal flexion and extension gaps.
Mediolateral difference 2.0 (5.0) in 0° extension (mm) Mediolateral difference 1.0 (2.5) in 90° flexion (mm) 0.5 (3.8) Flexion gap minus extension gap (mm)
0.0 (1.8)
0.013
0.001
0.5 (3.0)
0.561
0.158
0.75 (3.0)
0.773
0.481
Values shown as median (interquartile range (IQR)).
J. Joseph et al. / The Knee 20 (2013) 401–406
405
Fig. 8. Histogram of differences between the two groups in final overall limb alignment.
Of these 8 patients 4 had no pre-operative coronal plane deformity as measured by tibiofemoral angle on standing knee AP X-rays and the other 4 had varus deformity from 2° to 12°. They reported that they achieved balanced flexion and extension gaps within 1 mm in 47% of patients on the lateral side and 57% of patients on the medial side. They found that knees with a pre-operative fixed flexion deformity (FFD) were less accurately balanced than those without a FFD. They also found that their extension gaps were generally speaking greater than their flexion gaps. They postulated that surgeons may have a tendency to increase the extension gap relative to the flexion
gap to minimise the risk of post-operative FFD and flexion instability. This viewpoint is in contrast to Asano et al. [17] who in their study reported that for their patient population, who express a need for deep flexion, they aim for a 3 mm greater flexion than extension gap. Pang et al. [18] demonstrated more precise soft tissue balancing with computer assisted balancing than conventional balancing, with improved function scores in the navigated group at 6 months. Better gap balancing was also demonstrated with navigation by Lee at al. [19]. There is a degree of variance amongst surgeons in terms of how to address gap balance and the results achieved for balance and alignment. This study showed that computer navigation facilitates the surgeon to achieve more consistent and accurate bony cuts and overall limb alignment. In terms of overall balance of the soft tissue envelope, this study showed that computer navigation offered little advantage over the judgement of the experienced surgeon. However, the method employed in the navigated group did provide a reproducible and objective assessment of flexion and extension gaps and may therefore benefit surgeons in training.
Table 3 Table showing differences between the two groups for accuracy of bony cuts. Non-navigated
Navigated
Mean
Mean 95% CI
95% CI
Distal femur 0.00 −1.08–1.08 0.00 resection (°) Proximal tibia 0.61 −0.11–1.33 0.09 resection (°) −0.33 −2.28–1.62 0.15 Femoral rotation (°) Fig. 9. Box and whisker plot of differences between the two groups in final overall limb alignment.
p-Value p-Value (t-test) (Levene's)
−0.39–0.39 1.0
0.005
−0.31–0.49 0.189
0.018
−0.24–0.53 0.616
0.002
CI — Confidence interval. Varus given as a negative value, valgus given as a positive value. Internal rotation given as a negative value, external rotation as a positive value.
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Table 4 Table showing differences between the two groups in final overall limb alignment. Non-navigated
Final overall limb alignment (°)
Navigated
Mean
95% CI
Mean
95% CI
p-Value (Mann–Whitney)
p-Value (Levene's)
−1.14
−2.48–0.19
0.06
−0.53–0.65
0.096
0.023
Varus given as a negative value, valgus given as a positive value.
Table 5 Table showing differences between the two groups in ROM.
Initial ROM (°) (range, IQR) Final ROM (°) (range, IQR) Change in ROM (°) (range, IQR)
Non-navigated
Navigated
p-Value (Mann–Whitney)
123.5 (106–138, 7.8) 127.0 (113.5–142.2, 14.8) 3.5 (−6–13, 7.8)
121.75 (111–136, 12.8) 122.5 (109–140, 7.8) 3.0 (−16.5–10.5, 8.9)
0.764 0.433 0.426
Values shown as median, (range, IQR).
5. Conflict of interest statement
J Joseph PMS Simpson SL Whitehouse HW English
WJ Donnelly
I do not have any financial or personal relationships with other people or organisations that could bias my work. I have undertaken consultancy work for Stryker Orthopaedics regarding primary & revision knee replacement. Position partially funded via external organisation by Stryker Orthopaedics I receive grants for research projects from Smith and Nephew. My wife has a financial interest in Oceania Orthopaedics, neither product source is involved in this trial. I have done consultancy work for Stryker Orthopaedics regarding navigation. I have a financial interest in Oceania Orthopaedics.
No funding was directly received in relation to this project. Trial registered with Australian New Zealand Clinical Trials Registry (ANZCTR); Registration number: ACTRN12613000516785. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.knee.2013.06.007. References [1] Insall JN. Surgery of the knee. 2nd ed. New York: Churchill Livingstone; 1993. [2] Freeman MA, Sculco T, Todd RC. Replacement of the severely damaged arthritic knee by the ICLH (Freeman–Swanson) arthroplasty. J Bone Joint Surg Br Feb 1977;59(1):64–71.
[3] Insall J, Scott WN, Ranawat CS. The total condylar knee prosthesis. A report of two hundred and twenty cases. J Bone Joint Surg Am Mar 1979;61(2):173–80. [4] Wasielewski RC, Galante JO, Leighty RM, Natarajan RN, Rosenberg AG. Wear patterns on retrieved polyethylene tibial inserts and their relationship to technical considerations during total knee arthroplasty. Clin Orthop Relat Res Feb 1994;299:31–43. [5] Attfield SF, Wilton TJ, Pratt DJ, Sambatakakis A. Soft-tissue balance and recovery of proprioception after total knee replacement. J Bone Joint Surg Br Jul 1996;78(4): 540–5. [6] Pagnano MW, Hanssen AD, Lewallen DG, Stuart MJ. Flexion instability after primary posterior cruciate retaining total knee arthroplasty. Clin Orthop Relat Res Nov 1998;356:39–46. [7] Saragaglia D, Chaussard C, Rubens-Duval B. Navigation as a predictor of soft tissue release during 90 cases of computer-assisted total knee arthroplasty. Orthopedics Oct 2006;29(10 Suppl.):S137–8. [8] Martin A, Wohlgenannt O, Prenn M, Oelsch C, von Strempel A. Imageless navigation for TKA increases implantation accuracy. Clin Orthop Relat Res Jul 2007;460: 178–84. [9] Sparmann M, Wolke B, Czupalla H, Banzer D, Zink A. Positioning of total knee arthroplasty with and without navigation support. A prospective, randomised study. J Bone Joint Surg Br Aug 2003;85(6):830–5. [10] Chauhan SK, Scott RG, Breidahl W, Beaver RJ. Computer-assisted knee arthroplasty versus a conventional jig-based technique. A randomised, prospective trial. J Bone Joint Surg Br Apr 2004;86(3):372–7. [11] Matsumoto T, Muratsu H, Tsumura N, Mizuno K, Kurosaka M, Kuroda R. Soft tissue balance measurement in posterior-stabilized total knee arthroplasty with a navigation system. J Arthroplasty Apr 2009;24(3):358–64. [12] Chauhan SK, Clark GW, Lloyd S, Scott RG, Breidahl W, Sikorski JM. 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 Aug 2004;86(6):818–23. [13] Sasanuma H, Sekiya H, Takatoku K, Takada H, Sugimoto N. Evaluation of soft-tissue balance during total knee arthroplasty. J Orthop Surg (Hong Kong) Apr 2010;18(1):26–30. [14] Machin D, Campbell MJ, Fayers PM, Pinol APY. Sample size tables for clinical studies. Oxford: Blackwell Science; 1997. [15] Tanaka K, Muratsu H, Mizuno K, Kuroda R, Yoshiya S, Kurosaka M. Soft tissue balance measurement in anterior cruciate ligament-resected knee joint: cadaveric study as a model for cruciate-retaining total knee arthroplasty. J Orthop Sci Mar 2007;12(2):149–53. [16] Griffin FM, Insall JN, Scuderi GR. Accuracy of soft tissue balancing in total knee arthroplasty. J Arthroplasty Dec 2000;15(8):970–3. [17] Asano H, Hoshino A, Wilton TJ. Soft-tissue tension total knee arthroplasty. J Arthroplasty Aug 2004;19(5):558–61. [18] Pang HN, Yeo SJ, Chong HC, Chin PL, Ong J, Lo NN. Computer-assisted gap balancing technique improves outcome in total knee arthroplasty, compared with conventional measured resection technique. Knee Surg Sports Traumatol Arthrosc Sep 2011;19(9):1496–503. [19] Lee DH, Park JH, Song DI, Padhy D, Jeong WK, Han SB. Accuracy of soft tissue balancing in TKA: comparison between navigation-assisted gap balancing and conventional measured resection. Knee Surg Sports Traumatol Arthrosc Mar 2010;18(3):381–7.
Contents lists available at ScienceDirect
The Knee
The use of navigation to achieve soft tissue balance in total knee arthroplasty — A randomised clinical study J. Joseph a, P.M.S. Simpson a, S.L. Whitehouse a, H.W. English b,⁎, W.J. Donnelly b a b
Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia Brisbane Orthopaedic Specialist Services, Holy Spirit Northside Hospital, Brisbane, Queensland, Australia
a r t i c l e
i n f o
Article history: Received 14 February 2013 Received in revised form 14 May 2013 Accepted 23 June 2013 Keywords: Navigation Arthroplasty Tissue balance Surgery Total knee replacement
a b s t r a c t Background: Achieving soft tissue balance is an operative goal in total knee arthroplasty. This randomised, prospective study compared computer navigation to conventional techniques in achieving soft tissue balance. Methods: Forty one consecutive knee arthroplasties were randomised to either a non-navigated or navigated group. In the non-navigated group, balancing was carried out using surgeon judgement. In the navigated group, balancing was carried out using navigation software. In both groups, the navigation software was used as a measuring tool. Results: Balancing of the mediolateral extension gap was superior in the navigation group (p = 0.001). No significant difference was found between the two groups in balancing the mediolateral flexion gap or in achieving equal flexion and extension gaps. Conclusions: Computer navigation offered little advantage over experienced surgeon judgement in achieving soft tissue balance in knee replacement. However, the method employed in the navigated group did provide a reproducible and objective assessment of flexion and extension gaps and may therefore benefit surgeons in training. Level of evidence: Level I, RCT. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
1. Introduction It is widely accepted in orthopaedic practice that, during total knee arthroplasty, the surgeon should aim to achieve a balance in flexion and extension gaps and aim for rectangular gaps (i.e. balanced medial and lateral sides) [1–3]. This achievement of balance is thought to improve the outcome of total knee arthroplasty. Abnormal polyethylene wear patterns are thought to be associated with knee arthroplasties that are not equally balanced [4]. Adequate soft tissue balance has also been postulated to improve proprioception post knee arthroplasty [5]. Clinically apparent instability following knee arthroplasty can be due to flexion and extension gap mismatch [6]. There are a number of options available to the surgeon in terms of assessing or measuring whether balance has been achieved. In the opinion of the authors, it is felt that the majority of surgeons assess balance by means of ‘feel’. Other options include utilising tensiometers or spacer blocks; computer navigation is a possible further option as a tool to assess gap balance. Using navigation as an aid to soft tissue release in knee arthroplasty has been reported [7]. ⁎ Corresponding author at: Brisbane Orthopaedic Specialist Services, Holy Spirit Northside Hospital, 627 Rode Road, Chermside, Queensland 4032, Australia. Tel.: +61 1300 436 454; fax: +61 7 3256 4634. E-mail address: [email protected] (H.W. English).
A number of studies show the accuracy of computer navigation systems in terms of component positioning and overall limb alignment is reliable [8–10]. The short, medium and long-term benefits of this accuracy in terms of patient satisfaction and outcome are as yet not fully known. In the current literature, there is only one published study [11] that has reported on soft-tissue balancing in navigated knee arthroplasty. This study involved a single group of 30 patients undergoing unilateral knee arthroplasty. For measurements of joint space gaps, this study showed a good correlation between measurements obtained from a tensiometer and those obtained from the imageless navigation software. The validity of an imageless navigation software system as a measuring tool in terms of component position and alignment [12] and in terms of joint gap measurement [11] has been demonstrated. In this prospective, randomised, patient blinded study, the accuracy of ligament balancing in two groups of patients was compared. In one group, the non-navigated group, balancing was undertaken by using the surgeon's ‘feel’. In the other group, the navigated group, balancing was undertaken utilising imageless computer navigation to guide the surgeon. In both groups, the computer navigation software was used as a measuring tool to record gap measurements. Our aim was to show whether the use of computer navigation conferred greater accuracy in soft tissue balancing compared to a non-navigated technique.
0968-0160/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.knee.2013.06.007
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J. Joseph et al. / The Knee 20 (2013) 401–406
2. Materials and methods Power analysis indicated that with 80% power, 5% significance level and a standardised difference of 1.0 [13], a minimum of 17 patients were needed in each group. To ensure this minimum requirement was met, we aimed for 20 knees per group. Forty consecutive patients listed for primary knee arthroplasty (41 knee arthroplasties) were prospectively recruited by the operating surgeon into this study between October 2008 and May 2009 when the recruitment goal was reached. Ethical approval was obtained from our institution's ethics committee. Patients were provided with information sheets and gave informed consent to enter this study at the time of being listed for the procedure. No patients refused consent for this study. Randomisation was performed by a statistician (SLW) using the Sampsize program [14] with a block size of 4 and allocation ratio of 1:1, and stored in theatre by means of envelopes allocating patients to either a non-navigated or navigated group. Envelopes were opened sequentially in theatre prior to the incision being made. Patients were blinded as to whether they had been allocated to the navigated or non-navigated group. Patients with both varus and valgus coronal plane deformities were included. There were no exclusion criteria. 2.1. Surgical technique All patients received a Triathlon posterior stabilised, fixed bearing total knee replacement (Stryker Orthopaedics, Mahwah, NJ) inserted via a standardised medial para-patellar approach. This involved initial dissection of the medial collateral ligament (MCL) fibres sufficient to expose the mid-equatorial point of the tibial surface. Stryker navigation femoral and tibial trackers were placed in all patients in both groups. The trackers were attached to bone via 3 mm diameter Ortholock drill pins (Stryker Orthopaedics, Mahwah, NJ). The Stryker Image Free navigation system (version 4.0) was used to register the femoral and tibial landmarks in all patients. In the non-navigated group, the navigation software was used purely as a measuring tool whereas in the navigated group it was used to facilitate the acquisition of accurate bony cuts, to modify implant position and guide soft tissue release. A Stryker tensiometer (Stryker Orthopaedics, Mahwah, NJ) was utilised to provide a known fixed tension force across the joint in order to measure the gaps at 90° flexion and full extension. Actual gap readings were taken from the measurements recorded by the navigation software and recorded by an unscrubbed theatre assistant. In all cases, the surgeon aimed to cut the proximal tibia with a posterior slope of 0°. The surgeon aimed to remove 9 mm of proximal tibial bone from the non-affected side of the tibial plateau. All procedures were undertaken by the senior authors (HWE and WJD) who are experienced surgeons in both non-navigated and navigated total knee arthroplasty. All procedures were carried out under tourniquet inflated at 350 mm Hg. 2.1.1. Surgical technique non-navigated group The tibia was cut first in all cases using extra-medullary referencing. The distal femoral cut was then made using intra-medullary referencing. Standard techniques were used to size and finish off the femur using a 4 in 1 femoral cutting block. Following the removal of all osteophytes, a trial reduction was performed and soft tissue releases were undertaken based upon a subjective assessment of balance by the surgeon. Further releases were made after assessment of the mediolateral gaps and the flexion and extension gaps. This was done with the trial components in situ. The surgeon applied a manual varus/valgus strain through a full passive range of motion and assessed for inequality in gaps by ‘feel’. Once the surgeon was happy that he had achieved a balanced arthroplasty, the joint gaps were recorded at 90° flexion and at full extension, without the trial components in place and with the patella reduced. No further modifications could be made by the surgeon following
this. All measurements were carried out with a fixed tension of 135 N (Newton) provided by the tensiometer across the joint. 2.1.2. Surgical technique for navigated group The tibia was cut first in all cases. This cut was verified following completion and was modified if necessary to ensure it fell perpendicular to the mechanical axis +/− 2°. Following this, an initial measurement of the gaps at 90° flexion and full extension was undertaken with the tensiometer in situ. The Stryker version 4.0 software was able to calculate the size of the femoral component after registration of the epicondyles and registration of the bony morphology of the anterior and posterior femoral condyles. Based on the initial gap measurements, the surgeon had a number of options to equilibrate the flexion and extension gaps. These included downsizing the femoral prosthesis or modifying the position of the femoral prosthesis in the anteroposterior or proximodistal planes. The software used algorithms that took a mean value of the registered femoral transepicondylar axis and the registered femoral anteroposterior axis (Whiteside's line) to determine axial rotation of the femur. The surgeon aimed for the femoral bony cut to have a value of 0° +/− 2° external rotation based on the software measurement. After the femoral cuts, the gaps at 135 N were measured again. The surgeon then made further soft tissue releases as necessary to try and equalise the mediolateral gaps to within 2 mm of each other. Final gap measurements (without the trial components in place) were recorded once again at 135 N of tension. 135 N was chosen as the tension force as it was felt that this level of tension produced sufficient strain to overcome any laxity in the soft tissues to allow reliable measurement of gaps, and is similar to forces used in other studies [15]. In both groups of patients, the initial and final coronal plane alignment in 0° extension and initial and final on-table range of movement (ROM) were recorded intra-operatively. These values were measured by the navigation software after registration of the mechanical axis and bony surfaces. The values reflected the coronal plane deformity from the mechanical axis not the coronal plane deformity as given by the tibiofemoral anatomical axis angle. Also the accuracy of the bony cuts in terms of coronal plane alignment in the femur and tibia and femoral rotation were also recorded in both groups. Pre-operative patient demographics and measurements are shown in Table 1. In the non-navigated group there were 21 patients (21 knee replacements. In the navigated group there were 19 patients (20 knee replacements). Gender and age distribution was similar for both groups. The spectrum of deformity, in terms of the coronal and sagittal planes, was similar in both groups as was the pre-operative ROM. 2.2. Tensiometer The Stryker tensiometer (Fig. 1) used in this study consisted of two metal plates that sat on the cut surfaces of the tibia and femur. The surgeon was able to exert a known distraction force (135 N in this study) via a torque driver which was attached to the body of
Table 1 Baseline pre-operative demographics for each group.
n, knees (patients) Gender, male/female Mean age (range) Deformity (°) varus: n, mean (range) valgus: n, mean (range) FFD: mean (range) Median range of motion (°) range (IQR) FFD — fixed flexion deformity. IQR — inter-quartile range.
Non-navigated
Navigated
21 (21 patients) 11/10 65.5 (53–85)
20 (19 patients) 5/14 67.6 (52–86)
16, 6.5 (0.5–14.5) 5, 4.2 (1.0–8.5) 3.6 (9.5–20.0) 123.5 106–138 (7.8)
14, 6.1 (1.0–12.0) 6, 3.6 (1.0–6.0) 4.6 (−9.0–21.5) 121.8 111–136 (12.8)
J. Joseph et al. / The Knee 20 (2013) 401–406
Fig. 1. Stryker tensiometer.
the tensiometer to distract the two plates. The distance between the two plates was measured by the navigation software as the joint gap. The software showed the gap on the medial side and the lateral side of the joint. The tensiometer had a scale which measured the distance (in millimetres) between the two plates. As shown in the previously quoted study [11], the value shown on the tensiometer scale correlated well with that shown on the navigation monitor screen. The tensiometer also had a further scale to show angular deviation (in degrees) of the upper plate relative to the lower plate i.e. varus/valgus imbalance. The tensiometer measurements were not recorded in this study. The tensiometer was used solely as an instrument to provide a known, constant tension across the joint in order to facilitate joint gap measurements by the navigation software. It was found that recording the gaps from the monitor screen, whilst maintaining a constant joint distraction force with the tensiometer was easier practically and more ‘user friendly’ than recording the gaps from the tensiometer scale. In addition, it was found recording the imbalance between medial and lateral sides as a distance in millimetres, as opposed to an angular value in degrees read from the tensiometer scale, to be more practical and intuitive. The torque produced by the tensiometer was calibrated in the laboratory using a tensile tester (Instron 5848 Microtester) to verify the tension force produced was 135 N.
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Fig. 3. Box and whisker plot of differences between the two groups in achieving a balanced extension gap.
(the primary endpoint) and range of movement data was not normally distributed and so non-parametric methods were employed for analysis. Medians and interquartile ranges (IQR) are presented. The Mann–Whitney U test and Levene's test for homogeneity of variance were used to determine significance of differences in gap measurements between the non-navigated and navigated groups. Data for accuracy of bony cuts and final overall limb alignment was found to be normally distributed. The Student's t-test was used to establish if differences in mean values for bony cut accuracy and final alignment between the non-navigated and navigated groups were significant. Means and standard deviations are presented. Levene's test for homogeneity of variance was used to determine if variances for bony cut accuracy and final limb alignment between the two groups were significantly different. Adjustment for multiple testing was made using Bonferroni's method at each level.
3. Results
The results were analysed using SPSS for Windows (V18, SPSS Inc., Chicago, II). Normality testing indicated that the gap measurement
All 41 cases (40 patients) were included in the final analysis, as data collection at surgery was complete. With regard to comparing gap measurements, the results showed a statistically significant difference (Figs. 2 & 3) between the non-navigated and navigated groups in obtaining a balanced mediolateral extension gap in both median and variability (Mann–Whitney U-test p = 0.013, Levene's test for homogeneity of variance p = 0.001) (Table 2). The mediolateral extension gap was more accurately balanced in the navigated group. There was no statistically significant difference (Figs. 4 & 5) between the two groups for balancing the mediolateral flexion gap (p = 0.56 M-W, p = 0.16 Levene's test). There was also no statistically significant
Fig. 2. Histogram of differences between the two groups in achieving a balanced extension gap.
Fig. 4. Histogram of differences between the two groups in achieving a balanced flexion gap.
2.3. Statistical analysis
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Fig. 5. Box and whisker plot of differences between the two groups in achieving a balanced flexion gap.
Fig. 7. Box and whisker plot of differences between the two groups in achieving equal flexion and extension gaps.
difference (Figs. 6 & 7) between the two groups in obtaining equal flexion and extension gaps (p = 0.77 M-W, p = 0.48 Levene's test). With regard to comparing accuracy of bony cuts between the two groups, the results showed statistically significant greater accuracy in the navigated group for all bony cuts with regards to variability (Levene's test: distal femur p = 0.005, proximal tibia p = 0.018, femoral rotation p = 0.002) (Table 3). However, there was no statistically significant difference in the mean values between both groups (Student's t-test: distal femur p = 1.0, proximal tibia p = 0.19, femoral rotation p = 0.62). Final overall limb alignment was statistically less variable (Figs. 8 & 9) in the navigated group (Levene's test: p = 0.023) although no difference was found in mean values between the two groups (Student's t-test: p = 0.10) (Table 4). No significant difference was found between the two groups in terms of extent of final range of movement or change in range of movement (Table 5).
significantly better in the navigated group. In the navigated group, the coronal plane final alignment was accurate to within 1°. The joint tension force produced by the tensiometer was quantifiable and reproducible. It was also found that quantifying the flexion and extension gaps and the coronal plane imbalance using the navigation software readily facilitated the surgeon to carry out further soft tissue release or modify the component position in order to optimise the gaps. Having the measurements displayed on the monitor screen and also the change in subsequent measurements following soft tissue release and/or component position modification allowed practical and intuitive balancing procedures to be performed. This study demonstrated no advantage of computer navigation in improving on-table final ROM. The use of navigation for data recording in both groups minimised measurement bias and the use of the tensionometer reduced the variability in the stresses applied. In their study of 30 patients, Matsumoto et al. [11] achieved a mean joint component gap imbalance of 8.8 mm with the patella everted and 5.4 mm imbalance with the patella reduced, with flexion gaps being larger in both cases. They also reported a coronal plane ligament imbalance toward varus. Griffin et al. [16] measured flexion and extension gaps directly with a ruler during total knee arthroplasty procedures. In their study, they used lamina spreaders, placed medially and laterally, after bony cuts and soft tissue releases to produce a maximal manual tension across the joint and then measured the flexion and extension gaps. They reported perfect balance with equal, rectangular flexion and extension gaps in 8 out of 104 (7.7%) total knee arthroplasties.
4. Discussion This study showed significantly more accurate balancing of the mediolateral extension gap using the navigation system to guide the surgeon when compared to balancing by ‘feel’ alone. The surgeon could use the software to accurately alter the femoral component position either proximally or distally and also be guided as to the degree of necessary soft tissue release. There was no statistically significant difference between the two groups in balancing the mediolateral flexion gap or in achieving equal flexion and extension gaps. In this study, balancing of gaps in both groups was accurate to within 1–2 mm. The accuracy of the bony cuts and the final overall limb alignment was
Table 2 Table showing differences between the two groups for gap balancing. Non-navigated Navigated p-Value p-Value (Mann–Whitney) (Levene's)
Fig. 6. Histogram of differences between the two groups in achieving equal flexion and extension gaps.
Mediolateral difference 2.0 (5.0) in 0° extension (mm) Mediolateral difference 1.0 (2.5) in 90° flexion (mm) 0.5 (3.8) Flexion gap minus extension gap (mm)
0.0 (1.8)
0.013
0.001
0.5 (3.0)
0.561
0.158
0.75 (3.0)
0.773
0.481
Values shown as median (interquartile range (IQR)).
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Fig. 8. Histogram of differences between the two groups in final overall limb alignment.
Of these 8 patients 4 had no pre-operative coronal plane deformity as measured by tibiofemoral angle on standing knee AP X-rays and the other 4 had varus deformity from 2° to 12°. They reported that they achieved balanced flexion and extension gaps within 1 mm in 47% of patients on the lateral side and 57% of patients on the medial side. They found that knees with a pre-operative fixed flexion deformity (FFD) were less accurately balanced than those without a FFD. They also found that their extension gaps were generally speaking greater than their flexion gaps. They postulated that surgeons may have a tendency to increase the extension gap relative to the flexion
gap to minimise the risk of post-operative FFD and flexion instability. This viewpoint is in contrast to Asano et al. [17] who in their study reported that for their patient population, who express a need for deep flexion, they aim for a 3 mm greater flexion than extension gap. Pang et al. [18] demonstrated more precise soft tissue balancing with computer assisted balancing than conventional balancing, with improved function scores in the navigated group at 6 months. Better gap balancing was also demonstrated with navigation by Lee at al. [19]. There is a degree of variance amongst surgeons in terms of how to address gap balance and the results achieved for balance and alignment. This study showed that computer navigation facilitates the surgeon to achieve more consistent and accurate bony cuts and overall limb alignment. In terms of overall balance of the soft tissue envelope, this study showed that computer navigation offered little advantage over the judgement of the experienced surgeon. However, the method employed in the navigated group did provide a reproducible and objective assessment of flexion and extension gaps and may therefore benefit surgeons in training.
Table 3 Table showing differences between the two groups for accuracy of bony cuts. Non-navigated
Navigated
Mean
Mean 95% CI
95% CI
Distal femur 0.00 −1.08–1.08 0.00 resection (°) Proximal tibia 0.61 −0.11–1.33 0.09 resection (°) −0.33 −2.28–1.62 0.15 Femoral rotation (°) Fig. 9. Box and whisker plot of differences between the two groups in final overall limb alignment.
p-Value p-Value (t-test) (Levene's)
−0.39–0.39 1.0
0.005
−0.31–0.49 0.189
0.018
−0.24–0.53 0.616
0.002
CI — Confidence interval. Varus given as a negative value, valgus given as a positive value. Internal rotation given as a negative value, external rotation as a positive value.
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Table 4 Table showing differences between the two groups in final overall limb alignment. Non-navigated
Final overall limb alignment (°)
Navigated
Mean
95% CI
Mean
95% CI
p-Value (Mann–Whitney)
p-Value (Levene's)
−1.14
−2.48–0.19
0.06
−0.53–0.65
0.096
0.023
Varus given as a negative value, valgus given as a positive value.
Table 5 Table showing differences between the two groups in ROM.
Initial ROM (°) (range, IQR) Final ROM (°) (range, IQR) Change in ROM (°) (range, IQR)
Non-navigated
Navigated
p-Value (Mann–Whitney)
123.5 (106–138, 7.8) 127.0 (113.5–142.2, 14.8) 3.5 (−6–13, 7.8)
121.75 (111–136, 12.8) 122.5 (109–140, 7.8) 3.0 (−16.5–10.5, 8.9)
0.764 0.433 0.426
Values shown as median, (range, IQR).
5. Conflict of interest statement
J Joseph PMS Simpson SL Whitehouse HW English
WJ Donnelly
I do not have any financial or personal relationships with other people or organisations that could bias my work. I have undertaken consultancy work for Stryker Orthopaedics regarding primary & revision knee replacement. Position partially funded via external organisation by Stryker Orthopaedics I receive grants for research projects from Smith and Nephew. My wife has a financial interest in Oceania Orthopaedics, neither product source is involved in this trial. I have done consultancy work for Stryker Orthopaedics regarding navigation. I have a financial interest in Oceania Orthopaedics.
No funding was directly received in relation to this project. Trial registered with Australian New Zealand Clinical Trials Registry (ANZCTR); Registration number: ACTRN12613000516785. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.knee.2013.06.007. References [1] Insall JN. Surgery of the knee. 2nd ed. New York: Churchill Livingstone; 1993. [2] Freeman MA, Sculco T, Todd RC. Replacement of the severely damaged arthritic knee by the ICLH (Freeman–Swanson) arthroplasty. J Bone Joint Surg Br Feb 1977;59(1):64–71.
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