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Effect of Medial Soft Tissue Releases During Posterior-Stabilized Total Knee Arthroplasty on Contact Kinematics and Patient-Reported Outcomes
The Journal of Arthroplasty 34 (2019) 1110e1115
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Primary Arthroplasty
Effect of Medial Soft Tissue Releases During Posterior-Stabilized Total Knee Arthroplasty on Contact Kinematics and Patient-Reported Outcomes Mina W. Morcos, MD, MSc, FRCSC, Brent A. Lanting, MD, MSc, FRCSC *, Jared Webster, MSc, James L. Howard, MD, FRCSC, Dianne Bryant, PhD, Matthew G. Teeter, PhD Bone and Joint Institute, Western University, London, Ontario, Canada Division of Surgery, Department of Orthopaedics, London Health Sciences Centre, London, Ontario, Canada Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 December 2018 Received in revised form 3 February 2019 Accepted 14 February 2019 Available online 20 February 2019
Background: Minimal to extensive medial soft tissue releases are part of the exposure and achieving adequate varus knee balance in total knee arthroplasty (TKA). However, the effect of these releases on knee kinematics and patient-reported outcomes is unclear. Our objective was to compare the postoperative in vivo tibiofemoral contact kinematics of a posterior-stabilized TKA between patients who received minimal medial soft tissue releases intraoperatively to those who received extensive releases. We also compared these groups using patient-reported outcomes. Methods: A prospective imaging study was performed in a single-center over a 14-month period. Patients with end-stage osteoarthritis and varus deformity undergoing primary TKA were included. Baseline data were collected 1 month before surgery. The radiostereometric analysis imaging took place at least 1 year postoperatively and composed of weight-bearing radiographic stereo examinations of knee flexion starting in full extension and in 20 increments of flexion to a maximum of 120 . Intraoperative medial soft tissue releases were recorded. Patient-reported outcomes used included ShortForm 12, Western Ontario and McMaster Osteoarthritis Index, and Knee Society Score. Results: Fifty-one patients were included in the statistical analysis. Demographic characteristics were similar between all. Patients were divided into 3 groups depending on the amount of releases they received. No statistically significant differences in tibiofemoral contact positions or excursions on the medial or lateral condyles were found throughout flexion from 0 to 120 . Postoperative patient-reported outcome scores were not different. Conclusion: Correcting severe varus deformities with extensive medial soft tissue release largely did not alter knee kinematics or clinical outcome scores compared to those with minimal soft tissue release. © 2019 Elsevier Inc. All rights reserved.
Keywords: total knee arthroplasty soft tissue balancing contact kinematics osteoarthritis varus radiostereometric analysis
Investigation was performed at University Hospital, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada. One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2019.02.026. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. * Reprint requests: Brent A. Lanting, MD, MSc, FRCSC, Department of Orthopedic Surgery, University Hospital, Room B9 003, 339 Windermere Road, London, Ontario, N6A 5A5, Canada. https://doi.org/10.1016/j.arth.2019.02.026 0883-5403/© 2019 Elsevier Inc. All rights reserved.
The need for primary total knee arthroplasty (TKA) has been growing steadily over the last decade for individuals having debilitating arthritis. More than 700,000 TKAs are performed yearly in the United States with a projection of 673% increase in the demand for TKAs by 2030 [1]. Despite having excellent outcomes following TKA for most patients, numerous studies have shown dissatisfaction rates around 19% [2,3]. This can be due to numerous etiologies including aseptic loosening, infection, instability, and component malalignment which led investigators to examine different aspects of the surgical technique that may contribute to the undesired outcomes [4]. One of the main concerns is the achievement of proper coronal alignment in TKA which was shown to improve implant survival
M.W. Morcos et al. / The Journal of Arthroplasty 34 (2019) 1110e1115
and patient function [5]. The most common knee deformity is varus deformity which leads to the contracture of the medial structures [6]. Appropriate release of these structures is essential to obtain the correct coronal alignment and correct balancing in flexion and extension [7]. In order to achieve this alignment, several surgical techniques for soft tissues and bony procedures in varus knee were described and they depend on the amount of balancing required. Although there is a lot of literature on the indications and technique for these releases, the effect of soft tissue balancing on postoperative outcomes and knee kinematics [8] is less known. The majority of studies that have assessed ligament contributions to TKA stability [9] and the effect of sequential medial releases on tibiofemoral flexion and extension gaps [10,11] are cadaveric biomechanical studies although a few clinical studies have also been reported [7,12]. Tibiofemoral contact kinematics have been used to study the biomechanical aspect of the knee by examining changes from preTKA to post-TKA which provide valuable information related to implant function, wear, and migration [13,14]. Studies of contact kinematics have shown that a native knee has a medial pivot conformation during knee flexion. Moreover, posterior femoral rollback during deep flexion occurs on average 19.2 mm around the lateral femoral condyle and 3.4 mm around the medial condyle [12]. Few studies have prospectively investigated the postoperative contact kinematics and outcomes following various releases of the medial structures in varus knees following primary TKA. The primary objective of this study was to examine the postoperative in vivo tibiofemoral contact kinematics of a single-radius, posterior-stabilized (PS) TKA design between patients who received minimal amounts of medial soft tissue balancing intraoperatively and patients who required more extensive releases. Our secondary objectives were to compare these groups using the following patient-reported outcomes: The Short-Form 12 (SF-12), the Western Ontario and McMaster Osteoarthritis Index (WOMAC), and the Knee Society Score (KSS). Our final objective was to investigate whether an association exists between anterior-posterior (AP) excursion of the contact position and patient satisfaction. We hypothesized that the tibiofemoral contact kinematics would be different for patients who received minimal soft tissue release vs patients who required additional soft tissue release. We also hypothesized that no differences would be found in any of the collected patient-reported outcomes. Study Design This was a prospective study looking at patients who underwent primary TKA with different amounts of soft tissue modifications to correct a varus deformity. This study was performed in our institution over a 14-month period. Baseline data were collected approximately 1 month before surgery at the preadmission clinic visit. All imaging follow-up took place at least 1 year postoperatively. Institutional review board approval was obtained before the onset of the study. Inclusion criteria identified patients older than 18 years who received primary TKA for varus osteoarthritic knee. In addition, patients must have received a fixedbearing, single-radius, PS Triathlon knee system (Stryker, Mahwah, NJ) with cemented fixation by 1 of the 2 senior authors. Exclusion criteria included any patient whose soft tissue releases were not recorded intraoperatively or if they were physically unable to perform the imaging protocol or come for follow-up. Procedure The goal of surgery was to achieve a postoperative mechanical axis angle of 0 ± 3 . Each knee was exposed using a standard
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Table 1 Authors' Stepwise Medial Release Sequence for Correcting Varus Deformities. Soft Tissue Release/Bone Modification (1) (2) (3) (4) (5) (6) (7) (8)
50% Deep MCL (mid-coronal plane) Osteophytes Complete deep MCL Posterior capsule Semimembranosus and posterior oblique ligament Tibial reduction osteotomy Superficial MCL Medial epicondyle osteotomy
MCL, medial collateral ligament.
midline incision followed by a medial parapatellar arthrotomy. Half of TKA procedures were performed by 1 surgeon performing a measured resection technique. The other half of the knees were performed by 1 surgeon performing gap balancing technique. Similar tibiofemoral contact kinematic patterns have been found between measured resection and gap balancing techniques for this implant system [15]. All the knees had identical fixed-bearing, single-radius, PS TKA with cemented fixation of both femur and tibia. The sequence of medial soft tissue release and bone resections is shown in Table 1. All patients had a 50% release of the deep medial collateral ligament (dMCL) to the mid-coronal plane of the tibia during initial knee exposure then tibial and femoral osteophytes were removed. Following each step in the medial release sequence, a spacer block was inserted to assess gap symmetry until it was achieved. The intraoperative medial soft tissue releases were recorded and collected by the treating surgeon.
Radiostereometric Analysis Radiostereometric analysis (RSA) is an imaging technique originally developed by Selvik [16]. Although commonly used to measure orthopedic implant migration, RSA techniques can be applied to acquire tibiofemoral contact kinematics of individuals who underwent TKA without the use of implanted beads. In this study, static radiographs were taken at 0 , 20 , 40 , 60 , 80 , 100 , and 120 knee flexion from two different X-ray angles simultaneously. To induce the desired flexion angle, patients were instructed to stand upright with their knees straight and weight equally distributed between limbs and gradually squat with their heel on the ground until they reached the desired flexion angle measured by a manual goniometer. For the deep flexion angles (80 , 100 , 120 ), the knee of interest was elevated with a small step stool and patients were instructed to lunge until they reached the desired flexion angle. All examinations were performed with calibration cage (cage 43, RSA Biomedical, Umea, Sweden). The calibration cage is a radiolucent material that contains 2 sets of radioopaque markers that project onto the cassettes along with the object of interest. These markers are used to define the position and orientation of the global coordinate system. Model-based RSA software (RSAcore, Leiden, Netherlands) was used to perform 2D/ 3D registration of the manufacturer’s computer-aided design models for the femoral and tibial components to each pair of X-rays for each examination. The model-based RSA approach has been demonstrated to have an excellent accuracy, with errors of 0.19 mm for translations and 0.52 for rotations [17]. Using the registered computer-aided design models, the point with the shortest magnitude of separation between components was considered to be the contact position. Contact positions were recorded using a coordinate system specific to the tibial baseplate. Negative values represent posterior contact position translation relative to the AP
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Table 2 Completed Soft Tissue Balancing of the Entire Cohort. Release Progression
Number of Patients
(1) (2) (3) (4) (5) (6) (7) (8)
51 51 7 3 6 10 1 0
50% Deep MCL (mid-coronal plane) Osteophytes Complete deep MCL Posterior capsule Semimembranosus and posterior oblique ligament Tibial reduction osteotomy Superficial MCL Medial epicondyle osteotomy
MCL, medial collateral ligament.
center of the tibial baseplate while positive values represent anterior contact position translation. Postoperative Protocol
Table 3 Baseline Participant Demographics of Grouped Analysis 2 (Mean ± Standard Deviation). Demographic
Mild (N ¼ 24)
Moderate (N ¼ 16)
Extensive (N ¼ 11)
Sex
17 Females, 7 males 68.1 ± 7.3 166.5 ± 8.5 90.8 ± 18.9 32.9 ± 6.9
8 Females, 8 males 67.5 ± 7.6 166.5 ± 9.1 95.0 ± 22.3 34.3 ± 7.8
2 Females, 9 males 69.7 ± 7.5 171.7 ± 10.9 94.0 ± 21.8 31.6 ± 5.4
16 Right, 8 left 6.2 ± 4.4
8 Right, 8 left 8.2 ± 3.3
4 Right, 7 left 12.7 ± 3.6
Age at surgery (y) Height (cm) Mass (kg) Body mass index (kg/m2) Operative limb Preoperative HKA angle ( )
Negative HKA angle indicated varus deformity. HKA, hip-knee-ankle.
A standardized rehabilitation protocol was used for all patients including inpatient physiotherapy immediately postoperatively to start full weight-bearing and range of motion exercises.
and translates posteriorly from 60 to 120 . From 0 to 20 , greater posterior translation is seen on the lateral condyle indicating external femoral rotation as the knee begins flexion from full extension.
Outcome Measures
Demographic Information
The primary outcome was tibiofemoral contact kinematics measured at least 1 year postoperative using RSA to assess average AP contact position translation. Secondary outcomes consisted of patient-reported outcomes that included preoperative and postoperative SF-12, WOMAC, and KSS.
Our analysis consisted of 3 groups: those patients with mild soft tissue balancing (group 1; n ¼ 24), moderate soft tissue balancing (group 2; n ¼ 16), and extensive soft tissue balancing (group 3; n ¼ 11). Demographic characteristics were similar between groups (Table 3). Preoperative hip-knee-ankle angle was not significantly different between group 1 and group 2 (P ¼ .29) but was significantly different between groups 1 and 3 (P ¼ .0001) and groups 2 and 3 (P ¼ .01).
Statistical Analysis For the statistical analysis, the patients were divided into 3 groups: mild group where patients received up to and including osteophytes removal, moderate group where patients received complete release of the dMCL as well as up to the release of the semimembranosus and posterior oblique ligament, and finally extensive group where patients received at least a medial tibial reduction osteotomy (MTRO). Preoperative patient variables such as demographic characteristics were compared using a 2-sample t-test for continuous variables, Fisher exact test for binary variables, or chi-square test for multiple categorical variables. Continuous variables such as AP contact point position throughout flexion on the medial and lateral condyle for each release type and across the entire cohort are expressed as mean ± standard deviation while categorical variables are reported as absolute values and percentages. One-way analysis of variance tests and Kruskal-Wallis test were used to compare between the 3 groups. Results During the study period, 51 patients had prospective preoperative as well as postoperative data collected. The number of releases completed intraoperatively for this cohort is reported in Table 2. Patients were organized by the maximum level of balancing they required to attain a balanced knee. Ungrouped Analysis
Primary Outcome: Tibiofemoral Contact Kinematics Average Contact Positions Medial and lateral AP positions of groups 1, 2, and 3 throughout flexion are presented in Figure 1. The pattern of contact for all groups was similar; there were no significant differences between average AP contact positions between groups at any flexion angle. All groups demonstrated similar posterior translation of the contact position on the lateral condyle than the medial condyle (Figs. 1 and 2) indicating external rotation and medial pivot. The tibiofemoral contact pattern for the patient who received sMCL release relative to the mean and 95% confidence intervals of the extensive group is shown in Figure 3. On the medial condyle, the sMCL patient demonstrated posterior contact beyond the limits of the confidence intervals at 20 , 60 , 100 , and 120 of flexion. On the lateral condyle, the sMCL patient was posterior at 0 of flexion, and anterior at 40 . Secondary Outcome: Patient-Reported Outcomes Minimal, moderate, and extensive release groups significantly improved in all patient-reported outcomes preoperatively to postoperatively (P < .001). There were no differences between groups in the SF-12, WOMAC, or KSS outcome scores, preoperatively or postoperatively (Table 4).
Tibiofemoral Contact Kinematics Discussion Cohort averages showed the medial contact position translates posteriorly from 0 to 20 , anteriorly from 20 to 80 , and posteriorly from 80 to 120 . On the lateral condyle, the contact position translates posteriorly from 0 to 20 , stays stable from 20 to 60 ,
In this study, we compared the in vivo tibiofemoral contact kinematics of a PS-TKA during knee flexion in patients that ranged in the amount of soft tissue balancing received intraoperatively
M.W. Morcos et al. / The Journal of Arthroplasty 34 (2019) 1110e1115
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Fig. 1. Anterior-posterior (AP) translation (mean ± 95% confidence interval) on the medial condyle (A) and lateral condyle (B) between the mild, moderate, and extensive release groups from 0 to 120 of knee flexion.
and showed that there were no statistically significant differences between groups in average contact position of the medial condyle at any flexion angle and no differences in AP excursion on the medial and lateral condyles throughout flexion. On the lateral condyle, the only difference we observed was that patients with soft tissue release had more anterior contact than those without soft tissue release at 100 of flexion. A study by Bellemans et al investigated 35 consecutive TKA with preoperative varus deformity where they performed varus-valgus stress testing intraoperatively. They reported that the medial collateral structures are intrinsically shortened while the lateral soft tissues are stretched in knees with approximately 10 or more of varus [18]. Therefore, the residual laxity found in the lateral structures can explain why patients who required soft tissue release had different contact position at 100 on the lateral condyle compared to the no release group. Superficial medial collateral ligament is a very important structure for controlling medial laxity after TKA. Recently, Athwal et al [9] showed that sMCL is the primary medial restraint to coronal, sagittal, and axial axis in intact knee and following TKA, using 8, nonarthritic, intact, fresh-frozen knees in a robotic simulator. Given the importance of the sMCL for stability following TKA, the authors of the present study avoid sMCL release if possible. Only 1 patient in this study had his sMCL released. While only 1 patient is not representative of a population of patients, this patient did exhibit dramatic posterior translation of the medial condyle compared to the group average. Increasing the number of patients in this group would provide valuable in vivo data to support the sMCL’s importance for postoperative medial stability. Meanwhile, our recommendation is to maintain the integrity of the sMCL as much as possible.
To preserve the integrity of the sMCL while still achieving coronal plane mechanical alignment, authors of this study use the MTRO technique. Ahn and Back [19] compared their standard medial release progression (n ¼ 20) with bony resection of the proximal medial tibial (n ¼ 20) in patients with 10 anatomic varus deformity. At 6 months, there was no difference between groups for range of motion or hospital for special surgery scores, aligning with the patient-reported findings of our study. Another retrospective study by Martin et al. compared 67 MTRO patients and 67 matched controls who did not require an MTRO. They found that the MTRO group had significantly better postoperative KSS and produced similar corrections to coronal alignment as the control group [20]. In our study, the patients who received MTRO demonstrated similar tibiofemoral contact kinematics compared to the other groups which support the use of MTRO as a promising technique. Consistent with our expectations, the preoperative varus deformity was larger in the groups that required more extensive soft tissue balancing. All patient-reported outcome scores improved preoperatively to postoperatively, except for the SF-12 Mental Component Score which was expected because this is a generic measure of mental health. A large, multicenter, prospective study by Unitt et al. examined clinical outcome score difference in patients who received none or minimal (n ¼ 173), moderate (n ¼ 122), and extensive (n ¼ 115) amounts of soft tissue balancing during primary TKA [21]. Across multiple outcome measures, they found that the extensive release group had significantly greater preoperative to postoperative change scores than the other groups but had similar postoperative outcomes at 12 months. Finding no differences in postoperative patient-reported outcomes is consistent with our findings.
Fig. 2. Superior view of a tibial baseplate representing the average medial and lateral contact positions for the mild (A), moderate (B), and extensive (C) release groups from 0 to 120 of knee flexion.
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Fig. 3. Contact pattern on the medial (A) and lateral (B) condyles for the 1 patient who received a superficial MCL (sMCL) release. The meant contact pattern for the extensive release group (without sMCL patient included) is presented with upper and lower bounds of their 95% confidence intervals.
There were few limitations to this study. Hunt et al [8] published a literature review on medial release methods in TKA showing approximately 20 unique sequences that have been described. For this reason, the results of this study may not be generalizable. Although the sample size was small, 95% confidence intervals surrounding AP positions were narrow, extending approximately 1-2 mm around the means. This indicates reasonable precision was achieved for our primary outcome even with this small sample. Another limitation was that kinematic data were collected using a quasi-static technique (images taken in rapid succession with less than 5 seconds in between) instead of a continuous dynamic technique (15 images captured per second). The quasi-static technique was used because our RSA imaging system cannot acquire continuous images. However, compared to an imaging system that can acquire continuous images, our method produces higher accuracy of implant position. Saevarsson et al [22] collected weightTable 4 Patient-Reported Outcome Scores (Mean ± Standard Error). Time
Outcome Measure
Preop
SF-12 PCS MCS SF-12 PCS MCS WOMAC Pain Stiffness Function Total WOMAC Pain Stiffness Function Total KSS Symptoms Satisfaction Expectations Function Total KSS Symptoms Satisfaction Expectations Function Total
Postop
Preop
Postop
Preop
Postop
Mild
Moderate
bearing contact kinematics using both static and dynamic techniques and found that static and dynamic kinematics were comparable. The kinematic patterns of the present study were consistent with those of other studies of the same implant design indicating our image acquisition technique was acceptable. Finally, this study used a single-radius, PS TKA design where the role of the posterior cruciate ligament is fulfilled by a cam-post interaction that occurs between the femoral and tibial components. This interaction has been found to begin at approximately 82 ± 16 of flexion in the PS implant, which drives posterior femoral rollback in deep flexion [17]. This posterior translation of the contact position was seen in our results at a similar flexion angle. However, in cruciate-retaining implant designs, the posterior cruciate ligament is intact, and its tension contributes to the height of the flexion gap. Therefore, the interpretation of the results of the present study should not be extended to cruciate-retaining implant designs. Conclusion
Extensive
P Value
32.3 ± 2.3 57.8 ± 3.2
29.0 ± 2.5 57.0 ± 3.2
31.9 ± 2.5 54.9 ± 4.6
.56 .99
43.2 ± 2.2 52.1 ± 2.7
42.2 ± 2.5 54.6 ± 2.9
45.6 ± 2.3 58.9 ± 2.3
.66 .27
49.2 47.8 52.0 51.2
± ± ± ±
3.3 4.2 3.4 3.2
44.6 38.8 43.1 44.8
± ± ± ±
4.1 4.2 4.0 3.9
50.1 38.6 46.0 48.1
± ± ± ±
3.4 5.3 4.4 4.2
.54 .25 .23 .45
85.9 80.0 83.5 84.6
± ± ± ±
3.3 4.7 3.1 3.2
81.9 74.1 80.8 83.0
± ± ± ±
4.0 3.8 3.2 3.4
89.3 71.0 80.9 85.1
± ± ± ±
1.8 6.3 3.5 3.2
.72 .43 .79 .91
08.8 15.0 14.1 34.3 72.3
± ± ± ± ±
1.2 1.8 0.4 3.9 5.7
08.1 13.5 13.9 38.9 74.4
± ± ± ± ±
1.5 1.7 0.5 5.1 7.4
09.3 15.0 13.5 38.9 76.7
± ± ± ± ±
1.5 2.0 0.3 4.0 7.1
.85 .84 .14 .70 .91
21.0 32.5 08.9 74.0 135.4
± ± ± ± ±
0.9 2.1 0.7 3.8 7.2
20.3 32.9 11.3 71.8 136.2
± ± ± ± ±
1.3 1.9 0.8 4.3 7.7
21.8 35.6 09.7 77.1 144.3
± ± ± ± ±
0.7 0.9 0.7 3.7 5.1
.97 .52 .09 .70 .89
Preop, preoperative; Postop, postoperative; SF, short form; PCS, physical component score; MCS, Mental Component Score; WOMAC, Western Ontario McMaster Osteoarthritis Index; KSS, Knee Society Score.
Contact kinematics and clinical outcome scores were largely unaffected by greater levels of medial soft tissue release. This suggests that correcting severely varus patients to mechanically neutral coronal alignment does not compromise tibiofemoral contact kinematics or patient-reported satisfaction. References [1] Jaffe WL, Dundon JM, Camus T. Alignment and balance methods in total knee arthroplasty. J Am Acad Orthop Surg 2018;26:709e16. [2] Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KDJ. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res 2010;468:57e63. [3] Robertsson O, Dunbar M, Pehrsson T, Knutson K, Lidgren L. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand 2000;71:262e7. [4] Schroer WC, Berend KR, Lombardi AV, Barnes CL, Bolognesi MP, Berend ME, et al. Why are total knees failing today? Etiology of total knee revision in 2010 and 2011. J Arthroplasty 2013;28:116e9. [5] Cherian JJ, Kapadia BH, Banerjee S, Jauregui JJ, Issa K, Mont MA. Mechanical, anatomical, and kinematic axis in TKA: concepts and practical applications. Curr Rev Musculoskelet Med 2014;7:89e95. [6] Asano H, Hoshino A, Wilton TJ. Soft-tissue tension total knee arthroplasty. J Arthroplasty 2004;19:558e61. [7] Verdonk PC, Pernin J, Pinaroli A, Ait Si Selmi T, Neyret P. Soft tissue balancing in varus total knee arthroplasty: an algorithmic approach. Knee Surg Sports Traumatol Arthrosc 2009;17:660e6. [8] Hunt NC, Ghosh KM, Athwal KK, Longstaff LM, Amis AA, Deehan DJ. Lack of evidence to support present medial release methods in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014;22:3100e12. [9] Athwal KK, Daou HE, Kittl C, Davies AJ, Deehan DJ, Amis AA. The superficial medial collateral ligament is the primary medial restraint to knee laxity after cruciate-retaining or posterior-stabilised total knee arthroplasty: effects of
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implant type and partial release. Knee Surg Sports Traumatol Arthrosc 2016;24:2646e55. Chen W, Nagamine R, Kondo K, Todo M. Effect of medial soft-tissue releases during posterior-stabilised total knee arthroplasty. J Orthop Surg (Hong Kong) 2011;19:230e3. Matsumoto T, Muratsu H, Kubo S, Matsushita T, Kurosaka M, Kuroda R. The influence of preoperative deformity on intraoperative soft tissue balance in posterior-stabilized total knee arthroplasty. J Arthroplasty 2011;26: 1291e8. Teeter MG, Perry KI, Yuan X, Howard JL, Lanting BA. Contact kinematics correlates to tibial component migration following single radius posterior stabilized knee replacement. J Arthroplasty 2018;33:740e5. Li C, Hosseini A, Tsai TY, Kwon YM, Li G. Articular contact kinematics of the knee before and after a cruciate retaining total knee arthroplasty. J Orthop Res 2015;33:349e58. Okamoto N, Breslauer L, Hedley AK, Mizuta H, Banks SA. In vivo knee kinematics in patients with bilateral total knee arthroplasty of 2 designs. J Arthroplasty 2011;26:914e8. Teeter MG, Perry KI, Yuan X, Howard JL, Lanting BA. Contact kinematic differences between gap balanced vs measured resection techniques for single
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radius posterior-stabilized total knee arthroplasty. J Arthroplasty 2017;32: 1834e8. [16] Selvik G. A stereophotogrammetric system for the study of human movements. Scand J Rehabil Med Suppl 1978;6:16e20. [17] Pandit H, van Duren BH, Price M, Tilley S, Gill HS, Thomas NP, et al. Constraints in posterior-stabilised TKA kinematics: a comparison of two generations of an implant. Knee Surg Sports Traumatol Arthrosc 2013;21:2800e9. [18] Bellemans J, Vandenneucker H, Vanlauwe J, Victor J. The influence of coronal plane deformity on mediolateral ligament status: an observational study in varus knees. Knee Surg Sports Traumatol Arthrosc 2010;18:152e6. 19 Ahn JH, Back YW. Comparative study of two techniques for ligament balancing in total knee arthroplasty for severe varus knee: medial soft tissue release vs. bony resection of proximal medial tibia. Knee Surg Relat Res 2013;25:13e8. [20] Lanting BA, Lieberman JR, Callaghan JJ, Berend ME, MacDonald SJ. Ensuring a winner: the ABCs of primary total knee arthroplasty. Instr Course Lect 2015;64:369e79. [21] Capella M, Dolfin M, Saccia F. Mobile bearing and fixed bearing total knee arthroplasty. Ann Transl Med 2016;4:127. [22] Saevarsson SK, Romeo CI, Anglin C. Are static and dynamic kinematics comparable after total knee arthroplasty? J Biomech 2013;46:1169e75.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Primary Arthroplasty
Effect of Medial Soft Tissue Releases During Posterior-Stabilized Total Knee Arthroplasty on Contact Kinematics and Patient-Reported Outcomes Mina W. Morcos, MD, MSc, FRCSC, Brent A. Lanting, MD, MSc, FRCSC *, Jared Webster, MSc, James L. Howard, MD, FRCSC, Dianne Bryant, PhD, Matthew G. Teeter, PhD Bone and Joint Institute, Western University, London, Ontario, Canada Division of Surgery, Department of Orthopaedics, London Health Sciences Centre, London, Ontario, Canada Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 December 2018 Received in revised form 3 February 2019 Accepted 14 February 2019 Available online 20 February 2019
Background: Minimal to extensive medial soft tissue releases are part of the exposure and achieving adequate varus knee balance in total knee arthroplasty (TKA). However, the effect of these releases on knee kinematics and patient-reported outcomes is unclear. Our objective was to compare the postoperative in vivo tibiofemoral contact kinematics of a posterior-stabilized TKA between patients who received minimal medial soft tissue releases intraoperatively to those who received extensive releases. We also compared these groups using patient-reported outcomes. Methods: A prospective imaging study was performed in a single-center over a 14-month period. Patients with end-stage osteoarthritis and varus deformity undergoing primary TKA were included. Baseline data were collected 1 month before surgery. The radiostereometric analysis imaging took place at least 1 year postoperatively and composed of weight-bearing radiographic stereo examinations of knee flexion starting in full extension and in 20 increments of flexion to a maximum of 120 . Intraoperative medial soft tissue releases were recorded. Patient-reported outcomes used included ShortForm 12, Western Ontario and McMaster Osteoarthritis Index, and Knee Society Score. Results: Fifty-one patients were included in the statistical analysis. Demographic characteristics were similar between all. Patients were divided into 3 groups depending on the amount of releases they received. No statistically significant differences in tibiofemoral contact positions or excursions on the medial or lateral condyles were found throughout flexion from 0 to 120 . Postoperative patient-reported outcome scores were not different. Conclusion: Correcting severe varus deformities with extensive medial soft tissue release largely did not alter knee kinematics or clinical outcome scores compared to those with minimal soft tissue release. © 2019 Elsevier Inc. All rights reserved.
Keywords: total knee arthroplasty soft tissue balancing contact kinematics osteoarthritis varus radiostereometric analysis
Investigation was performed at University Hospital, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada. One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2019.02.026. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. * Reprint requests: Brent A. Lanting, MD, MSc, FRCSC, Department of Orthopedic Surgery, University Hospital, Room B9 003, 339 Windermere Road, London, Ontario, N6A 5A5, Canada. https://doi.org/10.1016/j.arth.2019.02.026 0883-5403/© 2019 Elsevier Inc. All rights reserved.
The need for primary total knee arthroplasty (TKA) has been growing steadily over the last decade for individuals having debilitating arthritis. More than 700,000 TKAs are performed yearly in the United States with a projection of 673% increase in the demand for TKAs by 2030 [1]. Despite having excellent outcomes following TKA for most patients, numerous studies have shown dissatisfaction rates around 19% [2,3]. This can be due to numerous etiologies including aseptic loosening, infection, instability, and component malalignment which led investigators to examine different aspects of the surgical technique that may contribute to the undesired outcomes [4]. One of the main concerns is the achievement of proper coronal alignment in TKA which was shown to improve implant survival
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and patient function [5]. The most common knee deformity is varus deformity which leads to the contracture of the medial structures [6]. Appropriate release of these structures is essential to obtain the correct coronal alignment and correct balancing in flexion and extension [7]. In order to achieve this alignment, several surgical techniques for soft tissues and bony procedures in varus knee were described and they depend on the amount of balancing required. Although there is a lot of literature on the indications and technique for these releases, the effect of soft tissue balancing on postoperative outcomes and knee kinematics [8] is less known. The majority of studies that have assessed ligament contributions to TKA stability [9] and the effect of sequential medial releases on tibiofemoral flexion and extension gaps [10,11] are cadaveric biomechanical studies although a few clinical studies have also been reported [7,12]. Tibiofemoral contact kinematics have been used to study the biomechanical aspect of the knee by examining changes from preTKA to post-TKA which provide valuable information related to implant function, wear, and migration [13,14]. Studies of contact kinematics have shown that a native knee has a medial pivot conformation during knee flexion. Moreover, posterior femoral rollback during deep flexion occurs on average 19.2 mm around the lateral femoral condyle and 3.4 mm around the medial condyle [12]. Few studies have prospectively investigated the postoperative contact kinematics and outcomes following various releases of the medial structures in varus knees following primary TKA. The primary objective of this study was to examine the postoperative in vivo tibiofemoral contact kinematics of a single-radius, posterior-stabilized (PS) TKA design between patients who received minimal amounts of medial soft tissue balancing intraoperatively and patients who required more extensive releases. Our secondary objectives were to compare these groups using the following patient-reported outcomes: The Short-Form 12 (SF-12), the Western Ontario and McMaster Osteoarthritis Index (WOMAC), and the Knee Society Score (KSS). Our final objective was to investigate whether an association exists between anterior-posterior (AP) excursion of the contact position and patient satisfaction. We hypothesized that the tibiofemoral contact kinematics would be different for patients who received minimal soft tissue release vs patients who required additional soft tissue release. We also hypothesized that no differences would be found in any of the collected patient-reported outcomes. Study Design This was a prospective study looking at patients who underwent primary TKA with different amounts of soft tissue modifications to correct a varus deformity. This study was performed in our institution over a 14-month period. Baseline data were collected approximately 1 month before surgery at the preadmission clinic visit. All imaging follow-up took place at least 1 year postoperatively. Institutional review board approval was obtained before the onset of the study. Inclusion criteria identified patients older than 18 years who received primary TKA for varus osteoarthritic knee. In addition, patients must have received a fixedbearing, single-radius, PS Triathlon knee system (Stryker, Mahwah, NJ) with cemented fixation by 1 of the 2 senior authors. Exclusion criteria included any patient whose soft tissue releases were not recorded intraoperatively or if they were physically unable to perform the imaging protocol or come for follow-up. Procedure The goal of surgery was to achieve a postoperative mechanical axis angle of 0 ± 3 . Each knee was exposed using a standard
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Table 1 Authors' Stepwise Medial Release Sequence for Correcting Varus Deformities. Soft Tissue Release/Bone Modification (1) (2) (3) (4) (5) (6) (7) (8)
50% Deep MCL (mid-coronal plane) Osteophytes Complete deep MCL Posterior capsule Semimembranosus and posterior oblique ligament Tibial reduction osteotomy Superficial MCL Medial epicondyle osteotomy
MCL, medial collateral ligament.
midline incision followed by a medial parapatellar arthrotomy. Half of TKA procedures were performed by 1 surgeon performing a measured resection technique. The other half of the knees were performed by 1 surgeon performing gap balancing technique. Similar tibiofemoral contact kinematic patterns have been found between measured resection and gap balancing techniques for this implant system [15]. All the knees had identical fixed-bearing, single-radius, PS TKA with cemented fixation of both femur and tibia. The sequence of medial soft tissue release and bone resections is shown in Table 1. All patients had a 50% release of the deep medial collateral ligament (dMCL) to the mid-coronal plane of the tibia during initial knee exposure then tibial and femoral osteophytes were removed. Following each step in the medial release sequence, a spacer block was inserted to assess gap symmetry until it was achieved. The intraoperative medial soft tissue releases were recorded and collected by the treating surgeon.
Radiostereometric Analysis Radiostereometric analysis (RSA) is an imaging technique originally developed by Selvik [16]. Although commonly used to measure orthopedic implant migration, RSA techniques can be applied to acquire tibiofemoral contact kinematics of individuals who underwent TKA without the use of implanted beads. In this study, static radiographs were taken at 0 , 20 , 40 , 60 , 80 , 100 , and 120 knee flexion from two different X-ray angles simultaneously. To induce the desired flexion angle, patients were instructed to stand upright with their knees straight and weight equally distributed between limbs and gradually squat with their heel on the ground until they reached the desired flexion angle measured by a manual goniometer. For the deep flexion angles (80 , 100 , 120 ), the knee of interest was elevated with a small step stool and patients were instructed to lunge until they reached the desired flexion angle. All examinations were performed with calibration cage (cage 43, RSA Biomedical, Umea, Sweden). The calibration cage is a radiolucent material that contains 2 sets of radioopaque markers that project onto the cassettes along with the object of interest. These markers are used to define the position and orientation of the global coordinate system. Model-based RSA software (RSAcore, Leiden, Netherlands) was used to perform 2D/ 3D registration of the manufacturer’s computer-aided design models for the femoral and tibial components to each pair of X-rays for each examination. The model-based RSA approach has been demonstrated to have an excellent accuracy, with errors of 0.19 mm for translations and 0.52 for rotations [17]. Using the registered computer-aided design models, the point with the shortest magnitude of separation between components was considered to be the contact position. Contact positions were recorded using a coordinate system specific to the tibial baseplate. Negative values represent posterior contact position translation relative to the AP
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Table 2 Completed Soft Tissue Balancing of the Entire Cohort. Release Progression
Number of Patients
(1) (2) (3) (4) (5) (6) (7) (8)
51 51 7 3 6 10 1 0
50% Deep MCL (mid-coronal plane) Osteophytes Complete deep MCL Posterior capsule Semimembranosus and posterior oblique ligament Tibial reduction osteotomy Superficial MCL Medial epicondyle osteotomy
MCL, medial collateral ligament.
center of the tibial baseplate while positive values represent anterior contact position translation. Postoperative Protocol
Table 3 Baseline Participant Demographics of Grouped Analysis 2 (Mean ± Standard Deviation). Demographic
Mild (N ¼ 24)
Moderate (N ¼ 16)
Extensive (N ¼ 11)
Sex
17 Females, 7 males 68.1 ± 7.3 166.5 ± 8.5 90.8 ± 18.9 32.9 ± 6.9
8 Females, 8 males 67.5 ± 7.6 166.5 ± 9.1 95.0 ± 22.3 34.3 ± 7.8
2 Females, 9 males 69.7 ± 7.5 171.7 ± 10.9 94.0 ± 21.8 31.6 ± 5.4
16 Right, 8 left 6.2 ± 4.4
8 Right, 8 left 8.2 ± 3.3
4 Right, 7 left 12.7 ± 3.6
Age at surgery (y) Height (cm) Mass (kg) Body mass index (kg/m2) Operative limb Preoperative HKA angle ( )
Negative HKA angle indicated varus deformity. HKA, hip-knee-ankle.
A standardized rehabilitation protocol was used for all patients including inpatient physiotherapy immediately postoperatively to start full weight-bearing and range of motion exercises.
and translates posteriorly from 60 to 120 . From 0 to 20 , greater posterior translation is seen on the lateral condyle indicating external femoral rotation as the knee begins flexion from full extension.
Outcome Measures
Demographic Information
The primary outcome was tibiofemoral contact kinematics measured at least 1 year postoperative using RSA to assess average AP contact position translation. Secondary outcomes consisted of patient-reported outcomes that included preoperative and postoperative SF-12, WOMAC, and KSS.
Our analysis consisted of 3 groups: those patients with mild soft tissue balancing (group 1; n ¼ 24), moderate soft tissue balancing (group 2; n ¼ 16), and extensive soft tissue balancing (group 3; n ¼ 11). Demographic characteristics were similar between groups (Table 3). Preoperative hip-knee-ankle angle was not significantly different between group 1 and group 2 (P ¼ .29) but was significantly different between groups 1 and 3 (P ¼ .0001) and groups 2 and 3 (P ¼ .01).
Statistical Analysis For the statistical analysis, the patients were divided into 3 groups: mild group where patients received up to and including osteophytes removal, moderate group where patients received complete release of the dMCL as well as up to the release of the semimembranosus and posterior oblique ligament, and finally extensive group where patients received at least a medial tibial reduction osteotomy (MTRO). Preoperative patient variables such as demographic characteristics were compared using a 2-sample t-test for continuous variables, Fisher exact test for binary variables, or chi-square test for multiple categorical variables. Continuous variables such as AP contact point position throughout flexion on the medial and lateral condyle for each release type and across the entire cohort are expressed as mean ± standard deviation while categorical variables are reported as absolute values and percentages. One-way analysis of variance tests and Kruskal-Wallis test were used to compare between the 3 groups. Results During the study period, 51 patients had prospective preoperative as well as postoperative data collected. The number of releases completed intraoperatively for this cohort is reported in Table 2. Patients were organized by the maximum level of balancing they required to attain a balanced knee. Ungrouped Analysis
Primary Outcome: Tibiofemoral Contact Kinematics Average Contact Positions Medial and lateral AP positions of groups 1, 2, and 3 throughout flexion are presented in Figure 1. The pattern of contact for all groups was similar; there were no significant differences between average AP contact positions between groups at any flexion angle. All groups demonstrated similar posterior translation of the contact position on the lateral condyle than the medial condyle (Figs. 1 and 2) indicating external rotation and medial pivot. The tibiofemoral contact pattern for the patient who received sMCL release relative to the mean and 95% confidence intervals of the extensive group is shown in Figure 3. On the medial condyle, the sMCL patient demonstrated posterior contact beyond the limits of the confidence intervals at 20 , 60 , 100 , and 120 of flexion. On the lateral condyle, the sMCL patient was posterior at 0 of flexion, and anterior at 40 . Secondary Outcome: Patient-Reported Outcomes Minimal, moderate, and extensive release groups significantly improved in all patient-reported outcomes preoperatively to postoperatively (P < .001). There were no differences between groups in the SF-12, WOMAC, or KSS outcome scores, preoperatively or postoperatively (Table 4).
Tibiofemoral Contact Kinematics Discussion Cohort averages showed the medial contact position translates posteriorly from 0 to 20 , anteriorly from 20 to 80 , and posteriorly from 80 to 120 . On the lateral condyle, the contact position translates posteriorly from 0 to 20 , stays stable from 20 to 60 ,
In this study, we compared the in vivo tibiofemoral contact kinematics of a PS-TKA during knee flexion in patients that ranged in the amount of soft tissue balancing received intraoperatively
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Fig. 1. Anterior-posterior (AP) translation (mean ± 95% confidence interval) on the medial condyle (A) and lateral condyle (B) between the mild, moderate, and extensive release groups from 0 to 120 of knee flexion.
and showed that there were no statistically significant differences between groups in average contact position of the medial condyle at any flexion angle and no differences in AP excursion on the medial and lateral condyles throughout flexion. On the lateral condyle, the only difference we observed was that patients with soft tissue release had more anterior contact than those without soft tissue release at 100 of flexion. A study by Bellemans et al investigated 35 consecutive TKA with preoperative varus deformity where they performed varus-valgus stress testing intraoperatively. They reported that the medial collateral structures are intrinsically shortened while the lateral soft tissues are stretched in knees with approximately 10 or more of varus [18]. Therefore, the residual laxity found in the lateral structures can explain why patients who required soft tissue release had different contact position at 100 on the lateral condyle compared to the no release group. Superficial medial collateral ligament is a very important structure for controlling medial laxity after TKA. Recently, Athwal et al [9] showed that sMCL is the primary medial restraint to coronal, sagittal, and axial axis in intact knee and following TKA, using 8, nonarthritic, intact, fresh-frozen knees in a robotic simulator. Given the importance of the sMCL for stability following TKA, the authors of the present study avoid sMCL release if possible. Only 1 patient in this study had his sMCL released. While only 1 patient is not representative of a population of patients, this patient did exhibit dramatic posterior translation of the medial condyle compared to the group average. Increasing the number of patients in this group would provide valuable in vivo data to support the sMCL’s importance for postoperative medial stability. Meanwhile, our recommendation is to maintain the integrity of the sMCL as much as possible.
To preserve the integrity of the sMCL while still achieving coronal plane mechanical alignment, authors of this study use the MTRO technique. Ahn and Back [19] compared their standard medial release progression (n ¼ 20) with bony resection of the proximal medial tibial (n ¼ 20) in patients with 10 anatomic varus deformity. At 6 months, there was no difference between groups for range of motion or hospital for special surgery scores, aligning with the patient-reported findings of our study. Another retrospective study by Martin et al. compared 67 MTRO patients and 67 matched controls who did not require an MTRO. They found that the MTRO group had significantly better postoperative KSS and produced similar corrections to coronal alignment as the control group [20]. In our study, the patients who received MTRO demonstrated similar tibiofemoral contact kinematics compared to the other groups which support the use of MTRO as a promising technique. Consistent with our expectations, the preoperative varus deformity was larger in the groups that required more extensive soft tissue balancing. All patient-reported outcome scores improved preoperatively to postoperatively, except for the SF-12 Mental Component Score which was expected because this is a generic measure of mental health. A large, multicenter, prospective study by Unitt et al. examined clinical outcome score difference in patients who received none or minimal (n ¼ 173), moderate (n ¼ 122), and extensive (n ¼ 115) amounts of soft tissue balancing during primary TKA [21]. Across multiple outcome measures, they found that the extensive release group had significantly greater preoperative to postoperative change scores than the other groups but had similar postoperative outcomes at 12 months. Finding no differences in postoperative patient-reported outcomes is consistent with our findings.
Fig. 2. Superior view of a tibial baseplate representing the average medial and lateral contact positions for the mild (A), moderate (B), and extensive (C) release groups from 0 to 120 of knee flexion.
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Fig. 3. Contact pattern on the medial (A) and lateral (B) condyles for the 1 patient who received a superficial MCL (sMCL) release. The meant contact pattern for the extensive release group (without sMCL patient included) is presented with upper and lower bounds of their 95% confidence intervals.
There were few limitations to this study. Hunt et al [8] published a literature review on medial release methods in TKA showing approximately 20 unique sequences that have been described. For this reason, the results of this study may not be generalizable. Although the sample size was small, 95% confidence intervals surrounding AP positions were narrow, extending approximately 1-2 mm around the means. This indicates reasonable precision was achieved for our primary outcome even with this small sample. Another limitation was that kinematic data were collected using a quasi-static technique (images taken in rapid succession with less than 5 seconds in between) instead of a continuous dynamic technique (15 images captured per second). The quasi-static technique was used because our RSA imaging system cannot acquire continuous images. However, compared to an imaging system that can acquire continuous images, our method produces higher accuracy of implant position. Saevarsson et al [22] collected weightTable 4 Patient-Reported Outcome Scores (Mean ± Standard Error). Time
Outcome Measure
Preop
SF-12 PCS MCS SF-12 PCS MCS WOMAC Pain Stiffness Function Total WOMAC Pain Stiffness Function Total KSS Symptoms Satisfaction Expectations Function Total KSS Symptoms Satisfaction Expectations Function Total
Postop
Preop
Postop
Preop
Postop
Mild
Moderate
bearing contact kinematics using both static and dynamic techniques and found that static and dynamic kinematics were comparable. The kinematic patterns of the present study were consistent with those of other studies of the same implant design indicating our image acquisition technique was acceptable. Finally, this study used a single-radius, PS TKA design where the role of the posterior cruciate ligament is fulfilled by a cam-post interaction that occurs between the femoral and tibial components. This interaction has been found to begin at approximately 82 ± 16 of flexion in the PS implant, which drives posterior femoral rollback in deep flexion [17]. This posterior translation of the contact position was seen in our results at a similar flexion angle. However, in cruciate-retaining implant designs, the posterior cruciate ligament is intact, and its tension contributes to the height of the flexion gap. Therefore, the interpretation of the results of the present study should not be extended to cruciate-retaining implant designs. Conclusion
Extensive
P Value
32.3 ± 2.3 57.8 ± 3.2
29.0 ± 2.5 57.0 ± 3.2
31.9 ± 2.5 54.9 ± 4.6
.56 .99
43.2 ± 2.2 52.1 ± 2.7
42.2 ± 2.5 54.6 ± 2.9
45.6 ± 2.3 58.9 ± 2.3
.66 .27
49.2 47.8 52.0 51.2
± ± ± ±
3.3 4.2 3.4 3.2
44.6 38.8 43.1 44.8
± ± ± ±
4.1 4.2 4.0 3.9
50.1 38.6 46.0 48.1
± ± ± ±
3.4 5.3 4.4 4.2
.54 .25 .23 .45
85.9 80.0 83.5 84.6
± ± ± ±
3.3 4.7 3.1 3.2
81.9 74.1 80.8 83.0
± ± ± ±
4.0 3.8 3.2 3.4
89.3 71.0 80.9 85.1
± ± ± ±
1.8 6.3 3.5 3.2
.72 .43 .79 .91
08.8 15.0 14.1 34.3 72.3
± ± ± ± ±
1.2 1.8 0.4 3.9 5.7
08.1 13.5 13.9 38.9 74.4
± ± ± ± ±
1.5 1.7 0.5 5.1 7.4
09.3 15.0 13.5 38.9 76.7
± ± ± ± ±
1.5 2.0 0.3 4.0 7.1
.85 .84 .14 .70 .91
21.0 32.5 08.9 74.0 135.4
± ± ± ± ±
0.9 2.1 0.7 3.8 7.2
20.3 32.9 11.3 71.8 136.2
± ± ± ± ±
1.3 1.9 0.8 4.3 7.7
21.8 35.6 09.7 77.1 144.3
± ± ± ± ±
0.7 0.9 0.7 3.7 5.1
.97 .52 .09 .70 .89
Preop, preoperative; Postop, postoperative; SF, short form; PCS, physical component score; MCS, Mental Component Score; WOMAC, Western Ontario McMaster Osteoarthritis Index; KSS, Knee Society Score.
Contact kinematics and clinical outcome scores were largely unaffected by greater levels of medial soft tissue release. This suggests that correcting severely varus patients to mechanically neutral coronal alignment does not compromise tibiofemoral contact kinematics or patient-reported satisfaction. References [1] Jaffe WL, Dundon JM, Camus T. Alignment and balance methods in total knee arthroplasty. J Am Acad Orthop Surg 2018;26:709e16. [2] Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KDJ. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res 2010;468:57e63. [3] Robertsson O, Dunbar M, Pehrsson T, Knutson K, Lidgren L. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand 2000;71:262e7. [4] Schroer WC, Berend KR, Lombardi AV, Barnes CL, Bolognesi MP, Berend ME, et al. Why are total knees failing today? Etiology of total knee revision in 2010 and 2011. J Arthroplasty 2013;28:116e9. [5] Cherian JJ, Kapadia BH, Banerjee S, Jauregui JJ, Issa K, Mont MA. Mechanical, anatomical, and kinematic axis in TKA: concepts and practical applications. Curr Rev Musculoskelet Med 2014;7:89e95. [6] Asano H, Hoshino A, Wilton TJ. Soft-tissue tension total knee arthroplasty. J Arthroplasty 2004;19:558e61. [7] Verdonk PC, Pernin J, Pinaroli A, Ait Si Selmi T, Neyret P. Soft tissue balancing in varus total knee arthroplasty: an algorithmic approach. Knee Surg Sports Traumatol Arthrosc 2009;17:660e6. [8] Hunt NC, Ghosh KM, Athwal KK, Longstaff LM, Amis AA, Deehan DJ. Lack of evidence to support present medial release methods in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014;22:3100e12. [9] Athwal KK, Daou HE, Kittl C, Davies AJ, Deehan DJ, Amis AA. The superficial medial collateral ligament is the primary medial restraint to knee laxity after cruciate-retaining or posterior-stabilised total knee arthroplasty: effects of
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