Randomized Controlled Trial of Sensor-Guided Knee Balancing Compared to Standard Balancing Technique in Total Knee Arthroplasty

Randomized Controlled Trial of Sensor-Guided Knee Balancing Compared to Standard Balancing Technique in Total Knee Arthroplasty

The Journal of Arthroplasty xxx (2020) 1e5 Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyj...

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The Journal of Arthroplasty xxx (2020) 1e5

Contents lists available at ScienceDirect

The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org

Randomized Controlled Trial of Sensor-Guided Knee Balancing Compared to Standard Balancing Technique in Total Knee Arthroplasty Thomas J. Wood, MD, FRCSC a, b, c, Mitchell J. Winemaker, MD, FRCSC a, b, c, Dale S. Williams, MD, FRCSC a, b, c, Danielle T. Petruccelli, MLIS, MSc b, c, *, Daniel M. Tushinski, MD, FRCSC a, b, c, Justin de V. de Beer, MD, FRCSC a, b, c a

Division of Orthopaedic Surgery, McMaster University, Hamilton, Ontario, Canada Complex Care and Orthopaedics Program, Hamilton Health Sciences Juravinski Hospital, Hamilton, Ontario, Canada c Hamilton Arthroplasty Group, Hamilton Health Sciences Juraviski Hospital, Hamilton, Ontario, Canada b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 July 2020 Received in revised form 18 August 2020 Accepted 18 September 2020 Available online xxx

Background: Despite advances in total knee arthroplasty (TKA) technology, up to 1 in 5 patients remain dissatisfied. This study sought to evaluate if sensor-guided knee balancing improves postoperative clinical outcomes and patient satisfaction compared to a conventional gap balancing technique. Methods: We undertook a prospective double-blind randomized controlled trial of patients presenting for elective primary TKA to determine a difference in TKA soft tissue balance between a standard gap balancing (tensiometer) approach compared to augmenting the balance using a sensor-guided device. The sensor-guided experimental group had adjustments made to achieve a balanced knee to within 15 pounds of intercompartmental pressure difference. Secondary outcomes included differences in clinical outcome scores at 6 months and 1 year postoperative, including the Oxford Knee Score and Knee Society Score and patient satisfaction. Results: The sample comprised of 152 patients, 76 controls and 76 experimental sensor-guided cases. Within the control group, 36% (27/76) of knees were unbalanced based on an average coronal plane intercompartmental difference >15 pounds, compared to only 5.3% (4/76) within the experimental group (P < .0001). There were no significant differences in 1-year postoperative flexion, Knee Society Score, or Oxford scores. Overall, TKA patient satisfaction at 1 year was comparable, with 81% of controls and experimental cases reporting they were very satisfied (P ¼ .992). Conclusion: Despite the use of the sensor-guided knee balancer device to provide additional quantitative feedback in the evaluation of the soft tissue envelope during TKA, we were unable to demonstrate improved clinical outcomes or patient satisfaction compared to our conventional gap balancing technique. © 2020 Elsevier Inc. All rights reserved.

Keywords: total knee arthroplasty sensor-guided balancing randomized controlled trial outcomes

Vast improvements in technology and surgical technique have made total knee arthroplasty (TKA) surgery a very successful operation [1]. However, given that approximately 1 in 5 TKAs have

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.2020.09.025. * Reprint requests: Danielle T. Petruccelli, MLIS, MSc, Hamilton Arthroplasty Group, Juravinski Hospital - Hamilton Health Sciences, 711 Concession St., Hamilton, Ontario, Canada L8V 1C3. https://doi.org/10.1016/j.arth.2020.09.025 0883-5403/© 2020 Elsevier Inc. All rights reserved.

suboptimal subjective clinical outcomes, there is certainly room for improvement [2,3]. Technical factors critical to the success of TKA are correct rotation, alignment, and soft tissue balance [4,5]. Although technology can aid surgeons in terms of navigated alignment and bone cuts, until recently soft tissue balance has been based on subjective surgeon interpretation, based on a “feel” that develops with experience, training, and volume necessitating skill in this area [1,6,7]. Approximately one-third of revision TKAs are related to soft tissue imbalance presenting as instability, stiffness, or early component loosening [1,4,5]. Furthermore, definitions of a “well-balanced” knee are varied and not based on empirical scientific data [1].

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Microelectronic technology has allowed for dynamic intraoperative assessment of tibiofemoral contact pressures during trialing of total knee replacements and thus potentially more objective soft tissue balancing. Such technology has been shown to improve short-term postoperative outcomes as well as satisfaction [1,8,9]. Quantitative balance has been defined as mediolateral intercompartmental loading difference less than 15 pounds [1,10]. This study sought to evaluate if sensor-guided knee balancing improves surgical accuracy compared to a conventional gap balancing technique, as determined based on rate of unbalanced TKAs, and to assess any improvement in postoperative clinical outcomes and patient satisfaction. Our hypothesis was that the use of a pressure sensor to help guide knee balancing would improve accuracy; however, this would not translate into patient-reported outcome improvements. Method A 2-surgeon, single-center, double-blinded randomized controlled study was undertaken at a high-volume academic arthroplasty center to determine outcomes of TKA using conventional soft tissue balancing with a tensiometer device (Monogram Balancer; Stryker, Mahwah, NJ) vs augmenting the soft tissue balancing using a sensor-guided device (Verasense; OrthoSensor, Dania Beach, FL). Balancing with a tensiometer was the standard method for balancing TKAs prior to this study for both surgeons. The primary outcome was the rate of unbalanced TKAs based on the quantitative sensor device definition of a well-balanced knee defined as a mediolateral intercompartmental loading difference of 15 pounds through range of motion (ROM) [1,10]. Secondary outcomes included differences in clinical outcome scores including flexion range, Knee Society Score (KSS) [11], and Oxford Knee Score [12] up to 1 year postoperative. Patient satisfaction was also measured at 1 year postoperative using a brief nonvalidated Likert scale survey. Upon Research Ethics Board approval, individual patient informed consent was obtained. Eligible patients were adults aged 18 years or older and scheduled to undergo elective primary unilateral TKA for a diagnosis of osteoarthritis. Patients who presented with inflammatory arthritis, collateral ligament insufficiencies (medial collateral ligament [MCL], lateral collateral ligament), contraindications to posterior cruciate retaining TKA including deformity >15 or fixed-flexion contracture >15 , posterior cruciate ligament (PCL) deficiency, previous high tibial osteotomy, or neuromuscular disorder were not considered for inclusion. Study patients were randomized to receive TKA with the Triathlon Cruciate TKA System (Stryker) in both the control and experimental groups according to (1) the control group with standard balancing techniques used and sensor data obtained in blinded fashion and not used to balance the TKA implant or (2) the experimental case group with sensor-guided balancing where sensor data were used to balance the TKA within defined parameters. Patients were randomized into 11 randomly permuted blocks of 14 participants in each, for a total of 154 participants, according to a computer-generated random number sequence (http://www. randomization.com). Both the patient and the clinical assessor were blinded to the treatment allocation. To ensure clinical equipoise and avoid any undue bias, the operating surgeon was blinded to the sensor data in the standard TKA balancer control group. Surgical Technique The TKA surgery was performed under a standardized surgical technique for the Triathlon (Stryker) Cruciate TKA system which all patients received. Bony resections were templated using X-rays as a

guide preoperatively, and a standard medial parapatellar knee approach was performed. A distal femoral resection of 8 mm was performed initially using intramedullary guidance of 5 valgus (uniformly) with additional resection performed as required to balance the extension gap. A preliminary medial subperiosteal release was performed and osteophytes tenting ligaments were removed and the anterior cruciate ligament was also removed. The proximal tibia was resected typically taking 9 mm off the side of the deformity while protecting the PCL. The leg was brought into full extension and the bone ends opposed to confirm satisfactory alignment and then distracted to confirm adequate gap to accommodate at least the minimum bearing insert of 9 mm. A tensor balancer device (Monogram Balancer; Stryker) was introduced into the knee in full extension and the tension was applied until the torque meter read 32, which has been deemed an appropriate tension based on prior study of the device [13]. The displacement or gap in millimeters was recorded and angular deformity was corrected to within 3 mm by further soft tissue release or bone resection. The knee was then flexed to 90 and the tensioner device was reapplied with the same torque and the displacement. Angular deformity was observed to help guide the rotation of the femoral component and any further resection to achieve a flexion extension gap difference to within 3 mm, and coronal plane deformity to within 3 throughout ROM which are parameters based on prior study [14]. The femoral implant was sized to maximize anterior femoral resection without notching the anterior femur and standard 8 mm posterior resection ± 1.5 mm to optimize flexion extension gap balance and mediolateral bone coverage. The remaining femoral anterior, posterior, and chamfer bone cuts were made in the rotation deemed to optimize tibiofemoral and patellar bony and soft tissue alignment. Any adjustment in bone cuts (eg, further distal femur resection, adding tibial slope or recutting tibia into more varus by 2 ) were recorded and any additional soft tissue releases beyond standard exposure, for example, superficial MCL partial release or pie crusting MCL or PCL, were recorded. Any inadvertent soft tissue damage or over release was recorded. Once optimal balance and position was achieved using this conventional technique, final tensioner device measurements were recorded. With the femoral implant applied, the tensioner device was inserted to 32 on the torque meter in full extension and at 90 of flexion. The gap in millimeters and angular asymmetry in degrees was recorded and appropriate bearing insert thickness was chosen. The tibial rotation was determined by observing where the tibial tray centered itself using trials and optimizing this position while adhering to optimal bone coverage and bony landmarks (Krackow’s Line). This position was marked and the tibial keel was punched for the appropriate size tibial metal-backed tray to optimize bone coverage. Regardless of the final balance, all patients in this study received a cruciate substituting insert for consistency in the study. In the control group where the sensor device (Verasense; OrthoSensor) was not used in the optimization of knee balance and alignment, the real implants were cemented in place and the sensor trial was inserted using a thickness based on prior standard bearing insert trialing. The sensor has a microprocessor and an integrated nanosensor system allowing for transmission of data to a portable graphic display. The sensor measures and localizes peak load on the medial and lateral tibiofemoral interfaces [10]. The knee was then cycled and the loads were recorded in the medial and lateral compartments at 10 , 45 , and 90 of flexion. This was repeated 3 times to ensure consistency of the recordings. The patella tracking was confirmed and need for lateral release was determined and recorded and ROM against gravity with a goniometer was recorded after closure of the wound. In the experimental group where the sensor device was used to optimize balance and alignment, the initial sensor trial was

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inserted and the tibial baseplate was rotated until the medial and lateral femoral contact points were seen as parallel on the graphic display. Quantitative “balance” was defined as a mediolateral intercompartmental loading difference of 15 pounds [1,9,10]. Flexion balance was achieved when femoral contact point position was within the midposterior third of the tibial insert and intercompartmental loads were balanced. A tight flexion gap intraoperatively creates excessive pressures in flexion and the peak contact point resides more posteriorly on the tibial insert. This was addressed by recession of the PCL or by increasing the tibial slope for example. The loads in the medial and lateral compartments were recorded at 10 , 45 , and 90 flexion. If the compartment loads differed by >15 pounds between compartments as defined as “unbalanced” by Gustke et al. [1,9], further soft tissue release/pie crusting (eg, pie crusting of PCL for tight flexion gap) or bone resection was performed and recorded to try and achieve a side-toside compartment pressure difference of <15 pounds. If this was not achieved or balance was determined to be suboptimal as defined by the sensor parameters, it was recorded with comments as to why (eg, over release of MCL or excessive bone resection). Final implants were cemented in place and final recordings were made using the sensor device. Outcome Measures Demographics, clinical data, and outcome scores were collected preoperatively (3-4 weeks prior to surgery). Intraoperative data included details specific to the surgical procedure, gap balancer data, and sensor data as provided on the sensor-guided graphical user interface for both the control group and experimental group prior to and after correction/fine tuning of soft tissue balancing. For all cases, balance of the knee was assessed in 3 positions: full extension at 10 , mid-flexion at 45 , and in 90 of flexion. Clinical assessment of function was measured by a nontreating clinical research nurse using the KSS [11] at the preoperative visit and by a blinded nontreating kinesiologist at 6 months and 1 year. The KSS clinical score is a disease-specific tool incorporating pain, stability, and ROM each rated on a 100-point scale where a score of 100 corresponds to excellent function [11]. At all intervals, including intraoperative prior to skin incision, varus/valgus and anteroposterior stability, extension lag, anatomic alignment, and ROM were recorded. Preoperative and postoperative patient subjective perception of physical function was measured using the Oxford Knee Score [12]. The Oxford Score is a 12-item measurement tool designed to determine patient perceived rating of knee pain and activity limitations scored from 12 (excellent function) to 60 (poor function) points [12]. In addition, patients were asked to complete a brief Likert scale satisfaction survey to determine satisfaction with their TKA overall. Sample Size and Statistical Analysis Per Gustke et al [1,9], 13% of cases in their sensor-guided TKA trial were unbalanced. Based on a 13% failure rate among controls where balancing will not be adjusted according to sensor-guided feedback, 70 cases with the sensor-guided device and 70 controls were required to be able to reject the null hypothesis that this relative risk equals 1 to obtain a study power of 80% (2-tailed hypothesis). Considering a conservative withdrawal estimate of 10%, total minimum sample size required was 154 patients including 77 cases and 77 controls. The type I error probability associated with this test of the null hypothesis was 0.05. Pearson’s chi-squared test statistic was used to evaluate the proportion of balanced TKAs among cases and controls. Difference in function and outcome scores was determined using independent

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samples t-test assuming normal distribution of data. For the descriptive analysis categorical variables were summarized as counts and proportions, whereas normally distributed continuous variables were summarized as means and standard deviation. Where normality assumptions were violated, median and interquartile range were reported. For non-normally distributed data differences between cases and controls were determined using nonparametric tests including Mann-Whitney U-test and Fisher’s exact test where appropriate. In all cases a value of P < .05 was considered statistically significant. All statistical analyses were performed using IBM SPSS Statistics v26 (IBM Corp, Armonk, NY). Results A total of 184 patients scheduled to undergo primary TKA were recruited and provided informed consent to participate in the trial. Of the study patients 32 were withdrawn preoperatively or intraoperatively; 6 were withdrawn prior to surgery due to patient request, surgery postponement, or cancellation, and an additional 26 patients were withdrawn intraoperatively prior to knee balancing due to anatomical protocol inclusion criteria violation determined at the time of surgery, or issue with/availability of sensor-guided study computer. A total of 152 patients were randomized into the study and included in the analysis. Of the 152 study patients, 76 were randomized to the control standard gap balancer arm and 76 to the experimental sensor-guided arm. Patient demographics were similar between the control and intervention groups (Table 1). Mean age of the control group was 69 years (±7.9) comprised of 57% female, and mean age of the experimental group was 67 years comprised of 53% female (Table 1). Preoperative flexion, KSS, and Oxford were comparable between the 2 groups (P > .05) (Table 2). Mean coronal plane side-to-side difference was significantly higher among controls (15.4 ± 9.8 ) compared to the experimental group (8.6 ± 4.4 ) (P < .0001) (Table 3). Of the controls, 35.5% (27/ 76) of TKAs were unbalanced based on an average coronal plane side-to-side difference >15 , compared to only 5.3% (4/76) within the experimental group (P < .0001) (Table 4). The proportion of unbalanced knees was significantly greater among the control group at 10 , 45 , and 90 (P < .0001) (Table 4). Additional releases were required in the sensor-guided group in 67.1% (51/76) of cases. The most common additional release in the sensor-guided group was pie crusting of the MCL (42.1%) (Table 5). Despite this, we could not demonstrate a significant difference in 6-month or 1-year postoperative flexion (6-month P ¼ .282, 1year P ¼ .256) or KSS (6-month P ¼ .927, 1-year P ¼ .271) between the 2 groups (Table 2). Although there was no statistical difference in Oxford at 1 year (P ¼ .176), 6-month Oxford was statistically inferior among controls (control group mean 23.1 ± 7.6 vs experimental group mean 20.0 ± 6.4, P ¼ .010) (Table 2). Intraoperatively, inadvertent structural damage occurred in 2 cases in the control group which included a partial MCL avulsion and a PCL avulsion, and in 1 case in the sensor-guided group which

Table 1 Preoperative Patient Characteristics. Variables Gender, n (%) Male Female Age, mean (SD) BMI (kg/m2), mean (SD)

Control Group (n ¼ 76)

Experimental Group (n ¼ 76)

33 43 66.7 33.8

36 40 67.1 32.3

(43.4%) (56.6%) (7.9) (6.0)

BMI, body mass index; SD, standard deviation.

(47.4%) (52.6%) (7.0) (5.9)

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Table 2 Preoperative and Postoperative Outcome Measures. Variables Knee Society Score, mean (SD) Preoperative 6 mo postoperative 1 y postoperative Oxford Knee Score, mean (SD) Preoperative 6 mo postoperative 1 y postoperative Flexion range ( ), mean (SD) Preoperative 6 mo postoperative 1 y postoperative

Control Group (n ¼ 76)

Table 4 Proportion of Cases With Coronal Plane Side-to-Side Difference Within 15 vs >15 . Experimental Group (n ¼ 76)

P-Value

49.6 (17.4) 89.1 (14.7) 92.0 (10.2)

49.7 (13.1) 88.9 (12.4) 90.0 (11.9)

.985 .927 .271

38.8 (7.6) 23.1 (7.0) 20.5 (5.7)

37.9 (7.1) 20.0 (6.4) 19.0 (7.0)

.441 .010a .176

105.4 (13.2) 114.3 (13.3) 116.2 (11.8)

109.3 (11.5) 116.6 (10.9) 118.2 (9.1)

.053 .282 .256

included a partial MCL avulsion (P ¼ .597). This inadvertent structural damage was minor and did not lead to compromised patient outcomes but was recorded as it was felt to influence sensor readings. Two patients in each group underwent postoperative manipulation for stiffness at 6 weeks postoperative. There were no revisions in either group up to 1 year postoperative. There was 1 patient death in the sensor-guided group at 7 months postoperative due to an unrelated cause. Overall, TKA patient satisfaction at 1 year postoperative was comparable between the 2 groups, with 81% of controls and experimental cases reporting they were very satisfied (P ¼ .992). We could not demonstrate a difference in patient satisfaction with regard to pain or function at 1 year postoperative (P > .05) (Table 6). Discussion Continued advancement of technology and improvement in surgical technique have made TKA surgery a very successful operation [1,9]. However, a substantial portion of patients continue to have suboptimal clinical outcomes, creating a need for exploration of all possible avenues to optimize satisfaction and function [15,16]. The purpose of this study is to determine if sensor-guided knee balancing improves surgical accuracy compared to a conventional gap balancing technique, as determined based on rate of unbalanced TKAs, and to assess any improvement in postoperative clinical outcomes and patient satisfaction. The results of this study show that an intercompartmental balance to within 15 pounds was significantly more likely when using the sensor guide compared to the standard gap balance technique with a tensiometer. However, using the sensor guide to balance to within 15 pounds of intercompartmental pressure did not improve clinical outcomes or satisfaction compared to those knees with >15 pounds differences. The sensor guide is a highly sensitive tool which responds to slight leg position changes and bony implant position (rotational or translational). If high-volume

Table 3 Mean Coronal Plane Side-to-Side Difference. Variables

Control Group (n ¼ 76)

Experimental Group (n ¼ 76)

P-Value

At 10 of flexion, mean (SD) At 45 of flexion, mean (SD) At 90 of flexion, mean (SD) Average, mean (SD)

17.1 15.2 14.1 15.4

8.8 8.6 8.3 8.6

.000a .000a .002a .000a

SD, standard deviation. a Statistically significant at 5% a-level.

At 10 of flexion, n (%) Within 15 >15 At 45 of flexion, n (%) Within 15 >15 At 90 of flexion, n (%) Within 15 >15 Overall average, n (%) Within 15 >15 a

SD, standard deviation. a Statistically significant at 5% a-level.

(14.6) (11.7) (14.5) (9.8)

Variables

(7.1) (7.2) (5.7) (4.4)

Control Group (n ¼ 76)

Experimental Group (n ¼ 76)

P-Value

42 (55.3%) 34 (44.7%)

63 (82.3%) 13 (17.1%)

.000a

52 (55.3%) 34 (44.7%)

67 (88.2%) 9 (11.8%)

.000a

48 (63.2%) 28 (36.8%)

67 (88.2%) 9 (11.8%)

.000a

49 (64.5%) 27 (35.5%)

72 (94.7%) 4 (5.3%)

.000a

Statistically significant at 5% a-level.

knee surgeons are indirectly measuring loads using a tensiometer and performing both bony and soft tissue driven releases with similar clinical and satisfaction outcomes, this definition of “balance” would appear too strict. The definition of soft tissue balance being a pressure difference medially and laterally within 15 pounds has been questioned in the literature [17]. In a retrospective study of 258 patients, Meneghini et al [17] showed that outcomes did not support mediolateral force difference of 15 pounds as “balanced.” The KSS objective, function, and satisfaction scores and EuroQol-5 dimension at 4 months postoperatively did not differ based on the magnitude of intercompartmental force difference [17]. Furthermore, our results show that there were no differences in postoperative flexion, functional scores, or satisfaction when comparing conventional soft tissue balancing using a tensiometer to augmenting soft tissue balance with a sensor guide. The evidence on this topic is mixed with different techniques used to achieve soft tissue balance in the surgeon-guided groups [9,16,17]. In a prospective randomized controlled trial of 135 patients, Gustke et al [9] showed a balanced cohort (intercompartmental pressures within 15 pounds) had significantly better KSS, Western Ontario and McMaster Universities Osteoarthritis Index, and mean activity scores compared to an unbalanced cohort at 1 year. Similarly, Golladay et al [16] in a prospective nonrandomized controlled trial of 322 patients, quantitatively balanced knees using a sensor guide with load differential less than 15 pounds at 10 , 45 , and 90 had better outcomes (Forgotten Joint Score, KSS expectation and satisfaction) at 6 weeks and 6 months compared to unbalanced knees. Both these studies were industry sponsored [9,16]. Although surgeon-driven soft tissue balancing is described as imperfect [1,9,16,17], there is a large spectrum of how this is done especially when considering navigation for bony cuts and the use of tensiometers. In our study, 2 experienced high-volume arthroplasty surgeons used a tensiometer, which provides compartmental pressure information in addition to following an algorithm for

Table 5 Additional Releases Performed in the Experimental Sensor-Guided Group. Variables

Proportion Experimental Cases (n ¼ 76)

Total cases with additional releases, % (n) Pie-crust medial collateral ligament Pie-crust posterior cruciate ligament Pie-crust iliotibial band Recut/shim tibia Removal/resection osteophyte or bone fragment Change in insert size Filled medial tibial plateau

67.1% 42.1% 11.8% 10.5% 9.2% 6.6% 3.9% 1.3%

(51) (32) (9) (8) (7) (5) (3) (1)

T.J. Wood et al. / The Journal of Arthroplasty xxx (2020) 1e5 Table 6 Patient Satisfaction at 1 Year Postoperative. Variables

Control Group (n ¼ 76)

Experimental Group (n ¼ 76)

Overall satisfaction with replaced knee, % Very satisfied 80.8% 80.9% Satisfied 15.4% 17.0% Neutral 3.8% 0.0% Dissatisfied 0.0% 0.0% Very dissatisfied 0.0% 2.1% Overall satisfaction with pain relief in replaced knee, % Very satisfied 75.0% 68.1% Satisfied 19.2% 27.7% Neutral 3.8% 0.0% Dissatisfied 1.9% 2.1% Very dissatisfied 0.0% 2.1% Overall, satisfaction with function of replaced knee, % Very satisfied 75.0% 61.7% Satisfied 19.2% 31.9% Neutral 3.8% 4.3% Dissatisfied 1.9% 0.0% Very dissatisfied 0.0% 2.1% a

P-Value

.992 .825 .496 e .475 .446 .321 .496 1.000 .475 .154 .147 1.000 1.000 .475

Statistically significant at 5% a-level.

standard soft tissue releases. Thus, it is not surprising that function and satisfaction scores are similar to the sensor-guided group which also uses compartmental pressure information. One concern about balancing to within 15 pounds of pressure is that soft tissue releases are done which are not part of the surgeon’s normal releases [16]. In the current study, 67.1% of sensor-guided knees required additional releases. Although it would appear that the knee is balanced at 10 , 45 , and 90, this may result in subtle laxities which are not uniform throughout an ROM [16,18]. Walking (particularly in the swing phase of gait), as well as stair climbing requires a dynamic process of muscular interaction which may not be captured when balancing the soft tissue envelope statically at specific points of motion [19]. Thus, based on the existing literature there is no uniform definition of what constitutes a truly balanced TKA [16,17,20]. Promising research is emerging with the use of robotics and the possibility of a better recreation of normal anatomy, which may result in less pain and better early function following TKA [21]. The strengths of this study are the methodology with a randomized protocol which was double blinded. This study was powered based on previous reports of the incidence of an unbalanced TKA using a sensor guide. Limitations include the recording of intraoperative load pressures before cementing. It is recognized that the cement may have fine-tuned the soft tissue balance and alignment as it set. Furthermore, the sensor guide is a sensitive tool which may be limited by the precision of the bony cuts and the extent to which this can be corrected through soft tissue releases. Navigation was not used in this study by the investigating surgeons. Furthermore, the measurements of the sensor represent static stability at predefined leg positions with slight alterations changing pressure outputs. Although this study was powered, the sample size of 152 may be considered small for this patient population which may limit generalizability. In conclusion, the use of pressure sensor guides to provide additional quantitative feedback in the evaluation of the soft tissue

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envelope during TKA did not improve clinical outcomes or patient satisfaction. This study confirms a standard approach to soft tissue and bony-driven releases that is augmented by tensiometer feedback provides acceptably balanced total knees with comparable patient satisfaction and clinical outcomes. Future areas of research should focus on dynamic stability of a TKA.

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