Are Patients More Satisfied With a Balanced Total Knee Arthroplasty?

Effect of Posterior Cruciate Ligament Resection on Gap Balancing in Robot-assisted Total Knee Arthroplasty

OBJECTIVE

Retention or sacrifice of the posterior cruciate ligament (PCL) is one of the most controversial issues while performing total knee arthroplasty (TKA). This study aimed to evaluate the impact of PCL resection on flexion-extension gaps, femoral component rotation, and bone resection amounts during robot-assisted TKA.

METHODS

This prospective study included 40 patients with knee osteoarthritis who underwent robot-assisted posterior-stabilized (PS) TKA between September 2021 and February 2022. Of the patients, 75% were women (30/40) with a mean age and BMI of 72.6 years and 27.4 kg/m2, respectively. The guidance module and camera stand assembly were used to capture gaps before and after PCL resection. Measurements of femoral component rotation and bone resection amounts were made in cruciate-retaining (CR) TKA mode and PS-TKA mode.

RESULTS

After PCL resection, the mean change in the medial and lateral compartments of flexion gaps increased by 2.0 and 0.6 mm, respectively (p < 0.001). Compared with the CR-TKA mode group, the bone resection amounts of the medial posterior condyle and the lateral posterior condyle in the PS-TKA mode group decreased by 2.0 ± 1.1 and 1.1 ± 1.1 mm, respectively, and the external rotation of the femoral prosthesis relative to the posterior condylar axis and trans-epicondylar line was reduced by 1.0° ± 1.3° and 1.2° ± 1.6°, respectively (p < 0.001).

CONCLUSION

The release of the PCL did not affect the extension gap, but significantly increased the flexion gap. Moreover, the increases in the medial flexion gap were greater than those of the lateral flexion gap. After PCL resection, less external rotation of the femoral prosthesis and fewer bone cuts of the posterior femur were needed in PS-TKA.

Enhancing soft tissue balance: Evaluating robotic-assisted functional positioning in varus knees across flexion and extension with quantitative sensor-guided technology

PURPOSE

Functional implant positioning (FIP) for total knee arthroplasty (TKA) is an evolution of kinematic alignment based on preoperative CT scan and robotic-assisted technology. This study aimed to assess the ligament balancing of image-based robotic-assisted TKA in extension, mid-flexion and flexion with an FIP using intraoperative sensor-guided technology. The hypothesis was that image-based robotic-assisted TKA performed by FIP would achieve ligament balancing all along the arc of knee flexion.

METHODS

This prospective monocentric study included 47 consecutive patients with varus knees undergoing image-based robotic-assisted TKA performed with FIP. After robotic-assisted bone cuts, trial components were inserted, and soft tissue balance was assessed using sensor-guided technology at 10°, 45° and 90° of knee flexion. A mediolateral balanced knee was defined by an intercompartmental pressure difference (ICPD) ≤ 15 lbf and medial and lateral compartment pressure ≤60 lbf. The mean age was 71.6 years old ±6.7, the mean BMI was 29.0 kg/m2 ± 4.9 and the mean preoperative HKA was 174° ± 5 [159; 183].

RESULTS

The mean postoperative knee alignment was 177.0° ± 2.2° [172; 181]. There were 93.6% of balanced knees (n = 44) at 10 and 90° of knee flexion versus 76.6% (n = 36) at 45° of knee flexion with a significant difference (p = 0.014). Median ICPD at 10, 45 and 90° of knee flexion were, respectively, 7.0 (interquartile range [IQR]: 9), 11.0 (IQR: 9.5) and 8.0 (IQR: 9.0). Pairwise analyses revealed differences for ICPD at 45° versus ICPD at 10° (p = 0.003) and ICPD at 90° versus ICPD at 45° (p = 0.007).

CONCLUSION

FIP with an image-based robotic-assisted system allowed the restoration of a well-balanced knee at 10° and 90° of flexion in varus knees. Nevertheless, some discrepancies occurred in midflexion, and more work is needed to understand ligament behaviour all along the arc of knee flexion.

LEVEL OF EVIDENCE

Level II.

Spacer rotation technique allows precise evaluation of gap balance in total knee arthroplasty

The symmetry of the flexion and extension gap influences the functional and long-term outcome after total knee arthroplasty (TKA). Most surgeons check it by applying varus and valgus stress using spacers. This technique has limited accuracy and could be easily extended by rotational movement of the spacer. The objective was to determine the detection threshold and interobserver reliability of this technique. In an in vitro setting with a human cadaveric knee, gap asymmetries were simulated by different medially and laterally applied forces. Using an optical measurement system, the pivot point of the spacer was calculated as a function of the gap symmetry in the first part of the experiment. In the second part, the detection threshold and interobserver reliability of 4 surgeons were determined. For this purpose, gap asymmetries were adjusted to between 0 and 120N in a blinded trial. With a symmetrical gap, the centre of rotation of the spacer was located in the centre of the tibia. With increasing gap asymmetry, the centre of rotation of the spacer shifted to the tight side. This shift was approximately linearly dependent on the force difference. A perfectly balanced gap was detected by the examiners in 50% of the cases. From a force difference of 40N, all examiners identified the gap asymmetry in all cases (ICC = 1.0). The method of spacer rotation described is suitable for reliably detecting gap differences at ≥ 40N, independently of the examiner.

Precision soft tissue balancing: grid-assisted pie-crusting in total knee arthroplasty

Introduction

The varus and valgus knee deformities result from imbalance in tension between medial and lateral soft tissue compartments. These conditions need to be addressed during total knee arthroplasty (TKA). However, there is no consensus on optimal soft-tissue release techniques for correcting varus and valgus deformities during TKA. We assessed the efficacy of a novel grid-based pie-crusting technique on soft-tissue release.

Methods

Cadaver knees were dissected, leaving only the femur and tibia connected by an isolated MCL or the femur and fibula connected by an isolated LCL. Bone cuts were made as performed during primary TKA. Mechanical testing was performed using an MTS machine. A 3D-printed 12-hole grid was placed directly over the MCL and LCL. Using an 18-gauge needle, horizontal in-out perforations were made 3 mm apart. Deformation and stiffness of the ligaments were collected after every 2 perforations. Means were calculated, and regression analyses were performed.

Results

A total of 7 MCL and 6 LCL knees were included in our analysis. The mean medial femorotibial (MFT) space increased from 6.018 ± 1.4 mm-7.078 ± 1.414 mm (R2 = 0.937) following 12 perforations. The mean MCL stiffness decreased from 32.15 N/mm-26.57 N/mm (R2 = 0.965). For the LCL group, the mean gap between the femur and fibula increased from 4.287 mm-4.550 mm following 8 perforations. The mean LCL stiffness decreased from 29.955 N/mm-25.851 N/mm. LCL stiffness displayed a strong inverse relationship with the number of holes performed (R2 = 0.988).

Discussion

Our results suggest that using this novel grid for pie-crusting of the MCL and LCL allows for gradual lengthening of the ligaments without sacrificing their structural integrity. Our proposed technique may serve as a valuable piece in the soft-tissue release toolkit for orthopaedic surgeons performing TKA in varus and valgus deformed knees.

Evaluation of painful total knee arthroplasty: an approach based on common etiologies for total knee arthroplasty revision

A differential diagnosis with emphasis on the common indications for revision should be utilized in the workup of painful total knee arthroplasty (TKA). The physician should identify the exact etiology of the patient's pain to maximize outcomes from treatment. Evaluation for infection should be completed using the Musculoskeletal Infection Society (MSIS) criteria. When common causes of revision TKA do not appear to be the cause of the pain, less likely causes should be not be ignored. Further advancements such as pressure sensing devices may be able to improve patient satisfaction and decrease the incidence of pain following TKA.

Improved Clinical Outcomes With Dynamic, Force-Controlled, Gap-Balancing in Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

Optimal soft-tissue management in total knee arthroplasty (TKA) may reduce symptomatic instability. We hypothesized that TKA outcomes using a computer-assisted dynamic ligament balancer that acquires medial and lateral gap sizes throughout the motion arc would show improved Knee Society Scores (KSS) compared to TKAs done with a traditional tensioner at 0 and 90°. We also sought to quantify the degree to which the planned femoral rotation chosen to optimize medio-lateral balance throughout the arc of motion deviated from the femoral rotation needed to achieve a rectangular flexion gap at 90° alone.

METHODS

Baseline demographics, clinical outcomes, KSSs, and femoral rotations were compared in 100 consecutive, computer-assisted TKAs done with the balancer (balancer group) to the immediately prior 100 consecutive computer-assisted TKAs done without the balancer (control group). Minimum follow-up was 13 months and all patients had osteoarthritis. Mean knee motion did not differ preoperatively (110.1 ± 13.6° balancer, 110.4 ± 12.5° control, P = .44) or postoperatively (119.1 ± 10.3° balancer, 118.8 ± 10.9° control, P = .42). Tourniquet times did not differ (93.1 ± 13.0 minutes balancer, 90.7 ± 13.0 minutes control, P = .13). Postoperative length of stay differed (40.2 ± 20.9 hours balancer, 49.0 ± 18.3 hours control, P = .0009). There were 14 readmissions (7 balancer, 7 control), 11 adverse events (4 balancer, 7 control), and 3 manipulations (1 balancer, 2 control). The cohorts were compared using Student's t-tests, Shapiro-Wilk normalities, Wilcoxon rank-sums, and multivariable logistic regression analyses.

RESULTS

Postoperative KSS improvements were higher in the balancer group (P < .0001). In multivariable regression analyses, the balancer group experienced 7 ± 2 point improvement in KSS Knee scores (P < .0001) and 4 ± 2 point improvement in KSS Function scores (P = .040) compared to the control group.

CONCLUSIONS

The statistically and clinically significant improvements in postoperative KSS demonstrated in the balancer cohort are likely driven by improved stability throughout the motion arc. Further study is warranted to evaluate replicability by non-design surgeons.

Ligament Tension and Balance before and after Robotic-Assisted Total Knee Arthroplasty - Dynamic Changes with Increasing Applied Force

The optimal force applied during ligament balancing in total knee arthroplasty (TKA) is not well understood. We quantified the effect of increasing distraction force on medial and lateral gaps throughout the range of knee motion, both prior to and after femoral resections in tibial-first gap-balancing TKA. Twenty-five consecutive knees in 21 patients underwent robotic-assisted TKA. The posterior cruciate ligament was resected, and the tibia was cut neutral to the mechanical axis. A digital ligament tensioning tool recorded gaps and applied equal mediolateral loads of 70 N (baseline), 90 N, and 110 N from 90 degrees to full extension. A gap-balancing algorithm planned the femoral implant position to achieve a balanced knee throughout flexion. After femoral resections, gap measurements were repeated under the same conditions. Paired t-tests identified gap differences between load levels, medial/lateral compartments, and flexion angle. Gaps increased from 0 to 20 degrees in flexion, then remain consistent through 90 degrees of flexion. Baseline medial gap was significantly smaller than lateral gap throughout flexion (p <0.05). Increasing load had a larger effect on the lateral versus medial gaps (p <0.05) and on flexion versus extension gaps. Increasing distraction force resulted in non-linear and asymmetric gap changes mediolaterally and from flexion to extension. Digital ligament tensioning devices can give better understanding of the relationship between joint distraction, ligament tension, and knee stiffness throughout the range of flexion. This can aid in informed surgical decision making and optimal soft tissue tensioning during TKA.

Intra-operative laxity and balance impact 2-year pain outcomes in TKA: a prospective cohort study

PURPOSE

The objective of this study was to determine if intra-operatively measured joint gaps are associated with 2-year pain outcomes in total knee arthroplasty (TKA) and whether balance and laxity windows could be defined throughout flexion to optimize 2-year pain outcomes. Our hypothesis is that intra-operative joint gaps are associated with 2 year post-operative pain outcome.

METHODS

A prospective study investigating 310 robotically assisted TKAs was performed. Final intra-operative joint gap data were recorded using a digital tensioner and component alignment data were recorded by the robotics system. Patient demographics and Knee Injury and Osteoarthritis Outcome Score (KOOS) were recorded pre-operatively and KOOS and Hospital for Special Surgery (HSS) satisfaction were recorded at 2 years post-op. A random search Simulated Annealing (SANN) optimisation algorithm was used to determine global optimum laxity and balance windows at different flexion angles which maximized the 2-year KOOS pain scores. The windows were combined to determine the impact of achieving optimal laxity and balance throughout flexion. To improve clinical utility, boundaries identified by the SANN algorithm were rounded to the nearest 0.5 mm before statistical analysis.

RESULTS

Laxity and balance windows were defined in extension (Med lax: -2.0 to 2.5 mm, Lat lax: -0.5 to 2.5 mm, Balance: -3.0 to 0.0 mm), mid-flexion (Med lax: -1.0 to 2.5 mm, Lat lax: -0.5 to 3.0 mm, Balance: -2.0 to 2.0 mm), and flexion (Med lax: -2.0 to 3.5 mm, Lat lax: -2.0 to 1.5 mm, Balance: -3.0 to 3.0 mm). When all windows were satisfied, the greatest difference in KOOS pain score was observed (100.0 vs 94.4, p < 0.0001). The highest percentage of knees satisfying the Patient Acceptable Symptom State (PASS) for KOOS pain was also observed in knees which satisfied all windows compared to knees which did not (93% vs 71%, p = 0.0009). The proportion of knees which satisfy the PASS threshold decreased in knees which only satisfied 1-3 (29%) or 4-6 (69%) windows (p ≤ 0.0018). No optimal windows were found between component alignment and KOOS pain outcome (p ≥ 0.1180). High satisfaction was found across all groups (≥ 95%).

CONCLUSION

Intra-operatively measured joint gaps are associated with all KOOS sub-score outcomes at 2 years after TKA. Optimal windows for a clinically relevant improvement in post-operative KOOS pain were defined for laxity and balance but not for alignment indicating balance may have a greater impact on outcome than alignment.

LEVEL OF EVIDENCE

II.

Functional alignment in total knee arthroplasty best achieves balanced gaps and minimal bone resections: an analysis comparing mechanical, kinematic and functional alignment strategies

PURPOSE

Key concepts in total knee arthroplasty include restoration of limb alignment and soft-tissue balance. Although differences in balance have been reported amongst mechanical alignment (MA), kinematic alignment (KA) and functional alignment (FA) techniques, it remains unclear whether there are differences in gap imbalance or resection thicknesses when comparing different constitutional alignment subgroups.

METHODS

MA (measured resection technique), KA (matched resections technique) and FA (technique based on the restricted KA boundaries) were compared in 116 consecutive patients undergoing 137 robotic-assisted cruciate-retaining total knee arthroplasties. The primary outcome was the proportion of balanced gaps (differential laxities ≤ 2 mm) for extension, flexion, medial and lateral gap measurements. Manual pre-resection laxity measurements were obtained for MA and KA and manual post-resection measurements were obtained for FA in 10° and in 90° of knee flexion. Secondary outcomes were resection depths and implant alignment. All outcomes were analysed per constitutional coronal alignment and joint line obliquity subgroups.

RESULTS

The proportions of balance in all four gap measurements were 54.7%, 66.4% and 96.5%, with MA, KA and FA, respectively. Across all constitutional alignment types, FA achieved the highest proportion of balance. MA resected the least amount of bone from the medial tibial plateau. KA had femoral components in most valgus and most internally rotated, tibial components in most varus and was the most bone-preserving for the posteromedial femoral condyle. FA had the most externally rotated femoral components and was most bone-preserving for the distal femoral resections.

CONCLUSION

The study shows that implant alignment to the mechanical axis or joint line anatomy (equal resections) alone does not guarantee a balanced total knee arthroplasty. FA resulted in the highest proportion of balanced knees across all analysed subgroups. Future research will consider whether one alignment philosophy leads to superior outcomes for different constitutional alignment subgroups.

LEVEL OF EVIDENCE

Level II.

High degree of alignment precision associated with total knee arthroplasty performed using a surgical robot or handheld navigation

PURPOSE

The purpose of this study was to compare the precision of bony resections during total knee arthroplasty (TKA) performed using different computer-assisted technologies.

METHODS

Patients who underwent a primary TKA using an imageless accelerometer-based handheld navigation system (KneeAlign2®, OrthAlign Inc.) or computed tomography-based large-console surgical robot (Mako®, Stryker Corp.) from 2017 to 2020 were retrospectively reviewed. Templated alignment targets and demographic data were collected. Coronal plane alignment of the femoral and tibial components and tibial slope were measured on postoperative radiographs. Patients with excessive flexion or rotation preventing accurate measurement were excluded.

RESULTS

A total of 240 patients who underwent TKA using either a handheld (n = 120) or robotic (n = 120) system were included. There were no statistically significant differences in age, sex, and BMI between groups. A small but statistically significant difference in the precision of the distal femoral resection was observed between the handheld and robotic cohorts (1.5° vs. 1.1° difference between templated and measured alignments, p = 0.024), though this is likely clinically insignificant. There were no significant differences in the precision of the tibial resection between the handheld and robotic groups (coronal plane 0.9° vs. 1.0°, n.s.; sagittal plane 1.2° vs. 1.1°, n.s.). There were no significant differences in the rate of overall precision between cohorts (n.s.).

CONCLUSIONS

A high degree of component alignment precision was observed for both imageless handheld navigation and CT-based robotic cohorts. Surgeons considering options for computer-assisted TKA should take other important factors, including surgical principles, templating software, ligament balancing, intraoperative adjustability, equipment logistics, and cost, into account.

LEVEL OF EVIDENCE

III.

SMART (self- monitoring analysis and reporting technology) and sensor based technology applications in trauma and orthopaedic surgery

Background

Innovations in implant designs and computer technology have led to the development of smart implants and prostheses in the field of orthopedics and trauma. Sensor-guided devices enable close monitoring of physical, chemical and biological environment around the implants, which has been purported to meliorate the intra-operative precision and post-operative surveillance of patients.

Objective

We evaluate the current applications of sensor-based technology in the management of patients with a spectrum of musculoskeletal conditions.

Material and methods

A thorough search of literature was performed on May 1, 2023, using the 5 databases (Embase, PubMed, Google Scholar, Cochrane Library and Web of Science) in order to identify suitable studies published between 2000 and 2023. All the studies which reported on SMART implants and Sensor based technology in the diverse sub-specialties of orthopedics like trauma, arthroplasty, spine surgery, infections, arthroscopy or sports medicine and paediatric orthopedics were considered. The keywords used for the search included 'Sensor technology', 'SMART implant' and "Orthopedics".

Results

Thirty articles were considered for this narrative review. A generation of SMART implants has been developed due to advancements in the microchip technology. Sensor based technology has been utilised in various subspecialties of arthroplasty (in assessing ligament balancing intra-operatively; or prosthetic loosening and gait analysis during follow-up), trauma surgery (as SMART instruments intra-operatively; or in the assessment of bone healing, distraction osteogenesis and functional recovery during follow-up), spine surgery (identification and protection of neural elements from iatrogenic injuries intra-operatively; and assessment of fusion across the instrumented levels during follow-up), paediatric orthopedics (compliance assessment for foot abduction orthosis in congenital talipes equinovarus), infection (monitoring of infection and biofilm formation), rehabilitation (gait analysis) and sports medicine (rotational stability and ligament compliance in patients with ligament injuries or reconstruction).

Conclusion

SMART implants and Sensor based technology have applications in the surgical planning, intra-operative performance, post-operative monitoring and patient surveillance diverse subspecialties of orthopedics and trauma. Future research in newer designs, cost-effective SMART implants and refinement of Sensor based technology will enhance Patient Related Outcome Measures (PROMs).

Laxity, Balance, and Alignment of a Simulated Kinematic Alignment Total Knee Arthroplasty

Background

Kinematic alignment (KA) and related personalized alignment strategies in total knee arthroplasty (TKA) target restoration of native joint line obliquity and alignment. In practice, deviations from exact restoration of the prearthritic joint surface are tolerated for either the femur or tibia to achieve ligamentous balance. It remains unknown what laxity, balance, and alignment would result if a pure resurfacing of both femur and tibia were performed in a KA TKA technique.

Methods

We used data from 382 robot-assisted TKA performed with a digital joint tensioner to simulate TKA with a pure resurfacing KA technique for both femur and tibia. All knees had the posterior cruciate ligament retained. Knees were subdivided into 4 groups based on preoperative coronal alignment: valgus, neutral, varus, and high varus. Medial and lateral laxity in extension and flexion, balance in extension and flexion, and coronal plane alignment were compared between groups using analysis of variance testing.

Results

In simulated pure resurfacing KA TKA across a range of preoperative coronal plane deformities, only 11%-31% of knees would have mediolateral extension ligament balance within ±1 mm, and 20%-41% would have a medial flexion gap that is looser than the lateral flexion gap. Over 45% of knees would have coronal hip-knee-ankle angle >3 degrees from mechanical neutral.

Conclusions

In simulations of pure resurfacing KA TKA, there was wide variability in the resulting laxity and alignment outcomes. Most knees had alignment and balance outcomes outside of normally accepted ranges. Techniques that deviate from pure resurfacing in order to achieve balance appear favorable.

Medial Varus Proximal Tibial Resection is Superior to Pie-Crusting of the Medial Collateral Ligament During Primary Total Knee Arthroplasty

BACKGROUND

Medial varus proximal tibial (MPT) resection or soft tissue releases (STR) of the medial collateral ligament (MCL) in form of pie-crusting can be performed to achieve a balanced knee in a varus deformity. Studies comparing the two modalities have not been addressed within the literature. Therefore, the aims of this study were to assess: 1) compartmental changes between the two methods; and 2) changes in patient-reported outcome measurements (PROMs).

METHODS

Using our institution's total joint arthroplasty registry, patients who underwent primary total knee arthroplasty from January 1, 2017 to December 31, 2019 were identified. The MPT resection and STR patients were 1:1 matched with baseline parameters yielding 196 patients. Outcomes of interest included: changes in compartmental pressures at 10, 45, and 90° degrees and change to the Short-Form 12 (SF-12), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Forgotten Joint Scores (FJS) at the two-year follow-up period. A P-value less than 0.05 was used as our threshold for statistical difference.

RESULTS

The MPT resection led to significant reductions in compartmental pressures at 10° [43 vs 19 pounds (lbs.), P<0.0001), 45° (43 vs 27 lbs., P<0.0001), and 90° degrees (27 vs. 16 lbs., P<0.0001) compared to STR. MPT resection also had significantly improved SF-12 (47 vs. 38, P<0.0001), WOMAC (9 vs. 21, P<0.0001), and FJS (79 vs. 68, P=0.005).

CONCLUSION

Bone modification was superior to pie-crusting of the MCL in achieving consistent pressure balancing and improved outcomes. The investigation can guide surgeons on the preferred method to achieve a well-balanced knee.

Collateral Ligament Tension and Balance Alone Does Not Ensure Improved Outcome after Total Knee Arthroplasty

BACKGROUND

It is hypothesized that suboptimal soft tissue and collateral ligament balance is a cause of patient dissatisfaction following total knee arthroplasty (TKA). This analysis examined the association between compartment pressures during TKA and patient reported outcome measurements (PROMs).

METHODS

This single-institution, retrospective cohort study of prospectively collected compartment pressure data measured during TKA comprised 145 patients who underwent surgery between 2015 and 2021 and completed 1-year follow-up PROMs. The primary outcome included pressures, in pounds (lbs), of the medial and lateral compartments in extension (5°), mid-flexion (45°), and flexion (90°), and associated PROMs. The difference been the 1-year and pre-operative PROMs was used to separate the top 25% from the bottom 75% performers. Pressures were compared using Student's T-tests and multivariate linear regressions, while controlling for preoperative deformity. A subgroup analysis of the most popular implant was performed.

RESULTS

Higher medial compartment pressures were seen in our total cohort (Knee Society Score (KSS) mid-flexion 24 vs 18lbs, P=.03, flexion 24 vs 17lbs p=.01) and within our subgroup analysis (Short form- Mental (SF-M) extension 32 vs 21lbs P=0.01, KSS mid-flexion 27 vs 16lbs P=.005, extension 31 vs 20lbs P=.003). This trend persisted in the subgroup analysis when controlling for pre-operative deformity (KSS extension +16.22lbs P=<.001, mid-flexion +17.6lbs. P=.001, and flexion +9.2lbs, P=.005).

CONCLUSION

Several groups demonstrated higher medial versus lateral pressures. However, this pattern was not consistent across PROMs, suggesting that compartment pressures at the time of TKA are an important factor, but not the sole predictor of patient satisfaction.

What is the Value of a Balanced Total Knee Arthroplasty? Getting it Right the First Time

INTRODUCTION

Instability is a leading cause of early failure following total knee arthroplasty. Enabling technologies can improve accuracy, but their clinical value remains undetermined. The purpose of this study was to determine the value of achieving a balanced knee joint at the time of TKA.

METHODS

A Markov model was developed to determine the value from reduced revisions and improved outcomes associated with TKA joint balance. Patients were modelled for the first 5 years following TKA. The threshold to determine cost-effectiveness was set at an Incremental Cost Effectiveness Ratio (ICER) of $50,000/quality-adjusted life year (QALY). A sensitivity analysis was performed to evaluate the influence of QALY improvement (ΔQALY) and Revision Rate Reduction (ΔRevision) on additional value generated compared to a conventional TKA cohort. The impact of each variable was evaluated by iterating over a range of ΔQALY (0 to 0.046) and ΔRevision (0 to 30%) and calculating the value generated while satisfying the ICER threshold. Finally, the impact of surgeon volume on these outcomes were analyzed.

RESULTS

The total value of a balanced knee for the first 5 years was $8,750, $6,575, and $4,417 per case, for low, medium, and high-volume surgeons, respectively. Change in QALY accounted for greater than 90% of the value gain with a reduction in revisions making up the rest in all scenarios. The economic contribution of revision reduction was relatively constant regardless of surgeon volume ($500/case).

CONCLUSIONS

Achieving a balanced knee had the greatest impact on QALY improvement over early revision rate. These results can help assign value to enabling technologies with joint balancing capabilities.

Verasense sensor-assisted total knee arthroplasty showed no difference in range of motion, reoperation rate or functional outcomes when compared to manually balanced total knee arthroplasty: a systematic review

PURPOSE

The aim of this systematic review was to investigate the clinical and functional knee outcomes after Verasense sensor-assisted total knee arthroplasty (VA TKA), and to compare these outcomes, where possible, with those from manually balanced total knee arthroplasty (MB TKA).

METHODS

A systematic literature search following PRISMA guidelines was conducted on PubMed, Embase, Medline and Scopus from the beginning of January 2012 until the end of June 2022, to identify potentially relevant articles for this review. Selection was based on the following inclusion criteria: full text English- or German-language clinical studies, published in peer-reviewed journals, which assessed clinical and functional outcomes following VA TKA. Not original research, preprints, abstract-only papers, protocols, reviews, expert opinion papers, book chapters, surgical technique papers, and studies pertaining only to unicondylar knee arthroplasty (UKA) or patellofemoral arthroplasty (PFA) were excluded. Several scores (Knee Society Score [KSS], Oxford Knee Score [OKS], Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC], Knee injury and Osteoarthritis Outcome Score-4 subscales [KOOS4] and Physical Function-Computerised Adaptive Testing [PF-CAT]), alongside postoperative measurements of range of motion [ROM], reoperation rates and the rate of manipulation under anaesthesia [MUA]) were used to evaluate clinical and functional outcomes. The quality of included papers, except randomised control trials (RCTs), was evaluated using the Methodological Index for Non-Randomised Studies (MINORS). For the assessment of included RCTs, the Jadad Scale was used.

RESULTS

The literature search identified 243 articles. After removing duplicates, 184 papers were included in the initial screening process. Fourteen of them met all the inclusion criteria following the selection process. Mean MINORS for non-comparative studies value was 11.5 (11-12), and for comparative studies 18.2 (13-21). Mean Jadad Scale score was 3.6 (2-5). Outcomes from a total number of 3633 patients were evaluated (mean age at surgery 68.5 years [32-88 years]). In terms of clinical outcomes, the overwhelming majority of studies observed an improvement after VA TKA, but no statistically significant difference in ROM and reoperation rate when compared to MB TKA. On the other hand, lower rates of MUA have been described in the VA TKA group. An increase in postoperative clinical and functional scores values, when compared to the preoperative ones, has been reported in both groups, although no statistically significant difference between them has been observed.

CONCLUSION

The use of Verasense pressure sensors in TKA leads to no significant improvement in ROM, reoperation rate or functional outcomes, when compared to the standard manually balancing technique. However, lower rates of MUA have been described in the VA TKA group. These findings highlight the importance of tools being able to measure ligament stresses or joint pressure for achieving an optimally balanced knee.

LEVEL OF EVIDENCE

III.

How does the use of quantified gap-balancing affect component positioning and limb alignment in robotic total knee arthroplasty using functional alignment philosophy? A comparison of two robotic platforms

PURPOSE

This study aimed to compare the effect of an image-based (MAKO) system using a gap-balancing technique with an imageless (OMNIbot) robotic tool utilising a femur-first measured resection technique.

METHODS

A retrospective cohort study was performed on patients undergoing primary TKA with a functional alignment philosophy performed by a single surgeon using either the MAKO or OMNIbot robotic systems. In all cases, the surgeon's goal was to create a balanced knee and correct sagittal deformity (eliminate any fixed flexion deformity). Intra-operative data and patient-reported outcomes (PROMS) were compared.

RESULTS

A total of 207 MAKO TKA and 298 OMNIbot TKAs were analysed. MAKO TKA patients were younger (67 vs 69, p=0.002) than OMNIbot patients. There were no other demographic or pre-operative alignment differences. Regarding implant positioning, in MAKO TKAs the femoral component was more externally rotated in relation to the posterior condylar axis (2.3° vs 0.1°, p<0.001), had less valgus femoral cuts (1.6° vs 2.7° valgus, p<0.001) and more varus tibial cuts (2.4° vs 1.9° varus, p<0.001), and had more bone resected compared to OMNIbot TKAs. OMNIbot cases were more likely to require tibial re-cuts than MAKO (15% vs 2%, p<0.001). There were no differences in femur recut rates, soft tissue releases, or rate of achieving target coronal and sagittal leg alignment between robotic systems. A subgroup analysis of 100 MAKO and 100 OMNIbot propensity-matched TKAs with 12-month follow-up showed no significant difference in OKS (42 vs 43, p=0.7) or OKS PASS scores (83% vs 91%, p=0.1). MAKO TKAs reported significantly better symptoms according to their KOOS symptoms score than patients that had OMNIbot TKAs (87 vs 82, p=0.02) with a higher proportion of KOOS PASS rates, at a slightly longer follow-up time (20 months vs 14 months, p<0.001). There were no other differences in PROMS.

CONCLUSION

A gap-balanced technique with an image-based robotic system (MAKO) results in different implant positioning and bone resection and reduces tibial recuts compared to a femur-first measured resection technique with an imageless robotic system (OMNIbot). Both systems achieve equal coronal and sagittal deformity correction and good patient outcomes at short-term follow-ups irrespective of these differences.

Achieving functional alignment in total knee arthroplasty: early experience using a second-generation imageless semi-autonomous handheld robotic sculpting system

PURPOSE

In order to minimize errors during achieving the targeted alignment of the total knee arthroplasty (TKA) components, robotic-assisted surgery has been introduced with the aim to help surgeons to improve implant survival, clinical outcomes, and patient satisfaction. The primary goal of this paper is to highlight surgical tips and tricks on how to achieve functional alignment (FA) through intra-operative boney mapping, numeric gap, and alignment data, using the next generation of imageless robotic surgical systems.

METHOD

This retrospective case-series contains planned and achieved data on the FA and joint gap data obtained from 526 patients captured and assessed with use of a semi-autonomous imageless handheld robotic sculpting systems. All patients were operated upon by two experienced TKA surgeons.

RESULTS

The mean difference between planned and achieved alignment was 1.46° (≥ 7° varus group), 1.02° (< 7° varus group), 1.16° (< 7° valgus group), and 1.43° (≥ 7° valgus group). The mean observed planned and achieved extension and flexion gaps were below 1.47 mm for medial extension gaps, 1.12 mm for the lateral extension gaps, 1.4 mm for the medial flexion gaps, and 1.16 mm for the lateral flexion gaps.

CONCLUSION

Analysis of these first cases highlights the capability of the next generation of imageless robotic-assisted total knee replacement using a semi-autonomous handheld robotic sculpting to maintain accuracy of the desired alignment. The system allows the surgeon to choose freely their own alignment philosophy while maintaining efficiency.

Variation in knee balance as a function of hip-knee-ankle angle and joint line obliquity in robotic assisted total knee arthroplasty

PURPOSE

To describe the mediolateral (ML) gap balance in pre-resection arthritic knees undergoing robot-assisted (RA) total knee arthroplasty (TKA) within the nine phenotypes of the Coronal Plane Alignment of the Knee (CPAK) classification.

METHODS

A total of 1124 RA TKA cases were retrospectively reviewed. ML balance was calculated using a digital ligament tensioning device following tibial resection and prior to any femoral resection throughout flexion (10°, 40°, and 90°). Lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were landmarked intra-operatively and adjusted for wear based on hip-knee-ankle angle (HKA). Knees were then subdivided into CPAK categories based on the arithmetic HKA (aHKA) and joint line obliquity (JLO). Differences in balance between CPAK phenotypes were compared.

RESULTS

For aHKA, a greater medial gap was observed in varus compared to neutral or valgus knees at 10° (5.2 ± 3.0 mm vs 3.3 ± 3.2 mm vs - 0.4 ± 5.0 mm respectively; p < 0.0001). A similar trend was observed for JLO in distal apex compared to neutral and proximal apex knees at 10° (3.4 ± 3.6 vs 1.1 ± 5.0 vs - 2.4 ± 6.3 respectively; p < 0.0001). The greatest ML balance differences were found when combining JLO and aHKA at 10° (type I vs type VI: ∆6.6 mm; p < 0.0001).

CONCLUSION

There is a high degree of variability in arthritic ML balance within and between each CPAK phenotype. A single alignment philosophy based on bony landmarks alone may not be sufficient to balance all knees. Utilisation of robotics and digital ligament tensioning devices serves as important adjuncts to characterize the patient-specific soft tissue profile.

Functional Alignment Philosophy in Total Knee Arthroplasty-Rationale and Technique for the Valgus Morphotype Using an Image Based Robotic Platform and Individualized Planning

Functional alignment (FA) is a novel philosophy to deliver a total knee arthroplasty (TKA) that respects individual bony and soft tissue phenotypes within defined limitations. The purpose of this paper is to describe the rationale and technique of FA in the valgus morphotype with the use of an image-based robotic-platform. For the valgus phenotype the principles are personalized pre-operative planning, reconstitution of native coronal alignment without residual varus or valgus of more than 3°, restoration of dynamic sagittal alignment within 5° of neutral, implant sizing to match anatomy, and achievement of defined soft tissue laxity in extension and flexion through implant manipulation within the defined boundaries. An individualized plan is created from pre-operative imaging. Next, a reproducible and quantifiable assessment of soft tissue laxity is performed in extension and flexion. Implant positioning is then manipulated in all three planes if necessary to achieve target gap measurements and a final limb position within a defined coronal and sagittal range. FA is a novel TKA technique that aims to restore constitutional bony alignment and balance the laxity of the soft tissues by placing and sizing implants in a manner that respects variations in individual anatomy and soft tissues within defined limits.

Extra-articular factors of the femur and tibia affecting knee balance in mechanically aligned total knee arthroplasty

PURPOSE

Although the joint gap distance and compartment loading of the knee are different parameters for obtaining balanced knees in patients with total knee arthroplasty (TKA), the extent to which a balanced knee is achieved in patients with mechanically aligned TKA (MA-TKA) is unclear. This study aimed to investigate the anatomical factors that affect the ligament balancing in MA-TKA according to a gap balancing technique by measured resection technique.

METHODS

The relationship between compartment loading, gap distance, and lower limb alignment was analysed in forty-three patients who underwent navigation-assisted MA-TKA with the minimum soft-tissue release. Radiographic parameters included hip-knee-ankle (HKA) angle, femorotibial angle, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle, posterior tibial slope, varus and valgus joint line convergence angle, femoral valgus angle, femoral shaft curve, and tibial shaft curve (TSC).

RESULTS

The postoperative HKA angle was 0.4±1.5°, with one coronal alignment outlier (2.3%). The gap distance showed four unbalanced knees for extension (9.3%) and flexion (9.3%), whereas the compartment loading identified 17 unbalanced knees (39.5%) at extension, 8 (18.6%) at 45° flexion, 7 (16.2%) at 90° flexion, and 10 (23.2%) at full flexion in MA-TKA. Mediolateral differentials of compartment loading correlated with femoral valgus angle (0°, 45°, and 90° flexion), mLDFA (45° and 90° flexion), and TSC (45° and 90° flexion). Femoral valgus angle and TSC were risk factors of the mediolateral differentials of compartment loading.

CONCLUSION

Extra-articular factors of femoral valgus angle, mLDFA, and TSC were associated with the mediolateral imbalance of compartmental loading, suggesting there is a limit to obtaining balanced knees in MA-TKA due to these unadjustable extra-articular factors.

LEVEL OF EVIDENCE

IV, therapeutic case series.

Impact of a Digital Balancing Tool on Femur and Tibial First Total Knee Arthroplasty: A Prospective Nonrandomized Controlled Trial

Background

Recent developments in intra-operative sensor technology provide surgeons with predictive and real-time feedback on joint balance. It remains unknown, however, whether these technologies are better suited to femur-first or tibia-first workflows. This study investigates the balance accuracy, precision and early patient outcomes between the femur-first and tibial-first workflows using a digital gap-balancing tool.

Methods

One-hundred six patients had posterior cruciate ligament sacrificing total knee arthroplasty using a digital joint tensioner. The participants were divided into 4 groups with different visibility to balance data 1) Femur-first blinded data, 2) Femur-first not blinded data, 3) Tibia-first blinded data, 4) Tibia-first not blinded data with predictive balancing. Knee Injury and Osteoarthritis Outcome Score and University of California at Los Angeles activity level were recorded at 1-year.

Results

Group 4 reported less midflexion imbalance (40°) compared to all other groups (1: 1.5 mm, 2: 1.7 mm, 3: 1.6 mm, 4: 1.0 mm, P < .031) and reduced variance compared to all other groups at 40° and 90° (P < .012), resulting in an increased frequency of joints balanced within 2 mm throughout flexion in group 4 (1: 69%, 2: 65%, 3: 67%, 4: 91%, P < .006). No differences were found between 3-month, 6-month, or 1-year outcome scores between technique.

Conclusions

Improvements in balance were observed in midflexion instability and balance variability throughout flexion when a tibia-first approach in combination with a digital balancing tool was used. The combination of a digital balancing tool and a tibia-first approach allowed a target joint balance to be achieved more accurately compared to a non-sensor augmented or femur-first approach.

Impact of Component Alignment and Soft Tissue Release on 2-Year Outcomes in Total Knee Arthroplasty

BACKGROUND

The objective of this study was to investigate the impact of alignment and soft tissue release on patient outcomes following total knee arthroplasty (TKA).

METHODS

In a multicenter study, soft tissue releases during TKA were prospectively documented in 330 robotic-assisted TKAs. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were captured postoperatively. Delphi analysis was used to determine inlier and outlier component alignment boundaries: Tibia Coronal (TC): ±3°, Femur Coronal (FC): ±3°, Femoral Axial (FA): 3°Int-6°Ext, Hip-Knee-Ankle (HKA): 3°Val-4°Var, and Tibiofemoral Axial (TFA): 3°Int-6°Ext. Kruskal-Wallis analysis of variance tests were used to compare groups.

RESULTS

No significant differences were found between any individual or grouped inlier and outlier alignment criterion and KOOS at any timepoint. Outlier alignment frequencies were: TC: 0%, FC: 12%, FA: 8%, HKA: 9%, TFA: 8%, and Any: 23%. Soft tissue releases were performed in 18% of cases. Knees with soft tissue releases reported significantly worse KOOS scores at: 6M: Symptoms (80.0 versus 75.3, P = .03), activities of daily living (ADL) (86.2 versus 80.8, P = .030), quality of life (70.1 versus 60.9, P = .008), 12M ADL (90.0 versus 85.1, P = .023), and 24M ADL (91.9 versus 87.2, P = .016). A higher proportion of patients achieved Minimal Clinically Important Difference for pain at 6 months for those having no releases versus released (92.3% versus 81.0%, P = .021). No significant associations were found between preoperative deformity and preoperative or postoperative KOOS.

CONCLUSION

The addition of soft tissue releases after bony cuts is associated with worse KOOS scores out to 2 years and was more prevalent in knees with worse deformity, while no such association was found for alignment.

Functional alignment achieves a more balanced total knee arthroplasty than either mechanical alignment or kinematic alignment prior to soft tissue releases

PURPOSE

Total knee arthroplasty with functional alignment uses pre-resection balancing to determine component position within the soft tissue envelope to achieve balance and restoration of native joint obliquity. The purpose of this study was to assess the balance achievable with a mechanical axis alignment and kinematic axis alignment plan, and the subsequent balance achievable after adjustment of the component position to functional alignment.

METHODS

A prospective cohort of 300 knees undergoing cruciate retaining total knee arthroplasty were included in this study. Of these, 130 were initially planned with mechanical alignment (MA) and 170 with kinematic alignment (KA). Maximal stressed virtual gaps were collected using an optical tracking software system. The gaps were measured medially and laterally in flexion and extension. Following assessment of balance, implant position was adjusted to balance the soft tissues in functional alignment (FA) and the maximal gaps reassessed. Gaps were considered to be balanced when within 2 mm of equality. Incidence of balance within each cohort was compared to independent samples proportions test.

RESULTS

Functional alignment obtained significantly better balance in extension, medially and overall than both MA and KA alignment without soft tissue release (p < 0.001). Overall balance was observed in 97% of FA knees, 73% of KA knees and in 55% of MA knees. The difference between KA and MA was also significant (p = 0.002). Whilst there was no difference observed in balanced achieved or limb alignment when FA was planned with either MA or KA, the joint line obliquity was maintained with an initial KA plan.

CONCLUSION

Functional alignment more consistently achieves a balanced total knee arthroplasty than either mechanical alignment or kinematic alignment prior to undertaking soft tissue release. Utilising an individualised KA plan allows FA to best achieve the stated goals of maintaining joint line plane and obliquity.

LEVEL OF EVIDENCE

Level III: retrospective cohort study.

Restricted kinematic alignment achieves similar relative lateral laxity and greater joint line obliquity compared to gap balancing TKA

PURPOSE

The purpose of this study was to compare ligament balance and laxity profiles achieved throughout flexion in restricted kinematic alignment (rKA) and gap balancing (GB). rKA and GB both aim to improve soft tissue balance and reduce ligament releases in total knee arthroplasty (TKA).

METHODS

One surgeon performed 68 rKA, another performed 73 GB TKAs using the same CR implant and robotic system. rKA limited femoral valgus and tibial varus to 6°, with tibial recuts performed to achieve balance. GB limited tibial varus and femoral valgus to 2°, with femoral resections adjusted to achieve mediolateral balance throughout flexion using predictive-gap planning software. Final joint laxity was measured using a robotic ligament tensioner. Statistical analyses were performed to compare differences in mediolateral balance and joint laxity throughout flexion. Further analyses compared alignment, joint line elevation and orientation (JLO), and frequency of ligament releases and bone recuts.

RESULTS

Both techniques reported greater lateral laxity throughout flexion, with GB reporting improved mediolateral balance from 10° to 45° flexion. GB resected 1.7 mm more distal femur (p ≤ 0.001) and had greater overall laxity than rKA throughout flexion (p ≤ 0.01). rKA increased JLO by 2.5° and 3° on the femur and tibia (p ≤ 0.001). Pre-operative and post-operative coronal alignment were similar across both techniques. rKA had a higher tibial recut rate: 26.5% vs 1.4%, p < 0.001.

CONCLUSIONS

rKA and GB both report lateral laxity but with different JLO and elevation. Use of a predictive-gap GB workflow resulted in greater mediolateral gap symmetry with fewer recuts.

LEVEL OF EVIDENCE

III, retrospective cohort study.

Arthritic knees with more than 10° valgus can have soft-tissue imbalance in flexion

PURPOSE

Valgus knees have inferior outcomes compared to varus knees. There is little data regarding soft-tissue balance in flexion which may influence outcome in valgus knees undergoing TKA. The purpose of this study was to evaluate whether there is imbalance between medial and lateral flexion gaps in valgus deformity. A secondary aim was to compare soft-tissue balance in knees with valgus deformity less than 10° with those exceeding 10°. The null hypothesis was that there was no soft-tissue imbalance in 90° of flexion irrespective of magnitude of deformity.

METHODS

64 valgus knees (52 female and 12 male) with deformity from 0.5 to 27.5° (mean 188.77, SD 6.21) were studied in 54 patients (mean age 67.81 y, SD 8.69) undergoing navigated TKA. Medial and lateral gaps in extension and at 90° of flexion were compared (using Independent-samples t test) between knees with valgus < 10° with those > 10° using a validated dynamic method after resection of cruciates, menisci and osteophytes, and then after final trialling.

RESULTS

Mean initial medial-lateral (ML) gap difference in extension was 2.63 mm (SD 2.63) and 2.09 mm (SD 3.78) in flexion, being tighter laterally. Initial ML gap differences in extension and flexion correlated with valgus deformity (R =  - 0.514; p = 0.00001; R =  - 0.325; p = 0.01, respectively). Initial ML gap differences in extension correlated with those in flexion (R = 0.42; p = 0.0005). Mean ML flexion and extension gap differences were 1.30 mm (SD 3.67) and 1.26 mm (SD 1.92) in knees with < 10° valgus, and 3.17 mm (SD 3.71) and 4.29 mm (SD 2.45) in those > 10° valgus; p values were 0.026 and < 0.001 respectively.

CONCLUSION

The lateral flexion gap in valgus knees may be narrower than the medial flexion gap, especially in knees with > 10° deformity. This contrasts with native and varus knees, in which it exceeds the medial gap. This novel study indicates the need to identify valgus knees with lateral flexion gap tightness by distracting the posterior femoral condyles from the proximal tibia by dynamic stressing of the soft-tissues after resection of cruciates, menisci, and osteophytes, with the knee flexed to 90°. These findings, highlighting the need for restoring flexion gap balance, may improve the inferior outcomes in valgus knees.

LEVEL OF EVIDENCE

IV.

Kinematic alignment fails to achieve balancing in 50% of varus knees and resects more bone compared to functional alignment

PURPOSE

Evidence is emerging that tibio-femoral compartmental balancing is related to clinical outcomes after total knee arthroplasty (TKA). The purpose of this study was to assess if kinematic alignment (KA) delivered a balanced knee in flexion and extension after TKA on varus deformity, compared to functional alignment (FA).

METHODS

This single-centre retrospective cohort study assessed 110 consecutive TKAs performed with an image-based robotic system for pre-operative varus deformity. The ligament balancing in the medial and lateral femorotibial compartments was assessed intra-operatively with a robotic system to evaluate if a KA plan would deliver a balanced knee. Balance was considered achieved if tibio-femoral compartments (medial/lateral) were equal to or less than 1.5 mm, or if the estimated final gap position more than 2 mm from the global implant thickness (17 mm). Implant positioning was modified within limits previously defined for a FA philosophy to achieve balancing. Resection thickness and implant positioning were compared with the KA plan and after the FA adjustments; and also, between the patients with a final balanced knee in extension and at 90° of flexion.

RESULTS

A total of 102 patients were eligible for final analysis. Mean age was 67.3 ± 8.2 years, average BMI was 29.1 ± 5.2 kg/m², mean pre-operative coronal alignment was 174.0° ± 3.3° and sagittal alignment 3.4° ± 5.9°. Mean post-operative coronal alignment was 177.7° ± 1.0° and sagittal alignment 0.8° ± 1.9°. A KA plan delivered medial-lateral tibio-femoral compartment balancing in 67 cases (65.7%) for the extension gap and in 50 cases (49.1%) for the flexion gap. All measured bone resection depths were significantly less for FA compared to KA. To achieve balancing targets, final femoral component position was more externally rotated relative to the posterior condylar axis, (0.5° with KA compared to 1.7° with FA (p < 0.0001), and the tibia in more varus (3.0° KA vs. 3.5° FA p = 0.0024). Only one soft tissue release was required.

CONCLUSION

KA failed to deliver a balanced TKA in more than 50% of cases, especially regarding the flexion gap. Consideration of soft tissue laxity led to significantly less bone resection, with more externally rotated femoral component and more varus tibial component.

Combining load sensor and robotic technologies for ligament balance in total knee arthroplasty

Good ligament balance in total knee arthroplasty (TKA) is thought to improve clinical results, but is highly surgeon-dependent when performed without technological assistance. We therefore describe a TKA technique using the Mako robotic arm (Stryker, Kalamazoo, Michigan, USA) as sole means of balancing ligament tension by bone recuts associated to control by the VERASENSE load sensor (Orthosensor, Inc, Dania Beach, Florida, USA). In this preliminary series of 29 patients, 27 (93%) showed a well-balanced knee in extension at end of procedure, and 23 (79%) showed a well-balanced knee in flexion and extension, without any periarticular soft-tissue release. The load sensor analyzes ligament balance after the initial bone cuts, and guides possible further femoral or tibial recuts. This technique enables quantifiable alignment and control of ligament tension. Collecting objective intraoperative data should improve knowledge in placing TKA prostheses.

Predictive Gap-balancing Reduces the Extent of Soft-tissue Adjustment Required After Bony Resection in Robot-assisted Total Knee Arthroplasty-A Comparison With Simulated Measured Resection

Background

To understand the extent and frequency of soft-tissue adjustment required to achieve mediolateral (ML) balance in measured resection (MR) vs gap-balancing (GB) total knee arthroplasty, this study compared ML balance and joint laxity throughout flexion between the 2 techniques. The precision of predictive GB in achieving ML balance and laxity was also assessed.

Methods

Two surgeons performed 95 robot-assisted GB total knee arthroplasties with predictive balancing, limiting tibial varus to 3° and adjusting femoral positioning to optimize balance. A robotic ligament tensioner measured joint laxity. Planned MR (pMR) was simulated by applying neutral tibial and femoral coronal resections and 3° of external femoral rotation. ML balance, laxity, component alignment, and resection depths were compared between planned GB (pGB) and pMR. ML balance and laxity were compared between pGB and final GB (fGB).

Results

The proportion of knees with >2 mm of ML imbalance in flexion or extension ranged from 3% to 18% for pGB vs 50% to 53% for pMR (P < .001). Rates of ML imbalance >3 mm ranged from 0% to 9% for pGB and 30% to 38% for MR (P < .001). The mean pMR laxity was 1.9 mm tighter medially and 1.1 mm tighter laterally than pGB throughout flexion. The mean fGB laxity was greater than the mean pGB laxity by 0.5 mm medially and 1.2 mm laterally (P < .001).

Conclusion

MR led to tighter joints than GB, with ML gap imbalances >3 mm in 30% of knees. GB planning improved ML balance throughout flexion but increased femoral posterior rotation variability and bone resection compared to MR. fGB laxity was likely not clinically significantly different than pGB.

No Benefit to Sensor-guided Balancing Compared With Freehand Balancing in TKA: A Randomized Controlled Trial

BACKGROUND

Soft tissue balancing in TKA has traditionally relied on surgeons' subjective tactile feedback. Although sensor-guided balancing devices have been proposed to provide more objective feedback, it is unclear whether their use improves patient outcomes.

QUESTIONS/PURPOSES

We conducted a randomized controlled trial (RCT) comparing freehand balancing with the use of a sensor-guided balancing device and evaluated (1) knee ROM, (2) patient-reported outcome measures (PROMs) (SF-12, WOMAC, and Knee Society Functional Scores [KSFS]), and (3) various surgical and hospital parameters (such as operative time, length of stay [LOS], and surgical complications) at a minimum of 2 years of follow-up.

METHODS

A total of 152 patients scheduled for primary TKA were recruited and provided informed consent to participate in this this study. Of these, 22 patients were excluded preoperatively, intraoperatively, or postoperatively due to patient request, surgery cancellation, anatomical exclusion criteria determined during surgery, technical issues with the sensor device, or loss to follow-up. After the minimum 2-year follow-up was accounted for, there were 63 sensor-guided and 67 freehand patients, for a total of 130 patients undergoing primary TKA for osteoarthritis. The procedures were performed by one of three fellowship-trained arthroplasty surgeons (RPS, HJC, JAG) and were randomized to either soft tissue balancing via a freehand technique or with a sensor-guided balancing device at one institution from December 2017 to December 2018. There was no difference in the mean age (72 ± 8 years versus 70 ± 9 years, mean difference 2; p = 0.11), BMI (30 ± 6 kg/m 2 versus 29 ± 6 kg/m 2 , mean difference 1; p = 0.83), gender (79% women versus 70% women; p = 0.22), and American Society of Anesthesiology score (2 ± 1 versus 2 ± 1, mean difference 0; p = 0.92) between the sensor-guided and freehand groups, respectively. For both groups, soft tissue balancing was performed after all bony cuts were completed and trial components inserted, with the primary difference in technique being the ability to quantify the intercompartmental balance using the trial tibial insert embedded with a wireless sensor in the sensor-guided cohort. Implant manufacturers were not standardized. Primary outcomes were knee ROM and PROMs at 3 months, 1 year, and 2 years. Secondary outcomes included pain level evaluated by the VAS, opioid consumption, inpatient physical therapy performance, LOS, discharge disposition, surgical complications, and reoperations.

RESULTS

There was no difference in the mean knee ROM at 3 months, 1 year, and 2 years postoperatively between the sensor-guided cohort (113° ± 11°, 119° ± 13°, and 116° ± 12°, respectively) and the freehand cohort (116° ± 13° [p = 0.36], 117° ± 13° [p = 0.41], and 117° ± 12° [p = 0.87], respectively). There was no difference in SF-12 physical, SF-12 mental, WOMAC pain, WOMAC stiffness, WOMAC function, and KSFS scores between the cohorts at 3 months, 1 year, and 2 years postoperatively. The mean operative time in the sensor-guided cohort was longer than that in the freehand cohort (107 ± 0.02 versus 84 ± 0.04 minutes, mean difference = 23 minutes; p = 0.008), but there were no differences in LOS, physical therapy performance, VAS pain scores, opioid consumption, discharge disposition, surgical complications, or percentages of patients in each group who underwent reoperation.

CONCLUSION

This RCT demonstrated that at 2 years postoperatively, the use of a sensor-balancing device for soft tissue balancing in TKA did not confer any additional benefit in terms of knee ROM, PROMs, and clinical outcomes. Given the significantly increased operative time and costs associated with the use of a sensor-balancing device, we recommend against its routine use in clinical practice by experienced surgeons.

LEVEL OF EVIDENCE

Level I, therapeutic study.

Equal bony resection of distal and posterior femur will lead to flexion/extension gap inequality in robot-assisted cruciate-retaining TKA

PURPOSE

Joint imbalance has become one of the main reasons for early revision after total knee arthroplasty (TKA) and it is directly related to the surgical technique. Therefore, a better understanding of how much bone has to be removed to obtain a balanced flexion/extension gap could improve current practice. The primary objective of this study was to analyse the amount of bone that needed to be removed from the distal and posterior femoral joint surfaces to obtain an equal flexion/extension gap in robot-assisted TKA. The second objective of this study was to evaluate whether the size of the knee joint influenced the amount of bony resection needed to achieve an equal flexion/extension gap in robot-assisted TKA.

METHODS

A retrospective analysis was performed on all patients receiving a robot-assisted TKA (Cruciate Retaining (n = 268)) by six surgeons from April 2018 to September 2019. The robot was used consecutively when available in all patients receiving Cruciate Retaining TKA. Gap assessment, bony resections, femoral implant size and hip-knee-ankle angle were evaluated with the robot. Femoral implant size was categorized into small (size 1-2), medium (size 3-5) and large (size 6-8).

RESULTS

The difference between the posterior and distal resection needed to obtain equal flexion and extension gap was on average 2.0 mm (SD 1.6) and 1.5 mm (SD 2.2) for the medial and lateral compartment, respectively. The discrepancy was smaller in the large implant group compared to the small implant group (p < .05 medial and lateral) and medium implant group (p < .05 medial). Varus knees required a larger differential resection compared to neutral and valgus knees (only laterally) (medial compartment: p < .05 (varus-neutral), p = .051 (varus-valgus); lateral compartment: p < .05 (varus-neutral and varus-valgus).

CONCLUSION

Removing an equal amount of bone from the distal and posterior femur will lead to flexion/extension gap imbalance in TKA. It was required to remove 1.5-2 mm more bone from the posterior femur compared to the distal femur to equalize flexion and extension gap. This effect was size dependent: in larger knees, the discrepancy between the distal and posterior resections was smaller.

LEVEL OF EVIDENCE

IV.

Tibial component rotation alters soft tissue balance in a cruciate retaining total knee arthroplasty

Our aim was to understand whether using different landmarks for tibial component rotation influenced articular contact pressures in a balanced total knee arthroplasty (TKA). Twelve patients underwent TKA (Triathlon CR, Stryker Inc., Mahwah, NJ) and contact pressures were assessed using a wireless sensor. Robotic arm assisted TKA using a functional alignment technique was performed, with balanced gaps between medial and lateral compartments. Compartment pressures were measured with the trial tibial component rotated to Akagi's line and to Insall's axis respectively. Rotating the tibial component to Akagi's line resulted in a significantly greater proportion of knees being balanced and lower contact pressures than when the tibial component was rotated to Insall's axis at 10°, 45° and 90° of flexion (p < 0.05). Medial compartment pressures were significantly increased in 10° of flexion, as were lateral compartment pressures in all positions when the tibial component was aligned to Insall's axis (p < 0.05). The mean difference in rotation observed with the two landmarks was 6.9° (range 4.1-9.1°). Rotational alignment of the tibial component using Akagi's line reduced contact pressures, improved balance and reduced the need for soft tissue release when compared with Insall's axis in robotic arm assisted TKA.

Intraoperative pressure sensors improve soft-tissue balance but not clinical outcomes in total knee arthroplasty: a multicentre randomized controlled trial

AIMS

Intraoperative pressure sensors allow surgeons to quantify soft-tissue balance during total knee arthroplasty (TKA). The aim of this study was to determine whether using sensors to achieve soft-tissue balance was more effective than manual balancing in improving outcomes in TKA.

METHODS

A multicentre randomized trial compared the outcomes of sensor balancing (SB) with manual balancing (MB) in 250 patients (285 TKAs). The primary outcome measure was the mean difference in the four Knee injury and Osteoarthritis Outcome Score subscales (ΔKOOS₄) in the two groups, comparing the preoperative and two-year scores. Secondary outcomes included intraoperative balance data, additional patient-reported outcome measures (PROMs), and functional measures.

RESULTS

There was no significant difference in ΔKOOS₄ between the two groups at two years (mean difference 0.4 points (95% confidence interval (CI) -4.6 to 5.4); p = 0.869), and multiple regression found that SB was not associated with a significant ΔKOOS₄ (0.2-point increase (95% CI -5.1 to 4.6); p = 0.924). There were no significant differences between groups in other PROMs. Six-minute walking distance was significantly increased in the SB group (mean difference 29 metres; p = 0.015). Four-times as many TKAs were unbalanced in the MB group (36.8% MB vs 9.4% SB; p < 0.001). Irrespective of group assignment, no differences were found in any PROM when increasing ICPD thresholds defined balance.

CONCLUSION

Despite improved quantitative soft-tissue balance, the use of sensors intraoperatively did not differentially improve the clinical or functional outcomes two years after TKA. These results question whether a more precisely balanced TKA that is guided by sensor data, and often achieved by more balancing interventions, will ultimately have a significant effect on clinical outcomes. Cite this article: Bone Joint J 2022;104-B(5):604-612.

Sensor-guided gap balance versus manual gap balance in primary total knee arthroplasty: a meta-analysis

Background

Despite Vast improvements in technology and surgical technique in total knee arthroplasty (TKA), approximately 15–25% TKAs, have suboptimal subjective clinical outcomes. Our study sought to evaluate if sensor-guided balancing improves postoperative clinical outcomes compared to a conventional gap balancing technique.

Methods

We searched Web of Science, Embase, PubMed, Cochrane Controlled Trials Register, Cochrane Library, Highwire, CBM, CNKI, VIP, and Wanfang database in March 2022 to identify studies involving sensor-guided balancing versus conventional gap balancing technique in TKA. Finally, we identified 2147 knees assessed in nine studies.

Results

Compared with manual gap balancing, Sensor-guided gap balancing resulted in less rate of Manipulation under anesthesia (MUA) (P = 0.02), however more rate of intraoperative additional procedures (P = 0.0003). There were no significant differences in terms of KSS (P = 0.21), KSS Function score (P = 0.36), OKS (P = 0.61), KOOS (P = 0.78), operative time (P = 0.17), Mechanical axis (P = 0.69) and rate of reoperation between two groups.

Conclusion

Compared with conventional manual gap balancing techniques, sensors have more balancing procedures being performed. However, it did result in a reduction in the rate of MUA. More extensive, high-quality RCTs are required to verify our findings further.

Functional Alignment Philosophy in Total Knee Arthroplasty – Rationale and technique for the varus morphotype using a CT based robotic platform and individualized planning

Introduction: Alignment techniques in total knee arthroplasty (TKA) continue to evolve. Functional alignment (FA) is a novel technique that utilizes robotic tools to deliver TKA with the aim of respecting individual anatomical variations. The purpose of this paper is to describe the rationale and technique of FA in the varus morphotype with the use of a robotic platform. Rationale: FA reproduces constitutional knee anatomy within quantifiable target ranges. The principles are founded on a comprehensive assessment and understanding of individual anatomical variations with the aim of delivering personalized TKA. The principles are functional pre-operative planning, reconstitution of native coronal alignment, restoration of dynamic sagittal alignment within 5° of neutral, maintenance of joint-line-obliquity and height, implant sizing to match anatomy and a joint that is balanced in flexion and extension through manipulation of implant positioning rather than soft tissue releases. Technique: An individualized plan is created from pre-operative imaging. Next, a reproducible and quantifiable method of soft tissue laxity assessment is performed in extension and flexion that accounts for individual variation in soft tissue laxity. A dynamic virtual 3D model of the joint and implant position that can be manipulated in all three planes is modified to achieve target gap measurements while maintaining the joint line phenotype and a final limb position within a defined coronal and sagittal range. Conclusion: Functional alignment is a novel knee arthroplasty technique that aims to restore constitutional bony alignment and balance the laxity of the soft tissues by placing and sizing implants in a manner that it respects the variations in individual anatomy. This paper presents the approach for the varus morphotype.

Improved total knee arthroplasty pain outcome when joint gap targets are achieved throughout flexion

PURPOSE

Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the definition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midflexion, and flexion are associated with improved outcome scores at one-year post-operatively and (2) whether these relationships can be used to identify windows of optimal gap balance throughout flexion.

METHODS

135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacrificing gap balancing technique. Joint gaps were measured under a controlled tension of 70-90 N from 10°-90° flexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to define clinically relevant joint gap target thresholds in extension, midflexion, and flexion. Gap thresholds were then combined to investigate the synergistic effects of satisfying multiple targets.

RESULTS

Significant linear correlations were found throughout extension, midflexion, and flexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1 mm compared to the final insert thickness in midflexion, and a medio-lateral imbalance of less than 1.5 mm in flexion generated subgroups that reported significantly improved KOOS pain scores at one year (median ∆ = 8.3, 5.6 and 2.8 points, respectively). Combining any two targets resulted in further improved outcomes, with the greatest improvement observed when all three targets were satisfied (median ∆ = 11.2, p = 0.002).

CONCLUSION

Gap thresholds identified in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacrificing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed.

LEVEL OF EVIDENCE

Level II.

Intraoperative Load Sensing in Total Knee Arthroplasty Leads to a Functional but Not Clinical Difference: A Comparative, Gait Analysis Evaluation

INTRODUCTION

Although Total Knee Arthroplasty (TKA) is a successful procedure, a significant number of patients are still unsatisfied, reporting instability at the mid-flexion range (Mid-Flexion Instability-MFI). To avoid this complication, many innovations, including load sensors (LS), have been introduced. The intraoperative use of LS may facilitate the balance of the knee during the entire range of motion to avoid MFI postoperatively. The objective of this study was to perform a Gait Analysis (GA) evaluation of a series of patients who underwent primary TKA using a single LS technology.

METHODS

The authors matched and compared two groups of patients treated with the same posterior stabilized TKA design. In Group A, 10 knees were intraoperatively balanced with LS technology, while 10 knees (Group B) underwent standard TKA. The correct TKA alignment was preoperatively determined aiming for a mechanical alignment. Clinical evaluation was performed according to the WOMAC, Knee Society Score (KSS) and Forgotten Joint Score, while functional evaluation was performed using a state-of-the-art GA platform.

RESULTS

We reported excellent clinical results in both groups without any statistical difference in patient reported outcome measurements (PROMs); from a functional standpoint, several GA space-time parameters were closer to normal in the sensor group when compared to the standard group, but a statistically significant difference was not reached.

CONCLUSIONS

Gait Analysis represents a valid method to evaluate TKA kinematics. This study, with its limitations, showed that pressure sensitive technology represents a valid aid for surgeons aiming to improve the postoperative stability of TKA; however, other factors (i.e., level of intra-articular constraint and alignment) may play a major role in reproducing the normal knee biomechanics.

Component placement accuracy in two generations of handheld robotics-assisted knee arthroplasty

INTRODUCTION

Total knee arthroplasty (TKA) is the gold standard for treatment of end-stage osteoarthritis. Previous studies have shown that successful outcomes following TKA depend on accurate implant alignment and soft tissue balancing. Robotic-assisted TKA have demonstrated improved accuracy in component placement and have been associated with better outcomes and patient satisfaction. This study aims to report on the execution accuracy of two generations of handheld robotic-assisted surgical systems.

METHODS

This was a retrospective analysis of TKA procedures with two sequential generations of the same handheld robotic-assisted surgical system. Intra-operative data captured included pre-operative limb deformity, limb axes, range of motion, kinematic balance, and the resulting plan for component placement in three-dimensional space. Patients were stratified based on their preoperative coronal lower limb mechanical alignment (> 3° varus, < 3° varus, < 3° valgus, and ≥ 3° valgus). Measurements of component placement (overall lower limb alignment, medial and lateral flexion gaps, and tibial and femoral resection depths) were assessed using descriptive statistics.

RESULTS

A total of 435 patients were included and stratified based on preoperative lower limb alignment: 229 with ≥ 3° varus, 78 with varus < 3° and 58 with valgus < 3°, and 70 with valgus > 3°. The mean difference between planned and achieved alignment in the lower limb valgus patients was < 1° across all groups. Mean differences between planned and achieved medial flexion gap was higher in the > 3° subgroup in the varus patient cohort ([< 3°]: 1.15 ± 1.92 vs. [> 3°]: 1.90 ± 2.57); this value was higher in the < 3° subgroup for valgus patients ([< 3°]: 1.34 ± 1.83 vs. [> 3°]: 0.956 ± 1.65). Average resection depth ranged from 9.46 to 10.4 mm in the posterior medial femur, 9.25 to 9.95 mm in the posterior lateral femur, 7.45 to 8.79 mm in the distal medial femur, 8.22 to 9.18 mm in the distal lateral femur, 6.70 to 7.07 mm in the medial tibial condyle and 6.40 to 7.19 mm in the lateral tibial condyle. Non-inferiority testing demonstrated the newer generation is non-inferior to the older generation.

CONCLUSION

Robotic-assisted knee replacement using handheld image-free systems is able to maintain accuracy of component placement. Further investigation of patient reported outcomes as well as long-term implant longevity are needed.

Impact of intra-operative predictive ligament balance on post-operative balance and patient outcome in TKA: a prospective multicenter study

INTRODUCTION

New technologies exist which may assist surgeons to better predict final intra-operative joint balance. Our objectives were to compare the impact of (1) a predictive digital joint tensioning tool on intra-operative joint balance; and (2) joint balance and flexion joint laxity on patient-reported outcomes.

MATERIALS AND METHODS

Two-hundred Eighty patients received posterior cruciate ligament sacrificing TKA with ultra-congruent tibial inserts using a robotic-assisted navigation platform. Patients were divided into those in which a Predictive Plan with a digital joint-tensioning device was used (PP) and those in which it was not (NPP), in all cases final post-operative joint gaps were collected immediately before final implantation. Demographics and KOOS were collected pre-operatively. KOOS, complications and satisfaction were collected at 3, 6 and 12 months post-operatively. Optimal balance difference between PP and NPP was defined and compared using area-under-the-curve analysis (AUC). Outcomes were then compared according to the results from the AUC.

RESULTS

AUC analysis yielded a balance threshold of 1.5 mm, in which the PP group achieved a higher rate of balance throughout flexion compared to the NPP group: extension: 83 vs 52%; Midflexion: 82 vs 55%; Flexion 89 vs 68%; Flexion to Extension 80 vs 49%; p ≤ 0.003. Higher KOOS scores were observed in knees balanced within 1.5 mm across all sub-scores at various time points, however, differences did not exceed the minimum clinically important difference (MCID). Patients with > 1.5 mm flexion laxity medially or laterally had an increased likelihood of 2.2 (1.1-4.4) and 2.5 (1.3-4.8), respectively, for failing to achieve the Patient Acceptable Symptom State for KOOS Pain at 12 months. Patient satisfaction was high in both the PP and NPP groups (97.4 and 94.7%, respectively).

CONCLUSIONS

Use of a predictive joint tensioning tool improved the final balance in TKA. Improved outcomes were found in balanced knees; however, this improvement did not achieve the MCID, suggesting further studies may be required to define optimal balance targets. Limiting medial and lateral flexion laxity resulted in an increased likelihood of achieving the Patient Acceptable Symptom State for KOOS Pain.

The MAKO robotic-arm knee arthroplasty system

INTRODUCTION

The Mako robotic arm knee arthroplasty system was initially indicated in unicompartmental knee arthroplasty followed by bicompartmental and total knee arthroplasty techniques. The system utilizes three elements: (1) Pre-op 3D CT based planning and image based intra-op navigation. (2) Pre-resection implant modifications with integrated alignment, implant position and gap data, and (3) A semi-constrained robotic arm assisted execution of bone resection with "haptic" boundaries, and cemented implants.

MATERIALS AND METHODS

This paper evaluates variable pre-op implant placement, and anatomic reference positioning; data entry with incorporation of alignment, implant congruency through range of motion, and gaps; bone resection with "haptic" boundaries, and final implant evaluation with kinetic sensors.

RESULTS

The Mako system allowed for improved implant placement utilizing CT guidance, bone resection accuracy, flexibility for functional implant placement with gap balancing. When combined with kinetic sensors, there was improved rotation and soft tissue balance.

CONCLUSION

The MAKO robotic system can assist the surgeon with anatomic landmarks, provides the flexibility for independent gap balance through implant and alignment refinement, and three-dimensional soft tissue balancing data to achieve functional stability. Registry data has shown improved outcome survivorship irrespective of the surgeons' volumes and learning curves.

Total Knee Arthroplasty and Intra-Articular Pressure Sensors: Can They Assist Surgeons with Intra-Operative Decisions?

PURPOSE OF REVIEW

Soft tissue imbalance, presenting as instability or stiffness, is an important cause of revision total knee arthroplasty (TKA). Traditional methods of determining soft tissue balance of the knee lack precision and are not reliable between operators. Use of intra-operative pressure sensors offers the potential to identify and avoid soft tissue imbalance following TKA. This review aims to summarise the literature supporting the clinical indication for the use of intra-articular pressure sensors during TKA.

RECENT FINDINGS

Analytical validation studies suggest that intra-operative pressure sensors demonstrate 'moderate' to 'good' intra-observer reliability and 'good' to 'excellent' interobserver reliability throughout the flexion arc. However, there are important errors associated with measurements when devices are used out-with the stated guidelines and clinicians should be aware of the limitations of these devices in isolation. Current evidence regarding patient benefit is conflicting. Despite positive early results, several prospective studies have subsequently failed to demonstrate significant differences in overall survival, satisfaction, and patient-reported outcome measures within 1 year of surgery. Surgeon-defined soft tissue stability appears to be significantly different from the absolute pressures measured by the intra-operative sensor. Whilst it could be argued that this confirms the need for intra-articular sensor guidance in TKA; the optimal 'target' balance remains unclear and the relationship with outcome in patients is not determined. Future research should (1) identify a suitable reference standard for comparison; (2) improve the accuracy of the sensor outputs; and (3) demonstrate that sensor-assisted TKA leads to patient benefit in patient-reported outcome measures and/or enhanced implant survival.

Current role of intraoperative sensing technology in total knee arthroplasty

PURPOSE

Sensors have been introduced within the last 10 years to quantify soft tissue balancing during total knee arthroplasty (TKA) and to give the surgeon objective data. These devices are fairly new and their impact on patient outcome remains uncertain. The aim of this systematic review was to summarize all the relevant surgical and clinical results of sensors for TKA.

METHODS

A PRISMA systematic review was conducted using five databases (PubMed, EMBASE, MEDLINE, GOOGLE SCHOLAR, and the COCHRANE LIBRARY) to identify all available literature that described the surgical and clinical results of sensors for TKA between 2000 and 2021. The main investigated outcome criteria were intraoperative data, postoperative functional and clinical outcome, knee range of motion, complications and revision rates.

RESULTS

Twenty-seven articles were finally included. The maximum reported follow-up was 26 months. A balanced knee with sensor corresponded to a mediolateral difference inferior to 15 lb and a stable posterior drawer test. The standard assessment of knee balance was a poor predictor of the true soft tissue balance when compared to sensor data. At least 60% of TKA needed an additional rebalancing procedure with the sensor, after conventional gap balancing. Achieving a quantitatively balanced knee resulted in a significantly higher patient satisfaction score. But the prospective comparative studies found no demonstrable improvement in clinical outcome, range of motion or complication rate at one year postoperatively for patients undergoing TKA using sensor-guided balancing compared with routine techniques.

CONCLUSION

Even though the use of the intraoperative sensing technology was not related to an improvement in clinical outcome, the current studies showed that using sensors facilitates the reproduction of natural joint stability, and improves the rate of achieving a balanced knee. Sensor use in complex cases could be particularly valuable, but their use in standard practice remains to be defined.

Tibiofemoral dynamic stressed gap laxities correlate with compartment load measurements in robotic arm-assisted total knee arthroplasty

Aims

It is unknown whether gap laxities measured in robotic arm-assisted total knee arthroplasty (TKA) correlate to load sensor measurements. The aim of this study was to determine whether symmetry of the maximum medial and lateral gaps in extension and flexion was predictive of knee balance in extension and flexion respectively using different maximum thresholds of intercompartmental load difference (ICLD) to define balance.

Methods

A prospective cohort study of 165 patients undergoing functionally-aligned TKA was performed (176 TKAs). With trial components in situ, medial and lateral extension and flexion gaps were measured using robotic navigation while applying valgus and varus forces. The ICLD between medial and lateral compartments was measured in extension and flexion with the load sensor. The null hypothesis was that stressed gap symmetry would not correlate directly with sensor-defined soft tissue balance.

Results

In TKAs with a stressed medial-lateral gap difference of ≤1 mm, 147 (89%) had an ICLD of ≤15 lb in extension, and 112 (84%) had an ICLD of ≤ 15 lb in flexion; 157 (95%) had an ICLD ≤ 30 lb in extension, and 126 (94%) had an ICLD ≤ 30 lb in flexion; and 165 (100%) had an ICLD ≤ 60 lb in extension, and 133 (99%) had an ICLD ≤ 60 lb in flexion. With a 0 mm difference between the medial and lateral stressed gaps, 103 (91%) of TKA had an ICLD ≤ 15 lb in extension, decreasing to 155 (88%) when the difference between the medial and lateral stressed extension gaps increased to ± 3 mm. In flexion, 47 (77%) had an ICLD ≤ 15 lb with a medial-lateral gap difference of 0 mm, increasing to 147 (84%) at ± 3 mm.

Conclusion

This study found a strong relationship between intercompartmental loads and gap symmetry in extension and flexion measured with prostheses in situ. The results suggest that ICLD and medial-lateral gap difference provide similar assessment of soft-tissue balance in robotic arm-assisted TKA.

Cite this article: Bone Jt Open 2021;2(11):974–980.

[Optimal lower limb alignment and soft tissue balancing strategy for robot-assisted total knee arthroplasty]

Lower limb alignment and soft tissue balance are important factors affecting patient satisfaction, clinical functional outcome, and prosthetic long-term survival rate after total knee arthroplasty (TKA). Robot-assisted TKA (rTKA) has the advantages of achieving precise osteotomy and soft tissue balance. However, rTKA under the guidance of classic mechanical alignment principles does not significantly improve the functional outcome after operation. The new TKA alignment principles, such as kinematic alignment (KA) and functional alignment (FA), can better consider the patient's own knee joint morphology and kinematic characteristics, which may help improve the clinical results of TKA. With the help of more objective and accurate soft tissue balance assessment tool such as pressure sensors, KA and FA have been proven to better achieve soft tissue balance. rTKA can achieve non-neutral alignment goals such as KA or FA more accurately and reproducibly. The use of these lower limb alignment and soft tissue balancing strategies will be expected to further increase the patients' satisfaction rate after rTKA.

Kinetic Sensors for Ligament Balance and Kinematic Evaluation in Anatomic Bi-Cruciate Stabilized Total Knee Arthroplasty

Sensor technology was introduced to intraoperatively analyse the differential pressure between the medial and lateral compartments of the knee during primary TKA using a sensor to assess if further balancing procedures are needed to achieve a “balanced” knee. The prognostic role of epidemiological and radiological parameters was also analysed. A consecutive series of 21 patients with primary knee osteoarthritis were enrolled and programmed for TKA in our unit between 1 September 2020 and 31 March 2021. The VERASENSE Knee System (OrthoSensor Inc., Dania Beach, FL, USA) has been proposed as an instrument that quantifies the differential pressure between the compartments of the knee intraoperatively throughout the full range of motion during primary TKA, designed with a J-curve anatomical femoral design and a PS “medially congruent” polyethylene insert. Thirteen patients (61.90%) showed a “balanced” knee, and eight patients (38.10%) showed an intra-operative “unbalanced” knee and required additional procedures. A total of 13 additional balancing procedures were performed. At the end of surgical knee procedures, a quantitatively balanced knee was obtained in all patients. In addition, a correlation was found between the compartment pressure of phase I and phase II at 10° of flexion and higher absolute pressures were found in the medial compartment than in the lateral compartment in each ROM degree investigated. Moreover, those pressure values showed a trend to decrease with the increase in flexion degrees in both compartments. The “Kinetic Tracking” function displays the knee’s dynamic motion through the full ROM to evaluate joint kinetics. The obtained kinetic traces reproduced the knee’s medial pivot and femoral rollback, mimicking natural knee biomechanics. Moreover, we reported a statistically significant correlation between the need for soft tissue or bone resection rebalancing and severity of the initial coronal deformity (>10°) and a preoperative JLCA value >2°. The use of quantitative sensor-guided pressure evaluation during TKA leads to a more reproducible “balanced” knee. The surgeon, evaluating radiological parameters before surgery, may anticipate difficulties in knee balance and require those devices to achieve the desired result objectively.

Can a robot help a surgeon to predict a good total knee arthroplasty?

AIMS

Neither a surgeon's intraoperative impression nor the parameters of computer navigation have been shown to be predictive of the outcomes following total knee arthroplasty (TKA). The aim of this study was to determine whether a surgeon, with robotic assistance, can predict the outcome as assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) for pain (KPS), one year postoperatively, and establish what factors correlate with poor KOOS scores in a well-aligned and balanced TKA.

METHODS

A total of 134 consecutive patients who underwent TKA using a dynamic ligament tensioning robotic system with a tibia first resection technique and a cruciate sacrificing ultracongruent TKA system were enrolled into a prospective study. Each TKA was graded based on the final mediolateral ligament balance at 10° and 90° of flexion: 1) < 1 mm difference in the thickness of the tibial insert and that which was planned (n = 75); 2) < 1 mm difference (n = 26); 3) between 1 mm to 2 mm difference (n = 26); and 4) > 2 mm difference (n = 7). The mean one-year KPS score for each grade of TKA was compared and the likelihood of achieving an KPS score of > 90 was calculated. Finally, the factors associated with lower KPS despite achieving a high-grade TKA (grade A and B) were analyzed.

RESULTS

Patients with a grade of A or B TKA had significantly higher mean one-year KPS scores compared with those with C or D grades (p = 0.031). There was no difference in KPS scores in grade A or B TKAs, but 33% of these patients did not have a KPS score of > 90. While there was no correlation with age, sex, preoperative deformity, and preoperative KOOS and Patient-Reported Outcomes Measurement Information System (PROMIS) physical scores, patients with a KPS score of < 90, despite a grade A or B TKA, had lower PROMIS mental health scores compared with those with KPS scores of > 90 (54.1 vs 50.8; p = 0.043). Patients with grade A and B TKAs with KPS > 90 were significantly more likely to respond with "my expectations were too low", and with "the knee is performing better than expected" compared with patients with these grades of TKA who had a KPS score of < 90 (40% vs 22%; p = 0.004).

CONCLUSION

A TKA balanced with robotic assistance to within 1 mm of difference between the medial and lateral sides in both flexion and extension had a higher KPS score one year postoperatively. Despite accurate ligament balance information, a robotic system could not guarantee excellent pain relief. Patient expectations and mental status also significantly affected the perceived success of TKA. Cite this article: Bone Joint J 2021;103-B(6 Supple A):67-73.

Accuracy of soft tissue balancing in total knee arthroplasty using surgeon-defined assessment versus a gap-balancer or electronic sensor

Background

Soft tissue balancing is essential for the success of total knee arthroplasty (TKA) and is mainly dependent on surgeon-defined assessment (SDA) or a gap-balancer (GB). However, an electronic sensor has been developed to objectively measure the gap pressure. This study aimed to evaluate the accuracy of soft tissue balancing using SDA and GB compared with a sensor.

Methods

Forty-eight patients undergoing TKA (60 knees) were prospectively enrolled. Soft tissue balancing was sequentially performed using SDA, a GB, and an electronic sensor. We compared the SDA, GB, and sensor data to calculate the sensitivity, specificity, and accuracy at 0°, 45°, 90°, and 120° flexion. Cumulative summation (CUSUM) analysis was performed to assess the surgeon’s performance during the sensor introductory phase.

Results

The sensitivity of SDA was 63.3%, 68.3%, 80.0%, and 80.0% at 0°, 45°, 90°, and 120°, respectively. The accuracy of the GB compared with sensor data was 76.7% and 71.7% at 0° and 90°, respectively.

Cohen’s kappa coefficient for the accuracy of the GB was 0.406 at 0° (moderate agreement) and 0.227 at 90° (fair agreement). The CUSUM 0° line achieved good prior performance at case 45, CUSUM 90° and 120° showed a trend toward good prior performance, while CUSUM 45° reached poor prior performance at case 8.

Conclusion

SDA was a poor predictor of knee balance. GB improved the accuracy of soft tissue balancing, but was still less accurate than the sensor, particularly for unbalanced knees. SDA improved with ongoing use of the sensor, except at 45° flexion.

Use of Fulcrum Positioning as a Balancing Tool During Total Knee Arthroplasty on a Robotic Platform

Total knee arthroplasty is a common procedure performed to improve pain and dysfunction attributed to arthritis, yet postoperative patient dissatisfaction rates remain relatively high. Patient satisfaction and outcomes have been linked to successful joint gap balancing in the coronal and sagittal planes intraoperatively. In previously described balancing techniques, the fulcrum used for alignment changes is customarily centered on the intramedullary axis generating symmetric changes in medial and lateral gaps. We propose a novel technique in the literature that, with the use of robotic-arm assisted technology or similar systems, allows manipulation of the fulcrum center of rotation during pre-resection planning and intraoperative gap establishment before bony cuts to asymmetrically influence medial and lateral, flexion and extension gaps to aid in balancing during total knee arthroplasty.

Soft-Tissue Balancing Technology for Total Knee Arthroplasty

» Improperly balanced total knee arthroplasties are at increased risk for complications including residual pain and/or instability, which are often corrected by a revision surgical procedure. » Because of the morbidity and financial burden associated with revision total knee arthroplasty, different technological applications, such as tibial insert sensors and computer-assisted gap balancing, are being used to assist with soft-tissue balancing during primary total knee arthroplasty. » Computer-assisted gap balancing increases the accuracy of mechanical alignment and improves the precision of balancing flexion and extension gaps during total knee arthroplasty. It is unclear whether this translates to improved short-term or long-term outcome measures. Considerations of this technology include increased cost, increased operative time, and a steep learning curve. » Intraoperative sensors increase the accuracy of balancing by quantifying the mediolateral intercompartmental load distribution through the range of motion, which may lead to improved outcome scores, patient satisfaction, higher activity levels, and decreased pain. The advantages of this technology compared with computer assistance include decreased cost and no disruption of operative time or workflow. Limited availability with constrained implants, limited implant choices, and a lack of long-term follow-up data have reduced utilization of intraoperative sensors. » Computer-assisted gap balancing and intraoperative sensors are not yet universally accepted, and the cost-benefit ratio associated with their use remains a consideration in today’s cost-conscious health-care environment. Future research should focus on longer-term follow-up to evaluate implant survivorship, cost-effectiveness, and clinical outcomes.

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

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 = .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.