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

Dynamic variation of tibiofemoral compression force during total knee arthroplasty: Implications for soft tissue balance and functional outcomes

BACKGROUND

Achieving precise alignment and soft tissue balance is crucial for optimal total knee arthroplasty (TKA) outcomes. We aimed to explore how tibiofemoral compression force (TFCF) varies with knee flexion and its correlation with functional outcomes.

METHODS

This prospective study included 60 patients undergoing cruciate-retaining TKA (FINE Total Knee System). Sensor-equipped trial inserts were used to measure the TFCF at 15° intervals, from full extension to 90° flexion. Patients were classified into anterior and posterior force groups based on whether the medial TFCF was higher in the anterior than in the posterior region at 60° flexion. The 2-year outcomes were assessed using the Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS-JR).

RESULTS

The total TFCF increased from 0° to 60° flexion and then decreased. The medial compressive forces were consistently higher than lateral forces. Anteromedial TFCF differed significantly between the anterior and posterior force groups at 60°, 75°, and 90° flexion. KOOS-JR scores showed a significant interaction between force type and time, with greater improvements in the anterior force group. Anteromedial TFCF at 60° flexion and KOOS-JR correlated significantly (R = 0.574).

CONCLUSION

Evaluating TFCF at multiple knee flexion angles provides valuable insights into optimising outcomes in TKA. TFCF variations, especially in the anteromedial compartment, considerably impact functional outcomes. Dynamic TFCF measurements during TKA may enhance soft tissue balance and improve outcomes. Further research is needed to validate these findings in diverse populations and with long-term follow ups.

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.

Technology in Total Knee Arthroplasty in 2023

Over the past few decades, instrumentation and techniques for total knee arthroplasty have evolved from conventional manual tools to a wide range of technologies, including calibrated guides for accurate bone cuts and alignment, smart tools, dynamic intraoperative sensors for soft tissue balancing, patient-specific guides, computer navigation, and robotics. This review is intended to provide an overview of the latest advancements in total knee arthroplasty technology, address potential challenges and solutions related to the application of these technologies, and explore their limitations.

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.

Individualizing a Total Knee Arthroplasty with Three-Dimensional Planning

Total knee arthroplasty (TKA) is evolving from mechanical alignment to more individualized alignment options in an attempt to improve patient satisfaction. Thirteen-year survival of kinematically aligned prostheses has recently been shown to be similar to mechanically aligned TKA, allaying concerns of long-term failure of this newer individualized technique. There is a complex inter-relationship of three-dimensional knee and limb alignment for a TKA. This article will review planning parameters necessary to individualize each knee, along with a discussion of how these parameters are related in three dimensions. Future use of computer software and machine learning has the potential to identify the ideal surgical plan for each patient. In the meantime, the material presented here can assist surgeons as newer individual alignment planning becomes a reality.

Patients Consistently Report Worse Outcomes Following Revision Total Knee Arthroplasty Compared to Primary Total Knee Arthroplasty

BACKGROUND

Differences in patient-reported outcome measures (PROMs) between primary TKA (pTKA) and revision TKA (rTKA) have not been well-studied. Therefore, we compared pTKA and rTKA patients by the rates of achieving the Minimal Clinically Important Difference for Improvement (MCID-I) and Worsening (MCID-W).

METHODS

A total of 2,448 patients (2,239 pTKAs/209 rTKAs) were retrospectively studied. Patients who completed the Knee Injury and Osteoarthritis Outcome Score-Physical Function Short Form (KOOS-PS), Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function Short Form 10a (PF10a), PROMIS Global-Mental, or PROMIS Global-Physical questionnaires were identified by Current Procedural Terminology (CPT) codes. Patient-reported outcome measures and MCID-I/MCID-W rates were compared. Multivariate logistic regression models measured relationships between surgery type and postoperative outcomes.

RESULTS

Patients who underwent rTKA (all causes) had lower rates of improvement and higher rates of worsening compared to pTKA patients for KOOS-PS (MCID-I: 54 versus 68%, P < .001; MCID-W: 18 versus 8.6%, P < .001), PF10a (MCID-I: 44 versus 65%, P < .001; MCID-W: 22 versus 11%, P < .001), PROMIS Global-Mental (MCID-I: 34 versus 45%, P = .005), and PROMIS Global-Physical (MCID-I: 51 versus 60%, P = .014; MCID-W: 29 versus 14%, P < .001). Undergoing revision was predictive of worsening postoperatively for KOOS-PS, PF10a, and PROMIS Global-Physical compared to pTKA. Postoperative scores were significantly higher for all 4 PROMs following pTKA.

CONCLUSION

Patients reported significantly less improvement and higher rates of worsening following rTKA, particularly for PROMs that assessed physical function. Although pTKA patients did better overall, the improvement rates may be considered relatively low and should prompt discussions on improving outcomes following pTKA and rTKA.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

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.

Optimizing Asymmetric Native Knee Flexion Gap Balance Promotes Superior Outcomes in Primary Total Knee Arthroplasty

INTRODUCTION

Replicating native knee kinematics remains the ultimate goal of total knee arthroplasty (TKA). Technology, such as robotics, provides robust intraoperative data; however, no evidence-based targets currently exist for improved clinical outcomes. Furthermore, some surgeons target a rectangular flexion space in TKA unlike the native knee. This study evaluated the effect of in vivo flexion gap asymmetry on patient-reported outcome measures (PROMs) in contemporary TKA.

METHODS

In vivo tibiofemoral joint space dimensions were measured during 129 TKAs using a calibrated tension device before and after complete posterior cruciate ligament resection. PROMs were compared based on the final dimensions and the change in flexion gap dimensions at 90° of flexion: (1) equal laxity, (2) lateral laxity, and (3) medial laxity. Groups did not differ by demographics ( P ≥ 0.347), clinical follow-up ( P = 0.134), tibiofemoral alignment ( P = 0.498), or preoperative PROMs ( P ≥ 0.093). Mean follow-up for the cohort was 1.5 years (range, 1-3).

RESULTS

Pain with climbing stairs, pain while standing upright, and knees "always feeling normal" scores were superior for patients with equal or lateral laxity compared with medial laxity ( P ≤ 0.064). Pain with level walking, University of California Los Angeles activity level, KOOS JR, and satisfaction scores also tended to be superior for patients with equal or lateral laxity, although it lacked statistical significance ( P ≥ 0.111).

DISCUSSION

Results of this study suggest that patients with either an equally tensioned rectangular flexion space or with later-flexion lateral laxity after posterior cruciate ligament resection may achieve superior PROMs. Findings support the clinical benefit of facilitating posterolateral femoral roll back in flexion, which mimics native knee kinematics and further helps define targets for advanced technology.

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.

Personalized alignment™ for total knee arthroplasty using the ROSA® Knee and Persona® knee systems: Surgical technique

Total knee arthroplasty (TKA) procedures are expected to increase up to 565% in the United States over the next 3 decades. TKAs were traditionally performed with neutral mechanical alignments that provided equal medial and lateral gaps in extension and flexion to reduce implant wear but were less successful at restoring native knee function and associated with high patient dissatisfaction. Kinematic alignment (KA) restores native anatomy and minimizes soft tissue release; however, KAs that recreate severe deformities and/or biomechanically inferior alignments result in significant increases in implant stress and risk of aseptic loosening. Restricted kinematic alignment (rKA) recreates pre-arthritic anatomy within a range of acceptable alignment boundaries, and improved patient clinical scores and faster recoveries have been reported with rKA techniques. Personalized Alignment™ is an evolution of rKA that relies heavily upon robotic assistance to reliably recreate patient anatomy, native soft tissue laxity, and accurate component placement to improve patients' clinical outcomes. The purpose of this surgical technique report is to describe the Personalized Alignment TKA method using the ROSA^® Knee System and Persona^® The Personalized Knee^® implants. Herein we provide specific procedures for pre-operative planning, anatomical landmarking and evaluation, intra-operative planning and adjustment of resections and cuts, cut validation and soft tissue evaluation with robotic-assisted personalized TKA.

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.