Intraoperative Sensing Technology to Achieve Balance in Primary Total Knee Arthroplasty: A Review of the Literature

Exploring the Performance of an Artificial Intelligence-Based Load Sensor for Total Knee Replacements

Using tibial sensors in total knee replacements (TKRs) can enhance patient outcomes and reduce early revision surgeries, benefitting hospitals, the National Health Services (NHS), stakeholders, biomedical companies, surgeons, and patients. Having a sensor that is accurate, precise (over the whole surface), and includes a wide range of loads is important to the success of joint force tracking. This research aims to investigate the accuracy of a novel intraoperative load sensor for use in TKRs. This research used a self-developed load sensor and artificial intelligence (AI). The sensor is compatible with Zimmer's Persona Knee System and adaptable to other knee systems. Accuracy and precision were assessed, comparing medial/lateral compartments inside/outside the sensing area and below/within the training load range. Five points were tested on both sides (medial and lateral), inside and outside of the sensing region, and with a range of loads. The average accuracy of the sensor was 83.41% and 84.63% for the load and location predictions, respectively. The highest accuracy, 99.20%, was recorded from inside the sensing area within the training load values, suggesting that expanding the training load range could enhance overall accuracy. The main outcomes were that (1) the load and location predictions were similar in accuracy and precision (p > 0.05) in both compartments, (2) the accuracy and precision of both predictions inside versus outside of the triangular sensing area were comparable (p > 0.05), and (3) there was a significant difference in the accuracy of load and location predictions (p < 0.05) when the load applied was below the training loading range. The intraoperative load sensor demonstrated good accuracy and precision over the whole surface and over a wide range of load values. Minor improvements to the software could greatly improve the results of the sensor. Having a reliable and robust sensor could greatly improve advancements in all joint surgeries.

Variability between the trial and final implant measurements during the sensor-guided total knee arthroplasty

PURPOSE

Compartmental load-sensing technology has been used in the attempt to achieve optimal soft tissue balance during total knee arthroplasty (TKA). This study was conducted to investigate the validity of such use of intraoperative sensing technology.

METHODS

Ninety-three knees scheduled to undergo total knee arthroplasty for knee osteoarthritis with a tibial sensor were prospectively enrolled. Measurements were divided into three groups according to the three different time points of intraoperative load testing: group Trial (with the trial components), group Final (with the definitive cemented implants and an open joint capsule), and group Closed (with the definitive cemented implants and a closed joint capsule). Load measurements and component rotational alignments were documented at 10°, 30°, 45°, 90°, and 120° of flexion for all three groups, and compared. One year postoperatively, the joint line obliquity angle was obtained radiographically in the valgus and varus stress views at 10° and 30° flexion to evaluate the clinical instability. The Knee Society, Hospital for Special Surgery, and Western Ontario McMaster Universities Osteoarthritis Index scores were used to determine functional outcomes. The correlations of the above outcomes with intraoperative load were evaluated.

RESULTS

There were significant differences in medial and lateral loads at all flexion angles (except at a 120° lateral load) between group Trial and group Final (p < 0.05). Tibial trays were internally rotated to a significantly higher degree in group Final than in group Trial (p = 0.010). The lateral compartmental load significantly decreased after patellar inversion (p = 0.037). There were no correlations of intraoperative load with clinical instability and functional outcomes.

CONCLUSION

Significant variability was observed between the trial and final implant measurements and intraoperative sensing data were not correlated with instability or functional outcomes over a 1-year period. Therefore, intraoperative sensor technology provides limited feedback and clinical efficacy in the adjustment of the soft tissue balance during TKA.

LEVEL OF EVIDENCE

Level II.

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.

Sensor-guided technology helps to reproduce medial pivot kinematics in total knee arthroplasty

METHODS

Two cohorts of 50 patients each were preoperatively matched to receive the same TKA, having a J-curve femoral design with an adapted "medially congruent" polyethylene insert; the second cohort (group B) underwent the intraoperative sensor-check. Intraoperative sensor data were recorded as tibiofemoral load at 10°, 45°, and 90°. We considered stable knees those with a pressure <50 lbs on the medial compartment, <35 lbs on the lateral, and a mediolateral inter-compartmental difference <15 lbs. Clinical outcomes were evaluated according to the Oxford Knee Score (OKS) and Knee Society Score (KSS).

RESULTS

All patients (group A: no sensor; group B: sensor) were available at 2-year minimum follow-up (FU; min. 24 months, max. 34 months); no preoperative statistical differences existed between groups in the average range of motion (ROM), OKS, KSS, and body mass index. There were no statistical differences at final FU between groups in the average OKS (group A: 41.1; group B: 41.5), in the average KSS (group A: 165.7; group B: 166.3), or in final ROM (group A: 123°; group B: 124°). One patient in each group required a manipulation under anesthesia. In the sensor group, an accessory soft tissue release/bone recut was necessary after sensor testing with trial components in 24% to obtain the desired loads; in the same group, the level of constraint in the final components was increased to posterior-stabilized in 12% because of an inter-compartmental difference >40 lbs. Surgical time was 8 min longer in the sensor group.

CONCLUSION

The use of this sensing technology did not improve the clinical outcome but supported multiple intraoperative decisions aimed to better reproduce the medial pivot kinematic of the normal knee.

Sensor guided unicompartmental to total knee arthroplasty revision: Surgical technique

Unicompartmental Knee Arthroplasty (UKA) is an effective surgical option for managing unicompartmental knee osteoarthritis; it represents 10% of all knee arthroplasties worldwide, increasing 32.5% annually in the United States alone. Despite evolution in surgical technique and implant design, success rate and long-term survivorship of UKA have been historically lower than Total Knee Arthroplasty (TKA). The most common causes of UKA failure leading to revision are polyethylene wear, progression of arthritis, aseptic loosening and patella-femoral symptoms due to poor patient selection in many cases. Historically, UKA revisions have presented technical challenges mainly related to managing residual bone defects and ligament insufficiency ultimately leading to knee instability: the fear of instability has often pushed surgeons to lower the threshold for an increase of the intra-articular level of constraint. Unfortunately, the use of more constrained implants requires sacrificing bone stock and has been related to higher rates of re-revision secondary to recurrence of aseptic loosening. Because of these challenges, the authors developed a surgical technique that could combine balancing the knee during revision surgery with the use of the less constrained polyethylene option. To achieve this, we started evaluating a novel device (VERASENSE, Orthosensor, FL) designed to support soft tissue balancing during primary TKA. This intraoperative sensing technology dynamically quantifies intra-articular loads during TKA trial with the goal of correcting any residual imbalance in real time. Herein we propose a novel surgical technique, which might allow use of a primary TKA design characterized by a lower level of constraint, instead of a constrained or hinged revision knee system, during UKA revision. A key aspect of this technique is the use of sensing technology during intraoperative stability testing.

How to Quantitatively Balance a Total Knee? A Surgical Algorithm to Assure Balance and Control Alignment

To achieve a balanced total knee, various surgical corrections can be performed, while intra-operative sensors and surgical navigation provide quantitative, patient-specific feedback. To understand the impact of these corrections, this paper evaluates the quantitative impact of both soft tissue releases and bone recuts on knee balance and overall limb alignment. This was achieved by statistically analyzing the alignment and load readings before and after each surgical correction performed on 479 consecutive primary total knees. An average of three surgical corrections were required following the initial bone cuts to achieve a well aligned, balanced total knee. Various surgical corrections, such as an arcuate release or increasing the tibial polyethylene insert thickness, significantly affected the maximum terminal extension. The coronal alignment was significantly impacted by pie-crusting the MCL, adding varus to the tibia, or releasing the arcuate ligament or popliteus tendon. Each surgical correction also had a specific impact on the intra-articular loads in flexion and/or extension. A surgical algorithm is presented that helps achieve a well-balanced knee while maintaining the sagittal and coronal alignment within the desired boundaries. This analysis additionally indicated the significant effect that soft tissue adjustments can have on the limb alignment in both anatomical planes.

Achieving a Balanced Knee in Robotic TKA

Total knee arthroplasty (TKA) surgery with manual instruments provides a quantitatively balanced knee in approximately 50% of cases. This study examined the effect of combining robotics technology with real-time intra-operative sensor feedback on the number of quantitatively balanced cases in a consecutive series of 200 robotic-assisted primary TKAs. The robotics platform was used to plan the implant component position using correctable poses in extension and a manual, centrally pivoting the balancer in flexion, prior to committing to the femoral cuts. During the initial trialing, the quantitative state of balance was assessed using an instrumented tibial tray that measured the intra-articular loads in the medial and lateral compartments. These sensor readings informed a number of surgical corrections, including bone recuts, soft-tissue corrections, and cement adjustments. During initial trialing, a quantitatively balanced knee was achieved in only 65% of cases. After performing the relevant soft-tissue corrections, bone recuts, and cement adjustments, 87% of cases ended balanced through the range of motion. Meanwhile, this resulted in a wide range of coronal alignment conditions, ranging from 6° valgus to 9° varus. It is therefore concluded that gaps derived from robotics navigation are not indicative for a quantitatively balanced knee, which was only consistently achieved when combining the robotics platform with real-time feedback from intra-operative load sensors.