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 (ΔKOOS. 4. ) 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 ΔKOOS. 4. 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 ΔKOOS. 4. (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

Complications after total knee arthroplasty (TKR) such as malalignment, instability, subluxation, excessive wear, and loosening have been attributed to poor soft-tissue balance. Traditional approaches for soft-tissue balance involve static measurements in full extension and at 90° flexion. A trial prosthesis instrumented with force transducers was used to measure soft-tissue balance through the entire range of flexion. The trial prosthesis was instrumented with four force transducers, one at each corner of the tibial tray, and was implanted in four cadaver knees and four patients intra-operatively. Tibial forces were recorded during passive knee flexion after the tibial and femoral bone cuts were made and again after soft-tissue balance was achieved using standard techniques. In all eight knees measurable imbalance was initially recorded. The differences in forces were a mean of 18 N (range, 6 to 72) mediolateral and a mean of 26 N (range, 13 to 108) anteroposterior. After a routine procedure of soft-tissue balancing, the mean imbalance between the transducers was reduced by 62 % to 87 % (p < 0.05). However, even the knees that appeared perfectly balanced at 0° and 90° flexion, some imbalance occurred [mean 22 N (range, 2 to 34)] at flexion angles other than 0° and 90°. Soft-tissue balance in TKR remains a complex concept. Even after accurate static balancing was achieved in extension and 90° flexion, dynamic measurements revealed discrepancies in mid flexion, which may explain the wide variation in knee kinematics reported after TKR and in the reported incidences of mid-flexion knee instability. Computer-aided surgical navigation systems can increase the precision and accuracy of component alignment. However, these systems cannot directly address soft-tissue balance and knee tightness. An instrumented tibial prosthesis could be a useful adjunct to enhance the value of these navigation tools

Introduction/Aim. Mid-flexion instability is a well-documented, but often poorly understood cause of failure of TKA. NAVIO robotic-assisted TKA (RA-TKA) offers a novel, integrative approach as a planning, execution as well as an evaluation tool in TKA surgery. RA-TKA provides a hybrid planning technique of measured resection and gap balancing- generating a predictive soft-tissue balance model, prior to making cuts. Concurrently, the system uses a semi-active robot to facilitate both the execution and verification of the plan, as it pertains to both the static and dynamic anatomy. The goal of this study was to assess the ability of the NAVIO RA-TKA to plan, execute and deliver an individualized approach to the soft-tissue balance of the knee, specifically in the “mid-flexion” arc of motion. Materials and Methods. Between May and September 2018, 50 patients underwent NAVIO RA-TKA. Baseline demographics were collected, including age, gender, BMI, and range of motion. The NAVIO imageless technique was used to plan the procedure, including: surface-mapping of the static anatomy; objective assessment of the dynamic, soft-tissue anatomy; and then application of a hybrid of measured-resection and gap-balancing technique. Medial and lateral gaps as predicted by the software were recorded throughout the entire arc of motion at 15° increments. After executing the plan and placing the components, actual medial and lateral gaps were recorded throughout the arc of motion. Results. In the assessment of coronal-plane balance, the average deviation from the predicted plan between 0–90° was 0.9mm in both the medial and lateral compartments (range 0.5–1.2mm). In the mid-flexion arc (15–75°), final soft-tissue stability was within 1.0mm of the predictive plan (range 0.9–1.2mm). Discussion/Conclusions. In this study, NAVIO RA-TKA demonstrated a highly accurate and reproducible surgical technique to plan, execute and verify a balanced a soft-tissue envelope in TKA. Objective soft-tissue balancing of the TKA can now be performed, including the mid-flexion arc of motion. Further analysis can determine if these objective measurements will translate into improved patient-reported outcome scores

Purpose

The purpose of this study is to evaluate stiff knees which have a preoperative arc of motion (AOM) < 65 degrees and maximum flexion < 90 degrees under anesthesia for primary TKA.

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal

Fifteen-year survivorship studies demonstrate that total knee replacements have excellent survivorship, with reports of 85% to 97%. However, excellent survivorship does not equate to excellent patient reported outcomes. Noble et al. reported that 14% of their patients were dissatisfied with their outcome with more than half expressing problems with routine activities of daily living. There is also a difference in the patient's subjective assessment of outcome and the surgeon's objective assessment. Dickstein et al. reported that a third of total knee patients were dissatisfied, even though the surgeons felt that their results were excellent. Most of the patients who report lower outcome scores due so because their expectations are not being fulfilled by the total knee replacement surgery.

Perhaps this dissatisfaction is a result of subtle soft tissue imbalance that we have difficulty in assessing intra-operatively and post-operatively. Soft tissue balancing techniques still rely on subjective feel for appropriate ligamentous tension by the surgeon. Surgical experience and case volume play a major role in each surgeon's relative skill in balancing the knee properly.

New technology of “smart trials” with embedded microelectronics and accelerometers, used in the knee with the medial retinaculum closed, can provide dynamic, intra-operative feedback regarding knee quantitative compartment pressures and component tracking. After all bone cuts are made using the surgeon's preferred techniques, trial components with the sensored tibial trial are inserted and the knee is taken through a passive range of motion. After visualizing the resultant compartment pressures and tracking data on a graphical interface, the surgeon can decide whether to perform a soft tissue balance or minor bone recuts. If soft tissue balancing is chosen, pressure data can indicate where to perform the release and allow the surgeon to assess the pressure changes as titrated soft tissue releases are performed.

A multi-center study using smart trials has demonstrated dramatically better outcomes out to three years.

INTRODUCION

Appropriate soft tissue balance is an important factor for postoperative function and long survival of total knee arthroplasty(TKA). Soft tissue balance is affected by ligament release, osteophyte removal, order of soft tissue release, cutting angle of tibial surface and rotational alignment of femoral components. The purpose of this study is to know the characteristics of soft tissue balance in ACL deficient osteoarthritis(OA) knee and warning points during procedures for TKA.

Aims

It is unknown whether kinematic alignment (KA) objectively improves knee balance in total knee arthroplasty (TKA), despite this being the biomechanical rationale for its use. This study aimed to determine whether restoring the constitutional alignment using a restrictive KA protocol resulted in better quantitative knee balance than mechanical alignment (MA).

Soft tissue balance is important for good clinical outcome and good stability after TKA. Ligament balancer is one of the devices to measure the soft tissue balance. The objective of this study is to clarify the effect of the difference in the rotational position of the TKA balancer on medial and lateral soft tissue balance.

Background

Bone preservation is desired for future revision in any knee arthroplasty. There is no study comparing the difference in the amount of bone resection when soft tissue balance is performed with or without computer navigation.

To determine the effect on bony cuts when soft tissue balance is performed with or without use of computer software by standard manual technique in total knee arthroplasty.

One hundred patients aged 50 to 88 years underwent navigated TKR for primary osteoarthritis. In group A, 50 patients had both soft tissue release and bone cuts done using computer-assisted navigation. In group B, 50 patients had soft tissue release by standard manual technique first and then bone cuts were guided by computer-assisted navigation.

In group A the mean medial tibial resection was 5 ± 2.3 mm and lateral was 8 ± 1 mm compared to 5 ± 2 mm (P = 0.100) and 8 ± 1 mm respectively in group B (P = 0.860). In group A the mean medial femoral bone cut was 9 ± 2.9 mm and lateral was 8 ± 2 mm as compared to 9.5 ± 2.9 mm (P = 0.316) and 10 ± 2.2 mm respectively in group B (P = 0.001). Average prosthesis size was 6 (range 3 to 8) in group A as compared to size 5 (range 2 to 7) in group B. Average navigation time in group A was 102 minutes (range 45 to 172) and in group B was 83 minutes (range 42 to 165, P = 0.031).

Our results show that performing soft tissue release and bone cuts using computer- assisted navigation is more bone conserving as compared to manual soft tissue release and bone cuts using computer navigation for TKR, thus preserving bone for possible future revision surgery.

Objective

The goal of total knee arthroplasty (TKA) is to achieve a stable and well-aligned tibiofemoral and patello-femoral (PF) joint, aiming at long-term clinical patient satisfaction. The surgical principles of both cruciate retaining (CR) and posterior stabilized (PS) TKA are accurate osteotomy and proper soft tissue balancing. We have developed an offset-type tensor, and measured intra-operative soft tissue balance under more physiological joint conditions with femoral component in place and reduced PF joint.

In this study, we measured intra-operative soft tissue balance and assessed the post-operative knee joint stability quantitatively at one month, six months and one year after surgery, and compared these parameters between CR and PS TKAs.

Aims. The aims of this study were: 1) to describe extended restricted kinematic alignment (E-rKA), a novel alignment strategy during robotic-assisted total knee arthroplasty (RA-TKA); 2) to compare residual medial compartment tightness following virtual surgical planning during RA-TKA using mechanical alignment (MA) and E-rKA, in the same set of osteoarthritic varus knees; 3) to assess the requirement of soft-tissue releases during RA-TKA using E-rKA; and 4) to compare the accuracy of surgical plan execution between knees managed with adjustments in component positioning alone, and those which require additional soft-tissue releases. Methods. Patients who underwent RA-TKA between January and December 2022 for primary varus osteoarthritis were included. Safe boundaries for E-rKA were defined. Residual medial compartment tightness was compared following virtual surgical planning using E-rKA and MA, in the same set of knees. Soft-tissue releases were documented. Errors in postoperative alignment in relation to planned alignment were compared between patients who did (group A) and did not (group B) require soft-tissue releases. Results. The use of E-rKA helped restore all knees within the predefined boundaries, with appropriate soft-tissue balancing. E-rKA compared with MA resulted in reduced residual medial tightness following surgical planning, in full extension (2.71 mm (SD 1.66) vs 5.16 mm (SD 3.10), respectively; p < 0.001), and 90° of flexion (2.52 mm (SD 1.63) vs 6.27 mm (SD 3.11), respectively; p < 0.001). Among the study population, 156 patients (78%) were managed with minor adjustments in component positioning alone, while 44 (22%) required additional soft-tissue releases. The mean errors in postoperative alignment were 0.53 mm and 0.26 mm among patients in group A and group B, respectively (p = 0.328). Conclusion. E-rKA is an effective and reproducible alignment strategy during RA-TKA, permitting a large proportion of patients to be managed without soft-tissue releases. The execution of minor alterations in component positioning within predefined multiplanar boundaries is a better starting point for gap management than soft-tissue releases. Cite this article: Bone Jt Open 2024;5(8):628–636

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

Computer assisted total knee arthroplasty helps in accurate and reproducible implant positioning, bony alignment, and soft-tissue balancing which are important for the success of the procedure. In TKR, there are two surgical techniques one is measured resection in which bony landmarks are used to guide the bone cuts and the other is gap balancing which equal collateral ligament tension in flexion and extension is done before and as a guide to final bone cuts. Both these procedures have their own advantages and disadvantages. We retrospectively collected the data of 128 consecutive patients who underwent computer-assisted primary TKA using either a gap-balancing technique or measured resection technique. All the operations were performed by a single surgeon using computer navigation system available during a period between June 2016 to October 2016. Inclusion criteria were all patients requiring a primary TKA, male or female patients, and who have given informed consent for participation in the study. All patients requiring revision surgery of a previous implanted TKA or affected by active infection or malignancy, who presented hip ankylosis or arthrodesis, neurological deficit or bone loss or necessity of more constrained implants were excluded from the study. Two groups measured resection and gap balancing was randomly selected. At 1-year follow-up, patients were assessed by a single orthopaedic registrar blinded to the type of surgery using the Knee Society score (KSS) and functional Knee Society score (FKSS). Outcomes of the 2 groups were compared using the paired t test. All the obtained data were analysed. Statistical analysis was performed using SPSS 11.5 statistical software (SPSS Inc. Chicago). Inter-class correlation coefficient (ICC) and paired t-test were used and statistical significance was set at P = 0.05. In the measured resection group, the mean FKSS increased from 48.8769 (SD, 2.3576), to 88.5692 (SD, 2.7178) respectively. In the gap balancing group, the respective scores increased from 48.9333 (SD, 3.6577) to 89.2133(SD, 7.377). Preoperative and Postoperative increases in the respective scores were slightly better with the gap balancing technique; the respective p values were 0.8493 and 0.1045. The primary goal of TKA is restoration of mechanical axis and soft-tissue balance. Improper restoration leads to poor functional outcome and premature prosthesis loosening. Computer navigation enables precise femoral and tibial cuts and controlled soft-tissue release. Well balanced and well aligned knee is important for good results. Mechanical alignment and soft-tissue balance are interlinked and corrected by soft tissue releases and precise proximal tibial and distal femoral cuts. The 2 common techniques used are measured resection and gap balancing techniques. In our study, knee scores of the 2 groups at 1-year follow-up were compared, as most of the improvement occurs within one year, with very little subsequent improvement. Some surgeons favour gap balancing technique, as it provides more consistent soft-tissue tension in TKA

Introduction and Aims: Complications after total knee arthroplasty (TKA) have been attributed to soft-tissue imbalance. The current approach to soft-tissue balance is static measurements in extension and 90 degrees flexion. Dynamic balancing during the entire range of flexion may be more valuable. Method: Complications after total knee arthroplasty (TKA) have been attributed to soft-tissue imbalance. The current approach to soft-tissue balance is static measurements in extension and 90 degrees flexion. Dynamic balancing during the entire range of flexion may be more valuable. Results: All knees (in vitro and in vivo) initially recorded imbalance in the tibial forces: mean 18N (6–72) in the mediolateral and 26N (13–108) in the anteroposterior direction. After soft-tissue balancing, the mean imbalance reduced by 87%. Even when knees appeared well balanced at zero and 90-degree flexion, there was imbalance [mean 22N (2–34)] at flexion angles between zero and 90 degrees. The 2mm thicker insert increased forces by a mean of 89% (22–180%). Conclusion: Soft-tissue balance in TKA remains a complex concept. The routine instruments used for soft-tissue balance only detect mediolateral imbalance. Even when accurate static balancing was achieved, dynamic measurements revealed imbalance in mid-flexion. These results explain some of the variability in knee kinematics after TKA and the incidence of mid-flexion instability

Introduction. Proper soft-tissue balance is important for achieving favorable clinical outcomes following TKA, as ligament imbalance can lead to pain, stiffness or instability, accelerated polyethylene wear, and premature failure of implants. Until recently, soft-tissue balancing was accomplished by subjective surgeon feel and by use of static spacer blocks. Now, nanonsensor-embedded implant trials allow surgeons to quantify peak load and center of load in the medial and lateral compartments during the procedure, and to adjust ligament tension and implant positioning accordingly. The purpose of this 3-year, multicenter study is to evaluate 500 patients who have received primary TKA with the use of intraoperative sensors in order to correlate quantified ligament balance to clinical outcomes. Methods. To date, 7 centers have contributed 215 patients who have undergone primary TKA with the use of intraoperative sensors. Patients are seen at a pre-operative visit (within 3 months prior to surgery), and post-operatively at 6 weeks, 6 months, and at 1, 2, and 3-year anniversaries. Standard demographic and surgical data is collected for each patient, including: age at time of surgery, BMI, operative side, gender, race, and primary diagnosis. At each interval, anatomic alignment and range of motion are assessed; KSS and WOMAC evaluations are administered; and a set of standard radiographs is collected, including: standing anteroposterior, standing-lateral, and the sunrise patellar view. Intraoperative loads were recorded for pre- and post-release joint states. All soft-tissue release techniques were recorded. “Optimal” soft-tissue balance was defined as a medial-lateral load difference of less than or equal to 15 lbs. Results. The average age of this cohort was 70 years: 63% are female and 37% are male, with a mean BMI of 30.6. Ninety five percent of cases had a primary diagnosis of osteoarthritis. The majority of cases (72.5%) exhibited suboptimal soft-tissue balance (>15 lbs. of medial-lateral compartmental loading difference) prior to ligamentous release. Using the intraoperative sensor for guidance, 82% (p < .01) of patients were released and confirmed to exhibit a state of optimal joint balance at closure. Patient self-reported outcome scores—both KSS and WOMAC—showed significant improvement (p < .01) from the pre-operative interval to the 6-month follow-up interval. The average increase for KSS at 6 months was 60 points. Discussion. Optimized ligament balance using intraoperative sensors led to significant improvement in KSS and WOMAC scores at a 6-month follow-up interval in 215 knees. Notably, the 60-point average increase in KSS, at 6 months, is approximately 200% greater than historical data, obtained from existing literature, using traditional methods of TKA balancing. Measuring the effect of specific ligamentous releases on subsequent load and balance can potentially enable the development of release algorithms to guide surgeons to balance TKA using sensor data. Further, correlating quantifiable data on peak load and center of load to patient outcomes will help clarify what truly defines “optimum balance.” Additional study subject accrual and further longitudinal follow-up is needed to affirm the early observation that sensor-quantified soft-tissue balancing improves patient outcomes in TKA

Introduction. The success of total knee arthroplasty (TKA) necessitates precise osteotomies and soft tissue balancing to realign the lower extremity to a neutral mechanical axis. While technological advances have facilitated precise osteotomies, soft tissue balancing has traditionally relied mostly on surgeons’ subjective and variable tactile feedback. As soft tissue imbalance accounts for 35% of early TKA revisions in North America, we aimed to compare outcomes when TKA was balanced free-hand versus a sensor-guided balancing device (VERASENSE, OrthoSensor, Inc (Dania, FL)). Methods. In a randomized-controlled fashion, patients underwent primary TKA soft tissue balancing either free-hand or with VERASENSE (Orthosensor Inc, Dania FL) at our institution beginning January 2018. With VERASENSE, soft-tissue balancing is considered when the pressure difference between the medial and lateral knee compartments was less than 15 pounds. Data regarding patient-reported outcomes, knee range of motion (ROM), pain level, opioid consumption, inpatient ambulation distance, length of stay (LOS), and incidence of arthrofibrosis was collected and analyzed in a two-year minimum follow-up and target patient goal of 120 patients. Results. The study cohort thus far consists of 53 patients, average age 72.4 ± 8.8 years. Soft-tissue balance was conducted freehand in 23 patients and the VERASENSE was used in 30 patients. In the free-hand cohort, preoperative patient-reported outcomes for SF-12 Physical, Mental, WOMAC (pain, stiffness, function) parameters, and knee society function score (KSFS) were 39.3, 45.8, 47.7, 37.5, 48.1, and 50.0, respectively and post-operative at 3 months were 45.0, 53.0, 79.5, 72.5, 81.0, and 72.5, respectively; difference between preoperative and post-operative ROM was +8.4 degrees; average VAS pain score in the first 3 post-operative days was 2.9 ± 2.3; average opioid consumption was 100.7 ± 103.3 mg morphine equivalents; average inpatient ambulation per day was 267.9 ± 187.4 feet; average LOS was 2.3 days. In the VERASENSE cohort, patient reported outcomes for SF-12 Physical, Mental, WOMAC (pain, stiffness, function) parameters, and knee society function score (KSFS) were 38.2, 48.6, 40.1, 30.3, 40.0, and 48.7, respectively and post-operative at 3 months were 41.9, 47.6, 67.2, 59.7, 69.1, and 56.7; difference between preoperative and post-operative ROM was +3.9 degrees; average VAS pain score in the first 3 post-operative days was 2.9 ± 2.3; average opioid consumption was 105.8 ± 86.7 mg morphine equivalents; average inpatient ambulation was 384.6 ± 316.1 feet; average LOS was 2.1 days. There was no incidence of arthrofibrosis and subsequent manipulation under anesthesia in the trial. Conclusion. Short-term follow up of this randomized-controlled trial demonstrates equivalent patient-reported and clinical outcomes when soft-tissue balancing in TKA is performed free-hand versus utilization of VERASENSE, though we hypothesize a difference in the long-term

Introduction. Acquiring adaptive soft-tissue balance is one of the most important factors in total knee arthroplasty (TKA). However, there have been few reports regarding to alteration of tolerability of varus/valgus stress between before and after TKA. In particular, there is no enough data about mid-flexion stability. Based on these backgrounds, it is hypothesized that alteration of varus/valgus tolerance may influence post-operative results in TKA. The purpose of this study is an investigation of in vivo kinematic analyses of tolerability of varus/valgus stress before and after TKA, comparing to clinical results. Materials and Methods. A hundred knees of 88 consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. The kinematic parameters of the soft-tissue balance, and amount of coronal relative movement between femur and tibia were obtained by interpreting kinematics, which display graphs throughout the range of motion (ROM) in the navigation system. Femoro-tibial alignments were recorded under the stress of varus and valgus before the procedure and after implantation of all components. In each ROM (0, 30, 60, 90, 120 degrees), the data of coronal relative movement between femur and tibia (tolerability) were analyzed before and after implantation. Furthermore, correlations between tolerability of varus/valgus and clinical improvement revealed by ROM and Knee society score (KSS) were analyzed by logistic regression analysis. Results. Evaluation of soft tissue balance with navigation system revealed that the tolerance of coronal relative movement between femur and tibia (varus/valgus) after implantation was significantly decreased compared with before implantation even in mid-flexion range. There were no significant correlations between tolerability of coronal relative movement and improvement of extension range and KSS. However, mid-flexion tolerability showed negative correlation with flexion range. Discussion. One of the most important principles for ligament balancing in TKA for varus knees is involved that the medial extension gap should be within 1–3mm to avoid flexion contracture and a feeling of instability, the medial flexion gap should be equal or 1–2mm larger to the medial extension gap, and lateral extension laxity up to 5 degrees is acceptable. However, there have been few reports measuring laxity from 30 to 60 degrees. In this study, the tolerance of coronal relative movement was significantly limited even in mid-flexion. However, mid-flexion tightness was not significantly correlated with clinical results except for flexion range. This result might be suggested that high tolerability of coronal relative movement in mid-flexion range may lead to widening of flexion range of motion of the knee after TKA. For any figures or tables, please contact authors directly

Introduction / Purpose. Many factors can influence postoperative knee flexion angle after total knee arthroplasty (TKA), and range of flexion is one of the most important clinical outcomes. Although many studies have reported that postoperative knee flexion is influenced by preoperative clinical conditions, the factors which affect postoperative knee flexion angle have not been fully elucidated. As appropriate soft-tissue balancing as well as accurate bony cuts and implantation has traditionally been the focus of TKA success, in this study, we tried to investigate the influence of intraoperative soft-tissue balance on postoperative knee flexion angle after cruciate-retaining (CR) TKA using a navigation system and offset-type tensor. Methods. We retrospectively analyzed 55 patients (43 women, 12 men) with osteoarthritis who underwent TKA using the same mobile-bearing CR-type implant (e.motion; B. Braun Aesculap, Germany). The mean age at the time of surgery was 74.2 (SD 7.3) years. The exclusion criteria for this study included valgus deformity, severe bony defect requiring bone graft or augmentation, revision TKA, active knee joint infection, and bilateral TKA. Intraoperative soft-tissue balance parameters such as varus ligament balance and joint component gap were measured in the navigation system (Orthopilot 4.2; B. Braun Aesculap) while applying 40-lb joint distraction force at 0°, 10°, 30°, 60°, 90°, and 120° of knee flexion using an offset-type tensor with the patella reduced. Varus ligament balance was defined as the angle (degree, positive value in varus imbalance) between the seesaw and platform plates of the tensor that was obtained from the values displayed by the navigation system. To determine clinical outcome, we measured knee flexion angle using a goniometer with the patient in the supine position before and 2 years after surgery. Correlations between the soft-tissue parameters and postoperative knee flexion angle were analyzed using simple linear regression models. Pre- and postoperative knee flexion angle were also analyzed in the same manner. Results. Mean pre- and postoperative flexion angle were 120.5 ± 1.9° and 121.9 ± 1.3°, which did not show significant improvement after surgery. Varus ligament balance at 90° of flexion was positively correlated with postoperative knee flexion angle (R = 0.56, P < 0.001) and calculated joint gap of the lateral compartment at 90° of flexion showed positive correlation with postoperative knee flexion angle (R = 0.51, P < 0.001), while no correlation was found between joint gap of the medial compartment at 90° of flexion and postoperative knee flexion angle. Also, as with some past studies, joint component gap at 90° of flexion was slightly correlated with postoperative knee flexion angle (R = 0.30, P < 0.05) and pre- and postoperative knee flexion angle showed a significant positive correlation (R = 0.63, P < 0.001). Conclusions. Varus ligament balance at mid to deep flexion was a factor that predicted postoperative knee flexion angle after CR-TKA. In addition to preoperative knee flexion angle and joint component gap at 90° of flexion, lateral laxity at 90° of flexion is one of the most important factors affecting postoperative knee flexion angle

Introduction. Instability after total knee arthroplasty (TKA) represents, in excess of, 7% of reasons for implant failure. This mode of failure is correlated with soft-tissue imbalance, and has continued to be problematic despite advances in implant technology. Thus, understanding the options available to execute safe and effective soft-tissue release is critical to mitigating future complications due to instability. This study aimed to use intraoperative sensors to evaluate a multiple needle puncturing technique (MNPT), in comparison with traditional transection-based release, to determine its biomechanical and clinical efficacy. Methods. Seventy-five consecutive, cruciate-retaining TKAs were performed, as part of an 8-site multicenter study. All procedures were performed with the use of an intraoperative sensor to ensure quantitative balance, as per previously reported literature. Of the 75-patient cohort, 50 patients were balanced with the MNPT; 20 patients were balanced with traditional transection. All patients were followed out to 1-year, and administered KSS, WOMAC, and satisfaction. Alignment and ROM was captured for all patients, pre-operatively and at the 1-year follow-up interval. Results. All patient joints could be released to a balanced joint state, regardless of technique used. There was no significant difference between the two groups (MNPT vs. transection), pre-operatively, with respect to range of motion or alignment (114° MNPT; 114° transection). At 1-year, post-operatively, there was no significant difference in WOMAC score, KSS scores, satisfaction, or ROM (Respectively: 13.1 MNPT vs. 14.6 transection; 174.9 MNPT vs.176.5 transection; 31.7 “Very Satisfied” MNPT vs. 32.2 “Very Satisfied” transection; 124° MNPT vs. 125° transection). No adverse outcomes related to balancing technique have been reported. Discussion. Instability contributes to the current 2.7 billion dollar TKA revision burden in the United States. Understanding the efficacy of different techniques in soft-tissue balancing may help to mitigate unfavorable complications. In this study, it was found that the MNPT is just as safe and effective at achieving soft-tissue balance as transectional release techniques, and showed no deviation from the achievement of optimal post-operative outcomes at 1-year. This technique, when used with intraoperative sensors to quantify joint balance, may thereby offer a more controlled way to release soft-tissue, incrementally, to achieve precise balance