Using a tensor for total knee arthroplasty (TKA) that is designed to facilitate soft tissue balance measurements with a reduced patello-femoral (PF) joint, we examined the influence of pre-operative deformity on intra-operative soft tissue balance during posterior-stabilized (PS) TKA. Joint component gap and varus angle were assessed at 0, 10, 45, 90 and 135° of flexion with femoral trial prosthesis placed and PF joint reduced in 60 varus type osteoarthritic patients. Joint gap measurement showed no significant difference regardless the amount of pre-operative varus alignment. With the procedures of soft tissue release avoiding joint line elevation, however, intra-operative varus angle with varus alignment of more than 20 degrees exhibited significant larger values compared to those with varus alignment of less than 20 degrees throughout the range of motion. Accordingly, we conclude that pre-operative severe varus deformity may have the risk for leaving post-operative varus soft tissue balance during PS TKA

Introduction. Accurate soft tissue balancing has been recognized as important as alignment of bony cut in total knee arthroplasty (TKA). In addition, using a tensor for TKA that is designed to facilitate soft tissue balance measurements throughout the range of motion with a reduced patello-femoral (PF) joint and femoral component in place, PF joint condition (everted or reduced) has been proved to have a significant effect for intra-operative soft tissue balance. On the other hand, effect of patellar height on intra-operative soft tissue balance has not been well addressed. Therefore, in the present study, we investigated the effect of patellar height by comparing intra-operative soft tissue balance of patella higher subjects (Insall-Salvati index>1) and patella lower subjects (Insall-Salvati indexâ‰/1). Materials and methods. The subjects were 30 consecutive patients (2 men, 28 women), who underwent primary PS TKA (NexGen LPS-flex PS: Zimmer, Warsaw, IN, USA) between May 2003 and December 2006. All cases were osteoarthritis with varus deformity. Preoperative Insall-Salvati index (ISI) was measured and patients were divided into two groups; the patella higher group (ISIï1/4ž1: 18 knees average ISI was 1.12) and the patella lower group (ISIâ‰/1; 12 knees average ISI was 0.94). Component gap and ligament balance (varus angle) were measured using offset-type tensor with 40lb distraction force after osteotomy with the PF joint reduced and femoral trial in place at 0, 10, 45, 90, 135 degrees of knee flexion. Data of two groups were compared using unpaired t test. Results. Component gap was increased from 0 to 90 degrees of knee flexion and decreased at 135 degrees of knee flexion in both groups. Component gaps of the patella higher group in average were 10.9, 14.3, 16.6, 18.2, 16.8 mm at 0, 10, 45, 90, 135 degrees of knee flexion, respectively. Component gaps of the patella lower group in average were 9.6, 13.6, 14.6, 15.5, 14.0 mm at 0, 10, 45, 90, 135 degrees of knee flexion, respectively. When comparing two groups, component gaps of the patella higher group showed larger trend than those of the patella lower group. Especially at 90 and 135 degrees of knee flexion, the patella higher group showed significant larger values than the patella lower group (p<0.05). Varus angles of the patella higher group in average were 2.2ï1/4Œ3.4ï1/4Œ5.0ï1/4Œ5.9ï1/4Œ6.1 degrees at 0, 10, 45, 90, 135 degrees of knee flexion, respectively. Varus angles of the patella lower group in average were 1.7ï1/4Œ2.8ï1/4Œ4.4ï1/4Œ4.9ï1/4Œ4.6 degrees at 0, 10, 45, 90, 135 degrees of knee flexion, respectively. Varus angles of the patella higher group showed slight larger trend than those of the patella lower group, however there was no significant differences between two groups. Discussion. In the present study, the patella higher group showed significant larger component gaps than the patella lower group at high flexion angles (90, 135 degree). This result suggests that smaller pressure on extensor mechanism of the patella higher group has led to larger component gaps at higher flexions. In conclusion, pre-operative measurement of ISI can help surgeons predict intra-operative soft tissue balance

Objective. Although both accurate component placement and adequate soft tissue balance have been recognized as essential surgical principle in total knee arthroplasty (TKA), the influence of intra-operative soft tissue balance on the post-operative clinical results has not been well investigated. In the present study, newly developed TKA tensor was used to evaluate soft tissue balance quantitatively. We analyzed the influence of soft tissue balance on the post-operative knee extension after posterior-stabilized (PS) TKA. Materials and Methods. Fifty varus type osteoarthritic knees implanted with PS-TKAs were subjected to this study. All TKAs were performed using measured resection technique with anterior reference method. The thickness of resected bone fragments was measured. Following each bony resection and soft tissue releases, we measured soft tissue balance at extension and flexion of the knee using a newly developed offset type tensor. This tensor device enabled quantitative soft tissue balance measurement with femoral trial component in place and patello-femoral (PF) joint repaired (component gap evaluation) in addition to the conventional measurement between osteotomized surfaces (osteotomy gap evaluation). Soft tissue balance was evaluated by the center gap (mm) and ligament balance (°; positive in varus) applying joint distraction forces at 40 lbs (178 N). Active knee extension in spine position was measured by lateral X-ray at 4 weeks post-operatively. The effect of each parameter (soft tissue balance evaluations, thickness of polyethylene insert and resected bone) on the post-operative knee extension was evaluated using simple linear regression analysis. P<0.05 was considered statistically significant. Results. The thickness of resected bone, flexion center gap and ligament balance at extension and flexion had no correlations to the knee extension angle. Thickness of polyethylene insert correlated positively to knee extension (r=0.38, p=0.007). Significant positive correlation were found between extension center gap in both osteotomy and component gap evaluation to the post-operative knee extension. The coefficient of correlations were 0.33 (p=.02) with osteotomy gap and 0.47 (p=0.0007) with component gap evaluation. Discussion and Conclusion. In the present study, extension center gap was found to positively correlate to the early post-operative knee extension. The extension center gap could be considered as the summation of the simultaneous gap from bone resections and the elongation of soft tissue envelope under joint distraction force applied by tensor. The soft tissue with the lower stiffness would be elongated more, and result in the larger center gap. Accordingly, the stiffness of the soft tissue envelope might play an important role on the magnitude of extension center gap and the post-operative knee extension. Furthermore, the center gap in component gap evaluation had higher coefficient of correlation comparing to that in osteotomy gap. Proposed component gap evaluation in soft tissue balance measurement might be more physiological and relevant to the joint condition after TKA, and useful to predict post-operative clinical results

Fifteen-year survivorship studies demonstrate that total knee replacement 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 intraoperatively and postoperatively. 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 a 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

Introductions. In cruciate-retaining total knee arthroplasty (TKA), among many factors influencing post-operative outcome, increasing the tibial slope has been considered as one of the beneficial factors to gain deep flexion because of leading more consistent femoral rollback and avoiding direct impingement of the insert against the posterior femur. In contrast, whether increasing the tibial slope is useful or not is controversial in posterior-stabilized (PS) TKA, Under such recognition, accurate soft tissue balancing is also essential surgical intervention for acquisition of successful postoperative outcomes in TKA. In order to permit soft tissue balancing under more physiological conditions during TKAs, we developed an offset type tensor to obtain soft tissue balancing throughout the range of motion with reduced patello-femoral(PF) and aligned tibiofemoral joints and have reported the relationship between intra-operative soft tissue balance and flexion angles. In this study, we therefore assessed the relationship between intra-operative soft tissue balance assessed using the tensor and the tibial slope in PS TKA. Materials and methods. Thirty patients aged with a mean 72.6 years were operated PS TKA(NexGen LPS-Flex, Zimmer, Inc. Warsaw, IN) for the varus type osteoarthritis. Following each bony resection and soft tissue release using measure resection technique, the tensor was fixed to the proximal tibia and femoral trial prosthesis was fitted. Assessment of the joint component gap (mm) and the ligament balance in varus (°)was carried out at 0, 10, 45, 90and 135degrees of knee flexion. The joint distraction force was set at 40lbs. Joint component gap change values during 10-0°,45-0°, 90-0°, 135-0° flexion angle were also calculated. The tibial slopes were measured by postoperative lateral radiograph. The correlation between the tibial slope and values of soft tissue balance were assessed using linear regression analysis. Results. Average joint component gaps were 11.2, 14.7, 16.7, 18.4 and 17.0 mm and ligament balance in varus were 2.2, 2.9, 5.3, 6.8 and 6.9°at 0, 10, 45, 90 and 135° of flexion, respectively. Average joint component gap changes were 3.5, 5.6, 7.2 and 5.7 mm at each range of motion between 10–0, 45-0, 90–0 and 135–0° of flexion, respectively. The mean tibial slope was 5.0(1.6–9.6) degrees. Joint component gap at 90 (R = 0.537, p<0.01),135(R=0.463, p<0.05) degrees of flexion, and joint component gap change value of 90–0° (R = 0.433, p<0.05) showed positive correlations with tibial slope. The other factors assessed in this study showed no correlation with tibial slope. Discussions. The joint gap toward mid-range of flexion might be measured at anterior part of the tibiofemoral joint, whereas the values of joint gap at high flexion where the femur shifted posterior due to femoral rollback were measured the widened posterior part of the joint gap. In addition, extensor mechanism as well as tibial slope might influence joint gap at deep flexion. In conclusion, even PS TKA, increasing the posterior tibial slope resulting in larger flexion gap compared to extension gap should be taken into account for the flexion-extension gap balancing

Aim: Accurate soft tissue balance in total knee arthroplasty (TKA) is not only technically challenging but also difficult to teach to trainees; we believe that computer navigation provides a very useful tool for objective and reproducible soft tissue balance. Methods: We studied 52 patients (31 females and 21 males) with knee osteoarthritis and recorded the change of the Medial (MCL) and Lateral Collateral Ligament (LCL) length at full extension and at 90o flexion. Pre- and post-operative results were compared. The assessment was performed by consultant orthopaedic surgeons using trackers and navigation knee replacement software. Data was analysed using the student t-test. Results: The navigation software programme was used to measure the change of the collateral ligament length. Ligament laxity is represented by a negative number and a positive number is used to represent stretching and apparent elongation of the ligament. The medial collateral (MCL) length at full extension ranged from −9mm to 11mm and post-operatively was reduced to −16mm and 8mm, (p=0.042). At 90o flexion the length ranged from −3mm to 9mm and postoperatively was reduced to −8mm and 10mm (p=0.025). The lateral collateral (LCL) length at full extension changed from −10mm to 9mm pre-operatively to −13mm and 6mm post-operatively (p=0.011). At 90o flexion the range from −8mm and 9mm pre-operatively changed to − 5mm and 11mm post-operatively (p=0.005). All the above changes correspond to improvement in the post-operative axial alignment. Conclusion: Our results demonstrate that computer navigation provides a useful adjunct to the accurate and reproducible soft tissue balance in knee arthroplasty which can be used to evaluate results and for training purposes

Introduction. Appropriate intraoperative soft tissue balancing is recognized to be essential in total knee arthroplasty (TKA). However, it has been rarely reported whether intraoperative soft tissue balance reflects postoperative outcomes. In this study, we therefore assessed the relationship between the intra-operative soft tissue balance measurements and the post-operative stress radiographs at a minimum 1-year follow-up in cruciate-retaining (CR) TKA, and further analyzed the postoperative clinical outcome. Methods. The subjects were 25 patients diagnosed with osteoarthritis with varus deformity and underwent primary TKA. The mean age at surgery was 72.0 ± 7.5 years (range, 47–84 years). The Surgeries were performed with the tibia first gap technique using CR-TKA (e motion, B. Braun Aesculap) and the image-free navigation system (Orthopilot). We intraoperatively measured varus ligament balance (°, varus angle; VA) and joint component gap (mm, center gap; CG) at 10° and 90° knee flexion guided by the navigation system, with the patella reduced. At a minimum 1-year follow-up, post-operative coronal laxity at extension was assessed by varus and valgus stress radiographs of the knees with 1.5 kgf using a Telos SE arthrometer (Fa Telos) and that at flexion was assessed by epicondylar view radiographs of the knees with a 1.5-kg weight at the ankle. After calculating postoperative VA and CG from measurements of radiographs, measurements and preoperative and postoperative clinical outcome, such as Knee Society Clinical Rating System (Knee score; KSS, Functional score; KSFS) and postoperative knee flexion, were analyzed statistically using linear regression models and Pearson's correlation coefficient. Results. The mean follow-up duration was 22.0 months (range, 12–36 months). The average pre-operative KSS and KSFS was 57.0 points and 62.8, respectively, and the average post-operative scores were 98.4 points and 91.5, respectively. The both scores were significantly improved. The mean preoperative knee flexion angle was 121.8°, and postoperative knee flexion angle was 124.8°.ã��The mean pre- and post-operative joint component gaps at extension and flexion were 14.4 and 14.4 mm, and 15.6 and 16.5 mm, respectively. The mean pre- and post-operative values of varus ligament balance at extension and flexion were 2.5° and 2.7°, and 1.7° and 4.4°, respectively. Regression analysis revealed that the intraoperative CG was positively correlated with the postoperative CG at both extension and flexion (R = 0.45, P < 0.05; R = 0.52, P < 0.05, respectively) and intraoperative VA was positively correlated with the postoperative VA at extension (R = 0.52, P < 0.05) (Figure 1). Furthermore, postoperative flexion angle was positively correlated with the postoperative CG and VA at flexion (R=0.43, p<0.05, R=0.44, p<0.05, respectively) (Figure 2). Conclusion. We revealed that intraoperative soft tissue balance reflect postoperative soft tissue balance in CR-TKA. Furthermore, postoperative lateral laxity at flexion may permit the improvement of postoperative flexion angle

INTRODUCTION. To obtain appropriate joint gap and soft tissue balance, and to correct the lower limb alignment are important factor to achieve success of total knee arthroplasty (TKA). A variety of computer-assisted navigation systems have been developed to implant the component accurately during TKA. Although, the effects of the navigation system on the joint gap and soft tissue balance are unclear. The purpose of the present study was to investigate the influence of accelerometer-based portable navigation system on the intraoperative joint gap and soft tissue balance. METHODS. Between March 2014 and March 2015, 36 consecutive primary TKAs were performed using a mobile-bearing posterior stabilized (PS) TKA (Vanguard RP; Biomet) for varus osteoarthritis. Of the 36 knees, 26 knees using the accelerometer-based portable computer navigation system (KneeAlign2; OrthAlign) (N group), and 10 knees using conventional alignment guide (femur side; intramedullary rod, tibia side; extramedullary guide) (C group). The intraoperative joint gap and soft tissue balance were measured using tensor device throughout a full range of motion (0°, 30°, 45°, 60°, 90°, 120°and full flexion) at 120N of distraction force. The postoperative component coronal alignment was measured with standing anteroposterior hip-to-ankle radiographs. RESULTS. The mean joint gaps at each flexion angle were maintained constant in N group, and there was a tendency of the joint gap at midflexion ranges to increase in C group. The joint gaps at 30°and 45°of flexion angle in C group were significantly larger than that of in N group. The mean soft tissue balance at 0°of flexion was significantly varus in N group than that of in C group. Postoperatively, in N group, the mean femoral component alignment was valgus 0.1°± 1.3°(range, varus 2°- valgus 3°), the mean tibial component alignment was valgus 1.1°± 1.7°(range, varus 1°- valgus 3°) to the coronal mechanical axis. In C group, the mean femoral component alignment was varus 2.3°± 1.9°(range, varus 6°- valgus 1°), the mean tibial component alignment was valgus 2.0°± 1.3°(range, 0°- valgus 5°) to the coronal mechanical axis. There was statistically significant difference in femoral component alignment, there was no statistically significant difference in tibial component alignment. DISCUSSION AND CONCLUSION. The present study demonstrated that navigation-assisted TKA was prevented the joint gaps from increasing at 30°and 45°of flexion. However, it was difficult to achieve soft tissue balance at extension. In conventional TKA, the femoral component alignment was usually varus. In contrast, accelerometer-based portable navigation system is superior to implant the femoral component accurately. However, there were several cases that femoral component alignment is valgus because of a variation in the accuracy of this navigation system. Surgeons should be aware of difficulty to accomplish all of appropriate joint gap and soft tissue balance, and lower limb alignment in navigation-assisted TKA

Introduction. Balancing of joint gap is a prerequisite in total knee arthroplasty (TKA). Recently, the tensor has been developed which can measure the joint gap with the patellofemoral joint reduced for more physiological assessment, and the results for osteoarthritis (OA) patients indicated that the flexion gap is larger than the extension gap during posterior-stabilized (PS) TKA. However with respect to the rheumatoid arthritis (RA) patients, the soft tissue balance in TKA is still unknown. Therefore, the purpose of this study was toinvestigate thecharacteristics of thejoint gap during TKAsurgeryforpatients with RA. Methods. We implanted 90 consecutive knees with a PS TKA using a NexGen LPS-flex (Zimmer, Warsaw, IN). OA was the underlying disease in 60 knees and RA was the disease in30 knees. Surgical procedure. We performed all operations with a measured resection technique. The rotational position of the femoral component was determined based on the epicondylar axis of the femur with anterior reference for anteroposterior sizing. Joint gap measurements. After bone cuts and soft tissue balancing, we measured the joint gap with the femoral component in position using seesaw-type tenser device with the patella reduced position after repair of the medial arthrotomy with a few stitches. The center width and asymmetry (tilting) of joint gaps under 40-lb distracting force were measured at 0 degree extension and 90 degrees of knee flexion. Results. The changes in the joint gap from 0 to 90 degrees were 3.2 ± 0.3 mm in OA group and 4.3 ± 0.4 mm in RA group. The increase of joint gap from 0 to 90 degrees in RA was significantly larger than that in OA group (Figure 1). The tilting angle of the joint gap (varus gap expressed as positive values) at 90 degrees of knee flexion in RA group (5.3 ± 0.5 degrees) was significantly larger than that in OA group (2.6 ± 0.4 degrees) (Figure 2). In RA group, there was a positive correlation (r= 0.34, p <0.05) between the increase of joint gap from 0 to 90 degrees and the tilting angle of the joint gap at 90 degrees of knee flexion (Figure 3). Discussion. In this study, the increase of joint gap from 0 to 90 degrees in RA group was significantly larger than that in OA group. In addition, the lateral gap in knee flexion, calculated from the tilting angle of the joint gap, was significantly larger in RA group and was correlated with the increase of joint gap from 0 to 90 degrees of knee flexion. These differences could be attributed to reduced stiffness of the lateral structure, such as lateral collateral ligament and popliteofibular ligament, as well as the extensor mechanism in patients with RA. Therefore, it is necessary to considerthe individual stiffness of soft tissues, together with the applied tension, to decide the rotation of femoral component by reference to the flexion gap during TKA for RA patients

Introduction: The importance of soft tissue balance in total knee arthroplasty (TKA) has been documented, and several authors have documented operative procedure of soft tissue release for soft tissue balancing. However, the quantity of change of soft tissue balance in each procedure has not been reported in detail, and the importance of each procedure of soft tissue release has not been well argued. This study is a quantitative evaluation of the effect of soft tissue release on soft tissue balance in TKA. Materials and methods: Forty-five varus knees in 42 patients with a preoperative femorotibial angle (FTA) of more than 180°underwent TKAs from 1996 to 2000, and these knees were evaluated in this study. The mean age of the subject was 70.1 years (from 33 to 87 years), including 5 knees in male and 40 knees in female. The extension and flexion gap of the knee joint was measured by the instrument applying the force of the moment of 50kg& #65381;cm to each medial and lateral joints. We decided the procedure of soft tissue balancing as follows and the extension and flexion gap were measured in each steps. The procedure were 1) exposure of posterior medial aspects of the tibia with release of the attachment of semimembranosis, 2) removal of osteophytes from the medial distal femur and proximal tibia, 3) resection of the posterior cruciate ligament (if necessary), 4) release of the superficial medial collateral ligament (MCL), 5) resection of the superficial MCL (if necessary). Results: The results of the change of the extension and flexion gap in each procedure were shown as below. Final gap was calculated as the difference against medial extension gaps. Procedure: The change of extension gap The change of flexion gap medial lateral medial lateral 1) (n=45) 1.2 ± 1.4 1.2 ± 1.2 1.9 ± 2.2 1.7 ± 2.6 2) (n=36) 1.9 ± 2.5 0.7 ± 1.2 1.7 ± 1.6 1.3 ± 2.0 3) (n=19) 1.8 ± 1.5 1.9 ± 1.8 2.7 ± 2.0 2.9 ± 2.2 4) (n=18) 2.0 ± 1.9 0.3 ± 0.5 2.4 ± 1.7 0.9 ± 1.1 5) (n=4) 2.8 ± 2.3 0.4 ± 0.8 4.1 ± 1.5 1.5 ± 1.4 Final gap 0 3.4 ± 2.6 0.5 ± 3.1 3.1 ± 3.4. Discussion: The change of soft tissue balance in each soft tissue procedure in TKA was evaluated quantitatively in this study. The amount of the changes in each steps were few and differed with cases. The procedure for medial osteophytes and MCL had a tendency of efficacy to medial tightness against lateral in knees with varus deformity

Purpose: A common difficulty with manually-performed total knee arthroplasties (TKAs) is obtaining accurate intra-operative soft tissue balancing, an aspect of this procedure that surgeons traditionally address through their “subjective feel” and experience with an unphysiological joint condition. We have therefore developed a new tensor for TKAs that enables us to assess for soft tissue balancing throughout the range of motion about the knee with a reduced patello-femoral (PF) joint and femoral component in place. This tensor permits us to intra-operatively reproduce the post-operative alignment of the PF and tibio-femoral joints. The main purpose of this study is to compare ligament balance in cruciate-retaining (CR) and posterior-stabilized (PS) TKAs. Methods: Using the tensor, we intra-operatively compared the ligament balance measurements of CR and PS TKAs performed at 0, 10, 45, 90 and 135° of flexion, with the patella both everted and reduced. From a group of 40 consecutive females (40 varus osteoarthritic knees) blinded to the type of implant received, we prospectively randomized 20 patients to receive a CR TKA (NexGen CR Flex) and the other 20 patients a PS TKA (NexGen LPS Flex). The CR TKA group had a mean age of 73.7 ± 1.3 years while the PS TKA group had a mean age of 73.8 ± 1.7 years. Results: The mean values of varus angle in CR TKA with the knee at 0, 10, 45, 90 and 135 degrees of flexion were 3.0, 3.2, 2.7, 4.2 and 5.1 ° with the patella everted, and 3.9, 4.2, 2.5, 2.0 and 2.0 ° with the patella reduced. The mean values of varus angle in PS TKA at these same degrees of flexion, respectively, were 3.0, 4.1, 6.0, 6.2 and 6.1 ° with the patella everted, and 3.8, 4.1, 6.3, 6.3 and 4.9 ° with the patella reduced. While the ligament balance measurements with a reduced patella of PS TKAs slightly increased in varus from extension to mid-range of flexion (p< 0.05), these values slightly decreased for CR TKA (p< 0.05). Additionally, the ligament balance at deep knee flexion was significantly smaller in varus for both types of prosthetic knees when the PF joint was reduced (p< 0.05). Conclusion: Accordingly, we conclude that the ligament balance kinematic patterns differ between everted and reduced patellae, as well as between PS and CR TKA

The influence of soft tissue balance in mobile-bearing posterior-stabilized (PS) total knee arthroplasty (TKA) on the patellofemoral (PF) joint was investigated in thirty varus-type osteoarthritis patients. Intraoperative soft tissue balance including joint component gap and varus/valgus ligament balance and the medial/lateral patellar pressure were measured throughout the range of motion after the femoral component placement and the PF joint repair. The lateral patellar pressure, which was significantly higher than the medial side in the flexion arc, showed inverse correlation with the lateral laxity at 60° and 90° of flexion. The lateral patellar pressure at 120° and 135° of flexion also inversely correlated with the postoperative flexion angle. Surgeons should take medial and lateral laxity into account when considering PF joint kinematics influencing postoperative flexion angle in PS TKA

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 early post-operative knee joint stability quantitatively, and compared these parameters between CR and PS TKA. Material and Method. Seventy patients with varus osteoarthritis of the knee underwent TKAs (35 CR TKAs: CR and 35 PS TKAs: PS). Mean varus deformity in standing position was 9.8 degrees in CR, and 10.7 degrees in PS (p = 0.45). All TKAs were performed by a single surgeon with measured resection technique. The external rotation of posterior femoral condyle osteotomy was performed according to surgical epicondylar axis (SEA) in pre-operative CT. We measured intra-operative soft tissue balance using an offset-type tensor with 40 lbs of joint distraction force at 0, 10, 30, 45, 60, 90, 120 and 135 degrees of flexion. The joint component gap (mm) and varus angle (degrees) were measured at each flexion angle. Four weeks after operation, we evaluated the knee stability at extension by varus and valgus stress radiography using Telos (10 kg) and at flexion by epicondylar view with 1.5 kg weight at the ankle. We measured joint separation distance at medial as medial joint looseness (MJL) and at lateral as lateral joint looseness (LJL). Joint looseness was defined as the average of MJL and LJL. Intra-operative measurements and post-operative joint stabilities were compared between CR and PS using unpaired t-test. Result. Joint gap kinematics was different between CR and PS (figure 1). Joint component gap in PS were significantly higher than CR from 30 to 120 degrees of flexion. Post-operative joint looseness were 2.7 mm and 3.7 mm at extension (p = 0.001, figure 2), and 1.1 mm and 1.9 mm at flexion (p = 0.021, figure 3) in CR and PS TKAs each respectively. At both extension and flexion, PS showed significantly higher joint looseness, especially with the higher MJL in PS comparing with CR. Discussion. We found significant differences in gap kinematics and also in the early post-operative joint stability between CR and PS. In the PS TKAs, component gaps were significantly larger than those in CR TKAs at mid-flexion to deep flexion of the knee. These different characteristics of the intra-operative soft tissue balance would be a possible reason for the differences in the post-operative joint stability between CR and PS TKAs. Our results suggested that TKAs performed by measured resection technique have significantly higher joint stability with CR than PS. These findings would be important issues in choosing prosthesis and operative technique. Conclusion. With measured resection technique, CR TKAs had more consistent joint gap kinematics and higher joint stability after surgery comparing to PS TKAs

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.

The ability to reliably balance a total knee replacement during surgery eliminates a number of postoperative issues often leading to recurrent joint pain and lower than expected clinical outcomes. Over the past few years a surgical instrument has been available to surgeons performing primary TKA’s to enhance their surgical ability to develop flexion space balance by customizing femoral rotation by developing equal relative forces in the medial and lateral femoral-tibial compartments instead of using rotational anatomic landmarks. Since this concept deviates from the current practice of using anatomic or “boney” landmarks, as in the TEA or AP axis to develop a balanced flexion space with femoral rotation, this study design evaluated the variation in femoral rotation between the force balanced rotation and the conventional external rotation developed from the TEA and AP axes. Using the premise from previous studies that; clinical instability presents itself when the flexion space is asymmetric by more than three degrees, data was analyzed on 50 total knee patients to establish the rotational difference between the force balanced rotation and the rotation using the two conventional axes. Computer navigation was used as the measuring tool in this study.

The study results showed that flexion space asymmetry would have been greater than the targeted three degrees in 38% of the knees in the study when utilising conventional anatomic reference based femoral rotation. The force balanced rotation created additional external rotation from a half to three degrees in these knees, improving patellar tracking.

Based on previous work evaluating laxity in total knee patients, the reliability offered by force sensing technology appears to improve the surgeon’s operative ability to balance a reconstructed knee within three degrees of symmetry in flexion. This new technique appears to improve reported postoperative complications associated with instability in a reconstructed total knee. Further studies utilizing CT scan data to validate the actual femoral rotation and clinical outcome studies are warranted to examine this potential improvement to clinical outcomes in primary TKA’s.

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

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. Materials and Methods. This study included with 50 knees of the 43 patients (6 males, 37 females) who had undergone TKA with ADLER GENUS system from March 2015 to January 2017. The mean age was 71.1±8.1 years. All patients were diagnosed with medial osteoarthritis of the knee. All implants was cruciate substituted type (CS type) and mobile bearing insert. We developed a new ligament balancer that could be fixed to the tibia with keel and insert trial could be rotated on the paddle. We measured the medial and lateral soft tissue balance during TKA with the new balancer. The A-P position of the balancer was fixed on tibia in parallel with the Akagi line (A-P axis 0 group) and 20 degrees internal rotation (IR group) and 20 degrees external rotation (ER group). Soft tissue balance was measured in extension and 90 degrees of knee flexion on each rotational position. Results. The mean angle of valgus and varus in IR group, 0 group and ER group were 4.6±2.2 degrees varus, 1.9±1.6 degrees varus and 0.4±2.4 degrees varus respectively in extension, and 5.5±3.0 degrees varus, 2.1±2.2 degrees varus and 0.7±3.2 degrees varus respectively in 90 degrees of knee flexion. There were significant differences between three groups in extension (p<0.0001) and flexion (p<0.0001). In other words, when the balancer was fixed on tibia with internal rotation against the Akagi line, the soft tissue balance indicated medial tightness. Conversely, when the balancer was fixed on tibia with external rotation against the Akagi line, the soft tissue balance showed lateral tightness. The insert trial significantly rotated to opposite side against the position of balancer fixed. Discussion. Ligament balancer is used to be inserted between femur and tibia. If balancer is not fixed on tibia, it may rotated and translated during measurement. That movement made impossible to measure the correct soft tissue balance. We created a new balancer that could be fixed to the tibia with keel and the insert trial could be rotated on the paddle. Furthermore, it is possible to measure the soft tissue balance after installation of the femoral trial. As a result, it is possible to check the real soft tissue balance after implantation. In conclusion, direction of A-P axis of the ligament balancer is important to measure the correct soft tissue balance in TKA. This result means that the implantation on excessive rotation of the tibial component affects on the medial and lateral soft tissue balance in fixed type TKA. In mobile type TKA, it is possible to substitute if it is within the possible range of rotation by rotational mobile insert

Purpose. Despite total knee arthroplasty (TKA) is a successful surgical procedure with end-stage knee osteoarthritis, approximately 20% of the patients who underwent primary TKA were still dissatisfied with the outcome. Thereby, numerous literatures have confirmed the relationship between soft tissue balancing and clinical result to improve this pressing issue. Recently, there has been an increased research interest in patient-reported outcome measures (PROMs) after TKA. However, there is little agreement on the association between soft tissue balancing and PROMs. Therefore, the purpose of this study was to determine whether intraoperative soft tissue balancing affected PROMs after primary TKA. We hypothesized that soft tissue balancing would be a predictive factor for postoperative PROMs at one-year post-surgery. Patients and Methods. The study included 20 knees treated for a varus osteoarthritic deformity using a cruciate-retaining TKA (Scorpio NRG) with a polyethylene insert thickness of 8 mm retrospectively. Following the osteotomy using the measured resection technique, the extension gap was measured with a femoral trial by using an electric tensor. This instrument could estimate the soft tissue balance applying continuous distraction force simultaneously from 0 to 40 lbf with an accuracy of the 0.1 lbf. We evaluated the association between a distraction force required for an extension gap of 8 mm, and the following potentially affected factors at one year postoperatively: knee flexion angle using a protractor with one degree increments; radiographic parameters of component alignment, namely the femoral and tibial component medial angle; and the Japanese Knee Osteoarthritis Measure (JKOM). This is a disease-specific and self-administered questionnaire, reflecting the specificity of the Japanese cultural lifestyle, consisting of 25 items scored from 0 to 100 points, with 100 points being worst. Outcomes. The median knee flexion angle was 130 degrees with the femoral and tibial component of 97 and 89 degrees, respectively. For an extension gap of 8 mm, a verified value of a distraction force did not demonstrate a correlation with, knee flexion angle (p = 0.29) or with the femoral (p = 0.20), and tibial component position (p = 0.09). The median JKOM totaled 20 points across 4 domains: pain and stiffness, condition in daily life, general activities, and health conditions with 5, 8, 2.5, and 2 points respectively. There was significant correlation between a required force and the JKOM (r. s. = 0.53, p = 0.02), and notably the domain of health conditions exhibited the highest coefficient of determination (r. s. = 0.54, p = 0.01). Discussion. This study highlights that distraction force for an extension gap of 8 mm is an independent variable in component position or knee flexion angle. We found that soft tissue balancing could influence short term postoperative PROMs. Our results will contribute to a better understanding of outcomes after TKA. This is a particularly critical issue as feasible strategies to avoid a persistent joint stiffness would improve long-term function after TKA and patient satisfaction

Aims. A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA). Methods. A radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type. Results. There was similar frequency distribution between healthy and arthritic groups across all CPAK types. The most common categories were Type II (39.2% healthy vs 32.2% OA), Type I (26.4% healthy vs 19.4% OA) and Type V (15.4% healthy vs 14.6% OA). CPAK Types VII, VIII, and IX were rare in both populations. Across all CPAK types, a greater proportion of KA TKAs achieved optimal balance compared to MA. This effect was largest, and statistically significant, in CPAK Types I (100% KA vs 15% MA; p < 0.001), Type II (78% KA vs 46% MA; p = 0.018). and Type IV (89% KA vs 0% MA; p < 0.001). Conclusion. CPAK is a pragmatic, comprehensive classification for coronal knee alignment, based on constitutional alignment and JLO, that can be used in healthy and arthritic knees. CPAK identifies which knee phenotypes may benefit most from KA when optimization of soft tissue balance is prioritized. Further, it will allow for consistency of reporting in future studies. Cite this article: Bone Joint J 2021;103-B(2):329–337

Fifteen-year survivorships 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. Total knee imbalance with either too tight or loose soft tissues account for up to 54% of revisions in one series. This may account for many of the 20% unsatisfactory total knee arthroplasty outcomes. Soft tissue balancing technique is more like an art. The surgeon relies on subjective feel for appropriate ligamentous tension. 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, intraoperative 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 sensor 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, imbalance situations such as a too tight MCL or ITB, an incompetent or too tight PCL, or malrotated femoral or tibial component can be identified. A decision can be made as to whether to recut the bone to realign components, do a soft tissue release, or a combination of both. Soft tissue releases can be titrated while observing equalizing compartment pressures. Sensor feedback improves soft tissue balancing. More balanced compartments occur using a sensor trial than with standard soft tissue balancing technique blinded to sensor information. A multicenter three year study has shown that having the medial and lateral compartments in flexion and extension balanced within 15 pounds provides better outcomes. Patients with quantitatively balanced TKA with <15lbf mediolateral load differential have better forgotten knee scores at six weeks and six months. Use of smart trials is a new approach to total knee replacement surgery allowing fine tune balancing and takes soft tissue balancing from art to science