Background. The most important factors affecting the outcome of a TKA are restoring the normal mechanical axis and achieving optimum soft tissue balance. In the measured resection technique may have accompanying problems in imbalanced patients. Secondly individual variability of the reference points may affect the alignment of the bony cuts and thereby the alignment of the implant. The gap balance technique blends the soft tissue balance with the bony cuts and tries to overcome this problem. However proponents of the measured resection technique argue that no consideration is given to the coronal and rotational alignment of the femoral component in the gap balance technique. The ligament specific navigation assisted gap balance technique, tries to overcome these fallacies. The lateral ligaments and soft tissues act as a reference against which the medial soft tissues are balanced. Thus the reference becomes individualized and any variability is taken care of. Navigation assistance ensures control of the coronal and rotational alignment of the femoral component. The aim of the present study was two fold: - To describe our methodology of ligament specific navigation assisted gap balance technique and analyze the clinico-radiological outcome of our technique over an eight year follow up. Methods. 79 patients (98 knees) with primary osteoarthritis with varus deformity and flexion deformity of were followed up for eight year duration. After obtaining an optimum gap balance and neutral axis in extension, tibial osteotomy perpendicular to the mechanical axis in both the coronal and sagittal planes was done. At this stage joint gaps were distracted in extension and 90â�° flexion. Based on the gap values patients were classified into three groups. Group 1 was the balanced group with flexion extension gap difference ≤2mm, group 2 was the flexion tight group with flexion gap smaller than the extension gap by ≥3mm and group 3 was the extension tight group with the extension gap smaller than the flexion gap by ≥3mm. Thereafter flexion gap balance was achieved only by adjusting the cutting levels of the distal and posterior condyles and adjusting the axial rotation of the femoral component without any further soft tissue release. Intraoperative navigation readings were recorded. All patients were followed clinico-radiologically at 1, 4, and 8 years post operatively. Results. The level of posterior condylar cut was significantly higher in the flexion tight group. The level of distal cut was higher in the extension tight group. Mean external rotation of the femoral component was 3.14â�°. Mean joint line change in all patients was < ±2.5mm. There was significant improvement in all the clinical scores, and ROM till the last follow up. There were no differences among the patients in the three groups. Conclusion. The ligament specific navigation assisted gap balance technique is a reliable technique for TKA with excellent clinico-radiological results over an eight year follow up period

The preoperative prediction of gap balance after robotic total knee arthroplasty (TKA) is difficult. The purpose of this study was to evaluate the effectiveness of a new method of achieving balanced flexion-extension gaps during robotic TKA. Fifty one osteoarthritic patients undergoing cruciate retaining TKA using robotic system were included in this prospective study. Preoperative planning was based on the amount of lateral laxity in extension and flexion using varus stress radiograph. After complete milling by the robot and soft tissue balancing, intra-operative extension and flexion gaps were measured using a tensioning device. Knees were subdivided into three groups based on lateral laxities in 0° and 90° of flexion, as follows; the tight extension group (≥ 2mm smaller in extension than flexion laxity), the tight flexion group (≥ 2mm smaller in flexion than extension laxity), and the balanced group (< 2mm difference between laxities). In addition, intra-operative gap balance results were classified as acceptable (0–3mm larger in flexion than in extension), tight (larger in extension than in flexion) or loose (> 3mm larger in flexion than in extension) based on differences between extension and flexion gaps. During preoperative planning, 34 cases were allocated to the balanced group, 16 to the tight extension group and 1 case was allocated to the tight flexion group. Intra-operative gap balance was acceptable in 46 cases, 4 cases had a tight result, and one case had a loose flexion gap. We concluded that preoperative planning based on the amount of lateral laxity determined using varus stress radiographs may be useful for predicting intraoperative gap balance and help to achieve precise gap balance during robotic TKA

Aims. The aims of this prospective study were to determine the effect of osteophyte excision on deformity correction and soft- tissue gap balance in varus knees undergoing total knee arthroplasty (TKA). Patients and Methods. Limb deformity in coronal (varus) and sagittal (flexion) planes, medial and lateral gap distances in maximum knee extension and 90° knee flexion and maximum knee flexion were recorded before and after excision of medial femoral and tibial osteophytes using computer navigation in 164 patients who underwent 221 computer-assisted, cemented, cruciate- substituting TKAs. Results. Mean varus and flexion deformities of 4.5°±3° (0.5° to 30° varus) and 4.9°±5.9° (−15° hyperextension to 30° flexion) reduced significantly (p<0.0001) to mean varus deformity of 1°±2.3° and mean flexion deformity of 2.7°±4.2° after excision of medial femoral and tibial osteophytes. The mean medio-lateral (ML) soft-tissue gap difference in maximum knee extension and 90°knee flexion of 2.7±3.6mm and 0.7±2.6mm reduced significantly (p<0.0001) to mean ML soft-tissue gap difference of 0.7±2.5mm in maximum knee extension and 0.1±1.9mm in 90°knee flexion. The mean maximum knee flexion (122.8°±8.4°) increased significantly to mean maximum knee flexion of (125°±8°). Conclusion. Excision of medial femoral and tibial osteophytes during TKA in varus knees significantly improves varus and flexion deformities, mediolateral soft-tissue gap imbalance in maximum extension and in 90°knee flexion and maximum knee flexion. Clinical Relevance. Excision of medial femoral and tibial osteophytes can be a useful, initial step towards achieving deformity correction and gap balance without having to resort to soft-tissue release during TKA in varus knees

Introduction. Patient specific surgical guide (PSSG) is a relatively new technique for accurate total knee arthroplasty (TKA), and there are many reports supporting PSSG can reduce the rate of outlier in the coronal plane. We began to use PSSG provided by Biomet (Signature®) and have reported the same results. Before using Signature, we performed TKA by modified gap technique (parallel cut technique) to get the well balanced flexion gap. Signature is the one of the measured resection technique using the anatomical landmarks as reference points on the images of CT or MR taken before surgery. We usually measure the center gap width and gap balance during operation with the special device “knee balancer”(Fig. 1) that can be used on patella reposition. After cutting all of the bone with Signature, gap balance in the extension position was very good but the gap balance was shown slight lateral opening in the 90 degrees flexion position. So we have changed the surgical procedure. We use Signature for cutting only distal femur and proximal tibia to get extension gap and apply the modified gap technique to decide the rotation of the femoral component (Signature with modified gap technique). The purpose of this study is to compare the gap balance between the two techniques. Materials & Methods. From November, 2012 through March, 2014, 50 CR type TKA (Vanguard Knee®, Biomet) in osteoarthritis patients were performed using Signature. 25 TKA were performed using only Signature (group S) and other 25 TKA were done using Signature with modified gap technique (group SG). After all osteotomies of femur and tibia were completed, applying femoral trial, center gap width and gap balance (plus means lateral opening angle) were measured using knee balancer with respect to 30 degrees of the knee flexion angle from zero to 120 degrees (Fig. 2). Results. From knee flexion angle 0 to 120 degrees, gap width was 10.8, 11.9, 11.3, 11, 2 10.8mm in group S, 11.9, 12.6, 11.9, 12.0, 11.8mm in group SG, the range of the gap width was small, 1.1mm and 0.8mm. Gap balance was 0.4, 0.6, 1.0, 2.6, 3.6 degrees in group S and 0.1, 0.1, 0.5, 0.6, 2.6 degrees in group SG. Discussion. With both techniques, Signature and Signature with gap technique, center gap width stayed constant. When it comes to gap balance, in Signature with gap technique group, gap balance were good and constant in knee flexion angle from zero to 90 degrees. But in Signature group, the more flexion angle increased, the more lateral opening angle enlarged. So Signature with gap technique is better than only Signature to get good gap balances during knee movement

Aims. The aims of this prospective study were to determine the effect of osteophyte excision on deformity correction and soft-tissue gap balance in varus knees undergoing computer-assisted total knee arthroplasty (TKA). Patients and Methods. Four-hundred twenty-five consecutive, cemented, cruciate-substituting TKAs were analysed. Pre-operative varus was calculated on long leg weight-bearing HKA film. Limb deformity in coronal (varus) and sagittal (flexion) planes, medial and lateral gap distances in maximum knee extension and 90° knee flexion and maximum knee flexion were recorded before and after excision of medial femoral and tibial osteophytes using computer navigation. Data was extracted and analysed to assess the effect of removal of osteophytes on the correction of deformity and soft tissue balance. Results. Before removal of any osteophytes or soft tissue releases, 138 out of 425 (32%) achieved correction of deformity (HKA 180+2°). In the remaining knees, after osteophyte removal 183 knees (43%) achieved correction of deformity. Overall, 75% knees achieved deformity correction after removal of osteophytes. For the remaining 25% knees, additional procedures (such as capsular release, semimembranosus release, reduction osteotomy) were needed for deformity correction. Conclusion. Three-fourths of all knees were aligned with no release or only removal of osteophytes. Excision of medial femoral and tibial osteophytes can be a useful, initial step towards achieving deformity correction and gap balance without having to resort to soft-tissue release during TKA in varus knees. This is useful information for surgeons to desist from any soft tissue releases till osteophytes have been meticulously excised. For figures, tables, or references, please contact authors directly

CAN TKR is aimed to improve accuracy in realignment with balanced knee joint. Variability in the force exerted during tissue tensioning depends on the viscoelastic nature of soft tissues. Aim: To measure gap balance to assess effectiveness of CAN on ligament balance using gap balancing approach with tibia 1st cut. Methods: OrthoPilot system with 4.3 software and Statistical evaluation with Testimate Version 6.0, IDV Gaunting Germany with a two sided Wilcoxon-Pratt test (P< 0.05) used simulating errors in extension and flexion gap balance. P1, control with 16 datasets created and P2-P7 (96 case series) was propagated with ±3mm variants in extension and flexion gap both medial and lateral, only varying 1, keeping others constant. Controls fixed: distal transverse plane cut at 0° to femoral mechanical axis in frontal plane and 3°external rotation in sagittal plane. Tibia cut 90° to mechanical axis. Mechanical axis constant at 0° and gap balance at 0 mm. Deviations in gap errors using trigonometrical calculations based on E-Motion femoral implant, size/thickness; 3/7mm and 4/8.5mm with variation of insert size 10/12mm equal to sum of gap and bone cut. Results: Over tensioning (OT) distal lateral extension gap (DLEG) causes tight distal medial extension gap (DMEG). Under tensioning (UT) DLEG causes loose posterior medial flexion gap (PMFG). UT DLEG causes tight DLEG. Impact factor > 2mm increased PMFG with lateral lift off with only PMFG as variant. Increasing PMFG > 2mm caused lax PMFG. UT even by 1mm PMFG causes error by notching and tight PMFG. A considerable number of errors observed in frontal plane of femur. Relationships between OT/UT analyzed by Spearman rank ratio p< 0.001. Conclusions: Change of tissue spreader tension in EG or FG causes improper registration with mismatch in EG/FG/Bone cut. This study provides a baseline to further assess and develop the concept of optimal soft tissue balance as ligaments function properly only with the desired isometry in gap balancing technique

Introduction:. Conventional understanding of knee kinematics suggests that the femoral component should be rotationally aligned parallel to the surgical epicondylar axis (SEA). In contrast, the balanced gap technique suggests the knee be balanced in extension and flexion to achieve proper kinematics and stability of the knee without reference to fixed bony landmarks. To investigate the functional flexion-extension axis (FFEA) when a balanced gap technique was used in the posterior-stabilized total knee arthroplasty (PS-TKA), the relationships between rotational alignment of the femoral component to the postoperative flexion gap balance and to the tibial mechanical axis were evaluated radiographically. Materials and Methods:. In this prospective study, 63 consecutive knees in 50 patients were included with medial osteoarthritis undergoing a primary PS-TKA (NexGen LPS-Flex, fixed surface, Zimmer; Warsaw, USA). All subjects completed written informed consent. The patient population was composed of 8 men and 42 women with a mean age of 73.0 ± 7.7 years. The average height, weight, BMI, weight-bearing femorotibial mechanical angle (FTMA), condylar twist angle (CTA), and the patella height (T/P ratio) were 150.9 ± 7.2 cm, 62.3 ± 10.1 kg, 27.3 ± 4.0 kg/m. 2. , 167.8 ± 5.5°, 5.9 ± 1.6° and 0.94 ± 0.15, respectively. All procedures were performed through a medial parapatellar approach and a balanced gap technique used a newly developed versatile tensor device. Pre- and post-operatively, the CTA was evaluated using computed tomography (CT). To assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was evaluated using the epicondylar view radiographs. The FTMA and coronal alignment of the tibial component in reference to the tibial mechanical axis (angle β) were evaluated using plain AP radiography. The FFEA (angle θ) of the knee was calculated as the following; (angle β) + (post-operative CTA) – (LOA). Correlations were analyzed with Pearson's correlation coefficient. Predictive variables were analyzed utilizing Stepwise regression. A value of p < 0.05 was considered significant. Results:. Only two knees (3.2%) needed a lateral retinaculum release due to poor patella tracking. The average post-operative FTMA, angle β, LOA, and CTA were 178.7 ± 3.0°, 89.6 ± 1.3°, 0.7 ± 1.5°, and 1.3 ± 2.3°, respectively. The average angle θ was 90.2 ± 2.8°, significantly correlating with the post-operative CTA (r = 0.77), angle β (r = 0.42) and the LOA (r=–0.37). Moreover, the predictive variables of the angle θ was the following, 68.41 + 1.04 × (post-operative CTA) + 0.12 × (post-operative FTMA) – 0.93 × (LOA). (R. 2. = 0.805). Discussion:. This study demonstrated that the clinical epicondylar axis (CEA) was closely perpendicular to the tibial mechanical axis in PS-TKA with well balanced extension-flexion gap achieved by the balanced gap technique. This result also suggests the possibility of that the femoral component which is rotationally aligned parallel to the CEA would make the flexion balance better when an anatomical measured resection technique is used in a PS-TKA. Conclusion:. The functional flexion-extension axis in a PS-TKA with well balanced extension-flexion gap closely approximates the clinical epicondylar axis

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.

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

Both gap balancing and measured resection for TKA will work and these techniques are often combined in TKA. The only difference is really the workflow. The essential difference in gap balancing is that you determine femoral component rotation by cutting the distal femur and the proximal tibia, and then using a spacer to determine femoral rotation. I prefer measured resection because I am, for most cases, a cruciate retaining surgeon. It is not ideal to determine femoral rotation based upon a gap balancing if you retain the cruciate. It is also important to maintain the joint line, especially in cruciate retention, in order to reproduce more normal kinematics and balance the knee throughout the range of flexion and extension. It is my opinion that the soft tissue balancing is easier to do with measured resection and the workflow is easier. The sequence of cuts and soft tissue balance is different if one is a gap balancing surgeon. This is more conducive for people who are cruciate substituters, but more difficult in a varus cruciate retaining knee. In that situation, if you determine femoral rotation by gap balancing with the tibia before you have cleared the posterior medial osteophytes in the varus knee, and remove the last bit of meniscus, you could artificially over rotate the femoral component causing posteromedial laxity. The major difference is that cutting the posterior cruciate will open the flexion space and allow the surgeon easier access to the posteromedial corner of the knee before the posterior femoral cut is made. It is also important to remember that in most cases cruciate substitution surgeons will make the flexion space 2 mm smaller than the extension space to compensate for the flexion space opening when the posterior cruciate is cut. The extensor mechanism plays an important role in flexion balance and should only be tested once the patella is prepared and the patella is back in the trochlear groove. I prefer gap balancing in most revision knees as I am virtually always substituting for the posterior cruciate in that case. My technique for measured resection is to assess the character of the knee prior to surgery. Is it varus? Is it valgus? Does it hyperextend? Does it have a flexion contracture? Would the knee be considered tight or loose? I cut the distal femur first, based upon measured resection. I use anatomic landmarks to determine femoral rotation. My most consistent landmark is the transtrochlear line, which is not always from the top of the notch to the bottom of the trochlea. I will use the medial epicondyle and the posterior reference in a varus knee, but not in a valgus knee. The tibial cut, also by measured resection, is easier once the femur has been prepared. The patellar cut is also a measured resection. Having done a preliminary soft tissue balance based upon the deformity, I will then use trial components to finish the soft tissue balance. In summary, both techniques can be used successfully in a cruciate substituting knee, but measured resection, in my opinion, is preferable especially in varus arthritis when the posterior cruciate is retained

Introduction. Soft tissue releases are often required to correct deformity and achieve gap balance in total knee arthroplasty (TKA). However, the process of releasing soft tissues can be subjective and highly variable and is often perceived as an ‘art’ in TKA surgery. Releasing soft tissues also increases the risk of iatrogenic injury and may be detrimental to the mechanically sensitive afferent nerve fibers which participate in the regulation of knee joint stability. Measured resection TKA approaches typically rely on making bone cuts based off of generic alignment strategies and then releasing soft tissue afterwards to balance gaps. Conversely, gap-balancing techniques allow for pre-emptive adjustment of bone resections to achieve knee balance thereby potentially reducing the amount of ligament releases required. No study to our knowledge has compared the rates of soft tissue release in these two techniques, however. The objective of this study was, therefore, to compare the rates of soft tissue releases required to achieve a balanced knee in tibial-first gap-balancing versus femur-first measured-resection techniques in robotic assisted TKA, and to compare with release rates reported in the literature for conventional, measured resection TKA [1]. Methods. The number and type of soft tissue releases were documented and reviewed in 615 robotic-assisted gap-balancing and 76 robotic-assisted measured-resection TKAs as part of a multicenter study. In the robotic-assisted gap balancing group, a robotic tensioner was inserted into the knee after the tibial resection and the soft tissue envelope was characterized throughout flexion under computer-controlled tension (fig-1). Femoral bone resections were then planned using predictive ligament balance gap profiles throughout the range of motion (fig-2), and executed with a miniature robotic cutting-guide. Soft tissue releases were stratified as a function of the coronal deformity relative to the mechanical axis (varus knees: >1° varus; valgus knees: >1°). Rates of releases were compared between the two groups and to the literature data using the Fischer's exact test. Results. The overall rate of soft tissue release was significantly lower in the robotic gap-balancing group, with 31% of knees requiring one or more releases versus 50% (p=0.001) in the robotic measured resection group and 66% (p<0.001) for conventional measured resection (table-1) [1]. When comparing as a function of coronal deformity, the difference in release rates for robotic gap-balancing was significant when compared to the conventional TKA literature data (p<0.0001) for all deformity categories, but only for varus and valgus deformities for robotic measured resection with the numbers available (varus: 33% vs 50%, p=0.010; neutral 11% vs 50%, p=0.088, valgus 27% vs 53%, p=0.048). Discussion. Robotic-assisted tibial-first gap-balancing techniques allow surgeons to plan and adjust femoral resections to achieve a desired gap balance throughout motion, prior to making any femoral resections. Thus, gap balance can be achieved through adjustment of bone resections, which is accurate to 1mm/degree with robotics, rather than through manual releasing soft tissues which is subjective and less precise. These results demonstrated that the overall rate of soft tissue release is reduced when performing TKA with predictive gap-balancing and a robotic tensioning system. For any figures or tables, please contact authors directly

Background. Surgeons generally perform total knee replacement using either a gap balancing or measured resection approach. In gap balancing, ligamentous releases are performed first to create an equal joint space before any bony resections are performed. In measured resection, bony resections are performed first to match anatomical landmarks, and soft tissue releases are subsequently performed to balance the joint space. Previous studies have found a greater rate of coronal instability and femoral component lift-off using the measured resection technique, but it is unknown how potential differences in loading translate into component stability and fixation. Methods. Patients were randomly assigned at the time of referral to a surgeon performing either the gap balancing or measured resection technique (n = 12 knees per group). Both groups received an identical cemented, posterior-stabilized implant. At the time of surgery, marker beads were inserted in the bone around the implants to enable radiostereometeric analysis (RSA) imaging. Patients underwent supine RSA exams at 0–2 weeks, 6 weeks, 3 months, 6 months, and 12 months. Migration of the tibial and femoral components including maximum total point motion (MTPM) was calculated using model-based RSA software. Knee Society Scores were also recorded for each group. Results. At 12 months follow-up, there were no revisions or adverse events. There were no differences in translation or rotation between the measured resection and gap balancing groups at 12 months, including for MTPM of the tibial component (mean 0.67 mm vs. 0.69 mm, p = 0.77, Fig. 1) and the femoral component (mean 0.71 mm vs. 0.51 mm, p = 0.25, Fig. 2). At 6 weeks, tibial components had greater (p = 0.01) anterior tilt in the measured resection group (0.08 deg) while the gap balancing group had greater posterior tilt (0.14 deg), but there were no differences from 3 months onwards (Fig. 3). Patients in both groups improved in Knee Society scores from pre- to post-operatively, with no difference in score between the groups at pre-operation (p = 0.56) or post-operation (p = 0.54). Discussion. Implants in both the gap balancing and measured resection groups were well fixed after 12 months, with no differences in translations or rotations between the two groups as of the latest time points. Both surgical techniques result in adequate fixation for total knee replacement. Future work will include measuring the contact location and possible condylar lift-off with flexion within this cohort. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Background. Stability of total knee arthroplasty (TKA) is dependent on correct and precise rotation of the femoral component. Multiple differing surgical techniques are currently utilized to perform total knee arthroplasty. Accurate implant position have been cited as the most important factors of successful TKA. There are two techniques of achieving soft gap balancing in TKA; a measured resection technique and a balanced gap technique. Debate still exists on the choice of surgical technique to achieve the optimal soft tissue balance with opinions divided between the measured resection technique and the gap balance technique. In the measured resection technique, the bone resection depends on size of the prosthesis and is referenced to fixed anatomical landmarks. This technique however may have accompanying problems in imbalanced patients. Prediction of gap balancing technique, tries to overcome these fallacies. Our aim in this study was twofold: 1) To describe our methodology of ROBOTIC TKA using prediction of gap balancing technique. 2) To analyze the clinico-radiological outcome our technique comparison of meseaured resection ROBOTIC TKA after 1year. Methods. Patients that underwent primary TKA using a robotic system were included for this study. Only patients with a diagnosis of primary degenerative osteoarthritis with varus deformity and flexion deformity of were included in this study. Patients with valgus deformity, secondary arthritis, inflammatory arthritis, and severe varus/flexion deformity were excluded. Three hundred ten patients (319 knees) who underwent ROBOTIC TKA using measured resection technique from 2004 – 2009. Two hundred twenty (212 knees) who underwent ROBOTIC TKA using prediction of gap balancing technique from 2010 – 2012. Clinical outcomes including KS and WOMAC scores, and ranges of motion and radiological outcomes including mechanical axis, prosthesis alignments, flexion varus/valgus stabilities were compared after 1year. Results. Leg mechanical axes were significantly different at follow-up 1year versus preoperative values, the mean axes in the Robotic-TKA with measured resection technique and Robotic-TKA with prediction of gap balancing technique improved from 9.6±5.0° of varus to 0.5±1.9° of varus, and from 10.6±5.5° to 0.4±1.3° of varus (p<0.001), respectively. However, no significant intergroup differences were found between mechanical axis or coronal alignments of femoral or tibial prostheses (pï¼ï¿½0.05). Mean varus laxities at 90° of knee flexion in measured resection and gap prediction technique group were 6.4° and 5.3°, respectively, and valgus laxities were 6.2 and 5.2 degrees, respectively, with statistical significance (p=0.045 and 0.032, respectively). KS knee and function scores and WOMAC scores were significantly improved at follow-up 1year (pï¼ï¿½0.05). However, no significant difference was found between the Robotic-TKA with measured resection technique and Robotic-TKA with prediction of gap balancing technique for any clinical outcome parameter at follow-up 1year (pï¼ï¿½0.05). Conclusions. Robotic assisted TKA using measured resection or gap prediction technique provide adequate and practically identical levels of flexion stability at 90° of knee flexion with accurate leg and prosthesis alignment. But, Robotic TKA using measured resection technique have less than flexion stability compared with gap prediction technique with statistical significance after follow-up 1year

Introduction. Instability is a common reason for revision after total knee arthroplasty. A balanced flexion gap is likely to enhance stability throughout the arc of motion. This is achieved differently by the gap balancing and measured resection techniques. Given similar clinical results with the two techniques, one would expect similar rotation of the femoral component in the axial plane. We assessed posterior-stabilized femoral component axial rotation placed with computer navigation and a modified gap balancing technique. We hypothesized that there would be little variation in rotation. Methods. 90 surgeons from 8 countries used a modified gap-balancing technique and the same posterior-stabilized implant for this retrospective study. Axial rotation of the femoral component was collected from a navigation system and reported relative to the posterior condylar line. Patients were stratified by their preoperative coronal mechanical alignment (≥ 3° varus, < 3° varus to < 3° valgus, and ≥ 3° valgus). Results. 2442 consecutive patients were included in the analysis; 835 with ≥ 3° varus, 1343 with < 3° varus to < 3° valgus, and 264 with ≥ 3° valgus. Mean rotation was external 2.4. 0. +/− 3.4. 0. (range, 10. 0. internal − 21. 0. external). In 16.4% of the cohort, axial rotation was set in a position of internal rotation. In 15.6% of the cohort, axial rotation was set at > 5. 0. of external rotation. Compared to both the neutral and varus groups, valgus knees required a different mean rotation to achieve a balanced flexion gap (p < .0001). Conclusion. These data show a wide range of femoral rotation was needed to achieve a rectangular flexion gap. This suggests that choosing a pre-determined femoral implant axial rotation (measured resection) may lead to flexion gap asymmetry more frequently compared to adjusting the axial rotation intraoperatively (gap-balancing). Correlation to clinical outcome scores is needed

Purpose. The purpose of the present study was to evaluate the intercompartmental loads with a sensor placed on implants after conventional gap balancing during total knee arthroplasty (TKA) with a tensiometer. Methods. Fifty sensor-assisted TKA procedures were performed prospectively between August and September 2018 with a cruciate-retaining prosthesis. After applying a modified measured technique, conventional balancing between the resected surfaces was achieved. The equal and rectangular flexion–extension gaps were confirmed using a tensiometer. Then, the load distribution was evaluated with a sensor. Results. The average load of the medial compartment was greater than that of the lateral compartment in both the flexion and extension of the knee. The proportion of medial–tight coronal load imbalance (medial load – lateral load ≥ 15 lb) was 50% in the extension and 28% in the flexion positions, respectively (p = 0.035). The loads in each medial and lateral compartment increased with extension of the knee; of note, the amount of increase was higher in the medial compartment (9.7 lb vs. 4.0 lb; p < 0.001). The proportion of the extension–tight sagittal load imbalance (extension load – flexion load ≥ 15lbs) was 34% in the medial compartment and 4% in the lateral compartment (p < 0.001). Conclusions. Coronal and sagittal load imbalances existed as determined by the sensor even after the achievement of appropriate conventional gap balance. The use of an intraoperative load sensor offers the advantage of being able to directly evaluate the load on TKA implants following surgery

Inverse Kinematic Alignment (iKA) and Gap Balancing (GB) aim to achieve a balanced TKA via component alignment. However, iKA aims to recreate the native joint line versus resecting the tibia perpendicular to the mechanical axis. This study aims to compare how two alignment methods impact 1) gap balance and laxity throughout flexion and 2) the coronal plane alignment of the knee (CPAK). Two surgeons performed 75 robotic assisted iKA TKA's using a cruciate retaining implant. An anatomic tibial resection restored the native joint line. A digital joint tensioner measured laxity throughout flexion prior to femoral resection. Femoral component position was adjusted using predictive planning to optimize balance. After femoral resection, final joint laxity was collected. Planned GB (pGB) was simulated for all cases posthoc using a neutral tibial resection and adjusting femoral position to optimize balance. Differences in ML balance, laxity, and CPAK were compared between planned iKA (piKA) and pGB. ML balance and laxity were also compared between piKA and final (fiKA). piKA and pGB had similar ML balance and laxity, with mean differences <0.4mm. piKA more closely replicated native MPTA (Native=86.9±2.8°, piKA=87.8±1.8°, pGB=90±0°) and native LDFA (Native=87.5±2.7°, piKA=88.9±3°, pGB=90.8±3.5°). piKA planned for a more native CPAK distribution, with the most common types being II (22.7%), I (20%), III (18.7%), IV (18.7%) and V (18.7%). Most pGB knees were type V (28.4%), VII (37.8%), and III (16.2). fiKA and piKA had similar ML balance and laxity, however fiKA was more variable in midflexion and flexion (p<0.01). Although ML balance and laxity were similar between piKA and pGB, piKA better restored native joint line and CPAK type. The bulk of pGB knees were moved into types V, VII, and III due to the neutral tibial cut. Surgeons should be cognizant of how these differing alignment strategies affect knee phenotype

Preoperative ligament laxity can be characterized intraoperatively using digital robotic tensioners. Understanding how preoperative knee joint laxity affects preoperative and early post-operative patient reported outcomes (PROMs) may aid surgeons in tailoring intra-operative balance and laxity to optimize outcomes for specific patients. This study aims to determine if preoperative ligament laxity is associated with PROMs, and if laxity thresholds impact PROMs during early post-operative recovery. 106 patients were retrospectively reviewed. BMI was 31±7kg/m. 2. Mean age was 67±8 years. 69% were female. Medial and lateral knee joint laxity was measured intraoperatively using a digital robotic ligament tensioning device after a preliminary tibial resection. Linear regressions between laxity and KOOS12-function were performed in extension (10°), midflexion (45°), and flexion (90°) at preoperative, 6-week, and 3-month time points. Patients were separated into two laxity groups: ≥7 mm laxity and <7 mm laxity. Student's t-tests determined significant differences between laxity groups for KOOS12-function scores at all time points. Correlations were found between preoperative KOOS12-function and medial laxity in midflexion (p<0.001) and flexion (p<0.01). Patients with <7 mm of medial laxity had greater preoperative KOOS12-function scores compared to patients with ≥7 mm of medial laxity in extension (46.8±18.2 vs. 29.5±15.6, p<0.05), midflexion (48.4±17.8 vs. 32±16.1, p<0.001), and flexion (47.7±18.3 vs. 32.6±14.7, p<0.01). No differences in KOOS12-function scores were observed between medial laxity groups at 6-weeks or 3-months. All knees had <5 mm of medial laxity postoperatively. No correlations were found between lateral laxity and KOOS12-function. Patients with preoperative medial laxity ≥7 mm had lower preoperative PROMs scores compared to patients with <7 mm of medial laxity. No differences in PROMs were observed between laxity groups at 6 weeks or 3 months. Patients with excessive preoperative joint laxity achieve similar PROMs scores to those without excessive laxity after undergoing gap balancing TKA

In total knee arthroplasty (TKA), rotational alignment of the femoral component is determined by the measured resection technique, in which anatomical landmarks serve as determinants, or by the gap balancing technique, in which the femoral component is positioned relative to the resected aspect of the tibia. The latter technique is considered logically more favorable for obtaining rectangular extension and flexion gaps. However, in patients with severe changes attributed to osteoarthritis and/or a severely limited range of motion, it is difficult to perform adequate posterior clearance (e.g. bone spur excision) before resecting the posterior femoral condyle, often causing unbalanced extension and flexion gaps after resection. Thus, the gap balancing technique is more technically demanding and requires higher skill. We employed a computed tomography (CT)-based navigation system to develop a simple and standardized surgical technique by performing two assessments: Assessment 1, we investigated the relationship between the position of the femoral component determined by the gap balancing technique and anatomical landmarks; and Assessment 2, we placed the femoral component at the position determined by the measured resection technique and within the acceptable gap-balanced range determined in Assessment 1. In Assessment 1, 18 knees with osteoarthritis were treated by posterior stabilized TKA for varus deformity. The extension-flexion balance after resection of the distal femoral condyle and the proximal tibia was within 3° in all cases. Posterior bone resection was performed parallel to the resected aspect of the tibia and at 90° of flexion under constant compression applied using a tensor. In other words, the rotational alignment of the femoral component was determined by the gap balancing technique, and its position relative to the posterior condylar axis (PCA) and clinical transepicondylar axis (CEA), which are landmarks in the measured resection technique, and the condylar twist angle (CTA; the angle between the CEA and PCA) were measured, and their relationships were quantitatively determined. The CTA, which was determined based on the preoperative CT data, was 4.7– 9.6° (mean, 7.05 ± 1.35°), while the aspect of the femoral resection was 3.0–8.3° externally rotated (mean, 5.6 ± 1.6°) to the PCA; a strong positive correlation was found between the rotational alignment of the femoral component and the CTA (p < 0.0001, R. 2. = 0.871). The aspect of the femoral resection was 0.3–2.6° internally rotated (mean, 1.4 ± 0.6°) to the CEA, and no correlation with the CTA was apparent. In Assessment 2, 39 knees with an extension-flexion balance ≤3° were examined to determine the internal-external rotation balance. Based on the results of Assessment 1, we employed the measured resection technique and placed the femoral component by rotationally aligning the target, which was 1.4° internally rotated to the CEA. The final rotational alignment of the femoral component was 2.0 ± 0.6° internally rotated to the CEA; the internal-external rotation balance at 90° of flexion was good and more toward external rotation by 0.72 ± 1.61°. The results demonstrated that the measured resection technique enables placement of the femoral component within an acceptable range of rotational alignment

Introduction. In order to achieve good clinical results in TKA, soft tissue balance is important. Soft tissue balance is closely related to knee kinematics which affects clinical results. Modified gap balancing technique is one of the standard techniques for posterior stabilized (PS) TKA. On the other hand, appropriate load for the measurement of gap balance has not been established. The purpose of the present study is to measure the mechanical properties of soft tissue structure of knee sleeve in flexion and extension during PS TKA using newly developed balancer. The understanding of the mechanical properties is crucial. In particular if these properties are used as input for surgical procedures, standard technique for many surgeons will be established. Materials and Methods. Medial compartmental osteoarthrosis (OA) patients (13 female and 7 male) were evaluated. Average age, BMI, and Varus deformity were 72.1 years, 26.9, and 12 degrees, respectively. The newly developed center paddle balancer consists of a built-in spring (Fig. 1). Figure 2 shows the sequence of surgery and measurements. In the surgery, we measured the balance (degrees in Figure 1, A) and distance (mm in Figure 1, B) in extension with a load (Figure 1,C) at transition zone of toe region to linear region. Then, applying the load until flexion gap was the same as that in extension with a patella reduction, we measured the femoral component rotation from the balancer (degrees in Figure 1, A). The anterior and posterior femoral cuts were performed according to measured femoral component rotation which angle is parallel to tibial cut surface. Results. Load deformation curves of a knee sleeve structures showed toe and linear regions. The average stability range (transition zone of toe region to linear region) is 150 to 160N in extension and 130 to 140N in flexion. The distance of stability range between tibia and femur in extension is almost the same as the thickness of tibial component and femoral component (21mm). The distance of stability range between the tibia and femur in flexion is the same as the thickness of tibial component (10mm). Discussion. In the present study, load deformation curves of knee sleeve structures showed bimodal patterns that is the same as ligaments and tendons. It has been reported that a load on ligament is below the transition zone during 80% of normal daily activity. The results indicated that the so called “palpable endpoint” is stability range. According to the present data, we propose a standard modified gap balance technique in PS TKA for medial compartmental OA. The ligament balance is confirmed in extension with 160N of distracting force after soft tissue release and distal femur and proximal tibial cut. The femoral component rotation is then decided with the load that will open the distance to the thickness of the tibial component in flexion

Introduction. Although gap balancing technique has been reported to be beneficial for the intra-operative soft tissue balancing in posterior-stabilized (PS)-TKA, excessive release of medial structures for achieving perfect ligament balance would be more likely to result in medial instability, which would deteriorate post-operative clinical results. We have modified conventional gap balancing technique and devised a new surgical concept; named as “medial gap technique” aiming at medial stability with permitting lateral looseness, as physiologically observed in normal knee. Objective. We compared intra-operative soft tissue balance between medial gap technique (MGT) and measured resection technique (MRT) in PS-TKAs. Materials and Methods. The subjects were 210 female patients with varus type osteoarthritic knees, underwent primary PS TKA. The surgical techniques were MGT in 96 patients and MRT in 114 patients. The extension gap was made in the same manners in both groups with medial releases limited until the spacer block could be easily inserted. The residual lateral laxity was permitted. In the MGT group, before posterior femoral osteotomies, varus angles (°) and center gaps (mm) at extension and flexion were measured using an offset type tensor with applying 40 lbs. (177.9N) of joint distraction force. The level and external rotation angle of posterior femoral osteotomies were determined based on the difference of center gaps and varus angles between extension and flexion respectively. Intra-operative joint gap kinematics was measured with femoral trial in place and patello-femoral joint reduced. We measured varus angle and component gap at 8 different knee flexion angles from 0° to 135°. From these component gaps and varus angles, we calculated a medial and lateral compartment gaps (MCG and LCG) by using a trigonometric function. Also we calculated the increase of both compartment gaps from those at full extension, named as joint gap loosening (mm). Both compartment gaps and joint gap loosening were compared between 2 groups using unpaired t-test, and the difference between MCG and LCG in each group were compared using paired t- test (p<0.05). Results. The mean MCGs showed significantly smaller value than LCGs at all flexion angles in both groups (Fig.1). Both medial and lateral joint gap loosening were significantly smaller in MGT group than MRT group from mid-flexion to deep flexion (Fig. 2, 3). Discussion. We have reported the joint distraction force affected varus imbalance due to the stiffness difference between medial and lateral structures. This might be a reason why gap technique was performed less quantitatively and with higher risk of medial instability. In MGT, we allowed persistent lateral looseness and applied the difference in varus angle between extension and flexion to the external rotation angle of femoral component. Results showed no medial looseness were observed in MGT like in MRT. The less joint gap loosening with knee flexion were achieved by MGT because the advantage of conventional gap balancing was also incorporated. We found “medial gap technique” was effective for quantitative soft tissue balancing with more stable joint gap kinematics and no medial looseness