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

The two distinct surgical techniques for total knee arthroplasty (TKA) are gap-balancing technique (GB) and measured resection technique (MR). The aim of this study was to compare coronal stability of the knee after TKA with GB or MR. A total of 80 TKA cases with at least 6 months follow up (average 34.4 months) were evaluated. The MR group comprised of 33 patients with an average age of 73.1 years, while the GB group comprised of 47 patients with an average age of 74.4 years. Zimmer NexGen LPS Flex was used for all cases. Coronal stability of the knee was examined by varus-valgus stress X-ray at full extension and in the 90 degree flexed position as reported by Kanekashu et al (CORR 2005). X-ray measurement was performed using the FUJI diagnostic imaging system FS-V673. The varus-valgus stress X-ray test at full extension showed a laxity of 4.7 + 2.1 degrees in the MR group and 3.9 + 1.9 degrees in the GB group. No significant difference was detected between the two groups. On the other hand, the varus-valgus stress X-ray in the 90 degree flexed position revealed a laxity of 8.7+4.1 degrees in the MR group and 5.3 + 2.7 degrees in the GB group (p<0.01, Student's t-test). Of the 11 knees that showed laxity of >11 degrees in the 90 degree flexed position, 10 were from the MR group and only one from the GB group (p<0.01, Fisher's exact probability test). Furthermore, the postoperative clinical score assessed by Japanese Orthopaedic Association criteria was significantly better in knees with a coronal laxity of <10 degrees in the 90 degree flexed position compared to those with >10 degrees (82.7 + 6.8 and 77.3 + 8.5 in the GB and MR groups, respectively). In conclusion, GB may contribute to improved functional performance after TKA by providing better coronal stability of the knee in the 90 degree flexed position

Backgrounds

Most of in vivo kinematic studies of total knee arthroplasty (TKA) have reported on varus knee. TKA for the valgus knee deformity is a surgical challenge. The purposes of the current study are to analyze the in vivo kinematic motion and to compare kinematic patterns between weight-bearing (WB) and non-weight-bearing (NWB) knee flexion in posterior-stabilized (PS) fixed-bearing TKA with pre-operative valgus deformity.

Postoperative functional outcomes and patients’ satisfaction after total knee arthroplasty are associated with postoperative range of motion. Severe deformities require surgical correction such as soft tissue release and appropriate bone resection. The goal of surgery is to correct the contracture and bring the knee to good range of motion. Using gap-balancing technique is one of the major techniques to obtain good range of motion. Although the gaps are well balanced, the thickness of tibial insert would affect the range of motion. In this study, we analyzed the difference between intraoperative extension joint gap and the thickness of implanted insert (DJI). The objective of this study was to investigate whether DJI affected the postoperative extension of the knee. A total of 155 knees were analyzed retrospectively. Subject included 27 males and 128 females with an average of 72.7 ± 7.0 years. The mean preoperative knee flexion angle was 136.1 ± 20.0°and the mean preoperative knee extension deficit was 4.0 ± 6.1°. All the patients had a diagnosis of varus-type osteoarthritis, identical prostheses (Stryker NRG posterior-stabilized type) implanted with a modified gap-balancing technique and no postoperative complications which may have affected the range of motion. Range of motion was measured using a goniometer before surgery and 12 months after surgery. Joint gap between femoral component and proximal tibia in full extension was measured by a tensor/ balancer device which added joint gap an expansion force by 30 inch pounds intra-operatively. Although we empirically regarded the appropriate DJI was 5 mm for this prosthesis, we determined the thickness of the tibial inserts considering preoperative range of motion. Thinner inserts compared with the joint gap was implanted for knees with flexion contracture and thicker inserts was implanted for knees with hyperextension. In this study, to determine the relationship of DJI and flexion contracture, the correlation coefficient between DJI and extension deficit was calculated. The diagram of DJI and postoperative extension angle is shown in Figure 1. The correlation coefficient between DJI and postoperative extension deficit was 0.24, which showed that DJI slightly affected the postoperative extension of the knee. Flexion contracture cannot be corrected by simply adjusting DJI

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

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

Introduction. Mid-flexion stability after total knee arthroplasty (TKA) is dependent, in large part, on implant design. Design variables include retention or sacrifice of the posterior cruciate ligament, conformity of the polyethylene tibial surface, and radius of curvature of the femoral component. In this study, we attempted to isolate the impact of femoral component design by comparing a single-radius design (SR) to a J-Curve design (JC). We selected cruciate-retaining implants to eliminate the effect of a cam-and-post mechanism. Mid-flexion performance these two designs were compared using the Lower-Quarter Y-Balance Test (YBT-LQ), as well as patient reported outcomes and measures of physical performance. The YBT-LQ is a simple functional test of unilateral lower extremity strength and balance. Reach of the contralateral limb is measured in three different directions (Figures 1–3). Our hypothesis was that the SR design would provide superior mid-flexion stability, and therefore, a greater reach distance in the YBT-LQ when compared to the JC group. Methods. Patients undergoing primary, unilateral TKA were prospectively enrolled and block randomized to receive either the SR (n=30) or JC (n=30) implant. All surgeries were performed by one surgeon using a gap-balancing technique with a cruciate-retaining implant design. Patients completed outcome measures (KOOS, KSS, UCLA Activity), performed the YBT-LQ, and completed physical performance measures (walking speed, timed up-and-go, sit-to-stand) before surgery and 1 year postoperatively. A series of 2×2 repeated measures ANOVAS (Implant group x Time) were completed. Results. One year post-operatively, 40 patients (20 SR, 20 JC) were available for analysis. The groups were closely matched for age, gender, BMI, and ASA score. No significant differences existed between implant groups for the YBT-LQ or any other variable of interest. Significant improvements in both implant groups were observed for all variables of interest when comparing pre-operative to one year post-operative. Conclusions. Both groups improved significantly across time in all measures, but no differences were seen between SR and JC designs. Based on reach distances achieved, it is probable that many patients were not able to achieve mid-flexion during the YBT-LQ test. With regards to mid-flexion function after TKA, the significant limitations in strength and balance in this cohort of patients likely outweigh any subtle differences in implant design. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Aim. Computer-navigated total knee arthroplasty has been shown to improve the outcome in outliers with consistent results. The aim of this study is to evaluate the clinical and radiographic outcomes of computer-navigated knee arthroplasty with respect to deformity and body mass index (BMI). Materials and Methods. Data was prospectively collected for 117 consecutive patients undergoing primary computer-navigated total knee arthroplasty using Ci Brainlab system with J&J PFC PS implants by a single surgeon utilising a tibia cut first, gap-balancing technique. Pre-operative and post-operative long-leg films, weight-bearing, films were taken and the long-axis was measured by a single observer. Intra-operative computer navigation long-axis values were stored as screenshots intra-operatively after registration and after implant was cemented. BMI, range of motion (ROM), SF 36 and Oxford knee scores were recorded both before surgery and on follow-up. Minimum 2-year follow-up. Eight patients were lost to follow-up and 8 had incomplete 2 year data. Data was analysed using the Chi-squared test for categorical variables and the t-test for continuous variables. Results. Eighty-four (83.2%) female, 17 (16.8%) male patients age 65.3±6.9 years with a pre-operative BMI of 27.2±4.1 (18.6 to 40.0). Eighty-eight (87.1%) met the Singapore definition of overweight with BMI>23 kg/m2. Forty-two (41.6%) had a BMI>27.5 kg/m2 indicative of obesity in Singapore. Pre-operative radiographic axis was 9.3±10.6° varus. Thirty (29.7%) patients had a pre-operative coronal plane deformity of more than 15°. Meanoperative duration 96.0±10.7 mins. Post-operative radiographic axis was 0.05±3.0° valgus. Significant improvement was seen in knee extension, knee flexion, SF 36 and Oxford knee scores at 2 years. No significant improvement in extensor lag and straight leg-raising at 2 years. Pre-operative axis >15° was not significantly related to operative duration. BMI>23 kg/m2 was significantly related to longer operative time (88.8±10.8 vs. 97.1±10.3 min, p<0.021). BMI >27.5 kg/m2 not significantly related to operative duration, pre-operative SF36 or Oxford knee scores. Post-operative axis deviation of more than 3° not significantly related to BMI > 23 or 27.5 kg/m2, similar to post-implant navigation axis. BMI >23 kg/m2 not significantly related to 2 year SF36, Oxford knee score and range of motion at 2 years. BMI >27.5 kg/m2 not significantly related to 2 year SF36 or Oxford knee scores. Conclusion. Although restoration of coronal alignment even in deformity >15° is possible with computer navigation, post-operative extensor lag and weakness is still a problem determined by pre-operative extensor lag and weakness in straight leg raising. Computer navigation is useful when exposure and landmarks to assess alignment are difficult such as in obesity where the standard external tibia jig doesn't sit well with the thick subcutaneous layer and for determining the epicondylar axis of the femur in a deep wound. Despite the technical challenges of performing a total knee arthroplasty with obesity, BMI is not a determinant of functional scores when computer navigation is used