Introduction. In total knee arthroplasty (TKA), component realignment with bone-based surgical correction (BBSC) can provide soft tissue balance and avoid the unpredictability of soft tissue releases (STR) and potential for more post-operative pain. Robotic-assisted TKA enhances the ability to accurately control bone resection and implant position. The purpose of this study was to identify preoperative and intraoperative predictors for soft tissue release where maximum use of component realignment was desired. Methods. This was a retrospective, single center study comparing 125 robotic-assisted TKAs quantitatively balanced using load-sensing tibial trial components with BBSC and/or STR. A surgical algorithm favoring BBSC with a desired final mechanical alignment of between 3° varus and 2° valgus was utilized. Component realignment adjustments were made during preoperative planning, after varus/valgus stress gaps were assessed after removal of medial and lateral osteophytes (pose capture), and after trialing. STR was performed when a BBSC would not result in knee balance within acceptable alignment parameters. The predictability for STR was assessed at four steps of the procedure: Preoperatively with radiographic analysis, and after assessing static alignment after medial and lateral osteophyte removal, pose capture, and trialing. Cutoff values predictive of release were obtained using receiver operative curve analysis. Results. STR was necessary in 43.5% of cases with medial collateral ligament (MCL) release being the most common. On preoperative radiographs, a medial tibiofemoral angle (mTFA) ≤177° predicted MCL release (AUC = 0.76. p< 0.01) while an mTFA ≥188° predicted ITB release (AUC = 0.79, p <0.01). Intraoperatively after removal of osteophytes, a robotically assessed mechanical alignment (MA) ≥8° varus predicted MCL release (AUC = 0.84. p< 0.01) while a MA ≥2° valgus (AUC = 0.89, p< 0.01) predicted ITB release. During pose-capture, in medially tight knees, an extension gap imbalance ≥2.5mm (AUC = 0.82, p <0.01) and a flexion gap imbalance ≥2.0mm (AUC = 0.78, p <0.01) predicted MCL release while in laterally tight knees, any extension or flexion gap imbalance >0 mm predicted ITB release (AUC = 0.84, p <0.01 and AUC = 0.82, p <0.01 respectively). During trialing, in medially tight knees, a medial>lateral extension load imbalance ≥18 PSI (AUC = 0.84. p< 0.01) and a flexion load imbalance ≥ 35 PSI (AUC = 0.83, p< 0.01) predicted MCL release while, in laterally tight knees, a lateral>medial extension load imbalance ≥3 PSI (AUC = 0.97, p< 0.01) or flexion load imbalance ≥ 9.5 PSI (AUC = 0.86, p< 0.01) predicted ITB release. Of all identified predictors, load imbalance at trialing had the greatest positive predictive value for STR. Conclusion. There are limitations to the extent that TKA imbalance that can be corrected with BBSC alone if one has a range of acceptable alignment parameters. The ability to predict STR improves from pose-capture to trialing stages during detection of load imbalance. Perhaps this may be due to posterior osteophytes that are still present at pose capture. Further investigation of the relationship between the presence, location and size of posterior osteophytes and need for STR during TKA is necessary

The Coronal Plane Alignment of the Knee (CPAK) is a recent method for classifying knees using the hip-knee-ankle angle and joint line obliquity to assist surgeons in selection of an optimal alignment philosophy in total knee arthroplasty (TKA)1. It is unclear, however, how CPAK classification impacts pre-operative joint balance. Our objective was to characterise joint balance differences between CPAK categories.

A retrospective review of TKA's using the OMNIBotics platform and BalanceBot (Corin, UK) using a tibia first workflow was performed. Lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were landmarked intra-operatively and corrected for wear. Joint gaps were measured under a load of 70–90N after the tibial resection. Resection thicknesses were validated to recreate the pre-tibial resection joint balance.

Knees were subdivided into 9 categories as described by MacDessi et al.1 Differences in balance at 10°, 40° and 90° were determined using a one-way 2-tailed ANOVA test with a critical p-value of 0.05.

1124 knees satisfied inclusion criteria. The highest proportion of knees (60.7%) are CPAK I with a varus aHKA and Distal Apex JLO, 79.8% report a Distal Apex JLO and 69.3% report a varus aHKA. Greater medial gaps are observed in varus (I, IV, VII) compared to neutral (II, V, VIII) and valgus knees (III, VI, IX) (p<0.05 in all cases) as well as in the Distal Apex (I, II, III) compared to Neutral groups (IV, V, VI) (p<0.05 in all cases). Comparisons could not be made with the Proximal Apex groups due to low frequency (≤2.5%).

Significant differences in joint balance were observed between and within CPAK groups. Although both hip-knee-ankle angle and joint line orientation are associated with joint balance, boney anatomy alone is not sufficient to fully characterize the knee.

Introduction

In total knee arthroplasty (TKA), tibial insert thickness is determined intraoperatively by applying forces that generate varus-valgus moments at the knee and estimating the resulting gaps. However, how the magnitude of applied moments and the surgeon's perception of gaps affect the thickness selection is unclear. We determined this relationship using an in vitro human cadaveric model.

The aim of mechanical alignment in total knee arthroplasty is to align all knees into a fixed neutral position, even though not all knees are the same. As a result, mechanical alignment often alters a patient’s constitutional alignment and joint line obliquity, resulting in soft-tissue imbalance. This annotation provides an overview of how the Coronal Plane Alignment of the Knee (CPAK) classification can be used to predict imbalance with mechanical alignment, and then offers practical guidance for bone balancing, minimizing the need for soft-tissue releases.

Cite this article: Bone Joint J 2024;106-B(6):525–531.

Background. Despite the success of total knee arthroplasty (TKA) restoration of normal function is often not achieved. Soft tissue balance is a major factor for poor outcomes including malalignment, instability, excessive wear, and subluxation. Computer navigation and robotic-assisted systems have increased the accuracy of prosthetic component placement. On the other hand, soft tissue balancing remains an art, relying on a qualitative feel for the balance of the knee, and is developed over years of practice. Several instruments are available to assist surgeons in estimating soft tissue balance. However, mechanical devices only measure the joint space in full extension and at 90° flexion. Further, because of lack of comprehensive characterization of the ligament balance of healthy knees, surgeons do not have quantitative guidelines relating the stability of an implanted to that of the normal knee. This study measures the ligament balance of normal knees and tests the accuracy of two mechanical distraction instruments and an electronic distraction instrument. Methods. Cadaver specimens were mounted on a custom knee rig and on the AMTI VIVO which replicated passive kinematics. A six-axis load cell and an infrared tracking system was used to document the kinematics and the forces acting on the knee. Dynamic knee laxity was measured under 10Nm of varus/valgus moment, 10Nm of axial rotational moment, and 200N of AP shear. Measurements were repeated after transecting the anterior cruciate ligament, after TKA, and after transecting the posterior cruciate ligament. The accuracy and reproducibility of two mechanical and one electronic distraction device was measured. Results. The maximum passive varus laxity measured over the range of flexion was 6.4°(±2.0) and maximum passive valgus laxity was 2.6°(±0.7), (p < 0.05). The maximum passive rotational laxity measured was 9.0°(±0.57) for internal and 14.1°(±1.6) for external rotation (p < 0.05). Average stiffness of the knee (Nm/deg) was 1.7 (varus), 2.4 (valgus), 0.8 (internal rotation), and 0.5 (external rotation). The difference in tibiofemoral gap between flexion and extension was 2.9mm (±1.6). The stiffness of the mechanical and electronic distractors was very linear over a distraction range of 0 to 6mm. At forces ranging from 40N to 120N, the accuracy and repeatability of the mechanical distractors was within 1mm, and that of the dynamic electronic distractor was 0.2mm. The electronic distractor measured the varus of the tibial cut and the distal femoral cut within 0.5°, and the rotation of the posterior femoral cut within 0.7° of surgical navigation measurements. Conclusions. The dynamic electronic distraction device was significantly more accurate than mechanical instruments and measured knee balance over the entire range of flexion. The stiffness of the normal knee was distinctly different in varus and valgus. The standard recommendation for equal medial and lateral gaps under distraction may have to be revisited. Combining implant design improvements with sophisticated balancing instruments is likely to make a significant impact on improving function after total knee arthroplasty

Aims. It is unknown whether kinematic alignment (KA) objectively improves knee balance in total knee arthroplasty (TKA), despite this being the biomechanical rationale for its use. This study aimed to determine whether restoring the constitutional alignment using a restrictive KA protocol resulted in better quantitative knee balance than mechanical alignment (MA). Methods. We conducted a randomized superiority trial comparing patients undergoing TKA assigned to KA within a restrictive safe zone or MA. Optimal knee balance was defined as an intercompartmental pressure difference (ICPD) of 15 psi or less using a pressure sensor. The primary endpoint was the mean intraoperative ICPD at 10° of flexion prior to knee balancing. Secondary outcomes included balance at 45° and 90°, requirements for balancing procedures, and presence of tibiofemoral lift-off. Results. A total of 63 patients (70 knees) were randomized to KA and 62 patients (68 knees) to MA. Mean ICPD at 10° flexion in the KA group was 11.7 psi (SD 13.1) compared with 32.0 psi in the MA group (SD 28.9), with a mean difference in ICPD between KA and MA of 20.3 psi (p < 0.001). Mean ICPD in the KA group was significantly lower than in the MA group at 45° and 90°, respectively (25.2 psi MA vs 14.8 psi KA, p = 0.004; 19.1 psi MA vs 11.7 psi KA, p < 0.002, respectively). Overall, participants in the KA group were more likely to achieve optimal knee balance (80% vs 35%; p < 0.001). Bone recuts to achieve knee balance were more likely to be required in the MA group (49% vs 9%; p < 0.001). More participants in the MA group had tibiofemoral lift-off (43% vs 13%; p < 0.001). Conclusion. This study provides persuasive evidence that restoring the constitutional alignment with KA in TKA results in a statistically significant improvement in quantitative knee balance, and further supports this technique as a viable alternative to MA. Cite this article: Bone Joint J. 2020;102-B(1):117–124

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

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

Introduction. Studies have shown that dissatisfaction following TKA may stem from poor component placement and iatrogenic factors related to variability in surgical execution. A CT-based robotic assisted system (RA) allows surgeons to dynamically balance the joint prior to bone resection. This study aimed to determine if this system could improve TKA planning, reduce soft tissue releases, minimize bone resection, and accurately predict component size in varus knee. Method. Four hundred and seventy four cases with varus deformity undergoing primary RATKA were enrolled in this prospective, single center and surgeon study. Patient demographics and intraoperative surgical details were collected. Initial and final 3-dimensional alignment, component position, bone resection depths, use of soft tissue releases, knee balancing gaps, and component size were collected intraoperatively. WOMAC and KOOS Jr. scores were collected 6 months, and 1 year postoperatively. Descriptive statistics were applied to determine the changes in these parameters between initial and final values. Results. Native deformity ranged from 1 to 19 degrees of varus. 86% of patients in this study did not require a soft tissue release regardless of their level of coronal or sagittal deformity. Complex deformities who required a soft tissue release were corrected on average to 3 degrees varus while cases without releases were corrected to 2 degrees varus on average with the overall goal as traditional mechanical alignment. All surgeons achieved their planned sizes on the tibia and femur more than 98% of the time within one size, and 100% of the time within two sizes. Flexion and extension gaps during knee balancing were within 2mm (mean 1mm) for all knees. At latest follow-up, radiographic evidence suggested well-seated and well-fixed components. Radiographs also indicated the patella components were tracking well within the trochlear groove. No revision and re-operation were reported. Mean WOMAC total score was improved from 23.8±8.0 pre-op to 8.9±7.9 1-year post-op (p<0.01). Mean KOOS Jr. score was improved from 46.8±11.6 pre-op to 77.9±14.8 1-year post-op (p<0.01). Discussion and Conclusions. New tools may allow for enhanced execution and predictable balance for TKA, which may improve patient outcomes. In this study, preoperative planning via CT scan allowed surgeons to assess bony deformities and subtly adjust component position to reduce soft tissue trauma. While this study has several limitations, RATKA for varus knees should continue to be investigated. For any figures or tables, please contact authors directly

Introduction. A careful evaluation of new technologies such as robotic-arm assisted total knee arthroplasty (RATKA) is important to understand the reduction in variability among users. While there is data reviewing the use of RATKA, the data is typically presented for experienced TKA surgeons. Therefore, the purpose of this cadaveric study was to compare the variability for several surgical factors between RATKA and manual TKA (MTKA) for surgeons undergoing orthopaedic fellowship training. Methods. Two operating surgeons undergoing orthopaedic fellowship training, each prepared six cadaveric legs for cruciate retaining TKA, with MTKA on one side (3 knees) and RATKA on the other (3 knees). These surgeons were instructed to execute a full RATKA or MTKA procedure through trialing and achieve a balanced knee. The number of recuts and final poly thickness was intra-operatively recorded. After completion of bone cuts, the operating surgeons were asked if they would perform a cementless knee based on their perception of final bone cut quality as well as rank the amount of mental effort exerted for required surgical tasks. Two additional fellowship trained orthopaedic assessment surgeons, blinded to the method of preparation, each post-operatively graded the resultant bone cuts of the tibia and femur according to the perceived percentage of cut planarity (grade 1, <25%; grade 2, 25–50%; grade 3, 51–75%; and grade 4, >76%). The grade for medial and lateral tibial bone cuts was averaged and a Wilcoxon signed rank test was used for statistical comparisons. Assessment surgeons also determined whether the knee was balanced in flexion and extension. A balanced knee was defined as relatively equal medial and lateral gaps under relatively equal applied load. Results. Operating surgeons used 9mm polys in all 6 RATKA specimens, and 3/6 MTKA specimens. Operating surgeons said they would do cementless in 4/6 RATKA specimens, and 1/6 MTKA specimen. In MTKA specimens, 5/6 cases had a recut on the tibia or femur to obtain knee balance. With RATKA, 1/6 cases had a recut on the tibia. With RATKA, operating surgeons performed a pre-resection balancing workflow, and made plan adjustments prior to resection. The operating surgeons reported reduced mental effort when performing bone measurements, tibial bone cutting, knee balancing, trialing, and post-resection adjustments with RATKA compared to MTKA. Mental effort was equivalent during femoral bone cutting between the two procedures and increased for RATKA during initial exposure and retractor setup. Assessment surgeons considered all 6 RATKA and 2/6 MTKA specimens to be balanced. Assessment surgeons assigned RATKA specimens a higher grade for perceived planarity (3.86 vs. 3.48, p=0.03) than MTKA specimens. DISCUSSION. In this cadaveric study, RATKA resulted in a higher usage of minimum poly thickness, greater tendency to want to use cementless components, higher number of balanced knees, higher perceived planarity, lower number of recuts, and reduced mental effort than MTKA cases. RATKA may give users more confidence in performing cementless TKA, especially for novice surgeons. Robotic-arm assisted TKA may allow for reduced surgical variability, which may improve patient outcomes, and should be investigated in a clinical setting

First generation condylar knee replacements suffered from 2 prominent observations: Difficulty in stair climbing and Limited range of motion. Improved understanding of knee kinematics, the importance of femoral rollback, and enhanced stability in flexion led to 2 differing schools of thought: posterior cruciate ligament retention or posterior cruciate substitution. The advantages of posterior cruciate substitution include predictable CAM-post engagement leading to rollback, predictable ROM, stability during stair climbing, ease of knee balancing regardless of degree of angular deformity, and avoidance of issues such as PCL tightness / laxity at time of index procedure, as well as late ligament disruption leading to late instability. Evolution has shown that human appendages that no longer served a purpose, slowly shrivel up. As we have seen with the appendix, the coccyx, and the erector pili muscles, these vestigial organs no longer are necessary for daily function and are destined for obsolescence. I submit: the PCL in knee arthroplasty IS THE VESTIGIAL ORGAN: not the posterior stabilizing mechanism!

Introduction and Aims: Computer-assisted bone and soft tissue balancing in total knee arthroplasty (TKA) may aid in achieving perfect knee alignment leading to better function and prosthesis survival. The ‘Measured Resection’ technique was compared to a ‘Computer Assisted Gap Equalisation’ (CAGE) technique of knee balancing in TKA. Method: TKAs were performed on eight pairs of cadaver knees. One side of each pair was randomly selected to the control group in which measured resection was used for balancing. The experimental technique (CAGE) using a computer-assisted ligament-tensioning device to equalise gap symmetry and load was used on the contralateral side. Post-operatively, a simulator applied forces to the quadriceps and hamstring tendons and a tibial load transducer measured compartmental force at five flexion angles (0, 30, 45, 60, 90 degrees). Outcome assessment consisted of measuring gap loads and symmetry under ligament tension pre-component insertion and compartmental force post-component insertion. Results: Although there was no significant difference between the two groups in the symmetry of the extension (p = 0.27) and flexion (p=0.07) gaps pre-component insertion, there was a trend towards improved gap symmetry in the CAGE group. As well, pre-component insertion there was a significant (p< 0.05) equalisation of flexion and extension gap loads in the CAGE group. However, post-component insertion there was no significant difference (p> 0.05 using 2-way repeated measures ANOVA) in medial to lateral compartment load balance between the two groups. As well, the measured loads with the knee in full extension (zero degrees of flexion) were significantly higher (p< 0.001) in both groups compared to other flexion angles. Conclusion: CAGE improves knee balance pre-component insertion by improving surgical accuracy with computer-assistance. However, component design, posterior capsular tension and tibial rotation preclude sustaining the improved balance post-component insertion leaving final knee balance unchanged. Further work is needed to translate the improved surgical accuracy into improved balance following component insertion

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

Introduction. Valgus deformity in an end stage osteoarthritic knee can be difficult to correct with no clear consensus on case management. Dependent on if the joint can be reduced and the degree of medial laxity or distension, a surgeon must use their discretion on the correct method for adequate lateral releases. Robotic assisted (RA) technology has been shown to have three dimensional (3D) cut accuracy which could assist with addressing these complex cases. The purpose of this work was to determine the number of soft tissue releases and component orientation of valgus cases performed with RA total knee arthroplasty (TKA). Methods. This study was a retrospective chart review of 72 RATKA cases with valgus deformity pre-operatively performed by a single surgeon from July 2016 to December 2017. Initial and final 3D component alignment, knee balancing gaps, component size, and full or partial releases were collected intraoperatively. Post-operatively, radiographs, adverse events, WOMAC total and KOOS Jr scores were collected at 6 months, 1 year and 2 year post-operatively. Results. Pre-operatively, knee deformities ranged from reducible knees with less than 5mm of medial laxity to up to 12° with fixed flexion contracture. All knees were corrected within 2.5 degrees of mechanical neutral. Average femoral component position was 0.26. o. valgus, and 4.07. o. flexion. Average tibial component position was 0.37. o. valgus, and 2.96. o. slope, where all tibial components were placed in a neutral or valgus orientation. Flexion and extension gaps were within 2mm (mean 1mm) for all knees. Medial and lateral gaps were balanced 100% in extension and 93% in flexion. The average flexion gap was 18.3mm and the average extension gap was 18.7mm. For component size prediction, the surgeon achieved their planned within one size on the femur 93.8% and tibia 100% of the time. The surgeon upsized the femur in 6.2% of cases. Soft tissue releases were reported in one of the cases. At latest follow-up, radiographic evidence suggested well seated and well fixed components. Radiographs also indicated the patella components were tracking well within the trochlear groove. No revision and re-operation is reported. Mean WOMAC total scores were improved from 24±8.3 pre-op to 6.6±4.4 2-year post-op (p<0.01). Mean KOOS scores were improved from 46.8±9.7 pre-op to 88.4±13.5 2-year post-op (p<0.01). Discussion. In this retrospective case review, the surgeon was able to balance the knee with bone resections and avoid disturbing the soft tissue envelope in valgus knees with 1–12° of deformity. To achieve this balance, the femoral component was often adjusted in axial and valgus rotations. This allowed the surgeon to open lateral flexion and extension gaps. While this study has several limitations, RATKA for valgus knees should continue to be investigated. For any figures or tables, please contact authors directly

Backgrounds. It is well accepted that gap balancing is one of the important step for total knee arthroplasty (TKA). In order to evaluate gap balancing during operation, many tension devises have been used and developed. However, during operation, proper load to be applied, ideal gap amount, appropriate angle formed between femoral component and tibial cut surface are not clearly defined. Understanding the relationship between applied load and gap pattern will provide important information. The purpose of this study is to precisely analyze gap amount and inclination in extension and flexion using digital analyzer during TKA and characterize gap pattern. Methods. We analyzed 39 knees in 39 cases that underwent TKA with Scorpio NRG PS knee prosthesis operated by modified gap balancing technique. A customized digital knee balancer was manufactured applying load cell, angle sensor, and gap sensor in the selected part within offset seesaw type balancer (Fig 1). It can measure three values (gap, angle and force) at the same time and automatically record the values. After bone cut for femur, tibia, and patella, femoral component trial was inserted to the femur. Then gap length and inclination angle between femoral condyle surface and tibial cut surface was analyzed in extension and at 90 degrees knee flexion with gradually increasing opening torque. Inclination was expressed by positive degrees when lateral side opened. Serial data was recorded automatically and analyzed. Results. In extension, average gap between femoral implant and tibial cut surface increased gradually from 7.3mm to 13.6mm with increasing load from 10 lbs. to 75 lbs. During this load increase, average inclination changed from 0.2 degrees to 0.7degrees. In flexion, average gap between femoral implant and tibial cut surface increased gradually from 7.4mm to 15.9mm with increasing load from 10 lbs. to 75 lbs. During this increase, average inclination change was from 0 to 3.5 degrees (Fig 2). Lateral opening was observed over 25lbs and this opening angle increased gradually thereafter. When the identical load is applied, average gap difference between extension and flexion was 0.1 to 2.38mm. Linear relationship between extension gap and flexion gap was obtained when each applied load was identical (Fig 3). Discussions. In this study, we have reported gap patterns using digital knee analyzer in vivo for the first time. This digital analyzer provides gap length, angle and applied force between tibia and femur with accuracy. We conclude that in extension lateral laxity is not affected even with increasing load up to 75lbs. On the other hand, in flexion, lateral laxity became remarkable with load increase and can cause more gap increase in flexion compared in extension. In determining the rotational alignment using modified gap technique, this tendency has to be kept in mind. Conclusions. Digital knee balancer provided precise gap pattern in TKA with femoral component in place. Gap length in extension and flexion has linear relationship Lateral laxity in flexion need to be analyzed carefully in TKA

Computer navigated Total Knee Arthroplasty is routinely performed with gratifying results. New navigation software is now designed to help surgeons balance soft tissues in Total Knee Arthroplasty (TKA). The aim of our study was to compare functional scores at two years between two different techniques of knee balancing. A prospective randomized control study was conducted between February 2007 and February 2008 involving 52 patients. Two different techniques of knee balancing were used namely, measured resection and gap balancing technique. Each group had 26 patients. Oxford and Knee society scores were done at two years to understand if one technique was better than other. Oxford and Knee Society Scores improved significantly in both the groups but gap balancing technique achieved slightly better functional scores which were not significant on statistical analysis. Computer assisted measured resection and gap balancing techniques in TKA reliably improves functional scores postoperatively. Either of the techniques if performed correctly with appropriate patient selection will have satisfactory outcomes

The February 2015 Knee Roundup. 360 . looks at: Intra-operative sensors for knee balance; Mobile bearing no advantage; Death and knee replacement: a falling phenomenon; The swings and roundabouts of unicompartmental arthroplasty; Regulation, implants and innovation; The weight of arthroplasty responsibility!; BMI in arthroplasty

First generation condylar knee replacements suffered from two prominent observations: 1) Difficulty in stair climbing, 2) Limited range of motion (ROM). Improved understanding of knee kinematics, the importance of femoral rollback, and enhanced stability in flexion led to 2 differing schools of thought: Posterior Cruciate ligament retention vs. Posterior Cruciate substitution. The advantages of posterior cruciate substitution include predictable cam-post engagement leading to rollback, predictable ROM, stability during stair climbing, ease of knee balancing regardless of degree of angular deformity, and avoidance of issues such as PCL tightness / laxity at time of index procedure, as well as late ligament disruption leading to late instability. Evolution has shown that human appendages that no longer served a purpose, slowly shrivel up. As we have seen with the appendix, the coccyx, and the erector pili muscles, these vestigial organs no longer are necessary for daily function and are destined for obsolescence. I submit: the PCL in knee arthroplasty IS THE VESTIGIAL ORGAN: not the posterior stabilizing mechanism!

Introduction. Close to 30% of the surgical causes of readmission within 90 days post-total knee arthroplasty (TKA) and nearly half of those occurring in the first 2 years are caused by instability, arthrofibrosis, and malalignment, all of which may be addressed by improving knee balance. Furthermore, the recently launched Comprehensive Care for Joint Replacement (CJR) initiative mandates that any increase in post-acute care costs through 90-days post-discharge will come directly from the bundle payment paid to providers. Post-discharge costs, including the cost of readmissions for complications are one of the largest drivers of the 90-day cost of care. It is hypothesized that balanced knees post-TKA will lower the true provider costs within the 90-day bundle. Methods. Cost, outcomes and resource utilization data were collected from three independent surgeons pre- and post- adoption of intraoperative technology developed to provide real-time, quantitative load data within the knee. In addition, data were collected from Medicare claims, hospital records, electronic medical records (EMR), clinical, and specialty databases. The cohorts consisted of 932 patients in the pre-adoption group and 709 patients in the post-adoption group. These 2 groups were compared to the CMS national average data from 291,201 cases. The groups were controlled for age, sex, state, and BMI with no major differences between cohorts. The cost factors considered were the length of hospital stay, physician visits and physical therapy visits in addition to post-operative complications (e.g., manipulation under anesthesia (MUA) and aseptic revision). Results. After adoption of technology to improve ligament balancing intra-operatively, all three surgeons decreased their patients’ hospital stay (3.0 days to 2.6 days), number of physician visits (2.3 to 2.1), number of outpatient physical therapy visits (14.9 to 10.6) and MUA rate (2.3% to 1.8%). These clinical benefits subsequently lowered the 90-day net cost of TKA an average of $443 per case. When compared to the national average, this cost savings was $725 per case. Conclusions. Appropriately balancing TKA patients intra-operatively might help mitigate costs associated with TKA procedures within the 90-day bundle. In this study, it was found that using new joint balancing technology generated a substantial cost-savings post-discharge, primarily due to patients requiring less outpatient physical therapy

Introduction. Partial knee arthroplasty (PKA) has demonstrated the potential to improve patient satisfaction over total knee arthroplasty. It is however perceived as a more challenging procedure that requires precise adaptation to the complex mechanics of the knee. A recently developed PKA system aims to address these challenges by anatomical, compartment specific shapes and fine-tuned mechanical instrumentation. We investigated how closely this PKA system replicates the balance and kinematics of the intact knee. Materials and Methods. Eight post-mortem human knee specimens (age: 55±11 years, BMI: 23±5, 4 male, 4 female) underwent full leg CT scanning and comprehensive robotic (KUKA KR140 comp) assessments of tibiofemoral and patellofemoral kinematics. Specimens were tested in the intact state and after fixed bearing medial PKA. Implantations were performed by two experienced surgeons. Assessments included laxity testing (anterior-posterior: ±100 N, medial-lateral: ±100 N, internal-external: ±3 Nm, varus- valgus: ±12 Nm) under 2 compressive loads (44 N, 500 N) at 7 flexion angles and simulations of level walking, lunge and stair descent based on in-vivo loading profiles. Kinematics were tracked robotically and optically (OptiTrack) and represented by the femoral flexion facet center (FFC) motions. Similarity between intact and operated curves was expressed by the root mean square of deviations (RMSD) along the curves. Group data were summarized by average and standard deviation and compared using the paired Student's T-test (α = 0.05). Results. During the varus-valgus balancing assessment the medial and lateral opening of the PKAs closely resembled the intact openings across the full arch of flexion, with RMSD values of 1.0±0.5 mm and 0.4±0.2 mm respectively. The medial opening was nearly constant across flexion, its average was not statistically different between intact (3.8±1.0 mm) and PKA (4.0±1.1 mm) (p=0.49). Antero-posterior envelope of motion assessments revealed a close match between the intact and PKA group for both compression levels. Net rollback was not statistically different, either under low compression (intact: 10.9±1.5 mm, PKA: 10.7±1.2, p=0.64) or under high compression (intact: 13.2±2.3 mm, PKA: 13.0±1.6 mm, p=0.77). Similarly, average laxity was not statistically different, either under low (intact: 7.7±3.2 mm, PKA: 8.6±2.5 mm, p=0.09) or under high (intact: 7.2±2.6 mm, PKA: 7.8±2.2 mm, p=0.08) compression. Activities of daily living exhibited a close match in the anterior-posterior motion profile of the medial condyle (RMSD: lunge: 2.2±1.0 mm, level walking: 2.4±0.9 mm, stair descent: 2.2±0.6 mm) and lateral condyle (RMSD: lunge: 2.4±1.4 mm, level walking: 2.2±1.4 mm, stair descent: 2.7±2.0 mm). Patellar medial-lateral tilt (RMSD: 3.4±3.8°) and medial-lateral shift (RMDS: 1.5±0.6 mm) during knee flexion matched closely between groups. Conclusion. Throughout the comprehensive functional assessments the investigated PKA system behaved nearly identical to the intact knee. The small residuals are unlikely to have a clinical effect; further studies are necessary as cadaveric studies are not necessarily indicative of clinical results. We conclude that PKA with anatomical, compartment specific shapes and fine-tuned mechanical instrumentation can be adapted precisely to the complex mechanics of the knee and replicates intact knee balance and kinematics very closely