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

The June 2023 Knee Roundup³⁶⁰ looks at: Cementless total knee arthroplasty is associated with early aseptic loosening in a large national database; Is cementless total knee arthroplasty safe in females aged over 75 years?; Could novel radiological findings help identify aseptic tibial loosening?; The Attune cementless versus LCS arthroplasty at introduction; Return to work following total knee arthroplasty and unicompartmental knee arthroplasty; Complications and downsides of the robotic total knee arthroplasty; Mid-flexion instability in kinematic alignment better with posterior-stabilized and medial-stabilized implants?; Patellar resurfacing does not improve outcomes in modern knees.

Background. Despite the success of total knee arthroplasty (TKA) restoration of normal function is often not achieved. Soft-tissue balance is a major factor leading to poor outcomes including malalignment, instability, excessive wear, and subluxation. Mechanical ligament balancers only measure the joint space in full extension and at 90° flexion. This study uses a novel electronic ligament balancer to measure the ligament balance in normal knees and in knees after TKA to determine the impact on passive and active kinematics. Methods. Fresh-frozen cadaver legs (N = 6) were obtained. A standard cruciate-retaining TKA was performed using measured resection approach and computer navigation (Stryker Navigation, Kalamazoo, MI). Ligament balance was measured using a novel electronic balancer (Fig 1, XO1, XpandOrtho, Inc, La Jolla, CA, USA). The XO1 balancer generates controlled femorotibial distraction of up to 120N. The balancer only requires a tibial cut and can be used before or after femoral cuts, or after trial implants have been mounted. The balancer monitors the distraction gap and the medial and lateral gaps in real time, and graphically displays gap measurements over the entire range of knee flexion. Gap measurements can be monitored during soft-tissue releases without removing the balancer. Knee kinematics were measured during active knee extension (Oxford knee rig) and during passive knee extension under varus and valgus external moment of 10Nm in a passive test rig. Sequence of testing and measurement:. Ligament balance was recorded with the XO1 balancer after the tibial cut, after measured resection of the femur, and after soft-tissue release and/or bone resection to balance flexion-extension and mediolateral gaps. Passive and active kinematics were measured in the normal knee before TKA, after measured resection TKA, and after soft-tissue release and/or bone resection to balance flexion-extension and mediolateral gaps. Results & Discussion. Overall the changes in knee balance affected passive kinematics more than active kinematics. Correcting a tight extension gap by resecting 4 mm from the distal femur had a significant effect on femoral rollback and tibial rotation and increased the varus-valgus laxity of the knee (Fig 2). Sequential release of the MCL increased active femoral rollback and tibial internal rotation primarily in flexion (Fig 3). Combinations of bone resections with ligament release had an additive effect. For example, MCL release combined with 2 mm resection of bone at the distal femoral cut increased total valgus laxity by 8° during passive testing. However, even after balancing the flexion-extension gap and the mediolateral gap knee kinematics were significantly different from the normal knee before TKA. Conclusions. The XO1 electronic balancer was very sensitive to changes in bone resection and sequential soft-tissue releases. Intraoperative ligament balance had a significant effect on active and passive kinematics. However, balancing the flexion-extension gap and the mediolateral gap did not restore kinematics to that of the normal knee. Ligament balance can have a profound impact on postoperative function, and that current recommendations for balancing the knee likely have to be reconsidered

Adequate soft tissue balance at the time of total knee arthroplasty (TKA) prevents early failure. In cases of varus deformity, once the medial osteophytes have been resected, a progressive release of the medial soft tissue sleeve (MSS) from the proximal medial tibia is needed to achieve balance. The “classic” medial soft tissue release technique, popularised by John Insall et al., consists of a sharp subperiosteal dissection from the proximal medial tibia that includes superficial and deep medial collateral ligament (MCL), semimembranosus tendon, posteromedial capsule, along with the pes anserinus tendons, if needed. However, this technique allows for little control over releases that selectively affect the flexion and extension gaps. When severe deformity is present, an extensive MSS release can cause iatrogenic medial instability and the need to use a constrained implant. It has been suggested that the MSS can be elongated by performing selective releases. This algorithmic approach includes the resection of the posterior osteophytes as the initial balancing gesture. If additional MSS release is necessary in extension, a subperiosteal release of the posterior aspect of the MSS is performed with electrocautery, detaching the posterior aspect of the deep MCL, posteromedial capsule and semimembranosus tendon for the proximal and medial tibia. Dissection is rarely extended more than 1.5 cm distal to the joint line. If additional release is necessary in extension, the medial compartment is tensioned with a laminar spreader and multiple needle punctures (generally less than 8) are performed in the taut portion of the MSS using an 18G or 16G needle. If additional release is necessary to balance the flexion gap, multiple needle punctures in the anterior aspect of the MSS are performed. This stepwise approach to releasing the MSS in a patient with a varus deformity allows the surgeon to target areas that selectively affect the flexion and extension gaps. Its use has resulted in diminished use of constrained TKA constructs and subsequent cost savings. We have not seen an increase in post-operative instability developing within the first post-operative year. We recommend caution when implementing this technique. Unlike the traditional release method, pie-crusting is likely technique-dependent and failure can occur within the MCL itself. Due to the critical importance of the MCL in knee stability, further research and continuous follow up of patients undergoing TKA with this technique are warranted. Intra-operative sensing technology may be useful to quantitate the effect of pie-crusting on the compartmental loads and overall knee balance

Background. Flexion-extension gap balancing is recognized as an essential part of total knee arthroplasty (TKA). The gap is often evaluated using spacer blocks, laminar spreader, or tensor device. The evaluation of gap balancing with the patella in the reduced position is more physiological and reproducible than with patellofemoral (PF) joint everted. However, in the knee with a reduced PF joint, it is difficult to comprehend the anteroposterior position of the tibia to the femur. So, we developed a new tensor to lift up the tibia ahead and fix the anteroposterior position of the tibia to the femur with the PF joint reduced [Fig.1]. Purpose. To investigate how accurate the extension and flexion gaps would be measured by comparing our new tensor with the conventional tensor which could not fix the position of the tibia to the femur. Methods. This study includes 60 knees in 48 patients underwent TKA using the Posterior Stabilized (PS) Prosthesis (Striker), for varus osteoarthritis. The mean age of patients was 78.2 (62 to 88) at the time of surgery. All knees were exposed using a standard medial parapatellar approach. The posterior cruciate ligament was sacrificed at the beginning of the procedure. A balanced gap technique was used for the femoral and tibial bone cuts. After the completion of bony resection, osteophyte removal, and soft-tissue balancing by the release of the medial collateral ligament (MCL), the offset knee balancer which consisted of an upper seesaw plate and a lower platform plate, and allowed the PF joint reduction during the measurement was inserted into the knee to balance on the knee flexion angles of 0 deg and 90 deg at 30 pounds. We prepared two plate types, one plate which was flat and conventionally-known plate, the other plate to which the claw hook was attached at the end. The tension device provides two measurements: the central gap length (mm) between femur and tibia which was cut, and as the ligament balance, the angle (°) between the seesaw plate and the platform plate with positive values representing varus imbalance. The joint gap measurement was performed at full extention or 90°of flexion using the both tensors. We calculated difference between the two extreme values of the values measured 3 times repeatedly using each tensor, and defined the difference as error span. Results. In the joint gap at full extention, the error span on the value measured with the claw hook type was 0.9±0.8mm, significantly small compared with the conventional type, 2.8±1.4mm [Fig.2]. On the other hand, the joint gap at 90°of flexion and the ligament balance at full extention and 90°of flexion were not significantly different between the claw hook type and the conventional type [Fig.3]. Conclusion. The tensor of claw hook type have proved to be useful in the joint gap measurement especially at full extention than the conventional type by preventing the tibia from falling posterior to the femur by gravity

Aims

The aim of this study was to investigate the distribution of phenotypes in Asian patients with end-stage osteoarthritis (OA) and assess whether the phenotype affected the clinical outcome and survival of mechanically aligned total knee arthroplasty (TKA). We also compared the survival of the group in which the phenotype unintentionally remained unchanged with those in which it was corrected to neutral.

Orthopaedic surgeons are currently faced with an overwhelming number of choices surrounding total knee arthroplasty (TKA), not only with the latest technologies and prostheses, but also fundamental decisions on alignment philosophies. From ‘mechanical’ to ‘adjusted mechanical’ to ‘restricted kinematic’ to ‘unrestricted kinematic’ — and how constitutional alignment relates to these — there is potential for ambiguity when thinking about and discussing such concepts. This annotation summarizes the various alignment strategies currently employed in TKA. It provides a clear framework and consistent language that will assist surgeons to compare confidently and contrast the concepts, while also discussing the latest opinions about alignment in TKA. Finally, it provides suggestions for applying consistent nomenclature to future research, especially as we explore the implications of 3D alignment patterns on patient outcomes.

Cite this article: Bone Joint J 2023;105-B(2):102–108.

The anatomic resection approach is based on the patient's unique anatomy adjusting for worn cartilage or bone loss. The femoral component is aligned around the primary transverse distal femoral axis around which the tibia follows a multi-radius of curvature. The tibia cut is made according to the patient's native anatomy adjusting for worn cartilage and bone loss, and applying an anatomic amount of tibial slope. This technique minimises the need for ligamentous releases to a large degree preserving the competence of the patient's soft tissue. Ligament and capsular releases can be used in difficult cases. Adjustments for the natural varus up to 3 degrees and slope of the tibial bone cut (3 – 10 degrees) further aids in knee balancing. The final alignment may not agree with a neutral hip-knee-ankle mechanical alignment on full length standing x-rays, leaving varus knees in slight varus, and valgus legs in neutral. Since little or no balance is required, this operation can be performed efficiently. Personalise the reconstruction and alignment as much as possible for each patient. The traditional “one size fits all” method where all patients have a center hip, knee, and ankle alignment needs to be reevaluated and reserved for the valgus leg

Background. Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) introduce significant anatomic modifications and secondary ligament imbalances. A restricted kinematic alignment (rKA) protocol was proposed to minimize these issues and improve TKA clinical results. Method. rKA tibial and femoral bone resections were simulated on 1000 knee CT-Scans from a database of patients undergoing TKA. rKA is defined by the following criteria: Independent tibial and femoral cuts within ± 5° of the bone neutral mechanical axis and; a resulting HKA within ±3° of neutral. Medial-lateral (ΔML) and flexion-extension (ΔFE) gap differences were calculated and compared with measured resection MA results. Results. Extension space ML imbalances ≥3mm occurred in 33% of TKA with MA technique versus 8% with rKA, and ≥5mm were present in up to 11% of MA knees versus 1% rKA (p<0.001). Using the MA technique, for the flexion space, higher ML imbalance rates were created by both MA techniques (using TEA or 3°PC) versus rKA (p<0.001). When all the differences between ΔML and ΔFE are considered together: using MA with TEA there were 41% of the knees with <3mm imbalances throughout; using PC this was 55% and using rKA it was 92% (p<0.001). Conclusion. Significantly less ML or FE gap imbalances are created using rKA versus MA for TKA. Using rKA may help the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range

Aims

This study compared patient-reported outcomes of three total knee arthroplasty (TKA) designs from one manufacturer: one cruciate-retaining (CR) design, and two cruciate-sacrificing designs, anterior-stabilized (AS) and posterior-stabilized (PS).

Measured resection approach (anatomic) is based on the patients' unique anatomy adjusting for worn cartilage or bone loss. The femoral component is aligned around the primary transverse distal femoral axis around which the tibia follows a multi-radius of curvature. The tibia cut is made according to the patient's native anatomy adjusting for worn cartilage and bone loss, and applying an anatomic amount of tibial slope. This technique minimises the need for partial ligamentous releases to a large degree preserving the competence of the patient's soft tissue, though ligament and capsular releases can be used in difficult cases. Adjustments for the varus/valgus (up to 3 degrees) or slope of the tibial bone cut (3–10 degrees) further aids in knee balancing. The final alignment may not agree with a neutral hip-knee-ankle mechanical alignment on full length standing x-rays, leaving varus knees in slight varus, and valgus legs in neutral. Since little balance is required this operation can be performed in less than 40 minutes

Aims

This systematic review aims to compare the precision of component positioning, patient-reported outcome measures (PROMs), complications, survivorship, cost-effectiveness, and learning curves of MAKO robotic arm-assisted unicompartmental knee arthroplasty (RAUKA) with manual medial unicompartmental knee arthroplasty (mUKA).

Introduction. A femoral rotational alignment is one of the essential factors, affecting the postoperative knee balance and patellofemoral tracking in total knee arthroplasty (TKA). To obtain an adequate alignment, the femoral component must be implanted parallel to the surgical epicondylar axis (SEA). We have developed “a superimposable Computed Tomography (CT) scan-based template”, in which the SEA is drawn on a distal femoral cross section of the CT image at the assumed bone resection level, to determine the precise SEA. Therefore, the objective of this study was to evaluate the accuracy of the rotational alignment of the femoral component positioned with the superimposed template in TKA. Patients and methods. Twenty-six consecutive TKA patients, including 4 females with bilateral TKAs were enrolled. To prepare a template, all knees received CT scans with a 2.5 mm slice thickness preoperatively. Serial three slices of the CT images, in which the medial epicondyle and/or lateral epicondyle were visible, were selected. Then, these images were merged into a single image onto which the SEA was drawn. Thereafter, another serial two CT images, which were taken at approximately 9 mm proximal from the femoral condyles, were also selected, and the earlier drawn SEA was traced onto each of these pictures. These pictures with the SEA were then printed out onto transparent sheets to be used as potential “templates” (Fig. 1-a). In the TKA, the distal femur was resected with the modified measured resection technique. Then, one template, whichever of the two potential templates, was closer to the actual shape, was selected and its SEA was duplicated onto the distal femoral surface (Fig. 1-b). Following that, the distal femur was resected parallel to this SEA. The rotational alignment of the femoral component was evaluated with CT scan postoperatively. For convention, an external rotation of the femoral component from the SEA was given a positive numerical value, and an internal rotation was given a negative numerical value. Results. The subjects were 4 knees in 4 males and 26 knees in 22 females. A mean age (for 30 knees) at the operation was 76.7 ± 6.1 years (range from 66.4 to 88.3). The posterior condylar angle was −0.27 ± 1.43, and the outlier, more than 3 degrees, was 1 case. Discussion. Conventionally, the SEA is palpated intraoperatively, however, the sulcus of the medial condyle sometimes cannot be identified precisely in osteoarthritic degeneration at the medial condyle. Also, the SEA is determined from the posterior condylar axis (PCA) by calculating the posterior condylar angle, which is between the SEA and the PCA, with the measurements from the preoperative CT scan. However, the residual cartilage thickness is not considered in this method, and thus, the SEA is possible to be inaccurate. The simple technology of our template allowed us to determine the SEA directly on the femoral surface, without any influence from bone degeneration. The femoral components could be implanted accurately, and therefore, the superimposed template was considered to improve TKA outcomes with the accurate SEA

Background. Total knee arthroplasty (TKA) surgical techniques attempt to achieve equal flexion and extension gaps to produce a well-balanced knee, but unexplainable unhappy patients persist. Mid-flexion instability is one proposed cause of unhappy patients. There are multiple techniques to achieve equal flexion and extension gaps, but their effects in mid-flexion are largely unknown. Purpose of study. The purpose of the study is to determine the effects that changing femur implant size and/or adjusting the femur and tibia proximal -distal and femur anterior-posterior implant positions have on cruciate retaining (CR) TKA mid-flexion ligament balance when equal flexion and extension gaps are maintained. Methods. A computational analysis was performed simulating knee flexion of two CR TKA designs (JOURNEY II CR and LEGION HFCR; Smith & Nephew) using previously validated software (LifeMOD/KneeSim; LifeModeler). Deviations from the ideal implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position and size (Table 1). Positioning the femur more proximal was accompanied by equal anterior femur and proximal tibia shifts to maintain equal flexion and extension gaps. The forces in ligaments connecting the femur and tibia, which included superficial and posterior MCL, LCL, popliteal-fibular ligament complex, iliotibial band, and anterior-lateral and posterior-medial PCL, were collected. Total tibiofemoral ligament load and PCL load for 15–75° knee flexion were analyzed versus proximal-distal implant position, implant size, implant design, and knee flexion using a MANOVA in Minitab 16 (Minitab). Results. Total tibiofemoral ligament load was significantly reduced by a more proximal implant position (p<.001) (Figure 1) but was not affected by implant size (p>0.6). PCL load was not affected by implant proximal-distal position or size (p>0.9) (Figure 2). Therefore, the PCL did not contribute to changes in mid-flexion balance caused by proximal-distal implant position. Implant design and knee flexion significantly influenced total tibiofemoral ligament and PCL loads (p<.05), but the interactions with implant proximal-distal position and size were not significant (p>0.7) indicating that the effects of implant proximal-distal position applies across the studied implant designs and 15°–75° knee flexion range. Conclusions. Our results suggest that a CR TKA can be well balanced at 0° and 90° knee flexion and be too tight or loose in mid-flexion. Since placement of implant was the variable studied, when the knee is too tight in mid-flexion, our recommendation to loosen the knee is to resect more distal and posterior femur, downsizing if necessary, and increase the tibial insert thickness. The opposite could be done to guard against the knee being too loose in mid-flexion. Finally, it is recommended to gauge balance in more than simply 0° and 90° to determine overall knee balance

INTRODUCTION. The extension and flexion gaps are affected by different factors in total knee arthroplasty (TKA). Flexion but not extension gap measurements are influenced by posterior cruciate ligament (PCL) preservation or resection and patella reduction or eversion and thigh weight. If the flexion gap is measured with the thigh placed on the tibia, the measurement results must include the thigh weight; nevertheless, there is no detailed report regarding the thigh weight influence on the flexion gap. In this study, we investigated how thigh weight affected flexion gap measurement. METHODS. Four knees of whole-body fresh-frozen cadavers (Mongolian race) were investigated. The femur and tibia were dissected with a standard measured resection technique. After the femoral component was set, the flexion gap was measured with a knee balancer. The distraction force of 20, 30, and 40 pounds were loaded at the joint level. For each measurement, the influences of the patella reduced or everted (PR or PE) and the PCL preserved or resected (CR or PS) were estimated. The flexion gap was measured five times in four different categories (CR/PR, CR/PE, PS/PR, PS/PE) and the thigh weight was reduced by weights (0, 0.5, 1.0, 2.0, 3.0 kg) using a string and pulley system. During measurement, the femur was just placed on the tibia, and the knee flexion angle was maintained at 90 degrees with a goniometer. After all measurements, the lower limbs were resected, and the thighs were weighed with a scale. Steel-Dwasstest (non-parametric multiple comparison test) were performed for statistical analysis, and p < 0.05 was considered significant. RESULTS. Flexion gap measurement results show over 10 mm difference between the maximum gap (PS/PE, 40 lbs, 3 kg weight reduction) and the minimum gap (CR/PR, 20 lbs distraction, no weight reduction) in this study. When a 0.5 kg weight reduction was applied, there were no significant flexion gap increases compared to no weight reduction situation in almost all categories except for “CR/PR and 40 lbs distraction”. According to the increase of the weight reduction, the flexion gap became larger in all categories. When a 3 kg weight reduction was applied, there were significant flexion gap increases compared to no weight reduction situation in all categories (Table 1-3). The mean thigh weight was 2.3 kg (2.0–2.6 kg). DISCUSSION. The flexion gap is usually measured with the thigh placed on the tibia in TKA, and the measurement results are considered to include the influence of the thigh weight even though this has not been discussed in the literature. From our results, the influence of the thigh weight reduction on the flexion gap was different according to heaviness of the reduction weight. When the reduction weight was over the thigh weight, flexion gap increase relative to the flexion gap without weight reduction was significant in all categories nevertheless different situations of the PCL, patella position, and joint distraction forces. To estimate adequate flexion gap and avoid post-operative flexion gap looseness, the thigh weight should be reduced when the flexion gap is measured

Introduction. 11%–19% of patients are unsatisfied with outcomes from Total Knee Arthroplasty (TKA). This may be due to problems of alignment or soft-tissue balancing. In TKA, often a neutral mechanical axis is established followed by soft tissue releases to balance and match the flexion/extension gaps with the distal femoral and proximal tibial resections at right angles to the mechanical axis. Potential issues with establishment of soft tissue balance are due to associated structures such as bone tissue of the knee, the static (or passive) stabilizers of the joint (medial and lateral collateral ligaments, capsule, and anterior and posterior cruciate ligaments), and the dynamic (or active) stabilizers around the knee. An optimized balance among these systems is crucial to the successful outcome of a TKA. Additionally, the importance of correct femoral rotation has been well documented due to its effect on patella alignment and flexion instability, range of motion, and polyethylene wear. There are several methods used in TKA procedures to establish femoral component rotation. The more prominent ones are a conventional method of referencing to the posterior condylar axis with a standard external rotation of 3° (PCR), anterior-posterior line or “Whiteside's line” (AP axis), transepicondylar axis (TEA) (Figure 1), and the gap balancing technique, however, it is not yet clear, which method is superior for femoral rotational component alignment. In the current study, we sought to investigate an alternative method based on soft-tissue, dynamic knee balancing (DKB) while using an alternative analysis approach. DKB dictates femoral component rotation on the basis of ligament balance and force measures. DKB has become more prominent in TKA surgeries. While retaining ligament balance in TKA, it is possible that this technique also leads to higher precision of rotational alignment to the anatomical axis. The primary objective of this study was to compare efficiency of DKB versus other methods for rotational implant alignment based on post-surgery computed tomography (CT). Methods. 31 patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a flexion gap balance device (Synvasive eLibra). Alternative, hypothetical alignments were assessed based on anatomical landmarks during the surgery. Postoperative computed tomography (CT) scans were analyzed to investigate post-surgery rotational alignment. Repeated measures ANOVA and Cochran's Q test were utilized to test differences between the DKB method and the other techniques. Results. Significant differences were observed between the DKB method and TEA method (p=0.02), between DKB and AP method (p=0.04), and DKB and PCR method (p=0.02): The DKB method showed the lowest rotational deviation from CT-determined true anatomical TEA (aTEA)(Figure 2). The DKB method established femoral rotation within ±3 more often than the other techniques (Figure 3), further analysis revealed a significant proportional difference between DKB and PCR method (p=0.01), between DKB and TEA (p=0.02) and DKB and AP (p=0.04). Conclusions. DKB showed promising results in our study regarding femoral rotation accuracy in comparison to other methods. DKB may be a valuable tool due to its ability to establish soft-tissue balance in addition to high accuracy of femoral rotation

Introduction. Evaluation of post-operative soft tissue balancing outcomes after Total Knee Arthroplasty (TKA) and other procedures can be measured by stability tests, with Anterior-Posterior (AP) drawer tests and Varus-Valgus (VV) ligamentous laxity tests being particularly important. AP stability can be quantified using a KT1000 device; however there is no standard way of measuring VV stability. The VV test relies on subjective force application and perception of laxity. Therefore we sought to develop and validate a device and method for quantifying knee balancing by analyzing VV stability. Materials and Methods. Our team developed a Smart Knee Fixture to measure VV angular changes using two dielectric elastomer stretch sensors, placed strategically over the medial and lateral collateral ligaments (see Figure 1). The brace is secured in position with the leg in full extension and the sensors locked with pre-tension. Therefore, contraction and elongation of either sensor is measured and the VV angular deviation of the long axis of the femur relative to that of the tibia is derived and displayed in real time using custom software. EMG muscle activity was previously investigated to confirm there is no resistive activity during the VV test obstructing ligamentous evaluations. The device was validated in two ways:. A bilateral lower body cadaver specimen, secured in a custom test rig, was used to compare the Smart Knee Fixture's readings to those measured from an optical surgical navigation system. Abduction and adduction force was gradually applied as varus and valgus moments with a wireless hand-held dynamometer up to 50N (19.8Nm) at 0 and 15° flexion. Two male volunteers were used to compare the Smart Knee Fixture's readings to those measured from fluoroscopic images. An arthroscopic distal thigh leg immobilizer was used to prevent rotation and lateral movements of the thigh when moments were applied at the malleoli. A C-arm Fluoroscope was then positioned focusing on the center of the joint. The tests were performed at full extension, 10 and 20° of flexion and force was gradually applied to 50N. Results and Discussion. R values were calculated to validate the Smart Knee Fixture's accuracy. Excellent correlation was observed between the Smart Knee Fixture and the gold standard of navigation (see Figure 2). The R values were 0.9909 and 0.9966. Correlation was also observed between Smart Knee Fixture and the measured fluoroscopic angular changes. The R values were 0.9118 and 0.7529. Conclusions. The strong R values allow us to conclude that the Smart Knee Fixture can potentially be used to accurately measure VV angular changes in a clinical setting and hence provide a quantified measure of coronal plane soft tissue balance. Clinical studies are underway to compare TKA patient outcomes to balancing measured by the Smart Knee Fixture. This information should further define balancing goals at the time of surgery. We also envisage broader applications to early detection of ligamentous injury associated with sporting activities, such as multiple ligamentous knee injuries in teenage females

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

Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture, which leads to femoral joint line elevation. There is a paucity of data describing the effect of joint line elevation on mid-flexion stability and knee kinematics. Thus, the goal of this study was to quantify the effect of joint line elevation on mid-flexion laxity.

Aims

Total knee arthroplasty (TKA) using functional alignment aims to implant the components with minimal compromise of the soft-tissue envelope by restoring the plane and obliquity of the non-arthritic joint. The objective of this study was to determine the effect of TKA with functional alignment on mediolateral soft-tissue balance as assessed using intraoperative sensor-guided technology.

Introduction. Accurate soft tissue balancing in knee arthroplasty is essential in order to attain good postoperative clinical results. In mobile-bearing UKA (Oxford Partial Knee unicompartmental knee arthroplasty, Biomet), since determination of the thickness of the spacer block depends on the individual surgeon, it will vary and it will be difficult to attain appropriate knee balancing. The first objective of the present study was to investigate flexion and extension medial unicompartmental knee gap kinematics in conjunction with various joint distraction forces. The second objective of the study was to investigate the accuracy of gap measurement using a spacer block and a tensor device. Methods. A total of 40 knees in 31 subjects (5 men and 26 women) with a mean age of 71.5 years underwent Oxford UKA for knee osteoarthritis and idiopathic osteonecrosis of the medial compartment. According to instructions of Phase 3 Oxford UKA, spacer block technique was used to make the extension gap equal to the flexion gap. Adequate thickness of the spacer block was determined so that the surgeon could easily insert and remove it with no stress. Following osteotomy, the tensor devise was used to measure the medial compartmental gap between the femoral trial prosthesis and the tibial osteotomy surface (joint component gap) (Fig. 1 and 2). The medial gap was measured at 20° of knee flexion (extension gap) and 90° of knee flexion (flexion gap) with 25N, 50N, 75N, 100N, 125N, 150N of joint distraction force. Corresponding size of bearing was determined for the prosthesis. The interplay gap was calculated by subtracting the thickness of the tibial prosthesis and the thickness of the selected size of bearing from the measured extension and flexion gaps. Results. The selected bearing size was 3 mm: 3 knees, 4 mm: 20 knees, 5 mm: 15 knees and 6 mm: 2 knees. The mean flexion gap in the medial compartment was 25N: 8.4 ± 1.6 mm, 50N: 9.4 ± 1.6 mm, 75N: 10.4 ± 1.5 mm, 100N: 11.0 ± 1.4 mm, 125N: 11.6 ± 1.5 mm, 150N: 11.9 ± 1.4 mm. The mean extension gap was 25N: 7.8 ± 1.6 mm, 50N: 8.8 ± 1.6 mm, 75N: 9.7 ± 1.6 mm, 100N: 10.4 ± 1.5 mm, 125N: 11.1 ± 1.5 mm, 150N: 11.4 ± 1.5 mm. The mean flexion interplay gap was 25N: 0.5 ± 1.2 mm, 50N: 1.5 ± 1.2 mm, 75N: 2.4 ± 1.1 mm, 100N: 3.1 ± 1.0 mm, 125N: 3.6 ± 1.1 mm, 150N: 4.0 ± 1.1 mm. The mean extension interplay gap was 25N: −0.2 ± 1.2 mm, 50N: 0.8 ± 1.1 mm, 75N: 1.7 ± 1.2 mm, 100N: 2.5 ± 1.2 mm, 125N: 3.1 ± 1.2 mm, 150N: 3.5 ± 1.2 mm. When flexion and extension of the interplay gap were compared, the extension interplay gap was shown to be significantly smaller compared with the flexion interplay gap at every joint distraction force (p < 0.05). Conclusion. The mean extension interplay gap was shown to be significantly smaller compared with the flexion interplay gap at every joint distraction force even though the extension gap was adjusted to the flexion gap using the spacer block. This suggests that in the actual UKA operative technique using a spacer block there is a potential that the extension gap will be smaller than the flexion gap. Surgeons should be aware of this fact and adjust the flexion and extension gaps with caution when performing mobile-bearing UKA

Deformity correction is a fundamental goal in total knee arthroplasty. Severe valgus deformities often present the surgeon with a complex challenge. These deformities are associated with abnormal bone anatomy, ligament laxity and soft tissue contractures. Distorted bone anatomy is due to bone loss on the lateral femoral condyle, especially posteriorly. To a lesser extent bone loss occurs from the lateral tibia plateau. The AP axis (Whiteside's Line) or epicondylar axis must be used as a rotational landmark in the severely valgus knee. Gap balancing techniques can be helpful in the severely valgus knee, but good extension balance must be obtained before setting femoral rotation with this technique. Coronal alignment is generally corrected to neutral or 2- to 3-degree overcorrection to mild mechanical varus to unload the attenuated medial ligaments. The goal of soft tissue releases is to obtain rectangular flexion and extension gaps. Soft tissue releases involve the IT band, posterolateral corner/arcuate complex, posterior capsule, LCL, and popliteus tendon. Assessment of which structures is made and then releases are performed. In general, pie crust release of the IT band is sufficient for mild deformity. More severe deformities require release of the posterolateral corner / arcuate and posterior capsule. I prefer a pie crust technique, while Ranawat has described the use of electrocautery to perform these posterior/ posterolateral releases. In most cases the LCL is not released, however, this can be released from the lateral epicondyle, if necessary. Good ligament balance can be obtained in most cases, however, some cases with severe medial ligament attenuation require additional ligament constraint such as a constrained condylar implant

Deformity correction is a fundamental goal in total knee arthroplasty. Severe valgus deformities often present the surgeon with a complex challenge. These deformities are associated with abnormal bone anatomy, ligament laxity and soft tissue contractures. Distorted bone anatomy is due to bone loss on the lateral femoral condyle, especially posteriorly. To a lesser extent bone loss occurs from the lateral tibia plateau. The AP Axis (Whiteside's Line) or Epicondylar axis must be used as a rotational landmark in the severely valgus knee. Gap balancing techniques can be helpful in the severely valgus knee, but good extension balance must be obtained before setting femoral rotation with this technique. Coronal alignment is generally corrected to neutral or 2- to 3-degree overcorrection to mild mechanical varus to unload the attenuated medial ligaments. The goal of soft tissue releases is to obtain rectangular flexion and extension gaps. Soft tissue releases involve the IT band, Posterolateral Corner/Arcuate Complex, Posterior Capsule, LCL, and Popliteus Tendon. Assessment of which structures is made and then releases are performed. In general Pie Crust release of the ITB is sufficient for mild deformity. More severe deformities require release of the Posterolateral Corner/Arcuate Complex and Posterior Capsule. I prefer a pie crust technique, while Ranawat has described the use of electrocautery to perform these posterior/ posterolateral releases. In most cases the LCL is not released, however, this can be released from the lateral epicondyle, if necessary. Good ligament balance can be obtained in most cases, however, some cases with severe medial ligament attenuation require additional ligament constraint such as a constrained condylar implant

This study was conducted to investigate the correlation between intra-operative Flexion Balance (IFB) and post-operative Flexion instability in Posterior-Stabilized Total Knee Arthroplasty (TKA). Eighty-three knees (4 males and 79 females, average 74 y/o) with primary TKA (Zimmer NexGen LPS flex fixed-bearing) for varus osteoarthritis in our hospital between January 2006 and December 2007, were included in this study. After bone-cutting independently and balancing manually, Extension Balance (EB) and IFB were measured with seesaw type tensor. Post-operative Flexion Balance (PFB) was evaluated as post-operative instability with Kanekasu’s Epicondylar view at the least more than 6 months postoperatively. Varus inclination (lateral joint opening) was indicated as plus. In addition, pre-operative standing FTA (femorotibial angle), the change of FB (CFB=PFB-IFB) and True Correction Angle (TCA=FTA-174-EB), we had defined, were calculated. The TCA was hypothesized to mean the extent of medial soft tissue release. With these data, the correlation between IFB and PFB, CFB and TCA were analyzed. Of these, furthermore, in the well-balanced knees (IFB ≥ ±2°), same analyses were done. Statistical analysis was performed with StatView software. Each data (n=83) in all subjects was as follows (Mean ± SD, degrees.); EB: 2.74 ±2.74, IFB: 1.61 ±3.67, PFB: 1.73 ±2.66, CFB: 0.01 ±4.25, FTA: 185.3 ±6.7, TCA: 8.65 ±6.52, respectively. Though there was no correlation between IFB and PFB (r=−0.09, p=0.57), CFB was correlated with TCA (r=0.40, p< 0.01). Each data in the well-balanced knees (n=43) was as follows, EB: 3.09 ±2.71, IFB: 0.70 ±1.30, PFB: 1.22 ±2.52, CFB: 0.57 ±2.3, FTA: 185.5 ±6.5, TCA: 8.42 ±6.09, respectively. There was a correlation between IFB and PFB (r=0.41, p< 0.01), however, FBC was not correlated with TCA (r=−0.26, p=0.10). Same rectangular balance has been thought to be one the most important factors to obtain the good postoperative stability in TKA. For correcting alignment of lower extremity, medial or posteromedial release are generally needed to perform mainly in extended knee. Even if well-balanced EB was achieved, IFB does not necessarily prove to be well, rather than sparse. This might be because intra-operative balance was not measured under physiological condition, especially after wide posteromedial release. Soft tissues released for balancing would be repaired and shortened over time, so it seems to be natural that intra-operative balance would change. We have reported that EB was correlated with post-operative instability in the previous congress (ISTA 2006). However, it remains unknown as for FB. Our study demonstrated that CFB increased in accordance with the extent of soft tissue release (TCA), and that IFB was correlated with PFB only in the well balanced knees. This means that the measurement of IFB was not useful for predicting PFB in the imbalanced knees. That’s why we should achieve adequate balance & gap during operation and should recognize that FB was influenced by various factors, not only soft tissues but also rotation and inclination of components. In the future, how to measure IFB, including tensor and measurement condition, should be considered and established to predict knee balancing for good clinical results

Aims. There is little literature about total knee arthroplasty (TKA) after distal femoral osteotomy (DFO). Consequently, the purpose of this study was to analyze the outcomes of TKA after DFO, with particular emphasis on: survivorship free from aseptic loosening, revision, or any re-operation; complications; radiological results; and clinical outcome. Patients and Methods. We retrospectively reviewed 29 patients (17 women, 12 men) from our total joint registry who had undergone 31 cemented TKAs after a DFO between 2000 and 2012. Their mean age at TKA was 51 years (22 to 76) and their mean body mass index 32 kg/m. 2. (20 to 45). The mean time between DFO and TKA was ten years (2 to 20). The mean follow-up from TKA was ten years (2 to 16). The prostheses were posterior-stabilized in 77%, varus-valgus constraint (VVC) in 13%, and cruciate-retaining in 10%. While no patient had metaphyseal fixation (e.g. cones or sleeves), 16% needed a femoral stem. Results. The ten-year survivorship was 95% with aseptic loosening as the endpoint, 88% with revision for any reason as the endpoint, and 81% with re-operation for any reason as the endpoint. Three TKAs were revised for instability (n = 2) and aseptic tibial loosening (n = 1). No femoral component was revised for aseptic loosening. Patients under the age of 50 years were at greater risk of revision for any reason (hazard ratio 7; p = 0.03). There were two additional re-operations (6%) and four complications (13%), including three manipulations under anaesthetic (MUA; 10%). The Knee Society scores improved from a mean of 50 preoperatively (32 to 68) to a mean of 93 postoperatively (76 to 100; p < 0.001). Conclusion. A cemented posterior-stabilized TKA has an 88% ten-year survivorship with revision for any reason as the endpoint. No femoral component was revised for aseptic loosening. Patients under the age of 50 years have a greater risk of revision. The clinical outcome was significantly improved but balancing the knee was challenging in 13% of TKAs requiring VVC. Overall, 10% of TKAs needed an MUA, and 6% of TKAs were revised for instability. Cite this article: Bone Joint J 2019;101-B:660–666

Deformity correction is a fundamental goal in Total Knee Arthroplasty. Severe valgus deformities often present the surgeon with a complex challenge. These deformities are associated with abnormal bone anatomy, ligament laxity and soft tissue contractures. Distorted bone anatomy is due to bone loss on the lateral femoral condyle, especially posteriorly. To a lesser extent bone loss occurs from the lateral tibia plateau. The AP Axis (Whiteside's Line) or Epicondylar axis must be used as a rotational landmark in the severely valgus knee. Gap balancing techniques can be helpful in the severely valgus knee, but good extension balance must be obtained before setting femoral rotation with this technique. Coronal alignment is generally corrected to neutral or 2 to 3 degree overcorrection to mild mechanical varus to unload the attenuated medial ligaments. The goal of soft tissue releases is to obtain rectangular flexion and extension gaps. Soft tissue releases involve the IT band, Posterolateral corner/Accurate Complex, Posterior Capsule, LCL, and Popliteus Tendon. Assessment of which structures is made and then releases are performed. In general Pie Crust release of the ITB is sufficient for mild deformity. More severe deformities require release of the Posterolateral corner/Accurate Complex and Posterior Capsule. I prefer a pie crust technique, while Ranawat has described the use of electrocautery to perform these posterior/ posterolateral releases. In most cases the LCL is not released, however, this can be released from the lateral epicondyle if necessary. Good ligament balance can be obtained in most cases, however, some cases with severe medial ligament attenuation require additional ligament constraint such as a constrained condylar implant

Introduction. In valgus knees, ligament balance remain difficult when implanting a total knee arthroplasty (TKA), this leads some authors to systematically propose the use of constrained devices. Others prefer reserving higher constraints to cases where it is not possible to obtain final satisfactory balance: less than 5 of residual frontal laxity in extension in each compartment, and a tibiofemoral gap difference not in excess to 3mm between flexion and extension. The goal of the study was to assess if is possible to establish preoperative criteria that can predict a constrained design prosthetic implantation at surgery. Materials and Methods. A consecutive series of 93 total knee prostheses, implanted to treat a valgus deformity of more than 5 was retrospectively analysed. Preoperatively, full weight bearing long axis AP views A-P were performed: hip knee angle (HKA) averaged 195 (186 to 226), 36 knees had more than 15 of valgus, and 19 others more than 20 of valgus. Laxity was measured by stress radiographies with a TelosTM system at 100 N. Fifty-two knees had preoperative laxity in the coronal plane of more than 10. Fourteen knees had more than 5 laxity on the convex (medial) side, 21 knees had more than 10 laxity on the concave (lateral) side. Statistical assessment, using univariate analysis, identified the factors that led, at surgery, to an elevated constraint selection level; these factors of independence were tested by multivariate analysis. Logistical regression permitted the classification of the said factors by their odds ratios (OR). Results. High-constraints prostheses (CCK type) were used in 26 out of 93 TKA, the other TKA were regular posterostabilized (PS) prostheses. Statistically, the preoperative factors that led to the choice of a constrained prosthesis were: (1) valgus severity as measured by HKA (PS = (PS = 193, CCK = 198), (2) increased posterior tibial slope (PS = 4.8, CCK = 6.5), (3) low patellar height (using Blackburne and Peel index PS = 0.89, CCK = 0.77), (4) severity of laxity in valgus (PS = 2.3, CCK = 4.3). Among all these factors, the only independent one was laxity in valgus (convex side laxity) (p = 0.0008). OR analysis showed a two-fold increased probability of implanting an elevated constraints prosthesis for each one degree increment of laxity in valgus. Discussion. This study demonstrated that it was not the valgus angle severity but rather the convex medial side laxity that increased the frequency of constrained prostheses implantation. Other factors, as a low patellar height or an elevated posterior tibial slope, when associated, potentiate this possible prosthetic switch (to higher constraints) and should make surgeons aware, in these situations, of encountering difficulties when establishing ligament balance

Introduction. The success of total knee arthroplasty depends on many factors, including the preoperative condition of the patient, the design and materials of the components and surgical techniques. It is important to position the femoral and tibial components accurately and to balance the soft tissues. Malpositioning of the component can lead to failures due to aseptic loosening, instability, polyethylene wear and dislocation of the patella. In order to improve post-operative alignment, computer-aid systems have been developed for total knee arthroplasty. Many clinical and experimental studies of these systems have shown that the accuracy of implanted components can be improved in spite of the increase in costs and operating time. This may not, however, improve the outcome in the short-term. Restoration of the normal mechanical axis of the knee and balancing of the surrounding soft tissues have been shown to have an important bearing on the final outcome of knee replacement operations. In severely deformed knees, whether varus or valgus, these goals may be difficult to achieve. We compared the radiologic results of the mechanical axis and implant position of Total Knee Arthroplasty using a robot-assisted method with conventional manually implanted method in severe varus deformed knee. Materials and Methods. A data set of 50 consecutive cases that were performed from April 2007 to December 2010 using the robot assisted TKA(Group A) were compared with a data set of 50 consecutive cases from the same period that were done using conventional manual TKA(Group B). All cases had a preoperative mechanical varus deformity >15° and one brand of implant was used on all cases. The diagnosis was primary osteoarthritis in all knees. The operations were performed by one-senior author with the same robot system, ROBODOC (ISS Inc., CA, USA) along with the ORTHODOC (ISS Inc., CA, USA) planning computer. (See Figure 1.) The radiological evaluations included mechanical axis, implant position (α,β,γ,δ angle) according to the system of American Knee Society. Results. There was a significant difference in the postoperative α, β, γ angle and mechanical axis between two group(p<0.05). In group A, mechanical axis angle changed from preoperative varus 18.5±3.3° to postoperative varus 0.6±1.5° without outlier. In group B, mechanical axis angle changed from varus 19.4±4.2° to varus 2.5±3.8° with 8 outliers. In group A, the mean α, β, γ, δ angle were 96.7°, 90.1°, 1.9°, 86.8° and 93.1°, 88.3°, 3.8°, 85.9° in group B. But we found no loosening and osteolysis at last follow up in both group. Conclusion. On the basis of our results, patients with severe varus knee(>15°) tended to have more postoperative varus mechanical alignment in conventional manual TKA group than robot-assisted TKA group. We think that robot-assisted TKA is helpful in excessive varus knee in aspect of not only mechanical alignment and implant position but also long term clinical results and implant longevity. However, a long term followup evaluation will be necessary and complications in robot system