INTRODUCTION:. A discrepancy exists between biomechanical and clinical outcome studies when comparing cruciate-retaining (CR) versus posterior stabilized (PS) component designs. The purpose of this study is to re-evaluate experimental model results using half-body specimens with intact extensor mechanisms and navigation to evaluate PS and CR component gaps though an entire range of motion. METHODS:. A custom-designed knee testing apparatus was used for secure anchoring of the lower half of cadaver pelvic, allowing full range of knee motion and the application of traction throughout that range. Eight sequential testing regimens: were conducted with knee intact, with CR TKA in place, with PS TKA with quadriceps tendon in place, with PS TKA with sectioned quadriceps tendon in place, with and without traction at each stage. At each stage, a navigated knee system with dedicated software was used to record component gapping through a full range of motion from 0° to 120°. The amount of traction used was 22N. Each knee (n = 10) was taken through 6 full ranges of motion at every stage. At each stage, corroboration of navigation findings was attempted using a modified gap balancer to take static gap measurements at 0° and 90° with 12 in. lbs of torque was applied. RESULTS:. The difference in component gapping between CR and PS knees resulted in a range from −0.85 mm to 0.62 mm. The range of component gapping was from −0.67 mm to 0.70 mm with both constructs under 22N traction load. There was no significant difference between loaded and unloaded component gaps, and there were no statistically significant differences in component gapping between CR and PS knees throughout a full range of motion. Static flexion-extension gap measurements, were significantly different from previously published data, notably at in 90° flexion gap measurement. The comparison of the sectioned unloaded and sectioned loaded quadriceps tendon constructs gave a range of distraction of tibio-femoral gaps from 1.85 to 5.22 mm and 1.46 to 4.60 mm, respectively. These measurements were significantly increased over previously reported findings. CONCLUSION:. There was no significant difference between the CR and PS TKA designs with respect to component gapping when measured through a complete range of motion with an intact extensor mechanism. This data contradicts earlier results, obtained from less complete specimens, and correlates with clinical studies which show no gap differences in CR and PS knees. We conclude that the sectioned quadriceps tendon influences knee flexion-extension gaps in a PS TKA construct model. This finding suggests that intact extensor mechanisms may be required to perform proper kinematic studies of TKA, and this may be a contributing factor in the discrepancies observed between previous biomechanical and clinical outcome studies. Clinical Relevance: The findings of this study may solve the controversy regarding differences of the CR and PS TKA designs observed using biomechanical models

INTRODUCTION. Mechanical alignment in TKA introduces significant anatomic modifications for many individuals, which may result in unequal medial-lateral or flexion-extension bone resections. The objective of this study was to calculate bone resection thicknesses and resulting gap sizes, simulating a measured resection mechanical alignment technique for TKA. METHODS. Measured resection mechanical alignment bone resections were simulated on 1000 consecutive lower limb CT-Scans from patients undergoing TKA. Bone resections were simulated to reproduce the following measured resection mechanical alignment surgical technique. The distal femoral and proximal tibial cuts were perpendicular to the mechanical axis, setting the resection depth at 8mm from the most distal femoral condyle and from the most proximal tibial plateau (Figure 1). If the resection of the contralateral side was <0mm, the resection level was increased such that the minimum resection was 0mm. An 8mm resection thickness was based on an implant size of 10mm (bone +2mm of cartilage). Femoral rotation was aligned with either the trans-epicondylar axis or with 3 degrees of external rotation to the posterior condyles. After simulation of the bone cuts, media-lateral gap difference and flexion-extension gaps difference were calculated. The gap sizes were calculated as the sum of the femoral and tibial bone resections, with a target bone resection of 16mm (+ cartilage corresponding to the implant thickness). RESULTS. For both the varus and valgus knees, the created gaps in the medial and lateral compartments were reduced in the vast majority of cases (<16mm). The insufficient lateral condyle resection distalises the lateral joint surface by a mean of 2.1mm for the varus and 4.4mm for the valgus knees. The insufficient medial tibial plateau resection proximalises the medial joint surface by 3.3mm for the varus and 1.2mm for the valgus knees. Medio-lateral gap imbalances in the extension space of more than 2mm) occurred in 25% of varus and 54% of valgus knees and significant imbalances of more than 5mm were present in up to 8% of varus and 19% of valgus knees. Higher medio-lateral gap imbalances in the flexion space were created with trans epicondylar axis versus 3 degrees to the posterior condyles (p<0.001). Using trans epicondylar axis, only 49% of varus and 18% of valgus knees had less than 3mm of imbalance in both media-lateral and flexion-extension gaps together. DISCUSSION AND CONCLUSION. A systematic use of the tested measured resection mechanical alignment technique for TKA leads to many cases with medio-lateral or flexion-extension gap asymmetries. Some medio-lateral imbalances may not be correctable surgically and may results in TKA instability. Other versions of the mechanical alignment technique or other alignment methods that better reproduce knee anatomies should be explored. For any figures or tables, please contact the authors directly

Objective. In Total Knee Arthroplasty (TKA), it is important to adjust the difference of the flexion-extension gap (gap difference) to get the good range of motion and the sufficient stability. However the effect of the gap adjustment on the post-operative knee flexion angle(KFA) is unknown. We investigated the relationship between the gap difference and the postoperative KFA improvement rate. Methods. 179 knees that underwent LCS RP TKA were investigated more than 6 months after surgery(Feb/2013∼Sep/2014). The patients were 49 men and 130 women, of average age 70.6 years (50∼88) and BMI 26.3 (17.0∼55.2). Among them, 175 knees were knee osteoarthritis and 2 joints were rheumatoid arthritis, 2 joints were avascular necrosis. The extension gap was typically prepared with a measured resection, and a small temporary flexion bone gap was prepared with a 4mm resection of the femoral posterior condyle using the pre-cut method(fig 1). Then we measured the gaps under the installation of the Pre-cut Trial(PT; Kaneyama 2011)by the off-set spacer with 1mm increments in patella reduction position(fig 2,3). The final amount of bone resection was determined by comparison of the measured gaps and gaps required for implantation. We calculated the differences between the final extension gap and the final flexion gap and their relationship with knee flexion angles at 6 months postoperatively were analyzed. Results. The gap difference was 0.66 ± 0.89mm (mean ± SD), minimum −1.75mm, maximum 3.00mm. The KFA was improved 119.2 ° to 125.2.°post operatively. We could find weak correlation between pre-operative flexion angle and post-operative flexion angle (R=0.37: Pearson) Between the gap difference and the postoperative KFA, we found no correlation with R = −0.09. We observed no correlation relationship between the size of the gap differenceup to 3mm and the KFA improvement. Conclusion. In PCL sparing LCS RP TKA that created gaps using PT, the value of the gap differenceshowed no correlation with the postoperative KFA. However the value of R shows a minus, thus we speculate that there is a possibility that the post-operative flexion angle could decrease in accordance with the increase of the gap difference. We infer that the improvement of the KFA couldn't be obtained by increasing thegap difference. The importance of flexion-extension gap adjustment in TKA has been emphasized in many articles, although few studies have reported the relationship between the gap difference and the post-operative range of motion of the knee. Enlargement of the flexion gap to improve knee flexion angle possibly causes the instability of the knee in flexion. Our study suggests that the size of flexion gap should not exceed the size of extension gap to achieve favorable knee flexion angle results

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

There is ample data to confirm that Computer-assisted total knee replacement improves alignment of the limb when compared with the conventional technique. There is also published evidence that optimum alignment correlates with longevity of implants. CAS enables accurate component alignment of both femoral and tibial components. It enables accurate restoration of the posterior tibial slope which has important consequences for flexion range and stability of the component in flexion especially if mobile bearing implants are considered. CAS also aids in correctly orienting rotation of the femoral component; this has value in minimizing patellar maltracking. We will present our data showing accurate restoration of joint line and posterior femoral offset. As CAS ensures alignment, rotation, sizing and positioning of components, the surgeon is free to devote his efforts to ensuring soft-tissue balance and stability, since TKA is really a ‘soft-tissue’ operation. How CAS is of immense value in deformity correction and soft-tissue balancing will be illustrated with examples. It helps in better understanding and quantification of the effects of soft-tissue release on flexion-extension gaps and this is of great value not only for minimal deformities (to minimise releases) but also for severe deformities (to ensure complete correction by adequate release). CAS is invaluable in helping equalize flexion-extension gaps; how it can help balance the flexion gap to the extension gap by ‘virtual surgery’ will be depicted with examples. It is particularly useful in presence of hardware in the femur or tibia and for concomitant extra-articular deformity. We have also found a consistent improvement in recovery of functional milestones with CAS with similar results for both unilateral and bilateral TKAs. Furthermore, there is evidence to support that ensuring alignment has important benefits in improving functional and quality of life scores. In addition, those with alignment of mechanical axis within 3 degrees of normal have been shown to have a shorter stay in hospital by 2 days. Studies have shown reduced blood loss and incidence of emboli after CAS TKA. Using CAS routinely for all cases, the author is ‘time neutral’. While there is always room for improvement with evolving technologies and CAS is no exception, it already has enormous benefits in the performance and outcome of TKA, and is an important part of the surgical armamentarium for a successful knee arthroplasty

INTRODUCTION. The results of modified gap balancing and measured resection technique have been still controversial. We compared PS-type TKAs for osteoarthritis performed using the modified gap technique and the measured resection to determine if either technique provides superior clinical results. METHODS. The modified gap technique was used in 85 knees, and the measured technique using preoperative CT was used in 70 knees. To compare intra-operative soft tissue balance, bone gap and component gap were measured using original two paddle tensor (20,30,40lb) at 0 degree extension and 90 degrees flexion. To assess the post-operative patella congruency and soft tissue balance, we measured patella tilt, condylar twist angle (CTA) and condylar lift-off angle (LOA) in radiographs. Finally, we evaluated postoperative clinical result (1–5 years) KOOS. Statistical analysis was used by StatView. RESULTS. (1). Component gaps in flexion at measured techniques were bigger than at gap techniques. Lateral flexion-extension gap and lateral-medial balance at 30lb or 40lb in the measured technique were statistically bigger than the gap technique. (2). There were no statistical correlations with patella tilt, CTA and LOA in both techniques. There were no significant differences between each of the two techniques. (3). KOOS of ‘pain during going up or down stairs’ for the measured technique were statistically worse than for the gap technique. DISCUSSION. Intra-operative lateral gap and flexion balance using measured technique were bigger than gap technique, but there were no statistical differences in post-operative LOA and PF congruency in radiographs. Post-operative pain on stairs might be affected by the differences in intra-operative gap and balance between the two techniques with the balanced ligament technique showing more positive results

Bicruciate ligament retaining total knee arthroplasty preserves all of the ligaments of the knee while still addressing the ligament balance and the flexion-extension gaps. The concept of cruciate ligament preservation is not new and both Townley and Cartier designed prostheses in the late 1980s that did preserve all of the ligaments. Their results were quite acceptable for that time in knee replacement surgery but the posterior stabilised and cruciate retaining designs controlled most of the market. The surgical technique for cruciate ligament preservation was more difficult, and without clear clinical benefit, most surgeons gravitated towards the cruciate retaining and posterior stabilised designs. In the late 1990s, evaluation of the total knee arthroplasty began to assess knee kinematics in addition to pain and functional outcomes. At the same time, studies on the unicondylar knee arthroplasty demonstrated impressive scores in motion and patient satisfaction with preservation of all of the ligamentous structures of the knee. Over the past two years, new designs that preserve all of the ligaments of the knee have returned to the market. The instruments have been improved and the prostheses have been changed to respect the kinematics of the knee. Fifteen to twenty percent of all total knee replacement patients are not completely satisfied with the surgery and the authors believe that complete ligament preservation may address this complaint

INTRODUCION. Appropriate soft tissue balance is an important factor for postoperative function and long survival of total knee arthroplasty(TKA). Soft tissue balance is affected by ligament release, osteophyte removal, order of soft tissue release, cutting angle of tibial surface and rotational alignment of femoral components. The purpose of this study is to know the characteristics of soft tissue balance in ACL deficient osteoarthritis(OA) knee and warning points during procedures for TKA. METHODS. We evaluated 139 knees, underwent TKA (NexGen LPS-Flex, fixed surface, Zimmer) by one surgeon (S.A.) for OA. All procedures were performed through a medial parapatellar approach. There were 49 ACL deficient knees. A balanced gap technique was used in 26 ACL deficient knees, and anatomical measured technique based on pre-operative CT was used in 23 ACL deficient knees. To compare flexion-extension gaps and medial- lateral balance during operations between the two techniques, we measured each using an original two paddles tensor (figure 1) at 20lb, 30lb and 40lb, for each knee at a 0 degree extension and 90 degree flexion. We measured bone gaps after removal of all osteophytes and cutting of the tibial surface, then we measured component gaps after insertion of femoral components. Statistical analysis was performed by t-test with significant difference defined as P<0.05. RESULTS. (1) There were 90 ACL remaining knees and 49 deficient knees. Each group's preoperative FTA was 184±4.4 degrees, 187±6.3 degrees, postoperative FTA was 174±2.7 degrees, 173±3.1 degrees, preoperative knee extension was −12.8±7.5 degrees, −14.5.±3.1 degrees, flexion was 122.4±13.7 degrees, 110.7±20.2 degrees, post-operative β angle was, 88.1±2.5 degrees, 88.5±2.5 degrees. Comparing bone gap, medial gap and lateral-medial gap at a 30lb flexion were significantly different(P<0.05). (2) Comparing component gaps using modified gap techniques (group G) and anatomical techniques (group A) in ACL deficient knees, extension of medial and lateral gaps at 30lb and 40 lb in anatomical technique was bigger. The lateral-medial gap at 30lb was bigger in anatomical techniques. (P<0.05). DISCUSSION. The present results showed that ACL deficient OA knee were looser at medial side compared with ACL remaining OA knees. It indicates that we performed medial rerelease carefully in ACL deficient TKA. When we used gap techniques, medial loosening caused malposition of femoral components, and when we used anatomical techniques, extension gap was bigger than using gap techniques because generally smaller femoral components were chosen. It is reported that lateral gaps are bigger in severe varus deformity OA than slightly deformed OA knees and the soft tissue on the medial side is not shorter. It is also reported the correlation of lateral thrust with ACL deficiency and the progression OA, and when OA is developed, lateral side becomes loose. Our study indicated that ACL deficient OA knee progress rotational instability, in addition to antero-posterior instability, and subsequent medial loosening and development of medial osteophyte. Medial preserving gap technique is recommended

Instability remains a common reason for revision after primary TKA. Careful preoperative examination is necessary to determine the exact direction of and reason for the instability. Radiographs and CT can be useful to evaluate component alignment and rotation. Obviously, ruling out concurrent infection should be a part of the routine preoperative workup. PCL insufficiency can be treated by conversion to a more “dished” insert if available, and all other component issues are acceptable. If dished inserts are not available, then revision to a posterior stabilised component can be effective. Flexion instability can occur with PCL substituting designs, and may require revision as well. Up-sizing, and posteriorising the femoral component (often requiring posterior augmentation) to tighten the flexion gap can be an effective strategy. With collateral ligament problems, so called CCK or “constrained” implants can be effective. While ligament advancement or augmentation techniques have been described, few surgeons are familiar with these techniques, and most “back up” such reconstructions with constrained implants. With more severe collateral ligament deficiencies, multi-directional instabilities, or massive flexion-extension gap mismatches, the use of so-called “hinged” implants can be effective. It is wise to have various levels of constraint available preoperatively when undertaking these challenging revisions

In primary TKA, non- or semi-constrained TKA implants might have their limitations in the absence of collateral ligaments, severe deformity, large osseous defects and gross flexion-extension instability. Although most primary TKA indications can be solved with modular, non-hinged implants, an adequate balancing might require a relevant soft tissue release. This consequently adds complexity and operative time with less predictable results in the elderly patient. The current literature reporting on short- to mid-term results of rotating hinged implants in primary osteoarthritis shows some quite diverse results and consequently different interpretations of this implant type in primary knee arthroplasty. Although some authors were able to show good and excellent clinical results in 91% of patients and consequent survival rates of a rotating hinge implant after 15 years up to 96% in primary indications, others found high complication rates of up to 25% of all operated patients, which remains unclear for us and is inconsistent with our clinical results in primary and revision TKA in over 30 years of experience with the ENDO-Model rotating hinge implant. Our potential indications in the elderly for a rotating or pure hinged implant in primary TKA include: Complete MCL instability; Severe varus or valgus deformity (>20 degrees) with necessary relevant soft tissue release; Relevant bone loss including insertions of collaterals; Gross flexion-extension gap imbalance; Ankylosis; One staged implantation with specific antibiotics after PJI. Due to general limited soft tissues or hyperlaxity, patients with neuropathic joints, or lack of extensor mechanism should be considered for a complete hinged implant. The ENDO-model hinge has only been minimally adapted since its development in the 70´s, including fully cemented long stems, in modular and non-modular versions. We strictly reserve a rotational hinge in primary indications for patients >70 years with a combined varus alignment, whereas in severe valgus deformities, a complete hinged implant version should be used for our implant design

Purpose. The tibia first technique in unicompartmental knee arthroplasty (UKA) may have the advantage that surgeons can obtain a balanced flexion-extension gap. However, changes of the soft tissue tension during UKA has not been elucidated yet. The purpose of this study was to examine the correlation between the soft tissue tension before the femoral osteotomy and after the femoral component in place using the tensor in UKA. Methods. Thirty UKAs for isolated medial compartmental osteoarthritis or idiopathic osteonecrosis were assessed. The mean age was 71.8±8.5 years old (range: 58–85), and the average coronal plane femorotibial angle (FTA) was 181.2±3.2 degree preoperatively. All the patients received a conventional medial Zimmer Unicompartmental High Flex Knee System (Zimmer Inc, Warsaw, Ind). The actual values of the proximal and posterior femoral osteotomy were calculated by adding the thickness of the bone saw blades to the thickness of the bony cut. Using a UKA tensor which designed to facilitate intra-operative soft tissue tension throughout the range of motion (ROM), the original gap before the femoral osteotomy, the component gap after the femoral osteotomy, and component placement were assessed under 20 lb distraction forces. (Figure 1). Results. The mean actual thickness of the distal femoral osteotomy 6.5 ± 1.3 mm and the posterior femoral osteotomy was 7.4 ± 1.3 mm. The distal thickness of the Zimmer UKA was set to 6.5 mm and the mean posterior thickness of the prosthesis used in this study was 5.8 ± 0.3 mm. There is a positive correlation between the original and component gap throughout the ROM (R > 0.5). The original and component gap showed the same kinematic pattern from full extension to 90 degrees of knee flexion. However, the component gap showed significantly higher compared to the original gap after 120 degrees of knee flexion (p < 0.001). (Figure 2). Conclusions. Despite the fact that the component gap showed significantly higher compared to the original gap in deep flexion, there is a positive correlation between the original and component gap throughout the ROM. The discrepancy during deep flexion was due to the posterior design of the prosthesis that is designed to be thinner than the actual thickness of the posterior osteotomy in order to prevent flexion gap tightness. These results suggest that the tibia first technique with the tensor have the advantage that surgeons can predict final soft tissue tension before femoral osteotomies with the comprehension of the prosthetic design and help restore natural knee kinematics, potentially improving implant survival and functional outcomes

In primary TKA, non- or semi-constraint TKA implants might have their limitations in the absence of collateral ligaments, severe deformity, large osseous defects and gross flexion - extension instability. Although most primary TKA indications can be solved with modular, non-hinged implants, an adequate balancing might require a relevant soft tissue release. This consequently adds complexity and operative time with less predictable results in the elderly patient. The current literature reporting on short to mid-term results of rotating hinged implants in primary osteoarthritis shows some quite diverse results and consequently different interpretations of this implant type in primary knee arthroplasty. Although some authors were able to show good and excellent clinical results in 91% of patients and consequent survival rates of a rotating hinge implant after 15 years up to 96% in primary indications, others found high complication rates of up to 25% of all operated patients, which remains unclear for us and is inconsistent with our clinical results in primary and revision TKA in over 30 years of experience with the Endo-Model rotating hinge implant. Our potential indications in the elderly for a rotating- or pure-hinged implant in primary TKA include: Complete MCL instability, Severe varus or valgus deformity (>20 degrees) with necessary relevant soft tissue release, Relevant bone loss including insertions of collaterals, Gross flexion-extension gap imbalance, Ankylosis, One staged implantation with specific antibiotics after PJI. Due to general limited soft tissues or hyper laxity, patients with neuropathic joints, or lack of extensor mechanism should be considered to a complete hinged implant. The ENDO-model hinge has only been minimal adapted since its development in the 70's, including fully cemented long stems, in modular and non-modular versions. We strictly reserve a rotational hinge in primary indications for patients >70 years with a combined varus alignment, whereas in severe valgus deformities, a complete hinged implant version should be used for our implant design

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

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

Introduction. Achieving proper ligament tension in knee flexion within cruciate retaining (CR) total knee arthroplasty (TKA) has long been associated with clinical success. The distal femoral joint line (DFJL) is routinely used as a variable to assist in achieving proper flexion-extension gap balancing. No prior study has observed the possible effects of properly restoring the DFJL may have on ligament tension in flexion. The purpose of this computational analysis was to determine what effect the DFJL may have on ligament strains and tibiofemoral kinematics of CR knee designs in flexion. Methods. A computational analysis was performed utilizing a musculoskeletal modeling system with ligaments modeled as non-linear elastic. Tibiofemoral kinematics, contact points estimated from the femoral condyle low points, and ligament strain, change in length relative to the unloaded length, were measured at 90° knee flexion during a deep knee bend activity. Two different knee implants, a High Flexion CR (HFCR) and a Guided Motion CR (GMCR) design were used. Simulations were completed for changes in superior-inferior (SI) positioning of the femoral implant relative to the femur bone, in 2mm increments to simulate over and under resection of the DFJL. Results. The medial condyle of the femoral implant was 0.67mm and 0.47mm more posterior relative to the tibia per 1mm elevation of the DFJL for the HFCR and GMCR designs respectively. The lateral condyle was 0.80mm and 1.06mm more posterior relative to the tibia per 1mm elevation of the DFJL for the HFCR and GMCR designs, respectively. The strain in the LCL and MCL changed less than 0.0005mm/mm per 1mm change in DFJL indicating that those structures were not affected. The PCL bundles and the ITB were affected by changes in DFJL with strain increasing 0.005 and 0.004mm/mm in the AL PCL bundle respectively for HFCR and GMCR, strain increasing 0.006mm/mm in the PM PCL for both HFCR and GMCR, and ITB strain decreasing 0.006 and 0.004mm/mm respectively for the HFCR and GMCR per 1mm elevation of the DFJL. Discussion. Our findings suggest that DFJL affects ligament tension at 90° knee flexion and therefore flexion balance for cruciate retaining implants. The effect on ligament tension results from changes in the position of the femur bone and its ligament attachments with respect to the tibia, which is dependent on the implant geometry. DFJL places greater strain on the PCL because the conformity of the medial condyle prevents the femoral implant from sitting more posterior by the full amount of the DFJL elevation, which would be necessary to maintain the same AP position of the of the femur bone relative to the tibia and avoid increasing PCL strain. These results indicate that elevating the DFJL to address a tight extension space in a CR knee while the flexion space is well balanced could result in increased flexion tension especially when the flexion-extension mismatch is large, so to achieve balanced flexion and extension the amount of DFJL elevation may need to be reduced and the tibial resection may also need to be increased

Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) may introduce significant anatomic modifications, as it is known that few patients have neutral femoral, tibial or overall lower limb mechanical axes. A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. MA tibial and femoral bone resections were simulated. Femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Medial-lateral (DML) and flexion-extension (DFE) gap differences were calculated. Extension space ML imbalances (3mm) occurred in 25% of varus and 54% of valgus knees and significant imbalances (5mm) were present in up to 8% of varus and 19% of valgus knees. For the flexion space DML, higher imbalance rates were created by the TEA technique (p < 0 .001). In valgus knees, TEA resulted in a DML in flexion of 5 mm in 42%, compared to 7% for PC. In varus knees both techniques performed better. When all the differences between DML and DFE are considered together, using TEA there were 18% of valgus knees and 49% of varus knees with < 3 mm imbalances throughout, and using PC 32% of valgus knees and 64% of varus knees. Significant anatomic modifications with related ML or FE gap imbalances are created using MA for TKA. Using MA techniques, PC creates less imbalances than TEA. Some of these imbalances may not be correctable by the surgeon and may explain post-operative TKA instability. Current imaging technology could predict preoperatively these intrinsic imitations of MA. Other alignment techniques that better reproduce knee anatomies should be explored

Introduction. Cruciate Retaining (CR) and Posterior Stabilizing (PS) are two common types of total knee arthroplasty (TKA) surgeries. The CR approach preserves the posterior cruciate ligament (PCL) while the PS approach sacrifices it. Implant size selection during a TKA surgery is primarily driven by the patient's bone size, but could also be affected by surgery types due to the influence of the PCL. The objective of this study was to investigate the effect of TKA surgery type on implant size selection, based on the clinical database of a well-established commercial implant system. Methods. A clinical database operated by Exactech, Inc. (Gainesville, FL, USA) was utilized for this study. The database contains TKA patient information of Optetrak® implant recipients from over 30 physicians in the US, UK, and Colombia since 1995. Patient height was used as a control factor for comparison of surgery types, and categorized by every 10 cm (e.g., the “170 cm” category contains patients from 170 to 179 cm). Taking primary TKA only and body heights from 130 cm to 199 cm, a total of 2,677 cases were examined. No statistical difference exists on patients' gender, body weight, or BMI within every height category between the CR and PS groups. The femoral implant size and tibial insert thickness were compared between the two groups. Results. The implant size generally increases with patient height for both CR and PS groups, except for those under 140 cm (Figure 1). For all height categories, the CR patients received consistently smaller implants than the PS patients (p<0.05). On average, a CR TKA was about 0.67 size smaller than a PS TKA (p<0.001). A 0.67 size corresponds to about 2.7 mm in femoral component's AP dimension. Tibial insert thickness does not vary substantially by patient size (Figure 2). The difference between CR and PS groups was also less significant. On average, the CR group's tibial insert was about 0.5 mm thinner than that of the PS group (10.4 mm vs. 10.9 mm). Discussion. Flexion-extension gap balancing is a key objective in a TKA surgery. Although it is commonly known in the TKA community that a CR knee tends to have tighter gaps (especially flexion gap) than a PS knee, a quantitative understanding of this subject is lacking. By utilizing a novel statistical method on a single-product database, this study was able to provide a relevant answer to this question. This study found that a CR TKA on average accepted a femoral implant 2.7 mm smaller in AP dimension and a 0.5 mm thinner tibial insert than a PS TKA. Assuming all other factors the same, tibial insert thickness is a reflection of extension gap, while tibial insert thickness plus the AP dimension of the femoral component is a reflection of flexion gap. Thus the gap difference between CR and PS knees is about 0.5 mm at extension and about 3.2 mm at flexion. With statistical evidences, this study indicated that CR surgeons tend to downsize implant (consciously or unconsciously) more often than PS surgeons

Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) introduces significant anatomic modifications and secondary ligament imbalances. A restricted kinematic alignment (rKA) protocol was proposed to minimise these issues and improve TKA clinical results. A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. rKA tibial and femoral bone resections were simulated. 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 MA results. With the MA technique, femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Extension space ML imbalances (>/=3mm) occurred in 33% of TKA with MA technique versus 8% of the knees with rKA (p /=5mm) were present in up to 11% of MA knees versus 1% rKA (p < 0 .001). Using the MA technique, for the flexion space ΔML, higher imbalance rates were created by the TEA technique (p < 0 .001). rKA again performed better than both MA techniques using TEA of 3 degrees PC techniques (p < 0 .001). When all the differences between ΔML and ΔFE are considered together: using TEA there were 40.8% of the knees with < 3 mm imbalances throughout, using PC this was 55.3% and using rKA it was 91.5% of the knees (p < 0 .001). Significantly less anatomic modifications with related ML or FE gap imbalances are created using rKA versus MA for TKA. Using rKA may help the surgeon to balance a TKA, whilst keeping the alignment within a safe range

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

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