Aims. Varus-valgus constrained (VVC) devices are typically used in revision settings, often with stems to mitigate the risk of aseptic loosening. However, in at least one system, the VVC insert is compatible with the primary posterior-stabilized (PS) femoral component, which may be an option in complex primary situations. We sought to determine the implant survivorship, radiological and clinical outcomes, and complications when this VVC insert was coupled with a PS femur without stems in complex primary total knee arthroplasties (TKAs). Methods. Through our institution’s total joint registry, we identified 113 primary TKAs (103 patients) performed between 2007 and 2017 in which a VVC insert was coupled with a standard cemented PS femur without stems. Mean age was 68 years (SD 10), mean BMI was 32 kg/m. 2. (SD 7), and 59 patients (50%) were male. Mean follow-up was four years (2 to 10). Results. The five-year survivorship free from aseptic loosening was 100%. The five-year survivorship free from any revision was 99%, with the only revision performed for infection. The five-year survivorship free from reoperation was 93%. The most common reoperation was treatment for infection (n = 4; 4%), followed by manipulation under anaesthesia (MUA; n = 2; 2%). Survivorship free from any complication at five years was 90%, with superficial wound infection as the most frequent (n = 4; 4%). At most recent follow-up, two TKAs had non-progressive radiolucent lines about both the tibial and femoral components. Knee Society Scores improved from 53 preoperatively to 88 at latest follow-up (p < 0.001). Conclusion. For complex primary TKA in occasional situations, coupling a VVC insert with a standard PS femur without stems proved reliable and durable at five years. Longer-term follow-up is required before recommending this technique more broadly. Cite this article: Bone Jt Open 2021;2(11):921–925

Aims. Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model. Methods. We performed TKA on eight cadaveric knees and loaded them using a robotic manipulator. We tested both PS and mid-level designs under loads simulating clinical exams via applied varus and valgus moments, internal-external (IE) rotation moments, and anteroposterior forces at 0°, 30°, and 90° of flexion. We measured the resulting tibiofemoral angulations and translations. We also quantified the forces carried by the medial and lateral collateral ligaments (MCL/LCL) via serial sectioning of these structures and use of the principle of superposition. Results. Mid-level inserts reduced varus angulations compared to PS inserts by a median of 0.4°, 0.9°, and 1.5° at 0°, 30°, and 90° of flexion, respectively, and reduced valgus angulations by a median of 0.3°, 1.0°, and 1.2° (p ≤ 0.027 for all comparisons). Mid-level inserts reduced net IE rotations by a median of 5.6°, 14.7°, and 17.5° at 0°, 30°, and 90°, respectively (p = 0.012). Mid-level inserts reduced anterior tibial translation only at 90° of flexion by a median of 3.0 millimetres (p = 0.036). With an applied varus moment, the mid-level insert decreased LCL force compared to the PS insert at all three flexion angles that were tested (p ≤ 0.036). In contrast, with a valgus moment the mid-level insert did not reduce MCL force. With an applied internal rotation moment, the mid-level insert decreased LCL force at 30° and 90° by a median of 25.7 N and 31.7 N, respectively (p = 0.017 and p = 0.012). With an external rotation moment, the mid-level insert decreased MCL force at 30° and 90° by a median of 45.7 N and 20.0 N, respectively (p ≤ 0.017 for all comparisons). With an applied anterior load, MCL and LCL forces showed no differences between the two inserts at 30° and 90° of flexion. Conclusion. The mid-level insert used in this study decreased coronal and axial plane laxities compared to the PS insert, but its stabilizing benefit in the sagittal plane was limited. Both mid-level and PS inserts depended on the MCL to resist anterior loads during a simulated clinical exam of anterior laxity. Cite this article: Bone Jt Open 2023;4(6):432–441

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). Methods. Patients scheduled for primary TKA were included in a single-centre, prospective, three-armed, blinded randomized trial (n = 216; 72 per group). After intraoperative confirmation of posterior cruciate ligament (PCL) integrity, patients were randomly allocated to receive a CR, AS, or PS design from the same TKA system. Insertion of an AS or PS design required PCL resection. The primary outcome was the mean score of all five subscales of the Knee injury and Osteoarthritis Outcome Score (KOOS) at two-year follow-up. Secondary outcomes included all KOOS subscales, Oxford Knee Score, EuroQol five-dimension health questionnaire, EuroQol visual analogue scale, range of motion (ROM), and willingness to undergo the operation again. Patient satisfaction was also assessed. Results. Patients reported similar levels of pain, function, satisfaction, and general health regardless of the prosthetic design they received. Mean maximal flexion (129° (95% confidence interval (CI) 127° to 131°) was greater in the PS group than in the CR (120° (95% CI 121° to 124°)) and AS groups (122° (95% CI 120° to 124°)). Conclusion. Despite differences in design and constraint, CR, AS, and PS designs from a single TKA system resulted in no differences in patient-reported outcomes at two-year follow-up. PS patients had statistically better ROM, but the clinical significance of this finding is unclear. Cite this article: Bone Joint J 2023;105-B(12):1271–1278

The influence of soft tissue balance in mobile-bearing posterior-stabilized (PS) total knee arthroplasty (TKA) on the patellofemoral (PF) joint was investigated in thirty varus-type osteoarthritis patients. Intraoperative soft tissue balance including joint component gap and varus/valgus ligament balance and the medial/lateral patellar pressure were measured throughout the range of motion after the femoral component placement and the PF joint repair. The lateral patellar pressure, which was significantly higher than the medial side in the flexion arc, showed inverse correlation with the lateral laxity at 60° and 90° of flexion. The lateral patellar pressure at 120° and 135° of flexion also inversely correlated with the postoperative flexion angle. Surgeons should take medial and lateral laxity into account when considering PF joint kinematics influencing postoperative flexion angle in PS TKA

Introduction. Manipulation under anesthesia (MUA) after total knee arthroplasty (TKA) helps restore range of motion. This study identifies MUA risk factors to support early interventions to improve functionality. Methods. Data was retrospectively reviewed in 2,925 primary TKAs from October 2013 through December 2015 from 13 orthopedic surgeons using hospital and private practice electronic medical records (EMR). Statistical analysis evaluated MUA and non-MUA groups, comparing demographic, operative, hospital-visit, and clinical factors. T-test, chi-square test, ANOVA and regression analysis were performed. Significance was set at p<0.05. Results. Of 2,925 TKAs, 208 MUAs were performed (7.1%) with no significant differences between groups in sex, BMI, or diabetes status. Mean age of the MUA group was 61.98 years old, and 66.89 years old in the non-MUA group (p<0.005). The ratio of MUA patients with high cholesterol was 3.37% (7/208), and 1.10% (30/2717) in the non-MUA group (p=0.014). The ratio of African-American patients in the MUA group was 6.73% (14/208), and 2.94% (80/2717) in the non- MUA group (p=0.003). Of cases with device data recorded in the EMR (n=1890), MUA incidence in patients receiving a cruciate-retaining (CR) device was 14.58% (50/343), and 9.57% (148/1547) in patients receiving a posterior-stabilized (PS) device (p=0.006). A CR-device patient was 52.35% more likely to undergo MUA than a PS-device patient (95% CI, 1.13–2.05). MUA rate by surgeon training was 6.7% for joint fellowship, 6.8% for general fellowship, and 12.0% for sports medicine fellowship (p=0.015). Further analysis showed that rate of CR-device use was 13.3% for joint-fellowship trained surgeons, 10.2% for general fellowship, and 74.7% for sports medicine fellowship (p<0.001). With the numbers available for this investigation, there were no significant differences found between groups in relation to surgeon, high-volume (>150 TKAs annually) or low-volume surgeons, length of stay, discharge disposition, or smoking status. Conclusion. MUA risk factors include a lower mean age, high cholesterol, African-American, surgeon fellowship training, and receiving a cruciate-retaining device

Introduction. There is current debate concerning the most biomechanically advantageous knee implant systems, and there is also currently great interest in improving patient satisfaction after knee arthroplasty. Additionally, there is no consensus whether a posterior-stabilized (PS) total knee device is superior to a more congruent, cruciate-substituting, medially-stabilized device (MS). This study compared the clinical outcomes of two such devices. The primary hypothesis was that the clinical outcomes, and specifically the patient satisfaction as measured by the Forgotten Joint Score, would be better in the MS group. Methods. This prospective, randomized, blinded Level 1 study compared the outcomes of 100 patients who received a Medacta GMK PS device and 101 patients who received a Medacta GMK medially-stabilized Sphere device (Medacta Intl., Lugano, Switzerland). All patients undergoing elective primary total knee arthroplasty were eligible for participation. Institutional Review Board approval and informed consent from participants were obtained. The devices were implanted using an anatomic alignment/calipered- measured resection surgical approach. Clinical and radiographic assessments were performed preoperatively, 6 weeks, 6 months, and annually. Data were compared using T-test with a significance level of 0.05. Results. The minimum follow-up period is 2 years. There were no statistically significant differences in demographic characteristics and preoperative scores; tourniquet time was 7.24% longer for the PS group (40.28 min vs 37.56 min, P < .0086). Alignment was not different between the groups (preoperative or postoperative). There were significant differences between groups for the 1 year and 2 years postop Knee Society scores, Forgotten Joint Score, and ROM; in every case where there was a statistically significant difference, the results were better in the MS group. For example, the FJS was 65.72 in the MS group at 2 years, 54.33 in the PS group (p=0.02). The maximum active flexion at 2 years was 129.75º in the MS group, in the PS group it was 122.27º (p=0.03). Conclusion. The clinical outcomes of the MS group at 1 and 2 years, including the Forgotten Joint Score and flexion, were better statistically, and there was a statistically longer tourniquet time for the PS group. At the minimum 2-year follow-up, the results demonstrate superiority of the medially-stabilized device in terms of multiple clinical outcomes, including patient satisfaction as measured by the Forgotten Joint Score. These findings support the use of a medially-stabilized knee implant system, and support the conclusion that this design, in conjunction with an anatomic alignment, calipered-measured resection surgical technique, offers improved biomechanics and kinematics

Background. The posterior slope of the tibial component in total knee arthroplasty (TKA) has been reported to vary widely even with computer assisted surgery. In the present study, we analyzed the influence of posterior tibial slope on one-year postoperative clinical outcome after posterior-stabilized (PS) -TKA to find out the optimal posterior slope of tibial component. Materials and Method. Seventy-three patients with varus type osteoarthritic (OA) knees underwent PS-TKA (Persona PS. R. ) were involved in this study. The mean age was 76.6 years old and preoperative HKA angle was 14.3 degrees in varus. Tibial bone cut was performed using standard extra-medullary guide with 7 degrees of posterior slope. The tibial slopes were radiographically measured by post-operative lateral radiograph with posterior inclination in plus value. The angle between the perpendicular line of the proximal fibular shaft axis and the line drawn along the superior margin of the proximal tibia represented the tibial slope angle. We assessed one-year postoperative clinical outcomes including active range of motion (ROM), patient satisfaction and symptoms scores using 2011 Knee Society Score (2011 KSS). The influences of posterior tibial slope on one-year postoperative parameters were analyzed using simple linear regression analysis (p<0.05). Results. The average posterior tibial slope was 6.4 ± 2.0 °. The average active ROM were −2.4 ± 6.6 ° in extension and 113.5± 12.6 ° in flexion. The mean one-year postoperative patient satisfaction and symptom scores were 29.3 ± 6.4 and 19.6 ± 3.9 points respectively. The active knee extension, satisfaction and symptom scores were significantly negatively correlated to the posterior tibial slope (r = −0.25, −0.31, −0.23). Discussion. In the present study, we have found significant influence of the posterior tibial slope on the one-year postoperative clinical outcomes in PS-TKA. The higher posterior slope would induce flexion contracture and deteriorate patient satisfaction and symptom. We had reported that the higher tibial posterior slope increased flexion gap and the component gap change during knee flexion in PS-TKA. Furthermore, another study reported that increase of the posterior tibia slope reduced the tension in the collateral ligaments and resulted in the knee laxity at flexion. The excessive posterior slope of tibial component would result in flexion instability, and adversely affected the clinical results including patient satisfaction and symptom. Conclusion. In the PS-TKA for varus type OA knees, excessive tibial posterior slope was found to adversely affect one-year postoperative knee extension and clinical outcome including patient satisfaction and symptom. Surgeons should aware of the importance of tibial slope on one-year postoperative clinical results and pay more attentions to the posterior tibial slope angle not to be excessive

Whether it is best to retain the posterior cruciate ligament in the degenerated knee, i.e. using a cruciate-retaining (CR) total knee prosthesis (TKP), or to use a more constraint posterior-stabilized (PS) TKP is of debate. There are limited studies comparing the effect of both methods on implant fixation and clinical outcome, leaving it up to the surgeon to base this decision on anything but conclusive evidence. We assessed the effect of two different philosophies in knee arthroplasty on clinical outcome and tibial component migration measured with radiostereometric analysis (RSA), by directly comparing the CR and PS version of an otherwise similarly designed cemented TKP. Sixty patients were randomized and received a Triathlon TKP (Stryker, NJ, USA) of either CR (n=30) or PS (n=30) design. RSA measurements (primary outcome) and clinical scores including the Knee Society Score and Knee injury and Osteoarthritis Outcome Score were evaluated at baseline, at three months postoperatively and at one, two, five and seven years. A linear mixed-effects model was used to analyse the repeated measurements. Both groups showed a similar implant migration pattern, with a maximum total point motion at seven years follow-up of around 0.8 mm of migration (mean difference between groups 95% CI −0.11 to 0.15mm, p=0.842). Two components (one of each group) were considered to have an increased risk of aseptic loosening. Both groups improved equally after surgery on the KSS and KOOS scores and no differences were seen during the seven years of follow-up. No differences in implant migration nor clinical results were seen seven years after cruciate-retaining compared to posterior-stabilized total knee prostheses

Introduction. Modified gap technique has been reported to be beneficial for the intraoperative soft tissue balancing in posterior-stabilized (PS) -TKA. We have found intraoperative ligament balance changed depending on joint distraction force, which might be controlled according to surgeons' fells. We have developed a new surgical concept named as “medial preserving gap technique (MPGT)” to preserve medial knee stability and provide quantitative surgical technique according to soft tissue balance measurement using a tensor device. The purpose of this study was to compare 3-years postoperative knee stability after PS-TKA in varus type osteoarthritic (OA) knees between MPGT and measured resection technique (MRT). Material & Method. The subjects were 94 patients underwent primary unilateral PS-TKA for varus type OA knees. The surgical technique was MPGT in 47 patients and MRT in 47 patients. An originally developed off-set type tensor device was used to evaluate intraoperative soft tissue balance. In MPGT, medial release was limited until the spacer block corresponding to the bone thickness from proximal lateral tibial plateau could be easily inserted. Femoral component size and external rotation angle were adjusted depending on the differences of center gaps and varus angles between extension and flexion before posterior femoral condylar resection. The knee stabilities at extension and flexion were assessed by stress radiographies at 1 and 3 years after TKA; varus-valgus stress test at extension and stress epicondylar view at flexion. We measured medial and lateral joint openings (MJO, LJO) at both knee extension and flexion. MJOs and LJOs at 2 time periods were compared in each group using paired t-test. Each joint opening distance was compared between 2 groups using unpaired t-test. The significance level was set as P < 0.05. Results. The mean extension MJOs at 1 and 3 years after TKA were 2.4, 2.6 mm in MPGT and 3.2, 3.1 mm in MRT respectively. The mean extension LJOs were 3.5, 3.5 mm in MPGT and 4.6, 4.5 mm in MRT. The mean flexion MJOs were 0.95, 0.77 mm in MPGT and 1.5, 1.2 mm in MRT, and the mean flexion LJOs were 2.2, 2.1 mm in MPGT and 3.0, 2.7 mm in MRT. MJOs were significantly smaller than LJOs in each group at 2 time periods. MJOs at extension and flexion, and LJOs at extension were significantly smaller in MPGT than MRT at 2 time periods. Discussion. Medial knee stabilities had been reported to be essential for postoperative clinical results. We reported medial compartment gap was more stable during mid-to-deep knee flexion in MPGT than MRT. MPGT provided the more stable intraoperative soft tissue balance than MRT in PS-TKA. MPGT was useful to preserve the higher medial knee stability than the lateral as well as MRT, and beneficial to enhance postoperative knee stabilities as long as 3-years after PS-TKA in varus OA knees. MPGT would be an objective and safer gap technique to enhance clinical outcomes

Using a tensor for total knee arthroplasty (TKA) that is designed to facilitate soft tissue balance measurements with a reduced patello-femoral (PF) joint, we examined the influence of pre-operative deformity on intra-operative soft tissue balance during posterior-stabilized (PS) TKA. Joint component gap and varus angle were assessed at 0, 10, 45, 90 and 135° of flexion with femoral trial prosthesis placed and PF joint reduced in 60 varus type osteoarthritic patients. Joint gap measurement showed no significant difference regardless the amount of pre-operative varus alignment. With the procedures of soft tissue release avoiding joint line elevation, however, intra-operative varus angle with varus alignment of more than 20 degrees exhibited significant larger values compared to those with varus alignment of less than 20 degrees throughout the range of motion. Accordingly, we conclude that pre-operative severe varus deformity may have the risk for leaving post-operative varus soft tissue balance during PS TKA

Introduction:. Proper component orientation and soft tissue balancing are essential for longevity of total knee arthroplasty (TKA), especially in young and active patients. The aim of this study was to evaluate long-term results and quality of TKA in young and active patients with extension first gap balancing technique, in 2 Posterior-Stabilized (PS) total knee designs with identical femoral component. Material and Methods:. 43 consecutive Rotating-Platform (RP-PS, 33 patients) and 38 Fixed-Bearing (FB-PS, 29 patients) with University of California Los Angeles (UCLA) activity score of 5 or above and mean age was 53 ± 1.5 years were followed prospectively for a minimum of 10 years. 18 random TKAs were analyzed for component rotation using MRI. Results:. The majority of patients (77%, 24 patients in RP-PS and 65%, 25 patients in FB-PS) were still participating in recreational activities at final follow-up. There was no case of early or late mid flexion instability causing spinout. There was no malalignment or patellofemoral maltracking. Non-progressive radiolucency was seen at the tibial zone 1 in one of the RP-PS and 3 of the FB-PS knees. The mean femoral rotation was 2 and 3 degrees of external in relation to the transepicondylar axis in RP-PS and in FB-PS, respectively. Two patients in the FB-PS were revised (one for per-prosthetic fracture and one for osteolysis and loosening). There were no revisions in the RP-PS group. Kaplan-Meier survivorship at 10 years was 100% in RP-PS and 97% in FB-PS. Discussion and Conclusions:. Extension first gap balancing technique is a safe, accurate, and reproducible with excellent alignment and long-term durability and high quality of function in young, active patients

Purpose. To investigate the tibiofemoral rotational profiles during surgery in navigated posterior-stabilized (PS) total knee arthroplasty (TKA) and investigated the effect on postoperative maximum flexion angles. Materials and Methods. At first, twenty-five consecutive subjects (24 women and 1 man; age: mean, 77 years; range, 58–85 years) with varus osteoarthritis treated with navigated PS TKA (Triathlon, Stryker, Mahwah, NJ) were enrolled in this study. Kinematic parameters, including the tibiofemoral rotational angles from maximum extension to maximum flexion, were recorded thrice before and after PCL resections, and after implantation. The effect of PCL resection and component implantation on tibiofemoral rotational kinematics was statistically evaluated. Then, the effect of tibiofemoral rotational alignment changes on the postoperative maximum angles were retrospectively examined with 96 subjects (84 women, 12 men; average age, 76 years; age range, 56–88 years) who underwent primary TKA. Results. The tibiofemoral kinematics revealed a significant tibial internal rotation after PCL resection, which further increased after implantation compared with that before PCL resection (p < 0.01 and p < 0.001, respectively). Furthermore, the tibial internal rotations at 60° and 90° flexion after PCL resection and implantation were significantly increased compared with those before PCL resection (p < 0.05). The amount of tibial internal rotation from 90° flexion to maximum flexion was significantly decreased after PCL resection and implantation compared with that before PCL resection (p < 0.05). Furthermore, multi-linear regression analysis found that the internal changes of the rotational alignment was independent factor for the worse improvement of the postoperative maximum flexion angles (R2=0.078, p=0.0067). There was a positive correlation between preoperative tibial external rotational alignment and the internal changes of the postoperative rotational alignment (R2=0.172, p<0.0001), however, no correlation was found between the preoperative rotational alignment and the improvement of the maximum flexion angles. Discussion and Conclusion. The study revealed that PCL resection changed the tibial rotational alignment and decreased the amount of tibial internal rotation. The implantation of PS components further increased the internal rotational alignment and could not compensate for the tibiofemoral rotation. Finally, the internal changes of rotational alignment affected the improvement of the maximum flexion angles, suggesting that rotational alignment is one of important factors to achieve better postoperative maximum flexion angles. Although the factors which affect the rotational alignment remains unknown in this study, these results suggest that further development of PS TKA, including the surgical technique and implant design, are needed to achieve better knee kinematics, following better clinical outcomes

Backgrounds. In order to permit soft tissue balancing under more physiological conditions during total knee arthroplasties (TKAs), we developed an offset type tensor to obtain soft tissue balancing throughout the range of motion with reduced patella-femoral (PF) and aligned tibiofemoral joints and reported the intra-operative soft tissue balance assessment in cruciate-retaining (CR) and posterior-stabilized (PS) TKA [1, 2]. However, the soft tissue balance in unicompartmental knee arthroplasty (UKA) is unclear. Therefore, we recently developed a new tensor for UKAs that is designed to assist with soft tissue balancing throughout the full range of motion. The first purpose of the present study is to assess joint gap kinematics in UKA. Secondly, we attempted to compare the pattern in UKA with those in CR and PS TKA with the reduced PF joint and femoral component placement, which more closely reproduces post-operative joint alignment. Methods. Using this tensor, we assessed the intra-operative joint gap measurements of UKAs performed at 0, 10, 30, 45, 60, 90, 120 and 135° of flexion in 20 osteoarthritic patients. In addition, the kinematic pattern of UKA was compared with those of CR and PS TKA that were calculated as medial compartment gap from the previous series of this study. Results. While the joint gap measurements of UKAs increased from full extension to extension (10 degrees of flexion), these values remained constant throughout the full range of motion. Of note, the gap values of CR TKA were significantly smaller from midrange to deep flexion compared with PS TKA, and furthermore UKA showed a significantly smaller gap from extension to midrange flexion compared with CR TKA. Conclusions. Accordingly, we conclude that the intra-operative joint gap kinematic pattern in UKA differs from the pattern in TKA

INTRODUCTION. Although several meta-analyses have been performed on total knee arthroplasty (TKA) using computer-assisted orthopaedic surgery (CAOS) [1], understanding the inter-site variations of the surgical profiles may improve the interpretation of the results. Moreover, information on the global variations of how TKA is performed may benefit the development of CAOS systems that can better address geographic-specific operative needs. With increased application of CAOS [2], surgeon preferences collected globally offers unprecedented opportunity to advance geographic-specific knowledge in TKA. The purpose of this study was to investigate geographic variations in the application of a contemporary CAOS system in TKA. Materials and Methods. Technical records on more than 4000 CAOS TKAs (ExactechGPS, Blue-Ortho, Grenoble, FR) between October 2012 and January 2016 were retrospectively reviewed. A total of 682 personalized surgical profiles, set up based on surgeon's preferences, were reviewed. These profiles encompass an extensive set of surgical parameters including the number of steps to be navigated, the sequence of the surgical steps, the definition of the anatomical references, and the parameters associated with the targeted cuts. The profiles were compared between four geographic regions: United States (US), Europe (EU), Asia (AS), and Australia (AU) for cruciate-retaining (CR) and posterior-stabilized (PS) designs. Clinically relevant statistical differences (CRSD, defined as significant differences in means ≥1°/mm) were identified (significance defined as p<0.05). Results. For resection parameters, CRSDs were found between regions in posterior tibial slope (PTS), tibial resection depth, as well as femoral flexion for both CR and PS profiles (marked in Table 1). Regarding anatomical references, US was the only region using posterior cruciate ligament (PCL) as the reference for CR resection depth (Table 1). Differences in percentage of preference were found in the anatomical references for tibial varus/valgus, tibial resection depth, femoral varus/valgus, femoral axial rotation, and ankle center (Table 1,2). For surgical steps, EU and AU were found to apply gap balancing technique as a common practice for the PS designs, while for the CR designs, EU and AU considerably adopted this technique (Table 2). For PS designs, EU and AU profiles preferred tibial first in the resection workflow, compared to a more balanced preference for other regions. For CR designs, US profiles were in favour of performing the femoral resection first in the workflow, compared to a strong favouring of tibial first resection workflow in EU and AS Am regions. Discussion. This study demonstrated clinically significant geographic differences may exist in the surgeons' preference of surgical parameters, anatomical references, and surgical workflow steps during TKA. These differences may reflect the geographic variations of surgeon training, surgical philosophy, or the specific characteristics of the patient population, which warrants further investigation. The strength of this study was that it is the first study to date that covered all the available surgical profiles spanning the application history of a specific CAOS system. As such, variation due to the operational differences of multiple systems was avoided. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Recently, tibial insert design of cruciate-substituting (CS) polyethylene insert is employed and widely used. However, in vivo kinematics of using CS polyethylene insert is still unclear. In this study, it is hypothesized that CS polyethylene insert leads to stability of femoro-tibial joint as well as posterior-stabilized (PS) polyethylene insert, even if PCL is sacrificed after TKA. The purpose of this study is an investigation of in vivo kinematics of femoro-tibial joint with use of CS polyethylene insert before and after PCL resction using computer assisted navigation system and tensor device intra-operatively in TKA. Materials and Methods. Sixty-one consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. During surgery, using a tensor device, after bony cut of femur and tibia, joint gaps were assessed in 0 and 90 degrees in flexion. Then, CS polyethylene tibial trial insert were inserted after trial implantation of femoral and tibial components, before and after resection of PCL, respectively. The kinematic parameters of the soft-tissue balance, and amount of coronal and sagittal relative movement between femur and tibia were obtained by interpreting kinematics, which display tables throughout the range of motion (ROM) in the navigation system. In each ROM (30, 45, 60, 90, max degrees), the data were analyzed with a ANOVA test, and mean values were compared by the multiple comparison test (Turkey HSD test) (p< 0.05). Results. Joint gap assessment revealed significant enlargement in both of extension and 90 degrees in flexion after PCL resection compared with before resection. In kinematic analyses in navigation system, regarding to amount of sagittal movement of tibia, there were significances between before and after PCL resection in 60 and 90 degrees in flexion, 1.2mm difference in 60 degrees, and 2.3mm difference in 90 degrees in flexion. There were no significance between before and after PCL resection in the other degrees in flexion. Regarding to the other analyses, varus/ valgus and rotation, there were no differences between before and after resection of PCL. In addition, concerning ROM, maximum extension angle is significantly lower, and maximum flexion angle is significantly higher after than before PCL resection. Discussion. These results demonstrated that CS polyethylene insert might have a stability of femoro-tibial joint nearly after PCL resection as well as before PCL resection. The main design feature of Triathlon CS insert is single radius and rotary arc, in addition, the posterior lip is same as that of Triathlon CR, which can be the factor to avoid paradoxical anterior movement and to permit internal and external rotation between femoral and tibial component. Due to the design features and benefits, there is a high possibility that use of CS insert without PCL can lead same stability as PCL remained, and improvement of ROM. Based on these backgrounds, it is suggested that CS insert may have an additional choice of PCL resection in case of tight gap of flexion in TKA

Purpose. The purpose of this study was to compare joint line changes between posterior-stabilized (PS) and cruciate-retaining (CR) computer navigated total knee arthroplasties (TKA) and to evaluate the impact on functional outcome. Background. Restoration of the native joint line has been a common goal in all TKA designs. Computer-navigated TKA in increasingly being favoured by many surgeons, due to increased precision and lesser complications. Few studies have reported the effect of computer navigated TKA on joint line restoration. It remains to be seen if the greater precision offered by computer-navigated TKA in restoration of joint line translates to improvement in functional outcome. Methods. This study assessed joint line changes following computer-assisted navigated total knee arthroplasty (TKA). A total of 195 patients were followed up for a period of 2 years following primary surgery. The change in the joint line was calculated based on the verified bony resections and the final thickness of the insert. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t-test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups at 6 months and 2 years of follow-up. Results. A total of 112 CR knees and 83 PS knees were analyzed. PS knees had a significantly greater joint line change as compared to CR knees with a p-value of 0.04 (Figure 1). Although the knee, function and oxford knee questionnaire scores were significantly better in the CR group at the 6-month follow-up, this did not translate into any significant difference in functional scores at the 2-year follow-up. It was also found that the PS group had significantly better final range of motion. Conclusion. CR knees are associated with significantly less joint line changes than PS knees in computer navigated TKA. PS knees have a greater range of motion at 2 years of follow-up. No significant difference in outcome was noted at 2 years follow-up

Introduction. Balancing of joint gap is a prerequisite in total knee arthroplasty (TKA). Recently, the tensor has been developed which can measure the joint gap with the patellofemoral joint reduced for more physiological assessment, and the results for osteoarthritis (OA) patients indicated that the flexion gap is larger than the extension gap during posterior-stabilized (PS) TKA. However with respect to the rheumatoid arthritis (RA) patients, the soft tissue balance in TKA is still unknown. Therefore, the purpose of this study was toinvestigate thecharacteristics of thejoint gap during TKAsurgeryforpatients with RA. Methods. We implanted 90 consecutive knees with a PS TKA using a NexGen LPS-flex (Zimmer, Warsaw, IN). OA was the underlying disease in 60 knees and RA was the disease in30 knees. Surgical procedure. We performed all operations with a measured resection technique. The rotational position of the femoral component was determined based on the epicondylar axis of the femur with anterior reference for anteroposterior sizing. Joint gap measurements. After bone cuts and soft tissue balancing, we measured the joint gap with the femoral component in position using seesaw-type tenser device with the patella reduced position after repair of the medial arthrotomy with a few stitches. The center width and asymmetry (tilting) of joint gaps under 40-lb distracting force were measured at 0 degree extension and 90 degrees of knee flexion. Results. The changes in the joint gap from 0 to 90 degrees were 3.2 ± 0.3 mm in OA group and 4.3 ± 0.4 mm in RA group. The increase of joint gap from 0 to 90 degrees in RA was significantly larger than that in OA group (Figure 1). The tilting angle of the joint gap (varus gap expressed as positive values) at 90 degrees of knee flexion in RA group (5.3 ± 0.5 degrees) was significantly larger than that in OA group (2.6 ± 0.4 degrees) (Figure 2). In RA group, there was a positive correlation (r= 0.34, p <0.05) between the increase of joint gap from 0 to 90 degrees and the tilting angle of the joint gap at 90 degrees of knee flexion (Figure 3). Discussion. In this study, the increase of joint gap from 0 to 90 degrees in RA group was significantly larger than that in OA group. In addition, the lateral gap in knee flexion, calculated from the tilting angle of the joint gap, was significantly larger in RA group and was correlated with the increase of joint gap from 0 to 90 degrees of knee flexion. These differences could be attributed to reduced stiffness of the lateral structure, such as lateral collateral ligament and popliteofibular ligament, as well as the extensor mechanism in patients with RA. Therefore, it is necessary to considerthe individual stiffness of soft tissues, together with the applied tension, to decide the rotation of femoral component by reference to the flexion gap during TKA for RA patients

Introduction. When performing total knee arthroplasty (TKA), surgeons often utilize a posterior-stabilized (PS) design which compensates for the loss of the posterior cruciate ligament (PCL). These designs attempt to replicate normal knee kinematics and loading using a cam and post to provide posterior restraint of the tibia during flexion. However, these designs may not be able to compensate for the increase in flexion space or the inherent loss of coronal stability after PCL release compared to a cruciate retaining (CR) design. This study aimed to compare stability of PS and CR TKA designs by assessing laxity in three planes. Methods. The specimens utilized in this study were lower extremities from fresh cadavers of donors who had previously undergone a total knee replacement (Medical Education and Research Institute (Memphis, TN) and Restore Life USA (Johnson City, TN)). IRB approval was obtained prior to performing the study. Twenty-three knee specimens (8 left, 15 right) were retrieved and all skin, subcutaneous tissue and muscle was removed. The femur and tibia were cut transversely 180 mm superior and inferior to the knee joint line, respectively, and specimens were mounted in a custom knee testing machine. Specimens were tested with the knee joint at full extension and at 30, 60, and 90 degrees of flexion. Laxity was assessed at 1.5 Nm of internal and external torque and 10 Nm varus and valgus torque, as well as a 35 N anterior and posterior force. Laxity was expressed as degrees of tibial displacement in the coronal plane under a varus/valgus torque and degrees of displacement in the transverse plane under an internal/external torque, as well as mm of anterior or posterior displacement. TKA components were retrieved to determine PS or CR design and grouped accordingly. Results. Of the 23 implants, 10 were PS designs and 13 were CR. PS posterior laxity was 1 mm greater in full extension (p = 0.02, Figure 1), and PS varus laxity increased by 6 degrees at 90 degrees of flexion over CR laxity (p = 0.04, Figure 3). Varus to valgus laxity range of PS knees was greater than CR knees for all flexion angles. PS external rotational laxity at 90 degrees of flexion was greater than that of CR laxity by 7 degrees (p = 0.02, Figure 2). Discussion. Results indicate significant laxity differences between PS and CR designs in both full extension and 90 degrees of flexion. PS designs have decreased coronal stability compared to CR, but appear to mimic AP constraint in midflexion and flexion. Mihalko et al. (2000) showed that loss of the PCL during TKA leads to a decrease in coronal stability, which is confirmed here. The post and cam mechanism of the PS designs restores AP stability during flexion but does not restore this coronal stability. These results may be limited by variations in implant design

Purpose. The purpose of this study was to analyze rotational kinematic patterns in knees treated with either cruciate-retaining (CR) or posterior-stabilized (PS) total knee arthroplasty (TKA), using an intra-operative navigation technique, and to clarify the factors that affect of the rotational kinematics and the difference rotational kinematics patterns between CR- and PS- TKA. Methods. A total of 35 knees (35 patients) were included in this study, deformed valgus, sever flexion contractures, and highly unstable knees were excluded. These knees were allocated to CR (NexGen CR-Flex) or PS (NexGen PS-Flex) implants and underwent TKA with a computer navigation technique (precision N Knee Navigation Software v4.0; Stryker). There was no significant difference in pre-operative parameters between CR- and PS-TKA group: age, femorotibial angle (FTA), and chondylar twist angle (CTA). We measured two points during surgery. First, the skin incision was made and subcutaneous tissue was exposed. The joint capsule was temporality closed by three or four strand suture. Second, after the surgery was completed with satisfactory alignment and soft tissue balance, immediately following wound closure the measurement procedure was repeated. The surgeon gently applied a manual range of motion from full extension to flexion. The angle of internal rotation in tibia to the functional plane of tibia and femur was measured automatically at max extension, 0, 30, 45, 60, 90 degrees, and max flexion throughout the passive knee motion. Result. We categorized the post-operative rotational kinematics patterns to five types. Type A was increasing with the internal rotation angle in tibia with knee flexion. Type B was decreasing the internal rotation with knee flexion. Type C was decreasing the internal rotation from 0 to 45 or 60 degrees, Then graduated increasing until full flexion. Type D was the opposite type of type C. Type E was not able to categorize any pattern. (Figure 1) The individual kinematic pattern was variable in pre- and post-operative knee motion. Both CR- and PS-TKA had a tendency to remain the preoperative kinematic pattern (CR-TKA 66% and PS-TKA 59%) by comparing the pre- and post-operative kinematic pattern. But, type A was increased in post-operative PS-TKA. (Figure 2) We analyzed factors (age, pre-operative FTA, CTA, pre-operative knee extension, and post-operative FTA) that affect the change of rotational kinematics patterns before and after TKA. In CR-TKR, there were not any factors that influence with the changes of kinematic pattern. In PS-TKR, pre-operative knee extension angle affected accompanied by significant difference in the change of rotational kinematics patterns. Discussion & Conclusion. We analyzed the rotational kinematics patterns in knees treated with either CR- or PS-TKR, using an intra-operative navigation. Pre- and post-operative knee kinematics of TKA patients had a variety of rotational kinematics patterns. Both CR- and PS-TKA had a tendency to remain the preoperative kinematic pattern by comparing the pre- and post-operative kinematic pattern Pre-operative knee extension affected to the change of rotational kinematics pattern in PS-TKR

Introduction. In addition to traditional posterior-stabilized (PS) designs with cam-post articulations, there are two new design concepts used in total knee replacement (TKR) to “substitute” for cruciate ligament function and restore anterior-posterior stability. These include i) guided-motion PS designs with a modified cam-post that is less restrictive to axial rotation; and ii) non-PS designs that incorporate progressive articular congruency to substitute the function of the resected anterior cruciate ligament (ACL-substituting). Early post-marketing surveillance of such new TKR designs is valuable because instability, loosening, and high complication rates within the initial 5 year follow-up interval have proven problematic for some design. This study reports the early clinical performance of sequential patients implanted with a new ACL-substituting TKR design at a German Center of Excellence for Arthroplasty (EPZ-Max) hospital. Methods. This is a single-site, multi-surgeon retrospective study with Institutional Review Board approval. The nine surgeons involved all used uniform surgical techniques, including a mid-vastus approach, PCL preservation with a bone block, tibial component alignment with the natural tibial slope, no patellar resurfacing, and cement fixation. All patients meeting the following inclusion criteria were contacted by phone: a) primary TKR from July 2008-June 2009; b) implanted with an ACL-substituting design (3D Knee™, DJO Surgical); c) no prior knee arthroplasty; and d) willing to consent to participate. Recorded outcomes at the 5 year follow-up interval included range of motion, Knee Society knee/function scores (KSS), and radiographic results (alignment, radiolucent lines, osteolysis). Additional surgery was classified as “revision” (metal components removed) or “reoperation” (metal components not removed). Results. Out of 166 sequential patients, a study cohort of 69 patients (84 TKR) consented to participate. Average follow-up was 6.2+0.6 (4.7–7.3) years. Maximum flexion averaged 115°+9° (85°–145°), including 39% at >120°. The TKR had stable function and average KSS scores of 94 (knee) and 94 (function). There were four patients (5 TKR, 6.3%) with function scores of <60 points who had considerable pre-operative extension lags (>10°) that lingered (5°–10°) at follow-up. No TKR had evidence of osteolysis or loosening. Non-progressive radiolucent lines were evident post-operatively in 10 TKR and in one additional TKR at last follow-up. Seven (8.3%) TKR required reoperation or revision. Five TKR in the 0–5 year interval required reoperation to treat acute infection, progressive patellar arthritis, and traumatic patellar fracture, and revision to treat pain of unknown etiology (2 TKR revised at another hospital). Two TKR in the 5–6 year interval required revision arthroplasty to treat pain associated with a loose tibial insert screw and unknown symptoms (1 TKR revised at another hospital). Conclusion. This new ACL-substituting design incorporates progressive congruency in the lateral compartment. These data, combined with previous studies (Table 1), provides evidence that this ACL-substituting TKR design restores stability while being robust to surgical and patient variations. These results for a fixed-bearing, non-PS TKR design are supported by international registry data from more than 370,000 TKR in six countries, which demonstrate that survivorship of fixed-bearing cruciate-retaining TKR designs is significantly higher than posterior-stabilized TKR designs, both with and without patella resurfacing