Background. Data on varus-valgus and rotational profiles can be obtained during navigated total knee arthroplasty (TKA). Such intraoperative kinematic data might provide instructive clinical information for refinement of surgical techniques, as well as information on the anticipated postoperative clinical outcomes. However, few studies have compared intraoperative kinematics and pre- and postoperative clinical outcomes; therefore, the clinical implications of intraoperative kinematics remain unclear. In clinical practice, subjects with better femorotibial rotation in the flexed position often achieve favorable postoperative range of motion (ROM); however, no objective data have been reported to prove this clinical impression. Hence, the present study aimed to investigate the correlation between intraoperative rotation and pre- and postoperative flexion angles. Materials and Methods. Twenty-six patients with varus osteoarthritis undergoing navigated posterior-stabilized TKA (Triathlon, Stryker, Mahwah, NJ) were enrolled in this study. An image-free navigation system (Stryker 4.0 image-free computer navigation system; Stryker) was used for the operation. Registration was performed after minimum soft tissue release and osteophyte removal. Then, maximum internal and external rotational stress was manually applied on the knee with maximum extension and 90° flexion by the same surgeon, and the rotational angles were recorded using the navigation system. After knee implantation, the same rotational stress was applied and the rotational angles were recorded again. In addition, ROM was measured before surgery and at 1 month after surgery. The correlation between the amount of pre- and postoperative tibial rotation and ROM was statistically evaluated. Results. The amount of tibial rotation at registration was positively correlated with that after surgery (p < 0.05). Although the amount of tibial rotation at maximum extension was not correlated with ROM, the amount of rotation at 90° flexion at registration was positively correlated with pre- and postoperative ROM (p < 0.05). Moreover, the amount of tibial rotation at 90° flexion was positively correlated with postoperative ROM (p < 0.05). Conclusion. It is well known that preoperative ROM affects postoperative ROM. Our results showed that better tibial rotation at 90° flexion predicts favorable postoperative ROM, suggesting that flexibility of the surrounding soft tissues as well as the quadriceps muscles is an important factor for obtaining better ROM. Further evaluation of navigation-based kinematics during TKA surgery may provide useful information on ROM

Introduction:. Proper rotational alignment of the tibial component is a critical factor in the outcome of total knee arthroplasty (TKA), and misalignment has been implicated as a major contributing factor to several mechanisms of TKA failure. In this study we examine the relationship between bony and soft tissue tibial landmarks against the knee motion axis (plane that best approximates tibiofemoral motion through range of motion). Methods:. The kinematic motions of 16 fresh-frozen lower limb specimens were analyzed in simulated lunging and squatting. All the tendons of the quadriceps and hamstrings were independently loaded to simulate a lunging or squatting maneuver. All specimens underwent CT scan and the 3D position of the knee was virtually reconstructed. Ten anatomic axes were identified using both the intact tibia and the resected tibial surface. Two axes were normal vectors to either the medial-lateral plateau center or the posterior tibial surface. Seven axes were defined between the tibial tubercle (the most prominent point, center of the tubercle, or medial third of the tubercle) and soft tissue landmarks of the tibia (the medial insertion of the patellar tendon, the center of the PCL and ACL, and the tibial spines). The last axis was the Knee Motion Axis (KMA), which was defined as the longitudinal axis of the femur from 30 to 90 degrees of flexion. Results:. The closest approximation of the KMA was provided by the axis from the PCL to Medial Tibial Spine Axis, which was internally rotated 1.9 ± 7.6 degrees (Table – 1). The closest axis to the KMA in external rotation was the axis from the tibial plateau center to the medial third of the tibial tubercle, which was externally rotated 2.8 ± 4.3 degrees. The most precisely located constant axis was from the center of the tibia to the center of the tibial tubercle, which was externally rotated by 14.9 ± 3.7 degrees. Conclusions:. The line connecting the center of the PCL and the mid-point between the medial and lateral tibial spines was the closest to the functional tibial rotation. Though no individual landmark exactly correlated with the KMA in all knees, we found that the average anteroposterior motion of the femur with the tibia from 30 to 90 degrees of the femur could be consistently described by these landmarks, and that the addition of soft-tissue landmarks to prior bony topography can provide reliable indications to the location of the KMA

Purpose. We aimed to investigate whether the anterior superior iliac spine could provide consistent rotational landmark of the tibial component during mobile-bearing medial unicompartmental knee arthroplasty (UKA) using computed tomography (CT). Methods. During sagittal tibial resection, we utilized the ASIS as a rotational landmark. In 47 knees that underwent postoperative CT scans after medial UKA, the tibial component position was assessed by drawing a line tangential to the lateral wall of the tibial component. Rotation of the tibial component was measured using two reference lines: a line perpendicular to the posterior cortical rim of the tibia (angle α) and Akagi's line (angle β). Instant bearing position and posterior cruciate ligament fossa involvement were also evaluated. External rotation of the tibial component relative to each reference line and external rotation of the bearing relative to the lateral wall of the tibial component were considered positive values. Results. The mean angle α and β were 8.0 ± 6.1° (range, −4.0 – 24.3) and 8.7 ± 4.8° (range, 1.9 – 25.2), respectively. The mean instant bearing position was 4.3 ± 28.6° (range, −52.9 – 179.7). One bearing showed complete 180° rotation at 2 weeks postoperatively. Fourteen knees (29.8%) showed posterior cruciate ligament fossa involvement of the tibial resection margin. Conclusions. Due to the wide variation in, and inherent difficulty in identification of, the ASIS during the operation, it is not recommended for guidance of sagittal tibial resection during mobile-bearing medial UKA. Level of Evidence: Level IV

Purpose. Surgeons sometimes encounter moderate or severe varus deformed osteoarthritic cases in which medial substantial release including semimembranosus is compelled to appropriately balance soft tissues in total knee arthroplasty (TKA). However, medial stability after TKA is important for acquisition of proper knee kinematics to lead to medial pivot motion during knee flexion. The purpose of the present study is to prove the hypothesis that step by step medial release, especially semimembranosus release, reduces medial stability in cruciate-retaining (CR) total knee arthroplasty (TKA). Methods. Twenty CR TKAs were performed in patients with moderate varus-type osteoarthritis (10° < varus deformity <20°) using the tibia first technique guided by a navigation system (Orthopilot). During the process of medial release, knee kinematics including tibial internal rotation and anterior translation during knee flexion were assessed using the navigation system at 3 points; (1) after anterior cruciate ligament resection (pre-release), (2) medial tibial and femoral osteophyte removal and release of minimum deep layer of medial collateral ligament (minimum release) and (3) release of semimembranosus (semimembranosus release). In addition, the kinematics after all prostheses implantation (semimembranosus release group) were assessed and compared with those assessed in another 20 patients in which only minimum release was performed (minimum release group). Results. Kinematic pattern in step by step medial release exhibited external tibial rotation during mid-range of flexion and then shifted to internal tibial rotation toward to 120 degrees of knee flexion (Fig. A). During 60 to 120 degrees of flexion, semimembranosus release significantly reduced the amount of internal tibial rotation compared with pre-release (Fig. 1B). Tibial anterior translation showed no significant differences among each procedure. After all prostheses implanted, the amount of tibial internal rotation during 60 to 120 degrees of knee flexion was significantly maintained in minimum release compared with semimembranosus release group (Fig. 2). Conclusions. Semimembranosus release reduces tibial internal rotation in CR TKA, suggesting that semimembranosus release should be avoided in case of moderate varus-type osteoarthritis for considering medial stability

The posterior drawer is a commonly used test to diagnose an isolated PCL injury and combined PCL and PLC injury. Our aim was to analyse the effect of tibial internal and external rotation during the posterior drawer in isolated PCL and combined PCL and PLC deficient cadaver knee. Ten fresh frozen and overnight-thawed cadaver knees with an average age of 76 years and without any signs of previous knee injury were used. A custom made wooden rig with electromagnetic tracking system was used to measure the knee kinematics. Each knee was tested with posterior and anterior drawer forces of 80N and posterior drawer with simultaneous external or internal rotational torque of 5Nm. Each knee was tested in intact condition, after PCL resection and after PLC (lateral collateral ligament and popliteus tendon) resection. Intact condition of each knees served as its own control. One-tailed paired student's t test with Bonferroni correction was used. The posterior tibial displacement in a PCL deficient knee when a simultaneous external rotation torque was applied during posterior drawer at 90° flexion was not significantly different from the posterior tibial displacement with 80N posterior drawer in intact knee (p=0.22). In a PCL deficient knee posterior tibial displacement with simultaneous internal rotation torque and posterior drawer at 90° flexion was not significantly different from tibial displacement with isolated posterior drawer. In PCL and PLC deficient knee at extension with simultaneous internal rotational torque and posterior drawer force the posterior tibial displacement was not significantly different from an isolated PCL deficient condition (p=0.54). We conclude that posterior drawer in an isolated PCL deficient knee could result in negative test if tibia is held in external rotation. During a recurvatum test for PCL and PLC deficient knee, tibial internal rotation in extension results in reduced posterior laxity

There are basically 4 ways advocated to determine the proper femoral component rotation during TKA: (1) The Trans-epicondylar Axis, (2) Perpendicular to the “Whiteside Line,” (3) Three to five degrees of external rotation off the posterior condyles, and (4) Rotation of the component to a point where there is a balanced symmetric flexion gap. This last method is the most logical and functionally, the most appropriate. Of interest is the fact that the other 3 methods often yield flexion gap symmetry, but the surgeon should not be wed to any one of these individual methods at the expense of an unbalanced knee in flexion. In correcting a varus knee, the knee is balanced first in extension by the appropriate medial release and then balanced in flexion by the appropriate rotation of the femoral component. In correcting a valgus knee, the knee can be balanced first in flexion by the femoral component rotation since balancing in extension almost never involves release of the lateral collateral ligament (LCL) but rather release of the lateral retinaculum. If a rare LCL release is anticipated for extension balancing, then it would be performed prior to determining the femoral rotation since the release may open up the lateral flexion gap to a point where even more femoral component rotation is needed to close down that lateral gap. It is important to know and accept the fact that some knees will require internal rotation of the femoral component to yield flexion gap symmetry. The classic example of this is a knee that has previously undergone a valgus tibial osteotomy that has led to a valgus tibial joint line. In such a case, if any of the first 3 methods described above is utilised for femoral component rotation, it will lead to a knee that is very unbalanced in flexion being much tighter laterally than medially. A LCL release to open the lateral gap will be needed, increasing the complexity of the case. My experience has shown that intentional internal rotation of the femoral component when required is well-tolerated and rarely causes problems with patellar tracking. It is also of interest to note that mathematical calculations reveal that internally rotating a femoral component as much as 4 degrees will displace the trochlear groove no more that 2–3 mm (depending on the FC size), an amount easily compensated for by undersizing the patellar component and shifting it medially those few mm. There are basically 3 ways to determine the proper tibial component rotation during TKA: (1) Anatomically cap the tibial cut surface with an asymmetric tibial component, (2) Align the tibial rotation relative to a fixed anatomic tibial landmark (most surgeons use this method and align relative to the medial aspect of the tibial tubercle), (3) Rotate the tibial component to a point where there is rotational congruency in extension between the femoral and tibial articulating surfaces. This third method must be used with fixed bearing arthroplasties (especially with conforming articulations) to avoid rotational incongruency between the components during weight-bearing that can create abnormal and deleterious torsional forces on posterior stabilised posts, insert tray interfaces and bone-cement interfaces. Rotating platform articulations can tolerate rotational mismatch unless it is to a point where the polyethylene insert rotates excessively and causes symptomatic soft tissue impingement

The anterior curve of the tibial plateau cortex represents a realiable and reproducible landmark which may help aligning the tibial component with the femoral component and the extensor mechanism. Few studies analyzed the tibial component rotational alignment during total knee arthroplasty. Malrotation can affect both patello-femoral and tibio-femoral postoperative function. We evaluated the rotational relationship between femur and tibia, and we investigated which tibial landmark consistently matches the rotation of the femoral epicondylar axis in full extension (Fig 1). Axial magnetic resonance images of 124 normal knees (statistical power 1-beta=0.8) were analyzed separately by three authors. Scanograms were obtained with the knee in full extension and with the long axis of the foot (second metatarsal bone) aligned on the neutral sagittal plane. The surgical epicondylar axis was drawn and projected over the proximal tibia and tibial tuberosity slices. Multiple anatomical tibial rotational landmarks were drawn and symmetric tibial component digital templates of different sizes were aligned according to each landmark. Alignment of the virtual tibial components was then compared to that of the projected femoral epicondylar axis (Fig 2). The best antero-posterior line to achieve rotational matching between the components was drawn on the proximal tibia slice of each patient. Results of rotation (positive = external rotation, negative = internal) relative to the epicondylar axis were (Fig 3): (a) Medial third-to the middle third of the tibial tubercle 1.2°+/−5.7, (b) Akagi's line (centre of the posterior cruciate ligament tibial insertion to the most medial part of the tibial tubercle) -11.5+/−6.5, (c) The anterior curved tibial plateau cortex (curve-on-curve matching between the tibial template and the anterior cortex) 1.0+/−2.9. Intraclass correlation coefficient resulted 0.923, 0,881, and 0.949 for the Akagi's line, Middle third of tibial tubercle, and the curve-on-curve reference respectively. The anterior curve of the tibial plateau cortex represents a realiable and reproducible landmark which may help aligning the tibial component with the femoral component and the extensor mechanism (Fig 4, 5)

Introduction. Tibial component malrotation is one of the commonest causes of pain and stiffness following total knee arthroplasties, however, the assessment of tibial component malrotation on imaging is not a clear-cut. Aim. The objective of this study was to assess tibial component rotation in cases with pain following total knee replacement using MRI with metal artifact reduction technique. Methods. In 35 consecutive patients presented to our clinic between January 2016 and April 2017 with persistent unexplained moderate to severe pain for at least 6 months following total knee arthroplasties after exclusion of infection, MRI evaluation of tibial component rotation using O-MAR technique-(Metal Artifact Reduction for Orthopedic implants) to improve visualization of soft tissue and bone by reducing artifacts caused by metal implants- was done according to the technique of Berger et al. Results. 25 cases showed internal rotation of tibial component, 5 cases showed neutral rotation, 5 cases showed external rotation with presence of abnormal intraarticular fibrous bands. Conclusion. Two main conclusions are obtained from this study:. Firstly: Internal rotation of tibial component must be excluded in all cases of persistent pain following total knee replacement. Secondly: Magnetic resonance imaging with the newly developed metal artifact reduction techniques is a very useful tool in evaluating cases of unexplained pain following total knee replacement

Background. Rotational alignment is important for the long-term success and good functional outcome of total knee arthroplasty (TKA). While the surgical transepicondylar axis (sTEA) is the generally accepted landmark on the distal femur, a precise and easily identifiable anatomical landmark on the tibia has yet to be established. Our aim was to compare five axes on the proximal tibia in normal and osteoarthritic (OA) knees to determine the best landmark for determining rotational alignment during TKA. Methods. One hundred twenty patients with OA knees and 30 without knee OA were recruited for the study. Computed tomography (CT) images were obtained and converted through multiplanar reconstruction so the angles between the sTEA and the axes of the proximal tibia could be measured. Five AP axes were chosen: the line connecting the center of the posterior cruciate ligament(PCL) and the medial border of the patellar tendon at the cutting level of the tibia (PCL-PT), the line from the PCL to the medial border of the tibial tuberosity (PCL-TT1), the line from the PCL to the border of the medial third of the tibia (PCL-TT2), the line from the PCL to the apex of the tibia (PCL-TT3), and the AP axis of the tibial prosthesis along with the anterior cortex of the proximal tibia (anterior tibial curved cortex, ATCC). Results. In OA knees, the mean angles were less than those in normal knees for all 5 axes tested. In normal knees, the angle of the ATCC axis had the smallest mean value (1.6° ± 2.8°) and the narrowest range. In OA knees, the angle of the PCL-TT1 axis had the smallest mean value (0.3° ± 5.5°); however, the standard deviation (SD) and range were wider than that of the angle of the ATCC axis. The mean angle of the ATCC axis was larger (0.8° ± 2.7°) than the angle of the PCL-TT1 axis, but the difference was not statistically significant (P =0.461). The angle of the ATCC axis had the smallest SD and the narrowest range. Conclusion. In OA knees, the AP axis of the proximal tibia showed greater internal rotation compared with normal knees. In our study, the ATCC was found to be the most reliable and useful anatomical landmark for tibial rotational alignment in TKA

Introduction. Post-operative clinical outcomes of TKA are dependent on a multitude of surgical and patient-specific factors. Malrotation of the femoral and/or tibial component is associated with pain, accelerated wear of the tibial insert, joint instability, and unfavorable patellar tracking and dislocation. Using the transepicondylar axis to guide implantation of the femoral component is considered to be an accurate anatomical reference and is widely used. However, no gold standard currently exists with respect to ensuring optimal rotation of the tibial tray. Literature has suggested that implantation methods, which reference the tibial tubercle, reduce positioning outliers with more consistency than other anatomical landmarks. Therefore, the purpose of this evaluation is to use data collected from intraoperative sensors to assess the true rotational accuracy of using the mid-medial third of the tibial tubercle in 98 TKAs. Methods. The data for this evaluation was retrieved from 98 consecutive patients who underwent primary TKA from the same highly experienced surgeon. Femoral component rotation was verified in every case via the use of the Whiteside line, referencing the transepicondylar axis, and confirming appropriate patellar tracking. Tibial tray rotation was initially established by location of the mid-medial third of the tibial tubercle. Rotational adjustments of the tibial tray were evaluated in real-time, as the surgeon corrected any tibiofemoral incongruency and tray malpositioning. The initial and final angles of tibial tray rotation were captured with intraoperative video feed, and recorded. A z-test of differences between pre- and post-rotational correction was performed to assess the statistical significance of malrotation present in this cohort. Results. All patients in this study received a primary TKA, using the mid-medial third of the tibial tubercle to dictate tibial tray rotation. After the sensor-equipped tibial insert was implanted, it was shown that 63.1% of patients exhibited unfavorable rotation. Of those patients, 70% were shown to have internal rotation; 30% were shown to have external rotation. The average malrotation of the tibial tray deviated from a neutral position by 6.3° ± 4.3°, ranging from 0.5° to 19.2°. The z-test of differences yielded a p-value <0.0001, indicating that the proportion of malrotation was statistically significant. The 95% confidence interval of this cohort was calculated to be between 44.8% and 71.8% of malrotation. Discussion. Malrotation in TKA isassociated with poor clinical outcomes. While no gold standard anatomic landmark currently exists for positioning the tibial tray, the mid-medial third of the tibial tubercle is widely used as a reference. However, the data from this evaluation demonstrates that, not only is this landmark insufficient for establishing optimal rotation (p < 0.0001), but that it had guided the surgeon to an average of 6.3° outside of the optimized implant congruency zone. The large confidence interval indicates that the rotational alignment of the tibial tray—based on the location of the mid-medial third of the tibial tubercle—is not only inaccurate, but also highly variable. Based on this intraoperative sensor data, we suggest that care should be taken when utilizing the tibial tubercle as the sole rotational landmark for the tibial tray

Background. Accurate implant positioning is of supreme importance in total knee replacement (TKR). The rotational profile of the femoral and tibial components can affect outcomes, and the aim is to achieve coronal conformity with parallelism between the medio-lateral axes of the femur and tibia. Aims. The aim of this study is to determine the accuracy of implant rotation in total knee replacement. Methods. Intra-operatively, the trans-epicondylar axis of the femur (TEA) and Whiteside's line were used as the reference points, aiming to externally rotate the femoral component by 1 degree. The medial third of the tibial tuberosity was used as the anatomical reference point, aiming to reproduce the rotation of the native tibia. Pre-and post-operative CT scans were reviewed. The difference in femoral rotation was calculated by determining the femoral posterior condylar axis (PCA) of the native femur pre-operatively and the implant post-operatively. Tibial rotational difference was calculated between the native tibial posterior condylar axis and tibial baseplate. Results. Pre and post-operative CT scans of 41 knees in 31 patients were analysed. All surgeries were carried out by a single surgeon using the same implant. The mean difference in rotation of the femur post-operatively was 1.2 degrees external rotation (ER), range −4.7 to 6.9 degrees ER. 83% of femoral components were within 3 degrees of the target rotation. Mean difference in tibial rotation was −3.8 degrees ER, range −11.1 to 12.4 ER. Only 39% of tibial components were within 3 degrees of the target rotation. A line perpendicular to the midpoint of the tibial PCA was actually medial to the tibial tubercle in 33 knees, and only corresponded to the medial 1/3 of the tibial tubercle in 8 of 41 knees. Conclusions. Femoral component rotation is seen to be more accurate than tibial in this group. It may be that the anatomical landmarks used intra-operatively to judge tibial rotation are more difficult to accurately identify. Posterior landmarks are difficult to locate in vivo. This study would suggest that using the anterior anatomical landmark of the medial 1/3 of the tibial tubercle does not allow accurate reproduction of tibial rotation in total knee replacement

Introduction. Kinematics post-TKA are complex; component alignment, component geometry and the patient specific musculoskeletal environment contribute towards the kinematic and kinetic outcomes of TKA. Tibial rotation in particular is largely uncontrolled during TKA and affects both tibiofemoral and patellofemoral kinematics. Given the complex nature of post- TKA kinematics, this study sought to characterize the contribution of tibial tray rotation to kinematic outcome variability across three separate knee geometries in a simulated framework. Method. Five 50. th. percentile knees were selected from a database of planned TKAs produced as part of a pre-operative dynamic planning system. Virtual surgery was performed using Stryker (Kalamazoo, MI) Triathlon CR and PS and MatOrtho (Leatherhead, UK) SAIPH knee medially stabilised (MS) components. All components were initially planned in mechanical alignment, with the femoral component neutral to the surgical TEA. Each knee was simulated through a deep knee bend, and the kinematics extracted. The tibial tray rotational alignment was then rotated internally and externally by 5° & 10°. The computational model simulates a patient specific deep knee bend and has been validated against a cadaveric Oxford Knee Rig. Preoperative CT imaging was obtained, landmarking to identify all patient specific axes and ligament attachment sites was performed by pairs of trained biomedical engineers. Ethics for this study is covered by Bellberry Human Research Ethics Committee application number 2012-03-710. Results and Discussion. From the 360 Knee Systems database, 1847 knees were analysed, giving an average coronal alignment of 4.25°±5.66° varus. Five knees were selected with alignments between 4.1° and 4.3° varus. Kinematic outcomes were averaged over the 5 knees. The component geometries resulted in characteristically distinct kinematics, in which femoral rollback was most constrained by the PS components, whereas tibiofemoral axial rotation was most constrained in MS components. Patella lateral shift was comparable amongst all components in extension, medialising in flexion. Patella shift remained more lateral in MS components compared to PS and CR. Average patella lateral shift, medial and lateral facet rollback separated by tibial tray rotation are shown for all component systems in Figure 1. Medial and lateral facet rollback in the PS and CR components are symmetrical and opposite, indicating that with tibial tray rotation, the tibiofemoral articulation point balances between component rotation and neutral alignment, reflecting the restoring force exerted by the simulated collateral ligaments. As such, with higher internal tibial rotation and subsequent lateralisation of the tubercle, patella lateral shift increases. MS medial and lateral facet rollback however are not symmetrical nor opposite, reflecting the chirality of the tibiofemoral articulation. With internal tibial tray rotation, relatively high lateral facet rollback is observed, lateralising the femoral component centre, giving the patella component a relatively more medial position. Conclusions. Component geometry was found here to produce characteristically distinct tibiofemoral and patellofemoral kinematics. Medial stabilised components reported asymmetric kinematic changes, compared to either CR or PS components, in which a higher rate of change was observed for internal tray rotation, indicating that neutral or external rotation of medial stabilised components will result in more predictable kinematic outcomes

Introduction. Total knee arthroplasty (TKA) designs evolve as evidence accumulates on natural and prosthetic knee function. TKA designs based upon a medially conforming tibiofemoral articulation seek to reproduce essential aspects of normal knee stability and have enjoyed good clinical success and high patient satisfaction for over two decades. Fluoroscopic kinematic studies on several medially conforming knee designs show extremely stable knee function, but very small ranges of tibial axial rotation compared to healthy knees. The GMK Sphere TKA is a recent evolution in medially-conforming TKA designs that adopts a sagittally unconstrained lateral tibiofemoral articulation to allow more natural tibial rotation. This study was conducted to quantify motions in knees with this prosthesis to address two questions:. Does the medially conforming GMK Sphere design provide an AP-stable articulation that provides for tibiofemoral translations that are comparable to, but not larger than, translations measured in natural knees?. Does the medially conforming GMK Sphere design provide sufficient rotatory laxity to allow tibiofemoral rotations comparable to, but not larger than, rotations measured in natural knees?. Materials and Methods. Fifteen patients (9 females), mean age 65 years and mean BMI of 30 ±3, consented to participate. Sixteen knees received the GMK Sphere TKA. Mean Oxford Knee Score (OKS) improved significantly from 19±7 to 40±3 six months post surgery (P< 0.0001). On the day of the study, the mean OKS, Knee Society Score, EQ5D and Heath status scores were 40, 87, 0.83 and 85 respectively. Mean ROM from active maximum extension till maximum supine flexion was 108°±8°. Motions in 16 knees were observed using pulsed-fluoroscopy during a range of activities. Subjects were observed in maximum flexion kneeling and lunging positions, and in stepping up/down on a 22cm step. Model-image registration methods were used to quantify three-dimensional knee motions from digitized fluoroscopic images. Results. Tibial internal rotation averaged 8° during lunge and kneeling activities. During lunging, the medial and lateral condyles were an average of 2mm and 8mm posterior to the tibial sulcus, respectively, and 2mm and 9mm posterior to the tibial sulcus during kneeling. During the stair-stepping activity, the medial condyle did not translate significantly, while the lateral condyle moved 5mm posteriorly with flexion, accompanying 5° tibial internal rotation. Discussion. The GMK Sphere TKA was designed to provide intrinsic stability through a medially conforming articulation, and provide for more natural tibial rotation with an unconstrained lateral articulation. Fluoroscopic observation of these knees during lunge, kneel and stair-stepping activities showed a stable medial articulation with little translation, and a lateral articulation translating in direct relation to tibial rotation. Tibial rotation during kneeling (8° average) was approximately twice that observed in knees with an earlier medially conforming TKA design (Moonot et al., Knee Surg Sports Traumatol Arthrosc, 2009) and similar to that observed in natural knees with medial osteoarthritis (Hamai et al., J Orthop Res, 2009). At only six months follow-up, knees with the GMK Sphere arthroplasty show functional kinematics that are AP stable and have more natural tibial rotation, consistent with the implant design intent

Introduction. Mobility at insert-tray articulations in mobile bearing knee implant accommodates lower cross-shear at polyethylene (PE) insert, which in turn reduces wear and delamination as well as decreasing constraint forces at implant-bone interfaces. Though, clinical studies disclosed damage due to wear has occurred at these mobile bearing articulations. The primary goal of this study is to investigate the effect of second articulations bearing mobility and surface friction at insert-tray interfaces to stress states at tibial post during deep flexion motion. Method & Analysis. Figure 1 shows the 3-D computational aided drawing model and finite element model of implant used in this study. LS-DYNA software was employed to develop the dynamic model. Four conditions of models were tested including fixed bearing, as well as models with coefficients of friction of 0.04, 0.10 and 0.15 at tibial-tray interfaces to represent healthy and with debris appearance. A pair of nonlinear springs was positioned both anteriorly and posteriorly to represent ligamentous constraint. The dynamic model was developed to perform position driven motion from 0° to 135° of flexion angle with 0°, 10° and 15° of tibial rotation. The prosthesis components were subjected with a deep squatting force. Results. Peak values of maximum shear stress for different coefficients of friction and fixed bearing, respectively, are shown in Figure 2. Peak value of maximum shear stress at tibial post of fixed bearing is significantly larger than mobile bearing with tibial rotation. The peak values are 63MPa and 46.7MPa with 10° and 15° tibial rotation respectively for fixed bearing while for mobile bearing the values range from 32MPa to 36.6MPa and from 35.3MPa to 40.6MPa with 10° and 15° tibial rotation respectively. It was found that peak value of maximum shear stress increases with coefficient of friction and tibial rotation. In contrast, with normal rotation, bearing mobility and surface friction do not give any significant effect on the shear stress at tibial post. Discussion & Conclusions. Appearance of second articulations in mobile bearing TKA provides an attribute in reducing force transmission via implant-bone interface which leads to lower shear stress induced in tibial post due to transmitted moment. However, higher surface friction will result in larger frictional force, which in turn induce larger moment at tibial post. Higher conformity will attribute to higher cross-shear level during knee motion. As a result, wear damage at tibiofemoral articular surface of mobile insert become worse

Introduction. Instability, loosening, and patellofemoral pain belong to the main causes for revision of total knee arthroplasty (TKA). Currently, the diagnostic pathway requires various diagnostic techniques such as x-rays, CT or SPECT-CT to reveal the original cause for the failed knee prosthesis, but increase radiation exposure and fail to show soft-tissue structures around TKA. There is a growing demand for a diagnostic tool that is able to simultaneously visualize soft tissue structures, bone, and TKA without radiation exposure. MRI is capable of visualising all the structures in the knee although it is still disturbed by susceptibility artefacts caused by the metal implant. Low-field MRI (0.25T) results in less metal artefacts and offers the ability to visualize the knee in weight-bearing condition. Therefore, the aim of this study is to investigate the possibilities of low field MRI to image, the patellofemoral joint and the prosthesis to evaluate the knee joint in patients with and without complaints after TKA. Method. Ten patients, eight satisfied and two unsatisfied with their primary TKA, (NexGen posterior stabilized, BiometZimmer) were included. The patients were scanned in sagittal, coronal, and transversal direction on a low field MRI scanner (G-scan Brio, 0.25T, Esaote SpA, Italy) in weight-bearing and non-weight-bearing conditions with T1, T2 and PD-weighted metal artefact reducing sequences (TE/TR 12–72/1160–7060, slice thickness 4.0mm, FOV 260×260×120m. 3. , matrix size 224×216). Scans were analysed by two observers for:. - Patellofemoral joint: Caton-Descamps index and Tibial Tuberosity-Trochlear Groove (TT-TG) distance. - Prosthesis malalignment: femoral component rotation using the posterior condylar angle (PCA) and tibial rotation using the Berger angle. Significance of differences in parameters between weight-bearing and non-weight-bearing were calculated with the Wilcoxon rank test. To assess the reliability the inter and intra observer reliability was calculated with a two-way random effects model intra class correlation coefficient (ICC). The two unsatisfied patients underwent revision arthroplasty and intra-operative findings were compared with MRI findings. Results. In the satisfied group, a significant difference was found between TT-TG distance in non-weight-bearing and weight-bearing condition (p=0.018), with a good interrater reliability ICC=0.89. Furthermore, differences between weight-bearing and non-weight-bearing were found for the CD ratio, however, not significant (p=0.093), with a good interrater reliability ICC=0.89. The Berger angle could be measured with an excellent interrater reliability (ICC=0.94). The PCA was hard to assess with a poor interrater reliability (ICC=0.48). For one unsatisfied patient a deviation was found for tibial component rotation, according to the perioperative findings as, ‘malposition of the tibial component’. For the other unsatisfied patient revision surgery was performed due to aseptic loosening in which the MRI showed a notable amount of synovitis. Conclusion. It is possible to image the patellofemoral joint and knee prosthesis with low field MRI. Patellofemoral measurements and tibial component rotation measurements can reliably be performed. For the two patients with complaints MRI findings were consistent with intra-operative findings. Further research should focus on a larger group of patients with complaints after TKA to verify the diagnostic capacity of low field MRI for peri-prosthetic knee problems. For any figures or tables, please contact authors directly

PURPOSE. Total knee arthroplasty (TKA) is a successful technique for treating painful osteoarthritic knees. However, the patients' satisfaction is not still comparable with total hip arthroplasty. Basically, the conditions with operated joints were anterior cruciate ligament (ACL) deficient knees, thus, the abnormal kinematics is one of the main reason for the patients' incomplete satisfaction. Bi-cruciate stabilized (BCS) TKA was established to reproduce both ACL and posterior cruciate ligament (PCL) function and expected to improve the abnormal kinematics. However, there were few reports to evaluate intraoperative kinematics in BCS TKA using navigation system. Hence, the aim in this study is to reveal the intraoperative kinematics in BCS TKA and compare the kinematics with conventional posterior stabilized (PS) TKA. Materials and Methods. Twenty five consecutive subjects (24 women, 1 men; average age, 77 years; age range, 58–85 years) with varus osteoarthritis undergoing navigated BCS TKA (Journey II, Smith&Nephew) were enrolled in this study. An image-free navigation system (Stryker 4.0 image-free computer navigation system; Stryker) was used for the operation. Registration was performed after minimum medial soft tissue release, ACL and PCL resection, and osteophyte removal. Then, kinematics including tibiofemoral rotational angles from maximum extension to maximum flexion were recorded. The measurements were performed again after implantation. We compared the kinematics with the kinematics of paired matched fifty subjects who underwent conventional posterior stabilized (PS) TKA (25 subjects with Triathlon, Stryker; 25 subjects with PERSONA, ZimmerBiomet) using navigation statistically. Results. Preoperative tibiofemoral rotational kinematics were almost the same between the three implants groups. Kinematics at post-implantation found that tibia was significantly internally rotated compared to the kinematics at registration in all three implants at maximum extension position (p<0.05), however the tibial rotational position with BCS TKA was significantly externally rotated at maximum extension position, compared to the other two implant position (p<0.05). The tibial rotational position with Triathlon PS TKA was externally rotated at 60 degrees of flexion compared to the other two implant position, however the results were not statistically significant. Discussion and Conclusion. Previous study found that PCL resection changed tibial rotational position and the amount of tibial internal rotation, affecting postoperative maximum flexion angles. This study found that BCS TKA can reduce the amount of rotational changes, compared to conventional PS TKA. Further studies are needed to investigate the kinematic changes in BCS TKA affect the postoperative clinical outcomes

Modern total knee replacements aim to reconstruct a physiological kinematic behaviour, and specifically femoral roll-back and automatic tibial rotation. A specific software derived from a clinically used navigation system was developed to allow in vivo registration of the knee kinematics before and after total knee replacement. The study was designed to test for the feasibility of the intra-operative registration of the knee kinematics during standard, navigated total knee replacement. The software measures the respective movement of the femur and the tibia, and specially antero-posterior translation and tibial rotation during passive knee flexion. Kinematic registration was performed twice during an usual procedure of navigated total knee replacement: 1) Before any bone resection or ligamentous balancing; 2) After fixation of the final implants. 200 cases of total knee replacement have been analysed. Post-operative kinematic was classified as following: 1) Occurrence of a normal femoral roll-back during knee flexion, no roll-back or paradoxical femoral roll-forward. 2) Occurrence of a normal tibial internal rotation during knee flexion, no tibial rotation or paradoxical tibial external rotation. All patients were followed up for a minimal period of 12 months, and reevaluated at the latest follow-up visit for clinical and functional results with completion of the Knee Society Scores. Recording the kinematic was possible in all cases. The results of both pre-operative and post-operative registrations were analysed on a qualitative manner. The results were close to those already published in both experimental and clinical studies. About femoral roll-back, 54% had a normal femoral roll-back during knee flexion after total knee replacement, 13% had no significant roll-back and 33% had a paradoxical femoral roll-forward. About tibia rotation, 65% had a normal tibia internal rotation during knee flexion, 16% had no significant tibia rotation and 19 had a paradoxical tibia external rotation. The mean Knee Score was 92/100 ± 10 points. There was a significant correlation between the post-operative kinematic behaviour and the Function Score, with better score for the patients having a physiological femoral roll-back and a physiological tibial internal rotation during knee flexion (p<0.01). Intra-operative analysis of the kinematic of the knee during total knee replacement may offer the chance to modify the kinematic behaviour of the implant and to choose the best fitted constraint to the patient's native knee in order to impact positively the functional result

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

Introduction. Total knee arthroplasty (TKA) has achieved excellent clinical outcomes and functional performances. However, there is a need for greater implant longevity and higher flexion by younger and Asian patients. We determined the relationship between mobility and stability of TKA product because they are essential for much further functional upgrading. This research evaluated the geometry characteristics of femorotibial surfaces quantitatively by measuring their force of constraint by computer simulation and mechanical test. Methods. We measured the force of constraint of femorotibial surfaces in order to evaluate the property of femorotibial surfaces. A total knee system was used for this evaluation, and has an asymmetrical joint surface, which restores the anatomical jointline in both sagittal and coronal planes, and is expected to permit normal kinematics, with cruciate-retaining fixed type. We performed computer simulation using finite element analyses (FEA) and mechanical tests using knee simulator to measure the force of constraint regarding anterior-posterior (AP) and internal-external (IE) rotational direction in extension position, 90-degree flexion and a maximum flexion of 140-degree. In the FEA, Young's modulus and Poisson's ratio were set to 213 GPa and 0.3 for Co-Cr-Mo alloy as the femoral component, and 1 GPa and 0.3 for UHMWPe as the tibial insert, respectively. The force load to AP direction of tibial tray was measured when the femoral component moved plus or minus 10 millimeters. The moment load to IE rotational direction of tibial tray was measured when the femoral component moved plus or minus 20 degrees. The vertical load of 710 N was loaded on the femoral component during these measurements. Results. Regarding AP direction, the results of FEA showed 506 N (0-degree), 421 N (90-degree), and 389 N (140-degree) as the maximum load for anterior direction, and 152 N (0-degree), 166 N (90-degree), and 174 N (140-degree) for posterior direction. The results of mechanical tests showed 463 N (0-degree), 387 N (90-degree), and 332 N (140-degree) as the maximum load for anterior direction, and 108 N (0-degree), 121 N (90-degree), and 197 N (140-degree) for posterior direction [Fig. 1]. As the maximum moment load to IE rotational direction, the results of FEA showed 7.0 N-m (0-degree), 6.6 N-m (90-degree), and 5.5 N-m (140-degree) to tibial internal rotation of femoral component, and 9.5 N-m (0-degree), 8.1 N-m (90-degree), and 5.5 N-m (140-degree) to tibial external rotation of femoral component. The results of mechanical tests showed 4.5 N-m to tibial internal rotation of femoral component in all position, 8.6 N-m (0-degree), 6.5 N-m (90-degree), and 5.2 N-m (140-degree) to tibial external rotation of femoral component [Fig. 2]. Discussion. The force to AP direction of constraint for posterior was obviously lower than one for anterior. The torque to IE rotation for tibial internal rotation was lower or equal than tibial external rotation. These results suggest that this total knee system permits femoral rollback and tibial internal rotation with medial pivot pattern, which is required to achieve high functional performance. Furthermore, computer simulation can be a good method in this evaluation for their consistency

Total joint arthroplasty is an extremely high quality medical intervention with measured benefit to individual patients and society as a whole. However, nearly 20% of patients following total knee arthroplasty (TKA) may report some level of dissatisfaction following surgery. Weight-bearing-in-flexion activities such as squatting and ascending/descending stairs are those activities with which patients most frequently report dissatisfaction. It is assumed that optimal functioning following TKA requires proper femoral and tibial implant positioning in all planes (sagittal, coronal, and axial), proper femoral-tibial balance in the coronal and sagittal plane and durable fixation irrespective of implant design and the manner in which the surgery is executed. Posterior stabilised (PS) and cruciate retaining (CR) TKA designs are the most predominant implants utilised yet their kinematics are infrequently close to normal. In addition, there is little clinical evidence that one design is superior to another. Alternative designs such as bi-cruciate and medially stabilised designs are much less frequently used and much less frequently studied. However, in both cases, isolated centers with relatively small volumes of patients studied have reported outcomes superior to PS and CR designs depending on the metric assessed. With respect to kinematics, bi-cruciate and medially stabilised designs have displayed certain patterns of behavior that more closely mimic the native knee both in-vitro and in-vivo. Normal knee kinematics, as described by Freeman and Pinskerova, includes lateral sided femoral rollback with progressive knee flexion (alternatively thought of as internal tibial rotation with flexion) and sagittal plane stability achieved through the medial compartment. In theory, both optimal sagittal plane stability and internal tibial rotation with progressive flexion (consistent with normal dynamic changes in tibial tubercle – trochlear groove distance) following TKA should optimise weight-bearing-in-flexion kinematics and load transfer. Patient-related satisfaction with such activities might thus reasonably improve and may help explain the separate findings of Pritchett and Hossain regarding outcomes following medially stabilised TKA. Medially stabilised TKA affords sagittal plane stability in mid-flexion and internal tibial rotation with flexion without the complexity and unique failure modes seen following bi-cruciate TKA. The work flow of performing medially stabilised TKA is similar to PS and CR surgical techniques and the surgeon need not climb a steep learning curve. In addition, similar to PS TKA, medial stabilised TKA is applicable to any primary state in which coronal plane balance can be achieved. Further investigation in well-designed trials is necessary to fully develop an understanding of how different contemporary TKA designs might impact patient reported outcome. Larger registry populations of medially stabilised TKA over time are also necessary to best assess survivorship compared to other contemporary designs