Lateral Contact Points Research Articles

Clinical outcomes and biomechanics in bicruciate-retaining total knee arthroplasty.

To clarify the influence of biomechanics on post-operative clinical outcomes in bicruciate-retaining total knee arthroplasty (BCR-TKA). Severe medial osteoarthritis who underwent BCR-TKA were examined. Each patient was asked to perform a squat (weight-bearing [WB]) and active assisted knee flexion (non-WB [NWB]) under single fluoroscopy surveillance. A 2D-to-3D registration technique was used. Patients were divided into two groups based on their 1-year post-operative patient-reported outcome measures (PROMs) using hierarchical cluster analysis. The rotational alignment on computed tomography, anterior stability at 30° of knee flexion, axial rotation of the femur relative to the tibial component and anteroposterior translation of the medial and lateral femorotibial contact points were measured. Components did not significantly differ between the groups, with 1.6 ± 5.0° and 5.4 ± 4.7° of femoral internal rotation in the low PROM (N = 28) and high PROM (N = 8) groups, respectively. Moreover, anterior stability did not significantly differ (low PROM: 4.9 ± 1.4 mm, high PROM: 5.3 ± 1.0 mm). The knee externally rotated from 0° to 70° and from 50° to 110° of flexion during WB and NWB, respectively. The low-PROM group exhibited more external rotation across all ranges of motion. Medial contact points moved backwards from 0° to 30° of flexion during WB, forward from 30° to 100° of flexion, and backwards from 100° to 110° of flexion. The low-PROM group was positioned more forward throughout the full range of motion during WB. Lateral contact points moved backwards at 0-30° of flexion, forward at 70-100° of flexion, and backwards at 100-110° of flexion during WB, while there was backward movement at 50° of flexion during NWB. Both activities exhibited a more posterior position in the low-PROM group throughout the full range of motion. The femoral component in the low-PROM group was externally rotated across all ranges of motion, and the lateral contact points were posteriorly located in BCR-TKA. Level II, prospective cohort study.

Can Cadaver Testing Replicate In Vivo Kinematics of Total Knee Arthroplasty?

Whether the kinematics of cadaveric knees recreate those of the patient's knees after total knee arthroplasty (TKA) remains unknown. This study compared in vivo and in vitro fluoroscopic kinematics of knees after TKA during knee bending using the same implant design. Patients who had undergone cruciate-retaining and cruciate-substituting total knee arthroplasty (CR-TKA and CS-TKA) did squatting motions. Fresh-frozen human cadaveric knees were tested under dynamic closed-chain knee extension in an Oxford knee rig. Fluoroscopic kinematics were measured in vivo and in vitro using a 2-dimensional to 3-dimensional registration technique. The axial rotation angle and anterior-posterior translation of medial and lateral contact points of the femoral implant relative to the tibial implant was evaluated in each flexion angle. No notable differences in the axial rotation angles were found between in vivo and in vitro measurements in both CR-TKA and CS-TKA. In early flexion, the medial and lateral contact points in cadaver knees were located more posterior than those in in vivo after CR-TKA. From early flexion to high flexion, the medial and lateral contact points in cadaver knees were located more posterior than those in in vivo after CS-TKA. The axial rotation angle of cadaveric knees in the Oxford knee rig was similar to that measured in vivo after TKA. However, the anterior-posterior location of the femoral implant in cadaver knee was more posterior than that in in vivo knees after TKA.

Medial pivot total knee arthroplasty for valgus knees provides equivalent medial stability compared to that for varus knees: In vivo kinematic study.

The efficacy of medial pivot total knee arthroplasty (MP TKA) in treating valgus knees that may cause medial instability is unknown. The purpose of this study was to investigate the in vivo kinematics of MP TKA for the valgus knees and compare them to those for the varus knees. The kinematics of 19 valgus knees and 19 varus knees operated in the MP TKA were investigated under fluoroscopy during squatting using a two- to three-dimensional registration technique. Accordingly, the valgus and varus knees were evaluated and compared in terms of knee flexion angle, anteroposterior translation for the medial and lateral low contact points, axial rotation and valgus-varus angle of the femoral component relative to the tibial component, as well as kinematic pathways. The knee flexion angle was found to be identical in both knees. There was no anterior translation on the medial side of the valgus knees, and no difference was detected between the two knees. On the lateral side, posterior translation was observed in both knees, with no difference between the two. Femoral external rotation was observed in both knees, and no difference was detected between the two. There was no valgus-varus change in the valgus knees, nor was there a difference between the two knees. The valgus knees demonstrated MP motion, whereas the varus knees demonstrated MP motion and bicondylar rollback. The medial side of the valgus knees treated with MP TKA showed comparable stable kinematics to the varus knees. The MP TKA is an effective procedure for valgus knees to stabilize the medial compartment. Level Ⅲ.

Lateral Subvastus Lateralis versus Medial Parapatellar Approach for Total Knee Arthroplasty: Patient Outcomes and Kinematics Analysis.

The conventional approach for total knee arthroplasty (TKA) is a medial parapatellar approach (MPA). We aimed to study patient outcomes and kinematics with a quadriceps sparing lateral subvastus lateralis approach (SLA). Patients with neutral/varus alignment undergoing primary TKA were consented to undergo the SLA. At 1-year postoperative, patients underwent radiostereometric analysis. Patients were administered the Short Form 12 (SF-12), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Society Score (KSS). Kinematics and outcome data were compared to a group undergoing TKA via conventional MPA. Fourteen patients underwent TKA via SLA with a mean age 71.5 ± 8.0 and mean body mass index (BMI) 31.0 ± 4.5. The MPA group had 13 patients with mean age 63.4 ± 5.5 (p = 0.006) and mean BMI 31.2 ± 4.6 (p = 0.95). The SLA resulted in a significantly more posterior medial contact point at 0 (p = 0.011), 20 (p = 0.020), and 40 (p = 0.039) degrees of flexion. There was no significant difference in medial contact point from 60 to 120 degrees, lateral contact point at any degree of flexion, or axial rotation. There was no difference in improvement in postoperative WOMAC, SF-12, KSS function, and total KSS knee scores between groups. The MPA group had a significantly greater improvement in KSS knee scores at 3 months (p < 0.001), 1 year (p = 0.003), and 2 years (p = 0.017). The SLA resulted in increased medial femoral rollback early in flexion. Although both approaches resulted in improved postoperative outcomes, the MPA group showed significantly greater improvements in KSS knee scores at 3 months, 1 year, and 2 years. Further studies are required to identify any benefits that the SLA may offer. LEVEL OF EVIDENCE: Therapeutic Level II.

Comparison of the in-vivo kinematics of three different knee prosthesis designs during a step-up movement

BackgroundThere is no consensus on the importance of the kinematics of the prosthetic joint for the clinical outcome after total knee arthroplasty. A 3-armed randomized controlled trial was done to determine and compare the in vivo kinematics of a posterior cruciate-retaining and two posterior cruciate-sacrificing (Anterior-Stabilized and Posterior-Stabilized) prosthetic designs from the same total knee arthroplasty system. Since the anterior-stabilized and posterior-stabilized designs are posterior cruciate ligament-sacrificing designs, we hypothesized they would have similar contact-point kinematics. Further, we hypothesized that the cruciate-retaining design would have contact-point kinematics different from the anterior-stabilized and the posterior-stabilized designs, but comparable to a native knee. MethodsThirty-nine patients with a well-functioning total knee arthroplasty one year postoperatively underwent kinematic analysis of a weight-bearing step-up movement under fluoroscopic recording. Model-based radiostereometric analysis was used to determine anteroposterior contact-point translations and rotations through the movement path to assess knee kinematics. FindingsThe cruciate-retaining and anterior-stabilized groups' medial and lateral contact-points displayed similar paradoxical posterior translations during step-up in the magnitude of 7 and 2 mm, respectively. In contrast, the posterior-stabilized group's contact-points translated anteriorly by 4 and 10 mm throughout the movement and were significantly more posterior than the cruciate-retaining and the anterior-stabilized groups from >100° to 40° of flexion. The femur rotated internally with all designs. InterpretationThe cruciate-retaining and anterior-stabilized designs displayed similar contact-point translation patterns during a step-up movement. Only the posterior-stabilized design showed a pattern comparable to native knees. Conversion from a cruciate-retaining to an anterior-stabilized design because of posterior cruciate ligament insufficiency will not change knee kinematics.

In vivo kinematic comparison of medial pivot total knee arthroplasty in weight-bearing and non-weight-bearing deep knee bending

BackgroundThis study aimed to determine the kinematics of medial pivot total knee arthroplasty by comparing weight-bearing and non-weight-bearing deep knee bending and to evaluate the effect of the weight-bearing state on the kinematics. MethodsThe kinematics of 19 knees were investigated under fluoroscopy during squatting (weight-bearing) and active-assisted knee bending (non-weight-bearing) using two- to three-dimensional registration technique. Accordingly, range of motion, anteroposterior translation for the medial and lateral low contact points, axial rotation of the femoral component relative to the tibial component and kinematic pathway were evaluated. FindingsThere was no difference in range of motion between the two states. The medial anteroposterior translation showed no significant movement with no anterior translation in both the weight-bearing and non-weight-bearing from 0° to 90° of flexion. Regarding the lateral anteroposterior translation, a posterior translation was observed during weight-bearing, whereas a slight anterior translation from 0° to 30° of flexion and subsequent posterior translation were found in the non-weight-bearing. Femoral external rotation was observed in the weight-bearing, whereas femoral internal rotation was seen from 0° to 30° of flexion and subsequent femoral external rotation was observed in the non-weight-bearing. The kinematic pathway showed medial pivot motion and subsequent bicondylar rollback in the weight-bearing, whereas only medial pivot motion was observed in the non-weight-bearing. InterpretationThe medial anteroposterior translation of the femur during deep knee bending showed no anterior motion in the two states. The lateral anteroposterior translation and femoral rotation were different in the mid-flexion range between the two states.

The influence of the lateral contact point trajectory and the rotation of the monoblock on the impact loads in railway turnouts

A new wheel–rail interaction model for the prediction of turnout impact forces is presented. Although the model is based on the classical “moving irregularity” approach, it is novel in the sense that it accounts for the lateral shift of the wheel–rail contact position during load transfer between the crossing nose and wing rail. This lateral shift increases the mobility of the track due to the rotational response of the monoblock under off-centred excitation. It is shown that the resulting stepwise variation of the wheel and track mobilities upon impact can profoundly influence the impact force time history. It is furthermore shown that these effects are particularly emphasized during the trailing move when the wheel impacts on the off-centred wing rail and much less during the facing move when the impact is absorbed by the crossing nose which is located in the plane of symmetry of the monoblock cross-section. Apart from the stepwise shift upon load transfer the lateral wheel–rail contact point position varies continuously along the longitudinal coordinate of the turnout. Simulations show that these continuous variations have a negligible influence on the impact force time histories and that a simplified model with constant shift gives satisfactory results. A comparison of the calculated crossing nose and wing rail accelerations shows encouraging agreement with field measurements. It is concluded that omission of the rotation leads to an overestimate of the track vibrations. Especially for the trailing move, this overestimate becomes substantial for frequencies above 100Hz.

Femoral rollback at high-flexion during squatting is related to the improvement of sports activities after bicruciate-stabilized total knee arthroplasty: an observational study

BackgroundIn bicruciate-stabilized total knee arthroplasty (BCS-TKA), the relationship between the postoperative kinematics and sports subscales in patient-reported outcome measures (PROMs) remains unknown. The purpose of this study was to determine the relationship between kinematics and sports subscales using the PROMs after BCS-TKA.MethodsSixty-one patients with severe knee osteoarthritis were examined at 13.5 ± 7.8 months after BCS-TKA. The patients performed squats under single fluoroscopic surveillance in the sagittal plane. Range of motion of the knee, axial rotation of the femur relative to the tibial component, and anteroposterior (AP) translation of the medial and lateral femorotibial contact points were measured using a 2D-to-3D registration technique. In addition, the relationship between the kinematics and improvement of the sports subscales in the Knee Injury and Osteoarthritis Outcome Score (KOOS) was evaluated.ResultsIn rotation angle, the femoral external rotation was observed from 0 to 50° of flexion. The amount of femoral external rotation did not correlate with PROMs-SP. In medial AP translation, posterior translation was observed from 0 to 20° and 80–110° of flexion. Mild anterior translation was observed from 20 to 80° of flexion. Beyond 80° of flexion, posterior translation was positively correlated with squatting. In lateral AP translation, posterior translation was observed from 0 to 20° and 80–110° of flexion. Beyond 80° of flexion, posterior translation was positively correlated with running, jumping, twisting/pivoting, and kneeling.ConclusionFemoral rollback at high flexion during squatting may be important to improve sports performance after BCS-TKA.

Snakes combine vertical and lateral bending to traverse uneven terrain

Terrestrial locomotion requires generating appropriate ground reaction forces which depend on substrate geometry and physical properties. The richness of positions and orientations of terrain features in the 3D world gives limbless animals like snakes that can bend their body versatility to generate forces from different contact areas for propulsion. Despite many previous studies of how snakes use lateral body bending for propulsion on relatively flat surfaces with lateral contact points, little is known about whether and how much snakes use vertical body bending in combination with lateral bending in 3D terrain. This lack had contributed to snake robots being inferior to animals in stability, efficiency, and versatility when traversing complex 3D environments. Here, to begin to elucidate this, we studied how the generalist corn snake traversed an uneven arena of blocks of random height variation five times its body height. The animal traversed the uneven terrain with perfect stability by propagating 3D bending down its body with little transverse motion (11° slip angle). Although the animal preferred moving through valleys with higher neighboring blocks, it did not prefer lateral bending. Among body-terrain contact regions that potentially provide propulsion, 52% were formed by vertical body bending and 48% by lateral bending. The combination of vertical and lateral bending may dramatically expand the sources of propulsive forces available to limbless locomotors by utilizing various asperities available in 3D terrain. Direct measurements of contact forces are necessary to further understand how snakes coordinate 3D bending along the entire body via sensory feedback to propel through 3D terrain. These studies will open a path to new propulsive mechanisms for snake robots, potentially increasing the performance and versatility in 3D terrain.

Differences in the flexion and extension phases during kneeling investigated by kinematic and contact point analyses: a cross-sectional study

BackgroundKneeling is necessary for certain religious and ceremonial occasions, crouching work, and gardening, which many people take part in worldwide. However, there have been few reports about kneeling activities. The purpose of this study was to clarify the kinematics of kneeling.MethodsThe subjects were 15 healthy young males. Kneeling activity was analysed within a knee flexion angle from 100° to maximum flexion (maxflex, mean ± SD = 161.3 ± 3.2°). The kinematic and contact point (CP) analyses were performed using a 2D/3D registration method, in which a 3D bone model created from computed tomography images was matched to knee lateral fluoroscopic images and analysed on a personal computer.ResultsIn the kinematic analysis, the femur translated 37.5 mm posteriorly and rotated 19.8° externally relative to the tibia during the knee flexion phase. During the knee extension phase, the femur translated 36.4 mm anteriorly, which was almost the same amount as in the knee flexion phase. However, the femur rotated only 7.4° internally during the knee extension phase. In the CP analysis, the amount of anterior translation of the CP in the knee extension phase was greater in the medial CP and smaller in the lateral CP than that of posterior translation in the knee flexion phase.ConclusionsIn kneeling, there was a difference in the rotational kinematics between the flexion phase and the extension phase. The kinematic difference between the flexion and extension phases may have some effect on the meniscus and articular cartilage.

Effect of weight-bearing in bicruciate-retaining total knee arthroplasty during high-flexion activities

BackgroundTo evaluate the effect of weight-bearing on the kinematics of the bicruciate-retaining total knee arthroplasty design during high knee flexion activities. MethodsThe kinematics of 21 bicruciate-retaining total knee arthroplasties were evaluated under fluoroscopy, with two- and three-dimensional image registrations, during squatting (weight-bearing) and active-assisted knee flexion (non-weight-bearing). The following variables were measured: knee range of motion, axis of femoral rotation and varus-valgus angle relative to the tibial component, anteroposterior translation of the medial and lateral contact points, and the kinematic pathway of the joint surfaces. FindingsFrom 20° to 100° of flexion, the femoral external rotation during weight-bearing was larger than that during non-weight-bearing. There were no differences in the varus-valgus angles between the two conditions. From 10° to 50° of flexion, the medial contact point during weight-bearing was located posterior to the point of contact during non-weight-bearing; this difference between the two weight-bearing conditions was significant. From 0° to 90° of flexion, the lateral contact point in weight-bearing was located posterior to the contact point in non-weight-bearing; this difference between the two weight-bearing conditions was also significant. InterpretationThe anteroposterior position of the medial and lateral contact points of the bicruciate-retaining total knee arthroplasty design was significantly more posterior in the mid-range of knee flexion in weight-bearing than in non-weight-bearing. However, no anterior translation of the bicruciate-retaining total knee arthroplasty design was observed. Therefore, bicruciate-retaining total knee arthroplasty appears to have good anteroposterior stability throughout the range of knee flexion, regardless of the weight-bearing condition.

Investigation of femoral condyle height changes during flexion of the knee: implication to gap balance in TKA surgery.

Gap balance of the knee at 0° and 90° of flexion has been pursued in total knee arthroplasty (TKA) with the trans-epicondyle axis (TEA) as a reference. This study investigated the height changes of the tibiofemoral articulation and compared the data with the femoral condyle height changes measured using different flexion axes. Twenty healthy knees were investigated during an invivo weightbearing flexion using a techniquecombining MRI anda dual fluoroscopic imaging system (DFIS). The tibiofemoral contact points and the femoral condyle heights [measured using: TEA, geometric center axis (GCA), and iso-height axis (IHA)] were determined at each flexion angle. The height changes of the articular contact points and the femoral condyles were compared along the flexion path. The changes of the medial and lateral contact point heights were within 2.5mm along the flexion path. The changes of the medial and lateral condyle heights were within 8.9mm for TEA, within 4.2mm for GCA and within 3.0mm for IHA. The height changes measured by the contact points and IHA are similar (p > 0.05), and both are significantly smaller than those measured using the TEA and GCA (p < 0.05). The TEA and GCA measured varying femoral condyle heights, but the IHA resulted in minimal condyle height changes and could better represent the articulation characteristics of the knee. The data suggested that the IHA could be used as an alternative reference to guide surgical preparation of gap balance along the knee flexion path during TKA surgeries.

Patellar resurfacing has minimal impact on in vitro tibiofemoral kinematics during deep knee flexion in total knee arthroplasty

BackgroundWhile patellar resurfacing can affect patellofemoral kinematics, the effect on tibiofemoral kinematics is unknown. We hypothesized that patellar resurfacing would affect tibiofemoral kinematics during deep knee flexion due to biomechanical alteration of the extensor mechanism. MethodsWe performed cruciate-retaining TKA in fresh-frozen human cadaveric knees (N = 5) and recorded fluoroscopic kinematics during deep knee flexion before and after the patellar resurfacing. To simulate deep knee flexion, cadaver knees were tested on a dynamic, quadriceps-driven, closed-kinetic chain simulator based on the Oxford knee rig design under loads equivalent to stair climbing. To measure knee kinematics, a 2-dimensional to 3-dimensional fluoroscopic registration technique was used. Component rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were calculated over the range of flexion. ResultsThere were no significant differences in femoral component external rotation (before patellar resurfacing: 6.6 ± 2.3°, after patellar resurfacing: 7.2 ± 1.8°, p = 0.36), and less than 1° difference in femorotibial varus-valgus angle between patellar resurfacing and non-resurfacing (p = 0.01). For both conditions, the medial and lateral femorotibial contact points moved posteriorly from 0° to 30° of flexion, but not beyond 30° of flexion. At 10° of flexion, after patellar resurfacing, the medial contact point was more anteriorly located than before patellar resurfacing. ConclusionDespite the potential for alteration of the knee extensor biomechanics, patellar resurfacing had minimal effect on tibiofemoral kinematics. Patellar resurfacing, if performed adequately, is unlikely to affect postoperative knee function.

The higher patient-reported outcome measure group had smaller external rotation of the femur in bicruciate-stabilized total knee arthroplasty.

The hypothesis of this study was that the kinematics of patients with higher patient-reported outcome measures (PROMs) differ from those of patients with lower PROMs after bicruciate-stabilized total knee arthroplasty (BCS-TKA). A total of 32 patients with severe knee osteoarthritis were examined 11.2 ± 3.2months after BCS-TKA. The patients performed squats under single fluoroscopic surveillance in the sagittal plane. To estimate the spatial position and orientation of the femoral and tibial components, a 2D-to-3D registration technique was used. This technique uses a contour-based registration algorithm, single-view fluoroscopic images and 3D computer-aided design models. Knee range of motion, varus-valgus alignment, axial rotation of the femur relative to the tibial component, anteroposterior translation of the medial and lateral femorotibial contact points, kinematic paths, and anterior and posterior post-cam engagement were measured. The patients were divided into two groups using hierarchical cluster analysis based on the 1-year postoperative Knee Injury and Osteoarthritis Outcome Score and 2011 Knee Society Score. The femoral component had significantly more external rotation in the low-score group than in the high-score group (5.1 ± 1.8° vs. 2.2 ± 2.7°, p = 0.02). The high-score group had a medial pivot pattern from 0 to 20° of flexion, without significant movement from 20 to 70°, and final bicondylar rollback beyond 70°. The low-score group had a medial pivot from 0 to 70° of flexion and bicondylar rollback beyond 70°. There were no significant between-group differences in the varus-valgus angle or post-cam engagement. The higher PROM group had smaller external rotation of the femur after BCS-TKA. Level III.

In vivo kinematics of a newly updated posterior-stabilised mobile-bearing total knee arthroplasty in weight-bearing and non-weight-bearing high-flexion activities

BackgroundThe purpose of this study was to clarify the in vivo kinematics of a newly updated posterior-stabilised (PS) mobile-bearing total knee arthroplasty during high-flexion activities in weight-bearing (WB) and non-weight-bearing (NWB) conditions. The hypothesis was that the kinematics would differ between the WB and NWB conditions, and the kinematics would be affected by the WB condition. MethodsThe kinematics of 19 knees were investigated under fluoroscopy during squatting (WB) and active-assisted knee flexion (NWB) with two- and three-dimensional registration technique. Accordingly, the range of motion, anteroposterior (AP) translation of the medial and lateral contact points, axial rotation of the femoral component relative to the tibial component, and kinematic pathway were evaluated. ResultsThere was no difference in the knee’s range of motion between the WB and NWB conditions. The medial AP translation of the femur did not differ in each flexion angle between WB and NWB conditions except for flexions of 70°. There was no difference in the lateral AP translation of the femur at all tested flexion angles between the WB and NWB conditions. The external femoral rotation and the medial pivot motion were observed throughout all flexion angles in WB conditions. The clinical relevance is that this implant could produce ideal medial AP stability and medial pivot motion. ConclusionThe medial AP translation of the femur was stable for AP direction when it was in both WB and NWB conditions. In WB conditions, the medial pivot motion was observed throughout all flexion angles.Level of Evidence: III.

Systematic effects of femoral component rotation and tibial slope on the medial and lateral tibiofemoral flexion gaps in total knee arthroplasty

PurposeTo quantify the effects of the systematic internal and external femoral component rotations and tibial slope on the medial and lateral tibiofemoral gaps in total knee endoprostheses. MethodsNineteen knee cadaver specimens with an intact ligament apparatus were fixed in a custom frame, facilitating physiological flexion motion. Virtual total knee arthroplasty (TKA) was performed on three-dimensional models obtained from computed tomography ​scans (0° and 90° flexions) with systematically altered femur rotations and tibial slopes. ResultsBoth the femur rotation and the tibial slope influenced the medial and lateral tibiofemoral flexion gaps (p ​< ​0.001), and the effects differed between the medial and lateral sides (p ​< ​0.001). The medial tibiofemoral flexion gap increased by 2.90 ​± ​0.34 ​mm and decreased by 2.66 ​± ​0.26 ​mm for 7° external and internal femur component rotations, respectively (both with p ​< ​0.001). The lateral tibiofemoral flexion gap decreased by 3.11 ​± ​0.31 ​mm and increased by 3.29 ​± ​0.33 ​mm for 7° external and internal femur component rotations, respectively (both with p ​< ​0.001). ConclusionFor established surgical methods, we recommend a neutral femur rotation for a 0° tibial slope and a 3° external femur rotation for a tibial slope of 9–10°. The translational potential of this research shows that while the rotation of the femoral component in extension has no effect on the gap size, owing to the axis of rotation being perpendicular to the gap, for a 90° flexion, we not only observe differences in the gap size between the medial and lateral ​but also unequal differences on either side depending on the inward or outward rotation. The main reason for this is the position of the axis of rotation, which is not precisely half way between the lateral and medial contact points. The results show that rotation of the femoral component always creates an unbalanced flexion gap. The translational potential of this articleThe article points out the differences in the tibiofemoral gap in total knee endoprostheses due to the systematic internal and external femoral component rotation. While in lower leg extension there are no differences seen, in 90° knee-flexion there are unequal differences within the medial and lateral compartment that show a mathematical relationship towards the femoral compartment rotation which needs to be intraoperatively considered.

In Vivo Kinematics of Bicruciate-Retaining Total Knee Arthroplasty with Anatomical Articular Surface under High-Flexion Conditions.

Bicruciate-retaining total knee arthroplasty (BCR-TKA) recreates normal knee movement by preserving the anterior cruciate and posterior cruciate ligaments. However, in vivo kinematics of BCR-TKA with the anatomical articular surface remains unknown. The objective of this study was to evaluate in vivo kinematics of BCR-TKA with the anatomical articular surface during high-flexion activities. For this purpose, 17 knees after BCR-TKA with an anatomical articular surface were examined. Under fluoroscopy, each patient performed squatting and cross-legged sitting motions. To estimate the spatial position and orientation of the knee, a two-dimensional or three-dimensional registration technique was used. Rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were evaluated in each flexion angle. The results showed that from 80 to 110° of flexion, the femoral external rotation during squatting was significantly larger than that during cross-legged sitting. At maximum flexion, the knees during sitting indicated significantly more varus alignment than during squatting. During squatting, a medial pivot pattern was observed from minimum flexion to 10° flexion, with no significant movement beyond 10° of flexion. Conversely, during cross-legged sitting, no significant movement was detected from minimum flexion to 60° of flexion, with a medial pivot beyond 60° of flexion. Therefore, the knees showed relatively normal kinematics after BCR-TKA with an anatomical articular surface; however, it varied during high-flexion activities depending on the activity.

Flexion gap stabilization by oversizing posterior condylar offset in deep-dished total knee replacement does not compromise flexion: A single-surgeon, retrospective, observational, mid-term series

IntroductionIn total knee replacement surgery, medio-lateral knee balancing is recognized as the key to achieving satisfactory functional results. But it may not be enough to stabilize the flexion gap using deep-dished implants. We achieved flexion gap balance by oversizing the femoral component, thus increasing the posterior condylar offset (PCO). The purpose of this study was to describe the applicability of this technique and to test whether it produced adverse effects on medium-term outcomes. We hypothesized that it would not compromise the results if used properly. We therefore asked: (1) at how many cases of flexion gap balance would require oversizing the femoral component; (2) if femoral components oversizing would modify the mid-term results as per forgotten joint score (FJS) scores and whether flexion gain would be comparable to patients in whom it was not increased. Materials and methodsNinety-four patients (120 knees) were operated between September 2009 and 2011 (age 68±9 years) using the cementless Hyperflex version of the Natural Knees (Zimmer, Warsaw, IN, USA). Postero stabilization was achieved using deep-dished inserts. The Gender configuration has provided narrow inserts to better adapt the female anatomy. A special navigation system measured the displacement of the lateral and medial femoro-tibial contact points with infra-millimetric precision. Adopting a tibial cut first, gap-balancing technique with anterior referencing, the decision to oversize the femoral component relied on the 90° flexion drawer test, which showed more than 6mm sagittal laxity before the femoral bone cuts. Eighty-one (105 knees) patients were reviewed with average 63±27-month follow-up. ResultsFemoral components were augmented by 1 size in 60 cases and by 2 sizes in 7 cases. At final review, knees with an oversized femoral component (60) achieved the same results as those implanted with a non-oversized femoral component (n=45) in terms of mean flexion gain (−5°±34 versus −4°±23, p=0.78), mean FJS (63±26 versus 61±23; p=0.56). ConclusionBalancing the Flexion gap by oversizing the femoral component did not compromise flexion range and functional results. Level of evidenceIV, Retrospective cohort study.

Age-Related Changes in In-Vivo 3D Knee Kinematics during Knee Joint Flexion Observed using 2D/3D Registration Technique

We aimed to identify 3D motion differences in knee joint articular surface kinematics in healthy young and old participants during weight-bearing knee flexion. Twelve healthy male volunteers, six in their 60s and six in their 20s, without any musculoskeletal system disease involving the knees participated. 3D bone models of the femur and tibia were obtained using CT and matched into the fluoroscopic images captured during split squatting. Translation and rotation of the tibia to the femur during weight-bearing flexion were compared between the groups. Translation of the nearest medial-lateral articular surface location and rotational angle of medial-lateral connecting lines were also compared. As the tibial internal-external rotation angle and medial contact point anterior-posterior translation were significantly correlated between the groups, they could not represent the characteristics of age-related changes. Similar to lateral contact point translation and contact points line angles were significantly different during the initial 10° flexion period. At the 40°-45° knee flexion period, a significant difference was detected in the contact point line angle and in the tibial superior-inferior translation. 3D knee joint kinematic differences between participants in their 20s and 60s, especially during initial and 40°-45° periods, can predict kinematic effects on age-related disease.

Bicruciate-stabilised total knee arthroplasty provides good functional stability during high-flexion weight-bearing activities.

Bicruciate-stabilised total knee arthroplasty (BCS-TKA) uses a dual-post-cam mechanism as a substitute for the anterior cruciate ligament and posterior cruciate ligament (PCL), with the surface geometry providing additional guidance for axial rotation and posterior translation. However, the effect of weight-bearing on the kinematics of BCS-TKA has not been investigated. Therefore, the aim of this study was to clarify the effect of weight-bearing on the kinematics of BCS-TKA during high-flexion activities. The kinematics of 11 BCS-TKAs were evaluated under fluoroscopy, with two- and three-dimensional image registration, during squatting weight-bearing and active-assisted knee flexion non-weight-bearing. The following variables were measured: knee range of motion, axis of femoral rotation relative to the tibial component, anteroposterior (AP) translation of the medial contact point, kinematic path of the joint surfaces, lateral femorotibial contact point, and anterior and post-cam engagement. The weight-bearing condition did not influence the range of knee flexion, axis of femoral rotation, medial pivot pattern during early flexion, or bicondylar rollback beyond mid-flexion. With regard to AP translation, both the medial and lateral contact points had more posterior locations in weight-bearing than in non-weight-bearing at the mid-flexion angle. Anterior engagement was identified in 6/11 knees (54.5%) in weight-bearing and 4/11 knees (36.3%) in non-weight-bearing. Post-cam engagement was observed in all knees, with the angle of flexion at engagement being larger in weight-bearing than in non-weight-bearing. Although weight-bearing resulted in a posterior location of the medial and lateral contact points of the BCS-TKA design compared with non-weight-bearing in the mid-range of knee flexion, the amount of anterior translation was small overall. Therefore, BCS-TKA provides good stability during high-flexion weight-bearing activities. However, BCS-TKA is associated with high rate of the anterior engagement during early flexion. Therefore, understanding a patient's activities is an important factor when selecting the most appropriate TKA method.