Condylar Contact Research Articles

ASSESSMENT OF TIBIOFEMORAL AND ALLOGRAFT LOADING AFTER OSTEOCHONDRAL ALLOGRAFT TRANSPLANTATION USING SHELL GRAFTS

In this study, we aimed to investigate tibiofemoral and allograft loading parameters after OCA transplantation using tibial plateau shell grafts to characterize the clinically relevant biomechanics that may influence joint kinematics and OCA osseointegration after transplantation. The study was designed to test the hypothesis that there are significant changes in joint loading after tibial plateau OCA transplantation that may require unique post-operative rehabilitation regimens in patients to restore balance in the knee joint.Fresh-frozen cadaveric knees (n=6) were thawed and mounted onto a 6 DOF KUKA robot. Specimens were size matched to +2 mm for the medial-to-lateral width of the medial tibial hemiplateaus. Three specimens served as allograft recipient knees and three served as donor knees. Recipient knees were first tested in their native state and then tested with size-matched medial tibial hemiplateau shell grafts (n=3) prepared from the donor knees using custom-cut tab-in-slot and subchondral drilling techniques. Tekscan sensors were placed in the joint spaces to evaluate the loading conditions under 90N biaxial loading at full extension of the knee before and after graft placement. The I-Scan system used in conjunction analyzed the total force, pressure distribution, peak pressure, and center of force within the joint space.Data demonstrated significant difference (p<0.05) in joint space loading after graft implantation compared to controls in both lateral and medial tibial plateaus. The I-Scan pressure mapping system displayed changes in femoral condylar contact points as well.The results demonstrated that joint space loading was significantly different (p<0.05) between all preoperative and postoperative cadaveric specimens. Despite the best efforts to size match grafts, slight differences in the host's joint geometry resulted in shifts of contact areas between the tibial plateau and femoral condyle therefore causing either an increase or decrease in pressure measured by the sensor. This concludes that accuracy in graft size matching is extremely important to restoring close to normal loading across the joint and this can be further ensured through postoperative care customized to the patient after OCA surgery.

Tibiofemoral Contact Forces Influence Intraoperative Kinematic Pivot Pattern Dependent on Posterior Cruciate Ligament Resection in Primary Total Knee Arthroplasty.

Background:Optimizing knee kinematics has the potential to increase patient satisfaction with total knee arthroplasty (TKA); however the ability to enact a particular kinematic pattern is variable and inconsistent. The purpose of this study was to determine whether intraoperative contact forces were predictive and can potentially drive a particular kinematic pivot pattern.Methods:All TKAs used sensor-embedded tibial trials to intraoperatively measure medial and lateral compartment forces, and the associated condylar contact points were used to calculate kinematic pivot patterns between preceding flexion angles.Results:After exclusions, 157 TKAs were analyzed. For posterior cruciate ligament–intact TKAs, no predictors of lateral pivot were identified in early flexion; however, increased medial compartment force and increased lateral compartment force were predictors of medial and lateral pivots for mid and late flexion, respectively (P ≤ 0.037). For posterior cruciate ligament–resected TKAs, increased lateral compartment force was a predictor of lateral pivot in early and midflexion (P ≤ 0.031) but not late flexion.Conclusion:The tibiofemoral compartment with greater contact force exhibited less anteroposterior translation at certain flexion ranges and correlated with kinematic pivot patterns. This information may benefit surgeons who are attempting to facilitate a particular kinematic pattern. Further research is recommended to confirm that intraoperative kinematics correlate with weight-bearing postoperative kinematics and clinical outcomes.

Assessment of paradoxical anterior translation in a CR total knee prosthesis coupling dynamic RSA and FE techniques

PurposeThe study aims were to assess the kinematic data, Internal-External (IE) rotation, and Antero-Posterior (AP) translation of the contact points between the femoral condyles and polyethylene insert and to develop a combined dynamic RSA-FE (Radiostereometric – Finite Element) model that gives results congruent with the literature.MethodsA cohort of 15 patients who underwent cemented cruciate-retaining highly congruent mobile-bearing total knee arthroplasty were analyzed during a sit-to-stand motor task. The kinematical data from Dynamic RSA were used as input for a patient-specific FE model to calculate condylar contact points between the femoral component and polyethylene insert.ResultsThe femoral component showed an overall range about 4 mm of AP translation during the whole motor task, and the majority of the movement was after 40° of flexion. Concerning the IE rotation, the femoral component started from an externally rotate position (− 6.7 ± 10°) at 80° of flexion and performed an internal rotation during the entire motor task. The overall range of the IE rotation was 8.2°.ConclusionsDuring the sit to stand, a slight anterior translation from 40° to 0° of flexion of the femoral component with respect to polyethylene insert, which could represent a paradoxical anterior translation. Despite a paradoxical anterior femoral translation was detected, the implants were found to be stable. Dynamic RSA and FE combined technique could provide information about prosthetic component’s stress and strain distribution and the influence of the different designs during the movement.

Asymmetrical tibial polyethylene geometry-cruciate retaining total knee arthroplasty does not fully restore in-vivo articular contact kinematics during strenuous activities.

A new CR TKA design with concave medial and convex lateral tibial polyethylene bearing components was introduced recently to improve functional outcomes. This study aimed to investigate in-vivo articular contact kinematics in unilateral asymmetrical tibial polyethylene geometry CR TKA patients during strenuous knee flexion activities. Fifteen unilateral CR TKA patients (68.4 ± 5.8years; 6 male/9 female) were evaluated for both knees during sit-to-stand, single-leg deep lunges and step-ups using validated combined computer tomography and dual fluoroscopic imaging system. Medial and lateral condylar contact positions were quantified during weight-bearing flexion activities. The Wilcoxon signed-rank test was performed to determine if there is a significant difference in articular contact kinematics during strenuous flexion activities between CR TKA and the non-operated knees. Contact excursions of the lateral condyle in CR TKAs were significantly more anteriorly located than the contralateral non-operated knee during sit-to-stand (3.7 ± 4.8mm vs - 7.8 ± 4.3mm) and step-ups (- 1.5 ± 3.2mm vs - 6.3 ± 5.8mm). Contact excursions of the lateral condyle in CR TKAs were significantly less laterally located than the contralateral non-operated knee during sit-to-stand (21.4 ± 2.8mm vs 24.5 ± 4.7mm) and single-leg deep lunges (22.6 ± 4.4mm vs 26.2 ± 5.7mm, p < 0.05). Lateral condyle posterior rollback was not fully restored in CR TKA patients during sit-to-stand (9.8 ± 6.7mm vs 12.9 ± 8.3mm) and step-ups (8.1 ± 4.8mm vs 12.2 ± 6.4mm). Lateral pivoting patterns were observed in 80%, 73% and 69% of patients during sit-to-stand, step-ups and single-leg deep lunges respectively. Although lateral femoral rollback and lateral pivoting patterns were observed during strenuous functional daily activities, asymmetric contact kinematics still persisted in unilateral CR TKA patients. This suggests the specific investigated contemporary asymmetrical tibial polyethylene geometry CR TKA design evaluated in this study does not fully replicate healthy knee contact kinematics during strenuous functional daily activities. III.

The Impact of ACL Laxity on a Bicondylar Robotic Knee and Implications in Human Joint Biomechanics.

Elucidating the role of structural mechanisms in the knee can improve joint surgeries, rehabilitation, and understanding of biped locomotion. Identification of key features, however, is challenging due to limitations in simulation and in-vivo studies. In particular the coupling of the patello-femoral and tibio-femoral joints with ligaments and its impact on joint mechanics and movement is not understood. We investigate this coupling experimentally through the design and testing of a robotic sagittal plane model. We constructed a sagittal plane robot comprised of: 1) elastic links representing cruciate ligaments; 2) a bi-condylar joint; 3) a patella; and 4) actuator hamstrings and quadriceps. Stiffness and geometry were derived from anthropometric data. [Formula: see text] squatting tests were executed at speeds of [Formula: see text] over a range of anterior cruciate ligament (ACL) slack lengths. Increasing ACL length compromised joint stability, yet did not impact quadriceps mechanical advantage and force required for squat. The trend was consistent through varying condyle contact point and ligament force changes. The geometry of the condyles allows the ratio of quadriceps to patella tendon force to compensate for contact point changes imparted by the removal of the ACL. Thus the system maintains a constant mechanical advantage. The investigation uncovers critical features of human knee biomechanics. Findings contribute to understanding of knee ligament damage, inform procedures for knee surgery and orthopaedic implant design, and support design of trans-femoral prosthetics and walking robots. Results further demonstrate the utility of robotics as a powerful means of studying human joint biomechanics.

Relationship Between Ligament Forces and Contact Forces in Balancing at Total Knee Surgery

BackgroundSpacer blocks, tensors, or instrumented tibial trials are current methods of balancing the knee during surgery but there are no current techniques for measuring ligament forces. Our goal was to study the relationship between the collateral ligament forces and the condylar contact forces to determine whether there was equivalence. MethodsA test rig was constructed modeling an artificial knee joint with collateral ligaments. The ligament forces as well as the lateral and medial tibial contact forces were measured during flexion for different positions of the femoral component on the femur, producing a set of forces for the simulated conditions. A regression analysis was used to study the correlation between the ligament and contact forces. ResultsThe combined medial and lateral ligament and contact forces showed a linear relation with a correlation coefficient of 0.98. For the medial and lateral sides separately, the correlations were 0.85 and 0.88, respectively, with more than 80% of points within a ±25% deviation from the linear relations. This deviation from the linear correlation is linked to differences in medial-lateral femoral-tibial contact point locations at different flexion angles. ConclusionWithin balancing accuracies generally achieved at surgery, the collateral ligament forces were linearly correlated to the condylar contact forces. These forces can also be equally correlated to the distraction forces as well as the moments at which condylar liftoff would occur from varus-valgus moments. This indicated a unification of the different balancing parameters, and hence such quantitative methods can be used interchangeably.

Stair Climbing and High Knee Flexion Activities in Bi-Cruciate Retaining Total Knee Arthroplasty: In Vivo Kinematics and Articular Contact Analysis

BackgroundBi-cruciate retaining (BCR) total knee arthroplasty (TKA) preserves both anterior and posterior cruciate ligaments with the potential to restore normal posterior femoral rollback and joint kinematics. However, there is limited information regarding articular contact behavior in the contemporary BCR TKA design during high knee flexion activities. This study aimed to investigate the articular knee contact performance in unilateral BCR TKA patients during strenuous flexion activities. MethodsTwenty-nine unilateral BCR TKA patients were evaluated for both knees during single deep lunges, step-ups, and sit-to-stand (STS) using a validated combined computer tomography and dual fluoroscopic imaging system. Medial and lateral condylar contact positions were quantified during weight-bearing flexion. ResultsContact excursions of the lateral condyle in BCR TKAs were significantly more anteriorly located than the contralateral non-operated knees during STS (−4.9 ± 3.1 vs −9.7 ± 4.6 mm, P < .05), single deep lunge (−5.7 ± 3.2 vs −10.0 ± 4.5 mm, P < .05), and step-ups (−4.8 ± 3.6 vs −9.1 ± 3.9 mm, P < .05). Contact points of BCR TKAs indicated reduced femoral external rotation during STS (2.1 ± 4.8° vs 7.7 ± 5.4°, P < .05), single deep lunges (1.8 ± 4.8° vs 7.0 ± 7.1°, P < .05), and step-ups (0.1 ± 4.1° vs 6.2 ± 4.9°, P < .05). Medial pivoting patterns were observed in only 59%, 56%, and 48% of the BCR TKA knees for step-ups, STS, and single deep lunge, respectively. ConclusionThe contemporary BCR TKA design demonstrated asymmetric femoral rollback, medial translation, as well as lateral pivoting in about half of the patient cohort, suggesting that in vivo tibiofemoral kinematic parameters were not fully restored in BCR patients during strenuous flexion activities.

Improvement in the medial meniscus posterior shift following anterior cruciate ligament reconstruction.

Anterior cruciate ligament (ACL) reconstruction can reduce the risk of developing osteoarthritic knees. The goals of ACL reconstruction are to restore knee stability and reduce post-traumatic meniscal tears and cartilage degradation. A chronic ACL insufficiency frequently results in medial meniscus (MM) injury at the posterior segment. How ACL reconstruction can reduce the deformation of the MM posterior segment remains unclear. In this study, we evaluated the form of the MM posterior segment and anterior tibial translation before and after ACL reconstruction using open magnetic resonance imaging (MRI). Seventeen patients who underwent ACL reconstructions without MM injuries were included in this study. MM deformation was evaluated using open MRI before surgery and 3months after surgery. We measured medial meniscal length (MML), medial meniscal height (MMH), medial meniscal posterior body width (MPBW), MM-femoral condyle contact width (M-FCW) and posterior tibiofemoral distance (PTFD) at knee flexion angles of 10° and 90°. There were no significant pre- and postoperative differences during a flexion angle of 10°. At a flexion angle of 90°, MML decreased from 43.7±4.5 to 41.4±4.5mm (P<0.001), MMH from 7.5±1.4 to 6.9±1.4mm (P=0.006), MPBW from 13.1±2.0 to 12.2±1.9mm (P<0.001) and M-FCW from 10.0±1.5 to 8.5±1.5mm (P<0.001) after ACL reconstruction. The PTFD increased from 2.1±2.8 to 2.7±2.4mm after ACL reconstruction (P=0.015). ACL reconstruction affects the contact pattern between the MM posterior segment and medial femoral condyle and can reduce the deformation of the MM posterior segment in the knee-flexed position by reducing abnormal anterior tibial translation. It possibly prevents secondary injury to the MM posterior segment and cartilage that progresses to knee osteoarthritis. IV.

Knee Cartilage Thickness, T1ρ and T2 Relaxation Time Are Related to Articular Cartilage Loading in Healthy Adults.

Cartilage is responsive to the loading imposed during cyclic routine activities. However, the local relation between cartilage in terms of thickness distribution and biochemical composition and the local contact pressure during walking has not been established. The objective of this study was to evaluate the relation between cartilage thickness, proteoglycan and collagen concentration in the knee joint and knee loading in terms of contact forces and pressure during walking. 3D gait analysis and MRI (3D-FSE, T1ρ relaxation time and T2 relaxation time sequence) of fifteen healthy subjects were acquired. Experimental gait data was processed using musculoskeletal modeling to calculate the contact forces, impulses and pressure distribution in the tibiofemoral joint. Correlates to local cartilage thickness and mean T1ρ and T2 relaxation times of the weight-bearing area of the femoral condyles were examined. Local thickness was significantly correlated with local pressure: medial thickness was correlated with medial condyle contact pressure and contact force, and lateral condyle thickness was correlated with lateral condyle contact pressure and contact force during stance. Furthermore, average T1ρ and T2 relaxation time correlated significantly with the peak contact forces and impulses. Increased T1ρ relaxation time correlated with increased shear loading, decreased T1ρ and T2 relaxation time correlated with increased compressive forces and pressures. Thicker cartilage was correlated with higher condylar loading during walking, suggesting that cartilage thickness is increased in those areas experiencing higher loading during a cyclic activity such as gait. Furthermore, the proteoglycan and collagen concentration and orientation derived from T1ρ and T2 relaxation measures were related to loading.

3D active-passive response of human knee joint in gait is markedly altered when simulated as a planar 2D joint.

Musculoskeletal models of the lower extremity make a number of important assumptions when attempting to estimate muscle forces and tibiofemoral compartmental loads in activities such as gait. The knee is commonly idealized as a planar 2D joint in the sagittal plane with no consideration of motions and equilibrium in remaining planes. With muscle forces predicted, the static equilibrium in the frontal plane is then used to estimate compartmental loads neglecting also joint passive resistance and assuming condylar contact centers. We aimed here to comprehensively investigate the effects of such assumptions on predicted results. While simulating gait and using a hybrid lower extremity model that incorporates a detailed validated 3D finite element model of the knee joint, analyses are repeated with out-of-sagittal plane rotations and moment equilibrium equations neglected (2D model) and tibial compartmental forces estimated using equilibrium in the frontal plane while disregarding passive resistance and assuming fixed contact centers (1D model). Large unbalanced out-of-sagittal plane moments reaching peaks of 30 Nm abduction moment and 12 Nm internal moment at 25% stance period are computed that are overlooked in the 2D model. Consideration of the knee as a planar 2D joint substantially diminishes muscle forces, anterior cruciate ligament force and tibiofemoral contact forces/stresses when compared to the 3D reference model. Total tibiofemoral contact force peaks at 25% stance at 4.2 BW in the 3D model that drops to 3.0 BW in the 2D model. The location of contact centers on each plateau also noticeably alters (by as much as 5 mm). Tibiofemoral contact forces further change when the location of contact centers on each plateau is fixed. Results highlight the importance of accurate simulation of 3D motions and equilibrium equations as well as passive joint properties and contact centers.

In vivo six‐degree‐of‐freedom knee‐joint kinematics in overground and treadmill walking following total knee arthroplasty

No data are available to describe six-degree-of-freedom (6-DOF) knee-joint kinematics for one complete cycle of overground walking following total knee arthroplasty (TKA). The aims of this study were firstly, to measure 6-DOF knee-joint kinematics and condylar motion for overground walking following TKA; and secondly, to determine whether such data differed between overground and treadmill gait when participants walked at the same speed during both tasks. A unique mobile biplane X-ray imaging system enabled accurate measurement of 6-DOF TKA knee kinematics during overground walking by simultaneously tracking and imaging the joint. The largest rotations occurred for flexion-extension and internal-external rotation whereas the largest translations were associated with joint distraction and anterior-posterior drawer. Strong associations were found between flexion-extension and adduction-abduction (R2 = 0.92), joint distraction (R2 = 1.00), and anterior-posterior translation (R2 = 0.77), providing evidence of kinematic coupling in the TKA knee. Although the measured kinematic profiles for overground walking were grossly similar to those for treadmill walking, several statistically significant differences were observed between the two conditions with respect to temporo-spatial parameters, 6-DOF knee-joint kinematics, and condylar contact locations and sliding. Thus, caution is advised when making recommendations regarding knee implant performance based on treadmill-measured knee-joint kinematic data. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1634-1643, 2017.

Finite element analysis of a condylar support prosthesis to replace the temporomandibular joint

This paper presents a finite element study of a temporomandibular joint (TMJ) prosthesis in which the mandibular component sits on the condyle after removal of only the diseased articular surface and minimal amount of condylar bone. The condylar support prosthesis (CSP) is customised to fit the patient and allows a large part of the joint force to be transmitted through the condyle to the ramus, rather than relying only on transfer of the load by the screws that fix the prosthesis to the ramus. The 3-dimensional structural finite element analysis compared a design of CSP with a standard commercial prosthesis and one that was modified to fit the ramus, to relate the findings to the different designs and geometrical features. The models simulated an incisal bite under high loading. In the CSP and in its fixation screws, the stresses were much lower than those in the other 2 prostheses and the bone strains were at physiological levels. The CSP gives a more physiological form of load transfer than is possible without the condylar contact, and considerably reduces the amount of strain on the bone around the screws.

Using a surrogate contact pair to evaluate polyethylene wear in prosthetic knee joints.

With recent improvements to the properties of ultra-high molecular weight polyethylene (UHMWPE) used in joint replacements, prosthetic knee and hip longevity may extend beyond two decades. However, it is difficult and costly to replicate such a long in vivo lifetime using clinically relevant in vitro wear testing approaches such as walking gait joint simulators. We advance a wear test intermediate in complexity between pin-on-disk and knee joint simulator tests. The test uses a surrogate contact pair, consisting of a surrogate femoral and tibial specimen that replicate the contact mechanics of any full-scale knee condyle contact pair. The method is implemented in a standard multi-directional pin-on-disk wear test machine, and we demonstrate its application via a two-million-cycle wear test of three different UHMWPE formulations. Further, we demonstrate the use of digital photography and image processing to accurately quantify fatigue damage based on the reduced transmission of light through a damage area in a UHMWPE specimen. The surrogate contact pairs replicate the knee condyle contact areas within -3% to +12%. The gravimetric wear test results reflect the dose of crosslinking radiation applied to the UHMWPE: 35 kGy yielded a wear rate of 7.4 mg/Mcycles, 55 kGy yielded 1.0 mg/Mcycles, and 75 kGy (applied to a 0.1% vitamin E stabilized UHMWPE) yielded 1.5 mg/Mcycles. A precursor to spalling fatigue is observed and precisely measured in the radiation-sterilized (35 kGy) and aged UHMWPE specimen. The presented techniques can be used to evaluate the high-cycle fatigue performance of arbitrary knee condyle contact pairs under design-specific contact stresses, using existing wear test machines. This makes the techniques more economical and well-suited to standardized comparative testing.

In vivo kinematic effects of ball and socket third condyle as a post-cam mechanism in tri-condylar knee implants

BackgroundTri-condylar implants containing a ball and socket third condyle as a post-cam mechanism were developed to accommodate a lifestyle requiring frequent deep flexion activities. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during a deep knee bend activity, and to confirm the contact status of the ball and socket joint. MethodsSeventeen knees implanted with tri-condylar implants were analyzed using a 3D to 2D registration approach. A distance of less than 1mm denoted ball and socket contact. Medial and lateral contact positions and axial rotation were compared before and after contact. Moreover, the contact position at the third condyle and the center of the ball joint were analyzed. ResultsAfter the third condyle contact, posterior translation of the medial and lateral contact positions increased considerably. Meanwhile, the angular rotation remained still. The center of the third condyle did not move after contact, and the contact position at the third condyle remained low. ConclusionsThe third condyle induced intensive posterior translation of both condyles, and did not prevent axial rotation, which was proved to work properly as a posterior stabilizing post-cam mechanism.

American Society of Biomechanics Clinical Biomechanics Award 2013: Tibiofemoral contact location changes associated with lateral heel wedging—A weight bearing MRI study

BackgroundVertically open magnetic resonance imaging permits study of knee joint contact during weight bearing. Lateral wedging is a low cost intervention for knee osteoarthritis that may influence load distribution and contact. This study assessed the ability of feedback-assisted weight bearing magnetic resonance imaging to detect changes in tibiofemoral contact associated with lateral wedging. MethodsOne knee in each of fourteen subjects with symptomatic knee osteoarthritis was studied, without specification of compartmental involvement. Knees were imaged during upright standing and at 20° knee flexion. Bilateral external heel wedges were used to provide non-wedged and 5° lateral wedging conditions. Computer modeling was used to measure the medial and lateral compartment contact patch center coordinates on the tibial plateau and the respective contact areas. FindingsLateral heel wedging in flexion was associated with a significant anterior shift of the contact patch of the lateral femoral condyle. Changes with knee flexion were similar to previous reports: both medial and lateral contact centers moved posteriorly with flexion, and lateral condyle contact also moved laterally. Lateral condyle contact area significantly reduced with flexion, while lateral wedging did not significantly affect contact areas. InterpretationIn symptomatic knee osteoarthritis patients standing in knee flexion, weight bearing magnetic resonance imaging recorded an anterior shift of lateral condyle contact in response to lateral heel wedging. Future studies may investigate lateral wedging effects more specifically in candidates for this clinical intervention.

Detecting condylar contact loss using single-plane fluoroscopy: A comparison with in vivo force data and in vitro bi-plane data

Knee contact mechanics play an important role in knee implant failure and wear mechanics. Femoral condylar contact loss in total knee arthroplasty has been reported in some studies and it is considered to potentially induce excessive wear of the polyethylene insert.Measuring in vivo forces applied to the tibial plateau with an instrumented prosthesis is a possible approach to assess contact loss in vivo, but this approach is not very practical. Alternatively, single-plane fluoroscopy and pose estimation can be used to derive the relative pose of the femoral component with respect to the tibial plateau and estimate the distance from the medial and lateral parts of the femoral component towards the insert. Two measures are reported in the literature: lift-off is commonly defined as the difference in distance between the medial and lateral condyles of the femoral component with respect to the tibial plateau; separation is determined by the closest distance of each condyle towards the polyethylene insert instead of the tibia plateau.In this validation study, lift-off and separation as measured with single-plane fluoroscopy are compared to in vivo contact forces measured with an instrumented knee implant. In a phantom study, lift-off and separation were compared to measurements with a high quality bi-plane measurement.The results of the in vivo contact-force experiment demonstrate a large discrepancy between single-plane fluoroscopy and the in vivo force data: single-plane fluoroscopy measured up to 5.1mm of lift-off or separation, whereas the force data never showed actual loss of contact. The phantom study demonstrated that the single-plane setup could introduce an overestimation of 0.22mm±±0.36mm. Correcting the out-of-plane position resulted in an underestimation of medial separation by −0.20mm±±0.29mm.In conclusion, there is a discrepancy between the in vivo force data and single-plane fluoroscopic measurements. Therefore contact loss may not always be determined reliably by single plane fluoroscopy analysis.

Femoral Condylar Contact Points Start and Remain Posterior in High Flexing Patients

This study compares kinematic patterns of 136 patients following total knee arthroplasty with high post-operative knee flexion (HighFlex) versus kinematics of 114 patients with limited knee flexion (LowFlex) using a blocked stratified random sampling study design to reduce confounding and bias. The kinematics was collected using fluoroscopy and 2D to 3D registration for a weight-bearing deep knee bend activity. Both the lateral and the medial condylar contact positions for the HighFlex subjects were significantly more posterior than the LowFlex subjects at full extension and remained that way at all flexion angles. The amount translation of the contact points, axial orientation angle and axial rotation were found to be similar for the two groups. Lift-off was significantly higher in the LowFlex indicating mid-flexion instability.

Constraints in posterior-stabilised TKA kinematics: a comparison of two generations of an implant

This study tests the hypothesis that the design changes incorporated in the newer generation Triathlon posterior-stabilised TKA design result in kinematics that more closely reproduce the kinematics observed in healthy knees than those achieved by the older generation Scorpio posterior-stabilised TKA design. Eleven patients with Triathlon posterior-stabilised TKA, twelve patients with Scorpio posterior-stabilised TKA, and 22 subjects with normal asymptomatic knees underwent fluoroscopic assessment of the knee during a step-up exercise and a weight-bearing deep knee bend. Two-dimensional and three-dimensional knee kinematics were assessed including the maximum flexion, the patella tendon angle (PTA), the patella flexion angle (PFA), the minimum distance between cam and post, and the tibio-femoral contact positions. The average maximum flexion achieved was 114° (SD 3°), 91° (SD 10°), and 143° (SD 14°) for the Triathlon, Scorpio, and Normal groups. The average cam/post mechanism engagement was at 63° (SD 24°) and 82° (SD 16°) for the Triathlon and Scorpio groups. The condylar contact points showed a paradoxical anterior slide for the Scorpio group which was not present in the Triathlon group. The PTA and PFA values of both implants showed significant differences from normal. Overall, the Triathlon implant design, as compared to Scorpio TKA, produced kinematics closer to that of normal knees as proposed by the hypothesis. However, despite being closer to normal, the kinematics exhibited by the Triathlon group were still different from normal. A comparison of kinematic performance, taking into account altered design parameters, will contribute to improved understanding and future design considerations.

Paper 111: Comparative Anatomy of the Knee and the ACL

The function of knee is determined by its complex anatomy. Anterior cruciate ligament (ACL) is an important structure of knee and controls the stability of knee, whereas the sizes and shapes of condyles determine the anterior-posterior and rotational motion of the knee. A comparison of the basic anatomy of modern human knee to ancestral human knees, and to those of other animals (mostly primates) can provide novel insights into the natural history of human knee structure and function. This study will help surgeons to better understand the correlation between anatomy and function. 1 - Review ACL anatomy and osseous landmarks in human and different animals, and correlate the anatomy of the ACL with knee function. 2 - Measure and compare the sizes and shapes of the medial and lateral femoral condyles. 1 - Animals in greater need of rotation of the knee will present with a larger ACL, more specifically of the PL bundle. 2 - The size of the overall medial femoral condyle contact area will be bigger than the size of lateral femoral condyle contact area. Animals with greater rotation will have a larger ratio between condyle sizes. 3 - The size of the distal femoral contact area of both condyles (contact area in extension) will be different than the posterior femoral contact area of condyles (contact area in flexion). Animal anatomy was studied on freshly frozen specimens. The ACL anatomy was studied by MR imaging, followed by dissection. Bones from different species were studied by using three-dimensional laser photography and 3D CT scans and measurements were done on specific software. We have found a large variety of ACL anatomy in the Animal Kingdom. The Nubian goat (Capra hircus), the springbok (Antidorcas marsupialis), the pig (Sus scrofa domestica) and the Rhesus monkey (Macaca mulatta) have three ACL bundles (AM, IM, PL). Human (Homo sapiens) has 2 bundles. The ostrich (Struthio camelus) and the chicken (Gallus gallus) have only one bundle. By studying the complexities of functional morphologic features of the knee in different animal species we can help surgeons better understand knee kinematics and the role of each ACL bundle in human being and this knowledge will help surgeons reconstruct anatomy more accurately and therefore perform a more precise knee surgery.

The role of patient, surgical, and implant design variation in total knee replacement performance

Clinical studies demonstrate substantial variation in kinematic and functional performance within the total knee replacement (TKR) patient population. Some of this variation is due to differences in implant design, surgical technique and component alignment, while some is due to subject-specific differences in joint loading and anatomy that are inherently present within the population. Combined finite element and probabilistic methods were employed to assess the relative contributions of implant design, surgical, and subject-specific factors to overall tibiofemoral (TF) and patellofemoral (PF) joint mechanics, including kinematics, contact mechanics, joint loads, and ligament and quadriceps force during simulated squat, stance-phase gait and stepdown activities. The most influential design, surgical and subject-specific factors were femoral condyle sagittal plane radii, tibial insert superior–inferior (joint line) position and coronal plane alignment, and vertical hip load, respectively. Design factors were the primary contributors to condylar contact mechanics and TF anterior–posterior kinematics; TF ligament forces were dependent on surgical factors; and joint loads and quadriceps force were dependent on subject-specific factors. Understanding which design and surgical factors are most influential to TKR mechanics during activities of daily living, and how robust implant designs and surgical techniques must be in order to adequately accommodate subject-specific variation, will aid in directing design and surgical decisions towards optimal TKR mechanics for the population as a whole.