Abstract. Introduction. Osteoarthritis (OA) affects more than four million people in the UK alone. Bone marrow lesions (BMLs) are a common feature of subchondral bone pathology in OA. Both bone volume fraction and mineral density within the BML are abnormal. The aim of this study was to investigate the effect of a potential treatment (bone augmentation) for BMLs on the knee joint mechanics in cases with healthy and fully degenerated cartilage, using finite element (FE) models of the joint to study the effect of BML size. Methods. FE models of a human tibiofemoral joint were created based on models from the Open Knee project (simtk.org). Following initial mesh convergence studies, each model was manipulated in ScanIP (Synopsys-Simpleware, UK) to incorporate a BML 2mm below the surface of the tibial contact region. Models representing extreme cases (healthy cartilage, no cartilage; BML region as an empty cavity or filled with bone substitution material (200GPa)) were generated, each with different sizes of BML. Models were tested under a representative physiological load of 2kN. Results. In the absence of cartilage, the stress distribution through the bone was more localized with higher peaks in comparison to models with cartilage. In models with cartilage, BML cavity led to changes in the stress distribution through the tibia, with increasing BML size leading to higher stresses. When the BML region was represented by the substitution material very little difference was seen in comparison to models with no defect at all. Conclusions. The results of this study illustrate how the cartilage and bone behaviour in the tibiofemoral joint are linked, and that augmentation of a BML with a bone substitute has the potential to reduce adverse loading of the surrounding bone. Funders. EPSRC, NIHR. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

In an attempt to alleviate symptoms of the disease, patients with knee osteoarthrosis (KOA) frequently alter their gait patterns. Understanding the underlying pathomechanics and identifying KOA phenotypes is essential for improving treatments. We aimed to investigate altered kinematics in patients with KOA to identify subgroups.

Sixty-six patients with symptomatic KOA scheduled for total knee arthroplasty and 12 age-matched healthy volunteers with asymptomatic knees were included. We used k-means to separate the patients based on dynamic radiostereometric assessed knee kinematics. Ligament lesions, KOA score, and clinical outcome were assessed by magnetic resonance imaging, radiographs, and patient reported outcome measures, respectively.

We identified four clusters that were supported by clinical characteristics. Compared with the healthy group; The flexion group (n=20): revealed increased flexion, greater adduction, and joint narrowing and consisted primarily of patients with medial KOA. The abduction group (n=17): revealed greater abduction, joint narrowing and included primarily patients with lateral KOA. The anterior draw group (n=10): revealed greater anterior draw, external tibial rotation, lateral tibial shift, adduction, and joint narrowing. This group was composed of patients with medial KOA, some degree of anterior cruciate ligament lesion and the greatest KOA score. The external rotation group (n=19): revealed greater external tibial rotation, lateral tibial shift, adduction, and joint narrowing while no anterior draw was observed. This group included primarily patients with medial collateral and posterior cruciate ligament lesions.

Patients with KOA can, based on their gait patterns, be classified into four subgroups, which relate to their clinical characteristics. The findings add to our understanding of associations between disease pathology characteristics in the knee and the pathomechanics in patients with KOA. A next step is to investigate if patients in the pathomechanic clusters have different outcomes following total knee arthroplasty.

Autologous osteochondral grafting has demonstrated positive outcomes for treating articular cartilage defects by replacing the damaged region with a cylindrical graft consisting of bone with a layer of cartilage, taken from a non-loadbearing region of the knee. Despite positive clinical use, factors that cause graft subsidence or poor integration are relatively unknown. The aim of this study was to develop finite element (FE) models of osteochondral grafts within a tibiofemoral joint and to investigate parameters affecting osteochondral graft stability. Initial experimental tests on cadaveric femurs were performed to calibrate the bone properties and graft-bone frictional forces for use in corresponding FE models, generated from µCT scan data. The effects of cartilage defects and osteochondral graft repair were measured by examining contact pressure changes using in vitro tests on a single cadaveric human tibiofemoral joint. Six defects were created in the femoral condyles which were subsequently treated with osteochondral autografts or metal pins. Matching µCT scan-based FE models were created, and the contact patches were compared. Sensitivity to graft bone properties was investigated. The bone material properties and graft-bone frictional forces were successfully calibrated from the initial tests with good resulting levels of agreement (CCC=0.87). The tibiofemoral joint experiment provided a range of cases to model. These cases were well captured experimentally and represented accurately in the FE models. Graft properties relative to host bone had large effects on immediate graft stability despite limited changes to resultant cartilage contact pressure. Model confidence was built through extensive validation and sensitivity testing, and demonstrated that specimen-specific properties were required to accurately represent graft behaviour. The results indicate that graft bone properties affect the immediate stability, which is important for the selection of allografts and design of future synthetic grafts. Acknowledgements. Supported by the EPSRC-EP/P001076

Abstract. Objectives. Investigate Magnetic Resonance Imaging (MRI) as an alternative to Computerised Tomography (CT) when calculating kinematics using Biplane Video X-ray (BVX) by quantifying the accuracy of a combined MRI-BVX methodology by comparing with results from a gold-standard bead-based method. Methods. Written informed consent was given by one participant who had four tantalum beads implanted into their distal femur and proximal tibia from a previous study. Three-dimensional (3D) models of the femur and tibia were segmented (Simpleware Scan IP, Synopsis) from an MRI scan (Magnetom 3T Prisma, Siemens). Anatomical Coordinate Systems (ACS) were applied to the bone models using automated algorithms. 1. The beads were segmented from a previous CT and co-registered with the MRI bone models to calculate their positions. BVX (60 FPS, 1.25 ms pulse width) was recorded whilst the participant performed a lunge. The beads were tracked, and the ACS position of the femur and tibia were calculated at each frame (DSX Suite, C-Motion Inc.). The beads were digitally removed from the X-rays (MATLAB, MathWorks) allowing for blinded image-registration of the MRI models to the radiographs. The mean difference and standard deviation (STD) between bead-generated and image-registered bone poses were calculated for all degrees of freedom (DOF) for both bones. Using the principles defined by Grood and Suntay. 2. , 6 DOF kinematics of the tibiofemoral joint were calculated (MATLAB, MathWorks). The mean difference and STD between these two sets of kinematics were calculated. Results. The absolute mean femur and tibia ACS position differences (Table 1) between the bead and image-registered poses were found to be within 0.75mm for XYZ, with all STD within ±0.5mm. Mean rotation differences for both bones were found to be within 0.2º for XYZ (Table 1). The absolute mean tibiofemoral joint translations (Table 1) were found to be within ±0.7mm for all DOF, with the smallest absolute mean in compression-distraction. The absolute mean tibiofemoral rotations were found to be within 0.25º for all DOF (Table 1), with the smallest mean was found in abduction-adduction. The largest mean and STD were found in internal-external rotation due to the angle of the X-rays relative to the joint movement, increasing the difficulty of manual image registration in that plane. Conclusion. The combined MRI-BVX method produced bone pose and tibiofemoral kinematics accuracy similar to previous CT results. 3. This allows for confidence in future results, especially in clinical applications where high accuracy is needed to understand the effects of disease and the efficacy of surgical interventions. Acknowledgements: This research was supported by the Engineering and Physical Sciences Research Council (EPSRC) doctoral training grant (EP/T517951/1). Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Summary Statement. An MRI-derived subject-specific finite element model of a knee joint was loaded with subject-specific kinetic data to investigate stress and strain distribution in knee cartilage during the stance phase of gait in-vivo. Introduction. Finite element analysis (FEA) has been widely used to predict the local stress and strain distribution at the tibiofemoral joint to study the effects of ligament injury, meniscus injury and cartilage defects on soft tissue loading under different loading conditions. Previous studies have focused on static FEA of the tibiofemoral joint, with few attempts to conduct subject-specific FEA on the knee during physical activity. In one FEA study utilising subject-specific loading during gait, the knee was simplified by using linear springs to represent ligaments. To address the gap that no studies have performed subject-specific FEA at the tibiofemoral joint with detailed structures, the present study aims to develop a highly detailed subject-specific FE model of knee joint to precisely simulate the stress distribution at knee cartilage during the stance phase of the gait cycle. Method. A detailed three-dimensional model of a healthy human knee was developed from MRI images of a living subject, including the main anatomical structures (bones, all principal ligaments, menisci and articular cartilages). The femur, tibia and fibula were considered as rigid bodies, while the menisci and articular cartilage were modelled as linearly elastic, isotropic and homogeneous while the ligaments were considered to be hyperelastic. Loading and boundary condition assignment was based on the kinematic and kinetic data recorded during gait analysis. Ten time intervals during the stance phase of gait were separately simulated to quantify the time–dependent stress distribution throughout the cycle from heel-strike to toe-off. Loading condition of the tibiofemoral joint varys during the gait cycle since the joint angle changes from extension to flextion, therefore different joint angles at relative time interval were determined to accurately simulate the varing loading condition. Results. The compressive stress and tensile strain distributions in the femoral cartilage, tibia cartilage and menisci of each selected time interval during the stance phase of gait cycle were quantified and corresponded to specific amount of varus/valgus knee moment obtained by inverse dynamics analysis of the kinematic and kinetic data from gait analysis. Therefore a correlation between stress/strain and the frontal movement was established and analysed. For example, at 10% of stance phase, the stress concentration was observed on the lateral compartment due to the valgus moment created at heel strike. At the next interval, the stress concentration shifted to the medial side as the frontal knee moment shifted to a varus orientation. Discussion. The results suggest that the stress distribution of tibiofemoral articular cartilage is qualitatively consistent with the valgus and varus moment observed during the stance phase of gait. The methods described could be applied to investigate the effects of injury and reconstruction on stress distribution within the tibiofemoral joint

Non-invasive, in vivo measurement of the three-dimensional (3-D) motion of the tibiofemoral joint is essential for the study of the biomechanics and functional assessment of the knee. Real-time magnetic resonance imaging (MRI) techniques enable the measurement of dynamic motions of the knee with satisfactory image quality and free of radiation exposures but are limited to planar motions in selected slice(s). The aims of the current study were to propose a slice-to-volume registration (SVR) method in conjunction with dual-slice, real-time MRI for measuring 3-D tibiofemoral motion; and to evaluate its repeatability during passive knee flexion. Eight healthy young adults participated in the current study, giving informed written consent as approved by the Institutional Research Board. A 3-T MRI system (Verio, Siemens, Erlangen, Germany) incorporated with a neck matrix coil was used to collect the MRI data. A 3-D scanning using the VIBE sequence was used to collect the volumetric data of the knee at fully extended position (TR = 4.64 ms, TE = 2.3 ms, flip angle = 15°, in-plane resolution = 0.39 × 0.39 mm. 2. and slice thickness = 0.8 mm). A real-time MRI using the refocused radial FLASH sequence (TR = 4.3 ms, TE = 2.3 ms, flip angle = 20°, in-plane resolution = 1.0 × 1.0 mm. 2. , slice thickness = 6 mm) was used to acquire a pair of image slices of the knee at a frame rate of 3 fps during passive flexion. The volumetric MRI data sets were segmented for the femur and tibia/fibula to isolate the sub-volumes containing bone segments. A slice-to-volume registration method was then performed to determine the 3-D poses of the bones based on the spatial matching between sub-volume of the bones and the real-time image slices. The bone poses for all frames were used to calculate the rigid-body kinematics of the tibiofemoral joint in terms of the flexion/extension (FE), internal/external rotation (IR/ER), abduction/adduction (Abd/Add) and joint center translations along three anatomical axis of the tibia. The procedures were carried out five times for repeatability analysis. The standard deviation (SD) of the rigid-body kinematics for each frame from the five trials were calculated and then averaged across all frames to give quantitative measures of the repeatability of the kinematic variables. The repeatability analysis showed that the mean±SD of the averaged SD in FE, Abd/Add and IR/ER components across all subjects were 0.25±0.09, 0.46±0.13 and 0.77±0.16 degrees, respectively. The corresponding values for the joint translations in anterior/posterior, proximal/distal and medial/lateral directions were 0.21±0.04, 0.11±0.03 and 0.43±0.09 mm. An SVR method in conjunction with dual-slice real-time MRI has been successfully developed and its repeatability in measuring 3-D motion of the tibiofemoral joint evaluated. The results show that the proposed method is capable of providing rigid-body kinematics with sub-millimeter and sub-degree precision (repeatability). The proposed SVR method using real-time MRI will be a valuable tool for non-invasive, functional assessment of the knee without involving ionizing radiation, and may be further developed for joint stability assessment

Abstract. Objectives. The need for gender specific knee arthroplasty is debated. This research aimed to establish whether gender differences in patellar tendon moment arm (PTMA), a composite measure that characterises function of both the patellofemoral and tibiofemoral joints, are a consequence of knee size or other variation. Methods. PTMA about the instantaneous helical axis was calculated from positional data acquired using optical tracking. First, data post-processing was optimised, comparing four smoothing techniques (raw, Butterworth filtered, generalised cross-validation cubic spline interpolated and combined filtered/interpolated) using a fabricated knee. Then PTMA was measured during open-chain extension for N=24 (11 female) fresh-frozen cadaveric knees, with physiologically based loading and extension rates (420°/s) applied. Gender differences in PTMA were assessed before and after accounting for knee size with epicondylar width. Results. Combined smoothing enabled sub-mm accuracy (root-mean-squared (RMS) error 0.16mm, max error 0.47mm), whereas large errors were measured for raw (RMS 3.61mm, max 23.71mm), filtered-only (RMS 1.19mm, max 7.38mm) and interpolated-only (RMS 0.68mm, max 1.80mm) techniques. Before scaling, average PTMA throughout knee flexion was 46mm and mean, maximum, and minimum absolute values of PTMA were larger in males (mean differences >8mm, p<0.001), as were the PTMAs at terminal extension and flexion, and the change in PTMA from peak to terminal extension (differences >4mm, p<0.05). After scaling, the PTMA in deep flexion and the change in PTMA from peak to terminal extension were still larger in male knees (differences >2mm, p<0.05). The flexion angle of peak PTMA, unaffected by scaling, was closer to terminal extension for female knee (female 15°, male 29°, p<0.05). Conclusion. Gender differences in PTMA were identified both before and after accounting for knee size, with implications for gender-specific arthroplasty and musculoskeletal models. The developed measurement framework could also be applied in vivo for accurate measurement of the PTMA. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Abstract. Objective. Explore whether high tibial osteotomy (HTO) changes knee contact forces and to explore the relationship between the external knee adduction moment (EKAM) pre and 12 months post HTO. Methods. Three-dimensional gait analysis was performed on 17 patients pre and 12-months post HTO using a modified Cleveland marker-set. Tibiofemoral contact forces were calculated in SIMM. The scaled musculoskeletal model integrated an extended knee model allowing for 6 degrees of freedom in the tibiofemoral and patellofemoral joint. Joint angles were calculated using inverse kinematics then muscle and contact forces and secondary knee kinematics were estimated using the COMAC algorithm. Paired samples t-test were performed using SPSS version 25 (SPSS Inc., USA). Testing for normality was undertaken with Shapiro-Wilk. Pearson correlations established the relationships between EKAM1 to medial KCF1, and EKAM2 to medial KCF2, pre and post HTO. Results. Total knee contact force peak 1 significantly reduced from 2.6 x body weight pre-HTO to 2.3 x body weight 12-months post-HTO. Medial contact force peak 1 significantly reduced from 1.7 x body weight pre-HTO to 1.5 x body weight 12-months post-HTO. Second peak lateral knee contact force significantly increased from 0.9 body weight pre-HTO to 1.1 x body weight 12-months post-HTO. Furthermore, this study found very strong correlations between EKAM1 and medial KCF1 pre-HTO (r=0.85) as well as post-HTO (r=0.91). There was a significantly moderate relationship between EKAM2 and medial KCF2 pre-HTO (r=0.625). Conclusion. HTO significantly reduced overall and medial KCF during the first half of stance whilst increasing second half of stance peak lateral knee contact force. This study demonstrated a strong relationship between EKAM peaks and respective medial KCF peaks, supporting the usefulness of EKAM as a surrogate measure of medial compartment tibiofemoral contact forces. This demonstrates HTO successfully offloads the tibiofemoral joint overall, as well as offloading the medial compartment

Focal cartilage defects (FCDs) found in medial and lateral compartments of the knee are accompanied with patient-reported pain and loss of joint function. There is a deficit of evidence to explain why they occur. We hypothesise that aberrant knee joint loading may be partially responsible for FCD pathology, therefore this study aims to use 3-dimensional motion capture (MoCap) analysis methods to investigate differences in gait biomechanics of subjects with symptomatic FCDs. 11 subjects with Outerbridge grade II FCDs of the tibiofemoral joint (5 medial compartment, 6 lateral compartment) and 10 non-pathological controls underwent level-gait MoCap analysis using an infra-red camera (Qualisys) and force-plate (Bertec) passive marker system. 6-degree of freedom models were generated and used to calculate spatio-temporal measures, and frontal and sagittal plane knee, hip and ankle rotation and moment waveforms (Visual 3D). Principle component analysis (PCA) was used to score subjects based on common waveform features, and PC scores were tested for differences using Mann-Whitney tests (SPSS). No group differences were found in BMI, age or spatio-temporal measures. Medial-knee FCD subjects experienced higher (p=0.05) overall knee adduction moments (KAMs) compared to controls. Conversely, lateral-knee FCD subjects found lower (p=0.031) overall KAMs. Knee flexion and extension moments (KFMs/KEMs) were relatively reduced (p=0.013), but only in medial FCD subjects. This was accompanied by a significantly (p=0.019) higher knee flexion angle (KFA) during late-stance. KAMs have been shown to be predictive of frontal plane joint contact forces, and therefore our results may be reflective of FCD subjects overloading their respective diseased knee condyles. The differences in knee sagittal plane knee moments (KFMs/KEMs) and angles (KFA) seen in medial FCD subjects are suggestive of gait adaptations to pain. Overall these results suggest treatments of FCDs should consider offloading the respective affected condyle for better surgical outcomes

Knee ligament injury is one of the most frequent sport injuries and ligament reconstruction has been used to restore the structural stability of the joint. Cycling exercises have been shown to be safe for anterior cruciate ligament (ACL) reconstruction and are thus often prescribed in the rehabilitation of patients after ligament reconstruction. However, whether it is safe for posterior cruciate ligament (PCL) reconstruction remains unclear. Considering the structural roles of the PCL, backward cycling may be more suitable for rehabilitation in PCL reconstruction. However, no study has documented the differences in the effects on the knee kinematics between forward and backward pedaling. Therefore, the current study aimed to measure and compare the arthrokinematics of the tibiofemoral joint between forward and backward pedaling using a biplane fluoroscope-to- computed tomography (CT) registration method. Eight healthy young adults participated in the current study with informed written consent. Each subject performed forward and backward pedaling with an average resistance of 20 Nm, while the motion of the left knee was monitored simultaneously by a biplane fluoroscope (ALLURA XPER FD, Philips) at 30 fps and a 14-camera stereophotogrammetry system (Vicon, OMG, UK) at 120 Hz. Before the motion experiment, the knee was CT and magnetic resonance scanned, which enabled the reconstruction of the bones and articular cartilage. The bone models were registered to the fluoroscopic images using a volumetric model-based fluoroscopy-to-CT registration method, giving the 3-D poses of the bones. The bone poses were then used to calculate the rigid-body kinematics of the joint and the arthrokinematics of the articular cartilage. In this study, the top dead center of the crank was defined as 0° so forward pedaling sequence would begin from 0° to 360°. Compared with forward pedaling, for crank angles from 0° to 180°, backward pedaling showed significantly more tibial external rotation. Moreover, both the joint center and contact positions in the lateral compartment were more anterior while the contact positions in the medial compartment was more posterior, during backward pedaling. For crank angles from 180° to 360°, the above-observed phenomena were generally reversed, except for the anterior-posterior component of the contact positions in the medial compartment. Forward and backward pedaling displayed significant differences in the internal/external rotations while the rotations in the sagittal and frontal planes were similar. Compared with forward cycling, the greater tibial external rotation for crank angles from 0° to 180° during backward pedaling appeared to be the main reason for the more anterior contact positions in the lateral compartment and more posterior contact positions in the medial compartment. Even though knee angular motions during forward and backward pedaling were largely similar in the sagittal and frontal planes, significant differences existed in the other components with different contact patterns. The current results suggest that different pedaling direction may be used in rehabilitation programs for better treatment outcome in future clinical applications

A correct ligament loading following TKA surgery is believed to minimize instability and improve patient satisfaction. The evaluation of the ligament stress or strain is however impractical in a surgical setting. Alternatively, tibial trial components containing force sensors have the potential to indirectly assess the ligament loading. These instrumented components quantify the medial and lateral forces in the tibiofemoral joint. Although this method finds clinical application already, the target values for both the force magnitude and medial / lateral force ratio under surgical conditions remain uncertain. A total of eight non-arthritic cadaveric knees have been tested mimicking surgical conditions. Therefore, the specimens are mounted in a custom knee simulator. This simulator allows to test full lower limb specimens, providing kinematic freedom throughout the range of motion. Knee flexion is obtained by lifting the femur (thigh pull). Knee kinematics are simultaneously recorded by means of a navigation system and based on the mechanical axis of the femur and tibia. In addition, the load transferred through the medial and lateral compartment of the knee is monitored. Therefore, a 2.4 mm thick sawing blade is used to machine a slot in the tibia perpendicular to the mechanical axis, at the location of the tibial cut in TKA surgery. A complete disconnection was thereby assured between the tibial plateau and the distal tibia. To fill the created gap, custom 3D printed shims were inserted. Through their specific geometry, these shims create a load deviation between two Tekscan pressure pads on the medial and lateral side. Following the insertion of the shims, the knee was closed before performing the kinematic and kinetic tests. Seven specimens showed a limited varus throughout the range of motion (ranging from 1° to 7° varus). The other knee was in valgus (4° valgus). Amongst varus knees, the results were very consistent, indicating high loads in full extension. Subsequently, the loads decrease as the knee flexes and eventually vanishes on the lateral side. This leads to consistently high compartmental load ratios (medial load / total load) in flexion. In full extension the screw-home mechanism results in increased loads, both medially and laterally. Upon flexion, the lateral loads disappear. This is attributed to slackening of the lateral collateral ligament, in turn linked to the femoral rollback and slope of the lateral compartment. The isometry of the medial collateral ligament contributes on the other hand to the near-constant load in the medial compartment. The above particularly applies for varus knees. The single valgus knee tested indicated a higher load transmission by the lateral compartment, potentially attributed to a contracture of the lateral structures. With respect to TKA surgery, these findings are particularly relevant when considering anatomically designed implants. For those implants, this study concludes that a tighter medial compartment reflects that of healthy varus knees. Be aware however that in full extension, higher and up to equal loads can be acceptable for the medial and lateral compartment

There has been only one limited report dating from 1941 using dissection which has described the tibiofemoral joint between 120° and 160° of flexion despite the relevance of this arc to total knee replacement. We now provide a full description having examined one living and eight cadaver knees using MRI, dissection and previously published cryosections in one knee. In the range of flexion from 120° to 160° the flexion facet centre of the medial femoral condyle moves back 5 mm and rises up on to the posterior horn of the medial meniscus. At 160° the posterior horn is compressed in a synovial recess between the femoral cortex and the tibia. This limits flexion. The lateral femoral condyle also rolls back with the posterior horn of the lateral meniscus moving with the condyle. Both move down over the posterior tibia at 160° of flexion. Neither the events between 120° and 160° nor the anatomy at 160° could result from a continuation of the kinematics up to 120°. Therefore hyperflexion is a separate arc. The anatomical and functional features of this arc suggest that it would be difficult to design an implant for total knee replacement giving physiological movement from 0° to 160°

Summary. This study describes the use of a quasi-static, 6DOF knee loading simulator using cadaveric specimens. Muscle force profiles yield repeatable results. Intra-articular pressure and contact area are dependent on loading condition and ACL integrity. Introduction. Abnormal contact mechanics of the tibiofemoral joint is believed to influence the development and progression of joint derangements. As such, understanding the factors that regulate joint stability may provide insight into the underlying injury mechanisms. Muscle action is believed to be the most important factor since it is the only dynamic regulator of joint stability. Furthermore, abnormal muscle control has been experimentally linked to the development of OA [Herzog, 2007] and in vivo ACL strain [Fleming, 2001]. However, the individual contributions to knee joint contact mechanics remain unclear. Thus, the purpose of this study was to examine the effects of individual muscle contributions on the tibiofemoral contact mechanics using an in-vitro experimental protocol. Methodology. Contact mechanics of 6 fresh frozen cadaver knee specimens were evaluated using the UofO Oxford knee loading device. Various combinations of quadriceps-hamstring co-contraction ratios were applied to the knee while it was “suspended” between the hip and foot components of the device. Loads of six muscle groups were computed using a hill-type musculoskeletal model [Buchanan, 2004]. Simulated ground reaction forces were also applied to the knee to represent force profiles of weight acceptance during gait as it has been shown to produce peak knee joint force in the gait cycle [Shelburne et al., 2006]. For respective medial and lateral joint compartments, the mean contact area (MC-CA and LC-CA), mean contact pressure (MC-CP and LC-CP), peak pressure (MC-PP and LC-PP), and centre of force displacement (MC-COFD and LC-COFD) were determined using a 4011 piezoelectric sensor form Tekscan (Tekscan Inc. Boston, MA). Additionally, the ACL was resected and measurements were repeated. Pearson correlations (r) examined the reliability of measurements as well as the effect an ACL transection on articular loads. Results. Positive correlations were computed for the following: COFD with intact ACL (r=0.99), COFD with resected ACL (r=0.82), MC-COFD pre vs. post ACL- resection (0.91). Furthermore, preliminary results indicated a positive correlation between MC-CA and ACL integrity (r=0.97). Discussion. The repeatability of the measured dependant variables validates the use of the knee-loading device. Interestingly, contact mechanics are more variable post ACL resection for a given muscle loading condition, indicating a decrease in knee joint stability. Also, the COFD is dependent on the different ratios of muscle loads applied to the knee, which demonstrates the importance of muscle action to the modulation of contact forces

Estimates of knee joint loadings were calculated for 12 normal subjects from kinematic and kinetic measures obtained during both level and downhill walking. The maximum tibiofemoral compressive force reached an average load of 3.9 times body-weight (BW) for level walking and 8 times BW for downhill walking, in each instance during the early stance phase. Muscle forces contributed 80% of the maximum bone-on-bone force during downhill walking and 70% during level walking whereas the ground reaction forces contributed only 20% and 30% respectively. Most total knee designs provide a tibiofemoral contact area of 100 to 300 mm. 2. The yield point of these polyethylene inlays will therefore be exceeded with each step during downhill walking. Future evaluation of total knee designs should be based on a tibiofemoral joint load of 3.5 times BW at 20° knee flexion, 8 times BW at 40° and 6 times BW at 60°

Summary Statement. We observed that severe muscle weakness leads to OA, whereas a transient inflammatory stimulus did not have a significant effect on cartilage degradation. This arises the thought that a severe but transient inflammation may not be an independent risk factor for OA. Introduction. Biomechanical disturbances and joint inflammation are known risk factors, which may provoke or advance osteoarthritis (OA). However, the effect of interactions of such risk factors on the onset and progression of OA are still poorly understood. Therefore, the goal of this study was to investigate the in vivo effects of muscle weakness, joint inflammation, and the combination of these two risk factors, on the onset and progression of OA in the rabbit knee. Patients & Methods. Thirty 1-year-old skeletally mature female New Zealand White rabbits (weight: average 5.7kg, range 4.8–6.6kg) were used in this study. The animals were divided into four experimental groups: (i) surgical transection of the nerve branch of the common femoral nerve leading to the vastus lateralis muscle; (ii) muscle weakness of the quadriceps muscle induced by a chronic intramuscular injection of Botulinum toxin A (BTX-A) (3); (iii) intraarticular injection in the experimental knee joint with commercially available sterile Carrageenan solution to induce a transient severe inflammatory reaction (4); (iv) administration of both intraarticular injection of Carrageenan and intramuscular injection of BTX-A. In each animal, one hind limb was randomly assigned to the experimental intervention, while the contralateral side acted as its own control. Ninety days following intervention, muscle mass, joint diameter and cartilage histology of the femur, femoral groove, tibia and patella were assessed and microscopically analyzed using the OARSI histology score. Results. Transection of the femoral branch leading to the vastus lateralis as well as the administration of BTX-A led to a significant muscle mass loss for the vastus lateralis and the total quadriceps group, respectively. Similar results were seen in the combined Carrageenan/BTX-A group. There were no changes in total quadriceps muscle mass in the Carrageenan group. Knee joint diameters of the experimental limb were significantly increased in the Carrageenan and Carrageenan/BTX groups. VL transection and BTX-A injection did not cause significant increases in joint diameter. Histologic assessment of the cartilage showed that weakness of the vastus lateralis resulted in significantly higher OARSI scores in the patella and femoral groove, but not the tibiofemoral articulation. The administration of BTX-A caused significant cartilage damage in all 4 compartments (patella, femur, tibia, femoral groove). Intraarticular injection of Carrageenan did not cause significant cartilage damage in any compartment compared to the contralateral side. The combination of BTX-A and Carrageenan resulted in severe cartilage damage in the patella in all four compartments of the knee. The most severe damage was found on the medial side of the tibiofemoral joint and the lateral side of the patellofemoral joint. Conclusion. Severe muscle weakness over a three months period leads to the onset and progression of OA in the rabbit knee. A transient local inflammatory stimulus did not promote cartilage degradation, nor did it enhance cartilage degradation when it was combined with muscle weakness. This result is surprising and adds to the literature the idea that a severe but transient inflammation may not be an independent risk factor for OA

Objectives

In this study, we compared the pain behaviour and osteoarthritis (OA) progression between anterior cruciate ligament transection (ACLT) and osteochondral injury in surgically-induced OA rat models.

The patellofemoral joint is an important source of symptoms in osteoarthritis of the knee. We have used a newly designed surgical model of patellar strengthening to induce osteoarthritis in BALB/c mice and to establish markers by investigating the relationship between osteoarthritis and synovial levels of matrix metalloproteinases (MMPs). Osteoarthritis was induced by using this microsurgical technique under direct vision without involving the cavity of the knee. Degeneration of cartilage was assessed by the Mankin score and synovial tissue was used to determine the mRNA expression levels of MMPs. Irrigation fluid from the knee was used to measure the concentrations of MMP-3 and MMP-9. Analysis of cartilage degeneration was correlated with the levels of expression of MMP.

After operation the patellofemoral joint showed evidence of mild osteoarthritis at eight weeks and further degenerative changes by 12 weeks. The level of synovial MMP-9 mRNA correlated with the Mankin score at eight weeks, but not at 12 weeks. The levels of MMP-2, MMP-3 and MMP-14 mRNA correlated with the Mankin score at 12 weeks. An increase in MMP-3 was observed from four weeks up to 16 weeks. MMP-9 was notably increased at eight weeks, but the concentration at 16 weeks had decreased to the level observed at four weeks.

Our observations suggest that MMP-2, MMP-3 and MMP-14 could be used as markers of the progression of osteoarthritic change.

Osteoarthritis (OA) is an important cause of pain, disability and economic loss in humans, and is similarly important in the horse. Recent knowledge on post-traumatic OA has suggested opportunities for early intervention, but it is difficult to identify the appropriate time of these interventions. The horse provides two useful mechanisms to answer these questions: 1) extensive experience with clinical OA in horses; and 2) use of a consistently predictable model of OA that can help study early pathobiological events, define targets for therapeutic intervention and then test these putative therapies. This paper summarises the syndromes of clinical OA in horses including pathogenesis, diagnosis and treatment, and details controlled studies of various treatment options using an equine model of clinical OA.

Malrotation of the femoral component is a cause of patellofemoral maltracking after total knee arthroplasty. Its precise effect on the patellofemoral mechanics has not been well quantified. We have developed an in vitro method to measure the influence of patellar maltracking on contact. Maltracking was induced by progressively rotating the femoral component either internally or externally. The contact mechanics were analysed using Tekscan. The results showed that excessive malrotation of the femoral component, both internally and externally, had a significant influence on the mechanics of contact. The contact area decreased with progressive maltracking, with a concomitant increase in contact pressure. The amount of contact area that carries more than the yield stress of ultra-high molecular weight polyethylene significantly increases with progressive maltracking. It is likely that the elevated pressures noted in malrotation could cause accelerated and excessive wear of the patellar button.

We have previously shown that joint distraction and movement with a hinged external fixation device for 12 weeks was useful for repairing a large articular cartilage defect in a rabbit model. We have now investigated the results after six months and one year. The device was applied to 16 rabbits who underwent resection of the articular cartilage and subchondral bone from the entire tibial plateau. In group A (nine rabbits) the device was applied for six months. In group B (seven rabbits) it was in place for six months, after which it was removed and the animals were allowed to move freely for an additional six months. The cartilage remained sound in all rabbits. The areas of type II collagen-positive staining and repaired soft tissue were larger in group B than in group A. These findings provide evidence of long-term persistence of repaired cartilage with this technique and that weight-bearing has a positive effect on the quality of the cartilage.