Evaluation of a subject-specific finite-element model of the equine metacarpophalangeal joint under physiological load

The equine metacarpophalangeal (MCP) joint is frequently injured, especially by racehorses in training. Most injuries result from repetitive loading of the subchondral bone and articular cartilage rather than from acute events. The likelihood of injury is multi-factorial but the magnitude of mechanical loading and the number of loading cycles are believed to play an important role. Therefore, an important step in understanding injury is to determine the distribution of load across the articular surface during normal locomotion. A subject-specific finite-element model of the MCP joint was developed (including deformable cartilage, elastic ligaments, muscle forces and rigid representations of bone), evaluated against measurements obtained from cadaver experiments, and then loaded using data from gait experiments. The sensitivity of the model to force inputs, cartilage stiffness, and cartilage geometry was studied. The FE model predicted MCP joint torque and sesamoid bone flexion angles within 5% of experimental measurements. Muscle–tendon forces, joint loads and cartilage stresses all increased as locomotion speed increased from walking to trotting and finally cantering. Perturbations to muscle–tendon forces resulted in small changes in articular cartilage stresses, whereas variations in joint torque, cartilage geometry and stiffness produced much larger effects. Non-subject-specific cartilage geometry changed the magnitude and distribution of pressure and the von Mises stress markedly. The mean and peak cartilage stresses generally increased with an increase in cartilage stiffness. Areas of peak stress correlated qualitatively with sites of common injury, suggesting that further modelling work may elucidate the types of loading that precede joint injury and may assist in the development of techniques for injury mitigation.     

A dynamic multibody model of the physiological knee to predict internal loads during movement in gravitational field

Obtaining tibio-femoral (TF) contact forces, ligament deformations and loads during daily life motor tasks would be useful to better understand the aetiopathogenesis of knee joint diseases or the effects of ligament reconstruction and knee arthroplasty. However, methods to obtain this information are either too simplified or too computationally demanding to be used for clinical application. A multibody dynamic model of the lower limb reproducing knee joint contact surfaces and ligaments was developed on the basis of magnetic resonance imaging. Several clinically relevant conditions were simulated, including resistance to hyperextension, varus–valgus stability, anterior–posterior drawer, loaded squat movement. Quadriceps force, ligament deformations and loads, and TF contact forces were computed. During anterior drawer test the anterior cruciate ligament (ACL) was maximally loaded when the knee was extended (392 N) while the posterior cruciate ligament (PCL) was much more stressed during posterior drawer when the knee was flexed (319 N). The simulated loaded squat revealed that the anterior fibres of ACL become inactive after 60° of flexion in conjunction with PCL anterior bundle activation, while most components of the collateral ligaments exhibit limited length changes. Maximum quadriceps and TF forces achieved 3.2 and 4.2 body weight, respectively. The possibility to easily manage model parameters and the low computational cost of each simulation represent key points of the present project. The obtained results are consistent with in vivo measurements, suggesting that the model can be used to simulate complex and clinically relevant exercises.     

Tibiofemoral joint contact force in deep knee flexion and its consideration in knee osteoarthritis and joint replacement

The aim of the study was to estimate the tibiofemoral joint force in deep flexion to consider how the mechanical load affects the knee. We hypothesize that the joint force should not become sufficiently large to damage the joint under normal contact area, but should become deleterious to the joint under the limited contact area. Sixteen healthy knees were analyzed using a motion capture system, a force plate, a surface electromyography, and a knee model, and then tibiofemoral joint contact forces were calculated. Also, a contact stress simulation using the contact areas from the literature was performed. The peak joint contact forces (M +/- SD) were 4566 +/- 1932 N at 140 degrees in rising from full squat and 4479 +/- 1478 N at 90 degrees in rising from kneeling. Under normal contact area, the tibiofemoral contact stresses in deep flexion were less than 5 MPa and did not exceed the stress to damage the cartilage. The contact stress simulation suggests that knee prosthesis having the contact area smaller than 200 mm2 may be problematic since the contact stress in deep flexion would become larger than 21 MPa, and it would lead damage or wear of the polyethylene.     

Computational biomechanics of knee joint in open kinetic chain extension exercises

Open kinetic chain (OKC) extension exercises are commonly performed to strengthen quadriceps muscles and restore joint function in performance enhancement programs, in exercise therapies and following joint reconstruction. Using a validated 3D nonlinear finite element model, the detailed biomechanics of the entire joint in OKC extension exercises are investigated at 0, 30, 60 and 90 degrees joint angles. Two loading cases are simulated; one with only the weight of the leg and the foot while the second considers also a moderate resistant force of 30 N acting at the ankle perpendicular to the tibia. The presence of the 30 N markedly influences the results both in terms of the magnitude and the trend. The resistant load substantially increases the required quadriceps, patellar tendon, cruciate ligaments and joint contact forces, especially at near 90 degrees angles with the exception of ACL force that is increased at 0 degrees angle. At post-ACL reconstruction period or in the joint with ACL injury, the exercise should preferably be avoided at near full extension positions under large resistant forces.     

The effects of knee support on the sagittal lower-body joint kinematics and kinetics of deep squats

Little work has been done to examine the deep squat position (>130° sagittal knee flexion). In baseball and softball, catchers perform this squat an average of 146 times per nine-inning game. To alleviate some of the stress on their knees caused by this repetitive loading, some catchers wear foam knee supports.ObjectivesThis work quantifies the effects of knee support on lower-body joint kinematics and kinetics in the deep squat position.MethodsSubjects in this study performed the deep squat with no support, foam support, and instrumented support. In order to measure the force through the knee support, instrumented knee supports were designed and fabricated. We then developed an inverse dynamic model to incorporate the support loads. From the model, joint angles and moments were calculated for the three conditions.ResultsWith support there is a significant reduction in the sagittal moment at the knee of 43% on the dominant side and 63% on the non-dominant side compared to without support. These reductions are a result of the foam supports carrying approximately 20% of body weight on each side.ConclusionKnee support reduces the moment necessary to generate the deep squat position common to baseball catchers. Given the short moment arm of the patella femoral tendon, even small changes in moment can have a large effect in the tibial-femoral contact forces, particularly at deep squat angles. Reducing knee forces may be effective in decreasing incidence of osteochondritis dissecans.     

The effect of short-term resistance training on hip and knee kinematics during vertical drop jumps

The purpose of this study was to determine the effect of a weight-bearing free weight resistance training program alone on knee flexion, hip flexion, and knee valgus during unilateral and bilateral drop jump tasks. Twenty-nine young adult females with previous athletic experience were randomly divided into a control (n = 16) and a resistance training (n = 13) groups. The resistance training group completed 8 weeks of lower extremity, weight-bearing exercises using free weights, whereas the control group did not train. A pre- and posttest was conducted to measure knee valgus, knee flexion, and hip flexion during unilateral (30 cm) and bilateral (60 cm) vertical drop jumps for maximum height. Joint angles were determined using 3-dimensional electromagnetic tracking sensors (MotionMonitor; Innovative Sports Training, Inc., Chicago, IL, USA). Initial training intensity for the bilateral squat was 50% of the subject's 1 repetition maximum (RM), which increased 5% each week to 85% during the final week. Sets and repetitions ranged from 2 to 4 and from 4 to 12, respectively. The training loads for all other exercises (lunge, step-up, unilateral squat, and Romanian deadlift) increased from 15RM to 6RM from the initial to the final week. A repeated measures analysis of variance was used to determine differences in the hip and knee joint angles. No significant differences for knee valgus and hip flexion measures were found between the groups after training; however, knee flexion angle significantly increased in the training group from the pretest (77.2 ± 4.1°) to posttest (83.2 ± 3.7°) during the bilateral drop jump. No significant changes occurred during the unilateral drop jump. Bilateral measures for knee flexion, hip flexion, and knee valgus were significantly (p < 0.05) greater than the unilateral measures during the drop jump task, which indicate an increased risk for anterior cruciate ligament (ACL) injury during unilateral drop jumps. The data support that the strength and conditioning specialist can implement resistance training alone during a short-term training period to reduce the risk of ACL injury by increasing knee flexion during a bilateral drop jump task. Increased knee flexion angles after resistance training may indicate a reduced risk for knee injury from improved neuromuscular control, resulting in a softer landing.     

In vitro forces in the normal and cruciate-deficient knee during simulated squatting motion

Three orthogonal components of the tibiofemoral and patellofemoral forces were measured simultaneously for knees with intact cruciate ligaments (nine knees), following anterior cruciate ligament resection (six knees), and subsequent posterior cruciate ligament resection (six knees). The knees were loaded using an experimental protocol that modeled static double-leg squat. The mean compressive tibial force increased with flexion angle. The mean anteroposterior tibial shear force acted posteriorly on the tibia below 50 deg flexion and anteriorly above 55 deg. Mediolateral shear forces were low compared to the other force components and tended to be directed medially on both the patella and tibia. The mean value of the ratio of the resultant tibial force divided by the quadriceps force decreased with increasing flexion angle and was between 0.6 and 0.7 above 70 deg flexion. The mean value of the ratio of the resultant tibiofemoral contact force divided by the resultant patellofemoral contact force decreased with increasing flexion and was between 0.8 and 1.0 above 55 deg flexion. Cruciate ligament resection resulted in no significant changes in the patellar contact forces. Following resection of the anterior cruciate ligament, the tibial anteroposterior shear force was directed anteriorly over all flexion angles tested. Subsequent resection of the posterior cruciate ligament resulted in an approximately 10 percent increase in the quadriceps tendon and tibial compressive force.     

Recruitment of knee joint ligaments

On the basis of earlier reported data on the in vitro kinematics of passive knee-joint motions of four knee specimens, the length changes of ligament fiber bundles were determined by using the points of insertion on the tibia and femur. The kinematic data and the insertions of the ligaments were obtained by using Roentgenstereophotogrammetry. Different fiber bundles of the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments were identified. On the basis of an assumption for the maximal strain of each ligament fiber bundle during the experiments, the minimal recruitment length and the probability of recruitment were defined and determined. The motions covered the range from extension to 95 degrees flexion and the loading conditions included internal or external moments of 3 Nm and anterior or posterior forces of 30 N. The ligament length and recruitment patterns were found to be consistent for some ligament bundles and less consistent for other ligament bundles. The most posterior bundle of each ligament was recruited in extension and the lower flexion angles, whereas the anterior bundle was recruited for the higher flexion angles. External rotation generally recruited the collateral ligaments, while internal rotation recruited the cruciate ligaments. However, the anterior bundle of the posterior cruciate ligament was recruited with external rotation at the higher flexion angles. At the lower flexion angles, the anterior cruciate and the lateral collateral ligaments were recruited with an anterior force. The recruitment of the posterior cruciate ligament with a posterior force showed that neither its most anterior nor its most posterior bundle was recruited at the lower flexion angles. Hence, the posterior restraint must have been provided by the intermediate fiber bundles, which were not considered in the experiment. At the higher flexion angles, the anterior bundles of the anterior cruciate ligament and the posterior cruciate ligament were found to be recruited with anterior and posterior forces, respectively. The minimal recruitment length and the recruitment probability of ligament fiber bundles are useful parameters for the evaluation of ligament length changes in those experiments where no other method can be used to determine the zero strain lengths, ligament strains and tensions.     

The mechanical environment of chondrocytes in articular cartilage

There is a growing literature concerning chondrocyte responses to mechanical loading, but relatively little is known about the mechanical environment these cells experience in a living joint. Calculations indicate that high forces are applied to limb joints whenever the joints are flexed, because flexion can cause body weight to act on long lever arms compared to the joint centre, whereas the muscles which extend the joint act on much shorter lever arms. As a result, joint reaction forces (which compress the cartilage) can rise to 3-6 times body weight during activities such as stair climbing. Articular cartilage tends to spread this load evenly over the joint surface, but is too thin to do this well, and compressive stresses can rise to 10-20 MPa. Within cartilage, matrix stresses vary locally, possibly as a result of variation in composition or undulations in the subchondral bone, and further modifications of stress occur within each chondron. Articular cartilage is a fibrous solid and cells within it are deformed by mechanical loading rather than subjected to a hydrostatic pressure. The mechanical environment of chondrocytes can best be reproduced in vitro by direct compression of the articular surface of cartilage which is supported naturally by adjacent cartilage and subchondral bone.     

In vivo gleno-humeral joint loads during forward flexion and abduction

To improve design and preclinical test scenarios of shoulder joint implants as well as computer-based musculoskeletal models, a precise knowledge of realistic loads acting in vivo is necessary. Such data are also helpful to optimize physiotherapy after joint replacement and fractures. This is the first study that presents forces and moments measured in vivo in the gleno-humeral joint of 6 patients during forward flexion and abduction of the straight arm. The peak forces and, even more, the maximum moments varied inter-individually to a considerable extent. Forces of up to 238%BW (percent of body weight) and moments up to 1.74%BWm were determined. For elevation angles of less than 90° the forces agreed with many previous model-based calculations. At higher elevation angles, however, the measured loads still rose in contrast to the analytical results. When the exercises were performed at a higher speed, the peak forces decreased. The force directions relative to the humerus remained quite constant throughout the whole motion. Large moments in the joint indicate that friction in shoulder implants is high if the glenoid is not replaced. A friction coefficient of 0.1-0.2 seems to be realistic in these cases.     

Cruciate coupling and screw-home mechanism in passive knee joint during extension--flexion

The screw-home mechanism and coupling between forces in cruciate ligaments during passive knee joint flexion were investigated for various boundary conditions, flexion axis alignments and posterior cruciate ligaments (PCL)/anterior cruciate ligament (ACL) conditions. A developed non-linear 3D finite element model was used to perform detailed elasto-static response analyses of the human tibiofemoral joint as a function of flexion angle varying from 10 degrees hyper-extension to 90 degrees flexion. The tibia rotated internally as the femur flexed and externally as the femur extended. The re-alignment of the flexion axis by +/-5 degrees rotation about the axial (distal-proximal) axis, transection of the ACL and changes in cruciate ligament initial strains substantially influenced the 'screw-home' motion. On the other hand, restraint on this coupled rotation diminished ACL forces in flexion. A remarkable coupling was predicted between ACL and PCL forces in flexion; forces in both cruciate ligaments increased as the initial strain or pretension in one of them increased whereas they both diminished as one of them was cut or became slack. This has important consequences in joint functional biomechanics following a ligament injury or replacement surgery and, hence, in the proper management of joint disorders.     

Analysis of muscle activation patterns during transitions into and out of high knee flexion postures

Increased risk of medial tibiofemoral osteoarthritis (OA) is linked to occupations that require frequent transitions into and out of postures which require high knee flexion (>90°). Muscle forces are major contributors to joint loading, and an association between compressive forces due to muscle activations and the degeneration of joint cartilage has been suggested. The purpose of this study was to evaluate muscle activation patterns of muscles crossing the knee during transitions into and out of full-flexion kneeling and squatting, sitting in a low chair, and gait. Both net and co-activation were greater when transitioning out of high flexion postures, with maximum activation occurring at knee angles greater than 100°. Compared to gait, co-activation levels during high flexion transitions were up to approximately 3 times greater. Co-activation was significantly greater in the lateral muscle group compared to the medial group during transitions into and out of high flexion postures. These results suggest that compression due to activation of the medial musculature of the knee may not be the link between high knee flexion postures and increased medial knee OA observed in occupational settings. Further research on a larger subject group and workers with varying degrees of knee OA is necessary.     

Effect of changes in cruciate ligaments pretensions on knee joint laxity and ligament forces

The knee joint cruciate ligaments are reconstructed with the rationale to avoid joint instability, recurrent injury, damage to soft tissues and osteoarthritis. Wide range of procedures with different stiffness, pretension, orientation and insertion locations have been proposed with the primary goal to restore the joint laxity. Apart from the general lack of success in preservation of force in the reconstructed ligament itself, the concern, not yet addressed, arises as to the effect of such perturbation on the other intact cruciate ligament. The interaction between cruciate ligament forces is hypothesized in this work. Using a 3-D nonlinear finite element model of the tibiofemoral joint, we examined this hypothesis by quantifying the extent of coupling between cruciate ligaments while varying the prestrain in each ligament under flexion with and without anterior-posterior (A-P) loads. A remarkable coupling was predicted between cruciate ligament forces in flexion thus confirming the hypothesis; forces in both cruciate ligaments increased as initial strain or pretension in one of them increased whereas they both diminished as one of them became slack. Moreover, changes in laxity and in ligament forces as a cruciate ligament prestrained or pretensioned varied with flexion angle and external loads. These findings have important consequences in joint functional biomechanics following a ligament injury or replacement surgery and in selection of laxity matched or ligament force matched pretensioning protocols.     

Biomechanics of changes in ACL and PCL material properties or prestrains in flexion under muscle force-implications in ligament reconstruction

The effects of changes in cruciate ligament material and prestrain on knee joint biomechanics following ligament reconstruction surgery by a tendon are not adequately known. A 3D nonlinear finite element model of the entire knee joint was used to investigate the joint response at different flexion angles under a quadriceps force while varying ACL and PCL initial strains or material properties. The ACL and PCL forces as well as tibiofemoral contact forces/areas substantially increased with greater ACL or PCL initial strains or stiffness. The patellofemoral contact force slightly increased whereas the tibial extensor moment slightly decreased with tenser or stiffer ACL. Reverse trends were predicted with slacker ACL. Results confirm the hypotheses that changes in the prestrain of one cruciate ligament substantially influence the force in the other cruciate ligament and the entire joint and that the use of the patellar tendon (PT) as a replacement for cruciate ligaments markedly alters the joint biomechanics with trends similar to those predicted when increasing prestrains. Forces in both ACL and PCL ligaments increased as one of them became tenser or stiffer and diminished as it became slacker. These results have important consequences in joint biomechanics following ligament injuries or replacement and tend to recommend the use of grafts with smaller prestrains (i.e. slacker than intact) when using the PT as the replacement material with stiffness greater than that of replaced ligament itself.     

Biomechanics of changes in ACL and PCL material properties or prestrains in flexion under muscle force-implications in ligament reconstruction

The effects of changes in cruciate ligament material and prestrain on knee joint biomechanics following ligament reconstruction surgery by a tendon are not adequately known. A 3D nonlinear finite element model of the entire knee joint was used to investigate the joint response at different flexion angles under a quadriceps force while varying ACL and PCL initial strains or material properties. The ACL and PCL forces as well as tibiofemoral contact forces/areas substantially increased with greater ACL or PCL initial strains or stiffness. The patellofemoral contact force slightly increased whereas the tibial extensor moment slightly decreased with tenser or stiffer ACL. Reverse trends were predicted with slacker ACL. Results confirm the hypotheses that changes in the prestrain of one cruciate ligament substantially influence the force in the other cruciate ligament and the entire joint and that the use of the patellar tendon (PT) as a replacement for cruciate ligaments markedly alters the joint biomechanics with trends similar to those predicted when increasing prestrains. Forces in both ACL and PCL ligaments increased as one of them became tenser or stiffer and diminished as it became slacker. These results have important consequences in joint biomechanics following ligament injuries or replacement and tend to recommend the use of grafts with smaller prestrains (i.e. slacker than intact) when using the PT as the replacement material with stiffness greater than that of replaced ligament itself.     

Quantifying plyometric intensity via rate of force development, knee joint, and ground reaction forces

Because the intensity of plyometric exercises usually is based simply upon anecdotal recommendations rather than empirical evidence, this study sought to quantify a variety of these exercises based on forces placed upon the knee. Six National Collegiate Athletic Association Division I athletes who routinely trained with plyometric exercises performed depth jumps from 46 and 61 cm, a pike jump, tuck jump, single-leg jump, countermovement jump, squat jump, and a squat jump holding dumbbells equal to 30% of 1 repetition maximum (RM). Ground reaction forces obtained via an AMTI force plate and video analysis of markers placed on the left hip, knee, lateral malleolus, and fifth metatarsal were used to estimate rate of eccentric force development (E-RFD), peak ground reaction forces (GRF), ground reaction forces relative to body weight (GRF/BW), knee joint reaction forces (K-JRF), and knee joint reaction forces relative to body weight (K-JRF/BW) for each plyometric exercise. One-way repeated measures analysis of variance indicated that E-RFD, K-JRF, and K-JRF/BW were different across the conditions (p < 0.05), but peak GRF and GRF/BW were not (p > 0.05). Results indicate that there are quantitative differences between plyometric exercises in the rate of force development during landing and the forces placed on the knee, though peak GRF forces associated with landing may not differ.     

In vivo knee moments and shear after total knee arthroplasty

Tibiofemoral loading is very important in cartilage degeneration as well as in component survivorship after total knee arthroplasty. We have previously reported the axial knee forces in vivo. In this study, a second-generation force-sensing device that measured all six components of tibial forces was implanted in a 74-kg, 83-year-old male. Video motion analysis, ground reaction forces, and knee forces were measured during walking, stair climbing, chair-rise, and squat activities. Peak total force was 2.3 times body weight (BW) during walking, 2.5 x BW during chair rise, 3.0 x BW during stair climbing, and 2.1 x BW during squatting. Peak anterior shear force at the tibial tray was 0.30 x BW during walking, 0.17 x BW during chair rise, 0.26 x BW during stair climbing, and 0.15 x BW during squatting. Peak flexion moment at the tray was 1.9% BW x Ht (percentage of body weight multiplied by height) for chair-rise activity and 1.7% BW x Ht for squat activity. Peak adduction moment at the tray was -1.1% BW x Ht during chair-rise, -1.3% BW x Ht during squatting. External knee flexion and adduction moments were substantially greater than flexion and adduction moments at the tray. The axial component of forces predominated especially during the stance phase of walking. Shear forces and moments at the tray were very modest compared to total knee forces. These findings indicate that the soft tissues around the knee absorbed most of the external shear forces. Our results highlight the importance of direct measurements of knee forces.     

Quantified in vitro tibiofemoral contact during bodyweight back squats

Squats are a common lower extremity task used in strength and conditioning, balance training, and rehabilitation. It is important to understand how slight alterations in lower extremity kinematics during a squat affect the internal joint loading of the knee. This study directly quantified tibiofemoral contact throughout the in vitro simulation of a bodyweight back squat performed two ways: a heel squat (knees in line with toes) and a toe squat (knees anterior to the toes) at peak knee flexion. Three cadaveric right lower extremities were instrumented and positioned into the University of Texas Joint Load Simulator. Kinematics, kinetics, and predicted muscle forces from a 20-year-old athletic male performing the two back squats were used as inputs for the in vitro simulations. The quantified tibiofemoral contact area, peak pressure, net force, and center of pressure location were significantly different between squat types (p > 0.05). Net contact area on the tibial plateau at peak knee flexion was significantly larger in the heel versus toe squat (599 ± 80 mm² vs. 469 ± 125 mm²; p < 0.05). Peak lateral pressure was significantly higher in the heel versus toe squat (2.73 ± 0.54 MPa vs. 0.87 ± 0.56 MPa; p < 0.05). Results suggest the heel squat generates an even load distribution, which is less likely to affect joint degeneration. Future in vitro simulations should quantify the effects lower extremity kinematics, kinetics, and individual muscle forces have on tibiofemoral contact parameters during common athletic tasks.     

Knee joint passive stiffness and moment in sagittal and frontal planes markedly increase with compression

Knee joints are subject to large compression forces in daily activities. Due to artefact moments and instability under large compression loads, biomechanical studies impose additional constraints to circumvent the compression position–dependency in response. To quantify the effect of compression on passive knee moment resistance and stiffness, two validated finite element models of the tibiofemoral (TF) joint, one refined with depth-dependent fibril-reinforced cartilage and the other less refined with homogeneous isotropic cartilage, are used. The unconstrained TF joint response in sagittal and frontal planes is investigated at different flexion angles (0°, 15°, 30° and 45°) up to 1800 N compression preloads. The compression is applied at a novel joint mechanical balance point (MBP) identified as a point at which the compression does not cause any coupled rotations in sagittal and frontal planes. The MBP of the unconstrained joint is located at the lateral plateau in small compressions and shifts medially towards the inter-compartmental area at larger compression forces. The compression force substantially increases the joint moment-bearing capacities and instantaneous angular rigidities in both frontal and sagittal planes. The varus–valgus laxities diminish with compression preloads despite concomitant substantial reductions in collateral ligament forces. While the angular rigidity would enhance the joint stability, the augmented passive moment resistance under compression preloads plays a role in supporting external moments and should as such be considered in the knee joint musculoskeletal models.     

The effect of meniscal tears and resultant partial meniscectomies on the knee contact stresses: a finite element analysis

Knee osteoarthritis (OA) is believed to result from high levels of contact stresses on the articular cartilage and meniscus after meniscal damage. This study investigated the effect of meniscal tears and partial meniscectomies on the peak compressive and shear stresses in the human knee joint. An elaborate three-dimensional finite element model of knee joint including bones, articular cartilages, menisci and main ligaments was developed from computed tomography and magnetic resonance imaging images. This model was used to model four types of meniscal tears and their resultant partial meniscectomies and analysed under an axial 1150 N load at 0° flexion. Three different conditions were compared: a healthy knee joint, a knee joint with medial meniscal tears and a knee joint following partial meniscectomies. The numerical results showed that each meniscal tear and its resultant partial meniscectomy led to an increase in the peak compressive and shear stresses on the articular cartilages and meniscus in the medial knee compartment, especially for partial meniscectomy. Among the four types of meniscal tears, the oblique tear resulted in the highest values of the peak compressive and shear stresses. For the four partial meniscectomies, longitudinal meniscectomy led to the largest increase in these two stresses. The lateral compartment was minimally affected by all the simulations. The results of this study demonstrate meniscal tear and its resultant partial meniscectomy has a positive impact on the maintenance of high levels of contact stresses, which may improve the progression of knee OA, especially for partial meniscectomy. Surgeons should adopt a prudent strategy to preserve the greatest amount of meniscus possible.