In vitro characterization of the relationship between the Q-angle and the lateral component of the quadriceps force

Although the Q-angle is routinely measured, the relationship between the Q-angle and the lateral component of the quadriceps force acting on the patella is unknown. Five cadaver knees were flexed on a knee simulator with a normal Q-angle, and flexed after increasing and decreasing the Q-angle by shifting the quadriceps origin laterally and medially, respectively. The motion of the femur, tibia and patella was tracked from 20 to 90 degrees of flexion using electromagnetic sensors. The motion of landmarks used to quantify the Q-angle was tracked to determine the 'dynamic Q-angle' during flexion. The lateral component of the force applied by the actuator secured to the quadriceps tendon was also quantified throughout flexion. Increasing the initial Q-angle significantly (p < 0.05) increased the dynamic Q-angle and the lateral force exerted through the quadriceps tendon throughout flexion. Decreasing the initial Q-angle significantly decreased the dynamic Q-angle at 90 degrees of flexion and significantly decreased the lateral force exerted through the quadriceps tendon from 20 to 40 degrees of flexion. Even though the dynamic Q-angle changes during flexion, an abnormally large initial Q-angle can be an indicator of an abnormally large lateral force acting on the patella during flexion.     

Muscle-ligament interactions at the knee during walking.

A two-dimensional mathematical model of the knee is used with gait analysis to calculate muscle, cruciate ligament and tibio-femoral contact forces developed at the knee during normal level walking. Ten normal adult subjects--four females and six males--participated. The knee model is based upon a four-bar linkage comprising the femur, tibia and two cruciate ligaments. It takes account of the rolling and sliding of the femur on the tibia during flexion/extension and the changes in direction of the ligaments and muscle tendons. We considered forces transmitted by six elements: quadriceps, hamstrings, gastrocnemius, anterior and posterior cruciate ligaments, and tibio-femoral contact. The equations of mechanics can be used to determine the absolute values of only three of the knee forces simultaneously, so that twenty limiting solutions of three of the six forces were considered. A limiting solution was rejected if any of the three forces were negative, corresponding to compressive muscle or ligament forces, or tensile contact forces. These constraints always reduced and at times removed the redundancy of the knee structures. The high incidence of predicted single muscle activity, supported by electromyography, suggested that the ligaments play a significant role in load transmission during gait. The temporal patterns of muscle and ligament activity and ligament force magnitudes were sensitive to the choice of model parameters. The analysis showed that each of four possible minimum principles of muscle selection--minimal muscle force, muscle stress, ligament force and contact force--was unlikely to be valid throughout the walking cycle.     

In-vitro measurement of the human knee joint motion during quadriceps leg raising

This paper represents a three-dimensional motion analysis of the human knee joint under given conditions of loading and constraint. As the knee is extended by a known force applied to the quadriceps tendon, relative displacements of the femur, tibia, and patella are measured using a video motion analysis system. The most prominent motion of the tibia is external rotation and anterior displacement relative to the femur during knee extension. The patellar flexion angle decreases from 70° to 0°. The moment arm of the knee extensor mechanism exhibits a characteristic bell shape which peaks somewhere in the 40°–60° region of flexion. In general, the quadriceps force results primarily from an increase in the torque exerted by the weight of the lower leg. In the range of 20°–60°, the quardricep force needed to extend the leg remains relatively constant. As the knee approaches full extension, the moment arm decreases due to the fact that the posterior capsule and the ACL begin to tighten in this region. Consequently, the quadriceps force increases rapidly.     

Maximum finger force prediction using a planar simulation of the middle finger

Maximum isometric finger-grip forces were predicted using a biomechanical model for plane motion of the middle finger. In the course of this study, mathematical representations of tendon displacement, the moment arm of tendon at the finger joints and muscle force-length relationship were investigated. The information gathered was applied to the model to estimate the maximum grip force of the middle finger gripping cylinders of different sizes. Muscle force per unit physiological cross-section area of 30 N/cm2 resulted in good agreement with measured force. However, for finger postures having an acute proximal interphalangeal joint angle, the estimated force was greater than that measured. Various joint angles were applied to the model to simulate the wrist and finger postures not limited to the cylinder grip. In general the finger force was greatest with the wrist in its extended position and at acute flexion of the proximal interphalangeal joint. The maximum finger force occurred at reduced metacarpophalangeal joint angles as the wrist joint changed from an extended position to a flexed one. It is also postulated that muscle force-length relationship is an important factor in muscle force predictions. The data obtained by this research are useful for the design of handles and the current model is applicable to the analysis of hand postures for workers using hand tools.     

The biomechanics of a validated finite element model of stress shielding in a novel hybrid total knee replacement

This study proposes a novel hybrid total knee replacement (TKR) design to improve stress transfer to bone in the distal femur and, thereby, reduce stress shielding and consequent bone loss. Three-dimensional finite element (FE) models were developed for a standard and a hybrid TKR and validated experimentally. The Duracon knee system (Stryker Canada) was the standard TKR used for the FE models and for the experimental tests. The FE hybrid device was identical to the standard TKR, except that it had an interposing layer of carbon fibre-reinforced polyamide 12 lining the back of the metallic femoral component. A series of experimental surface strain measurements were then taken to validate the FE model of the standard TKR at 3000 N of axial compression and at 0 degreeof knee flexion. Comparison of surface strain values from FE analysis with experiments demonstrated good agreement, yielding a high Pearson correlation coefficient of R(2)= 0.94. Under a 3000N axial load and knee flexion angles simulating full stance (0O degree, heel strike (200 degrees, and toe off (600 degrees during normal walking gait, the FE model showed considerable changes in maximum Von Mises stress in the region most susceptible to stress shielding (i.e. the anterior region, just behind the flange of the femoral implant). Specifically, going from a standard to a hybrid TKR caused an increase in maximum stress of 87.4 per cent (O0 degree from 0.15 to 0.28 MPa), 68.3 per cent (200 degrees from 1.02 to 1.71 MPa), and 12.6 per cent (600 degrees from 2.96 to 3.33 MPa). This can potentially decrease stress shielding and subsequent bone loss and knee implant loosening. This is the first report to propose and biomechanically to assess a novel hybrid TKR design that uses a layer of carbon fibrereinforced polyamide 12 to reduce stress shielding.     

Biomechanical simulation of an amputated forearm with and without a prosthesis

In this study a computer simulation was developed for analysing the performance of a below-elbow amputated forearm, with and without a prosthesis. The upper extremity was represented in terms of two rigid bodies, the arm and the forearm. Five muscles, three elbow flexors and two elbow extensors, were included in the model. The muscle model used was the five-component model, including the contractile, parallel, series and viscous elements and the muscle mass. Dynamic and static simulations were conducted, with and without prosthesis, to study parametrically the effects of stump length, tendon distal transfer, tendon or muscle shortening and muscle physiological cross-sectional area. The performance measures which were the most affected included flexion moment of the forearm about the elbow, muscle moment, force in the joint, flexion rate and mechanical energy. The simulation presented an interesting case when the amputation site is more proximal than the anatomical insertion point of a muscle, necessitating shortening of the muscle to avoid the situation where it exerts no force. It was also found that, of the changeable parameters, the most beneficial changes in the forearm parameters for improved dynamic performance were: (a) tendon distal transfer and (b) increase of the muscle cross-sectional area, the latter achievable by means of physical training.     

Effect of twisting hamstring tendon grafts on strength and joint laxity through the range of knee movement

Twisting or braiding of hamstring tendon grafts for use in anterior cruciate ligament reconstructions has been advocated to increase their strength and stiffness under load. In this study, a two-dimensional model was used to determine the failure strength of twisted and parallel grafts and associated knee laxity under simulated physiological loading conditions. For validation, mechanical tests of tendon grafts were also simulated with these models. The simulated physiological loading of the graft models showed that knees with twisted grafts had greater laxity than knees with parallel grafts, although there was little difference in failure load between the two graft configurations. The tensile loading of the graft models showed little difference in failure load when the tendons were modelled using line segments. When the tendons were considered as three-dimensional helical elements, which more accurately describe the tendon structure, the failure load of the twisted graft decreased significantly. This research provided no evidence to support the belief that a twisted tendon graft is a superior graft configuration relative to a parallel tendon graft.     

Mechanics of the passive knee joint. Part 2: interaction between the ligaments and the articular surfaces in guiding the joint motion

The aim of this study was to examine how the interaction between ligament tensions and contact forces guides the knee joint through its specific pattern of passive motion. A computer model was built based on cadaver data. The passive motion and the ligament lengthening and force patterns predicted by the model were verified with data from the literature. The contribution of each ligament and contact force was measured in terms of the rotational moment that it produced about the tibial medial plateau and the anterior-posterior (AP) force that it exerted on the tibia. The high tension of the anterior cruciate ligament (ACL) and the geometric constraints of the anterior horns of the menisci were found to be key features that stabilized the knee at full extension. The mutual effect of the cruciates was found as the reason for the screw-home mechanism at early flexion. Past 300, the AP component of contact force on the convex geometry of the lateral tibial plateau and tension of the lateral collateral ligament (LCL) were identified as elements that control the joint motion. From 60 degrees to 90 degrees, reduction in the tension of the ACL was determined as a reason for continuation of the tibial anterior translation. From 90 degrees to 120 degrees, increase in the tension of the posterior cruciate ligament and the AP component of the contact force on the convex geometry of the lateral tibial plateau pushed the tibia more anteriorly. This anterior translation was limited by the constraining effects of the ACL tension and the AP component of the contact force on the medial meniscus. The important guiding role observed for the LCL suggests that it should not be overlooked in knee models.     

The effect of cartilage deformation on the laxity of the knee joint

In this paper, deformation of the articular cartilage layers is incorporated into an existing two-dimensional quasi-static model of the knee joint. The new model relates the applied force and the joint displacement, as measured in the Lachmann drawer test, and allows the effect of cartilage deformation on the knee joint laxity to be determined. The new model augments the previous knee model by calculating the tibio-femoral contact force subject to an approximate 'thin-layer' constitutive equation, and a method is described for finding the configuration of the knee under a specified load, in terms of a displacement from a zero-load reference configuration. The results show that inclusion of deformable cartilage layers can cause a reduction of between 10 and 35 per cent in the force required to produce a given tibial displacement, over the range of flexion angles considered. The presence of cartilage deformation was found to be an important modifier of the loading response but is secondary to the effect of ligamentous extension. The flexion angle dependence of passive joint laxity is much more strongly influenced by fibre recruitment in the ligaments than by cartilage deformation.     

Knee and hip joint forces--sensitivity to the degrees of freedom classification at the knee

Previous research has demonstrated that the number of degrees of freedom (DOF) modelled at a given joint affects the antagonistic muscle activity predicted by inverse dynamics optimization techniques. This higher level of muscle activity in turn results in greater joint contact forces. For instance, modelling the knee as a 3 DOF joint has been shown to result in higher hip and knee joint forces commensurate with a higher level of muscular activity than when the knee is modelled with 1 DOF. In this study, a previously described musculoskeletal model of the lower limb was used to evaluate the sensitivity of the knee and hip joint contact forces to the DOF at the knee during vertical jumping in both a 1 and a 3 DOF knee model. The 3 DOF knee was found to predict higher tibiofemoral and hip joint contact forces and lower patellofemoral joint contact forces. The magnitude of the difference in hip contact force was at least as significant as that found in previous research exploring the effect of subject-specific hip geometry on hip contact force. This study therefore demonstrates a key sensitivity of knee and hip joint contact force calculations to the DOF at the knee. Finally, it is argued that the results of this study highlight an important physiological question with practical implications for the loading of the structures of the knee; that is, the relative interaction of muscular, ligamentous, and articular structures in creating moment equilibrium at the knee.     

Long-term results for Kinemax and Kinematic knee bearings on a six-station knee wear simulator

A long-term wear test was performed on Kinemax and Kinematic (Howmedica Inc.) knee bearings on the Durham six-station knee wear simulator. The bearings were subjected to flexion/extension of 65-0 degrees, anterior-posterior translation of between 4.5 and 8.5 mm and a maximum axial load of 3 kN. Passive abduction/adduction and internal/external rotation were also permitted, however, two of the stations had a linkage system which produced +/- 5 degrees active internal/external rotation. The bearings were tested at 37 degrees C in a 30 per cent bovine serum solution and the test was run to 5.6 x 10(6) cycles. The bearings from stations 2 and 3, and stations 4 and 5 were swapped during the test to investigate the effects of interstation variability. The average wear rate and standard error was 3.00 +/- 0.98 mg/10(6) cycles (range 1.33-4.72 mg/10(6) cycles) for the Kinemax bearings and 3.78 +/- 1.04 mg/10(6) cycles (range 1.87-4.89 mg/10(6) cycles) for the Kinematic bearings. There were no significant differences in wear rates between the different bearing designs, the addition of active internal/external rotation or a change of stations. However, the wear tracks were different for the two types of bearings and with active internal/external rotation. The wear rates and factors were generally lower than previously published in vitro wear results; however, this may have been due to a difference in the axial loads and lubricants used. The appearance of the wear tracks with active internal/external rotation was comparable with those seen on explanted knee bearings.     

Intersegmental dynamics of the lower limb in vertical jumps

The purpose of this study was to investigate changes in intersegmental dynamics of the lower limb at the instant of push-off in vertical jumps. Using a mathematical model including dynamic equations, the net joint moment (NET) was decomposed into a muscle moment (MUS), gravitational moment, and interaction moment (INT) in terms of joint acceleration and velocity. Ten subjects performed two submaximal jumps(60% and 80% of maximal height) and one maximal jump. Results showed that the hip and ankle joints mainly utilized MUS to generate NET at the push-off instant, while the knee joint primarily used INT at the instant of push-off. The hip MUS increased with increasing jump height because the deep countermovement (larger flexion angle of hip and knee joint at the push-off instant) in maximal jump was a disadvantage from intersegmental dynamics, but may be neurophysiologically advantageous.     

The effects of trochlear groove geometry on patellofemoral joint stability--a computer model study

The effect of the variation in the femoral groove geometry on patellofemoral joint stability was studied using a two-dimensional transverse plane model with deformable articular surfaces. The femoral and patellar bony structures were modelled as rigid bodies with their profiles expressed by splines. The articular cartilage was discretized into compression springs, distributed along the femoral and patellar profiles, based on the rigid-body spring model. The medial and lateral retinacula were modelled as linear tensile springs, and the quadriceps muscles and patellar tendon as strings with known tension. The anatomical data were obtained from the transverse plane magnetic resonance images of a normal knee flexed at 20 degrees and from the literature. A dynamic analysis approach was employed to solve the governing equations of the model, i.e. three static equilibrium equations of the patella and a constraint equation for each cartilage spring, explicitly. The results of the model suggest that alteration of the sulcus angle from 139 degrees to 169 degrees causes a lateral shift and tilt of less than 3 mm and 4 degrees. This effect increased slightly with increasing total quadriceps force, however, to significantly more than 7 mm and 18 degrees respectively when the medial retinaculum was released. It was suggested that this might be the combined effect of the medial retinaculum deficiency and trochlear dysplasia that is responsible for patellar subluxation and, particularly, dislocation disorders.     

An AFM study of the nanostructural response of New Zealand white rabbit Achilles tendons to cyclic loading

The nanostructural response of New Zealand white rabbit Achilles tendons to a fatigue damage model was assessed quantitatively and qualitatively using the endpoint of dose assessments of each tendon from our previous study. The change in mechanical properties was assessed concurrently with nanostructural change in the same non-viable intact tendon. Atomic force microscopy was used to study the elongation of D-periodicities, and the changes were compared both within the same fibril bundle and between fibril bundles. D-periodicities increased due to both increased strain and increasing numbers of fatigue cycles. Although no significant difference in D-periodicity lengthening was found between fibril bundles, the lengthening of D-periodicity correlated strongly with the overall tendon mechanical changes. The accurate quantification of fibril elongation in response to macroscopic applied strain assisted in assessing the complex structure–function relationship in Achilles tendons.     

Three-dimensional contact dynamic model of the human knee joint during walking

It is well known that the geometry of the articular surface has a major role in determining the position of articular contact and the lines of action for the contact forces. The contact force calculation of the knee joint under the effect of sliding and rolling is one of the most challenging issues in this field. We present a 3-D human knee joint model including sliding and rolling motions and major ligaments to calculate the lateral and medial condyle contact forces from the recovered total internal reaction force using inverse dynamic contact modeling and the Least-Square method. As results, it is believed that the patella, muscles and tendon affect a lot for the internal reaction forces at the initial heel contact stage. With increasing flexion angles during gait, the decreasing contact area is progressively shifted to the posterior direction on the tibia plateau. In addition, the medial side contact force is larger than the lateral side contact force in the knee joint during normal human walking. The total internal forces of the knee joint are reasonabe compared to previous studies.     

An optimal control model for determining articular contact forces at the human knee during rising from a static squat position

A two-dimensional dynamic model of the knee joint was incorporated into a four-segment, eight-muscle model of the human body to determine the muscle, ligament, and articular contact forces transmitted at the knee as humans stand up from a static squatting position. Our optimal control model predicted peak tibiofemoral contact forces 8 times as high as body weight. Furthermore, ligament forces, especially those in the anterior-cruciate, were nearly body weight as knee flexion approached 90 degrees. Ligament and tibiofemoral contact loads were dominated by the forces exerted by muscles during the movement.     

Effect of ultra-high molecular weight polyethylene thickness on contact mechanics in total knee replacement

One of the important design parameters in current knee joint replacements is the thickness of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert, yet there is no clear definition of the upper limit of the 'thick' polyethylene insert. Using one design knee implant and subjecting it to the physiological loads encountered throughout the gait cycle, measurements of the lengths of contact imprints generated were compared with the corresponding theoretical predictions for different insert thicknesses under the same applied load. Multiple regression analysis was applied to test whether the dimensions of contact imprints are influenced by UHMWPE thickness. Good agreement was obtained between the theoretical predictions and the experimental measurements of the dimensions of contact imprints when the knee was at 60 degrees flexion. Therefore, it was possible to estimate the contact pressure at the articulating surface using the theoretical model. Contact imprint dimensions increased with increasing applied load. Statistical analysis of the experimental data revealed that, at 0 degree flexion, the overall imprint dimensions increased as the UHMWPE thickness increased from 8 to 20 mm. However, the increment was not significant when the thickness subinterval 10-15 mm was considered. Furthermore, at 60 degrees flexion, thickness was not a significant factor for the overall imprint dimensions. No evidence was found from the data to suggest that an increment in polyethylene thickness over 10 mm would significantly reduce the contact imprint dimensions. These findings suggest that thicker inserts can be avoided, as they require unnecessary bone resection.     

简支梁在移动载荷作用下的最大剪力和最大弯矩

应用剪力图、弯矩图和代数二次函数极值的知识,对简支梁受移动载荷作用时的最大剪力和最大弯矩的计算方法进行了论证。     

Influence of the varus-valgus instability on the contact of the femoro-tibial joint

The varus-valgus instability of the knee joint is mainly due to ruptured or lax collateral ligaments. The purpose of this investigation was to study the influence of the varus-valgus instability on the contact pressures of the femoro-tibial joint. Six fresh knee specimens of human cadavers were tested to measure the contact pressure on the tibia plateau of the knee joint at varus or valgus alignment under various loads and at full extension. Pressure transducers and Bourdon tube pressure gauges were used simultaneously for recording pressure. At neutral alignment of the knee with the menisci intact, the peak pressure increased linearly with forces up to 4 MPa. With increasing varus alignment, the peak contact pressure on the medial plateau not covered by the menisci increased up to a maximum of 7.3 MPa at 5 degrees varus, and at 5 degrees valgus, the peak pressure on the lateral plateau was 7.8 MPa. After total meniscectomy, the contact pressure increased up to a maximum of 7.4 MPa at a force of 2700 N. With increasing varus alignment, the contact pressure on the medial plateau increased to 8.1 MPa at 5 degrees varus and on the lateral plateau 9.2 MPa at 5 degrees valgus.     

Modeling of the dynamics of tendon-driven robotic mechanisms with flexible tendons

In this paper, a systematic methodology for the dynamic analysis of tendon-driven robotic mechanisms with compliant tendons is presented. The compliance of tendons and inertias of the intermediate links in the mechanism are taken into account. Representing the tendon force by use of a rectifying operator, the unidirectional force transmission characteristic of tendons can be preserved. The dynamic equations can then be systematically established in a recursive manner using the Newton–Euler equations. The joint reaction forces and the tension in each segment of tendon can be also obtained. The methodology can be applied to both endless and open-ended tendon-driven robotic mechanisms.