Ligament fibre recruitment and forces for the anterior drawer test at the human ankle joint

Although the anterior drawer test at the ankle joint is commonly used in routine clinical practice, very little is known about the sharing of load between the individual passive structures and the joint response at different flexion angles.A mathematical model of the ankle joint was devised to calculate ligament fibre recruitment and load/displacement curves at different flexion angles. Ligaments were modelled as three-dimensional arrays of fibres, and their orientations at different flexion angles were taken from a previously validated four-bar-linkage model in the sagittal plane. A non-linear stress/strain relationship was assumed for ligament fibres and relevant mechanical parameters were taken from two reports in the literature. Talus and calcaneus were assumed to move as a single rigid body. Antero/distal motion of the talus relative to the tibia was analysed.The ankle joint was found to be stiffer at the two extremes of the flexion range, and the highest laxity was found around the neutral position, confirming previous experimental works. With a first dataset, a 20N anterior force produced 4.3, 5.5, and 4.4mm displacement respectively at 20 degrees plantarflexion, at neutral, and at 20 degrees dorsiflexion. At 10 degrees plantarflexion, for a 6mm displacement, 65% of the external force was supported by the anterior talofibular, 11% by the deep anterior tibiotalar and 5.5% by the tibionavicular ligament. Corresponding results from a second dataset were 1.4, 2.4 and 1.8mm at 40N force, and 80%, 0% and 2% for a 3mm displacement. A component of the contact force supported the remainder.     

Evaluation of a cruciate ligament model: sensitivity to the parameters during drawer test simulation

The knowledge of how cruciate ligaments stabilize the knee joint could be very useful during the execution of daily living activities for the development of clinical procedures. The objective of this study was to evaluate a cruciate ligament model that could achieve this knowledge while avoiding any destructive measurements in living healthy subjects. Subject-specific geometries and kinematic data, acquired from a living subject, were the foundations of the devised model. Each cruciate ligament was modeled with 25 linear-elastic elements and their geometrical properties were subject specific. The anteroposterior drawer test was simulated, and the sensitivity to the reference length and the elastic modulus was performed. Laxity, anterior, and posterior stiffness were calculated and compared with the literature. The laxity was most sensitive to reference length but fitted the literature well considering the reference length estimated from the subject. Both stiffnesses were most sensitive to elastic modulus variations. At full extension, anterior stiffness overestimated the literature, but at 90 degrees good comparisons with the literature were obtained. Posterior stiffness showed smaller overestimations. The devised model, when properly improved, could evaluate the role of the cruciate ligaments of a living subject during the execution of daily living activities.     

Required test duration for group comparisons in ligament viscoelasticity: a statistical approach

The goal of this study was to determine the duration of time that ligaments from a study group need to be loaded in order to adequately determine their collective viscoelastic behavior. Rat ligaments were subjected either to creep or stress relaxation for 1,000 s or stress relaxation for 10,000 s to compare estimates of viscoelastic behavior for different test durations. Stresses versus time (relaxation) or strains versus time (creep) were fit with power law models (tbeta where beta is the rate of creep or relaxation on a log-log scale). Time intervals were separated by logarithmic decade and analyzed using a Random Coefficients approach to compute residual specimen error as a function of the number of decades of data analyzed. Standard Regression was also used for comparison. Results show that by testing for 相似文献   

An instrumented,dynamic test for anterior laxity of the ankle joint complex

Evaluation of anterior laxity of the ankle joint complex is a difficult clinical problem. Currently, the prime determinant for anterolateral ligament function is the subjective manual examination of anterior laxity of the ankle joint complex. An instrumented dynamic test was developed for objective measurement of anterior laxity of the ankle joint complex. The principle of the test was to apply a force-impulse to the calcaneus, within the muscle reflex time, and to measure anterior–posterior and mediolateral rotation. The test was performed on a cadaver specimen and on 15 volunteers of which five subjects suffered from chronic one-sided lateral ankle ligament instability.

In the cadaver test, anterior translation values increased from 5 to 11 mm, after cutting the anterior talofibular ligament and subsequently cutting the calcaneofibular ligament. In the 10 normal subjects, the mean anterior translation value was 6.7 mm (±1.9 mm). The relative variation of the test result within a measurement session was 2.5% (±1.6%). Between the sessions the relative laxity variation was 2.6% (±2.6%). In the ten normal subjects the mean right–left difference was not significantly different from zero. In four out of the five patients it was more than 2 mm. As in the cadaver test in all measurements, the mediolateral rotations were small (<2.5°). The volunteers complained about same pain at the heel after multiple test sessions.

In conclusion the dynamic, functional test appears to be capable of objectively measuring a value for anterior laxity of the ankle joint complex reflecting the functional status of the anterolateral ankle ligaments.     

The effects of tibial-femoral angle on the failure mechanics of the canine anterior cruciate ligament

A series of canine femur-ACL-tibia complexes were subjected to tensile tests with axial tibial orientation and 0 degree, 45 degrees or 90 degrees femoral orientation with respect to load direction. A deflection rate of 51.0 cm min-1 was used in all tests. Marked differences occurred in ultimate loads, deflection and energy absorbed as a consequence of differences in femoral-tibial orientation. The mode of structural failure, as determined by post-test examination, also varied markedly as a function of femoral-tibial orientation. It is concluded that differences both in measured mechanical properties and observed failure details are a consequence of varying the loading pattern of the fiber bundles across the finite breadth of the ligament.     

The anterior ligament of the human malleus.

The authors have studied the anterior ligament of the malleus (ALM) from a morphological and embryological point of view. Classical textbooks of anatomy stress the correlation between the ALM and the anterior pin of the sphenoid and define the ligament as a residual of Meckel's cartilage. This study demonstrates the y-shaped form of the ligament, one arm of which reaches the capsule of the temporomandibular joint and the other the pin of the sphenoid bone. Meckel's cartilage pilots the fibres of the ligament itself. Several clinical implications may be hypothesised on the basis of this study.     

Cholesterol-induced effects on the viscoelasticity of monoglyceride bilayers.

Changes in the viscoelastic properties of glycerol monooleate bilayers resulting from the incorporation of cholesterol into the membranes have been measured. The interface tension increases with the cholesterol concentration, reaching saturation for a 4.2:1 mole ratio of cholesterol:lipid in the film-forming solution. Incorporation of cholesterol in the membrane causes the appearance of a large intrinsic viscosity; this also increases with the sterol content of the membrane. Molecular models of lipid-sterol interactions and packing are considered to explain both the observed changes in membrane properties and similarities with comparable lipid systems.     

Size effects in the elasticity and viscoelasticity of bone

 Size effects of large magnitude are observed in the torsional shear modulus and damping of bovine plexiform bone. Damping increases and stiffness decreases with specimen size over all sizes studied. Measurements were conducted in torsion using a laser-based micromechanics apparatus capable of viscoelastic studies over a range of frequencies up to 100 kHz, upon samples of various size, with no parasitic friction or other errors that could mimic any size effect. Torsional tan δ at 1 Hz varies by about a factor of five over the size range 2.8–6.2 mm thick, and is more dependent on specimen thickness at 1 Hz than it is at higher frequency. The size effects are attributed to compliance and viscoelasticity of the interfaces between laminae. These laminae must be substantially stiffer than whole bone. Observed size effects are likely to play a role in understanding scaling laws of bones in living organisms. Received: 12 February 2002 / Accepted: 22 November 2002 R.S. Lakes is also at the Department of Biomedical Engineering, Department of Engineering Physics, Materials Science Program and Rheology Research Center all at the University of Wisconsin. We thank the Whitaker foundation for their support of this work.     

The effects of femoral graft placement on cartilage thickness after anterior cruciate ligament reconstruction

Altered joint motion has been thought to be a contributing factor in the long-term development of osteoarthritis after ACL reconstruction. While many studies have quantified knee kinematics after ACL injury and reconstruction, there is limited in vivo data characterizing the effects of altered knee motion on cartilage thickness distributions. Thus, the objective of this study was to compare cartilage thickness distributions in two groups of patients with ACL reconstruction: one group in which subjects received a non-anatomic reconstruction that resulted in abnormal joint motion and another group in which subjects received an anatomically placed graft that more closely restored normal knee motion. Ten patients with anatomic graft placement (mean follow-up: 20 months) and 12 patients with non-anatomic graft placement (mean follow-up: 18 months) were scanned using high-resolution MR imaging. These images were used to generate 3D mesh models of both knees of each patient. The operative and contralateral knee models were registered to each other and a grid sampling system was used to make site-specific comparisons of cartilage thickness. Patients in the non-anatomic graft placement group demonstrated a significant decrease in cartilage thickness along the medial intercondylar notch in the operative knee relative to the intact knee (8%). In the anatomic graft placement group, no significant changes were observed. These findings suggest that restoring normal knee motion after ACL injury may help to slow the progression of degeneration. Therefore, graft placement may have important implications on the development of osteoarthritis after ACL reconstruction.     

Intrinsic viscoelasticity of blood cell suspensions: effects of erythrocyte deformability

The intrinsic viscoelasticity of erythrocyte suspensions holds great potential for specifying the deformability of the individual, noninteracting cells in an oscillatory shear flow field. In order to extrapolate to zero cell concentration, the complex viscoelastic modulus was measured as a function of hematocrit using 2 Hertz oscillatory flow and a shear rate of 10/sec. This was done for both normal cells and cells with severely reduced deformability when hardened with glutaraldehyde. Suspension media were blood plasma, isotonic saline, and Dextran solutions. The real parts of the complex intrinsic visco-elasticities were obtained by an extrapolation using a regression fit to Huggins' equation. For normal cells in native plasma the values ranged from 1.7 to 2, increasing to the range 2.4 to 3.1 when the plasma was diluted with isotonic saline solution. For hardened cells the value obtained was near 3.5. These results are compared with theories for suspensions of both rigid and deformable particles. Several theories for deformable particles predict an increase in intrinsic viscoelasticity with increases in the ratio of the viscosity of the interior of the particle to that of the suspending medium. This ratio controls the balance between rotational and deformational response of the cell in the flow field. The trends of these theories were observed in the measurements.     

Results of the surgical reconstruction of the anterior cruciate ligament

Results of the surgical reconstruction of the anterior cruciate ligament (ACL), using as a graft fourfold hamstring tendons (gracilis and semitendinosus) and middle third of the patellar ligament, were compared. In all patients that were participating in this study clinical examination and magnetic resonance showed ACL rupture, and apart from the choice of the graft, surgical technique was identical. We evaluated 112 patients with implemented patellar ligament graft and fourfold hamstring tendons graft six months after the procedure. Both groups were similar according to age, sex, activity level, knee instability level and rehabilitation program. The results showed that there was no significant difference between groups regarding Lysholm Knee score, IKDC 2000 score, activity level, musculature hypotrophy, and knee joint stability 6 months after the surgery. Anterior knee pain incidence is significantly higher in the group with patellar ligament graft (44% vs. 21%). Both groups had a significant musculature hypotrophy of the upper leg of the knee joint that was surgically treated, six months after the procedure. Both grafts showed good subjective and objective results.     

Effect of testosterone on the female anterior cruciate ligament

Injuries to the anterior cruciate ligament (ACL) result in immediate and long-term morbidity and expense. Young women are more likely to sustain ACL injuries than men who participate in similar athletic and military activities. Although significant attention has focused on the role that female sex hormones may play in this disparity, it is still unclear whether the female ACL also responds to androgens. The purpose of this study was to determine whether the female ACL was an androgen-responsive tissue. To identify and localize androgen receptors in the female ACL, we used Western blotting and immunofluorescent labeling, respectively, of ACL tissue harvested during surgery from young women (n = 3). We then measured ACL stiffness and assessed total testosterone (T) and free [free androgen index (FAI)] testosterone concentrations, as well as relative estradiol to testosterone ratios (E(2)/T and E(2)/FAI) at three consecutive menstrual stages (n = 20). There were significant rank-order correlations between T (0.48, P = 0.031), FAI (0.44, P = 0.053), E(2)/T (-0.71, P < 0.001), E(2)/FAI (-0.63, P = 0.003), and ACL stiffness near ovulation. With the influences of the other variables controlled, there were significant negative partial rank-order correlations between ACL stiffness and E(2)/T (-0.72, P < 0.001) and E(2)/FAI (-0.59, P = 0.012). The partial order residuals for T and FAI were not significant. These findings suggest that the female ACL is an androgen-responsive tissue but that T and FAI are not independent predictors of ACL stiffness near ovulation. Instead, the relationship between T, FAI, and ACL stiffness was likely influenced by another hormone or sex hormone binding globulin.     

An examination of possible quadriceps force at the time of anterior cruciate ligament injury during landing: A simulation study

Anterior cruciate ligament (ACL) rupture is a common and traumatic injury. Although, identifying the mechanism of ACL injury has received considerable research attention, there are still many unanswered questions. One proposed mechanism asserts that the ACL is injured due to an aggressive quadriceps muscle contraction. However, recently it has been questioned if the magnitude of quadriceps force needed to tear the ACL is physiologically realistic under the conditions where injury occurs during landing (e.g. near full knee extension and within 50ms after impact). To answer this question, a simple simulation model was developed to examine the upper bounds of quadriceps force that can be developed under these conditions. The model included force-length, and force-velocity properties as well as activation dynamics. Model parameters were chosen to provide a high estimate for possible quadriceps force in a young healthy man. The effects of varying quadriceps pre-activation levels were also examined. When using realistic pre-activation levels, the simulated quadriceps force was less than half of what has been shown to cause ACL injury. Even when using maximum pre-activation, the quadriceps force still did not reach close to the level shown to cause injury. Therefore, we conclude that quadriceps force alone seems to be an unlikely mechanism for ACL injury.     

Time course of the effects of vibration on quadriceps function in individuals with anterior cruciate ligament reconstruction

Quadriceps dysfunction is a common, chronic complication following anterior cruciate ligament reconstruction (ACLR) that contributes to aberrant gait biomechanics and poor joint health. Vibration enhances quadriceps function in individuals with ACLR, but the duration of these effects is unknown. This study evaluated the time course of the effects of whole body vibration (WBV) and local muscle vibration (LMV) on quadriceps function. Twenty-four volunteers with ACLR completed 3 testing sessions during which quadriceps isometric peak torque, rate of torque development, and EMG amplitude were assessed prior to and immediately, 10, 20, 30, 45, and 60 min following a WBV, LMV, or control intervention. WBV and LMV (30 Hz, 2g) were applied during six one-minute bouts. WBV increased peak torque 5–11% relative to baseline and control at all post-intervention time points. LMV increased peak torque 6% relative to baseline at 10 min post-intervention and 4–6% relative to control immediately, 10 min, and 20 min post-intervention. The interventions did not influence EMG amplitudes or rate of torque development. The sustained improvements in quadriceps following vibration, especially WBV, suggest that it could be applied at the beginning of rehabilitation sessions to “prime” the central nervous system, potentially improving the efficacy of ACLR rehabilitative exercise.