Hip and knee joint kinematics during a diagonal jump landing in anterior cruciate ligament reconstructed females

Anterior cruciate ligament (ACL) injury is a common injury encountered by sport medicine clinicians. Surgical reconstruction is the recommended treatment of choice for those athletes wishing to return to full-contact sports participation and for sports requiring multi-directional movement patterns. The aim of ACL reconstruction is to restore knee joint mechanical stability such that the athlete can return to sporting participation. However, knowledge regarding the extent to which lower limb kinematic profiles are restored following ACL reconstruction is limited. In the present study the hip and knee joint kinematic profiles of 13 ACL reconstructed (ACL-R) and 16 non-injured control subjects were investigated during the performance of a diagonal jump landing task. The ACL-R group exhibited significantly less peak knee joint flexion (P=0.01). Significant between group differences were noted for time averaged hip joint sagittal plane (P<0.05) and transverse plane (P<0.05) kinematic profiles, as well as knee joint frontal plane (P<0.05) and sagittal plane (P<0.05) kinematic profiles. These results suggest that aberrant hip and knee joint kinematic profiles are present following ACL reconstruction, which could influence future injury risk.     

Effect of knee musculature on anterior cruciate ligament strain in vivo

Squatting is a commonly prescribed exercise following reconstruction of the anterior cruciate ligament (ACL). The objective of this paper was to measure the in vivo strain patterns of the normal ACL and the load at the knee for the simple squat and for squatting with a “sport cord”. A sport cord is a large elastic rubber tube used for added resistance. Strain patterns were deduced using displacement data from a Hall Effect Strain Transducer (HEST), while joint loads were determined by a mathematical model with inputs from a force plate and electrogoniometers. ACL strain for the free squat in one subject had a maximum of 2% at a knee angle of 10° and was slack for knee angles >17°. In squatting with a sport cord, peak strain was 1% at 10° and was slack at knee angles >14°. Since these peak strains are low, squatting appears to be a safe exercise for conservative rehabilitation of ACL reconstruction patients. In addition, the sport cord is a recommended augmentation to the activity. We believe that the decrease in strain with the sport cord results from added joint stiffness due to greater compressive forces at the tibiofemoral joint. This greater compressive force results from the approximately 10% increase in quadriceps activity. From shear force data predicted by the mathematical model, the maximum anterior drawer force for free squatting (50 N) was considerably less than for sport cord squatting (430 N). Therefore, the value of shear force at the tibiofemoral joint only partially determines the load placed on the ACL.     

A wearable system to assess risk for anterior cruciate ligament injury during jump landing: measurements of temporal events, jump height, and sagittal plane kinematics

The incidence of anterior cruciate ligament (ACL) injury remains high, and there is a need for simple, cost effective methods to identify athletes at a higher risk for ACL injury. Wearable measurement systems offer potential methods to assess the risk of ACL injury during jumping tasks. The objective of this study was to assess the capacity of a wearable inertial-based system to evaluate ACL injury risk during jumping tasks. The system accuracy for measuring temporal events (initial contact, toe-off), jump height, and sagittal plane angles (knee, trunk) was assessed by comparing results obtained with the wearable system to simultaneous measurements obtained with a marker-based optoelectronic reference system. Thirty-eight healthy participants (20 male and 18 female) performed drop jumps with bilateral and unilateral support landing. The mean differences between the temporal events obtained with both systems were below 5 ms, and the precisions were below 24 ms. The mean jump heights measured with both systems differed by less than 1 mm, and the associations (Pearson correlation coefficients) were above 0.9. For the discrete angle parameters, there was an average association of 0.91 and precision of 3.5° for the knee flexion angle and an association of 0.77 and precision of 5.5° for the trunk lean. The results based on the receiver-operating characteristic (ROC) also demonstrated that the proposed wearable system could identify movements at higher risk for ACL injury. The area under the ROC plots was between 0.89 and 0.99 for the knee flexion angle and between 0.83 and 0.95 for the trunk lean. The wearable system demonstrated good concurrent validity with marker-based measurements and good discriminative performance in terms of the known risk factors for ACL injury. This study suggests that a wearable system could be a simple cost-effective tool for conducting risk screening or for providing focused feedback.     

Elevated gastrocnemius forces compensate for decreased hamstrings forces during the weight-acceptance phase of single-leg jump landing: implications for anterior cruciate ligament injury risk

Approximately 320,000 anterior cruciate ligament (ACL) injuries in the United States each year are non-contact injuries, with many occurring during a single-leg jump landing. To reduce ACL injury risk, one option is to improve muscle strength and/or the activation of muscles crossing the knee under elevated external loading. This study?s purpose was to characterize the relative force production of the muscles supporting the knee during the weight-acceptance (WA) phase of single-leg jump landing and investigate the gastrocnemii forces compared to the hamstrings forces. Amateur male Western Australian Rules Football players completed a single-leg jump landing protocol and six participants were randomly chosen for further modeling and simulation. A three-dimensional, 14-segment, 37 degree-of-freedom, 92 muscle-tendon actuated model was created for each participant in OpenSim. Computed muscle control was used to generate 12 muscle-driven simulations, 2 trials per participant, of the WA phase of single-leg jump landing. A one-way ANOVA and Tukey post-hoc analysis showed both the quadriceps and gastrocnemii muscle force estimates were significantly greater than the hamstrings (p<0.001). Elevated gastrocnemii forces corresponded with increased joint compression and lower ACL forces. The elevated quadriceps and gastrocnemii forces during landing may represent a generalized muscle strategy to increase knee joint stiffness, protecting the knee and ACL from external knee loading and injury risk. These results contribute to our understanding of how muscle?s function during single-leg jump landing and should serve as the foundation for novel muscle-targeted training intervention programs aimed to reduce ACL injuries in sport.     

The effect of weightbearing and external loading on anterior cruciate ligament strain

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anterior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing conditions. Our objective was to compare the ACL strain response under weightbearing and non-weightbearing conditions and in combination with three externally applied loadings: (1) anterior-posterior shear forces, (2) internal-external torques, and (3) varus-valgus moments. A strain transducer was implanted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20 degrees of flexion. A significant increase in ACL strain was observed as the knee made the transition from non-weightbearing to weightbearing. During anterior shear loading, the strain values produced during weightbearing were greater than those of the non-weightbearing knee (shear loads <40N). At higher shear loads, the strain values became equal. During axial torsion, an internal torque of 10Nm strained the ACL when the knee was non-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbearing with the application of external torques and low internal torques (<3Nm). The strains became equal for higher internal torques. For V-V loading, the ACL was not strained in the non-weightbearing knee. However, weightbearing increased the ACL strain values over the range of moments tested. These data have important clinical ramifications in the development of rehabilitation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft.     

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.     

Forward-dynamics simulation of anterior cruciate ligament forces developed during isokinetic dynamometry

A mathematical (computer) model was developed and used to study the mechanics of the human knee during extension exercises employing an isokinetic dynamometer. All parts of the body were fixed to ground, except for the right shank and foot, which were free to move in the parasagittal plane. A linkage attached the dynamometer to the shank; tibiofemoral articulation consisted of single-point contact, allowing both sliding and rolling to occur. Physiologically based representations of ligaments and muscles imparted forces to the shank. A forward dynamics simulation was performed to calculate the forces developed in the knee for isokinetic speeds ranging from 0 (isometric exercise) to 300 degrees /s. Simulations were conducted for a constant-speed phase during isokinetic knee extension exercise. It was assumed for the duration of each simulated exercise that the quadriceps were fully activated and the other muscles were fully deactivated. The force in the anterior cruciate ligament was found to be governed by the force-velocity properties of the quadriceps; the model predicts that 300 deg/sec isokinetic exercise can reduce the force transmitted to the ACL by almost a factor of two compared with that present during isometric knee extension.     

Quantifying in vivo laxity in the anterior cruciate ligament and individual knee joint structures

A custom knee loading apparatus (KLA), when used in conjunction with magnetic resonance imaging, enables in vivo measurement of the gross anterior laxity of the knee joint. A numerical model was applied to the KLA to understand the contribution of the individual joint structures and to estimate the stiffness of the anterior-cruciate ligament (ACL). The model was evaluated with a cadaveric study using an in situ knee loading apparatus and an ElectroForce test system. A constrained optimization solution technique was able to predict the restraining forces within the soft-tissue structures and joint contact. The numerical model presented here allowed in vivo prediction of the material stiffness parameters of the ACL in response to applied anterior loading. Promising results were obtained for in vivo load sharing within the structures. The numerical model overestimated the ACL forces by 27.61–92.71%. This study presents a novel approach to estimate ligament stiffness and provides the basis to develop a robust and accurate measure of in vivo knee joint laxity.     

Pattern of anterior cruciate ligament force in normal walking

The goal of this study was to calculate and explain the pattern of anterior cruciate ligament (ACL) loading during normal level walking. Knee-ligament forces were obtained by a two-step procedure. First, a three-dimensional (3D) model of the whole body was used together with dynamic optimization theory to calculate body-segmental motions, ground reaction forces, and leg-muscle forces for one cycle of gait. Joint angles, ground reaction forces, and muscle forces obtained from the gait simulation were then input into a musculoskeletal model of the lower limb that incorporated a 3D model of the knee. The relative positions of the femur, tibia, and patella and the forces induced in the knee ligaments were found by solving a static equilibrium problem at each instant during the simulated gait cycle. The model simulation predicted that the ACL bears load throughout stance. Peak force in the ACL (303 N) occurred at the beginning of single-leg stance (i.e., contralateral toe off). The pattern of ACL force was explained by the shear forces acting at the knee. The balance of muscle forces, ground reaction forces, and joint contact forces applied to the leg determined the magnitude and direction of the total shear force acting at the knee. The ACL was loaded whenever the total shear force pointed anteriorly. In early stance, the anterior shear force from the patellar tendon dominated the total shear force applied to the leg, and so maximum force was transmitted to the ACL at this time. ACL force was small in late stance because the anterior shear forces supplied by the patellar tendon, gastrocnemius, and tibiofemoral contact were nearly balanced by the posterior component of the ground reaction.     

The effects of femoral graft placement on in vivo knee kinematics after anterior cruciate ligament reconstruction

Achieving anatomical graft placement remains a concern in Anterior Cruciate Ligament (ACL) reconstruction. The purpose of this study was to quantify the effect of femoral graft placement on the ability of ACL reconstruction to restore normal knee kinematics under in vivo loading conditions. Two different groups of patients were studied: one in which the femoral tunnel was placed near the anterior and proximal border of the ACL (anteroproximal group, n=12) and another where the femoral tunnel was placed near the center of the ACL (anatomic group, n=10) MR imaging and biplanar fluoroscopy were used to measure in vivo kinematics in these patients during a quasi-static lunge. Patients with anteroproximal graft placement had up to 3.4mm more anterior tibial translation, 1.1mm more medial tibial translation and 3.7° more internal tibial rotation compared to the contralateral side. Patients with anatomic graft placement had motion that more closely replicated that of the intact knee, with anterior tibial translation within 0.8mm, medial tibial translation within 0.5mm, and internal tibial rotation within 1°. Grafts placed anteroproximally on the femur likely provide insufficient restraint to these motions due to a more vertical orientation. Anatomical femoral placement of the graft is more likely to reproduce normal ACL orientation, resulting in a more stable knee. Therefore, achieving anatomical graft placement on the femur is crucial to restoring normal knee function and may decrease the rates of joint degeneration after ACL reconstruction.     

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.     

Development of a traumatic anterior cruciate ligament and meniscal rupture model with a pilot in vivo study

The current study describes the development of a small animal, closed-joint model of traumatic anterior cruciate ligament (ACL) and meniscal rupture. This model can be used in future studies to investigate the roles of these acute damages on the long-term health of an injured knee joint. Forty-two Flemish Giant rabbits received an insult to the left tibiofemoral joint ex vivo in order to document optimal energy and joint orientation needed to generate ACL and meniscal rupture, without gross fracture of bone. Impact energies ranged from 10 J to 22 J, and joint flexion angle ranged from 60 deg to 90 deg. Three in vivo animals were impacted at 13 J with the knee flexed at 90 deg, as this was determined to be the optimal load and joint orientation for ACL and meniscal ruptures, and sacrificed at 12 weeks. Impact data from the ex vivo group revealed that 13 J of dropped-mass energy, generating approximately 1100 N of load on the knee, would cause ACL and meniscal ruptures, without gross bone fracture. Acute damage to the lateral and medial menisci was documented in numerous ex vivo specimens, with isolated lateral meniscal tears being more frequent than isolated medial tears in other cases. The in vivo animals showed no signs of ill health or other physical complications. At 12 week post-trauma these animals displayed marked degeneration of the traumatized joint including synovitis, cartilage erosion, and the formation of peripheral osteophytes. Histological microcracks at the calcified cartilage-subchondral bone interface were also evident in histological sections of these animals. A closed-joint model of traumatic ACL and meniscal rupture was produced, without gross bone fracture, and a pilot, in vivo study showed progressive joint degeneration without any other noticeable physical impairments of the animals over 12 weeks. This closed-joint, traumatic injury model may be useful in future experimental studies of joint disease and various intervention strategies.     

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.     

Side-to-side differences in anterior cruciate ligament volume in healthy control subjects

Examination of anterior cruciate ligament (ACL) anatomy is of great interest both in studying injury mechanisms and surgical reconstruction. However, after a typical acute ACL rupture it is not possible to measure the dimensions of the ACL itself due to concomitant or subsequent degeneration of the remaining ligamentous tissue. The contralateral ACL may be an appropriate surrogate for measuring anatomical dimensions, but it remains unknown whether side-to-side differences preclude using the contralateral as a valid surrogate for the ruptured ACL. This study examined whether the ACL volume is significantly different between the left and right knees of uninjured subjects. ACL volumes were calculated for the left and right sides of 28 individuals using a previously validated MRI-based method. The mean ACL volume was not significantly different (p=0.2331) between the two sides in this population. Side-to-side ACL volume was also well correlated (correlation=0.91, p<0.0001). The results of this study show that the volume of the contralateral ACL is a valid surrogate measure for a missing ACL on the injured side. This non-invasive, in vivo technique for measuring ACL volume may prove useful in future large-scale comprehensive studies of potential risk factors for ACL rupture, in quantifying potential loading effects on ACL size as a prophylactic measure against ACL rupture, and in the use of ACL volume as a screening tool for assessing risk of injury.     

Kinematic motion of the anterior cruciate ligament deficient knee during functionally high and low demanding tasks

The purpose of this study was to determine whether mechanical adaptations were present in patients with anterior cruciate ligament (ACL)-deficient knees during high-demand activities. Twenty-two subjects with unilateral ACL deficiency (11 males and 11 females, 19.6 months after injury) performed five different activities at a comfortable speed (level walking, ascending and descending steps, jogging, jogging to a 90-degree side cutting toward the opposite direction of the tested side). Three-dimensional knee kinematics for the ACL-deficient knees and uninjured contralateral knees were evaluated using the Point Cluster Technique. There was no significant difference in knee flexion angle, but an offset toward the knee in less valgus and more external tibial rotation was observed in the ACL-deficient knee. The tendency was more obvious in high demand motions, and a significant difference was clearly observed in the side cutting motions. These motion patterns, with the knee in less valgus and more external tibial rotation, are proposed to be an adaptive movement to avoid pivot shift dynamically, and reveal evidence in support of a dynamic adaptive motion occurring in ACL-deficient knees.     

Association between matrix metalloproteinase-3 polymorphism and anterior cruciate ligament ruptures

Anterior cruciate ligament (ACL) ruptures are considered to be the most severe joint injury in sports. However, the precise etiologies of ACL injuries are not fully understood. Recently, the gene encoding the matrix metalloproteinase-3 (MMP-3, stromelysin-1) was shown to be associated with anterior cruciate ligament ruptures. The 5A/6A polymorphism in the promoter of the MMP-3 gene affects the regulation of MMP-3 gene expression. We examined the association between polymorphism within -1612 of the MMP-3 gene and ACL rupture in an independent population. Eighty-six participants between 20 and 40 years of age with surgically diagnosed ACL ruptures and 100 healthy controls between 18 and 28 years of age without history of ligament or tendon injuries were recruited for the study. All participants were genotyped for the MMP-3 polymorphism (-1612 5A/6A). Statistical analyses of genotype frequencies between patients and healthy controls were performed by the chi-square test. A significant difference was found between ACL rupture subgroups in terms of genotype association (5A+ (5A/5A, 5A/6A): 37.5% in contact sports vs 20% in non-contact sports; P = 0.02). In allelic association, there were significant differences (6A: 81.2% in contact sports vs 89.1% in non-contact sports, 5A: 18.8% in contact sports vs 10.9% in non-contact sports, P = 0.01). The 5A+ genotype of MMP-3 was represented in ACL ruptures in contact sport participants. We propose that this sequence variant is a specific genetic element that should be included in a multifactorial model to understand the etiologies and risk factors for ACL rupture.     

Sensitivity of insertion locations on length patterns of anterior cruciate ligament fibers

A technique is demonstrated, employing an instrumented spatial linkage, for the determination of the length patterns of discrete fiber bundles within a ligament under controlled loading conditions. The instrumented spatial linkage was used to measure the three-dimensional joint motion. The linkage was also used as a three-dimensional coordinate digitizer to determine the spatial location of bony landmarks and the ligament's insertion areas. The length of pseudo fiber bundles was determined as the straight line distance between bone attachments. A comparison is presented, showing good agreement, between elongation patterns obtained from this method and those measured using an instrumented fine wire cable fiber. A sensitivity analysis was performed to evaluate the influence of tibial and femoral attachment location on the length pattern of fiber bundles of the anterior cruciate ligament. It was found that the relationship between fiber elongation and knee flexion depended strongly on the fibers femoral attachment location but not on its tibial attachment location.     

Age-dependent expression of VEGF isoforms and receptors in the rabbit anterior cruciate ligament

Vascular endothelial growth factor (VEGF) gene gives rise to several distinct isoforms of VEGF. Those isoforms differ in biochemical and biological properties, and it has been reported that their expression patterns are tissue and age specific as well. We investigated the expression levels of VEGF isoforms (VEGF121, VEGF165, VEGF183, VEGF189) and its receptors (VEGFR-1, flt-1 and VEGFR-2, flk-1/KDR) in the anterior cruciate ligament (ACL) of 2- to 3-week-, 2-month-, and 18-month-old New Zealand White rabbits using Sybr green Real-Time RT-PCR. VEGF isoforms and both receptors were expressed in the ACL at all investigated ages. VEGF121 was found to be the most abundant isoform at the ages under investigation, followed by VEGF165, VEGF189 and VEGF183. All isoforms showed decreased expression levels with age, however the larger membrane bound isoforms, VEGF183 and VEGF189, showed the most striking age-associated decrease in expression level. VEGFR-1 expression levels increased with age, while the expression level of VEGFR-2 expression was highest at 2-3 weeks and was significantly lower at 2 and 18 months of age. Distinct age-associated differences in the expression level of VEGF isoforms as well as their receptors suggest differential physiological functions during development, maturation and ageing of the ACL.