Anterior Cruciate Ligament Tension Research Articles

In Vivo Kinematics and Cruciate Ligament Tension Are Not Restored to Normal After Bicruciate-Preserving Arthroplasty

BackgroundWhether cruciate ligament forces in cruciate-preserving designs, such as unicompartmental knee arthroplasty (UKA) or bi-cruciate-retaining total knee arthroplasty (BCR-TKA), differ from those in normal knees remains unknown. The purpose of this study was to compare the in vivo kinematics and cruciate ligament force in knees before and after UKA or BCR-TKA to those in normal knees during high-flexion activity. MethodsOverall, twenty normal knees, 17 knees with medial UKA, and 15 knees with BCR-TKA were fluoroscopically examined while performing a squatting activity. A 2-dimensional or 3-dimensional registration technique was employed to measure tibio-femoral kinematics. Ligament strains and tensions in the anteromedial bundle of the anterior cruciate ligament and posterolateral bundle of the anterior cruciate ligament and the anterolateral bundle of the posterior cruciate ligament (aPCL) and posteromedial bundle of the posterior cruciate ligament (pPCL) during knee flexion were analyzed. ResultsTension in both bundles of the anterior cruciate ligament decreased with flexion. At 60° of flexion, anteromedial bundle of the anterior cruciate ligament tension in postoperative UKA knees was greater than that in normal knees. At 30° of flexion, posterolateral bundle of the anterior cruciate ligament tension in postoperative UKA knees was greater than that in normal knees. On the other hand, aPCL and pPCL tensions increased with flexion. From 40 to 110° of flexion, the postoperative aPCL tension in UKA knees was greater than that in normal knees. At 110° of flexion, the preoperative pPCL tension in UKA knees was greater than that in normal knees. In addition, the postoperative pPCL tension in UKA knees was larger than that in normal knees beyond 20° of flexion. Furthermore, the pPCL tension of postoperative BCR-TKA knees was larger than that in normal knees from 20 to 50° and beyond 90° of flexion. ConclusionsThe cruciate ligament tensions, especially posterior cruciate ligament tension in knees after UKA, were greater than those in the normal knees. Surgeons performing bi-cruciat-preserving knee arthroplasties should therefore balance cruciate ligament tension more carefully in flexion and extension.

Mechanical properties of a bioabsorbable magnesium interference screw for anterior cruciate ligament reconstruction in various testing bone materials

Tears of the anterior cruciate ligament (ACL) negatively impact the stability and kinematics of the knee. Interference screws (ISs) are used for graft fixation in ACL reconstruction and provide sufficient fixation strength to withstand the patients' activities during the graft-to-bone integration process. Magnesium is a novel material used to manufacture IS given its strength and bioabsorbability. In previous studies, the selected magnesium IS design showed a better fixation performance in comparison to the conventional IS design due to its shape design and surface condition. In this study, bioabsorbable magnesium ISs were tested for their insertion (insertion torque and a number of turns to implement the IS) and fixation performance (pull-out and dynamic test). To obtain a reliable initial assessment of IS performance, ISs were implanted in 15 per cubic foot (PCF) Sawbones polyurethane foam blocks, Sawbones biomechanical tibia models with 17 PCF foam cores, and human cadaveric tibiae. Porcine tendons were used in the foam block pull-out test, and nylon ropes were used in all other test setups to prevent influences of the ligament graft material itself. In the pull-out test, the graft was subjected to tensile stress at a rate of 6 mm/min. For the dynamic test, 1000 cycles between 0 and 200 N were performed, followed by a final pull-out test. After each test, the tunnel widening pattern was observed by measuring the aspect ratio of the tunnel at the insertion site. The insertion torque lies within the normal insertion torque of the ISs as well as the average ligament tension before the insertion. In the foam block setup, the nylon rope showed a higher pull-out force than the porcine tendon. The comparison of each setup using nylon rope for both pull-out and pull-out after the dynamic test showed no significant difference between the foam block and cadaver setup. However, all tibia model setup shows unexpectedly high pull-out force due to the influence of its cortical layer. There were no statistically significant differences in tunnel widening between foam block-porcine tendon and foam block-nylon rope constructs. The pull-out resistance of magnesium ISs falls within the typical ACL tension range during daily activities. Even though the test results of the magnesium ISs are different in each bone material, the magnesium IS shows adequate fixation ability and workability during insertion without material failure.

In-office needle arthroscopic assessment after primary ACL repair: short-term results in 15 patients

PurposeIn-office needle arthroscopy has been reported as a diagnostic tool for different knee pathologies. In addition, ACL repair has seen a resurgence with the advent of innovative orthopedic devices. The aim of this study was to assess clinical, radiological, and in-office needle arthroscopic findings in 15 adult patients who underwent acute (within 14 days from injury) anterior cruciate ligament (ACL) repair.MethodsFifteen patients voluntarily participated in the study. A second-look arthroscopy was performed with an in-office needle arthroscopy at an average of 7.2 months after the primary repair. The parameters included in the investigation were the continuity of the anatomical footprint of the repaired ACL, subjective assessment of the ACL tension with the probe, and synovial coverage of the ACL. All patients had a Magnetic Resonance Imaging (MRI) at 6 months after repair and an arthrometric evaluation with the KT-1000. Clinical evaluation with the scores, Tegner Lysholm Knee Scoring Scale (TLKSS), the Knee Injury and Osteoarthritis Outcome Score (KOOS), and International Knee Documentation Committee (IKDC) was performed at the final follow-up of 2 years. Moreover, a correlation between the characteristics of ACL appearance at the time of the second look in-office needle arthroscopy, MRI and KT-1000 was performed.ResultsThe mean TLKSS was 97.86, the mean KOOS was 98.08 and the mean subjective IKDC was 96.71. The objective IKDC was A in 10 patients and B in 5 patients. ACL healing was graded as A in 11 patients and B in 4 patients. Synovial coverage was graded as good in 10 patients and fair in 5 while MRI assessment showed a type I ACL in 10 patients, type II in 4 patients and type III in 1 patient.ConclusionIn-office needle arthroscopy is a reliable tool to assess the condition of a repaired ACL. In addition, ACL repair performed in acute proximal tears demonstrated excellent clinical results.

A lower leg surrogate study to investigate the effect of quadriceps–hamstrings activation ratio on ACL tensile force

ObjectivesMany studies have investigated the relationship between muscle activation and tensile force of the anterior cruciate ligament. These studies lacked a holistic representation of the muscle status. For instance, they were limited with respect to the peak muscle forces, number of muscles, and possible muscle activation patterns. DesignThis study used a knee surrogate including ten muscles with motor-controlled muscle force activation crossing the knee joint, thus providing a fully muscle-supported knee joint. Methods: Anterior cruciate ligament tensile force is measured in different knee flexion and extension movements to evaluate ratios of quadriceps/hamstring muscle activations in low hip angle setups. ResultsIncreasing the extension of the leg increased anterior cruciate ligament tension forces. Different quadriceps/hamstring ratios had different effects on anterior cruciate ligament tension forces during unrestricted flexion and extension movements. This was dependent on the direction of movement. Sole hamstring activation increased the anterior cruciate ligament tensile forces in extension movements compared with flexion movements. Sole quadriceps activation provoked greater anterior cruciate ligament tensile forces in flexion than in extension. This was not prominent in the test in which the other muscle groups counteracted the dominant muscle group. ConclusionsThe findings from the present study demonstrate that active hamstring activation can reduce the load on the anterior cruciate ligament, and the dominant quadriceps increase anterior cruciate ligament loads for knee flexions of less than 40°. Moreover, the anterior cruciate ligament is loaded differently in flexion or extension movements with flexion movements, resulting in higher anterior cruciate ligament loads.

The Effects of External Loads and Muscle Forces on the Knee Joint Ligaments during Walking: A Musculoskeletal Model Study

A musculoskeletal model was developed to analyze the tensions of the knee joint ligaments during walking and to understand how they change with changes in the muscle forces. The model included the femur, tibia, patella and all components of cruciate and collateral ligaments, quadriceps, hamstrings and gastrocnemius muscles. Inputs to the model were the muscle forces, estimated by a static optimization approach, the external loads (ground reaction forces and moments) and the knee flexion/extension movement corresponding to natural walking. The remaining rotational and translational movements were obtained as a result of the dynamic equilibrium of forces. The validation of the model was done by comparing our results with literature data. Several simulations were carried out by sequentially removing the forces of the different muscle groups. Deactivation of the quadriceps produced a decrease of tension in the anterior cruciate ligament (ACL) and an increase in the posterior cruciate ligament (PCL). By removing the hamstrings, the tension of ACL increased at the late swing phase, while the PCL force dropped to zero. Specific effects were observed also at the medial and lateral collateral ligaments. The removal of gastrocnemius muscles produced an increase of tension only on PCL and lateral collateral ligaments. These results demonstrate how musculoskeletal models can contribute to knowledge about complex biomechanical systems as the knee joint.

Length of anterior cruciate ligament affects knee kinematics and kinetics using a musculoskeletal computer simulation model

IntroductionThe tension of anterior cruciate ligament (ACL) graft has an important role in antero-posterior (AP) and rotational stability of the knee. The purposes of this study were to analyze the kinematics and kinetics of normal knee models with loose and tight ACL tension, and to evaluate the effect of the tension of ACL on knee kinematics and kinetics. Materials and methodsSlack and tight ACL models were constructed in a musculoskeletal computer simulation. The effect of ACL tension on kinematics, and femorotibial contact force during various activities was analyzed. ResultsDuring stair descent activity in the slack ACL models, the lateral femoral condyles were positioned posterior, and more external rotation of the femur was observed in comparison with the normal model. The contact forces at the lateral compartment in the tight models increased during all activities, and the tension of the medial collateral ligament (MCL) in the slack models increased during the stair descent activity, compared with the normal knee model. ConclusionAP and rotational instability and excessive MCL tension were observed in the ACL slack knees especially during stair descent movement, whereas the tibiofemoral contact force of the lateral compartment increased in the tight ACL knees.

Treatment of Acute Proximal Anterior Cruciate Ligament Tears-Part 1: Gap Formation and Stabilization Potential of Repair Techniques.

Background:Recently, there has been a resurgence of interest in primary repair of the anterior cruciate ligament (ACL), with fixation techniques evolving. However, to date, there have been no biomechanical studies comparing fixed to adjustable fixation repair techniques.Hypothesis:Adjustable ACL repair provides for improved stabilization compared with fixed techniques with respect to both gap formation and residual load-bearing capability.Study Design:Controlled laboratory study.Methods:A total of 4 different ACL repair techniques (n = 5 per group), including single– and double–cinch loop (CL) cortical button fixation as well as knotless single–suture anchor fixation, were tested using a porcine model. For adjustable single-CL loop fixation, additional preconditioning (10 cycles at 0.5 Hz) was performed. The force after fixation and the actuator displacement to achieve a time-zero preload of 10 N were measured for fixed techniques. Incrementally increasing cycling (1 mm/500 cycles) from 1 to 8 mm was performed for 4000 cycles at 0.75 Hz before pull to failure (50 mm/min). The final residual peak load and gap formation for each test block were analyzed as well as ultimate strength.Results:Knot tying of a single-CL over a button (mean ± SD, 0.66 ± 0.23 mm) and knotless anchor fixation (0.20 ± 0.12 mm) resulted in significant time-zero gaps (P < .001) and significantly higher overall gap formation at reduced residual loading (analysis of covariance, P < .001) compared with both the double-CL loop and adjustable fixation techniques. The adjustable group showed the highest failure load and stiffness, at 305.7 N and 117.1 N/mm, respectively. The failure load of the knotted single-CL group was significantly reduced compared with all other groups (P < .001).Conclusion:Adjustable single-CL cortical button fixation with intraoperative preconditioning optimized time-zero ACL tension and led to significantly improved stabilization and reduced gap formation, with the highest ultimate strength. Single-CL loop knot tying over the button and knotless anchor fixation resulted in time-zero gaps to achieve slight tension on the ACL and significantly higher gap formation at reduced load-bearing capability.Clinical Relevance:Although the clinical relevance of gap formation is uncertain, a biomechanical understanding of the stabilization potential of current ACL repair techniques is pertinent to the continued evolution of surgical approaches to enable better clinical outcomes.

EMG-Informed Musculoskeletal Modeling to Estimate Realistic Knee Anterior Shear Force During Drop Vertical Jump in Female Athletes.

The anterior cruciate ligament is the primary structural restraint to tibial anterior shear force. The anterior force occurring at the knee during landing contributes to anterior cruciate ligament injury risk, but it cannot be directly measured experimentally. The objective of this study was to develop electromyography-informed musculoskeletal simulations of the drop vertical jump motor task and assess the contribution of knee muscle forces to tibial anterior shear force. In this cross-sectional study, musculoskeletal simulations were used to estimate the muscle forces of thirteen female athletes performing a drop vertical jump using an electromyography-informed method. Muscle activation and knee loads that resulted from these simulations were compared to the results obtained with the more common approach of minimization of muscle effort (optimization-based method). Quadriceps-hamstrings and quadriceps-gastrocnemius co-contractions were progressively increased and their contribution to anterior shear force was quantified. The electromyography-informed method produced co-contraction indexes more consistent with electromyography data than the optimization-based method. The muscles that presented the largest contribution to peak anterior shear force were the gastrocnemii, likely from their wrapping around the posterior aspect of the tibia. The quadriceps-hamstring co-contraction provided a protective effect on the ACL and reduced peak anterior shear force by 292N with a co-contraction index increase of 25% from baseline (31%), whereas a quadriceps-gastrocnemius co-contraction index of 61% increased peak anterior shear force by 797N compared to baseline (42%). An increase in gastrocnemius contraction, which might be required to protect the ankle from the impact with the ground, produced a large quadriceps-gastrocnemius co-activation, increasing peak anterior shear force. A better understanding of each muscle's contribution to anterior shear force and, consequently, anterior cruciate ligament tension may inform subject-specific injury prevention programs and rehabilitation protocols.

Comparison of the Angular Compartment of Hip Flexion Before and After Training in 11 to 12-Year-old Soccer Players.

An anterior cruciate ligament (ACL) injury is an important cause of rest in athletes. In most cases, ACL injuries do not require external contact and they are associated with biomechanical risk factors that increase ACL tension. The increase of the hip flexion angle (HF) is included within these. The ACL requires cooperation of the periarticular musculature of the knee, muscle groups, hip stabilizers and CORE muscles; consequently, fatigue caused by exercise would alter the balance and put this ligament at risk. The objective of the study is to determine the angular behavior for HF before and after a physical load (a standardized training) in children between 11 and 12 years old. A non-randomized clinical study was carried out. The sample consisted of 50 soccer school students born between 11 and 12 years old. The angular behavior of HF was compared before and after performing a training session. The angular behavior was measured through the Drop Jump test (DJ), with data obtained by inertial sensors. After the exercise, there was a significant increase in HF. It was concluded that the angular behavior of HF increases significantly in both extremities after training and that preventive measures must be applied for neuromuscular control of the hip.

Classical target coronal alignment in high tibial osteotomy demonstrates validity in terms of knee kinematics and kinetics in a computer model.

The purpose of this study was to determine the ideal coronal alignment under dynamic conditions after open-wedge high tibial osteotomy (OWHTO). It was hypothesised that, although the classical target alignment was based on experimental evidence, it would demonstrate biomechanical validity. Musculoskeletal computer models were analysed with various degrees of coronal correction in OWHTO during gait and squat, specifically with the mechanical axis passing through points at 40%, 50%, 60%, 62.5%, 70%, and 80% of the tibial plateau from the medial edge, defined as the weight-bearing line percentage (WBL%). The peak load on the lateral tibiofemoral (TF) joint, the medial collateral ligament (MCL), and anterior cruciate ligament (ACL) tensions, and knee kinematics with or without increased posterior tibial slope (PTS) were evaluated. The classical alignment with WBL62.5% achieved sufficient load on the lateral TF joint and maintained normal knee kinematics after OWHTO. However, over-correction with WBL80% caused an excessive lateral load and non-physiological kinematics. Increased WBL% resulted in increased MCL tension due to lateral femoral movement against the tibia. With WBL80%, abnormal contact between the medial femoral condyle and the medial intercondylar eminence of the tibia occurred at knee extension. The screw-home movement around knee extension and the TF rotational angle during flexion were reduced as WBL% increased. Increased PTS was associated with increased ACL tension and decreased TF rotation angle because of ligamentous imbalance. The classical target alignment demonstrated validity in OWHTO, and over-correction should be avoided as it negatively impacts clinical outcome. IV.

Open-Wedge Valgus High Tibial Osteotomy Technique With Inverted L-Shaped Configuration

High tibial osteotomy (HTO) is a useful alternative in the treatment of symptomatic varus malalignment. However, among its drawbacks is the tendency to decrease patellar height and increase the posterior tibial slope. The increased tibial slope increases anterior cruciate ligament tension and may compromise its function. On the other hand, patella baja often causes anterior knee pain and, over time, may favor degeneration of the patellofemoral joint. The aim of this study is to describe a technical modification of the standard open-wedge HTO. It consists of a double inverted L-shaped cut, which includes the anterior tibial tuberosity in the proximal fragment, to avoid any alteration of patellar height and control the eventual increase of the posterior tibial slope.

In Vivo Kinematic Comparison of a Bicruciate Stabilized Total Knee Arthroplasty and the Normal Knee Using Fluoroscopy

BackgroundThe bicruciate stabilized (BCS) total knee arthroplasty (TKA) features asymmetrical bearing geometry and dual substitution for the anterior cruciate ligament and posterior cruciate ligament (PCL). Previous TKA designs have not fully replicated normal knee motion, and they are characterized by lower magnitudes of overall rollback and axial rotation than the normal knee. MethodsIn vivo kinematics were derived for 10 normal knees and 40-second generation BCS TKAs all implanted by a single surgeon. Mobile fluoroscopy and three-dimensional-to-two-dimensional registration was used to analyze anterior-posterior motion of the femoral condyles and femorotibial axial rotation during weight-bearing flexion. Statistical analysis was conducted at the 95% confidence level. ResultsFrom 0° to 30° of knee flexion, the BCS subjects exhibited similar patterns of femoral rollback and axial rotation compared to normal knee subjects. From 30° to 60° of knee flexion, BCS subjects experienced negligible anterior-posterior motions and axial rotation while normal knees continued to rollback and externally rotate. Between 60° and 90° the BCS resumed posterior motion and, after 90°, axial rotation increased in a normal-like fashion. ConclusionSimilarities in early flexion kinematics suggest that the anterior cam-post is supporting normal-like anterior-posterior motion in the BCS subjects. Likewise, lateral femoral rollback and external rotation of the femur in later flexion provides evidence for appropriate substitution of the PCL via the posterior cam-post. Being discrete in nature, the dual cam-post mechanism does not lend itself to adequate substitution of the cruciate ligaments in mid-flexion during which anterior cruciate ligament tension is decreasing and PCL tension is increasing in the normal knee.

In-situ mechanical behavior and slackness of the anterior cruciate ligament at multiple knee flexion angles

In this study the in-situ tensile behavior and slackness of the anterior cruciate ligament (ACL) was evaluated at various knee flexion angles. In four cadaveric knees the ACL was released at the tibial insertion, after which it was re-connected to a tensiometer. After pre-tensioning (10 N) the ACL in full-extension, the knee was flexed from 0° to 150° at 15° increments, during which the ACL tension was measured. At each angle the ACL was subsequently elongated and shortened under displacement control, while measuring the ACL tension. In this manner, the pre-tension or the slackness, and the mechanical response of the ACL were measured. All ACL's displayed a higher tension at low (0°–60°) and high (120°–150°) flexion angles. The ACL slackness depended on flexion angle, with the highest slackness found at 75°–90°. Additionally, the ACL stiffness also varied with flexion angle, with the ACL behaving stiffer at low and high flexion angels. In general, the ACL was stiffest at 150°, and most compliant at 90°. The results of this study contribute to understanding the mechanical behavior of the ACL in-situ, and may help tuning and validating computational knee models studying ACL function.

Comparison of Estimated Anterior Cruciate Ligament Tension During a Typical and Flexed Knee and Hip Drop Landing Using Sagittal Plane Knee Modeling

Noncontact mechanisms, such as landing from a jump, account for over 70% of all anterior cruciate ligament injuries. Increased knee and hip flexion during landing has been suggested to decrease anterior cruciate ligament tension; however, current literature utilizing knee modeling approaches has not investigated this. Our purpose was to compare estimated anterior cruciate ligament tension in females between a typical and flexed knee and hip drop landing performance. A sagittal plane knee model based on kinematic, kinetic, electromyography, and cadaveric data was used to estimate forces on the anterior cruciate ligament during a typical and flexed drop landing for 23 females. Model estimated peak anterior cruciate ligament tension decreased by 10% during the flexed landing performance (p=0.008). This was accounted for by an increase in hamstring shear force by 6% of body weight and a reduction in patellar tendon shear force and femur-tibia shear force by 3% of body weight each. Results suggest that simple verbal cues for increased knee and hip flexion during landing may be effective in reducing anterior cruciate ligament tension and potential risk of injury during landing.

Estimation of In Vivo ACL Force Changes in Response to Increased Weightbearing

Accurate knowledge of in vivo anterior cruciate ligament (ACL) forces is instrumental for understanding normal ACL function and improving surgical ACL reconstruction techniques. The objective of this study was to estimate the change in ACL forces under in vivo loading conditions using a noninvasive technique. A combination of magnetic resonance and dual fluoroscopic imaging system was used to determine ACL in vivo elongation during controlled weightbearing at discrete flexion angles, and a robotic testing system was utilized to determine the ACL force-elongation data in vitro. The in vivo ACL elongation data were mapped to the in vitro ACL force-elongation curve to estimate the change in in vivo ACL forces in response to full body weightbearing using a weighted mean statistical method. The data demonstrated that by assuming that there was no tension in the ACL under zero weightbearing, the changes in in vivo ACL force caused by full body weightbearing were 131.4 ± 16.8 N at 15 deg, 106.7 ± 11.2 N at 30 deg, and 34.6 ± 4.5 N at 45 deg of flexion. However, when the assumed tension in the ACL under zero weightbearing was over 20 N, the change in the estimated ACL force in response to the full body weightbearing approached an asymptotic value. With an assumed ACL tension of 40 N under zero weightbearing, the full body weight caused an ACL force increase in 202.7 ± 27.6 N at 15 deg, 184.9 ± 22.5 N at 30 deg, and 98.6 ± 11.7 N at 45 deg of flexion. The in vivo ACL forces were dependent on the flexion angle with higher force changes at low flexion angles. Under full body weightbearing, the ACL may experience less than 250 N. These data may provide a valuable insight into the biomechanical behavior of the ACL under in vivo loading conditions.

20901 筋骨格モデルによる人膝前十字靱帯の変形解析(OS9 バイオエンジニアリング(1),オーガナイズドセッション)

In this study, we propose a musculoskeletal model that can investigate the mechanical properties of the ACL (Anterior Cruciate Ligament) as a function of knee flexion angle. The knee joint in the model is more detailed modeling introducing the contact conditions of the knee joint surfaces, i.e. the knee joint surfaces are capable of the relative motion such a sliding and rolling during flexion or extension The inverse dynamic analysis was used to investigate the ACL mechanical properties under the influence of muscle recruitments. As the results of the analysis, ACL length decreases with increasing flexion angle and, at less than 30°, ACL tension rapidly increases with increasing flexion angle, subsequently tension decreases. For the future, we need to improve the modelling by introducing patella and mimic viscoelasticity characteristics.

Varus Alignment Leads to Increased Forces in the Anterior Cruciate Ligament

Background Varus thrust of the knee is a dynamic increase of an often preexisting varus angle and it is suspected to be a major reason for failure of anterior cruciate ligament reconstructions. However, it is not known if a direct relationship exists between varus thrust and forces in the anterior cruciate ligament. Hypothesis Forces in the anterior cruciate ligament increase with increasing varus alignment, and consequently an anterior cruciate ligament deficiency in a varus-aligned leg leads to more lateral tibiofemoral joint opening. Study Design Controlled laboratory study. Methods Six human cadaver legs were axially loaded with 3 different weightbearing lines—a neutral weightbearing line, a weightbearing line that passes through the middle of the medial tibial plateau (50% varus), and a line passing the edge of the medial tibial plateau (100% varus)—that were used to create a varus moment. The resulting lateral tibiofemoral joint opening and corresponding anterior cruciate ligament tension were measured. The tests were repeated with and without the anterior cruciate ligament in place. Results In the neutral aligned legs, there was no apparent lateral joint opening, and no anterior cruciate ligament tension change was noted. The lateral joint opening increased when the weightbearing line increased from 0% to 50% to 100%. The lateral joint opening was significantly higher in 10° of knee flexion compared with knee extension. In the 100% varus weightbearing line, the anterior cruciate ligament tension was significantly higher (53.9 N) compared with neutral (31 N) or the 50% weightbearing line (37.9 N). A thrust could only be observed in the 100% weightbearing line tests. In the absence of an anterior cruciate ligament, there was more lateral joint opening, although this was only significant in the 100% weightbearing line. Conclusion There is a direct relationship between varus alignment and anterior cruciate ligament tension. In the absence of an anterior cruciate ligament, the amount of lateral opening tends to increase. With increasing lateral opening, a thrust can sometimes be experimentally observed. Clinical Relevance A varus alignment in an anterior cruciate ligament—deficient knee does not necessarily lead to a varus thrust and therefore does not always need operative varus alignment correction. However, in an unstable anterior cruciate ligament—deficient knee with a varus thrust, it might be safer to perform a high valgus tibial osteotomy to minimize the risk of an anterior cruciate ligament reconstruction failure.

Estimation of anterior cruciate ligament tension from inverse dynamics data and electromyography in females during drop landing

Background Recent human performance studies have shown that various kinematic and kinetic parameters may be implicated in non-contact anterior cruciate ligament (ACL) injury during landing and cutting. In this paper, a phenomenological sagittal plane model was used to estimate the ACL tension during drop landing from the net knee moments and forces, obtained from inverse dynamics and electromyography. Methods Model parameters were determined with data from anatomical and ACL loading studies of cadaveric specimens. The model was used to process averaged data from 60 cm drop landing trials of sixteen healthy females. Findings ACL loading during drop landing occurred during the between toe and heel impact with a peak tension of 0.15 body weight. The factors that contributed to ACL tension were the patellar tendon force and the tibial slope in combination with the joint axial loads. Factors responsible for reducing ACL tension were hamstring and ground reaction forces. Interpretation Sagittal plane results largely confirmed a previous forward dynamics study of landing. The knee appeared to be largely stabilized against abduction moments due to the large axial loads present during drop landing for typical landing trials. Rotational moments were small in drop landing and contributed little to ACL tension. Estimates from this model can be used in human performance studies to determine the relative amount of ACL tension produced in different landing scenarios.

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.

ACL graft can replicate the normal ligament’s tension curve

The anatomical femoral insertion of the normal anterior cruciate ligament (ACL) lies on the deep portion of the lateral wall of the intercondylar fossa. Following the deep bone-cartilage border, it stretches from 11 o'clock high in the notch all the way down to its lowest border at 8 o'clock. The tension curve of the normal ACL during passive flexion-extension shows a characteristic pattern with two tension peaks, one in full extension and the other in deep flexion. Low tension in mid-flexion is measured between those two peaks. Standard ACL reconstructions use a femoral insertion at 11 o'clock, which results in non-physiological tension curves with one peak in full extension only. The hypothesis was that it is possible to reproduce the typical tension curve of the normal ACL by placing the femoral tunnel into the low part of the normal ACL footprint. In a controlled laboratory study, three different femoral tunnel positions at 9, 10 and 11 o'clock were tested in four cadaver knees while using the identical standard tibial tunnel each time. The tension curve was measured during passive flexion-extension with a custom-made tension measurement device, using an artificial Dacron graft. The tension curve of grafts in the 9 o'clock tunnels showed the characteristic pattern of the normal ACL's tension curve with tension peaks in extension as well as in deep flexion. The tunnels in the 10 and 11 o'clock positions failed to reproduce the normal ACL's tension curve with high-tension values in extension only. If an ACL graft is placed low within the normal femoral footprint, the physiological tension curve of the normal ACL can be reproduced.