Tibial Force Research Articles

Rearfoot Impact More Likely To Induce Knee Valgus And Internal Rotation As Well As Increased Tibial Axial Force In Side-cut Task

Rearfoot Impact More Likely To Induce Knee Valgus And Internal Rotation As Well As Increased Tibial Axial Force In Side-cut Task

Anterior Cruciate Ligament Function in Providing Rotational Stability Assessed by Medial and Lateral Tibiofemoral Compartment Translations and Subluxations

Background: Rotational knee stability provided by the anterior cruciate ligament (ACL) in the pivot-shift phenomena involves analysis of more complex robotic testing profiles and resulting tibiofemoral compartment kinematics and subluxations. Hypotheses: Using anterior-posterior tibial forces along with internal and valgus tibial moments will produce a major anterior subluxation of both tibiofemoral compartments not obtained with internal and valgus moments alone. Increasing the internal torque in pivot-shift testing will constrain the anterior subluxations of the medial and central tibial compartments. Study Design: Controlled laboratory study. Methods: A 6 degrees of freedom robotic knee testing system applied anterior translation and rotational loading profiles in 10 cadaveric knees before and after ACL sectioning. Changes in knee motion limits were measured, and medial and lateral tibiofemoral compartment translations were determined by digitization of tibial plateau anatomic landmarks. Loading profiles simulated Lachman and tibial rotation tests as well as typical pivot-shift loading profiles from prior in vitro and in vivo studies. Results: After ACL sectioning, anterior tibial translation increased by 10.3 ± 3.7 mm at 25° of flexion (P < .001). Internal tibial rotation increased by 1.6° ± 1.1° (5 N·m; P > .05). In pivot-shift tests (anterior translation, 100 N; internal rotation, 1 N·m; valgus, 7 N·m), the tibial rotation center shifted outside the medial tibial margin, with abnormal anterior translation of both compartments (medial, 12.9 ± 3.9 mm; lateral, 7.5 ± 3.7 mm; P < .001), with internal rotation decreasing by 4.1° ± 3.5° (P < .05). A greater internal rotation torque (5 vs 1 N·m) in the pivot-shift test constrained and limited anterior tibial translation and prevented anterior subluxation of the medial compartment (P < .001). Conclusion: Sectioning of the ACL produces major increases in tibiofemoral compartment translations and only small increases in internal tibial rotation. The simulation of the pivot shift requires a combined loading profile of anterior translation, internal rotation, and valgus, which produces the greatest anterior subluxation of the medial and lateral tibiofemoral compartments. This testing profile is recommended to be included along with other loading profiles for future ACL studies. The application of a high internal rotation torque in cadaveric pivot-shift tests constrains anterior tibial subluxation of the medial and center compartments and appears less ideal for analysis of ACL function and graft reconstructions. Clinical Relevance: Surgeons should be cautious in interpreting conclusions on ACL function and graft reconstructions without knowing the resulting tibiofemoral subluxations or loading conditions that may limit maximum anterior tibial femoral subluxations.

ACL forces and knee kinematics produced by axial tibial compression during a passive flexion–extension cycle

Application of axial tibial force to the knee at a fixed flexion angle has been shown to generate ACL force. However, direct measurements of ACL force under an applied axial tibial force have not been reported during a passive flexion-extension cycle. We hypothesized that ACL forces and knee kinematics during knee extension would be significantly different than those during knee flexion, and that ACL removal would significantly increase all kinematic measurements. A 500 N axial tibial force was applied to intact knees during knee flexion-extension between 0° and 50°. Contact force on the sloping lateral tibial plateau produced a coupled internal + valgus rotation of the tibia, anterior tibial displacement, and elevated ACL forces. ACL forces during knee extension were significantly greater than those during knee flexion between 5° and 50°. During knee extension, ACL removal significantly increased anterior tibial displacement between 0° and 50°, valgus rotation between 5° and 50°, and internal tibial rotation between 5° and 15°. With the ACL removed, kinematic measurements during knee extension were significantly greater than those during knee flexion between 5° and 45°. The direction of knee flexion-extension movement is an important variable in determining ACL forces and knee kinematics produced by axial tibial force.

The Effect of the Variation in ACL Constitutive Model on Joint Kinematics and Biomechanics Under Different Loads: A Finite Element Study

The biomechanics and function of the anterior cruciate ligament (ACL) have been widely studied using both experimental and simulation methods. It is known that a constitutive model of joint tissue is a critical factor in the numerical simulation. Some different ligament constitutive models have been presented to describe the ACL material behavior. However, the effect of the variation in the ligament constitutive model on joint kinematics and biomechanics has still not been studied. In this paper, a three-dimensional finite element model of an intact tibiofemoral joint was reconstructed. Three ACL constitutive models were compared under different joint loads (such as anterior tibial force, varus tibial torque, and valgus tibial torque) to investigate the effect of the change of the ACL constitutive model. The three constitutive models corresponded to an isotropic hyperelasticity model, a transversely isotropic hyperelasticity model with neo-Hookean ground substance description, and a transversely isotropic hyperelastic model with nonlinear ground substance description. Although the material properties of these constitutive equations were fitted on the same uniaxial tension stress-strain curve, the change of the ACL material constitutive model was found to induce altered joint kinematics and biomechanics. The effect of different ACL constitutive equations on joint kinematics depended on both deformation direction and load type. The variation in the ACL constitutive models would influence the joint kinematic results greatly in both the anterior and internal directions under anterior tibial force as well as some other deformations such as the anterior and medial tibial translations under valgus tibial torque, and the medial tibial translation and internal rotation under varus torque. It was revealed that the transversely isotropic hyperelastic model with nonlinear ground substance description (FE model III) was the best representation of the realistic ACL property by a linear regression between the simulated and the experiment deformation results. But the comparison of the predicted and experiment force of ligaments showed that all the three ACL constitutive models represented similar force results. The stress value and distribution of ACL were also altered by the change in the constitutive equation. In brief, although different ACL constitutive models have been fitted using the same uniaxial tension curve and have the similar longitudinal material property, the ACL constitutive equation should still be carefully chosen to investigate joint kinematics and biomechanics due to the different transverse material behavior.

Multibody Muscle Driven Model of an Instrumented Prosthetic Knee During Squat and Toe Rise Motions

Detailed knowledge of knee joint kinematics and dynamic loading is essential for improving the design and outcomes of surgical procedures, tissue engineering applications, prosthetics design, and rehabilitation. The need for dynamic computational models that link kinematics, muscle and ligament forces, and joint contacts has long been recognized but such body-level forward dynamic models do not exist in recent literature. A main barrier in using computational models in the clinic is the validation of the in vivo contact, muscle, and ligament loads. The purpose of this study was to develop a full body, muscle driven dynamic model with subject specific leg geometries and validate it during squat and toe-rise motions. The model predicted loads were compared to in vivo measurements acquired with an instrumented knee implant. Data for this study were provided by the "Grand Challenge Competition to Predict In-Vivo Knee Loads" for the 2012 American Society of Mechanical Engineers Summer Bioengineering Conference. Data included implant and bone geometries, ground reaction forces, EMG, and the instrumented knee implant measurements. The subject specific model was developed in the multibody framework. The knee model included three ligament bundles for the lateral collateral ligament (LCL) and the medial collateral ligament (MCL), and one bundle for the posterior cruciate ligament (PCL). The implanted tibia tray was segmented into 326 hexahedral elements and deformable contacts were defined between the elements and the femoral component. The model also included 45 muscles on each leg. Muscle forces were computed for the muscle driven simulation by a feedback controller that used the error between the current muscle length in the forward simulation and the muscle length recorded during a kinematics driven inverse simulation. The predicted tibia forces and torques, ground reaction forces, electromyography (EMG) patterns, and kinematics were compared to the experimentally measured values to validate the model. Comparisons were done graphically and by calculating the mean average deviation (MAD) and root mean squared deviation (RMSD) for all outcomes. The MAD value for the tibia vertical force was 279 N for the squat motion and 325 N for the toe-rise motion, 45 N and 53 N for left and right foot ground reaction forces during the squat and 94 N and 82 N for toe-rise motion. The maximum MAD value for any of the kinematic outcomes was 7.5 deg for knee flexion-extension during the toe-rise motion.

Paper 203: Contributions of the Posterolateral Bundle of the Anterior Cruciate Ligament to Anterior-Posterior Knee Laxity and Ligament Forces

The purpose of this study was to measure changes in anterior-posterior laxity and graft forces after cutting the posterolateral (PL) bundle of the anterior cruciate ligament (ACL). Twelve fresh frozen cadaveric knees underwent anterior-posterior (AP) laxity testing at + 100N of applied tibial force. Resultant forces in the ACL were recorded during passive extension from 120° to 0° with no tibial force, 100N anterior tibial force, 100N quadriceps force, and 5 N-m internal tibial torque. The femoral origin of the PL bundle was identified, the ligament fibers were dissected from bone, and tests were repeated. Cutting the PL bundle significantly increased mean laxity +1.3 mm (at 0°), +1.1 mm (at 10°), and +0.5 mm (at 30°). For the passive knee extension tests, cutting the PL bundle significantly decreased mean ACL force at 0° for all loading modes; mean decreases were 31N (no tibial force), 50N (100N anterior force), 33N (100N quadriceps force), and 40N (5 N-m internal torque). The decreases in ACL force at 0° from cutting the PL bundle are consistent with the commonly accepted view that the PL bundle tightens with knee extension. Cutting the taut PL bundle did significantly increase AP laxity between 0° and 30°, but the increases were relatively small. Therefore we conclude that the PL bundle plays a relative minor role in controlling anterior tibial translation.

Quantification of Tibiofemoral Shear and Compressive Loads Using an MRI-Based EMG-Driven Knee Model

The purpose of this study is to describe an MRI-based EMG-driven knee model to quantify tibiofemoral compressive and shear forces. Twelve healthy females participated. Subjects underwent 2 phases of data collection: (1) MRI assessment of the lower extremity to quantify muscle volumes and patella tendon orientation and (2) biomechanical evaluation of a drop-jump task. A subject-specific EMG-driven knee model that incorporated lower extremity kinematics, EMG, and muscle volumes and patella tendon orientation estimated from MRI was developed to quantify tibiofemoral shear and compressive forces. A resultant anterior tibial shear force generated from the ground reaction force (GRF) and muscle forces was observed during the first 30% of the stance phase of the drop-jump task. All of the muscle forces and GRF resulted in tibiofemoral compression, with the quadriceps force being the primary contributor. Acquiring subject-specific muscle volumes and patella tendon orientation for use in an EMG-driven knee model may be useful to quantify tibiofemoral forces in persons with altered patella position or muscle atrophy following knee injury or pathology.

Leg intramuscular pressures and in vivo knee forces during lower body positive and negative pressure treadmill exercise

Quantifying muscle and joint forces over a broad range of weight bearing loads during exercise may provide data required to improve prosthetic materials and better protect against muscle and bone loss. Collectively, leg intramuscular pressure (IMP), ground reaction force (GRF), and the instrumented tibial tray force measurements provide a comprehensive assessment of leg muscle and joint biomechanical effects of gravity during exercise. Titration of body weight (BW) by lower body negative pressure (LBNP) and lower body positive pressure (LBPP) can reproducibly modulate IMP within leg muscle compartments. In addition, previous studies document peak tibial forces during various daily activities of 2.2 to 2.5 BW. The study objective was to determine the IMPs of the leg, axial compressive force on the tibia in vivo, vertical GRF, and knee range of motion during altered BW levels using LBPP and LBNP treadmill exercise. We hypothesize that peak GRF, peak tibial forces, and peak IMPs of the leg correlate linearly with percent BW, as generated across a broad range of upright LBPP and supine LBNP exercise. When running at 2.24 m/s the leg IMPs significantly increased over the loading range of 60% to 140% BW with LBPP and LBNP (P < 0.001); as expected, leg IMPs were significantly higher when running compared with standing (P < 0.001). During upright LBPP, total axial force at the knee increased linearly as a function of BW at 0.67 m/s (R(2) = 0.90) and 1.34 m/s (R(2) = 0.98). During supine LBNP, total axial force at the knee increased linearly as a function of BW at 0.67 m/s (R(2) = 0.98) and 1.34 m/s (R(2) = 0.91). The present study is the first to measure IMPs and peak tibial forces in vivo during upright LBPP, upright LBNP, and supine LBNP exercise. These data will aid the development of rehabilitation exercise hardware and prescriptions for patients and astronauts.

Force Measurements in the Medial Meniscus Posterior Horn Attachment

Background: Tears of the medial meniscus posterior horn attachment (PHA) occur clinically, and an anterior cruciate ligament (ACL)–deficient knee may be more vulnerable to this injury. Hypothesis: The PHA forces from applied knee loadings will increase after removal of the ACL. Study Design: Controlled laboratory study. Methods: A cap of bone containing the medial meniscus PHA was attached to a load cell that measured PHA tensile force. Posterior horn attachment forces were recorded before and after ACL removal during anteroposterior (AP) laxity testing at ±200 N and during passive knee extension tests with 5 N·m tibial torque and varus-valgus moment. Selected tests were also performed with 500 N joint load. Results: For AP tests with no joint load, ACL removal increased laxity between 0° and 90° and increased PHA force generated by applied anterior tibial force between 30° and 90°. For AP tests with an intact ACL, application of joint load approximately doubled PHA forces. Anteroposterior testing of ACL-deficient knees was not possible with joint load because of bone cap failures from high PHA forces. Removal of the ACL during knee extension tests under joint load significantly increased PHA forces between 20° and 90° of flexion. For unloaded tests with applied tibial torque and varus-valgus moment, ACL removal had no significant effect on PHA forces. Conclusion: Applied anterior tibial force and external tibial torque were loading modes that produced relatively high PHA forces, presumably by impingement of the medial femoral condyle against the medial meniscus posterior horn rim. Under joint load, an ACL-deficient knee was particularly susceptible to PHA injury from applied anterior tibial force. Clinical Relevance: Because tensile forces developed in the PHA are also borne by meniscus tissue near the attachment site, loading mechanisms that produce high PHA forces could also produce complete or partial radial tears near the posterior horn, a relatively common clinical observation.

The effect of kneepads on balance while kneeling or squatting

In all industries, maintaining balance is essential to ensure that workers can safely perform their job duties. In low-seam underground coal mines, workers perform their duties while kneeling, squatting, and crawling with kneepads. In this study, researchers examined the effects of kneeling and squatting on balance measures under the right knee (for kneeling) and right foot (for squatting) with and without kneepads. Results showed that kneepads did not significantly affect balance. Posture had a significant effect on balance measures, with squatting postures showing reduced balance compared to the kneeling postures. For the kneeling postures, ground force measurements were also correlated to balance measures. Posterior tibial forces were shown to have the greatest correlation to mediolateral and anteroposterior average velocities. Force and balance measures highlight a compromise between loading and balance, where improved balance is achieved with increased knee loading.

Correlation of axial impact forces with knee joint forces and kinematics during simulated ski-landing

Anterior cruciate ligament (ACL) rupture, during ski-landing, is caused by excessive knee joint forces and kinematics, like anterior tibial translation, internal tibial rotation, and valgus rotation. It is not well understood how these forces/kinematics are directly related to ski-landing impact. In the present study, we applied simulated ski-landing impact to knee specimens, and examined joint force/kinematic responses and their correlations with impact force. Ten human cadaveric knees were subjected to axial impact loading at 70° of flexion to simulate ski-landing impact. Impact was repeated with incremental magnitude until ACL failure. Axial impact forces, anterior-posterior and medial-lateral tibial forces were measured using a tri-axial load cell. Anterior-posterior tibial translation, internal-external tibial rotation, and valgus-varus rotation were determined using a motion-capture system. We found positive correlations of axial impact force with anterior tibial force, medial tibial force, anterior tibial translation, internal tibial rotation, and valgus joint rotation. Axial impact forces were more strongly correlated with anterior tibial forces (R 2 = 0.937 ± 0.050), anterior tibial translation (R 2 = 0.916 ± 0.059), and internal tibial rotation (R 2 = 0.831 ± 0.141) than medial tibial force (R 2 = 0.677 ± 0.193) and valgus joint rotation (R 2 = 0.630+0.271). During ski-landing, these joint forces/kinematics can synergistically act to increase ACL injury risk, whereby the failure mechanism would be dominated by anterior tibial forces, anterior tibial translation, and internal tibial rotation.

The 2011 ABJS Nicolas Andry Award: ‘Lab’-in-a-Knee: In Vivo Knee Forces, Kinematics, and Contact Analysis

Tibiofemoral forces are important in the design and clinical outcomes of TKA. We developed a tibial tray with force transducers and a telemetry system to directly measure tibiofemoral compressive forces in vivo. Knee forces and kinematics traditionally have been measured under laboratory conditions. Although this approach is useful for quantitative measurements and experimental studies, the extrapolation of results to clinical conditions may not always be valid. We therefore developed wearable monitoring equipment and computer algorithms for classifying and identifying unsupervised activities outside the laboratory. Tibial forces were measured for activities of daily living, athletic and recreational activities, and with orthotics and braces, during 4 years postoperatively. Additional measurements included video motion analysis, EMG, fluoroscopic kinematic analysis, and ground reaction force measurement. In vivo measurements were used to evaluate computer models of the knee. Finite element models were used for contact analysis and for computing knee kinematics from measured knee forces. A third-generation system was developed for continuous monitoring of knee forces and kinematics outside the laboratory using a wearable data acquisition hardware. By using measured knee forces and knee flexion angle, we were able to compute femorotibial AP translation (-12 to +4 mm), mediolateral translation (-1 to 1.5 mm), axial rotation (-3° to 12°), and adduction-abduction (-1° to +1°). The neural-network-based classification system was able to identify walking, stair-climbing, sit-to-stand, and stand-to-sit activities with 100% accuracy. Our data may be used to improve existing in vitro models and wear simulators, and enhance prosthetic designs and biomaterials.

Internal Tibial Forces and Moments in Runners with a History of Stress Fractures

Gait kinematics and external forces have been associated with stress fracture in runners. These factors may act in concert to increase internal bone forces and moments, key elements of bone stress. PURPOSE: to quantify internal tibial forces and moments in runners with and without a history of tibial stress fracture (fx). METHODS: Thirty-three age and gender matched runners, 11 cases and 22 controls, ran across a force platform at a self-selected 5K race pace ± 5% while three dimensional kinematic and kinetic data were collected. A combination of inverse dynamics and musculoskeletal modeling was used to estimate internal forces and moments acting along a centroid path through the tibia. Group differences for internal forces and moments at 25%, 50%, and 75% of the distance from the proximal tibia were compared using effect sizes (ES) and 95% confidence intervals (CI) of the ES. SUMMARY OF RESULTS: Groups did not differ on experience, weekly mileage, heel strike index, or 5k race pace. Anterioposterior (AP) shear forces differed between groups at the proximal, mid and distal tibia (ES = 0.75, CI95% = 0.01, 1.49; ES = 0.83, CI95% = 0.08, 1.58; ES = 0.82, CI95% = 0.07, 1.57, respectively). On average, the stress fx group experienced AP shear forces that were 8-12% greater than the control group. Additionally, moments about the AP axes, longitudinal and mediolateral (ML) axes of the distal tibia were greater in the stress fx group (ES = 0.98, CI95% = 0.22, 1.74; ES = 3.46, CI95% = 2.35, 4.56; ES = 0.09, CI95% = 0.09, 1.59, respectively). The stress fx group underwent, on average, 33% more medial surface tension, 263% greater internal torsion, and 26% more anterior surface tension at the distal tibia. CONCLUSION: The results of this preliminary study suggest that differences between internal tibial forces and moments may exist between runners with and without a history of stress fx. The stress fx group experienced greater AP shear forces, bending moments and torsional moments at the distal tibia, a common site for stress fx. The CI of the ES associated with these variables was large, likely due to the small sample size, variability inherent to the data, and that data were not stratified by gender. Nonetheless, this study provides some evidence that magnitude of applied loading in runners with stress fx may be related to injury status.

Biomechanical Comparisons Between 4-Strand and Modified Larson 2-Strand Procedures for Reconstruction of the Posterolateral Corner of the Knee

Background: The posterolateral corner (PLC) resists tibial varus angulation, external rotation, and, to a lesser extent, posterior translation. It is important that reconstructions of posterolateral knee injuries restore joint laxity and patient function, but residual laxities are often observed. Hypothesis: The knee laxity after a new 4-strand PLC reconstruction would be closer to normal than after a 2-strand “modified Larson” reconstruction. Study Design: Controlled laboratory study. Methods: Fourteen intact cadaveric knees were mounted in a 6 degrees of freedom rig and subjected to the following external loading conditions: a 90-N posterior tibial force, a 5-N·m external rotation torque, and 5-N·m varus moment. Knee kinematics were recorded with an active optical tracking system for the intact, PLC-deficient, modified Larson PLC reconstruction and 4-strand PLC reconstruction. Results: With external tibial torque, the rotational laxity in 4-strand reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P = .0112) and did not differ significantly from intact laxity at any angle of flexion. In response to posterior load, posterior translation did not change in any of the tested conditions, while the coupled external rotation laxity in 4-strand PLC reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P < .0486) and was not significantly different from the intact movements for both reconstructions. The varus angulation-versus-flexion curves were significantly different between the PLC-deficient and both PLC reconstructions (P < .0001). The varus laxity was not significantly different between the modified Larson reconstruction, the 4-strand reconstruction, and the intact knee. Conclusion: This study showed that the rotational knee laxity in response to both external rotation and posterior translation load were significantly better after the 4-strand PLC reconstruction than after the modified Larson reconstruction, although significant differences were not found between the 2 procedures for varus laxity. Clinical Relevance: The 4-strand PLC reconstruction may produce a better biomechanical outcome, especially during external rotation and posterior translation tibial load. The authors suggest that this relates to load sharing among 4 graft strands crossing the joint.

A new approach to evaluate anterior knee joint laxity

BackgroundKnee instability after Anterior Cruciate Ligament (ACL) reconstructive surgery may lead to osteoarthritis.ObjectiveTo complete current evaluation of anterior knee laxity.DesignCross-sectional pilot study.SettingPhysical therapy unit of the Clinique d'Eich, Centre Hospitalier...

An implant-free double-bundle reconstruction of the anterior cruciate ligament: Operative technique and influence on tibiofemoral kinematics

Background Reconstruction of the anterior cruciate ligament is a standard surgical procedure in sports traumatology. The widespread replacement method using hamstring tendons has an important shortcoming namely delayed or missing bony healing in contrast to patellar tendon grafts where implant-free fixation is established by using the adjacent bone blocks. The purpose of this study was to describe a new implant-free surgical procedure using hamstring tendon grafts and to analyse the influence on tibiofemoral kinematics in vitro. Methods Nine human knee specimens with arthroscopically transected anterior cruciate ligaments were mounted on a dynamic knee simulator and weight-bearing muscle-loaded knee flexions were simulated while a robotic universal force sensor system was used to provide external tibial loads. Three different loading conditions were simulated including partial body weight only, an additional 50 N anterior tibial force or an additional Five Nm of internal rotational torque. After reconstruction of the anterior cruciate ligament using a tibial bone block hybrid technique these three trials were repeated. The kinematics was measured with an ultrasonic measuring system and different loading and ligament conditions were examined. Graft tunnel placement was verified by computed tomography. Findings Our fixation method achieved stability to anterior tibial drawer force whereas internal tibial rotation did not change before and after the reconstruction. Computed tomography confirmed anatomical graft and tunnel placement. Interpretation The presented operative procedure is technically feasible and leads to reproducible results concerning knee joint kinematics and graft placement.

Biomechanical Comparison of Anatomic Double-Bundle, Anatomic Single-Bundle, and Nonanatomic Single-Bundle Anterior Cruciate Ligament Reconstructions

Background: Although both anatomic double-bundle and single-bundle anterior cruciate ligament reconstruction procedures are in use, it remains controversial whether the anatomic double-bundle procedure is biomechanically superior. Hypothesis: The anatomic double-bundle procedure would be better than both laterally placed anatomic and nonanatomic transtibial single-bundle procedures at restoring to normal the tibial anterior translation, internal rotation, and pivot-shift instability. It was also hypothesized that tibial internal rotation would be closer to normal after laterally placed anatomic single-bundle reconstruction than after the nonanatomic reconstruction. Study Design: Controlled laboratory study. Methods: Eight cadaveric knees were mounted in a 6 degrees of freedom rig and tested using the following loading conditions: 90-N anterior and posterior tibial forces, 5-N·m internal and external tibial rotation torques, and a simulated pivot-shift test. Tibiofemoral kinematics during the flexion-extension cycle were recorded with an optical tracking system for (1) intact, (2) anterior cruciate ligament–deficient knee, (3) anatomic double-bundle reconstruction, (4) nonanatomic single-bundle reconstruction, and (5) laterally placed single-bundle reconstruction. Results: Rotational laxity with internal tibial torque and anterior laxity in the simulated pivot shift were significantly less in the double-bundle reconstruction and laterally placed single-bundle reconstruction compared with the nonanatomic single-bundle reconstruction. There were no significant differences between the 3 procedures when anterior and posterior tibial translation forces and external rotation torques were applied. In addition, there were no significant differences between the double-bundle reconstruction and laterally placed single-bundle reconstruction. Conclusion: The postoperative rotational and pivot-shift laxity after anatomic double-bundle anterior cruciate ligament reconstruction was significantly better than that after nonanatomic single-bundle reconstruction. However, there were no significant differences between the double-bundle reconstruction and laterally placed single-bundle reconstruction. Clinical Relevance: This work suggests that a single-bundle reconstruction may be better able to control both knee laxity and pivot-shift instability if the femoral tunnel is moved to a more lateral position and that then the double-bundle reconstruction may not offer significant further advantages.

The Anterior Cruciate Ligament Provides Resistance to Externally Applied Anterior Tibial Force But Not to Internal Rotational Torque During Simulated Weight-Bearing Flexion

We investigated knee kinematics during simulated weight-bearing flexion and determined the effect of 3 different parameters of external tibial loading on the kinematics of the anterior cruciate ligament (ACL)-intact and ACL-deficient knee. Ten human knee specimens were mounted on a dynamic knee simulator, and weight-bearing muscle-loaded knee flexions were simulated while a robotic/universal force sensor system was used to provide external tibial loads during the motion. Three different loading conditions were simulated: partial body weight only, an additional 50 N of anterior tibial force (ATD), or an additional 5 Nm of internal rotational tibial torque (IRT). After arthroscopic transection of the ACL, these 3 trials were repeated. The kinematics were measured with an ultrasonic measuring system for 3-dimensional motion analysis, and different loading and knee conditions were examined. When the ACL was intact, ATD and IRT barely changed the anterior tibial translation. However, in the absence of the ACL, ATD significantly increased the anterior tibial translation by 5 mm whereas IRT did not. The application of IRT increased the internal tibial rotation of ACL-intact knees, but there was no difference in the internal rotation before and after transection of the ACL. Regardless of ACL status, the difference in the anterior tibial translation and the internal tibial rotation across different external tibial loadings was greater at lower flexion angles and gradually diminished with increasing flexion angles. We established an experimental protocol, incorporating a dynamic knee simulator and a robotic/universal force sensor system, to successfully measure the kinematics of the knee joint while applying external forces in weight-bearing flexion. Our findings suggest that, in muscle-loaded knee flexion, the ACL provides substantial resistance to externally applied ATD but not to IRT. Information from this study allows us to better understand the function of the ACL and, hence, treatment of injuries to this important stabilizing ligament.

レッグプレス動作における姿勢の違いが脛骨引き出し力や筋力に与える影響

前十字靱帯（ACL）再建術術後の大腿四頭筋筋力訓練の一つにレッグプレス運動がある．本研究では，レッグプレス運 動において，姿勢の違いがACL にかかる負荷である脛骨引き出し力や筋張力に与える影響について考察した．矢状面から動作計測を行い，下肢関節角度と足部に作用する反力から筋骨格モデルを用いて脛骨引き出し力や筋張力を推定した．11 種の姿勢について検討した結果，脛骨へは常に後方引き出し力が作用しACL 再建術術後の大腿四頭筋筋力訓練としてレッグプレス運動は安全であること，体幹を屈曲させることでより大きな後方引き出し力が作用しより安全に行えることが示唆された．

A Cadaverically Evaluated Dynamic FEM Model of Closed-Chain TKR Mechanics

Knowledge of the behavior and mechanics of a total knee replacement (TKR) in an in vivo environment is key to optimizing the functional outcomes of the implant procedure. Computational modeling has shown to be an important tool for investigating biomechanical variables that are difficult to address experimentally. To assist in examining TKR mechanics, a dynamic finite-element model of a TKR is presented. The objective of the study was to develop and evaluate a model that could simulate full knee motion using a physiologically consistent quadriceps action, without prescribed joint kinematics. The model included tibiofemoral (TFJs) and patellofemoral joints (PFJs), six major ligament bundles and was driven by a uni-axial representation of a quadricep muscle. An initial parameter screening analysis was performed to assess the relative importance of 31 different model parameters. This analysis showed that ligament insertion location and initial ligament strain were significant factors affecting simulated joint kinematics and loading, with the contact friction coefficient playing a lesser role and ligament stiffness having little effect. The model was then used to simulate in vitro experiments utilizing a flexed-knee-stance testing rig. General model performance was assessed by comparing simulation results with experimentally measured kinematics and tibial reaction forces collected from two implanted specimens. The simulations were able to reproduce experimental differences observed between the test specimens and were able to accurately predict trends seen in the tibial reaction loads. The simulated kinematics of the TFJ and PFJ were less consistent when compared with experimental data but still reproduced many trends.