Biomedical subjects

Richard E Debski

Publications and source records attributed to Richard E Debski.

At least 19 recordsLinked to original sources

PubMed2007

Effects of slip testing parameters on measured coefficient of friction.

Slips and falls are a major cause of injuries in the workplace. Devices that measure coefficient of friction (COF) of the shoe-floor-contaminant interface are used to evaluate slip resistance in various environments. Testing conditions (e.g. loading rate, timing, normal force, speed, shoe angle) are believed to affect COF measurements; however, the nature of that relationship is not well understood. This study examines the effects of normal force (NF), speed, and shoe angle on COF within physiologically relevant ranges. A polyvinyl chloride shoe was tested using a modified industrial robot that could attain high vertical loads and relatively high speeds. Ground reaction forces were measured with a loadcell to compute COF. Experiment #1 measured COF over a range of NF ( approximately 100-500 N) for two shoe angles (10 degrees and 20 degrees ), four speeds (0.05, 0.20, 0.35, and 0.50 m/s), and two contaminants (diluted detergent and diluted glycerol). Experiment #2 further explored speed effect by testing seven speeds (0.01, 0.05, 0.20, 0.35, 0.50, 0.75, and 1.00 m/s) at a given NF (350 N) and shoe angle (20 degrees ) using the same two contaminants. Experiment #1 showed that faster speeds significantly decreased COF, and that a complex interaction existed between NF and shoe angle. Experiment #2 showed that increasing speed decreased COF asymptotically. The results imply that COF is dependent on film thickness separating the shoe and the heel, which is dependent on speed, shoe angle, and NF, consistent with tribological theory.

Accidental Falls↗

PubMed2006

Acromial morphology: effects of suboptimal radiographs.

Acromial morphology is one of the important factors related to rotator cuff pathology, especially if there is acromial encroachment onto the supraspinatus tendon. This is the rationale for many surgeons performing an acromioplasty, based on preoperative radiographs, in their treatment of rotator cuff disease. However, geometric measurements of the acromion are dependent on the radiographic view, and suboptimal radiographs of the scapula might bias the acromial morphology on the radiographs. Our objective was to study the effect of suboptimal lateral-view radiographs of the scapula on 6 acromial angles, which have been correlated with rotator cuff pathology, by use of a computational method. Anatomic landmarks were digitized on 12 cadaveric scapulae via a spatial linkage system. A coordinate system based on the scapula was then created that allowed projection of the anatomic landmarks on the sagittal plane and simulated the optimal lateral-view radiograph of the scapula. By rotating the coordinate system in the coronal plane (cranial and caudal projections) and axial plane (anterior and posterior projections) with 5 degrees, 10 degrees, 15 degrees, and 20 degrees increments, 16 suboptimal lateral-view radiographs of the scapula were simulated. Significant differences in the 6 acromial angles (P < .01) between the optimal and suboptimal lateral-view radiographs of the scapula were found in almost every cranial and caudal projection. Rotating the projection in the axial plane did not significantly affect the acromial angles (P > .05) up to 20 degrees of rotation in the anterior and posterior direction. Of the 6 different acromial angles, the acromial slope was least affected when the projection was varied. In contrast, the anterior slope of the acromion was highly affected by errors in the projection.

Acromion↗

PubMed2006

Orientation feedback during simulated simple translation tests has little clinical significance on the magnitude and precision of glenohumeral joint translations.

The repeatability of shoulder instability clinical examinations has been reported to be poor, producing a large range of translations. The objective of this study was to determine the effect of providing the clinician with joint orientation feedback on the magnitude and precision of glenohumeral joint kinematics. A 6-degree of freedom magnetic tracking system was used to determine the kinematics of the humerus with respect to the scapula (n=8 cadaveric shoulders). The joints were preconditioned with simple loading tests five times. At 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension, a clinician then applied an anterior and posterior load to the humerus until a manual maximum simulating a simple translation test (STT) was achieved at 0, 30, and 60 degrees of external rotation with and without angular orientation feedback of the humerus with respect to the scapula. The precision for the external rotation was within 4.3 degrees for the feedback group and 17.5 degrees for the no feedback group over all external rotations. For achieving the target external rotation of 30 degrees , there was a significant difference in precision between the feedback and no feedback groups (p<0.05). The magnitudes of the anterior translations were 18.2+/-5.3, 15.5+/-5.1, and 9.9+/-5.5 mm for the feedback group and 19.3+/-6.6, 17.5+/-4.9, and 11.5+/-5.3 mm for the no feedback group, at 0, 30, and 60 degrees of external rotation, respectively. There was a significant difference in the precision of anterior translation at 30 and 60 degrees of external rotation for 4 of 8 specimens (p<0.05). Significant differences in the precision of the posterior translation was only detected at 0 degrees of external rotation for 3 of 8 specimens (p<0.05). Based on the data obtained, providing orientation feedback to a clinician performing a simulated STT results in increased precision for not only the target external rotations but also the resulting glenohumeral translations. While providing feedback may be a necessary step to achieving precise results for experimental studies, the magnitudes of translations in the anterior and posterior directions were relatively similar for the feedback and no feedback states indicating little benefit for clinical examinations.

Biomechanical Phenomena↗

PubMed2006

Decreasing glenoid inclination improves function in shoulders with simulated massive rotator cuff tears.

BACKGROUND: A massive rotator cuff tear leads to poor shoulder function as evidenced by diminished glenohumeral abduction and superior translation of the humeral head compared to its normal position. The inclination angle of the glenoid has been associated with rotator cuff tears. The objective of this study was to quantify the effect of a decreased glenoid inclination angle on glenohumeral kinematics during active abduction in shoulders with a simulated, massive rotator cuff tear. METHODS: Eight fresh-frozen full upper extremities were tested using a dynamic shoulder testing apparatus. After recording the kinematics of the intact shoulder, a massive rotator cuff tear was surgically simulated. An osteotomy of the glenoid was then performed and the inclination angle was decreased by 30 degrees . The translation of the humeral head during abduction and the maximum abduction angle were recorded. FINDINGS: With an intact rotator cuff minimal humeral head translation on the glenoid occurred and the maximum abduction angle was mean 85.5 degrees (SD 7.4 degrees ). A massive rotator cuff tear resulted in superior translation of the humeral head with impingement on the acromion. The maximum abduction angle was mean 15.5 degrees (SD 9.4 degrees ). Decreasing the inclination angle of the glenoid resulted in a significant reduction of superior humeral head translation during abduction and there was no impingement on the acromion. The maximum abduction achieved was mean 28.5 degrees (SD 17.0 degrees ). INTERPRETATION: From a clinical perspective the reduced superior translation may decrease shoulder pain since the humeral head no longer impinges on the acromion. Further investigations are necessary to assess if the improvement in abduction is clinically significant.

Cadaver↗

PubMed2006

Methodology and sensitivity studies for finite element modeling of the inferior glenohumeral ligament complex.

The objectives of this research were to develop a methodology for three-dimensional finite element (FE) modeling of the inferior glenohumeral ligament complex (IGHL complex) as a continuous structure, to determine optimal mesh density for FE simulations, to examine strains and forces in the IGHL complex in clinically relevant joint positions, and to perform sensitivity studies to assess the effects of assumed material properties. A simple translation test in the anterior direction was performed on a cadaveric shoulder, with the humerus oriented at 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension, at 0 degrees , 30 degrees and 60 degrees of humeral external rotation. The geometries of the relevant structures were extracted from volumetric CT data to create a FE model. Experimentally measured kinematics were applied to the FE model to simulate the simple translation test. First principal strains, insertion site forces and contact forces were analyzed. At maximum anterior humeral translation, strains in the IGHL complex were highly inhomogeneous for all external rotation angles. The motion of the humerus with respect to the glenoid during the simple translation test produced a tangential load at the proximal and distal edges of the IGHL complex. This loading was primarily in the plane of the inferior glenohumeral ligament complex, producing an in-plane shear-loading pattern. There was a significant increase in strain with increasing angle of external rotation. The largest insertion site forces occurred at the axillary pouch insertion to the humerus (36.7N at 60 degrees of external rotation) and the highest contact forces were between the anterior band of the IGHL complex and the humeral cartilage (7.3N at 60 degrees of external rotation). Strain predictions were highly sensitive to changes in the ratio of bulk to shear modulus of the IGHL complex, while predictions were moderately sensitive to changes in elastic modulus of the IGHL complex. Changes to the material properties of the humeral cartilage had little effect on predicted strains. The methodologies developed in this research and the results of the mesh convergence and sensitivity studies provide a basis for the subject-specific modeling of the mechanics of the IGHL complex.

Biomechanical Phenomena↗

PubMed2006

Differences in torsional joint stiffness of the knee between genders: a human cadaveric study.

BACKGROUND: In many sports, female athletes have a higher incidence of anterior cruciate ligament injury than do male athletes. Among many risk factors, the lower rotatory joint stiffness of female knees has been suggested for the increased rate of anterior cruciate ligament injuries. HYPOTHESIS: In response to combined rotatory loads, female knees have significantly lower torsional joint stiffness and higher rotatory joint laxity than do male knees at low flexion angles, despite the fact that no such gender differences would be found in response to an anterior tibial load. STUDY DESIGN: Comparative laboratory study. METHODS: Joint kinematics of 82 human cadaveric knees (38 female, 44 male) in response to (1) combined rotatory loads of 10 N x m valgus and +/- 5 N x m internal tibial torques and (2) a 134-N anterior-posterior tibial load were measured using a robotic/universal force-moment sensor testing system. RESULTS: In response to combined rotatory loads, female knees had as much as 25% lower torsional joint stiffness (female: 0.79 N x m/deg; 95% confidence interval, 0.67-0.91; male: 1.06 N x m/deg; 95% confidence interval, 0.95-1.17) and up to 35% higher rotatory joint laxity (female: 26.2 degrees; 95% confidence interval, 24.5 degrees-27.9 degrees; male: 20.5 degrees; 95% confidence interval, 18.8 degrees-22.2 degrees) than did male knees (P < .05), whereas there were no gender differences in response to the anterior tibial load (P > .05). CONCLUSION: Female knees had lower torsional joint stiffness and higher rotatory joint laxity than did male knees in response to combined rotatory loads. CLINICAL RELEVANCE: Larger axial rotations of female knees in response to rotatory loads may affect the distribution of forces in soft tissues and the function of muscles that provide knee stability. Control algorithms used during the biomechanical testing of cadaveric knees and computational knee models might need to be gender specific.

Biomechanical Phenomena↗

PubMed2006

Thoracohumeral muscle activity alters glenohumeral joint biomechanics during active abduction.

Normal function of the glenohumeral joint depends on coordinated muscle forces that stabilize the joint while moving the shoulder. These forces can either provide compressive forces to press the humeral head into the glenoid or translational forces that may destabilize the glenohumeral joint. The objective of this study was to quantify the effect of pectoralis major and latissimus dorsi muscle activity on glenohumeral kinematics and joint reaction forces during simulated active abduction. Nine fresh-frozen whole upper extremities were tested using a dynamic shoulder testing apparatus. Seven muscle force combinations were examined: a standard combination and 10%, 20%, or 30% of the deltoid force applied to the latissimus dorsi or pectoralis major tendon, respectively. Pectoralis major and latissimus dorsi muscle activity decreased the maximum angle of glenohumeral abduction and external rotation, and increased the maximum horizontal adduction angle compared to the standard muscle combination. Thoracohumeral muscle activity also created a more anteriorly directed joint reaction force that resulted in anterior translation compared to the standard muscle combination. Therefore, the ratio between anteriorly directed translational forces and compressive forces increased during abduction due to this muscle activity, suggesting that thoracohumeral muscle activity may decrease glenohumeral stability based on the joint position and applied loads. A better understanding of the contribution of muscle forces to stability may improve rehabilitation protocols for the shoulder aimed at maximizing compression and minimizing translation at the glenohumeral joint.

Aged↗

PubMed2005

Estimation of ACL forces by reproducing knee kinematics between sets of knees: A novel non-invasive methodology.

In situ force in the anterior cruciate ligament (ACL) has been quantified both in vitro in response to relatively simple loads by means of robotic technology, as well as in vivo in response to more complex loads by means of force transducers and computational models. However, a methodology has been suggested to indirectly estimate the in situ forces in the ACL in a non-invasive, non-contact manner by reproducing six-degree of freedom (six-DOF) in vivo kinematics on cadaveric knees using a robotic/UFS testing system. Therefore, the objective of this study was to determine the feasibility of this approach. Kinematics from eight porcine knees (source knees) were collected at 30 degrees , 60 degrees , and 90 degrees of flexion in response to: (1) an anterior load of 100 N and (2) a valgus load of 5 N m. The average of each kinematic data set was reproduced on a separate set of eight knees (target knees). The in situ forces in the ACL were determined for both sets of knees and compared. Significant differences (rho<0.05) were found between the source knees and the target knees for all flexion angles in response to an anterior load. However, in response to valgus loads, there was no significant difference between the source knees and the target knees at 30 degrees and 90 degrees of flexion. It was noted that there was a correlation between anterior knee laxity (the distance along the displacement axis from the origin to the beginning of the linear region of the load-displacement curve) and internal-external rotation. These data suggest that in order to obtain reproducible results one needs to first match knees to knees with comparable anterior knee laxity. Thus, an estimate of the in situ forces in the ACL during in vivo activities might be obtainable using this novel methodology.

Animals↗

PubMed2005

A novel methodology to reproduce previously recorded six-degree of freedom kinematics on the same diarthrodial joint.

The objective of this study was to develop a novel method to more accurately reproduce previously recorded 6-DOF kinematics of the tibia with respect to the femur using robotic technology. Furthermore, the effect of performing only a single or multiple registrations and the effect of robot joint configuration were investigated. A single registration consisted of registering the tibia and femur with respect to the robot at full extension and reproducing all kinematics while multiple registrations consisted of registering the bones at each flexion angle and reproducing only the kinematics of the corresponding flexion angle. Kinematics of the knee in response to an anterior (134 N) and combined internal/external (+/-10 N m) and varus/valgus (+/-5 N m) loads were collected at 0 degrees , 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. A six axes, serial-articulated robotic manipulator (PUMA Model 762) was calibrated and the working volume was reduced to improve the robot's accuracy. The effect of the robot joint configuration was determined by performing single and multiple registrations for three selected configurations. For each robot joint configuration, the accuracy in position of the reproduced kinematics improved after multiple registrations (0.7+/-0.3, 1.2+/-0.5, and 0.9+/-0.2 mm, respectively) when compared to only a single registration (1.3+/-0.9, 2.0+/-1.0, and 1.5+/-0.7 mm, respectively) (p<0.05). The accuracy in position of each robot joint configuration was unique as significant differences were detected between each of the configurations. These data demonstrate that the number of registrations and the robot joint configuration both affect the accuracy of the reproduced kinematics. Therefore, when using robotic technology to reproduce previously recorded kinematics, it may be necessary to perform these analyses for each individual robotic system and for each diarthrodial joint, as different joints will require the robot to be placed in different robot joint configurations.

Biomechanical Phenomena↗

PubMed2005

Varying femoral tunnels between the anatomical footprint and isometric positions: effect on kinematics of the anterior cruciate ligament-reconstructed knee.

BACKGROUND: Knee kinematics and in situ forces resulting from anterior cruciate ligament reconstructions with 2 femoral tunnel positions were evaluated. HYPOTHESIS: A graft placed inside the anatomical footprint of the anterior cruciate ligament will restore knee function better than a graft placed at a position for best graft isometry. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were tested in response to a 134-N anterior load and a combined 10-N.m valgus and 5-N.m internal rotation load. A robotic universal force-moment sensor testing system was used to apply loads, and resulting kinematics were recorded. An active surgical robot system was used for positioning tunnels in 2 locations in the femoral notch: inside the anatomical footprint of the anterior cruciate ligament and a position for best graft isometry. The same quadrupled hamstring tendon graft was used for both tunnel positions. The 2 loading conditions were applied. RESULTS: At 30 degrees of knee flexion, anterior tibial translation in response to the anterior load for the intact knee was 9.8 +/- 3.1 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 13.8 +/- 4.6 mm; position 2: 16.6 +/- 3.7 mm; P < .05). There was a significant difference between the 2 tunnel positions. At the same flexion angle, the anterior tibial translation in response to the combined load for the intact knee was 7.7 +/- 4.0 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 10.4 +/- 5.5 mm; position 2: 12.0 +/- 5.2 mm; P < .05), with a significant difference between the tunnel positions. CONCLUSION: Neither femoral tunnel position restores normal kinematics of the intact knee. A femoral tunnel position inside the anatomical footprint of the anterior cruciate ligament results in knee kinematics closer to the intact knee than does a tunnel position located for best graft isometry. CLINICAL RELEVANCE: Anatomical femoral tunnel position is important in reproducing function of the anterior cruciate ligament.

Adult↗

PubMed2005

Bi-directional mechanical properties of the posterior region of the glenohumeral capsule.

The objective of this study was to determine the mechanical properties of the posterior region of the glenohumeral capsule in the directions perpendicular (transverse) and parallel (longitudinal) to the longitudinal axis of the posterior band of the inferior glenohumeral ligament. A punch was used to excise one transverse and one longitudinal tissue sample from the posterior capsule of 11 cadaveric shoulders. All tissue samples exhibited the typical nonlinear behavior reported for ligaments and tendons. Significant differences (p < 0.05) were detected between the transverse and longitudinal tissue samples for ultimate stress (1.5+/-1.4 and 4.9+/-2.9 MPa, respectively) and tangent modulus (10.3+/-6.6 and 31.5+/-12.7 MPa, respectively). No significant differences (p > 0.05) were observed between the ultimate strain (transverse: 22.3+/-12.5%, longitudinal: 22.8+/-11.1%) and strain energy density (transverse: 27.2+/-52.8 MPa, longitudinal: 67.5+/-88.2 MPa) of the transverse and longitudinal tissue samples. The ratio of the longitudinal to transverse moduli (4.8+/-4.2) was similar to that found for the axillary pouch (3.3+/-2.8) in a previous study. Thus, both the axillary pouch and the posterior capsule function to stabilize the joint multi-axially. Future analytical models of the glenohumeral joint should consider the properties of the posterior capsule in its transverse and longitudinal directions to fully describe the behavior of the glenohumeral capsule. These models will be clinically important by providing a more accurate representation of the intact capsule as well as simulated capsular injuries and surgical repair procedures.

Anisotropy↗

PubMed2004

Biomechanical function of the posterior horn of the medial meniscus: a human cadaveric study.

Partial and total meniscectomies have been known to develop a high rate of osteoarthritis, but not in quantitative terms. In this study, we investigated the role of the posterior horn of the medial meniscus (PMM) by measuring the changes in the multiple degrees of freedom knee kinematics. Using a robotic/universal force-moment testing system, the 5-degree-of-freedom kinematics at selected flexion angles of human cadaveric knees (age, 35-72 years) in response to a 10 N.m varus torque were measured. Ten knees were studied with the knee at full extension and at 30 degrees, 60 degrees, and 90 degrees of flexion. Each knee was tested in a series of four conditions: intact, with one-third of PMM resected, with two-thirds PMM resected, and finally with the entire PMM resected. Anterior tibial translation increased significantly by 1.4 mm and 4.1 mm at 30 degrees of knee flexion when the two-thirds and entire PMM were resected, respectively. Similarly, external tibial rotation significantly increased 2.2 degrees and 6.7 degrees at 30 degrees of knee flexion with the two-thirds and entire PMM resected, respectively. These results suggest that resecting more than two-thirds of the PMM will have a significant effect on the kinematics of the knee.

Adult↗

PubMed2004

Biomechanical function of surgical procedures for acromioclavicular joint dislocations.

PURPOSE: Surgical procedures for treatment of acromioclavicular (AC) joint dislocation replace the coracoclavicular (CC) ligaments to minimize motion, allow scarring, and increase the subsequent stability of the joint. The purpose of this study was to evaluate the biomechanical function of the surgically repaired or reconstructed (CC Sling, Rockwood Screw [DePuy Orthopaedics, Warsaw, IN], and Coracoacromial [CA] Ligament Transfer Construct) AC joint after AC joint dislocation. TYPE OF STUDY: A cadaver study using a convenience sample. METHODS: Twelve cadaveric shoulders were tested using a robotic/UFS testing system. Three external loading conditions (anterior, posterior, or superior load of 70 N) were applied to intact and surgically repaired or reconstructed AC joint. The resulting kinematics of the AC joint and in situ forces in the CC ligaments or surgical constructs was determined. RESULTS: For the CC Sling, anterior and posterior translation significantly increased by 110% and 330% in response to an anterior and posterior load, respectively. However, the posterior translation for the Rockwood Screw significantly decreased by 60%. Anterior, posterior, and superior translation for the CA Ligament Transfer Construct significantly increased by 110%, 360%, and 100%, respectively. The coupled translations also significantly increased for the CC Sling and CA Ligament Transfer Construct in response to all loading conditions. In contrast, the coupled translations for the Rockwood Screw tended to decrease. Furthermore, the in situ forces increased significantly for all 3 surgical constructs compared with the intact CC Ligaments in response to an anterior and posterior load. CONCLUSIONS: At time zero, increases in the primary and coupled motion for the CC Sling and CA Ligament Transfer Construct could comprise the initial healing period prescribed for AC joint dislocation. Our findings also suggest that the Rockwood Screw provides a highly rigid fixation and may explain the complications frequently seen in clinical practice. CLINICAL RELEVANCE: Current surgical procedures do not have the appropriate stiffness to restore the stability of the intact joint before healing. Therefore, our results may lead to the design and development of new repairs, reconstructions, and rehabilitation protocols for AC joint dislocation.

Acromioclavicular Joint↗

PubMed2004

Active stability of the glenohumeral joint decreases in the apprehension position.

BACKGROUND: Muscle forces that compress the glenohumeral joint during mid-ranges of motion may lead to increased translational forces in end-range positions, such as the apprehension position, where symptoms of anterior instability occur. OBJECTIVE: The objective of this study was to quantify active stability provided by eight shoulder muscles in mid-range and end-range positions through muscle force vector analysis. METHODS: Lines of action were derived from a geometric model and muscle force magnitudes were estimated with electromyography-based techniques. Resultant muscle force vectors were calculated by summing individual muscle force vectors. RESULTS: Compared to mid-range positions, lines of action of resultant force vectors were more anteriorly directed in end-range positions compared to 15 degrees of abduction, up to 26 degrees. Consequently, anterior stability was lowest in the apprehension position. The magnitudes of the resultant force vectors were comparable to other studies. Based on a sensitivity analysis, lines of action of resultant force vectors vary up to 6 degrees within the population. CONCLUSIONS: Data obtained from this model will improve conservative management, post-surgical rehabilitation, and strength training protocols.

Computer Simulation↗

PubMed2004

Multidirectional kinematics of the glenohumeral joint during simulated simple translation tests: impact on clinical diagnoses.

At the end ranges of motion, the glenohumeral capsule limits translation of the humeral head in multiple directions. Since the 6-degree of freedom kinematics of clinical tests are commonly utilized to diagnose shoulder injuries, the objective of this study was to determine the magnitude and repeatability of glenohumeral joint kinematics during a simulated simple anteroposterior translation test in the anterior and posterior directions. A magnetic tracking system was used to determine the kinematics of the humerus with respect to the scapula in eight cadaveric shoulders. At 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension, a clinician applied anterior and posterior loads to the humerus at 0 degrees, 30 degrees, and 60 degrees of external rotation until a manual maximum (simulating a simple translation test) was achieved. Prior to each test, the reference position of the humerus shifted posteriorly 1.8+/-2.0 and 4.1+/-3.8 mm at 30 degrees and 60 degrees of external rotation, respectively. Anterior translation decreased significantly (p < 0.05) from 18.2+/-5.3 mm at 0 degrees of external rotation to 15.5+/-5.1 and 9.9+/-5.5 mm at 30 degrees and 60 degrees, respectively. However, no significant differences were detected between the posterior translations of 13.4+/-6.4, 17.1+/-5.0, and 15.8+/-6.0 mm at 0 degrees, 30 degrees, and 60 degrees of external rotation, respectively. Coupled translations (perpendicular to the direction of loading) at 0 degrees (6.1+/-4.0 and 3.8+/-2.9 mm), 30 degrees (4.7+/-2.7 and 5.9+/-3.1 mm), and 60 degrees (2.3+/-2.3 and 5.0+/-3.5 mm) of external rotation were in the inferior direction in both the anterior and posterior directions, respectively. Based on the data obtained, performing a simulated simple translation test should result in coupled inferior translations and anterior translations that are a function of external rotation. The low standard deviations demonstrate that the observed translations should be repeatable. Furthermore, capsular stretching or injury to the anterior-inferior region of the capsule should be detectable during clinical examination if excessive coupled translations exist or no posterior shift of the reference position with external rotation is noted.

Biomechanical Phenomena↗

PubMed2004

A three-dimensional finite element model of the human anterior cruciate ligament: a computational analysis with experimental validation.

In this study, the force and stress distribution within the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) in response to an anterior tibial load with the knee at full extension was calculated using a validated three-dimensional finite element model (FEM) of a human ACL. The interaction between the AM and PL bundles, as well as the contact and friction caused by the ACL wrapping around the bone during knee motion, were included in the model. The AM and PL bundles of the ACL were simulated as incompressible homogeneous and isotropic hyperelastic materials. The multiple-degrees-of-freedom (DOF) knee kinematics of a cadaveric knee were first obtained using a robotic/universal force-moment sensor testing system. These data were used as the boundary conditions for the FEM of the ACL to calculate the forces in the ACL. The calculated forces were compared to the in situ force in the ACL, determined experimentally, to validate the model. The validated FEM was then used to calculate the force and stress distribution within the ACL under an anterior tibial load at full extension. The AM and PL bundles shared the force, and the stress distribution was non-uniform within both bundles with the highest stress localized near the femoral insertion site. The contact and friction caused by the ACL wrapping around the bone during knee motion played the role of transferring the force from the ACL to the bone, and had a direct effect on the force and stress distribution of the ACL. This validated model will enable the analysis of force and stress distribution in the ACL in response to more complex loading conditions and has the potential to help design improved surgical procedures following ACL injuries.

Anterior Cruciate Ligament↗

PubMed2004

Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads.

The anterior cruciate ligament (ACL) can be anatomically divided into anteromedial (AM) and posterolateral (PL) bundles. Current ACL reconstruction techniques focus primarily on reproducing the AM bundle, but are insufficient in response to rotatory loads. The objective of this study was to determine the distribution of in situ force between the two bundles when the knee is subjected to anterior tibial and rotatory loads. Ten cadaveric knees (50+/-10 years) were tested using a robotic/universal force-moment sensor (UFS) testing system. Two external loading conditions were applied: a 134 N anterior tibial load at full knee extension and 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion and a combined rotatory load of 10 Nm valgus and 5 Nm internal tibial torque at 15 degrees and 30 degrees of flexion. The resulting 6 degrees of freedom kinematics of the knee and the in situ forces in the ACL and its two bundles were determined. Under an anterior tibial load, the in situ force in the PL bundle was the highest at full extension (67+/-30 N) and decreased with increasing flexion. The in situ force in the AM bundle was lower than in the PL bundle at full extension, but increased with increasing flexion, reaching a maximum (90+/-17 N) at 60 degrees of flexion and then decreasing at 90 degrees. Under a combined rotatory load, the in situ force of the PL bundle was higher at 15 degrees (21+/-11 N) and lower at 30 degrees of flexion (14+/-6 N). The in situ force in the AM bundle was similar at 15 degrees and 30 degrees of knee flexion (30+/-15 vs. 35+/-16 N, respectively). Comparing these two external loading conditions demonstrated the importance of the PL bundle, especially when the knee is near full extension. These findings provide a better understanding of the function of the two bundles of the ACL and could serve as a basis for future considerations of surgical reconstruction in the replacement of the ACL.

Aged↗

PubMed2004

An evaluation of the quasi-linear viscoelastic properties of the healing medial collateral ligament in a goat model.

The viscoelastic properties of the healing medial collateral ligament (MCL) at 12 weeks after isolated injury were investigated in a goat model. The stress-strain relationships, static and cyclic stress-relaxation behaviors of the healing MCL up to 5% strain were determined experimentally using a femur-MCL-tibia complex. These experimental data were used in combination with the quasi-linear viscoelastic (QLV) theory of Fung (1972) to characterize the reduced relaxation function, G(t) (described by constants C, tau1, and tau2) and the elastic response, sigmae(epsilon) (described by constants A and B) of this tissue. It was found that the percentage of stress relaxation for the healing MCLs was significantly greater than those for sham-operated controls (49.0 +/- 12.1% vs. 26.5 +/- 8.1%, respectively; p < 0.05). The product of constants A x B, i.e. the initial slope of the stress-strain curves, was found to be significantly lower for healing MCLs compared to those for sham-operated controls (32.9 +/- 15.8 MPa vs. 118.8 +/- 48.3 MPa; p < 0.05). The dimensionless constant C, i.e. the magnitude of the viscous response, was nearly three times greater for healing MCLs, while constant tau1 was found to be similar between the two groups (0.80 +/- 0.43 s vs. 0.89 +/- 0.52 s, respectively). Constant tau2 for the healing MCL was significantly less than the controls (1269 +/- 38 s vs. 1845 +/- 431 s; p < 0.05) indicating that the stress relaxation reached a plateau earlier. These constants of the QLV theory used to describe the healing MCL were validated for the strain level utilized in this experiment (approximately equal to 4.5%) by predicting the peak stresses during a cyclic stress-relaxation experiment. The theoretically determined values closely matched the experimentally measured values. Thus, this study demonstrates that the QLV theory could be successfully used to describe the viscoelastic behavior of the MCL during the early phases of healing.

Animals↗