An evaluation of occupant dynamics during moderate-to-high speed side impacts.

The present study examined trends in occupant dynamics during side impact testing in vehicle models over the past decade. "Moderate-to-high" speed side impacts (delta-V ≥15 km/h) were analyzed. The Insurance Institute for Highway Safety (IIHS) side impact crash data was examined (N = 126). The test procedure involved a moving deformable barrier (MDB) impacting the sides of stationary vehicles at 50.0 km/h. Instrumented 5th-percentile female SID IIs dummies were positioned in the driver and left rear passenger seats. Occupant head, neck, shoulder, torso, spine, and pelvis/femur responses (times histories, peaks, and time-to-peak values) were evaluated and compared to injury assessment reference values (IARVs). The effects of delta-V, vehicle model year, vehicle body type, and occupant seating position on dynamic responses were examined. The vehicle lateral delta-Vs ranged from 15.9 to 34.5 km/h. The MY2018-2020 demonstrated lower peak dynamics than MY2010-2013, for the driver head acceleration (53.7 ± 11.3g vs 46.4 ± 11.6g), shoulder lateral forces (1.7 ± 0.7 kN vs 1.5 ± 0.2 kN), average rib deflection (29.8 ± 8.3 mm vs 28.4 ± 6.2 mm), spine accelerations at T4 (51.4 ± 23.4g vs 39.6 ± 5.9g) and T12 (56.3 ± 18.5g vs 45.2 ± 9.6g), iliac forces (1.9 ± 1.0 kN vs 1.2 ± 0.9 kN), and acetabular forces (1.9 ± 0.8 kN vs 1.3 ± 0.5 kN). The driver indicated statistically higher dynamic responses than the left rear passenger. Higher wheelbase vehicles generally showed lower occupant loading than the smaller vehicles. In conclusion, a reduction in occupant loading and risks for injury was observed in vehicle models over the past decade. This provides further insight into injury mechanisms, occupant dynamics simulations, and seat/restraint design.

Use of pre-clinical surgically induced models to understand biomechanical and biological consequences of PTOA development.

Post-traumatic osteoarthritis (PTOA) development is often observed following traumatic knee injuries involving key stabilising structures such as the cruciate ligaments or the menisci. Both biomechanical and biological alterations that follow knee injuries have been implicated in PTOA development, although it has not been possible to differentiate clearly between the two causal factors. This review critically examines the outcomes from pre-clinical lapine and ovine injury models arising in the authors' laboratories and differing in severity of PTOA development and progression. Specifically, we focus on how varying severity of knee injuries influence the subsequent alterations in kinematics, kinetics, and biological outcomes. The immediate impact of injury on the lubrication capacity of the joint is examined in the context of its influence on biomechanical alterations, thus linking the biological changes to abnormal kinematics, leading to a focus on the potential areas for interventions to inhibit or prevent development of the disease. We believe that PTOA results from altered cartilage surface interactions where biological and biomechanical factors intersect, and mitigating acute joint inflammation may be critical to prolonging PTOA development. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:454-465, 2017.

Ligament and meniscus loading in the ovine stifle joint during normal gait.

BACKGROUND: The ovine stifle joint is an ideal preclinical model to study knee joint biomechanics. Knowledge of the ovine ligamentous and meniscal loading during normal gait is currently limited. METHODS: The in vivo kinematics of the ovine stifle joint (N=4) were measured during "normal" gait using a highly accurate instrumented spatial linkage (ISL, 0.3±0.2mm). These motions were reproduced in vitro using a unique robotic testing platform and the loads carried by the anterior/posterior cruciate ligaments (ACL/PCL), medial/lateral collateral ligaments (MCL/LCL), and medial/lateral menisci (MM/LM) during gait were determined. RESULTS: Considerable inter-subject variability in tissue loads was observed. The load in the ACL was near zero at hoof-strike (0% gait) and reached a peak (100 to 300N) during early-stance (~10% gait). The PCL reached a peak load (200 to 500N) just after hoof-strike (~5% gait) and was mostly unloaded throughout the remainder of stance. Load in the MCL was substantially lower than the cruciate ligaments, reaching a maximum of 50 to 100N near the beginning of stance. The LCL carried a negligible amount of load through the entire gait cycle. There was also a major contribution of the MM and LM to load transfer from the femur to the tibia during normal gait. The total meniscal load reached a maximum average between 350 and 550N during gait. CONCLUSION: Knowledge of joint function during normal motion is essential for understanding normal and pathologic joint states. The considerable variability in the magnitudes and patterns of tissue loads among animals simulates clinical variability in humans. LEVEL OF EVIDENCE: III.

Relationship between increased in vivo meniscal loads and abnormal tibiofemoral surface alignment in ACL deficient sheep is varied.

The aim of this study was to quantify how abnormal dynamic tibiofemoral surface alignment affects the load bearing function of menisci in vivo. Using a sheep model of ACL deficiency, we tested the hypothesis that increased in vivo meniscal loads correlate with greater tibiofemoral surface alignment abnormality. Stifle kinematics were recorded using a bone-mounted instrumented spatial linkage in four sheep before, and at four and twenty weeks (w) after ACL transection. A parallel robotic manipulator was used to quantify stifle kinetics by reproducing each animal׳s in vivo kinematics and measuring tissue loads during gait. Meniscal resultant loads were estimated from the change in joint reaction force after sequentially removing load-bearing tissues. Tibiofemoral subchondral surfaces were then traced and modeled using thin plate splines. Proximity disturbance is a surface interaction measure used to quantify dynamic tibiofemoral surface alignment abnormality. ACL transection increased meniscal loads by 30-145% at 20w post-ACL transection, whereas the degree of dynamic tibiofemoral subchondral surface alignment varied between sheep. Positive and significant correlations between increased meniscal loads and proximity disturbance values >10mm were observed (R2=0.04-0.57; p≤0.05). Our results suggest that the proximity disturbance measure reflects abnormal meniscal loads following ACL injury; however given the range of R2 values, perturbations in dynamic tibiofemoral subchondral surface alignment do not explain abnormal joint kinetics entirely, and point to the presence of other dynamic compensatory mechanisms that may have a significant bearing on in vivo joint function and long-term joint health.

An instrumented spatial linkage for measuring knee joint kinematics.

BACKGROUND: In this study, the design and development of a highly accurate instrumented spatial linkage (ISL) for kinematic analysis of the ovine stifle joint is described. The ovine knee is a promising biomechanical model of the human knee joint. METHODS: The ISL consists of six digital rotational encoders providing six degrees of freedom (6-DOF) to its motion. The ISL makes use of the complete and parametrically continuous (CPC) kinematic modeling method to describe the kinematic relationship between encoder readings and the relative positions and orientation of its two ends. The CPC method is useful when calibrating the ISL, because a small change in parameters corresponds to a small change in calculated positions and orientations and thus a smaller optimization error, compared to other kinematic models. The ISL is attached rigidly to the femur and the tibia for motion capture, and the CPC kinematic model is then employed to transform the angle sensor readings to relative motion of the two ends of the linkage, and thereby, the stifle joint motion. RESULTS: The positional accuracy for ISL after calibration and optimization was 0.3±0.2mm (mean +/- standard deviation). The ISL was also evaluated dynamically to ensure that accurate results were maintained, and achieved an accuracy of 0.1mm. CONCLUSIONS: Compared to the traditional motion capture methods, this system provides increased accuracy, reduced processing time, and ease of use. Future work will be on the application of the ISL to the ovine gait and determination of in vivo joint motions and tissue loads. CLINICAL RELEVANCE: Accurate measurement of knee joint kinematics is essential in understanding injury mechanisms and development of potential preventive or treatment strategies.

Increased meniscal loading after anterior cruciate ligament transection in vivo: a longitudinal study in sheep.

INTRODUCTION: Meniscal injury has been well documented as a frequent consequence of both acute and chronic ACL deficiency. The purpose of this study was to evaluate the effect of ACL deficiency on meniscal loads in vivo and determine how these loads would change over time after ACL injury. METHODS: The in vivo kinematics of the stifle joint of five sheep were measured during normal gait, as well as 4 and 20 weeks after ACL transection. A unique robotic testing platform was then programmed to reproduce all the previously recorded kinematics and the loads carried by medial and lateral menisci during gait were estimated. RESULTS: The results demonstrated a significant increase in both medial and lateral meniscal loads 20 weeks following ACL transection, mainly during mid-stance phase of gait (p = 0.007 and p = 0.003, respectively), with interesting inter-subject variability. A moderate correlation (R(2) ≥ 0.5) between in situ meniscal loads and anterior tibial translations was also detected over time after injury, increased translations post injury generally corresponded to larger meniscal loads. CONCLUSION: The dramatic increase in meniscal loads long term post ACL transection probably explains the meniscal changes or injuries reported clinically in many chronic ACL-deficient knees.

A novel testing platform for assessing knee joint mechanics: a parallel robotic system combined with an instrumented spatial linkage.

Assessing joint function following trauma and its inter-relation with degenerative changes requires an understanding of the normal state of structural loading in the joint. Very few studies have attempted to reproduce joint specific in vivo motions in vitro to quantify the actual loads carried by different tissues within the knee joint. The most significant challenge in this area is the very high sensitivity of the loads in joint structures to motion reproduction accuracy. A novel testing platform for assessing knee joint mechanics is described, comprised of a highly accurate (0.3 ± 0.1 mm, 0.3 ± 0.1°) six-degree-of-freedom (6-DOF) instrumented spatial linkage (ISL) for in vivo joint kinematic assessments and a unique 6-DOF parallel robotic manipulator. A position feedback system (ISL and position controller) is used for accurate reproduction of in vivo joint motions and estimation of "in situ" joint/tissue loads. The parallel robotic manipulator provides excellent stiffness and repeatability in reproducing physiological motions in 6-DOF, compared to the commonly used serial robots. The position feedback system provides real-time feedback data to the robot to reproduce in vivo motions and significantly enhances motion reproduction accuracy by adjusting for robot end-effector movements. Using this combined robot-ISL system, in vivo motions can be reproduced in vitro with very high accuracy (0.1 mm, 0.1°). Our results indicate that this level of accuracy is essential for meaningful estimation of tissue loads during gait. Using this novel testing platform, we have determined the normal load-carrying characteristics of different tissues within the ovine knee joint. The application of this testing system will continue to increase our understanding of normal and pathological joint states.

Decreased posterior cruciate and altered collateral ligament loading following ACL transection: a longitudinal study in the ovine model.

Although ACL deficiency is shown to lead to joint degeneration, few quantitative data are reported on its effect on soft tissue structures surrounding the knee joint, specifically, the posterior cruciate and collateral ligaments. The kinematics of the stifle joint of sheep (N = 5) were measured during "normal" gait, as well as 4 and 20 weeks after ACL transection. These motions were reproduced using a unique robotic manipulator and the loads borne by PCL, MCL, and LCL during gait were determined. Our results demonstrated a significant decrease in mean PCL loads 20 weeks post-ACL injury, at hoof-strike (0% of gait, p = 0.034), hoof-off (66% of gait, p = 0.006), peak-swing (85% of gait, p = 0.026), and extension-before-hoof-strike (95% of gait, p = 0.028). Mean MCL loads did not significantly increase following ACL transection, maybe due to large between-animal variation. Finally, mean LCL loads indicated a significant decrease (p < 0.047) at 20 weeks across the entire gait cycle. From a clinical perspective, the load redistributions observed in cruciate and collateral ligaments following ACL injury indicate that these tissues can carry/adapt to the altered mechanical environment of the joint. The considerable variability in the magnitudes of change following ACL injury among animals also simulates clinical variability in humans after trauma.

Kinematic and kinetic interactions during normal and ACL-deficient gait: a longitudinal in vivo study.

The interactions between different tissues within the knee joint and between different kinematic DOF and joint flexion during normal gait were investigated. These interactions change following ACL transection, in both short (4 weeks) and long (20 weeks) term. Ten skeletally mature sheep were used in control (N = 5) and experimental (N = 5) groups. The 6-DOF stifle joint motion was first measured during normal gait. The control group were then euthanized and mounted on a unique robotic testing platform for kinetic measurements. The experimental group underwent ACL transection surgery, and kinematics measurements were repeated 4 and 20 weeks post-operatively. The experimental group were then euthanized and underwent kinetic assessment using the robotic system. Results indicated significant couplings between joint flexion vs. abduction and internal tibial rotation, as well as medial, anterior, and superior tibial translations during both normal and ACL-deficient gait. Distinct kinetic interactions were also observed between different tissues within the knee joint. Direct relationships were found between ACL vs. LM/MM, and PCL vs. MCL loads during normal gait; inverse relationships were detected between ACL vs. PCL and PCL vs. LM/MM loads. These kinetic interaction patterns were considerably altered by ACL injury. Significant inter-subject variability in joint kinematics and tissue loading patterns during gait was also observed. This study provides further understanding of the in vivo function of different tissues within the knee joint and their couplings with joint kinematics during normal gait and over time following ACL transection.

Inter-insertional distance is a poor correlate for ligament load: analysis from in vivo gait kinetics data.

In many analytic models of the knee joint, inter-insertional distance is used as the measure to define the load in a ligament. In addition, the direction of the load is taken to be the direction between the two insertions. Our in vivo data on the ovine ligament loads during gait, however, indicate that a wide range of forces is possible in the ligament for any specified inter-insertional distance. To understand the complex relationship between the bone orientations and ligament load better, an artificial neural network (ANN) model was developed. The six degree-of-freedom (6-DOF) in vivo kinematics of femur relative to tibia (joint kinematics) was used as input, and the magnitude of the anterior cruciate ligament (ACL) load was used as output/target. While the trained network was able to predict peak ligament loads with remarkable accuracy (R-square=0.98), an explicit relationship between joint kinematics and ACL load could not be determined. To examine the experimental and ANN observations further, a finite element (FE) model of the ACL was created. The geometry of the FE model was reconstructed from magnetic resonance images (MRI) of an ACL, and an isotropic, hyperelastic, nearly incompressible constitutive model was implemented for the ACL. The FE simulation results also indicate that a range of loads is possible in the ACL for a given inter-insertional distance, in concordance with the experimental/ANN observations. This study provides new insights for models of the knee joint; a simple force-length relationship for the ligament is not exact, nor is a single point to single point direction. More detailed microstructure-function data is required.

Functional activity of the anterior and posterior cruciate ligaments under in vivo gait and static physiological loads.

The loading of the anterior and posterior cruciate ligaments (ACL and PCL) during normal gait has not been quantified. Also, it is not clear whether ligaments under "static" physiological loads commonly used in cadaveric studies behave similarly to normal gait experienced in vivo. We measured the in vivo kinematics of the stifle joint of sheep (N = 4) during "normal gait," then reproduced these gait paths using a robotic system. The loads borne by the cruciate ligaments were determined using the principle of superposition and plotted against each other. This indicated some functional interaction between the ACL and PCL under in vivo physiological loads. To examine this relationship under static loading conditions, cadaveric knees (N = 6) were tested in the anterior-posterior (AP) direction, along the axes of the ACL and the PCL, as well as under combined AP and tibial rotations. The same process was repeated after either the ACL (N = 3) or the PCL (N = 3) was transected. Our results show a mutually exclusive relationship in ACL and PCL load bearing under both "in vivo gait" and "static" loading conditions. High ACL loads were associated with low PCL loads and vice versa. This is a novel study quantifying the actions of the cruciate ligaments during gait and comparing them to commonly used static loading conditions in cadaveric studies.

Characterization of the location and extent of myocardial infarction using heart vector analysis.

An innovative method was proposed on the basis of vectorcardiography to characterize the location and extent of moderate to large, relatively compact infarcts using ECG evidence. It is assumed that heart vector is proportional to relevant active depolarization area(s). The normal VCG was then used to examine our ideas based on the information of location, amplitude, and direction of heart vector at any instant that is included in it. The model-based comparison of cases under study and relevant normal VCGs gives region and extent of myocardial infarction. Three criteria were finally defined to evaluate the presented method based on Physionet database. EPD, which is the percentage discrepancy between the extent of the infarct as estimated from our proposed method and as determined from the gold standard. SO, which was defined as the overlap between the sets of infarct segments as estimated and as determined from the gold standard. And CED, which is the distance between the centroid (geometrical center) of the infarct as estimated from our method and as determined from the gold standard. Finally, we gained the values of EPD equal to 32, SO equal to 0.933 and CED equal to 1. The presented method is not applicable in cases of hypertrophy, Bundle Branch Block (BBB) and arrhythmia which can be a plan for future work.