Development of a finite element model of the human shoulder

Development and Validation of the Total HUman Model for Safety (THUMS) Version 5 Containing Multiple 1D Muscles for Estimating Occupant Motions with Muscle Activation During Side Impacts

Accurate prediction of occupant head kinematics is critical for better understanding of head/face injury mechanisms in side impacts, especially far-side occupants. In light of the fact that researchers have demonstrated that muscle activations, especially in neck muscles, can affect occupant head kinematics, a human body finite element (FE) model that considers muscle activation is useful for predicting occupant head kinematics in real-world automotive accidents. In this study, we developed a human body FE model called the THUMS (Total HUman Model for Safety) Version 5 that contains 262 one-dimensional (1D) Hill-type muscle models over the entire body. The THUMS was validated against 36 series of PMHS (Post Mortem Human Surrogate) and volunteer test data in this study, and 16 series of PMHS and volunteer test data on side impacts are presented. Validation results with force-time curves were also evaluated quantitatively using the CORA (CORrelation and Analysis) method. The validation results suggest that the THUMS has good biofidelity in the responses of the regional or full body for side impacts, but relatively poor biofidelity in its local level of responses such as brain displacements. Occupant kinematics predicted by the THUMS with a muscle controller using 22 PID (Proportional-Integral- Derivative) controllers were compared with those of volunteer test data on low-speed lateral impacts. The THUMS with muscle controller reproduced the head kinematics of the volunteer data more accurately than that without muscle activation, although further studies on validation of torso kinematics are needed for more accurate predictions of occupant head kinematics.

Development of numerical models for injury biomechanics research: a review of 50 years of publications in the Stapp Car Crash Conference

Numerical analyses frequently accompany experimental investigations that study injury biomechanics and improvements in automotive safety. Limited by computational speed, earlier mathematical models tended to simplify the system under study so that a set of differential equations could be written and solved. Advances in computing technology and analysis software have enabled the development of many sophisticated models that have the potential to provide a more comprehensive understanding of human impact response, injury mechanisms, and tolerance. In this article, 50 years of publications on numerical modeling published in the Stapp Car Crash Conference Proceedings and Journal were reviewed. These models were based on: (a) author-developed equations and software, (b) public and commercially available programs to solve rigid body dynamic models (such as MVMA2D, CAL3D or ATB, and MADYMO), and (c) finite element models. A clear trend that can be observed is the increasing use of the finite element method for model development. A review of these modeling papers clearly indicates the progression of the state-of-the-art in computational methods and technologies in injury biomechanics.

Non-injurious and injurious impact response of the human shoulder three-dimensional analysis of kinematics and determination of injury threshold

Seven Post Mortem Human Subjects were submitted to three low velocity impacts (v=1.5 m/s) to the right shoulder at three different angles in the horizontal plane (-15 degrees , 0 degrees , +15 degrees ). Then, the left shoulder was submitted to a purely lateral high velocity impact (v=3, 4, 6 m/s). The load was delivered by a 23.4 kg impactor fitted with a rigid rectangular impacting plate. Shoulder and thoracic bone structures were equipped with tri-axial accelerometers and photographic markers, whose trajectories were tracked in 3D by seven high-speed cameras. The results were scaled in order to account for the differences between the subjects' anthropometry and to define response corridors for the evaluation of the dummies' shoulders. Impact forces as well as several shoulder deflections were analyzed with respect to each subject's injury survey in order to find the most relevant parameters for the prediction of injuries. In the case of oblique impacts, slight modifications in the shoulder responses were observed, with higher force peaks obtained for the +15 degrees impacts in comparison to the 0 degrees and -15 degrees impacts. Acromion-to-sternum deflection peak values were closely linked with a clavicle fracture, but could not predict other types of fracture for which acromion-to-acromion deflection was a better predictor.

Mechanical Properties of the Shoulder Ligaments under Dynamic Loading

Thirty-three fresh human cadaver shoulders were harvested and bone-ligament-bone specimens of acromioclavicular joint, coracoclavicular joint and sternoclavicular joint were obtained. A test fixture and clamps specifically designed for this ligament study and a high-speed Instron machine were used. One quasi-static rate (nominally 0.1 %/sec) and two high rates (nominally, high rate 1 = 40,000 %/sec and high rate 2 = 15,000 %/sec) were used in this study. In the acromioclavicular joint tests, ligament failure was the most common failure mode. Bone fractures occurred most often at the clavicle rather than acromion. In the coracoclavicular joint tests, the majority of specimens failed at the ligament and bone fractures occurred at the coracoid. In the sternoclavicular joint tests, the specimen failed at the bone in most cases. In the acromioclavicular joint and coracoclavicular joint tests, high rate 2 tests and quasi-static tests had more bone fracture cases than high rate 1 tests. Cross sectional area, deflection at failure, load at failure, strain at failure, stress at failure and Young's modulus of these three shoulder joints were found. The Young's modulus, ultimate stress and ultimate load of the three joints were found to be significantly lower in the quasi-static rate tests compared to the high rate 2 tests but not significantly different between high rate 1 and high rate 2 tests. There are no significant relationships between cross-sectional area and age, height or weight, nor between the mechanical properties of the shoulder joint and age, height or weight.

Structural Response of Lower Leg Muscles in Compression: A Low Impact Energy Study Employing Volunteers, Cadavers and the Hybrid III

Little has been reported in the literature on the compressive properties of muscle. These data are needed for the development of finite element models that address impact of the muscles, especially in the study of pedestrian impact. Tests were conducted to characterize the compressive response of muscle. Volunteers, cadaveric specimens and a Hybrid III dummy were impacted in the posterior and lateral aspect of the lower leg using a free flying pendulum. Volunteer muscles were tested while tensed and relaxed. The effects of muscle tension were found to influence results, especially in posterior leg impacts. Cadaveric response was found to be similar to that of the relaxed volunteer. The resulting data can be used to identify a material law using an inverse method.

Injury and response of the shoulder in lateral sled tests

The biomechanical response and injury tolerance of the shoulder in lateral impacts is not well understood. These data are needed to better understand human injury tolerance, validate finite element models and develop biofidelic shoulders in side impact dummies. Seventeen side impact sled tests were performed with unembalmed human cadavers. Data analyzed for this study include T1-Y acceleration, shoulder and thoracic load plate forces, upper sternum x and y accelerations, and struck side acromion x, y and z accelerations. One dimensional deflection at the shoulder level was determined from high-speed film by measuring the distance between a target on T1 and the impacted wall. Force-time response corridors were obtained for tests with 9 m/s pelvic offset, 10.5 m/s pelvic offset, 9 m/s unpadded flat wall, 6.7 m/s unpadded flat wall, 9 m/s soft padding and 9 m/s stiff padding. Maximum shoulder plate forces in unpadded 9 m/s tests (5.5 kN) were larger than in 6.7 m/s tests (3.3 kN). The peak force at the shoulder was larger than at the thorax plate in unpadded and soft padded tests. T1-Y accelerations were larger in unpadded 9 m/s flat wall tests and unpadded pelvic offset 10.5 m/s tests (peak values of 130 and 145 g's) than in other test conditions. Deflections between T1 and the struck wall ranged from 88 to 154 mm in unpadded tests and 95 to 128 mm in stiff and soft padded tests. Eighteen AIS 2 level shoulder injuries occurred in 11 test subjects. These injuries included left acromion fracture in five subjects, left acromioclavicular separation in ten subjects and left clavicle fracture in three subjects. Average MAIS to the shoulder was 0.86 in seven subjects which impacted 4 to 6 inches (101.6 to 152.4 mm) of soft or stiff padding and 1.6 in ten subjects which impacted no padding or 3 inches (76.2 mm) of stiff padding. Previous findings from this test series were reported by Irwin et al. (1993) for seven tests and focused on detailed analysis of shoulder deflection (T5 to shoulder edge). The current study is expanded to 17 tests and includes force, acceleration response and analysis of shoulder deflection (T1 to shoulder edge). Padding of 4 to 6 inches (101.6 mm to 152.4 mm) reduced shoulder injury approximately one AIS level. A combination of ASA10 and deflection was the best shoulder injury predictor. Shoulder deflection of 106 mm predicts 50% probability of MAIS 2.