Development and verification of a physiologically motivated internal controller for the open-source extended Hill-type muscle model in LS-DYNA

Nowadays, active human body models are becoming essential tools for the development of integrated occupant safety systems. However, their broad application in industry and research is limited due to the complexity of incorporated muscle controllers, the long simulation runtime, and the non-regular use of physiological motor control approaches. The purpose of this study is to address the challenges in all indicated directions by implementing a muscle controller with several physiologically inspired control strategies into an open-source extended Hill-type muscle model formulated as LS-DYNA user-defined umat41 subroutine written in the Fortran programming language. This results in increased usability, runtime performance and physiological accuracy compared to the standard muscle material existing in LS-DYNA. The proposed controller code is verified with extensive experimental data that include findings for arm muscles, the cervical spine region, and the whole body. Selected verification experiments cover three different muscle activation situations: (1) passive state, (2) open-loop and closed-loop muscle activation, and (3) reflexive behaviour. Two whole body finite element models, the 50th percentile female VIVA OpenHBM and the 50th percentile male THUMS v5, are used for simulations, complemented by the simplified arm model extracted from the 50th percentile male THUMS v3. The obtained results are evaluated additionally with the CORrelation and Analysis methodology and the mean squared error method, showing good to excellent biofidelity and sufficient agreement with the experimental data. It was shown additionally how the integrated controller allows simplified mimicking of the movements for similar musculoskeletal models using the parameters transfer method. Furthermore, the Hill-type muscle model presented in this paper shows better kinematic behaviour even in the passive case compared to the existing one in LS-DYNA due to its improved damping and elastic properties. These findings provide a solid evidence base motivating the application of the enhanced muscle material with the internal controller in future studies with Active Human Body Models under different loading conditions.

Role of Rotated Head Postures on Volunteer Kinematics and Muscle Activity in Braking Scenarios Performed on a Driving Simulator

Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.

Excessive testosterone production in a patient with Nelson syndrome and bilateral testicular tumors

Bilateral primary testicular tumors are rare and usually consist of either interstitial cells or hypertrophic testicular adrenal remnant tissue. Their differentiation on clinical presentation and histologic examination remains difficult but is essential because of the different therapeutic approaches. We report a rare case of excessive testosterone production by bilateral testicular tumors in a patient with Nelson syndrome (ACTH-secreting pituitary adenoma after bilateral adrenalectomy in patients with Cushing's disease). Increased ACTH stimulation in this patient supports the thesis of pluripotent cells within the testis which can undergo differentiation to cells which are not only morphologically similar to Leydig cells but also have the functional property of these cells. Our clinical findings support the diagnosis of hyperplasia of adrenal remnant or pluripotent cells rather than a true Leydig cell tumor. We emphasize the need for hormonal evaluations which should be assessed in the context of the size of these nodular tumors prior to therapeutic decisions. In cases with elevated serum ACTH and small nodular hyperplasia, we would favor a 'wait-and-see' strategy with appropriate hormonal therapy. In large tumors with clinical signs of hormonal activity, patient noncompliance with steroid replacement regimens or with local symptoms, scrotal exploration and tumor enucleation are indicated.

[Risk oriented urologic preparation of children for kidney transplantation]

Among 1050 consecutive renal transplants (Rtx) performed in Heidelberg since 1967 we have gained experience with 163 children and adolescents under the age of 16, receiving a Rtx since 1969. 30% of these were terminally renal insufficient due to congenital obstructive uropathy, mainly infravesical obstruction and/or reflux nephropathy. A special diagnostic work-up (flow chart) for evaluating and eliminating potential pre- and posttransplant risk factors consisted of noninvasive screening methods (ultrasonography and uroflow) followed step by step by more invasive imaging procedures (MR, MCU) and finally invasive methods of evaluating upper urinary tract and voiding disorders (complete urodynamic work-up). We emphasize the preservation or rehabilitation of urinary bladder function, eradication of significant UTI and pre-Rtx surgical treatment of otherwise hard to handle nephrogenic hypertension. Unnecessary psychologically and somatically traumatizing pretransplant diagnostic and therapeutic procedures can be avoided in pediatric non-obstructive nephropathy patients.

[Neurofibromatosis of the bladder in infancy. 10 years' follow-up]

Urinary tract involvement in neurofibromatosis is rare. We found 51 cases documented in the literature, the majority of these (n = 31) were children. More than half of these (n = 18) developed upper urinary tract obstruction. A report is given of a 10-month-old boy with neurofibromatosis of the bladder. Treatment consisted in radical surgery with cystoprostatectomy and uretero-transureterocutaneostomy. Follow-up of 10 years presents a good result. The different modalities of treatment are reviewed in the literature.