This study was conducted to determine the biomechanics of the human head under quasistatic and dynamic loads. Twelve unembalmed intact human cadaver heads were tested to failure using an electrohydraulic testing device. Quasistatic loading was done at a rate of 2.5 mm/s. Impact loading tests were conducted at a rate of 7.1 to 8.0 m/s. Vertex, parietal, temporal, frontal, and occipital regions were selected as the loading sites. Pathological alterations were determined by pretest and posttest radiography, close-up computed tomography (CT) images, macroscopic evaluation, and defleshing techniques. Biomechanical force-deflection response, stiffness, and energy-absorbing characteristics were obtained. Results indicated the skull to have nonlinear structural response. The failure loads, deflections, stiffness, and energies ranged from 4.5 to 14.1 kN, 3.4 to 16.6 mm, 467 to 5867 N/mm, and 14.1 to 68.5 J, respectively. The overall mean values of these parameters for quasistatic and dynamic loads were 6.4 kN (+/- 1.1), 12.0 mm (+/- 1.6), 812 N/mm (+/- 139), 33.5 J (+/- 8.5), and 11.9 kN (+/-0.9), 5.8 mm (+/- 1.0), 4023 N/mm (+/- 541), 28.0 J (+/- 5.1), respectively. It should be emphasized that these values do not account for the individual variations in the anatomical locations on the cranium of the specimens. While the X-rays and CT scans identified the fracture, the precise direction and location of the impact on the skull were not apparent in these images. Fracture widths were consistently wider at sites remote from the loading region. Consequently, based on retrospective images, it may not be appropriate to extrapolate the anatomical region that sustained the impact forces. The quantified biomechanical response parameters will assist in the development and validation of finite element models of head injury.

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The lateral extracavitary approach to the spine was used for resection of displaced bpne and disc located anterior to the dura in 62 patients with traumatic lesions of the thoracic and lumbar spine. Fifty-two patients had closed vertebral fractures and 10 had gunshot wounds. The spinal cord was involved in 44 patients, and the cauda equina in 18. A spinal subarachnoid block was demonstrated in 17 of 57 preoperative gas myelograms. Evoked potential recordings, although related to preception of joint rotation, tended to reflect the overall neurological condition and had some prognostic value. Significant improvement followed surgery in 46 patients with incomplete neurological lesions, and one was transiently worse. Before operation 18 patients were able to walk; nine with assistance and nine without. After operation 47 patients were able to walk; 12 with assistance and 35 without. Adequate bladder function was present in 17 patients before surgery, and in 44 after surgery. A laminectomy had been done previously in 16 patients, 11 of whom improved significantly after anterior resection. Spine fusions were required in 26 patients, five of whom had a prior laminectomy. The major factor in the pathogenesis of the incomplete neurological deficit appeared to be distortion of the cord and roots by displaced bone and disc. Consequently, the primary object of treatment was the restoration and maintenance of normal anatomical relationships between the spinal cord or cauda equina and the spinal canal.

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A review is presented of the existing finite-element (FE) models for the biomechanics of human head injury. Finite element analysis can be an important tool in describing the injury biomechanics of the human head. Complex geometric and material properties pose challenges to FE modelling. Various assumptions and simplifications are made in model development that require experimental validation. More recent models incorporate anatomic details with higher precision. The cervical vertebral column and spinal cord are included. Model results have been more qualitative than quantitative owing to the lack of adequate experimental validation. Advances include transient stress distribution in the brain tissue, frequency responses, effects of boundary conditions, pressure release mechanism of the foramen magnum and the spinal cord, verification of rotation and cavitation theories of brain injury, and protective effects of helmets. These theoretical results provide a basic understanding of the internal biomechanical responses of the head under various dynamic loading conditions. Basic experimental research is still needed to be determine more accurate material properties and injury tolerance criteria, so that FE models can fully exercise their analytical and predictive power for the study and prevention of human head injury.

✓ In 18 patients with cancer and intractable pain, capacitatively coupled pulses of 0.25 msec duration were delivered transcutaneously at 100 Hz to sets of five in-line electrodes implanted subdurally over the dorsal columns. Averaged somatosensory-evoked potentials were recorded from scalp electrodes before, during, and after application of current. All but one patient experienced relief of pain during stimulation, persisting for as long as several hours afterward. Eleven patients developed hyperactive deep reflexes, pathological reflexes, and decreased perception of joint rotation, pain, and touch below the level of current application. Somatosensory-evoked potential amplitudes were markedly reduced. All neurological findings returned to control values within 1 hour after each of repeated applications of current. Histological examination of spinal cord sections from four cancer patients showed no changes secondary to long-term current application. Similar currents were applied to the spinal cord of 15 monkeys with chronically implanted bipolar recording or stimulating electrodes over the lower, middle, and upper thoracic cord, in nucleus ventralis posterior lateralis (VPL), and over the sensory motor cortex (SMC). With application of current, the responses in VPL and SMC to peripheral stimulation were abolished. Evoked potential responses were abolished between bipolar stimulating electrodes and bipolar recording electrodes separated by the five in-line electrodes used to supply the 100 Hz current. However, when both stimulating and recording electrodes were either above or below the five in-line electrode set, evoked responses were unaffected. The findings indicate that applied currents blocked neuronal transmission by producing local changes in the cord. The prolonged alteration of cerebral evoked potentials and relief of pain, however, could also be related to involvement of supraspinal neurons.

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