Analysis of compressive creep behavior of the vertebral unit subjected to a uniform axial loading using exact parametric solution equations of Kelvin-solid models--Part I. Human intervertebral joints.

The creep response phenomena observed on 47 human intervertebral discs subjected to a constant axial compressive stress was analytically studied by two-, three- and four-parameter-solid models employing the Burns- Kaleps 'exact analysis scheme'. The mechanical properties (Young's moduli and viscosity coefficients) associated with each model were calculated for each of the 47 disks, with superior results obtained for the latter two models. Results for the two-parameter-solid model suggest its possible usefulness in simulating creep response that is characteristic of disk degeneration. Results for the three- and four-parameter-solid models were excellent, with an average error for the model predicted strain, epsilon(ti)cal, values from the experimentally measured, epsilon(ti)exp, values of 2.314% for the former model and 4.446% for the latter model on the 47 human spinal segments analyzed. The three-parameter-solid model was most sensitive in its predictability of strain behavior for ti greater than 1 min; whereas the four-parameter-solid model demonstrated greater simulation sensitivity in the 0 less than ti less than or equal to 1 min range.

Analysis of compressive creep behavior of the vertebral unit subjected to a uniform axial loading using exact parametric solution equations of Kelvin-solid models--Part II. Rhesus monkey intervertebral joints.

The simulation of long-term creep response behavior, observed on 54 Rhesus monkey intervertebral joints subjected to a constant axial compressive stress, is attempted by two- and three-parameter-solid models utilizing the Burns- Kaleps 'exact analysis scheme'. Model parameters identified by the analysis of each specimen's experimental strain data were optimized via a computer program and the mechanical properties (Young's moduli and the viscosity coefficient) appropriate to each model were calculated for individual spinal segments. Simulation results for the two-parameter-solid (one- Kelvin -unit) model demonstrate its general ineptness in predicting the observed strain-time behavior of normal spinal sements . The three-parameter-solid model yielded excellent results in the simulation of observed spinal segment compressive creep phenomena. It produced an average error between the model predicted and experimental strain values that ranged from a low of 0.4000% to a high of 3.290% for the 54 Rhesus monkey intervertebral joints, with a collective average error for all specimens of only 1.363%.

The vertebral cartilaginous endplate of the preadult rhesus monkey (Macaca mulatta). A correlative scanning electron-and light-microscopic study.

The microanatomy of the preadult rhesus monkey (Macaca mulatta) vertebral cartilaginous endplate was investigated with scanning electron microscopy and light microscopy. The plate contains three zones: an outer noncalcified zone adjacent to the intervertebral disc, a middle zone of acellular islands of calcification surrounded by cellular hyaline cartilage, and an inner zone resembling a cartilaginous growth plate. Fibers from the annulus fibrosus pass through an outer zone into the middle zone. Trabecular bone of a developing annular epiphysis is present in the periphery of the plate. Vertical columns of cartilage traverse the nuclear region of the endplate and occasionally surround blood vessels. These columns and their associated blood vessels probably represent notochordal and fetal blood vessel remnants.

The scanning electron microscopy of compressed vertebral bodies.

Scanning electron microscopy was used in this study to determine the effects of compression at different rates on the structure of trabecular bone in primate vertebral bodies. Rhesus monkey vertebral bodies were subjected to compressive loads at two different strain rates (8.89 x 10(-1) m/sec and 8.89 x 10(-5) m/sec). Each vertebral body was compressed to 50% of its original height. S-shaped bending of trabeculae was present in bodies compressed at the lower strain rate, while fractures were more predominant at the higher strain rate. The percentage of recovered height following compression was greater at the lower strain rate. Recovery of compressed vertebral bodies probably occurs through an unfolding of bent trabeculae. The more severe the damage to the vertebral trabeculae, the less recovery occurs.

Poroelastic dynamic structural models of rhesus spinal motion segments.

Finite element models (FEMs) and analytical and experimental models based on poroelastic constitutive laws were developed for rhesus spinal motion segments (SMSs). Long-time creep, transient creep, and impact were studied for SMSs with normal and simulated degenerated discs. The results suggested that long-time creep observed in excised SMSs may be reduced in the in vivo SMS. The fluid phase included in these FEMs was shown to play a significant role in the mechanical response of SMSs. Relative fluid motion fields predicted in the SMS could be related to nutritional paths to the avascular interior of the disc and were found to be very sensitive to changes in discal stiffness. Reduced disc height, increased discal bulge, altered fluid motion, and stresses were quantified and may be related to mechanical failure, disc degeneration, and low-back pain.

Creep characteristics of the human spinal column.

Thirty-two static compression tests were carried out on 52 intervertebral disks and their posterior articular facet joints. The spinal units were tested within a uniquely designed test apparatus. Following the experiment, each intervertebral disk was examined macroscopically to assess the degree of disk degeneration. Three experiments were carried out at suitably chosen load levels, which were statically appropriate for a given vertebral level and its loading history. In the first experiment a constant load was applied to a spinal segment and its decrease in height was measured as a function of time. The results were as follows: Under the application of a constant load, the vertebral unit suffers a gradual change in its dimensions. This typical behavioral response pattern is identified as creep. Creep may be defined as the time dependent part of the deformation that accompanies the application of a load to the disk. The measured creep did not continue indefinitely but decreased with time until the vertebral specimen was equilibrated. The time to equilibration was a function of disk grade. The rate of creep was found to be dependent upon the condition of the nucleus pulposus. Creep is of considerable importance because of its influence on the kinetics and kinematics of the vertebral unit. The effect of creep is to increase the modulus of elasticity with time; hence a reduction occurs in the compliance of the spinal unit. In the second experiment, incremental loads were applied to a spinal unit. The unit was allowed to equilibrate and an additional load was applied. Its purpose was to further delineate spinal unit mechanics in terms of constant load and creep behavior. It was concluded from these tests that the nucleus plays an important mechanical role in influencing the behavioral response of the vertebral unit to constant compressive load. As nuclear maturation occurs, the stiffness characteristics of the spinal unit were noted to increase as dis its deflection characteristics. Spinal unit geometry no doubt also plays a role in influencing these results. In the last experiment, load-deflection curves were determined for the vertebral unit. It was found that load-deflection curves are not uniquely defined by the relationship between the variables of load and deflection. The time each value of load is maintained must also be taken into account. The physiological and biochemical factors responsible for the observed spinal unit behavior are outlined, and the importance of the articular facet joints in governing spinal unit deflection stressed. Although it has long been known that the intervertebral disk suffers a slow and continuous deformation when subjected to mechanical load, the concept of spinal unit deformation as a time dependent function of load is comparatively new.

Identification and classification of vertebral fractures following emergency capsule egress from military aircraft.

This paper deals with systematically classifying the type, level, and severity of traumatic lesions to the spinal column associated with the crew module escape system. Its objectives are to describe characteristic spinal injury encountered in the crew escape module and to shed additional light on the pathomechanics and dynamics of spinal column damage. An analysis of this type is necessary for complete understanding of the clinical, roentgenographic, and pathological findings. Knowledge of the orthopaedic biomechanics of injury is required before the factors responsible for spinal injury are identified and meaningful corrective actions are taken.

Active muscle force and moment response of the human arm and shoulder.

This paper is concerned with collection of active muscle force and moment response data of the human arm and the shoulder complex when the arm is subjected to various external forces. The major components of the specially designed and built experimental apparatus for this research are a subject restraint system, a force application device which employs three sonic emitters, and an upper arm cuff with four sonic emitters. The sonic emitters are utilized to determine the direction and the location of the force application on the arm and the orientation of the upper arm with respect to the torso. The numerical results are presented from experiments conducted on three male and three female subjects to determine their active muscle resistance against the external forces to dislodge their arms from several initial configurations. Some representative results determining the active muscle force capability of the subjects when their arms are dislodged from the initial configuration are also presented. Incorporation of the results of the present research into the multi-segmented models of the human body should improve the long-time response of capabilities of these models. This type of response capability of the mathematical models is essential for the proper stimulation of the biodynamic events which take place prior to flail injuries.

Spinal injuries in the F/FB-111 crew escape system.

During the years 1970-75, a larger than expected number of aircrewmen, forced to use the F/FB-111 crew escape module, experienced acute spinal trauma during otherwise uneventful ejection. This trend in the incidence and severity of F/FB-111 aircrew spinal injuries attracted considerable attention and stimulated extensive inquiry concerning the ethiology of the trauma in order to implement appropriate corrective measures. In response to the expressed concerns, an investigation was initiated to analyze the biodynamic pathogenetic mechanism associated with ejection in the F/FB-111 crew escape module. The purpose of this retrospective investigation is to identify the frequency and severity of spinal trauma in the F/FB-111 crew escape module and to shed additional light on the patterns and severity along with the orthopaedic biomechanics of spinal injury.

Effect of rotopositioning on the growth and maturation of mandibular bone in immobilized rhesus monkeys.

As part of an ongoing effort to mimic the hypokinesia and hypogravity of spaceflight, the effects of 14 d immobilization and rotopositioning on mandibular bone osteon growth (= radial rate of closure) was assessed in 12 juvenile Rhesus monkeys by tetracycline labeling. The monkeys had been restrained in a supine position and rotated 908 every 30 min through a full 3608 arc for 14 d. Osteon growth was also assessed after the immobilized/rotopositioned animals had been permitted to recover in metabolism cages for periods of 28 and 56 d. The closure rates of osteons in the cortex of the inferior border of the mandible were not abnormal during immobilization/rotopositioning or during recovery. The regression line plots yielded slopes of: Controls = 0.946-1.000; Immobilized/Rotopositioned = 1.045; 28 d Recovery = 0.833; 56 d Recovery = 0.829. Microradiographs indicated a normal distribution of osteons of different mineral density: lowly (28%), moderately (53%), and highly mineralized (18%). Bone porosity values also remain within the normal range (18.3 6 4.1%). These results suggested that 14 d immobilization/rotopositioning did not effect abnormal changes in the rates of bone formation and mineralization in the mandibular cortex of the juvenile Rhesus monkey.

The effects of hypokinesia in primates on bone strength.

A 14 days ground based primate hypokinesia investigation was conducted to determine what changes, if any, in bone strength may be demonstrated following 2 weeks cast immobilization and at 14 davs after removal from casts. Controlled compressive loads were applied to vertebral bodies excised from control, 2 weeks immobilization and 2 weeks post immobilization Rhesus monkeys. The material properties reported herein are ultimate load, displacement to ultimate load, stiffness and energy to ultimate load. These results show a decrease in bone strength following immobilization and a still further decrease in bone strength after 14 days.

[Use of the principle of reverse problems for detecting processes, occurring in cells suspended in culture. I. Distribution in the exponential growth phase of the age component of the cell population by its dynamic characteristics]. / Primenenie printsipa obratnykh zadach dliia vyiavleniia protsessov, proiskhodiashchikh v kletkakh pri ikh suspenzionnom kul'tivirovanii. I. Opredelenie v éksponentsial'noi faze rosta vozrastnogo sostava kletochnoi populiatsii po ee dinamicheskim kharakteristikam.

A mathematical model of age distribution in the suspension culture was verified. This model used the principle of reverse problems and allowed determination of age distribution from the cell numbers dynamics in the population. The verification was based on the complex non-destructive measurement of the microorganism parameters, which allowed simultaneous determination of the cell population dynamics and the distribution of cells according to their projection areas. The experiments were carried out on E. coli culture.

[Use of the principle of reverse problems for detecting processes, occurring in cells suspended in culture. II. Distribution of glutathione, SH groups, and optical density in the E. coli cell cycle]. / Primenenie printsipa obratnykh zadach dliia vyiavleniia protsessov, proiskhodiashchikh v kletkakh pri ikh suspenzionnom kul'tirovanii. II. Opredelenie glutationa, SH-grupp i opticheskoi plotnosti v kletochnom tsikle E. coli.

A method was proposed for calculating the content of intracellular components during the cell cycle of an individual cell. The principle of reverse problems was used in the mathematical model proposed. The model allowed us to calculate changes of intracellular parameters of an individual cell from corresponding parameters measured in the whole culture. Optical density, total SH-group and glutathione content in synchronous culture of E. coli were the parameters studied. The proposed method may be applied for both synchronous and asynchronous cell cultures.

[Diabetogenic properties of Coxsackie A13 and Coxsackie B4 viruses in experimental infection in mice]. / Diabetogennye svoistva virusov Koksaki A13 i Koksaki B4 pri éksperimental'noi infektsii u myshei.

Studies of diabetogenic properties of Coxsackie A13 and B4 viruses in mice sensitive to diabetes (males, DBA line) and resistant (males and females F1(CBA X C57BL/6), females DBA/2 using in the latter case the subdiabetogenic doses of alloxan revealed in the infected animals biochemical changes manifested by reduction of glucose tolerance and disorders in the synthesis of immunoreactive insulin. Most marked changes were observed in males of DBA/2 line infected with Coxsackie B4 virus and in males F1 (CBA X C57BL/6) and females DBA/2 infected with Coxsackie A14 virus. With Coxsackie A13 virus such data have been obtained for the first time.

[The role of the pallidum in regulating cortical activity]. / Rol' palliduma v reguliatsii korkovoi aktivnosti

Bilateral ablation of the pallidum halves the duration of extinction of conditioned motor food reflexes and contributes to 30 to 50% extinction of the electro-defensive reflexes. Pallidum functional depression by potassium chloride or novacaine leads to a temporary total depression of conditioned motor food reflexes. Depending on the frequency of pallidum stimulation, synchronization or desynchronization of the cortical bioelectrical activity is observed. Ablation of the pallidum in anaesthetized cats results in a high amplitude and low-frequency cortical activity. Injection of large doses of potassium chloride into the pallidum results in a forced running forward which lasts 30 to 40 min. The pallidum is considreed as a structure controlling the cortex activity, which takes part in the mechanisms of sensory information processes in the course of adaptive behaviour.