OBJECTIVETo investigate the variation in movement traces of different condylar reference points.

METHODSIn 30 healthy subjects, mandibular movements were recorded during protrusion and open-closing of the jaw. The kinematic center and terminal hinge axis point of the condyle were used as reference points.

RESULTSThe kinematic center was located anteriorly and superiorly with respect to the terminal hinge axis point. The trace distance of the kinematic center was longer than that of the terminal hinge axis point of the condyle during opening. In contrast to differences in trace distances of the left and right condylar terminal hinge axis points, no such left-right differences were found for the kinematic centers. The ratio between the distance of opening trace and the distance of protrusion trace of the kinematic center was above 1.5.

CONCLUSIONSIn comparison to the terminal hinge axis, the kinematic center shows fewer variations in the movement traces.

By creating two kinds of stress environment in the same animal model, we performed a three-point bending test and a compressing test on the rat femurs growing under different stress conditions to characterize the effect of stress on bone mechanical properties. The right hindlimbs were subjected to sciatic nerve resection to become cripple and were used as unloading group; the left hindlimbs bore excess load and made up the overloading group; the normal rats were used as control group. The animals were encouraged to exercise for half an hour everyday in the morning, noon and evening. The experiment observation finished in four weeks. The biomechanical parameters of femur diaphyses were measured. The experiment results showed that stress environment may change several mechanical parameters of rat femurs. This study indicated that bone tissues can adapt to its stress environment by changing its mechanical properties. The experimental model in this article is practical and reliable.
Animals ; Biomechanical Phenomena ; Diaphyses ; physiology ; Femur ; physiology ; Rats ; Stress, Mechanical

The advance of experimental cell division and proliferation in the field of cell biomechanics is presented in this paper. The emphasis is placed on the research in the mechanics mechanism of cleavage furrow and in the measurement of constricting force about cleavage furrow.
Biomechanical Phenomena ; Cell Division ; physiology ; Cytokinesis ; physiology ; Humans

In contrast to traditional representational perspectives in which the motor cortex is involved in motor control via neuronal preference for kinetics and kinematics, a dynamical system perspective emerging in the last decade views the motor cortex as a dynamical machine that generates motor commands by autonomous temporal evolution. In this review, we first look back at the history of the representational and dynamical perspectives and discuss their explanatory power and controversy from both empirical and computational points of view. Here, we aim to reconcile the above perspectives, and evaluate their theoretical impact, future direction, and potential applications in brain-machine interfaces.
Biomechanical Phenomena ; Brain-Computer Interfaces ; Motor Cortex/physiology* ; Neurons/physiology*

Biomechanical evaluation of neck muscles has important significance in the diagnosis and treatment for cervical spondylosis, the neck muscle strength and soft tissue stiffness test is two aspects of biomechanical testing. Isometric muscle testing operation is relatively simple, the cost is lower, which can evaluate the muscle force below grade 3. However, isokinetic muscle strength testing can assess the muscle strength of joint motion in any position. It is hard to distinguish stiffness difference in different soft tissues when the load-displacement curve is used to evaluate the local soft tissue stiffness. Elasticity imaging technique can not only show the elastic differences of different tissues by images, but also quantify the elastic modulus of subcutaneous tissues and muscles respectively. Nevertheless, it is difficult to observe the flexibility of the cervical spine by means of the analysis of the whole neck stiffness. In a word, a variety of test method will conduce not only the biomechanical evaluation of neck muscles, but also making an effective biomechanics mathematical model of neck muscles. Besides, isokinetic muscle testing and the elasticity imaging technology still need further validation and optimization before they are better applied to neck muscles biomechanical testing.
Biomechanical Phenomena ; Humans ; Muscle Strength ; Neck Muscles ; physiology

This paper introduces the development on the research of measuring theory for orthopaedic biomechanics in detail. Then, the measuring method and corresponding measuring device are also mentioned. Advantages, disadvantages and development for the device are also introduced. Finally, the research prospect for it is introduced.
Biomechanical Phenomena ; Bone and Bones ; physiology ; physiopathology ; Physics ; instrumentation ; methods

We observed the effect of vibration parameters on lumbar spine under different vibration conditions using finite element analysis method in our laboratory. In this study, the CT-images of L1-L5 segments were obtained. All images were used to develop 3D geometrical model using the Mimics10. 01 (Materialise, Belgium). Then it was modified using Geomagic Studio12. 0 (Raindrop Geomagic Inc. USA). Finite element (FE) mesh model was generated by Hypermesh11. 0 (Altair Engineering, Inc. USA) and Abaqus. Abaqus was used to calculate the stress distribution of L1-L5 under different vibration conditions. It was found that in a vibration cycle, tensile stress was occurred on lumbar vertebra mainly. Stress distributed evenly and stress concentration occurred on the left rear side of the upper endplate. The stress had no obvious changes under different frequencies, but the stress was higher when amplitude was greater. In conclusion, frequency and amplitude parameters have little effect on the stress distribution in vertebra. The stress magnitude is positively correlated with the amplitude.
Biomechanical Phenomena ; Finite Element Analysis ; Humans ; Lumbar Vertebrae ; physiology ; Vibration

BACKGROUNDTransfacet pedicle screws provide another alternative for standard pedicle screw placement for plate fixation in the lumbar spine. However, few studies looking at transfacet pedicle screw fixation in the cervical spine are available. Therefore, cervical transfacet pedicle screw fixation and standard pedicle screw fixation techniques were biomechanically compared in this study.

METHODSTen fresh human cadaveric cervical spines were harvested. On one side, transfacet pedicle screws were placed at the C3-4, C5-6, and C7-T1 levels. On the other side, pedicle screws were placed at the C3, C5, and C7 levels. The screw insertion technique at each level was randomized for right or left. The starting point for the transfacet pedicle screw insertion was located at the midpoint of the inferolateral quadrant of the lateral mass and the direction of the screw was about 50 degrees caudally in the sagittal plane and about 45 degrees toward the midline in the axial plane. Screws were placed from the inferior articular process, across the facet complex and the pedicle into the body of the caudal vertebra. The entry point for the pedicle screw was located at the midpoint of the superolateral quadrant of the lateral mass, and the direction of the screw was about 45 degrees toward the midline in the axial plane and toward the upper third of the vertebral body in the sagittal plane. After screw placement we performed axial pullout testing.

RESULTSAll the cervical transfacet pedicle screws and the pedicle screws were inserted successfully. The mean pullout strength for the transfacet pedicle screws was 694 N, while for the pedicle screws 670 N (P=0.013). In all but six instances (10%), the pedicle screw pullout values exceeded the values for the transfacet pedicle screws; this occurred three times at the C3/C4 level, twice at the C5/C6 level and once at the C7/T1 level. The greatest pullout strength difference at a single level was observed at the C5/C6 level, with a mean difference of 38 N (t=-1.557, P=0.154). The C7/T1 level had a mean difference of 26 N and the C3/C4 level had a mean difference of 14 N.

CONCLUSIONSCervical transfacet pedicle screws exhibited higher pullout strength than pedicle screws. Posterior transfacet pedicle screw fixation in the cervical spine may afford an alternative to standard screw placement for plate fixation and cervical stabilization.

The biomechanical properties of eight human corneas from four normal Chinese fresh corpses were investigated by use of one dimension tensile test, tensile stress relaxation and creep test. The destructive load, stretchy ratio, spreading stress, spreading strain and elastic modulus were determined. Also obtained were the stress relaxation and creep data and curves. After reduction of data, the reduced stress relaxation and creep data and curves were worked out. The regression method was used to get the regression coefficient. The least square method was employed to fit the data of stress and strain; then the stress-strain formula was expressed and the curves of human cornea were plotted. The constitutive equation is K (lambda,t) = G(t) T(e) (lambda) and some conclusions are drawn.
Biomechanical Phenomena ; Cornea ; physiology ; Elastic Modulus ; Humans ; Stress, Mechanical

Biomechanical Phenomena ; Eye Movements ; Neurons/physiology* ; Pursuit, Smooth ; Saccades