The purpose of this study is to investigate age-dependent changes in the architecture and mechanical properties of tendon in TGF-beta inducible early gene-1 (TIEG) knockout mice. Wild-type and TIEG knockout mice, aged 1, 2, and 15 mo, were used. The mechanical properties of tail tendons isolated from these mice were determined using uniaxial tensile ramp (0.05 mm/s) and relaxation (5 mm/s) tests, with a strain of 10%. Mechanical parameters (Young's modulus from the ramp test; fast and static stresses from the relaxation test) were measured and recorded. The structure of the tail tendon fascicle was characterized by transmission electron microscopy. The results of the mechanical testing revealed no significant difference between the knockout and wild-type groups at 1 or 15 mo of age. However, the fascicles of the knockout mice at 3 mo of age exhibited decreased fast and static stresses compared with those of the wild-type mice. Electron microscopy revealed an increase in fibril size in the knockout mouse tendons relative to wild-type controls at 1 and 3 mo of age. These data indicate an important role for TIEG in tendon microarchitecture and strength in adult mice.
Background-The quasistatic neutral zone is a surrogate for neutral region stiffness of spinal motion segments. No similar measure of dynamic stiffness has been validated. Because parameters related to stiffness are likely to be affected by loading rate and disc degeneration, we examined the effect of those factors on motion parameters derived from continuous motion data.
Methods-Fifteenhuman lumbar motion segments were tested with continuous flexion-extension pure moments at 0.5, 3.0 and 6.0 degrees/second. Range of motion, width of the hysteresis loop, transitional zone width, and slopes of the upper and lower arms of the hysteresis loop within the transitional zone were measured. Discs were then graded for degeneration.Findings-As the loading rate increased from 0.5 to 6.0 degree/second there were significant increases in ROM, hysteresis area, hysteresis loop width, and the upper and lower transitional zone slopes. At the same time transitional zone width decreased significantly. Degeneration had a significant effect on all parameters except hysteresis loop width. The transition zone slopes appeared to best discriminate between normal and degenerative discs.Interpretation-Loading rate had a significant effect on all parameters. As degeneration increased consistent effects were observed indicating decreasing stiffness from grade 1 to grade 3 then slightly increased stiffness in grade 4 specimens. The slopes of the transitional zone have potential to be a useful measure of neutral region stiffness during dynamic motion testing.
Robotics recently spread to spine biomechanical research. The aim of the present work is to describe and validate a new method for in vitro studying of a multisegmental spinal specimen under dynamic conditions. This method relies on the use of a simulator with six degrees of freedom (to impose movements in all directions), an optoelectric apparatus (for collecting kinematics data) and an original system for attaching kinematic markers, allowing their precise removal and replacement under different examination conditions. The accuracy of measurements as well as their reproducibility under static and dynamic conditions is reported here in the study of a human lumbar spinal specimen (L1-sacrum). The method appears to be reliable and reproducible, and should therefore enable future studies of variations in mobility between healthy and pathological spines, to better understand the influence of different implants on spinal kinematics.
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