Due to lack of the practical technique to measure the biomechanical properties of the ocular cornea in vivo, clinical ophthalmologists have some difficulties in understanding the deformation mechanism of the cornea under the action of physiological intraocular pressures. Using Young's theory analysis of the corneal deformation during applanation tonometry, the relation between the elasticity moduli of the cornea and the applanated corneal area and the measured and true intraocular pressures can be obtained. A new applanation technique has been developed for measuring the biomechanical properties of the ocular cornea tissue in vivo, which can simultaneously acquire the data of the applanation area and displacement of the corneal deformation as well as the exerted applanation force on the cornea. Experimental results on a rabbit's eyeball demonstrated that the present technique could be used to measure the elasticity moduli and creep properties of the ocular cornea nondestructively in vivo.
Objective To explore the feasibility of pre-implantation of high-intensity suture into tendon grafts to prevent postoperative graft relaxation and creep in anterior cruciate ligament (ACL) reconstruction. Methods Thirty-six specimens of ACL reconstruction graft were made using adult swine’s Achilles tendon. All the specimens were randomly divided into experimental group (groups A and C) and control group (groups B and D), 9 specimens each group. One double-strand Ultrabraid No.2 high-intensity suture was pre-implanted into the grafts of groups A and C. Groups A and B underwent a 1 000-cycles load test while groups C and D underwent a 3 000-cycles load test. Then a pull-out test was performed until failure. The displacements at different cycles (100, 500, 1 000, 2 000, and 3 000) in all groups and yield loads of groups C and D were measured and analyzed. Results The displacement of group A was significantly smaller than that of group B at the cycles of 100, 500, and 1 000 (P<0.05); the displacement of group C was significantly smaller than that of group D at every cycle (P<0.05). Additionally, the yield load of group C was significantly higher than that of group D (t=4.816,P=0.001). Conclusion Pre-implantation of high-intensity suture into tendon grafts play an important role in the prevention of postoperative graft creep and relaxation in ACL reconstruction.
In order to study the mechanical behavior of degeneration and nucleotomy of lumbar intervertebral disc, compression experiments with porcine lumbar intervertebral discs were carried out. The lumbar intervertebral discs with trypsin-treated and nucleus nucleotomy served as the experimental group and the normal discs as the control group. Considering the effects of load magnitude and loading rate, the relationship between stress and strain, instantaneous elastic modulus and creep property of intervertebral disc were obtained. The creep constitutive model was established. The results show that the strain and creep strain of the experimental group increase significantly with the increase of compression load and loading rate, whereas the instantaneous elastic modulus decreases obviously, compared with the control group. It indicates that the effect of load magnitude and loading rate on load-bearing capacity of intervertebral disc after nucleotomy is larger obviously than that of normal disc. The creep behavior of the experimental group can be still predicted by the Kelvin three-parameter solid model. The results will provide theoretical foundation for clinical treatment and postoperative rehabilitation of intervertebral disc disease.
ObjectiveTo summarize the research progress in creep characteristics of lumbar intervertebral disc.MethodsThe relevant literature at home and abroad was systematically searched. Then, the concept and structural basis of lumbar disc creep, the description of creep characteristics, and the latest progress of its influencing factors were summarized and analyzed.ResultsThe intervertebral disc is viscoelastic. After loading, the deformation increases with time. However, the degree of increase is not linear with time. That is creep, which plays an important role in buffering the load generated by human activities and absorbing energy in order to maintain stable movement of the spine. Both experimental and simulation studies can well describe the creep behavior of intervertebral disc. Various models including standard linear solid model and corresponding constitutive equations can quantify and compare the creep characteristics, which can be obviously changed by the degeneration of intervertebral disc and the mode of loading stress.ConclusionCreep is an important mechanical properties of intervertebral discs, and an in-depth understanding of the creep characteristics of lumbar intervertebral discs is of great guiding significance for the intervention and treatment of low back pain.