ABSTRACT
Objective To compare the stress relaxation and mechanical properties of creep viscoelasticity in the young and old’s spine and to provide the reference for the mechanical mechanism of viscoelasticity of yellow ligament degeneration. Method Twenty specimens of elderly patients with degenerative lumbar yellow ligament degeneration as the older group, and twenty specimens of young patients with lumbar yellow ligament injuries as the youth group were used respectively. All the yellow ligament specimens were from the yellow ligament between the fourth and fifth of lumbar vertebra (L4~L5). Stress relaxation experiment and creep experiment were conducted on the specimens by the strain increasing speed as 1%/s and the stress increasing speed as 0.5 MPa/s respectively. The experimental temperature was (36.5±0.5) ℃ and the experimental time was 7 200 s. Ninety stress relaxation and creep data were collected, and the data were dealt with the statistical analysis and normalization methods. Results The 7 200 s stress of yellow ligament in the youth group decreased by 1.42 MPa, while the 7 200 s stress of yellow ligament in the older group decreased by 1.91 MPa. The 7 200 s strain of yellow ligament in the youth group increased by 3.39%, while the 7 200 s strain of yellow ligament in the older group increased by 2.07%. The 7 200 s stress in two groups all increased and the increased strain data showed statistically significance (P<0.05). The stress relaxation curve changed in the form of logarithm and the creep curve changed in the form of index. Conclusions The 7 200 s stress relaxation and creep in the yellow ligament of the older group all decreased and the mechanical properties of viscoelasticity changed.