Rest cannot always recover the dynamic properties of fatigue-loaded intervertebral disc.
METHODS
An in vitro biomechanical study using adolescent porcine discs.


OBJECTIVE
To find the effect of fatigue loading and rest on the dynamic properties of healthy intervertebral disc.


BACKGROUND
The fatigue loading is a risk factor for low back pain. The disc dynamic properties describe the shock attenuation capability of disc. Knowledge of effect of fatigue loading and rest on the disc dynamic properties can be beneficial for the study of fatigue loading induced spinal disorder.


METHODS
Specimens were divided into short-term (0.5 hours at 5 Hz, n = 9) and long-term (2 hours at 5 Hz, n = 9) fatigue loading groups. The specimen was applied with fatigue loading, followed by a 12-hours rest, and then applied with the second fatigue loading again. The impulse loading was applied at 0, 10, 20, and 30 minutes during short-term group and at 0, 0.5, 1, and 2 hours during long-term group using a drop-tower apparatus. The stiffness, damping coefficient, and ratio were calculated using impulse loading information. Dynamic properties between first and second fatigue loading were compared.


RESULTS
The stiffness increased, but the damping coefficient and ratio decreased with fatigue loadings. A 12-hours rest can fully restore the dynamic properties of fatigue loaded disc to original status. However, the degradation of dynamic properties during the subsequent fatigue loading was faster than the previous fatigue loading if the disc experienced a long-term fatigue loading.


CONCLUSIONS
A 12-hours rest can largely restore disc dynamic properties during fatigue loading; hence fully recover disc dynamic properties. A long-term fatigue loading squeezes the disc fluid and injures the disc integrity. The 12-hours rest can recover the fluid loss but not the injury of disc. Hence, the disc degradation during the second fatigue loading was faster than the first fatigue loading.
Wang
Jaw-Lin
JL
Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan. jlwang@ntu.edu.tw
Wu
Tai-Kuan
TK
Lin
Tzu-Cheng
TC
Cheng
Chih-Hsiuch
CH
Huang
Shyh-Chin
SC
D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D019245:Compressive Strength / Q000502:physiology; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D012146:Rest / Q000502:physiology*; D013552:Swine; D016474:Weight-Bearing / Q000502:physiology*