Mechanical behavior of the human lumbar spine. II. Fatigue strength during dynamic compressive loading
✍ Scribed by T. H. Hansson; Dr. T. S. Keller; D. M. Spengler
- Publisher
- Elsevier Science
- Year
- 1987
- Tongue
- English
- Weight
- 816 KB
- Volume
- 5
- Category
- Article
- ISSN
- 0736-0266
No coin nor oath required. For personal study only.
✦ Synopsis
Seventeen cadaveric human lumbar motion segments from eight spines were cyclically loaded in vitro under axial compression. Loading frequency and magnitude were chosen to simulate rigorous activity within an in vivo physiological level. The load magnitude was determined as a percentage of the ultimate compressive load, the latter estimated from the bone mineral content (BMC) of lumbar vertebrae determined by dual-photon absorptiometry. Following testing, the degree of macroscopic disc degeneration was assessed and the type of fracture in each specimen was determined from serial sagittal sections. Fractures were found in all but one specimen. Three types of fractures were formed: the node of Schmorl and Junghanns (type I), central endplate fracture (type 11), and a crush or burst fracture (type 111). The results suggested that type I fractures were predominantly associated with segments with normal discs, type I1 fractures were found primarily in segments with moderately degenerated discs, and type 111 fractures were associated with segments that failed on the first cycle. Segment stiffness and fatigue strength (cycles to failure) were correlated with disc degeneration, age, and segment BMC, the latter an in vivo measure of bone density. Fatigue strength also decreased in proportion to a power coefficient with increasing relative stress (cyclic stress rangehltimate stress).