Biomechanical properties of lumbar endplates and their correlation with MRI findings of lumbar degeneration.

How stiffness and strength of the human lumbar endplate vary with location, spinal level, and its correlation with MRI findings of lumbar degeneration, has not been reported in detail. 27 lumbar spines (16 male, 11 female, 31-49yrs) were harvested from cadavers without history of lumbar lesion or trauma. Disc and endplate degeneration was evaluated from MRI. Micro-CT was used to evaluate endplate microstructure. Indentation tests were performed to quantify stiffness and strength at 23 sites on each endplate from load-displacement graphs. Results showed that stiffness and strength increased from the centre of the endplate towards its periphery. There was no general age-related reduction in endplate stiffness or strength, although strength decreased slightly with age opposite the inner annulus. Disc degeneration was associated with a 39-46% decrease in stiffness, and a 21-30% decrease in strength, with effects being greatest near the endplate periphery. The presence of Modic changes had a similar effect. Strength and stiffness consistently increased at lower spinal levels, and were consistently greater in the inferior endplate (relative to the vertebra). Gender had little influence, although stiffness in the peripheral endplate was greater in males. BV/TV, SMI, Tb.Th and BMD were positively correlated with strength. We conclude that endplate properties reflect compressive stresses within adjacent intervertebral discs. Weaker and softer endplates may indicate reduced mechanical loading in decompressed discs that are stress-shielded by the neural arch. Preoperative MRI evaluation of endplate integrity could reduce the risk of implant subsidence following inter-body fusion.