Bone mineral density of lumbar vertebral end plates in the aging male sand rat spine.

STUDY DESIGN

Lumbar vertebral segments from young and old male sand rats were assessed for quantitative determination of lumbar end plate bone mineral density.

OBJECTIVES

To determine whether bone mineral density increases in the lumbar end plate with age in the male sand rat and to investigate its relationship to disc degeneration.

SUMMARY OF THE BACKGROUND DATA

Few basic science studies evaluated the end plate and disc degeneration. The sand rat provides an excellent economical model in which disc degeneration is reliable and well characterized.

METHODS

Bone mineral density data on cranial and caudal lumbar end plates of young (mean age 6.8 months) and old (mean age 23.3 months) male sand rats were assessed for changes related to age, lumbar position, and radiologic features.

RESULTS

Mean bone mineral density was significantly greater in end plates in older compared to younger males (P <or= 0.0018). Mean end plate bone mineral density within young animals was not significantly different in levels L5 to L7; in old animals, bone mineral density was significantly different (greater) progressing from L5 to L7 (P < 0.0001). In older animals, mean end plate bone mineral density for each disc showed a significant increase with lower lumbar sites (P = 0.0068). Mean end plate bone mineral density was significantly greater in animals with radiographic evidence of disc wedging (P = 0.006). End plate bone mineral density correlated positively with age.

CONCLUSIONS

Results provide quantitative bone mineral density data on end plate sclerosis in male sand rats. Data reveal site specificities and show that in old animals, end plate bone mineral density is greater than in young animals. Mean end plate bone mineral density was significantly greater at sites with radiographic disc wedging (P = 0.006). Data support the hypothesis that end plate sclerosis may play a role in disc degeneration.