Mechanical Modulation Of Vertebral and Tibial Growth: Diurnal Versus Full-time Loading

PURPOSE: Determine if growth retardation caused by mechanical compression differed between nighttime loading or daytime loading.

METHODS: An Ilizarov-type fixator was used to apply 0.1 Mpa compression across the growth plates of a caudal vertebra and the proximal tibia of 19 Sprague-Dawley rats. The animals were divided into full-time loading, day loading, night loading, and sham. After 8 days the animals were euthanized and the growth plates were analyzed to measure growth (Calcein label), chondrocyte proliferation rate (BrdU), and chondrocyte height.

RESULTS: The day and night loaded animals had about 50% of the growth retardation seen in the full-time group; there was no difference between day and nighttime loading. Decreased chondrocyte cell height explained about half of the growth effect in the full-time group, but was not altered in the day or nighttime loaded groups.

CONCLUSIONS: The decreased growth in the full-time group was produced by a decrease in the number of proliferating chondrocytes and a decrease in chondrocyte cell height.