Direct and indirect measurements of osteoid seam width in human iliac crest trabecular bone

The osteoid thickness index, calculated from the relative osteoid volume and surface, has been compared with the mean osteoid seam width, measured directly, in iliac crest trabecular bone from 57 normal subjects and 33 patients with privational or malabsorption metabolic bone disease. In normal biopsies the osteoid thickness index overestimated mean osteoid seam width by a variable amount and the two variables were only weakly correlated (r = 0.32, P less than 0.01). In patients with hyperosteoidosis there was a stronger correlation between the osteoid thickness index and the true mean seam width (r = 0.89, P less than 0.001). Examination of the mean width of individual seams pooled from 15 randomly selected patients in each group revealed a skewed distribution with thin seams predominating, especially in normal biopsies. Median seam width was significantly lower than mean seam width in both groups studied. We conclude that osteoid thickness index is an inaccurate method of predicting the mean osteoid seam width, especially in biopsies with normal osteoid amount. Median values of osteoid seam width are more representative of average seam width, both in normal and abnormal biopsies.