COMPARISON BETWEEN THE LENGTHS OF INDIVIDUAL OSTEOID SEAMS AND RESORPTION CAVITIES IN HUMAN ILIAC CREST CANCELLOUS BONE

The current concept of bone remodelling is based on the belief that bo ne resorption and formation are coupled both in time and space; this i mplies that the surface extent of bone eroded in a bone remodelling un it would approximate to the surface extent of the osteoid seam formed subsequently. The greater total surface extent of osteoid as opposed t o erosion is generally attributed to the longer life-span of bone form ation, but no comparison of the length of eroded surface and osteoid s eam within individual bone remodelling units has been reported. In thi s study we have compared the length of individual osteoid seams, resor ption cavities and bone structural units in iliac crest trabecular bon e obtained from normal subjects and from patients with renal osteodyst rophy. Values for osteoid seam and bone packet length were significant ly greater than resorption cavity length in both the normal and patien t groups (P < 0.001), the ratio of osteoid seam and eroded length bein g similar in the two groups (1:0.44 and 1:0.40, respectively). These r esults indicate that the discrepancy between total osteoid and eroded surface extent cannot be wholly explained on the basis of a longer for mation life-span. Possible additional explanations include underestima tion of eroded surface by light microscopic techniques, initiation of bone formation within a cavity before the completion of resorption, th e presence of arrested resorption cavities, non-random distribution of resorption cavities on the trabecular surface and bone formation on q uiescent bone surfaces.