The sealed osteons of cortical diaphyseal bone. Early observations revisited with scanning electron microscopy

The frequency, structure, mode of formation and significance of sealed osteons remain unsettled. Sealed osteons have been reported as an unusual finding in the cortical bone of experimental animals: we extended the observation to human cortical bone studied with SEM. Tibial bone specimens from three patients who sustained a traumatic below-the-knee amputation were used in the study. The observed total mean density of osteons was 19.25/mm(2) and the percentage of sealed and partially sealed osteons was 4.2% and 1.7% respectively. The material sealing the central canal showed an X-ray microanalysis spectrum with the same Ca/P ratio as the peripheral lamellae and a lower carbon signal. The morphology suggested a reactivation of bone apposition triggered by exclusion of the occluded canal from blood flow rather than a physiological evolution of the closing process of secondary osteons. This presupposes collapse and degeneration of the central vessel before the osteoblasts resting on the inner surface of the canal could start to lay down new bone matrix. This explanation is consistent with a dynamic model of intracortical blood flow.