The resorption of vital and devitalized bone in vitro: Significance for bone grafts

Several studies have suggested that devitalized bone is less satisfactory t han live tissue for surgical grafting purposes because an initial resorptio n step, prior to new formation, is lacking. We have compared the osteoclast ic resorption of cultured bone containing living osteocytes with that of si milar bone in which the osteocytes were dead. In experiment I, transverse s lices cut from freshly harvested adult rabbit femora were either placed in phosphate buffered saline (Set 1) or subjected to freezing and thawing (Set 2). In experiment II, a heated set (Set 3) was prepared in addition. All s lices were cultured with osteoclasts for 24 hours, eight slices per set bei ng seeded with bone cells in experiment I and three per set in experiment I I. The areas and volumes of resorption pits formed during the culture perio d were measured using reflection confocal microscopy. In both experiments, the mean values for the areas of the pits were smaller in the bone containi ng live osteocytes (P < 0.03, Mann Whitney test), and in experiment II the volumes of the pits in Set 1 were smaller than those in Set 3 (P < 0.0001, Mann Whitney test). However, in neither experiment was there a significant difference between the Sets in the volume:area ratios (mean depths) of the pits. The findings show that devitalized bone is resorbed by osteoclasts at least as readily as bone containing vital osteocytes in vitro, and indicat e that if grafted devitalized bone resorbs less well in vivo it is not beca use the bone tissue is intrinsically resistant to osteoclastic resorption.