JBMR

COMMENTARY

Repair Mechanisms for Microdamage in Bone David B Burr Department of Anatomy and Cell Biology, Indiana University School of Medicine, and Department of Biomedical Engineering, Indiana University‐ Purdue University, Indianapolis, IN, USA

hen Harold Frost first identified microdamage generated in vivo in bone, he was referring only to linear microcracks that were discrete and whose edges could be identified microscopically.(1) Whether these were real or artifactual was a source of debate for many years until, in the early 1990s, more than a few laboratories had observed them using Frost’s en bloc staining technique.(2–12) A veritable feeding frenzy of microdamage‐ related research ensued as the scientific community attempted to understand how linear microcracks affected the mechanical properties of bone(13,14) and whether they were a stimulus for the initiation of bone remodeling and self‐repair.(15–17) Now, Seref‐ Ferlengez and colleagues present the first quantitative data to show conclusively that diffuse damage can be repaired directly in vivo, without the intervening step of bone remodeling.(18) It was well known from the materials and engineering literature that microscopic cracks in materials grew by developing smaller secondary cracks at the front of the developing linear microcrack where the stresses are high, a region known as the damage process zone. This suggested that damage could occur at different levels and size scales.(19) However, damage at smaller size scales was not really recognized as an entity unto itself until the later 1990s, when several groups began to identify regions of diffuse staining that were found to be associated with collections of very small (

Repair mechanisms for microdamage in bone.

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