Induction of Microdamage Through Application of Acoustic Energy to Cortical Bone

Abstract

Extracorporeal shock waves (ESW) are used routinely to break up kidney stones. Recently ESW has been implemented in the orthopaedic arena to treat heel spurs, although the mechanism underlying this therapeutic effect is not known. Acoustic energy has been shown to increase transport in bone. Furthermore, naturally occurring microdamage in bone has been implicated as a trigger for the onset of remodeling. We hypothesize that controlled application of ESW to bone tissue increases transport and stimulates bone turnover through production of low-level microdamage. The goal of this study was to identify the bandwidth and the application regime of acoustic energy to produce such damage. Transverse sections of sheep metacarpi (1 cm) were subjected to acoustic loading regimes of varying shock wave number and intensity. Thereafter, the blocks were bulk-stained with procion dye, embedded in PMMA, and sectioned into 100 mm slices for confocal microscopy and analysis. The blocks loaded with the highest energy regimes showed marked diffuse microdamage and microcracks, usually at sites of discontinuity along the periosteal edge. These results provide a first step in testing our hypothesis and ultimately may provide a basis for the exploitation of ESW to prevent osteopenia and/or osteoporosis.