Biological effects of shock waves: in vivo effect of high energy pulses on rabbit bone

Extracorporeal shock waves have recently been introduced to treat pseudarthrosis and aseptic bone necrosis. Only little information exists up to now about the morphological effects of shock waves on normal bone. To study both their acute effect on bone and their long-term effect on its remodelling, 1500 shock waves generated with a Dornier XL1 experimental electrohydraulic lithotripter were applied at 27.5 kV to 19 rabbits divided into five groups. Changes were evaluated after 6, 11, 41, 59 and 85 days. The discharges were focused to the right femur 1 cm above the knee joint. Bone remodelling was assessed in four groups by four-colour fluorescent labelling with labels administered sequentially over 8-day periods during the first month after shock-wave application. Radiographs were taken at dissection to detect fractures. As a result, shock waves were found to induce periosteal detachment with subperiosteal haemorrhages and to press marrow contents out of the medullary cavity. In the medullary cavity, diffuse haemorrhages, haematomas and foci of fractured and displaced bony trabeculae were found. The bone cortex and the knee joint were normal. Radiographs showed lucencies in the marrow but no fractures. During the weeks following shock-wave application, there was intense apposition of new cortical bone resulting in considerable cortical thickening while trabecular remodelling in the medullary cavity was only minor. The displacement of bony trabeculae and marrow contents point to the action of cavitation as the major mechanism of shockwave damage to bone.