The effect of the extracorporeal shock wave lithotriptor on the bone-cement interface in dogs

The extracorporeal shock wave lithotriptor (ECSWL) is a machine that generates shock waves that transfer energy through biologic materials. This study focused the wave at a composite bone-cement (polymethylmethacrylate) interface and evaluated the effects both quantitatively and qualitatively. Six matched sets of dog femora were selected. The intramedullary canals were packed uniformly with cement. One of the set was randomly selected for treatment with impulses while the other served as the control. The bone was then sectioned transversely into discs, and scanning electron microscopy and mechanical push-out studies were performed. The results indicated that the ECSWL does have a loosening effect on the bone-cement interface. Using a paired Student's t-test, the shear strength was significantly less in the treated group than in the control (p less than 0.003). Microscopically, the treated specimens revealed relative sparing of the surrounding bone. At the bone-cement interface, however, microfractures, loose bodies, and widening were seen. Revision total arthroplasty has a significant morbidity, which can be partially attributed to cement extraction. The results of this study indicate that the ECSWL may be a useful adjunct in revision surgery by facilitating the extraction of polymethylmethacrylate and thereby reducing the morbidity.