The effect of extracorporeal shock wave lithotripsy on the prosthesis interface in cementless arthroplasty....

The effect of extracorporeal shock wave lithotripsy on interfacial strength between prosthesis and bone in cementless arthroplasty was examined using a rabbit model. Paired femora, each implanted with fiber mesh porous coated titanium implants, were harvested from rabbits 15 weeks after implantation. In group I, one femur from each pair was exposed to lithotripsy treatment consisting of 2,000 shocks at 20 kV. In group II, one femur from each pair was exposed to 2,000 shocks at 26 kV. Contralateral femora from each pair served as controls in both groups. Mechanical pushout tests were conducted on the implants using a 1321 Instron testing machine at a constant rate of 1 mm/minute. Shock waves generated at 20 kV were found to have no significant decrease on either the prosthesis/bone interfacial strength or energy to failure of cementless implants. Shock waves generated at 26 kV produced a mean 17.45% decrease in the prosthesis/bone interfacial strength, which approached statistical significance (P = .062), and a 7.84% mean decrease in the energy to failure (P = .268). However, in four of the seven group II specimens, cortical fractures occurred. These findings suggest that lithotripsy will not aid in the removal of uncemented porous coated devices and lithotripsy inadvertently focused at an uncemented device will not disrupt significantly the prosthesis-bone interface.