[Modified intracorporeal lithotripsy for cement removal in hip prosthesis exchange operations--experimental principles].

INTRODUCTION

Particularly problematic in total hip revision arthroplasty is the cement removal out of the depth of the femoral canal; it is also costly in time and effort. The extracorporal shock wave lithotripsy proved to be an unsuitable method. With the present paper we proved experimentally a newly developed endoscopically controlled modified intracorporal lithotripter (Swiss Orthoclast) for the removal of bone cement.

METHODS

We tested the efficiency on standardized cement specimens of different manufacturers in vitro. We compared both conventional removing techniques with mallet and chisel and a pneumatically powered chisel with formalin fixed human femora. During these experiments we measured the intrafemoral pressure distally to the cement layer.

RESULTS

We achieved a high energy (max. 450 mJ) and a very effective fragmentation of the cement (40 mg fragments calculated on the single impulse of 350 mJ). The endoscopic control ensures a safe control of the cement removal even in the depth of the femoral canal. No bone damage occurred macroscopically and radiologically. No heat or toxic products developed. Using the Swiss Orthoclast the intrafemoral pressure was the lowest possible (7 mbar). Even with hammer and chisel or the pneumatically powered chisel the pressure was too low (max. 55 mbar with mallet and chisel) to cause a fat embolic syndrome.

CONCLUSION

As a result of these experiments we started with clinical trials (with permission of the Ethic commission) to evaluate the practicability of the modified intracorporal lithotripter (Swiss Orthoclast) for cement removal.