Comparison of Ho:YAG laser and coblation for interface tissue removal in minimally invasive hip refixation procedures.

Aseptic loosening is the major failure mode for hip prostheses. Currently, loosened prostheses are revised during open surgery. Because of a high complication rate, this demanding procedure cannot be performed in patients with a poor general health. We are developing an alternative minimally invasive refixation procedure that leaves the prostheses in place, but relies on removing the interface membrane and replacing it with bone cement. The aim of this study was to evaluate two interface tissue removal techniques - Ho:YAG laser and coblation - based on two criteria: thermal damage and the ablation rate. In vitro a loosened hip prosthesis was simulated by implanting a prosthesis in each of 10 cadaver femora. Artificially created peri-prosthetic lesions were filled with chicken liver as an interface tissue substitute. We measured temperatures in vitro at different radial distances from the site of removal. Temperatures during removal were recorded both inside the interface tissue and in the surrounding bone. This study demonstrated that temperatures generated in the bone do not result in thermal damage (increasing less than 10°C relative to body temperature). Temperatures inside the interface tissue are sufficiently high to destroy the interface tissue (T>50°C, duration>1 min). Using laser instead of coblation for the removal of interface tissue resulted in higher temperatures - thus a faster removal of interface tissue. This is in accordance with the ablation rate test. Ho:YAG laser is advantageous compared to coblation. We consider Ho:YAG laser a promising tool for interface tissue removal.