Wednesday, May 4, 2011

Total shoulder replacement: avoiding heat damage

One of the concerns about fixation of the glenoid component in total shoulder replacement is the observation that 'radiolucent lines (RLL's)' may develop between the bone on one hand and the component and cement on the other. These RLL's suggest that the connection of the component to bone is not as strong as it should be. Of greater concern is that these RLLs are often progressive, that is, the fixation of the component becomes less secure with time. This is well shown in the article by Walch et al in the SUNDAY, MAY 1, 2011 post. 

There has been little study of the factors that may contribute to the development and progression of RLL's, especially in cases where no lucent lines are seen immediately after surgery.

One factor that we have studied is the possibility of heat damage to the bone of the glenoid causing local death and resorption of the bone over time with progressive mechanical loosening.  In a study with shoulder fellows Churchill, Boorman and Fehringer, Glenoid cementing may generate sufficient heat to endanger the surrounding bonewe found that the amount of heat generated was related to the volume of cement used in fixing the glenoid component. This is because cement cures with an exothermic, or heat generating reaction. With larger amounts of cement, the temperature of bone can rise to a level that can kill the bone.

This observation led us to explore methods of glenoid fixation that used only minimal amounts of cement: precise 'carpentry' with the removal of a minimal amount of bone.

In second study by shoulder fellows Clinton and Lynch along with resident Olson, we found that reaming of the bone could cause thermal damage: Thermal effects of glenoid reaming during shoulder arthroplasty in vivo. The figure below was taken during surgery using a thermal camera. 

We found that irrigating the wound with cool saline solution at the time of reaming kept the temperature of the bone within safe limits.


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