Effect of flexible drive diameter and reamer design on the increase of pressure in the medullary cavity during reaming.

Reaming the medullary cavity before insertion of an intramedullary nail, results in an increase in both temperature and pressure. This may lead to aseptic necrosis of the cortex and to fat embolism, whereby the increased pressure in the medullary cavity plays a significant role. This paper aims to determine whether a reduction of the drive diameter combined with a different reamer design reduces the amount of intramedullary pressure. The pressure levels were measured in plexiglass tubes filled with a mixture of vaseline and paraffin. The viscoelastic properties of this mixture at 20 degrees C were equivalent to those of bovine medullary fat at 36 degrees C. In comparison with the conventional reamer system (9.0 mm drive + 9.5 mm AO reamer), the 7.0 mm drive+AO reamer and the 7.0 mm drive+hollow reamer, the pressure values were reduced as follows: 1. 9.0 mm drive + 9.5 mm hollow reamer: diaphyseally by 19%, metaphyseally by 21% 2. 7.0 mm drive + 9.5 mm AO reamer: diaphyseally by 48%, metaphyseally by 49% 3. 7.0 mm drive + 9.5 mm hollow reamer: diaphyseally by 61%, metaphyseally by 66%. If the gap between the flexible shaft and the wall of the plexiglass tube became large enough, only small pressure values were recorded for all three types of reamer. In summary, it can be stated that the reduction of the drive diameter causes a sustained reduction in the intramedullary pressure, but that the newly developed hollow reamer only leads to a further reduction in pressure in combination with a thin flexible drive.