EXPERIMENTAL STUDIES ON THE ROLE OF THE I NTRAMEDULLARY ALIGNMENT RODIN THE DEVELOPMENT OF FAT-EMBOLISM DURING TOTAL KNEE REPLACEMENT

Fat embolism syndrome (FES) during implantation of an uncemented resur facing type of total knee replacement is the leading cause of postoper ative mortality. A possible explanation might be the insertion of a so lid intramedullary alignment rod, resulting in an intrafemoral pressur e increase. On 45 cadaveric human femora we measured the resulting int ramedullary pressure during insertion of three different alignment rod s: a solid rod and a hollow shaped guiding rod, both 10 mm in diameter , and a fluted alignment rod of 8.5 mm in diameter. The highest intram edullary pressures occurred after placement of a solid 10 mm alignment rod (3.77+/-0.44 bar), followed by a fluted 8.5 mm rod (2.53+/-0.28 b ar). In both cases, the increased pressure led to an extrusion of bone marrow contents through the venous system of the proximal femur, The least increase occurred after insertion of a hollow shaped alignment r od (0.26+/-0.03 bar) without any fat extrusion. Our study confirmes th e hypothesis that insertion of solid intramedullary alignment rods dur ing preparation of the femoral shaft results in a dangerous pressure i ncrease, so that embolization can occur. To minimize the risk of a FES , instruments should be modified in a manner, that only hallow shaped alignment rods are used.