Experimental Parametric Study of the Factors Leading to Elevated Femoral Intramedullary Pressure and Fat Embolus Syndrome in Orthopaedic Procedures

Abstract

During orthopaedic procedures such as total knee arthroplasty (TKA), total hip arthroplasty (THA), and intramedullary nailing, it is necessary to hammer implants into the intramedullary canal of long bones. This hammering action can generate a high intramedullary pressure, leading to the release of bone marrow fat globules into the cardiovascular system, and ultimately, the possible development of fat embolism syndrome. In the present study, the effect of parameters such as implant tip geometry, peak impact force, hammer tip material, bone to implant radial gap, and marrow viscosity, on the resulting intramedullary pressure generated when hammering implants into a simulated femur analogue was examined. The bone analogue consisted of a porous plastic cylinder, having similar porosity and pore size to human femoral bone, with bone marrow being represented by a paraffin wax/petroleum jelly mixture. It was found that intramedullary pressure is only slightly lowered by a change in implant tip geometry, and that the use of a steel tipped (as opposed to rubber) hammer resulted in an increase in average pressure in the proximal portion of the bone, but a decrease distally. A lower implant insertion speed, lower hammering force, and a larger bone to implant radial gap were found to significantly reduce the intramedullary pressure. The number of hammer strikes required to insert an implant was found to increase significantly with marrow viscosity, but the average intramedullary pressure was found to decrease with increasing viscosity. Numerical modelling was also found to offer great promise for analysing hammering procedures for orthopaedic research into fat embolism syndrome. Numerical and experimental results were matched with approximately a 20% deviation.