Experimental characterization of the pressure buildup in the intramedullary canal during orthopaedic reaming using a synthetic bone analogue

During certain orthopaedic procedures such as total hip or total knee arthroplasty, it is necessary to ream the intramedullary canal of long bones prior to the insertion of the implant. This reaming procedure can generate significant intramedullary pressure elevations, potentially leading to the release of embolic fat into the blood stream, and thus increasing the risk of a potentially fatal complication, i.e., fat embolism syndrome. In this thesis, a two layer synthetic bone analogue with open cell porosity and mechanical properties similar to that of real bone was developed and used to evaluate the effect of reaming parameters such as RPM, advancement speed, reamer size, bone marrow viscosity and clogged reamer on resulting intramedullary pressure elevations. All the aforementioned parameters, except the reamer size, were found to significantly influence the medullary pressure. It was found that increases in the reamer advancement speed increased the pressure, whereas increases in the reamer RPM decreased the pressure. The correlation between the simulated intramedullary pressure, imposed forces to the bone and applied torque to the reamer was also assessed. No significant correlations between these variables could be established.

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

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.

Experimental characterization of the pressure buildup in the intramedullary canal during orthopaedic reaming using a synthetic bone analogue

During certain orthopaedic procedures such as total hip or total knee arthroplasty, it is necessary to ream the intramedullary canal of long bones prior to the insertion of the implant. This reaming procedure can generate significant intramedullary pressure elevations, potentially leading to the release of embolic fat into the blood stream, and thus increasing the risk of a potentially fatal complication, i.e., fat embolism syndrome. In this thesis, a two layer synthetic bone analogue with open cell porosity and mechanical properties similar to that of real bone was developed and used to evaluate the effect of reaming parameters such as RPM, advancement speed, reamer size, bone marrow viscosity and clogged reamer on resulting intramedullary pressure elevations. All the aforementioned parameters, except the reamer size, were found to significantly influence the medullary pressure. It was found that increases in the reamer advancement speed increased the pressure, whereas increases in the reamer RPM decreased the pressure. The correlation between the simulated intramedullary pressure, imposed forces to the bone and applied torque to the reamer was also assessed. No significant correlations between these variables could be established.

A finite element analysis approach to predicting intramedullary pressure during the insertion of prosthetic implants

Fat embolism syndrome is a serious post-operative complication of orthopaedic procedures such as fracture fixation and total joint replacement. Fat embolism syndrome can be a result of increased intramedullary pressure during the insertion of prosthetic implants in long bones. A macro was developed that automates the creation of finite element models representing a simplified bone/fluid/implant system and a hammering event. The finite element models were validated by computing the peak stresses at various locations in the bone and comparing them to pressures measured at similar locations in experimental tests. Finite element models were used to test the effect of using hollow implants on intramedullary pressure in the bone, in some cases yielding an average reduction of 19.1%. It has been shown that it is acceptable to use finite element models for such parametric studies and that hollow implants have the potential to decrease intramedullary pressure during insertion.

A finite element analysis approach to predicting intramedullary pressure during the insertion of prosthetic implants

Fat embolism syndrome is a serious post-operative complication of orthopaedic procedures such as fracture fixation and total joint replacement. Fat embolism syndrome can be a result of increased intramedullary pressure during the insertion of prosthetic implants in long bones. A macro was developed that automates the creation of finite element models representing a simplified bone/fluid/implant system and a hammering event. The finite element models were validated by computing the peak stresses at various locations in the bone and comparing them to pressures measured at similar locations in experimental tests. Finite element models were used to test the effect of using hollow implants on intramedullary pressure in the bone, in some cases yielding an average reduction of 19.1%. It has been shown that it is acceptable to use finite element models for such parametric studies and that hollow implants have the potential to decrease intramedullary pressure during insertion.

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

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.