PROXIMAL FEMORAL PRESSURES DURING THE STEM INSERTION PHASE OF A CEMENTED HIP REPLACEMENT: COMPARISION OF THREE MODALITIES.

Abstract

Poor proximal femoral pressures obtained during a cemented, primary hip replacement may lead to poor fixation of the stem to the cement and cement to bone, contributing to early aseptic loosening of the prosthesis. Occlusion of the proximal femoral area during stem insertion, especially in the region of the calcar, may help in achieving a uniform and sustained rise distally and proximally.

An In-vitro analysis of femoral pressures was performed. Dental plaster was used to prepare femoral moulds in aluminium cylinders and the stem insertion phase of a cemented hip replacement was simulated with a number 3 Exeter stem, with no proximal occlusion, with thumb occlusion over the calcar and with the Exeter Horse collar. Pressure transducers were attached to the moulds. 54 experiments were performed. Of these 18 experiments were done with Palacos R cement, with the stem inserted at the recommended time of insertion and 18 with a delayed time of insertion. The last 18 experiments were performed with low viscosity Simplex P cement.

Good distal pressures were obtained in all cases. However, digital occlusion helped achieve sustained, high proximal pressures as well as early, high distal pressures. The Horse collar did achieve high pressures, but only towards the end of the stem insertion phase. This was much more appreciable with low viscosity cement, where peak pressures obtained with the collar were higher than with digital occlusion.

Our results show that occluding the medial cal car area is an effective way of achieving and sustaining high-pressures in the proximal and distal femur, during a hip replacement. The Exeter Horse collar is an effective means of increasing the pressure, towards the end of stem insertion, especially with low viscosity cement. Animal or cadaveric bone studies are required to show the actual penetration of cement in bone, achieved with these high pressures.