Enhancing Proximal Femoral Pressure during Cemented Stem Insertion

Poor proximal femoral pressures during a cemented primary hip replacement may compromise proximal fixation and cause early aseptic loosening. Occlusion of the calcar, during stem insertion, achieves a uniform and sustained rise in the proximal intra-medullary pressure, which should enhance cement penetration into bone and improve long-term survival of the prosthesis.

54 Exeter stems were cemented into femoral moulds prepared from plaster of Paris. Pressure transducers were connected to the proximal, middle and distal zones of the mould. After cement insertion, stems were implanted with occlusion of the calcar by either nothing, a thumb placed medially or an Exeter horse-collar. 18 stems each were inserted into Palacos-R at 3 1/2 – 4 minutes and 4 – 4 1/2 minutes after mixing and Simplex-P 6 – 6 1/2 minutes after mixing and the intra-medullary pressures were measured. Data were subjected to regression analysis using SPSS.

Proximal and distal intra-medullary pressures were significantly higher (P <0.01 – 0.001) with proximal occlusion in all cements. The highest pressures were achieved with Palacos-R at 4 – 4 1/2 minutes after mixing, with proximal thumb occlusion. Stem insertion into Palacos-R at 3 1/2 – 4 min. or 4 – 4 1/2 min. after mixing, gave higher pressures than into Simplex-P regardless of the method of occlusion. With Simplex-P, there was a trend to higher proximal intra-medullary pressures with the horse-collar.

Occluding the calcar during stem insertion into cement achieves and sustains high intra-medullary pressures in both the proximal and distal femur. The highest pressures are obtained with stem insertion into Palacos-R at 4 – 4 1/2 minutes after mixing, with proximal thumb occlusion. A horse-collar achieves slightly higher pressures with Simplex-P.