INTRAMEDULLARY PRESSURE INCREASE FOR DIFFERENT COMMERCIAL AND EXPERIMENTAL REAMING SYSTEMS - AN EXPERIMENTAL INVESTIGATION

Objective: To measure the differences in intramedullary (IM) pressure for commercial namer systems. Design: IM pressure values for the follo wing systems were measured: AO, Biomet, Howmedica grey reamer, Richard s, and Zimmer. To investigate the influence of shaft diameter, the AO reamer head was additionally connected to a small shaft (A6/A7). The p ressures were measured in plexiglass tubes filled with a mixture of pe troleum jelly and paraffin oil with flow properties at 20 degrees C eq uivalent to those of bovine medullary fat at 36 degrees C. The reaming assemblies were inserted into the tubes using a materials testing mac hine at a constant speed. In addition, pressure measurements were made using five pairs of human femora to compare Biomet reamers with the A O reamer with thin, flexible drives (A6/A7). Results: The following pr essure distributions were obtained (millimeters of mercury; mean value +/- standard deviation): 9.5-millimeter reamer: low for Biomet (272 /- 39); moderate for Richards (810 +/- 101); and high for Howmedica (9 90 +/- 132), AO conventional (1,000 +/- 97), and Zimmer (1,140 +/- 183 ); 13.0-millimeter reamer: low for Biomet (132 +/- 21), Howmedica (204 +/- 45), and Zimmer (226 +/- 33): moderate for AO conven tional (474 +/- 42); and very high for Richards (1,734 +/- 127). The second worst system (AO conventional: 1,000 +/- 97) became the second best system b y simple reduction of the shaft diameter (A6/A7: 378 +/- 33). Conclusi on: A comparison of shaft diameters and pressure increase clearly show ed that the system with the thinnest shaft produced the lowest pressur e values and vice versa.