Intramedullary Pressure Increase for Different Commercial and Experimental Reaming Systems: An Experimental Investigation

Objective: To measure the differences in intramedullary (IM) pressure for commercial reamer systems. Design: IM pressure values for the following systems were measured: AO, Biomet, Howmedica grey reamer, Richards, and Zimmer. To investigate the influence of shaft diameter, the AO reamer head was additionally connected to a small shaft (A6/A7). The pressures were measured in plexiglass tubes filled with a mixture of petroleum jelly and paraffin oil with flow properties at 20°C equivalent to those of bovine medullary fat at 36°C. The reaming assemblies were inserted into the tubes using a materials testing machine at a constant speed. In addition, pressure measurements were made using five pairs of human femora to compare Biomet reamers with the AO reamer with thin, flexible drives (A6/A7). Results: The following pressure 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 (990 ± 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 conventional (474 ± 42); and very high for Richards (1,734 ± 127). The second worst system (AO conventional: 1,000 ± 97) became the second best system by simple reduction of the shaft diameter (A6/A7: 378 ± 33). Conclusion: A comparison of shaft diameters and pressure increase clearly showed that the system with the thinnest shaft produced the lowest pressure values and vice versa.