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 degrees C equivalent to those of bovine medullary fat at 36 degrees 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.

The development of the distal femur Less Invasive Stabilization System (LISS).

Fractures around the knee typically require operative fixation to achieve an acceptable, functional outcome. The idea behind the Less Invasive Stabilization System (LISS) was to combine the advantages of both interlocked intramedullary nailing techniques and the early advances of the so-called biological plating technique into one system. This paper introduces the mechanical concept of a locked internal fixator and details some important aspects of the anatomical and biomechanical development of the LISS.