Comparison of Mechanical Loads Produced by Current Intramedullary Reamer Systems

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Abstract

Objective:

This study evaluated the mechanical loading experienced by four clinically used intramedullary reamer cutter designs to evaluate the effects of variations in speed and feed rate on reamer system performance.

Design:

Biomechanical laboratory study.

Setting:

Research laboratory.

Main Outcome Measure:

Four clinically used reamer systems with detachable cutters were tested using a computer-controlled machining system at representative reaming and drilling speeds of 250 and 750 revolutions per minute (RPM), respectively. Hard oak blocks with mechanical properties similar to cortical bone were reamed using cutter heads with diameters from nine to fourteen millimeters (in 0.5-millimeter increments) at feed rates of 1.0 and 7.6 centimeters per second. Reactive axial loads and torques were recorded and analyzed.

Results:

All systems demonstrated reduced maximal loads/torques for small reamer sizes (9 to 10.5 millimeters) at drilling speeds rather than reaming speeds. Individual systems demonstrated measurable differences in sensitivity to alterations in operating speed, indicating that some designs are not amenable to operation at increased speeds. In tests where reamer head cutting characteristics were isolated by using identical solid drive shafts, the deeply fluted design with a long lead taper and a rounded, burrlike body consistently produced significantly lower mechanical loading at all speeds and feed rates. In addition, two of the four systems tested use a larger flex shaft diameter for reamer head sizes of thirteen millimeters or greater. There was no indication of a need to use larger flex shafts for the larger reamers, based on mechanical load/torque data for those systems.

Conclusions:

The tests performed demonstrate that appropriate control of reaming speeds (RPM) can be used to minimize mechanical loading for all systems. Caution should be exercised, however, so that any operational changes that reduce resistive loads and torques do not lead the surgeon to increased feed rates. Additional study is required to investigate the variable effects of increasing the operating speed of each system on localized thermal changes.

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