COMPARISON OF MECHANICAL LOADS PRODUCED BY CURRENT INTRAMEDULLARY REAMER SYSTEMS

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 perf ormance. Design: Biomechanical laboratory study. Setting: Research lab oratory. Main Outcome Measure: Four clinically used reamer systems wit h detachable cutters were tested using a computer-controlled machining system at representative reaming and drilling speeds of 250 and 750 r evolutions per minute (RPM), respectively. Hard oak blocks with mechan ical properties similar to cortical bone were reamed using cutter head s with diameters from nine to fourteen millimeters (in 0.5-millimeter increments) at feed rates of 1.0 and 7.6 centimeters per second. React ive axial loads and torques were recorded and analyzed. Results: All s ystems demonstrated reduced maximal loads/torques for small reamer siz es (9 to 10.5 millimeters) at drilling speeds rather than reaming spee ds. Individual systems demonstrated measurable differences in sensitiv ity to alterations in operating speed, indicating that some designs ar e not amenable to operation at increased speeds. In tests when reamer head cutting characteristics were isolated by using identical solid dr ive shafts, the deeply fluted design with a long lead Gaper and a roun ded, burrlike body consistently produced significantly lower mechanica l loading at all speeds and feed rates. In addition, two of the four s ystems tested use a larger flex shaft diameter for reamer head sizes o f thirteen millimeters or greater. There was no indication of a need t o use larger flex shafts for the larger namers, based on mechanical lo ad/torque data for those systems. Conclusions: The tests performed dem onstrate that appropriate control of reaming speeds (RPM) can be used to minimize mechanical loading for all systems. Caution should be exer cised, however, so that any operational changes that reduce resistive loads and torques do not lead the surgeon to increased feed rates. Add itional study is required to investigate the variable effects of incre asing the operating speed of each system on localized thermal changes.