OTA 2006 Posters

Scientific Poster #98 Basic Science

·Biomechanical Effects of Harvesting Bone Graft with the Reamer/Irrigator/Aspirator
Jeremy J. McCormick, MD1 (*); Mark A. Reed, MD2 (*), Andrew Morse1 (*); Elias Wilson3 (*); Kristen L. Billiar, PhD3 (*); John J. Wixted, MD1 (a-Synthes);
1University of Massachusetts Medical School, Worcester, Massachusetts, USA;
2University of Alabama Medical School, Birmingham, Alabama, USA;
3Worcester Polytechnic Institute, Worcester, Massachusetts, USA

Purpose: The Reamer/Irrigator/Aspirator (RIA) is a one-pass flexible reamer designed to limit the amount of embolic debris from the reaming process. Large volumes of particulate bone debris can be filtered from the aspirate, and some authors have used this particulate matter for grafting large segmental defects. To our knowledge, the biomechanical effect of reaming an intact femur for harvesting bone graft has not been investigated. We hypothesize that reaming an intact femur with the RIA system to obtain bone graft will not degrade the properties of the femur sufficiently to warrant postreaming fixation.

Methods: 14 human femora were harvested from embalmed cadaveric specimens including four matched pairs. Seven specimens, including one from each matched pair, underwent one-pass RIA reaming to 15 mm. All specimens were marked in the center and both ends were cut perpendicular to the longitudinal axis of the femur a standardized distance from the center. Using a customized jig system to ensure uniformity of the central axis, femurs were potted using anchoring cement. After the anchoring cement had fully cured, specimens were tested in torsion using a servohydraulic test frame (Model 858 Mini Bionix, MTS Systems). All samples were loaded to 110 Nm torque at 10°/sec or to failure, whichever occurred first. Torque-angle curves were generated for each specimen and the torsional stiffness (slope of the curve) was determined by linear regression. Following testing, the specimens were cut in half at the center point, and the inner and outer diameters were measured with a caliper to calculate shear strain, shear stress, and shear modulus for each specimen. To determine if reaming produced a significant change in the torsional behavior of the specimens, torsional stiffness was compared for all unreamed and reamed specimens using an unpaired Student t test and for matched pairs using a paired Student t test.

Results: Material properties were calculated for all specimens, including shear stress, shear strain, and the shear modulus. Additionally, mean torsional stiffness for the unreamed group was 7.02 N/m2 (SD 1.80). Mean torsional rigidity for the unreamed group was 1.33 N/m2 (SD 0.35). Mean torsional stiffness for the reamed group was 7.57 N/m2 (SD 4.04) and mean torsional rigidity for the reamed group was 1.44 N/m2 (SD 0.77). Student t test for reamed vs. unreamed torsional stiffness was not significant, (P = 0.37) and Student t test for reamed vs. unreamed torsional rigidity was also not significant (P = 0.37). Paired t-tests for the 4 matched pairs was also not significant for either torsional stiffness or torsional rigidity (P = 0.323 and P = 0.320).

Conclusions: Based on these data, reaming intact femoral shafts to 15 mm did not appear to dramatically affect the structural properties of the specimens. Bone is weakest in torsion, and should be most at risk for failure in this mode. Our data suggest that much of the torsional stiffness and torsional rigidity is maintained, and the structural properties of the femur are not greatly diminished after reaming to 15 mm. This study is clearly limited, however, in that we tested only a small number of embalmed cadaveric femurs and our data only represent four matched pairs. While embalmed specimens may represent a worst-case scenario, the study lacks power to draw definitive conclusions about subtle changes in the structural properties of the specimens.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.
· The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an "off label" use). · · FDA information not available at time of printing.