Biomechanical effects of harvesting bone graft with the Reamer/Irrigator/Aspirator on the adult femur: a cadaver study

Objectives: Test the biomechanical properties of femurs that have undergone reaming with the Reamer Irrigator Aspirator (RIA) device with an aim to prove no difference in torsional strength between matched pairs.

Methods: Intact femurs were harvested from embalmed cadavers, representing 19 matched pairs. One femur from each pair was randomly selected to undergo reaming using the RIA to 15 mm. The bones were then cut and potted using a uniform jig for testing. Each specimen was tested in torsion and torsional stiffness was calculated for each pair. Samples were loaded until fracture or 11 3 N·m of torque.

Results: Nine of the reamed specimens and 13 of the unreamed samples remained intact until the machine limit of 113 N·m was reached, representing approximately four times the peak torque of 30N·m seen with stair climbing [Garino J, Beredjiklian P. Core Knowledge in Orthopaedics: Adult Reconstruction and Arthroplasty. Chapter 1, page 33. Mosby, 2007]. Mean torsional stiffness for the reamed group was 532.1 N·m/rad (SD = 208.2), and the unreamed was 546.2 N·m/rad (SD=206). Torsional load capacity was calculated for all specimens and compared in groups in which both reamed and unreamed specimens failed. In these five groups, mean load capacity was 80.6 Nm (SD = 9.5) for the reamed group, and 85 Nm (SD = 16.1) for the unreamed group.

Conclusions: 17 of our reamed specimens and all of our unreamed specimens withstood normal physiologic load seen with stair climbing. In addition, 16 of 19 reamed specimens remained intact at twice this load. The specimen in the reamed group with the lowest torsional load capacity was eccentrically reamed in the distal anterior cortex highlighting potential complications. Given these findings, reaming the cortex of the femur with the RIA device for the purpose of harvesting bone graft does not appear to dramatically diminish the mechanical properties of the cortex or require postoperative weight bearing restrictions. However, careful attention must be paid to technique as eccentric reaming either proximally or distally may result in catastrophic failure. Careful attention must be paid to the use of irrigating fluid and post operative blood loss, and a thorough discussion of risk factors including postoperative fracture should be covered when obtaining informed consent.