Session IX - Tibia

The Effect of Intramedullary Reamer Design on Cortical Bone and Blood Flow in a Canine Tibia Fracture Model

Jamie Lever, MD; Sergei Aksenov, MD; Emil H. Schemitsch, MD, FRCS(C), St. Michael's Hospital, Toronto, Ontario, Canada

Purpose: Segmental tibia fractures result from high-energy injuries, often causing devascularization of the bone as it is stripped from its soft tissue envelope. Fracture healing may be compromised as a result. Furthermore, the effect of fracture fixation on bone perfusion must also be taken into consideration. Reamer design has been shown to produce differences in intramedullary pressures and temperatures during preparation of the intramedullary canal. The purpose of this investigation was to study the effects of different intramedullary reamer designs on cortical bone blood flow.

Materials and Methods: Midshaft tibial osteotomies to create a 2.5-cm segment of devascularized diaphyseal bone were performed. The fractures were repaired using 6.5-mm x 180-mm intramedullary nails with interlocking. Fifteen skeletally mature dogs were randomly assigned to one of three reamer designs [S (n=5), Z (n=5), H (n=5)] used to prepare the intramedullary canals. All tibial canals were reamed from six to nine millimeters in diameter, in increments of one millimeter. Bone blood flow was assessed using Laser Doppler Flowmetry (LDF). Cortical bone perfusion measurements were made at 3 locations (proximal, segmental, and distal diaphysis) and at 5 time intervals (pre osteotomy, post-osteotomy, post-nailing, post- locking, 11 weeks post-nailing). LDF values were normalized to the pre- osteotomy levels to eliminate inter-animal variability.

Results: Tibial canal diameters did not significantly differ between the three groups of animals (p=0.22). Following diaphyseal osteotomy, each experimental group suffered a similar (p=0.79), yet significant, decrease in overall mean bone perfusion to an average of 69% of pre-fracture values (p=0.004). Individually, the S, Z and H reamer groups produced further significant reductions in blood flow to 54% (p=0.06), 52% (p=0.009) and 29% (p=0.01) respectively, with significance relative to post osteotomy measurements. Further analysis however, did not reveal a significant difference in reduction of blood flow between the three reamer systems. After insertion and locking of the intramedullary nail, final perfusion values dropped to S=35%, Z=38% and H=25% with no significant difference between the three reamer systems. At 11 weeks, there were also no differences between the experimental groups.

Discussion: Our investigation demonstrated a progressive decline in cortical bone perfusion following introduction of a reamed, locked intramedullary nail for tibial fracture stabilization. Reamer design has been shown to produce differences in intramedullary pressures and temperatures during preparation of the intramedullary canal. While there was a trend for the H reamer to cause a greater decrease in perfusion, following nail insertion there were no differences in osseous perfusion between the three reamer systems.

Conclusions: The type of reamer design did not factor in the overall extent of blood flow reduction witnessed following introduction of a reamed, locked intramedullary nail for tibial fracture stabilization. While specific reamer design factors may determine the extent of blood flow reduction following reaming, these effects are lost following intramedullary nail insertion.