Session I - Tibia Fractures

The Effect of Limited and Standard Reaming on Cortical Bone Blood Flow and Early Strength of Union following Segmental Fracture

Thomas M. Hupel, MD, Sergei A. Aksenov, MD, Emil H. Schemitsch, MD, FRCS(C)

St. Michael's Hospital, Univ. of Toronto, Toronto, Ontario, Canada

Introduction: Limited reaming prior to insertion of an intramedullary nail has been recommended to make passage of the implant easier. Many studies have determined the effect of extensive or standard reaming on cortical bone blood flow but the effect of limited reaming has not been previously investigated. The purpose of this investigation was to determine the effects of limited and standard intramedullary canal reaming on cortical bone perfusion and to evaluate their effect on the biomechanical properties of the united fracture.

Methods: Midshaft tibial osteotomies to create a 2.5cm segment of diaphyseal bone were created in 10 adult dogs (>25 kg). Prior to insertion of a 6.5 mm locked intramedullary nail, the tibia was reamed to either 7.0 mm (n=5) or 9.0 mm (n=5). 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 6 time intervals (pre and post osteotomy, post reaming, post nailing, post locking, and at 11 weeks post nailing). Bending stiffness in the anteroposterior (AP) and the medial-lateral (ML) plane and the load to failure were determined for each healed tibia. Biomechanical and LDF values were normalized to the biomechanical values obtained for the intact contralateral tibia and the pre-osteotomy LDF values, respectively.

Results: Tibial canal diameters did not significantly differ between the two groups of animals (p=0.15). Overall tibial blood flow was reduced for the limited and the fully reamed groups by 63% (p=0.0008) and 83% (p=0.002), respectively. Perfusion was reduced more in the fully reamed group compared to the limited reamed group overall (p=0.046) and at the distal diaphyseal site (p=0.003). At 11 weeks post nailing all fractures had healed. Overall cortical perfusion increased in both the limited and the fully reamed groups, compared to the post locking values (p=0.05 and p=0.004). At sacrifice, perfusion increased to the same extent in both groups (p=0.43) and the values were not significantly different from the pre-osteotomy levels (p=0.2, and p=0.29 for the limited and the fully reamed groups, respectively). Bending stiffness, in both the AP and ML planes was reduced for both the limited (p=0.001, p=0.002) and the fully reamed groups (p=0.0003, p=0.01). Load to failure was reduced to 35% and 22% of the load required to fracture the intact tibia, for the limited (p=0.003) and the fully (p=0.002) reamed groups. Bending stiffness in the AP plane was reduced less in the fully reamed group (p=0.004), but stiffness in the ML plane and load to failure were reduced to the same extent in both groups (p=0.12, p=0.25).

Discussion/Conclusion: Limited canal reaming spares cortical perfusion at the time of nail insertion. Tibial perfusion increased to baseline levels by 11 weeks post nailing in both groups. Biomechanical properties of the healed fracture were similar in both groups. Limited intramedullary reaming, prior to nail insertion, may be advantageous initially for the stabilization of tibial fractures in which the circulation is already severely compromised. This early advantage, of limited reaming, is not maintained as fracture healing occurs.