Session IX - Tibia

The Effect of Unreamed, Limited Reamed and Standard Reamed Intramedullary Nailing on Cortical Bone Porosity and New Bone Formation

Thomas M. Hupel, MD; Sergei Aksenov, MD; Emil H. Schemitsch, MD, FRCS (C), Saint Michael's Hospital, University of Toronto, Toronto, ON, Canada

Purpose: Segmental tibial fractures usually have significant associated soft tissue damage and a compromised circulation to the underlying cortex. The purpose of this investigation was to compare the effects of unreamed nail insertion and limited or standard canal reaming, prior to insertion of an intramedullary nail, on cortical bone porosity and new bone formation.

Methods: Midshaft tibial osteotomies to create a 2.5 cm segment of diaphyseal bone were performed in 15 adult dogs. In the unreamed group (n=5), the tibia was stabilized with a 6.5 mm, locked intramedullary nail. In the reamed group, the canal was reamed to 7.0 mm (n=5) or to 9.0 mm (n=5). To measure new bone formation, three fluorochrome dyes were administered to the animals at 3, 6, and 10 weeks postoperatively. Cross sections from the proximal, segmental, and distal diaphysis were removed from the operated limb. One midshaft cross section was removed from the nonoperated, contralateral (control) tibia. Cortical porosity was determined using a semiautomated image analyzer. For both operated and control tibiae, cortical porosity, defined as the percent of the cortex occupied by pores, was measured in the tibial cortex of each cross section. New bone formation was determined by calculating the ratio of flourochrome labelled osteons to unlabelled osteons within the cortex of each of the 3 cross sections. The mineral apposition rate (MAR) was determined by measuring the distance between 2 fluorochrome labels within each osteon.

Results: Tibial canal diameters did not differ between the three groups of animals (p=0.44). Cortical porosity was significantly greater in the unreamed, limited reamed and standard reamed groups compared to the intact control tibiae (p<0.01, for all groups). Porosity was lower in the limited reamed group compared to the unreamed (p=0.003) and the standard reamed (p=0.05) groups. Overall, new bone formation was greater in all 3 experimental groups compared to control values (p<0.01 for all groups). Overall, the percent labelled osteons and the MAR were similar in all 3 groups (p=0.11, p=0.70).

Discussion: Osteotomy and intramedullary nailing, with and without reaming, resulted in a significant osseous injury as evidenced by increased porosity and new bone formation in all areas of the cortex. Limited reaming prior to insertion of a locked intramedullary nail resulted in less cortical bone injury than did passage of the same nail without prior reaming, and with standard reaming prior to nail insertion.

Conclusions: The technique of limited reaming may be advantageous for the treatment of tibial fractures with a compromised circulation when stabilization with an intramedullary nail is being considered.