Session III Tibia

Cortical Bone and Soft Tissue Blood Flow in Loose and Tight Fitting Locked Unreamed Intramedullary Nailing: A Canine Segmental Tibia Fracture Model

Thomas M. Hupel MD, S.A. Aksenov MD, E.H. Schemitsch MD, FRCS(C)

Musculoskeletal Research Laboratory, St. Michael's Hospital, University of Toronto, Toronto, Ontario, CANADA

Segmental tibial fractures have significant associated soft tissue injuries. To minimize further devascularization unreamed, locked intramedullary nails have been recommended. The purpose of this study was to determine the extent to which loose and tight fitting unreamed, locked intramedullary nails devascularize cortical bone, and to determine the effect of unreamed intramedullary nailing on the perfusion of the surrounding musculature.

Methods: Midshaft tibial osteotomies to create a 2.5 cm segment of devascularized diaphyseal bone were performed in 12 adult mongrel dogs (>25 kg). The animals were randomized into two groups: stabilization of the tibia with either a 5.0 mm (n=6) or 6.5 mm (n=6) unreamed, locked intramedullary nail. Bone blood flow was assessed using laser Doppler flowmetry (LDF). Cortical bone and anterior compartment muscle 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, and at 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 two groups of animals (p=0.25). Insertion of both sizes of nails caused a significant reduction in overall tibial blood flow. For the 5.0 mm and 6.5 mm nails, the overall tibial blood flow was reduced by 58% and 72%, relative to the pre osteotomy values, respectively (p=0.00l, p=0.00004). The 6.5 mm nail reduced overall tibial perfusion more than the 5.0 mm nail (p=0.02). A site specific comparison demonstrated that the 6.5 mm nail reduced blood flow more than the 5.0 mm nail at the distal diaphyseal site (p=0.0005). At 11 weeks post nailing, all fractures had healed. Overall tibial perfusion had improved significantly in both groups of animals. For the 5.0 mm and 6.5 mm nails, overall tibial perfusion was 93% and 54% of the pre osteotomy values, respectively. These are both significantly increased from the post locking values (p=0.002, p=0.0006). Overall tibial perfusion improved more in the 5.0 mm nail group than in the 6.5 mm nail group, at 11 weeks post nailing (p=0.04). At the end of the nailing procedure, overall muscle perfusion decreased in both the 5.0 and 6.5 mm nail groups (p=0.02, p=0.007). Muscle perfusion was reduced by the same extent in both groups (p=0.08). At 11 weeks post nailing, anterior compartment blood flow in both groups was similar (p=0. 19) and returned to the pre osteotomy values.

Discussion: Our results demonstrate that both loose and tight fitting, unreamed intramedullary nails significantly disrupt diaphyseal cortical bone and surrounding muscle circulation. The loose fitting nail spared cortical bone perfusion more than the tight fitting nail, at the time of nail insertion. The loose fitting nail allowed more complete cortical reperfusion at 11 weeks post nailing. This study suggests that a loosely fitting, unreamed locked intramedullary nail, being less disruptive of cortical bone circulation, may be advantageous for stabilization of segmental or other tibial fractures in which the circulation is already severely compromised.