Session I - Combined Session (International Society for Fracture Repair)

The Effect of Muscle Contusion on Cortical Bone and Muscle Perfusion after Reamed Intramedullary Nailing: A Novel Canine Tibia Fracture Model

Henry Koo, MD; Alex Tov, MD; Emil H. Schemitsch, MD, FRCS(C); St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada

Purpose: High-energy tibia fractures are often associated with significant soft tissue injury. The appropriate management of these injuries remains controversial. Previous studies have assessed perfusion of the fractured tibia and surrounding soft tissues in the setting of a normal soft tissue envelope. The purpose of this study was to determine the effects of muscle contusion on blood flow to the tibial cortex and muscle during reamed intramedullary nailing of a tibia fracture.

Methods: Eleven adult canines were randomized into two groups: contusion or no contusion. Under general anesthesia, the left tibia of each canine underwent segmental osteotomy followed by limited reaming and locked intramedullary nailing. Six of the eleven canines had the anterior muscle compartment contused, at the level of the osteotomy, in a standardized fashion. Laser Doppler flowmetry (LDF) was used to measure cortical bone and muscle perfusion during each step of the procedure. Repeat LDF measurements were taken of the cortical bone and muscle 11 weeks later. The animals were then killed.

Results: Following a standardized contusion, muscle perfusion in the contusion group was higher than in the no-contusion group (P = 0.0001). This difference was transient because muscle perfusion returned to normal levels by the end of the procedure. The hyperemic response was most profound within the zone of injury. Reaming did not increase muscle perfusion. Bone perfusion decreased to a larger extent in the contusion group after contusion and osteotomy (P = 0.003). The difference between the two groups remained significant throughout the procedure. At 11 weeks, muscle perfusion was similar in both groups. Site-specific analysis did not reveal any differences between the sites or between the two groups. There was a sustained decrease in overall bone perfusion in the contusion group, at 11 weeks, compared with the no-contusion group (P = 0.001).

Discussion: The results of this study show that injury to a soft tissue envelope has regional effects on blood flow to the bone and muscle. The hyperemic response observed in the muscle of the contusion group was not sustained. Furthermore, the larger decrease in bone perfusion observed in the contusion group was sustained. One possible explanation for the unsustained hyperemia of the damaged muscle is vasodilation during the acute inflammatory response. However, due to severe damage to the tissue and vessels, a sustained response was not possible. This explanation could also account for the sustained decrease in tibial blood flow. Acutely, the local hyperemic response in the muscle could have diverted blood flow away from the bone. Chronically, a damaged and dysfunctional soft tissue envelope may be unable to provide support to the intraosseous circulation.

Conclusion: The results of our study show that injury to the soft tissue envelope may have deleterious effects on fracture healing by decreasing intraosseous circulation. In addition, the positive effects of reaming on muscle perfusion, as shown in previous studies, seem to be compromised when the muscle itself is damaged. This finding may influence the method of fixation in tibia fractures associated with significant soft tissue injury.