Injury of the Tibial Nutrient Artery Canal during External Fixation for Lower Extremity Fractures: A Computed Tomography Study.

The tibial nutrient artery (TNA) is the major diaphyseal artery of the tibia supplying two thirds of the inner osseous cortex. Hence, iatrogenic injury of the TNA endangers the integrity of the tibial blood supply and may compromise fracture healing. The incidence of its injury in the setting of external fixation for lower limb fractures has not been previously investigated. The aim of this study was to evaluate the incidence of TNA injury in the context of external fixation and to characterize the topography of the fixator pins in relation to the TNA canal (TNAC). Patients who underwent external fixation for distal femoral fractures and for tibial (proximal, shaft, and distal) fractures and had a postoperative computed tomography study were retrospectively included. The following parameters were retrieved: 1) Pin characteristics (orientation and cortical position of the pins), 2) The anatomic relationship between the TNAC and external fixation pin (topography above/below and at the level of the TNAC, and the distance between the pin and medial tibial plateau and/or the medial malleolus), and 3) The incidence of TNAC injury (complete/partial disruption of TNA lumen). A total of 105 patients with 214 tibial pins were analyzed. In 27 patients (26%), the TNAC was completely injured by the pins of the external fixator. In 13 patients (12%), the TNAC was partially injured. Of the 214 analyzed pins, 85 pins (40%) were located at the level of the TNAC (the TNAC and the pin are seen on the same axial slice). Most pins that were applied at the level of the TNAC belonged to a knee-bridging external fixator. Of those, ninety-three percent of the pins were anteromedially applied according to published surgical guidelines. Six percent of the pins were applied through the tibial crest and 1% anterolaterally. Of those 85 pins, 42 pins (49%) injured the TNAC at least partially. Based on the analyzed pins and the incidence of partial and complete injury of the TNAC, we observed that the tibial segment at which the tibial nutrient artery is endangered was located approximately (95% CI: 13-15 cm) from the medial tibia plateau and (95% CI: 22-25 cm) from the medial malleolus. Thus, TNAC injury by external fixation pins in the context of lower limb fractures can be considered common. Almost half of the pins applied at the middle third of the tibia injured the TNA, despite adherence to published surgical guidelines for external fixation. When possible, pin application at the middle third of tibia should be avoided to circumvent iatrogenic injury of the TNA and to safeguard tibial blood supply.