Avoiding Iatrogenic Vascular Injury in Tibial External Fixation with Half Pins. An In-vivo Study Based on CT Angiography

SLR - April 2022 - Asher Cherian

Reference: Hussain S, Balamoody S, Wright S, Bose D, Fenton P. Avoiding Iatrogenic Vascular Injury in Tibial External Fixation with Half Pins. An In-vivo Study Based on CT Angiography. J Clin Orthop Trauma. 2022 Jan 24;25:101777. doi: 10.1016/j.jcot.2022.101777. PMID: 35145847; PMCID: PMC8810568.

Level of Evidence: Level III

Scientific Literature Review

Reviewed By: Asher Cherian, DPM
Residency Program: Temple University Hospital – Philadelphia, PA

Podiatric Relevance: External fixation is utilized for a variety of applications in the lower extremity. This fixation technique can be used not only for reconstructive procedures, but also in trauma surgery. A key pearl in applying an external fixator is building a construct with inherent stability. This is achieved using many different components, while uniting with the lower extremity with half pins or wires. Placement of wires and pins through soft tissue and osseous structures within safe zones has been thoroughly described in the literature. Poorly placed pins can cause injury to vulnerable neurovascular structures. Nerve impingement, vessel occlusion, and impingement are among the tissue injuries previously described in the literature. The purpose of this paper was to present findings of CT angiograms performed in patients with external fixators on the tibia, and to outline optimal trajectories for half pin insertion.

Methods: A retrospective study was performed of patients with tibial fractures having external fixators from 2013 to 2021. All patients included had contrast enhanced computed tomographic angiogram (CTA) for vascular mapping as part of preoperative workup. Inclusion criteria included patients who had CTA with an in situ non-spanning external fixator on the tibia. Exclusion criteria included patients undergoing vascular repair as part of the initial debridement, as well as patients who had a CTA done as part of the trauma scan and patients with half pins in either the femur or the foot. Different variables were measured from the CTA studies, including distance of half pin entry point from the anterior tibia crest, angle that half pin makes with the medial surface of the tibia, level of over penetration of the far cortex by half pin in millimeters, and the distance in millimeters from nearest named vessel from the tip of the half pin. Tip to vessel distance (TVD) was measured in millimeters from tip of the half pin to the nearest named vessel, and a distance of 5 millimeters or less was considered a critical distance.

Results: Fifty-onepatients were included in this study. A total of 134 half pins within the tibia were analyzed. In 47 percent of half pins, over penetration of the far cortex was more than 5 millimeters, while it was more than 10 millimeters in a further 16 percent of the pins. One fifth of the half pins were found to be within 5 millimeters from the vessel at risk. In one patient, there was no contrast run off in the posterior tibial artery distal to the proximal pin, and in another there was obliteration of contrast flow in the anterior tibial artery.

Conclusions: This study concluded that penetration of the far cortex with a half pin of more than 5 millimeters is consistent with reduced TVD, endangering neurovascular structures. It also advocated for the use of intraoperative fluoroscopy when advancing the half pin. These findings are important to consider as foot and ankle surgeons when affixing external fixators to the tibia and being mindful of delicate neurovascular structures.