Microvasculature of the Talus Following Subtalar and Talonavicular Fusion: A Cadaveric Micro-Computed Tomography Analysis

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Nonunion rates for talonavicular (TN) and subtalar (ST) fusions have been reported in the literature to be as high as 20% and 15%, respectively. Disruption to the blood supply might be a contributing factor. There is limited data on the effect of TN and ST fusion on the surrounding microvasculature. The primary aim of this study was to identify microvasculature structures at risk for iatrogenic injury during open TN and ST fusion using MicroCT perfusion studies. Methods: Twenty-two fresh-frozen cadaveric limbs (11 matched-pairs) were disarticulated at the knee. The popliteal artery was cannulated using an 18-gauge angiocath. The arterial system was perfused with 50mL of radiopaque contrast (50% barium sulfate/2.5% gelatin). The talus and navicular were resected in the control limbs (n=11) and scanned using MicroCT (Sky-Scan-1275, Bruker MicroCT) to establish the baseline arterial anatomy. The experimental limbs underwent open TN (medial approach) and ST (sinus tarsi approach) fusion. Joint surfaces were scraped with a curette and fenestrated with a 2.0 drill bit. The TN fusion was fixed with two 4.5mm cannulated screws (one medial, one dorsolateral). The ST fusion was fixed with two 7.3mm cannulated screws inserted through the calcaneal tuberosity across the joint in a posterior-plantar to anterior-dorsal orientation. After fixation the talus and navicular were then resected (n=11) and MicroCT scans performed to identify injured microvasculature structures. Results: Baseline anatomy of the extraosseous vessels and their intraosseous branches were visualized, including branches of the dorsalis pedis, artery of tarsal canal, deltoid artery, tarsal sinus artery, and lateral tarsal artery. One matched pair did not have a visible lateral tarsal artery. In total, there were 7 (63.7%) injuries to the artery of the tarsal canal, 3 (27.3%) injuries to the tarsal sinus artery, 2 (20%) injuries to the lateral tarsal artery. Branches of the dorsalis pedis and deltoid artery were preserved in all experimental specimens. Conclusion: Talonavicular and subtalar fusion using standard open techniques resulted in iatrogenic microvascular injury, most commonly to the artery of the tarsal canal and its branches. This may be due to subtalar joint preparation and/or subtalar screw trajectory. The tarsal sinus artery and lateral tarsal arterial branches were less prone to injury, while the dorsalis pedis and deltoid arterial branches were relatively preserved. The clinical implication of these findings remain unclear. However, when feasible, surgeons should mitigate dissection and joint preparation in the area of the tarsal canal during subtalar fusion.