Fate of the Flexor Hallucis Longus Muscle at the Donor Site After Fibula Flap Harvest: Assessing Muscle Viability Using Novel MRI Techniques – A Cohort Study

Fibula flap dissection sacrifices the blood vessels to the flexor hallucis longus (FHL) and other calf muscles. This novel MRI study investigates perfusion and fibrosis of the FHL muscle after fibula flap harvest. A cohort study from September 2018 to January 2021, we prospectively recruited head and neck cancer patients who were planned to receive fibula flap transfer for jaw reconstruction. All participants received MRI before and one year after the operation. Muscle fibrosis was quantified via extracellular volume matrix fraction (ECV); muscle perfusion via time to peak (TTP), T2* change, and T2* slope by BOLD sequence. Muscle fibrosis and perfusion were compared before and after the operation. Total of 18 patients completed the study (mean age: 48.83 years). Significantly increased fibrosis was seen in the postoperative FHL muscle via elevated ECV (11.23%-32.54%, p < 0.001). Despite prolonged TTP in postoperative FHL (38.17-51.83 s, p = 0.343), increased T2* change (8.43%-9.53%, p = 0.369), and increased T2* slope (0.22%-0.23%/s, p = 0.766), these muscle perfusion changes were not statistically significant. Postoperative complications, such as great toe clawing and donor site infection, were not observed. Despite severe fibrosis within the FHL muscle after extensive dissection during fibula harvest and peroneal arterial ligation, the FHL muscle perfusion could be retained from an MRI perspective.