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105 Surgery: skeletal muscle mass and free fibula flap reconstruction sarcopenia could provide valuable information to aid surgical decision analysis and whether or not to opt for a direct microvascular reconstruction. Exact definitions and cutoff values for sarcopenia differ between studies and a uniformed definition has not been stated for patient groups and ethnicities. The cutoff value to define low SMM in our study, is based on the SSM cutoff value developed in a separate cohort of patients with HNC in The Netherlands. 17 To our knowledge, no sex-specific cut-off values to define low SMM have been established in head and neck cancer patients. In spite of the different cutoff values used throughout the literature for sarcopenia, low muscularity seems to be strongly linked with poorer surgical outcomes and decreased survival in cancer patients. In this study, SMI at the level of C3 was measured, since imaging at this anatomical site is almost always readily available as part of a head and neck cancer workup. Measurement of SMI at the level of C3 is based on a previously published study. 21 We validated the measurement of SMI at the level of C3 with total body muscle area as measured on whole body MRI and found a strong correlation (manuscript in preparation). We included both CT scans and MRI scans of the head and neck area to evaluate SMM, since some patients did not have CT scans as part of their workup. Most published articles on SMM in patients with cancer is performed using CT imaging. However, the CTmeasurement method for SMMwas formulated on MRI-based research. 12,45 A recent study showed that bothmethods, CT and MRI, have a strong agreement inmeasurement of skeletal muscle mass (r 2 =0.94, p<0.01). 46 The retrospective design and the relatively limited number of cases, 78 patients in 16 years, are limitations of this study. The present study, however, is the only report that has sought to examine the impact of skeletal muscle mass on fibula free flap reconstruction, but it remains a single-center analysis. The relatively limited number of cases and events may influence the statistical robustness of the results. Therefore, other independent confirmatory studies would be required before extending these findings into surgical treatment planning. One other essential limitation is that cancer-related skeletal muscle depletion is a continuous process, this study only assessed SMM preoperatively, there at a single point in time. Changes in SMM can occur over time and its relationship with cancer survival is of considerable interest and should be the subject of future research. In conclusion, low SMM at initial diagnosis had a negative effect on fibula flap related com - plications, other postoperative complications and OS in patients undergoing resection for locally advanced oral cavity cancers. Future prospective studies should be performed to find an effective prehabilitation strategy to improve skeletal muscle status and to establish if SSM might be part of a selection plan for surgical reconstruction of large oromandibular defects. 6