Learning Curve for Performing Targeted Nipple Areola Complex Reinnervation (TNR) for Gender Mastectomy- Moving from Nerve Graft Reconstruction to Direct Nerve Coaptation

BACKGROUND: Targeted Nipple Areola Complex Reinnervation (TNR) is a nerve preservation and reconstruction technique shown to restore baseline sensation at the chest and nipple areola complex (NAC) after gender affirming mastectomy (GAM) with free nipple grafting (FNG). We describe the senior authors learning curve for nerve dissection allowing for primary use of direct coaptation instead of nerve graft over time. Further, this study explores the postoperative time to sensation and sensory outcomes between direct repair and use of nerve allografts. METHODS: 60 patients who underwent GAM/ FNG at two institutions were prospectively enrolled from November 2021 through September 2023. Three groups with 20 patients each were compared: GAM/FNG + TNR with nerve allograft reconstruction (group 1), GAM/FNG + TNR with direct coaptation (group 2), and a control group GAM/FNG - TNR (group 3). Demographics, mastectomy weight, operative time, intraoperative nerve anatomy and nerve reconstruction technique were collected. Semmes Weinstein filament testing was used preoperatively, and at one, three-, six-and twelve months postoperatively. Monofilament index values included 2.83, 3.61, 4.34, 4.56 and 6.65, with lower values indicate lower threshold for detection, and therefore higher sensitivity. Chi-square analysis was used to detect sensation return differences between groups. RESULTS: Average preoperatively sensation was 3.56 at the chest and 3.87 at the NAC. A learning curve was associated with nerve branch dissection and coaptation with only the first 20 patients requiring a nerve graft. Demographics were comparable between all groups (p > 0.05). Per mastectomy, an average of 2 ICN branches were used for direct coaptation. Median allograft length was 3.5 cm (1.5-4.0). Preoperative sensation was comparable between groups (p= 0.77). NAC and chest skin sensation were significantly worse as compared to baseline in all groups at the one-month post-operative visit (p < 0.01). At 3 months postoperatively, NAC and Chest skin sensation values in group 1 and group 2 were significantly improved as compared to group 3 (p< 0.05). At 6 months, 72.7% of patients within group 2 demonstrated NAC sensation equal or improved from baseline. In comparison only 28.1% group 1 had NAC sensation equal to or improved from baseline (p <0.05). Similarly, at 6 months postoperatively 72.7% of patients in group 2 had equal or returned chest sensation, compared to 38.9% of patients in group 1. By 12 months, all sensation level were comparable between groups 1 and group 2 (p>0.05): 70% of group 1 and 83% of group 2 had equal or improved chest sensation, and 79.2% of group 1 and 100% of group 2 had equal or improved NAC sensation. Group 3 continued to have less sensation than the other groups, with 18% having equal or improved NAC sensation and 58% having equal or improved chest sensation. CONCLUSION: After a short learning curve to improve nerve dissection, TNR with direct coaptation is efficacious and cost effective in restoring chest wall sensation for patients undergoing GAM, with promising results for return of sensation. Both allograft reconstruction and direct repair are feasible options with similar sensory outcomes at 12 months postoperatively.