Iatrogenic Post-Stapedectomy SNHL - Dead Ear

A 45-year-old woman undergoes stapedectomy for otosclerosis. Preoperatively, she has moderate conductive hearing loss with a Carhart notch at 2000 Hz and an air-bone gap of 35–40 dB. Forty-eight hours postoperatively, she develops sudden profound unilateral sensorineural hearing loss, severe vertigo, nausea, and spontaneous nystagmus beating toward the contralateral ear. Postoperative audiometry reveals thresholds >90 dB across all frequencies in the operated ear with absent word recognition. The contralateral ear remains at baseline. The audiometric pattern marked **A** in the diagram represents this complication. Which of the following is the most likely mechanism of this iatrogenic injury?