Review Question - QID 217023

A 35-year-old heavy laborer presents to your clinic with worsening lateral-sided ankle and foot pain. He recalls that his symptoms began after spraining his ankle a few months prior. On exam, there is mild swelling about the posterolateral aspect of his ankle. An MRI is obtained and a select cut is demonstrated in Figure A. Which of the following correctly describes the anatomic structure likely responsible for this patient's symptoms?