Review Question - QID 212199

A 75-year-old female presents to your office complaining of a painful foot, and saying, "her arch has collapsed." She reports that her foot has caused her pain for many years and has recently become debilitating. She has obvious valgus deformities to her ankle and hindfoot. These deformities do not passively correct on examination. Radiographs demonstrate moderate ankle arthritis. You recommend retrograde hindfoot nailing to achieve tibiotalar calcaneal arthrodesis. In follow-up, radiographs are obtained as shown in Figure A. You are concerned with the length of the distal interlocking screw adjacent to the sustentaculum. What structure is most likely to be affected?