Anatomic Considerations of Retrograde Intramedullary Nail Placement in Distal Ulna Fractures.

PURPOSE: To characterize the anatomic relationship between retrograde intramedullary nail placement in distal ulna fractures and important surrounding structures, with particular focus on the triangular fibrocartilage complex (TFCC).

METHODS: Eight fresh-frozen cadaveric upper extremity specimens underwent simulated distal ulnar neck fracture fixation using a 4.5 mm retrograde intramedullary threaded nail. Pre- and postinsertion arthroscopy was performed to assess TFCC integrity. Dissection was used to evaluate proximity to surrounding structures, including the extensor retinaculum, extensor carpi ulnaris, extensor digiti minimi, and dorsal cutaneous branch of the ulnar nerve. TFCC involvement was classified by location and quantified using surface area analysis.

RESULTS: The nail path disrupted the distal extensor retinaculum in all specimens, with no direct injury to the extensor carpi ulnaris, extensor digiti minimi, or dorsal cutaneous branch of the ulnar nerve, although these structures were in close proximity. The superficial TFCC and the deep radioulnar ligament footprint were involved in the majority of specimens, with the dorsal peripheral region most commonly penetrated. However, the overall surface area of the TFCC impacted was minimal.

CONCLUSIONS: Retrograde intramedullary nail placement for distal ulna fractures frequently involves both the superficial TFCC and deep radioulnar ligament footprint, with perforations most common in the dorsal peripheral region rather than the central disc of the TFCC. Despite this, the overall surface area of involvement is limited.

CLINICAL RELEVANCE: Surgeons should be aware of the proximity of important surrounding structures and the likelihood of TFCC involvement when using a retrograde intramedullary approach for distal ulna fractures.