Background:
Trans-ulnar fracture–dislocations of the elbow are rare injuries with complex fracture patterns and variable outcomes. Traditional classification systems offer limited prognostic value. A recently introduced coronoid-centric Mayo classification distinguishes injury subtypes based on coronoid attachment and identifies trans-ulnar basal coronoid (TUBC) fractures as a particularly challenging entity. This study evaluated outcomes across Mayo fracture types and explored factors associated with inferior results in TUBC injuries.

Materials and methods:
In this retrospective cohort study, surgically treated trans-ulnar elbow fracture–dislocations managed at a level I trauma center between 2010 and 2022 were identified and classified according to the Mayo system. Demographic data, injury characteristics, surgical management, radiographic outcomes, and complications were recorded. Functional outcomes were assessed after a minimum follow-up of 12 months using the Mayo Elbow Performance Score (MEPS); Oxford Elbow Score (OES); Quick Disabilities of Arm, Shoulder and Hand Questionnaire (QuickDASH); European Quality of Life Five-Dimension, Five-Level Version (EQ-5D-5L); and range-of-motion measurements. Radiographs were analyzed for union, instability, heterotopic ossification, and post-traumatic osteoarthritis (OA).

Results:
A total of 52 patients were included (14 trans-olecranon, 28 TUBC, 10 Monteggia-variant). TUBC injuries were the most common subtype (53.8%). Post-traumatic OA was significantly more frequent in TUBC injuries than in fractures with coronoid attachment to a major fragment (88% versus 61%, P = 0.047). Higher-grade OA and persistent instability were associated with inferior functional outcomes. Although functional scores tended to be lower in TUBC injuries, differences compared with other subtypes were not consistently statistically significant. Within the TUBC group, poorer outcomes were observed when stable screw fixation of the basal coronoid fragment could not be achieved.

Conclusions:
TUBC fracture–dislocations represent a high-risk subgroup of trans-ulnar elbow injuries. Stable fixation of the coronoid base appears critical for achieving favorable outcomes. The Mayo classification provides clinically relevant stratification and prognostic insight for these complex injuries.