The anatomic - magnetic resonance imaging study of distal triceps brachii tendon.

Purpose: The study aimed to describe the distal triceps brachii insertion on the olecranon and to correlate the findings with those seen in normal MR (Magnetic Resonance) anatomy of the triceps brachii insertion.

Materials and methods: 14 un-paired fresh frozen elbows were included according to the institution guidelines and dissected. Histologic examination was performed to the distal triceps brachii insertion. The dimension of the distal triceps brachii tendon insertion was measured and defined based on its layer. The measurement of distal triceps brachii insertion was performed with image processing program (Image J, National Institute of Health, Bethesda, Maryland). T1-weighted elbow MR images (3.0 T) of a 102 patients were acquired and analyzed according to its sagittal plane.

Results: All specimens shows that distal triceps brachii tendon is with three distinct insertional areas in the olecranon which are: (1) capsular, (2) deep muscular, (3) superficial tendinous insertion with the areas of 80.7 mm², 56.4 mm², and 175.2 mm², respectively. The superficial tendinous insertion was observed with a thickened portion, the "central cord" with 0.5 occupation ratio. MR analysis showed that 30% (31/102) of the distal biceps brachii insertion was with a cleft between the bipartite insertion of the superficial tendinous and the deep muscular insertion on olecranon which designated as the "lacuna" which was also found in 35% (5/14) of the specimens.

Conclusions: The distal triceps brachii has three distinct insertion on the olecranon. The superficial tendinous layer was separated with the deep muscular layer by a cleft in one third of the cases. Knowledge of this anatomy will help surgeon to understand the partial triceps injury and to avoid iatrogenic injury to the distal triceps tendon during surgery.