Extensor Carpi Ulnaris Tendon Anatomy May Mimic Tears

Background: Asymptomatic, incidental extensor carpi ulnaris (ECU) tendon abnormalities are frequently noted on imaging studies of the wrist. The aim of this investigation was to determine if variations in gross tendon anatomy existed that could possibly account for these findings on MRI and ultrasound (US) imaging. Methods: The upper extremities of eleven (6 male and 5 female) formalin preserved cadavers were dissected and examined under loupe magnification with attention to the dorsal-ulnar wrist and hand and the ECU tendon. The tendons were inspected for anatomic variations, degenerative changes, and any other pathologies. The presence of intra-tendinous splits arising within the ECU tendon was noted and measured. The distances of the splits from the distal tendon insertion and the edge of the extensor retinaculum were recorded. Statistical correlations between age and the tendon splits were considered using R-squared to assess a linear regression. Results: 17 ECU tendons were dissected and examined, and 5 ECU tendons were excluded due to poor preservation of that upper extremity; all five were right sided upper extremities. Eleven of the 17 specimens demonstrated at least one split in the distal tendon: Seven had 1 split, 1 had 2 splits, and 3 had 3 splits. The mean length of the tendon split was 3.52 cm. The mean distance of the distal edge of the split to the tendon insertion site was 2.4 cm. A linear regression was calculated and showed no correlation between age and number of tendon splits. Conclusions: 64% of specimens showed a longitudinal split in the distal ECU tendon. The location of these frequent splits corresponds to imaging abnormalities on MRI and US in prior studies.