Hing Yee Eng MD, Presenter: Nothing to Disclose

Carlos Luis Benitez MD, Abstract Co-Author: Nothing to Disclose

The anconeus epitrochlearis muscle (AEM) is an anomalous accessory muscle in the elbow, coursing from the medial olecranon to the medial epicondyle. Several cases in the literature have suggested the association of this muscle with ulnar compression neuropathy. The purpose of this study is to review the MRI findings of the AEM, assess the relationship between muscle size and ulnar nerve morphology, and investigate the muscle's correlation with ulnar compression neuropathy.

Thirty two cases of elbow MRI studies of patients with an AEM from July 2007 to March 2014 were reviewed retrospectively. All of these patients presented with elbow pain and/or numbness with mean age of 40 years (range 18 to 60 years). The following parameters were evaluated: ulnar nerve diameter proximal, within, and distal to the cubital tunnel (CT); AEM cross sectional area (MA) and volume (MV); and encroachment ratio of the muscle at the superior and inferior aspects of the CT. Changes in ulnar nerve caliber and signal were also assessed.

The mean ulnar nerve diameters proximal, within, and distal to the CT were 3.63, 3.97, and 3.39 mm respectively. The mean MA was 68.47 mm2 and mean MV was 6300 mm3. The mean encroachment ratio of the AEM in the CT was 0.58 superiorly and 0.56 inferiorly. There was no statistically significant correlation between the ulnar nerve diameter within the CT and MA (r = 0.05) or MV (r = 0.06). There were positive correlations between the MA and both the superior (r = 0.66) and inferior (r = 0.64) encroachment ratios as well as between the MV and the superior (r = 0.65) and inferior (r = 0.57) encroachment ratios. The most common abnormalities involved the common extensor (n = 17) and biceps (n = 6) tendons. Four of the thirty two cases demonstrated focal T2 hyperintensity and/or thickening of the ulnar nerve consistent with ulnar neuritis, three within the CT and one just proximal to the CT.

Most findings of anconeus epitrochlearis muscle are incidental and asymptomatic without ulnar compression neuropathy. There is no significant correlation between anconeus epitrochlearis muscle size and ulnar nerve caliber in the cubital tunnel.

Anconeus epitrochlearis muscle is usually incidentally found and not associated with symptoms or ulnar compression neuropathy. This knowledge can help the clinician in the management of elbow pain.

Eng, H, Benitez, C, Quantitative MRI Analysis of the Relationship between the Anconeus Epitrochlearis Muscle and Ulnar Compression Neuropathy.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011734.html