SCIENTIFIC ARTICLE The aponeurotic expansion of the supraspinatus tendon: anatomy and prevalence in a series of 150 shoulder MRIs Thomas P. Moser & Étienne Cardinal & Nathalie J. Bureau & Raphaël Guillin & Pascale Lanneville & Detlev Grabs Received: 27 February 2014 /Revised: 11 August 2014 /Accepted: 18 August 2014 # ISS 2014 Abstract Objective To describe the aponeurotic expansion of the supraspinatus tendon with anatomic correlations and deter- mine its prevalence in a series of patients imaged with MRI. Materials and methods In the first part of this HIPAA- compliant and IRB-approved study, we retrospectively reviewed 150 consecutive MRI studies of the shoulder obtain- ed on a 1.5-T system. The aponeurotic expansion at the level of the bicipital groove was classified as: not visualized (type 0), flat-shaped (type 1), oval-shaped and less than 50 % the size of the adjacent long head of the biceps section (type 2A), or oval-shaped and more than 50 % the size of the adjacent long head of the biceps section (type 2B). In the second part of this study, we examined both shoulders of 25 cadavers with ultrasound. When aponeurotic expansion was seen at US, a dissection was performed to characterize its origin and termination. Results An aponeurotic expansion of the supraspinatus locat- ed anterior and lateral to the long head of the biceps in its groove was clearly demonstrated in 49 % of the shoulders with MRI. According to our classification, its shape was type 1 in 35 %, type 2A in 10 % and type 2B in 4 %. This structure was also identified in 28 of 50 cadaveric shoulders with ultrasound and confirmed at dissection in 10 cadavers (20 shoulders). This structure originated from the most anterior and superficial aspect of the supraspinatus tendon and inserted distally on the pectoralis major tendon. Conclusion The aponeurotic expansion of the supraspinatus tendon can be identified with MRI or ultrasound in about half of the shoulders. It courses anteriorly and laterally to the long head of the biceps tendon, outside its synovial sheath. Keywords Shoulder . Anatomy . Supraspinatus tendon . Biceps tendon . MRI . Ultrasound Introduction Recent advances in magnetic resonance imaging (MRI) tech- niques have been dramatically beneficial for complex muscu- loskeletal examinations, increasing the conspicuity of normal anatomical structures that were previously inaccessible to the radiologist. As an example, the rotator cuff cable is now routinely demonstrated at shoulder MRI [1]. Recently, our group and other authors became aware of a tendon-like structure coursing in a vertical direction, along the anterior aspect of the long head of the biceps [2, 3]. The index case that prompted our study is illustrated in Fig. 1. Gheno et al. described this structure as an accessory biceps tendon in two out of ten cadaveric shoulder specimens studied by con- ventional MRI and MR arthrography with anatomical corre- lation [2]. However, other anatomical studies have demon- strated an accessory slip or aponeurotic expansion of the supraspinatus tendon in this exact same location [4, 5]. T. P. Moser (*) : N. J. Bureau Department of Radiology and Research Center, Centre Hospitalier de l’Université de Montréal, Montréal, QC, Canada e-mail: thomas.moser@umontreal.ca É. Cardinal Radiologie Laënnec, Montréal, QC, Canada R. Guillin Radiology Department, Centre Hospitalier Universitaire de Rennes, Rennes, France P. Lanneville Pathology Department, Hôpital du Centre-de-la-Mauricie, Shawinigan, QC, Canada D. Grabs Anatomy Department, Université du Québec à Trois-Rivières, Trois-Rivières, QC, Canada Skeletal Radiol DOI 10.1007/s00256-014-1993-4