ORIGINAL ARTICLE Fibrocartilaginous metaplasia identified in the long head of the biceps brachii Carlo Bottegoni, MD, Luca Farinelli, MD, Alberto Aquili, MD, Sandra Manzotti, BS, Marco Baldini, Antonio Gigante, MD* Clinical Orthopaedics, Department of Clinical and Molecular Science, School of Medicine, Università Politecnica delle Marche, Ancona, Italy Background: In the glenohumeral joint, the long head of biceps brachii (LHBB) is exposed to tension and compression loading. The short head of biceps brachii (SHBB) works only in tension. It is known that tendon under compression might develop fibrocartilaginous metaplasia that improves the resistance to compression but reduces the resistance to tension. This study evaluated the presence of cartilage in LHBB and SHBB samples, supporting its possible role in tendon tear. Methods: Between 2014 and 2016, 13 samples of LHBB and SHBB were collected during surgery for shoulder instability, glenohumeral arthritis, and massive rotator cuff tears. The samples were stained with hematoxylin and eosin, safranin-O, and Alcian blue (pH 1.0) for light microscopy. Immunohistochemis- try was performed using anti-S100, anti-collagen I and II, and anti–tenascin-C antibodies. Results: Histochemistry: LHBB samples showed matrix disorganization, with clusters of chondrocyte sur- rounded by collagen fibers and glycosaminoglycans. Safranin-O showed evident metachromasia. SHBB samples did not show any matrix disorganization or cartilaginous metaplasia. Immunohistochemistry: In all LHBB samples, anti-S100 and anti-collagen II showed cartilage in proximity of the tendon tear. Tenascin C immunostained closely to the disorganized matrix areas. SHBB, however, showed no positive areas for S-100, anti-collagen II, or tenascin C. Conclusions: According to our results, we hypothesize that the repeated stimulation in compression may induce the formation of fibrous cartilage. However, to date its role in tendon pathology remains to be clearly defined. Level evidence: Basic Science Study; Histology © 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Cartilage metaplasia; tendon rupture; tendon degeneration; compression loading; long head of the biceps brachii; short head of the biceps brachii Several causes have been suggested to explain long head biceps brachii (LHBB) pathology. Despite the absence of general consensus, proposals to explain the wide range of LHBB disorders include trauma, overuse, anatomy of the bicipital groove, rotator cuff tears, impingement, and aging. 12 To date, bicipital disorders are recognized to actually range from tendinitis to partial tearing, tendinosis, instability, and rupture. 19 A huge overlap clearly exists between these cat- egories, and biceps pathology is very rarely a single entity. 9 Pfahler et al 21 recognized significant correlations between bi- cipital groove anatomy and LHBB disorders. Some abnormalities, such as osteophytes or a shallow and narrow shape, can cause attrition of the tendon in the bicipital groove, This basic science study did not require Institutional Review Board approval. *Reprint requests: Antonio Gigante, MD, Clinical Orthopaedics, Department of Clinical and Molecular Sciences, Università Politecnica delle Marche, Via Tronto 10/A, I-60126 Ancona, Italy. E-mail address: a.gigante@univpm.it (A. Gigante). www.elsevier.com/locate/ymse ARTICLE IN PRESS 1058-2746/$ - see front matter © 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. https://doi.org/10.1016/j.jse.2018.02.042 J Shoulder Elbow Surg (2018) ■■, ■■–■■