Variations of the intra-articular portion of the long head of the biceps tendon: A classification of embryologically explained variations

Background: Although the intra-articular portion of the long head of the biceps (LHB) usually runs free, different types of fusions with the inferior surface of the capsule are known to be possible. Anatomic variations of this part of the LHB have been previously described and were nearly always considered to be innocent. Materials and methods: Out of 2 populations of 1500 arthroscopies each, we collected prospectively and retrospectively all possible variations of the proximal portion of the LHB. Results: We included 57 cases (1.91%) of this total population in an attempt to describe the complete range of these form variants: the simple vinculum or pulley-like sling, the partial or complete mesotenon between biceps and capsule, the complete adherent LHB, the double-tendon origin, the reversed-type split-tendon, and the complete absence of the LHB. We suggest a classification of 12 variations of the intra-articular portion of the LHB. Discussion: By taking into account an extensive literature review, we suggest that these conditions are congenital and consider them as a result of partial detachment from the mesothelial or synovial fusion with the inferior surface of the capsule. The incidence of these variants and their associated pathologies are investigated. Conclusion: By offering this new classification and a physiopathologic hypothesis, we try to explain why some of these anatomic variants may also acquire a pathologic significance.