Extraarticular variants of the long head of the biceps brachii: a reminder of embryology.

Developmental anomalies of the long head of the biceps tendon are rare and have been described in the literature mainly dealing with anatomy and embryology. Because most basic embryologic research on this topic was conducted before 1966, a literature search was performed from archived anatomy textbooks and manuscript references. These data were compared with the scarce case descriptions of developmental anomalies of the long head of the biceps tendon. An additional case illustration from our own experience was provided. From the literature, it appears that during the embryologic phase of development, a staged migration of the long head of the biceps tendon occurs from a position between the fibrous capsule and synovial layer to an intraarticular position. Recent anatomic and arthroscopic case reports have shown that interruption of this migration can occur in any of these stages. Given the recent increase in arthroscopic shoulder surgery, anomalies of the long head of the biceps tendon will be encountered more frequently. Knowledge of their existence and origin can help in evaluating unexpected anatomic variations or the absence of the biceps tendon in preoperative medical imaging or during an arthroscopic procedure.