Development of the long head of the biceps brachial tendon: a possible explanation of the anatomical variations.

The anatomical variations of the proximal portion of the long head of the biceps brachii tendon (LHBT) are rarely observed in clinical practice. However, an increase in the rate of shoulder arthroscopic surgery has led to an increase in the observation of anatomical variations of this region. The aim of this work was to analyze the development of the LHBT in 23 human embryos ranging from the 6th to 8th weeks of development. The LHBT develops from the glenohumeral interzonal mesenchyme in the 6th week. By week 7, the myotendinous junction of the LHBT develops. The anlage of the LHBT is separated from that of the glenohumeral capsule during week 8. Our results suggest that the most important period for the LHBT development occurs between the 6th and 8th weeks of embryonic development. Alterations during this critical period may cause anatomical variations of the LHBT. An additional case report from our own experience is provided as Supplementary material.