Methods to analyse the long head of the biceps in the management of distal ruptures of the supraspinatus tendon. Part 1: the concept of the "biceps box": dynamic rotator interval approach. Incidence of lesions of the long head of the biceps tendon.

Introduction: The area encompassing the long head of the biceps (LHB) can be represented as a rectangular parallelepiped. This geometric view can be likened to a box, the "biceps box", where the sides are the extrinsic structures and the LHB is the intrinsic structure. Since these structures are mobile in relation to each other, a dynamic "biceps box" model can modify assessments of the LHB, in its healthy or pathological state, and make the therapeutic approach to treating LHB lesions less arbitrary.

Material And Method: In order to describe the different sides of the "biceps box", and to understand their possible physiological and pathological consequences, a literature review using PRISMA methodology was used.

Results: The supraspinatus (SSP) has expansions on its anterior aspect that project anteriorly and cross the coracohumeral ligament (CHL). The most functionally important expansion is the fasciculus obliquus, which extends perpendicular to the axis of the tendon fibers of the SSP, divides the CHL into a deep and a superficial layer, and terminates on the superficial aspect of the subscapularis. The humeral insertion of the SSP may be binary, making a bridge over the LHB, with a posterior branch inserting on the greater tuberosity and an anterior branch on the lesser tuberosity. The superior glenohumeral ligament (SGHL) has a twisted course, downward and forward, and ends at the proximal opening of the bicipital groove with a flap on which the LHB rests. The bicipital pulley is not an independent structure but an arciform structure resulting from the fusion of several tissues.

Discussion: The presence of structures linked together by common expansions in the 3 planes of space validates the relevance of a "biceps box" as a functional geometric model. The structure that acts as a crossroads through which all expansions pass is the CHL. An extrinsic SSP lesion can be compensated for by other "biceps box" structures, whereas an extrinsic SGHL lesion rarely exists without the presence of an intrinsic LHB lesion. The CHL constitutes a connective tissue crossed by a vasculonervous pedicle from the lateral pectoral nerve, which may explain some anterior shoulder pain attributed to the biceps.

Conclusion: The LHB can be likened to an intrinsic structure contained in a box whose sides are made up of different interconnected stabilizing structures defining the extrinsic structures. The concept of a dynamic "biceps box" allows LHB lesions to be accurately classified, separating extrinsic and intrinsic lesions, and thus potentially modifying therapeutic approaches to the LHB.

Level Of Evidence: IV; systematic review.