Inside

The glenoid labrum is a collagenous structure that is approximately 4 mm thick and attaches to the glenoid circumferentially ( ). It functions to deepen the otherwise shallow glenoid fossa and increase its radius of curvature and also acts as an attachment site for capsule and ligamentous structures ( ). The morphology of the superior labrum is distinct, with more of a meniscal-type attachment that consists of thin elastic tissue than that of the inferior portion of the labrum ( ). It has been proposed that the more elastic nature of the anterosuperior labrum exists to accommodate tensile stresses within the rotator interval, which may also make this region more vulnerable to injury ( ). The vascularity of the superior labrum arises from an anastomotic vascular network emanating from the anterior humeral circumflex, posterior humeral circumflex, and suprascapular arteries, without vascular contribution from the glenoid itself ( ), The most poorly vascularized region is the anterosuperior labrum, which may also contribute to vulnerability to injury and impaired healing capacity.

Several variations of normal labral anatomy have been described, including a synovial reflection at the superior aspect of the glenoid, which varies in depth that may result in a meniscoid superior labrum that appears as redundant labrum (2.6- to 7.3-mm overhang) with more of a recessed attachment ( ). Other variations include a sublabral foramen and Buford complex. A sublabral foramen is quite common and reported to be present in 12% of patients ( ). A Buford complex is identified as absent anterior-superior labrum in association with a cordlike middle glenohumeral ligament and is less common (1.5%). In each case, it is important that these normal variants are identified as such intraoperatively and not mistaken for pathology to avoid untoward morbidity associated with inappropriate attempted repair (meniscoid superior labrum or recessed attachment) or overtightening the rotator interval (sublabral foramen and Buford complex).

The biceps anchor includes attachment to both the supraglenoid tubercle as well as the superior glenoid labrum. The supraglenoid tubercle is approximately 5 mm medial to the superior glenoid rim. examined 105 cadaveric specimens and found direct attachment to the supraglenoid tubercle only 50% of the time; the remaining specimens demonstrated primary attachment to the superior labrum and a variable pattern, which they further classified into four types. Type I attachment was entirely to the posterior labrum, type II attachment was predominantly posterior but included some anterior labral attachment, type III included equal attachment to the anterosuperior and posterosuperior labrum, and type IV represented a predominantly anterosuperior labral attachment. The majority of specimens demonstrated type I or type II (prominently posterior) attachment sites.

Junction

The intraarticular segment of the long head of the biceps tendon measures approximately 2.5 to 3.4 cm in length ( ) and is 6.6 mm in diameter ( ). During normal shoulder motion, the long head of the biceps tendon experiences 19 mm of excursion ( ). The vascular supply to the long head of the biceps tendon emanates primarily from tributaries of the superior labrum proximally and ascending branches of the anterior humeral circumflex artery more distally ( ). As a result, there is a vascular watershed area that occurs 12 to 30 mm from the biceps anchor and has been proposed as a rationale for susceptibility of tendon rupture in this region ( ). evaluated the long head of the biceps tendon histologically and found a dense network of sensory and sympathetic neural elements that were most dense within the proximal intraarticular segment of tendon.

The biceps pulley is a structure along the articular margin consisting of the proximal portion of the bicipital groove (zone 1 of the bicipital tunnel) and a confluence of fibers from the superior glenohumeral ligament, coracohumeral ligament, subscapularis tendon, and supraspinatus tendon. The biceps pulley acts as a proximal tether to the long head of the biceps tendon to resist shear forces and prevent abnormal medial excursion ( ).

Bicipital Tunnel

described the bicipital tunnel and defined its anatomy and histology subsequently. The bicipital tunnel encompasses the extraarticular segment of the long head of the biceps tendon and its constraining fibro-osseous enclosure. The bicipital tunnel can further be divided into three anatomic zones that have diagnostic and therapeutic significance ( Fig. 18.2 ).

Using a cadaveric model, the entire bicipital tunnel was harvested en bloc and fixed in formalin. Cross-sections were then taken from each of the three zones of the bicipital tunnel, including zone 1 (yellow) , zone 2 (red), and zone 3 (black). Plain radiographs were taken demonstrating the osseous architecture of the bicipital tunnel floor from each zone. Histologic evaluation demonstrated that zones 1 and 2 were consistently enclosed by dense connective tissue and contained synovium. Zone 3 had significantly more percent empty tunnel and lacked the same dense connective tissue boundaries. BS, Bicipital sheath; FL, falciform ligament; LD, latissimus dorsi; LHBT, long head biceps tendon; PM, pectoralis major tendon; SS, subscapularis.

With permission from Taylor SA, Fabricant PD, Bansal M, et al. The anatomy and histology of the bicipital tunnel of the shoulder. J Shoulder Elbow Surg . 2015;24:511-519.

Zone 1 (bicipital groove) of the bicipital tunnel refers to what was traditionally considered the bony bicipital groove. It begins at the articular margin and extends to the distal margin of the subscapularis. The floor of zone 1 is made up of a relatively deep osseous groove that can be quite variable among specimens ( ) but has an average depth of 4.3 mm and an average width ranging from 8.8 mm proximally and 5.4 mm more distally ( ). The roof of zone 1 is composed of what was formerly termed the transverse humeral ligament but has been more recently shown to be an expansion of the subscapularis attachment as well as contributions from the supraspinatus and coracohumeral ligament attachments ( ). Synovial tissue is present in 100% of specimens in this area ( ).

Zone 2 (“no man’s land”) is defined proximally by the distal margin of the subscapularis tendon and distally by the proximal margin of the pectoralis major tendon insertion on the humerus. It has been deemed “no man’s land” because of its relative invisibility to arthroscopic evaluation from above and from subpectoral evaluation below. Within zone 2, the osseous floor is represented by more of a shallow trough and is covered by periosteum as well as an extension of fibers from the latissimus dorsi and subscapularis. The roof of the bicipital sheath that encloses zone 2 is made up of axially oriented dense connective tissue as well as histologically discrete perpendicularly oriented fibers emanating from the expansion of the pectoralis major attachment to the humerus traditionally referred to as the falciform ligament ( ). Importantly, synovium was identified and 67% of specimens within zone 2, which contrasts with previous reports that synovial reflection occurs more proximally ( ). Furthermore, zone 2 is consistently a closed space that may harbor pathologic lesions and contains statistically similar percent empty tunnel to that of zone 1 ( ).

Zone 3 (sub-pectoral region) is marked anatomically by the superior margin of the pectoralis major tendon. Its osseous floor is relatively flat and architecture and covered by fibers of the latissimus dorsi and periosteum. The percent empty tunnel is significantly greater within zone 3 than in zones 1 and 2, suggesting that space-occupying lesions may be of less significance in this area. Partial extension of synovium was identified and 18% of specimens within zone 3 ( ).