Glenoid Labrum

Original Editor - Priyanka Chugh

Top Contributors - Priyanka Chugh, Kim Jackson, Lucinda hampton, Naomi O'Reilly, Wendy Snyders, 127.0.0.1 and Wanda van Niekerk

Description

The glenoid labrum (glenoid ligament) is a fibrocartilaginous rim attached around the margin of the glenoid cavity in the shoulder blade. The shoulder joint is considered a ball and socket joint. However, in bony terms the 'socket' (the glenoid fossa of the scapula) is quite shallow and small, covering at most only a third of the 'ball' (the head of the humerus). The socket is deepened by the glenoid labrum.

The labrum is triangular in section, the base is fixed to the circumference of the cavity, while the free edge is thin and sharp.

It is continuous above with the tendon of the long head of the biceps brachii, which gives off two fascicles to blend with the fibrous tissue of the labrum.

Structure

The glenoid labrum is similar to the meniscus of the knee. It is a fibro-cartilaginous rubbery structure which encircles the glenoid cavity deepening the socket providing static stability to the glenohumeral joint. It acts and looks almost like a washer, sealing the two sides of the joint together.The labrum is described like a clock face with 12 o'clock being at the top (superior), 3 o'clock at the front (anterior), 6 o'clock at the bottom (inferior) and 9 o'clock at the back (posterior). Clinicans may reverse the 3 o'clock and 9 o'clock for left shoulder describing 3 o'clock at the back. This can be confusing, so the European Society of Shoulder & Elbow Surgeons (SECEC) has agreed to keep 3 o'clock at the front for either shoulder.

The glenoid labrum is approximately 4 mm thick and is round or triangular in cross section. 

The capsule of the glenohumeral joint attaches to the glenoid labrum. The glenoid labrum is continuous with:

superiorly: tendon of the long head of biceps brachii
anteriorly:
anterior band of the inferior glenohumeral ligament
middle glenohumeral ligament (variably)

Clinical relevance

Most instabilities or pain syndromes are associated with injuries or morphologic changes in the glenoid labrum complex or long head of the biceps tendon origin. The first anatomic descriptions go back to Fick in 1910 and since then many authors have described the anatomy of these structures. It was Snyder who introduced the term SLAP lesions, classifying superior, anterior, posterior labrum changes into four grades. It is still unclear whether all of the described and arthroscopically observed changes are due to a post-traumatic, acquired lesion or whether anatomic variations can be present as well. In order to elucidate this problem, 36 cadaver shoulder joints were inspected macroscopically and sectioned for microscopic evaluation. Here the glenoid could be divided into an superior and an anterior- superior area demonstrating a wide variety of morphologic labral glenoid changes, while the dorsal and inferior sectors of the glenoid showed a relatively uniform anatomy of a firm labrum-glenoid bond. Four types of biceps tendon attachments could be identified similar to the description given by Vangsness. In addition, a variety of anterior-superior changes could be found. The sublabral hole as described by Esch in the clinical setting was found to be a physiologic variant. Precise knowledge of the anatomic morphology of the normal glenoid in its variations seems to be necessary to understand variants and allow for distinguishing between physiologic anatomic variants and pathoanatomic changes in imaging and the clinical setting.

Anatomic Variants

The main variants occur in sectors 1 and 2.

1. Superior region, or sector 1

This is probably the area with the most anatomic variants. In young subjects, the labrum adheres strongly to the edge of the glenoid cavity, but with age, a recess develops, although this is not pathological . It is certainly normal as long as there remains joint cartilage up to the most peripheral insertion of the labral fibers.

2. Anterosuperior region, or sector 2

Here again there are many anatomic variants, more or less related to age. Normally, the labrum is rounded, and mobile with respect to the edge of the glenoid cavity (sublabral or Weitbrecht's foramen).

The most frequent variants are: free (13.5%) or no labrum and narrow, “cord-like” middle glenohumeral ligament (MGHL) in continuity with the biceps footplate (Buford complex) (12%) .

2.3. Biomechanics

The labrum has several functions, and 3 in particular:

•
it increases the contact area between humeral head and scapula, by 2 mm anteroposteriorly and 4.5 mm supero-inferiorly;
•
it contributes to the “viscoelastic piston” effect, maintaining -32 mmHg intra-articular negative pressure; this is especially effective against traction stress and, to a lesser extent, against shear stress;
•
it provides insertion for stabilizing structures (capsule and glenohumeral ligaments), as a fibrous “crossroad”. Labrum and ligaments are in synergy in a genuine complex, each structure's contribution varying with the position of the limb: in abduction and external rotation (ABER), the inferior glenohumeral ligament (IGHL) absorbs 51% of the stress, the superior glenohumeral ligament (SGHL) 22% and the MGHL 9% .

Assessment

The ability to predict the presence of a glenoid labral tear by physical examination was compared with that of magnetic resonance imaging (conventional and arthro gram) and confirmed with arthroscopy. There were 37 men and 17 women (average age, 34 years) in the study group. Of this group, 64% were throwing athletes and 61% recalled specific traumatic events. Clinical assessment included history with specific attention to pain with overhead activities, clicking, and instances of shoulder instability. Physical examination included the apprehension, relocation, load and shift, inferior sulcus sign, and crank tests. Shoulder arthroscopy confirmed labral tears in 41 patients (76%). Magnetic resonance imaging produced a sensitivity of 59% and a specificity of 85%. Physical examination yielded a sensitivity of 90% and a specificity of 85%. Physical examination is more accurate in predicting glenoid labral tears than magnetic resonance imaging. In this era of cost con tainment, completing the diagnostic workup in the clinic without expensive ancillary studies allows the patient's care to proceed in the most timely and economic fashion.

The different lesions of the glenoid labrum are described. They may involve the antero-inferior, the posterior or the superior (SLAP lesions) part of the labrum. CT-arthrography is the gold standard imaging modality in this field of shoulder abnormalities.