Glenoid Labrum

Original Editor - Priyanka Chugh

Top Contributors - Priyanka Chugh and Naomi O'Reilly

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.[1]

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.[2]

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)[3]

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.[4]

Anatomic Variants

The main variants occur in Sectors 1 and 2.

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 [5]. It is certainly normal as long as there remains joint cartilage up to the most peripheral insertion of the labral fibers.

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
  • Narrow, “Cord-like” Middle Glenohumeral Ligament in continuity with the Biceps Footplate (Buford Complex) (12%) [6].

Biomechanics

The labrum has several functions, and 3 in particular:

  1. Increases the contact area between humeral head and scapula, by 2 mm Antero-posteriorly and 4.5 mm Supero-inferiorly;
  2. 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;
  3. 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 Middle Glenohumeral Ligament (MGHL) 9% .[7]

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.[8]

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.[9]

Epidemiology

The term SLAP ("superior labrum anterior posterior") was initially coined by Snyder and his colleagues while performing a retrospective review of a large sample of shoulder arthroscopies [10]. While the true overall incidence of SLAP tears is unknown, the incidence among patients undergoing arthroscopy is reported to be between 6 and 26 percent [11].

Classification

Four types of SLAP injuries were described initially:

  1. Type I demonstrated degenerative fraying with intact biceps insertion
  2. Type II, detachment of the biceps insertion
  3. Type III, a bucket-handle tear with intact biceps tendon attachment to bone
  4. Type IV, an intrasubstance tear of the biceps tendon with bucket-handle tear of the superior labrum

Risk Factors

In a prospective observational study of 544 consecutive shoulder arthroscopies that included 139 SLAP tears, different tear types were associated with particular conditions or activities. Type I tears were associated with increased age, rotator cuff disease, and osteoarthritis; Type II tears were associated with overhead sports; and Type III and IV tears were associated with high-demand occupations . The authors of the study did not define high-demand occupations or speculate why such occupations were associated with Type III or IV lesions, as few such injuries were identified in the study.

Mechanisms of Injury

Given these associations, different types of SLAP injuries likely involve different mechanisms of injury. According to a retrospective review of 84 arthroscopically diagnosed labral tears, the most common mechanism involved an inferior traction-type injury either from a fall or a sudden pull when lifting a heavy object[12] . Other common mechanisms included traumatic glenohumeral dislocation or repetitive shoulder abduction and external rotation (eg, throwers and other overhead athletes). A direct blow to the shoulder or a fall onto an outstretched hand may also cause a SLAP tear. A predisposition to sustaining certain types of SLAP injuries may stem from underlying shoulder comorbidities, such as multidirectional instability or chronic degenerative changes.

According to some researchers, the "peel-back" mechanism accounts for Type II labral injuries [13]. In this mechanism, excessive stress on the biceps tendon attachment when the shoulder is placed in abduction and maximal external rotation leads to separation and tearing of the superior posterior labrum from the glenoid. Overhead throwing athletes (eg, baseball pitchers, cricket bowlers) and laborers who swing tools overhead frequently assume this position.

During repetitive overhead motions that involve abduction to 90 degrees and maximal external rotation, increases in external rotation range can be seen over time. Often, this increase is associated with a loss of internal rotation, a pattern termed glenohumeral internal rotation deficit (GIRD) [14]. While it remains unclear how GIRD develops, it can lead to tightening of the posterior capsule, which in turn changes the translational mechanics of the humeral head within the glenoid. These changes can lead to internal impingement and posterior labral injury.[15]

Treatment

Postoperative Treatment and Results

Typically requires six months and often as long as 12 months to return to throwing after surgical repair of a SLAP lesion. Healing must not be rushed. The patient should work through the appropriate stages of rehabilitation gradually and clinicians must guard against the patient progressing prematurely. Given the complexity and importance of post-operative rehabilitation, patients are best served by participating in a rehabilitation program under the supervision of a knowledgeable physical therapist, athletic trainer, or comparable clinician.

The post-operative rehabilitation program is typically divided into three stages:

  1. Phase 1 Maximal protection phase (approximately six weeks duration)
  2. Phase 2 Moderate protection phase (approximately six weeks duration)
  3. Phase 3 Minimum protection phase (approximately 14 weeks duration)

Phase 1 Maximal Protection Phase

The maximal protection phase begins the day after surgery until around six weeks. During this phase the primary goal is to protect the surgical repair from re-injury and to minimize pain and inflammation. The patient is typically in a sling for the full six weeks; avoiding any motion that loads the biceps tendon is critical. The patient begins to perform passive and active assisted range of motion (ROM) exercises during this phase but these are limited. Protected motion begins with passive motion below 90 degrees of shoulder flexion and abduction, and progresses gradually after the first two weeks. Limited active motion is introduced gradually. Toward the end of this stage, the patient begins to perform some basic isometric strength exercises.

Phase 2 Moderate Protection Phase

The moderate protection phase begins at approximately week seven and continues through week 12. During this phase, one major goal is to regain full active range of motion. Around week 10, active loading of the biceps tendon can begin. If full ROM is not obtained with the basic program, additional focused stretching and mobilization exercises may be required. Increasing levels of resistance are used for scapular and rotator cuff exercises. Exercises for developing core strength are performed during this phase.

Phase 3 Minimum Protection Phase

The minimum protection phase begins at approximately week 13 and continues through week 26. During this phase, the patient may gradually resume throwing or overhead occupational activities until full function is restored. Throwing from a mound may begin around 24 to 28 weeks after surgery in most cases. It is critical that full shoulder mobility is achieved. Full strength and motion of the scapular stabilizers and rotator cuff muscles should be achieved before full activity is resumed. To prevent reinjury, it is important that a pitcher’s throwing mechanics be assessed and any problems resolved, and that appropriate guidelines regarding the type and number of pitches thrown be followed .

For the patient who follows up with a primary care or sports medicine physician, failure to progress through the phases in a reasonable time frame (approximately three months for phases 1 or 2 and six months for phase 3) merits consultation with the orthopedic surgeon who completed the repair. Similarly, if the patient develops unexpected pain or dysfunction during the post-operative rehabilitation, the patient should return to their orthopedic surgeon for evaluation. The surgeon should have the final say about whether the patient is ready to resume full activity.

A systematic review of studies of the management of Type 2 SLAP tears (506 patients included) found that 83 percent of patients reported good-to-excellent results following operative repair . However, only 73 percent of patients returned to their prior level of function, while only 63 percent of overhead throwing athletes returned to their previous level of play. Should primary repair fail, biceps tenodesis often relieves pain. About 40 percent of patients report an excellent outcome with this surgery, while approximately 4 percent experience significant complications . Common long-term disabilities after a failed surgical repair include pain and instability with overhead or abducted and externally rotated shoulder positions. It is unclear whether SLAP tears increase the risk for glenohumeral osteoarthritis.[16]

See also

class="researchbox">http://bmjopensem.bmj.com/content/2/1/e000209

References

  1. https://en.wikipedia.org/wiki/Glenoid_labrum
  2. https://www.shoulderdoc.co.uk/article/1399
  3. https://radiopaedia.org/articles/glenoid-labrum
  4. https://www.ncbi.nlm.nih.gov/pubmed/12883756
  5. http://www.sciencedirect.com/science/article/pii/S0749806305801057
  6. https://www.scopus.com/record/display.uri?eid=2-s2.0-29644447279&origin=inward&txGid=F68392337D64C9A9DE1B71C5B7CB7B6A.wsnAw8kcdt7IPYLO0V48gA%3a2
  7. http://www.sciencedirect.com/science/article/pii/S1877056814003259
  8. http://journals.sagepub.com/doi/abs/10.1177/036354659602400205
  9. https://www.ncbi.nlm.nih.gov/pubmed/9810074
  10. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears/abstract/1
  11. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears/abstract/2
  12. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears/abstract/3
  13. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears/abstract/4
  14. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears/abstract/5
  15. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears
  16. https://www.uptodate.com/contents/superior-labrum-anterior-posterior-slap-tears