Relevant Anatomy of Glenohumeral Instability.

Last updated Friday, February 04, 2005

Figure 5

The scapulohumeral ligaments

Redundancy

By virtue of their mandatory redundancy, the capsule and its ligaments are lax throughout most of the range of joint motion. Thus they can exert major stabilizing effects only when they come under tension as the joint approaches the limits of its range of motion.

The three anterior glenohumeral ligaments were first described by Schlemm. (Schlemm, 1853) Since then many observers have described their anatomy and their roles in limiting glenohumeral rotation and translation. (Delorme, 1910; DePalma, 1970; Ferrari, 1990; Fick, 1904; McLaughlin, 1960; Moseley and Overgaard, 1962; O'Connell et al, 1990; Reeves, 1968b; Turkel et al, 1981; Weitbrecht, 1969)

Codman (Codman, 1934) and others pointed out the variability of the ligaments. (Delorme, 1910; DePalma, 1973; Ferrari, 1990; Moseley and Overgaard, 1962; O'Brien et al, 1990b; Williams et al, 1994) These authors also demonstrated a great variation in the size and number of synovial recesses that form in the anterior capsule above, below, and between the glenohumeral ligaments. They observed that if the capsule arises at the labrum, there are few if any synovial recesses (in this situation there is a generalized blending of all three ligaments, which leaves no room for synovial recesses or weaknesses, and hence the anterior glenohumeral capsule is stronger). However, the more medially the capsule arises from the glenoid (i.e., from the anterior scapular neck), the larger and more numerous are the synovial recesses. The end result is a thin, weak anterior capsule. Uhthoff and Piscopo (Uhthoff and Piscopo, 1985) demonstrated in an embryological study that in 52 specimens the anterior capsule inserted into the glenoid labrum in 77 per cent and into the medial neck of the scapula in 23 per cent.

The superior glenohumeral ligament (SGHL) is identified as the most consistent capsular ligament. (DePalma et al, 1949) It crosses the rotator interval capsule lying between the supraspinatus and subscapularis tendons. Another interval capsular structure, the coracohumeral ligament (CHL), originates at the base of the coracoid, blends into the cuff tendons and inserts into the greater and lesser tuberosities. (Clark et al, 1990; Harryman et al, 1992; Jerosch et al, 1990; Kuboyama, 1991; Ovesen and Nielsen, 1985a; Steiner and Hermann, 1989)

Harryman et al have pointed out that these two ligaments and the rotator interval capsule come under tension with glenohumeral flexion, extension, external rotation and adduction. (Harryman et al, 1992) When they are under tension, these structures resist posterior and inferior displacement of the humeral head. Clinical and experimental data have shown that releasing or surgically tightening the rotator interval capsule increases or decreases the allowed posterior and inferior translational laxity, respectively. (Basmajian and Bazant, 1959; Harryman et al, 1992; Neer et al, 1989; Nobuhara and Ikeda, 1987; Warner et al, 1992)

It is these ligaments and capsule as well as the inferior glenoid lip that provide static restraint against inferior translation. (Basmajian and Bazant, 1959) It is of anatomical interest and clinical significance that when the lateral scapula is allowed to droop inferiorly, the resulting passive abduction of the humerus relaxes the rotator interval capsule and the superior ligaments; as a result the humeral head can be "dumped" out of the glenoid fossa (see figure 5). (Matsen et al, 1994) Drooping of the lateral scapula is normally prevented by the postural action of the scapular stabilizers, particularly the trapezius and serratus. Elevation of the lateral scapula with the arm at the side enhances inferior stability in two ways: the resulting glenohumeral adduction tightens the superior capsule and ligaments and secondly the scapular rotation places more ofthe inferior glenoid lip beneath the humeral head. (Itoi et al, 1992; Warner et al, 1992)

While the SGHL and CHL come under tension with external rotation in adduction, the middle glenohumeral ligament (MGHL) is tensioned by external rotation when the humerus is abducted to 45 degrees. (Symeonides, 1972; Terry, 1991; Turkel et al, 1981) The MGHL originates antero-superiorly on the glenoid and inserts mid-way along the anterior humeral articular surface adjacent to the lesser tuberosity. In over a third of shoulders, the MGHL is absent or poorly defined, a situation which may place the shoulder at greater risk for anterior glenohumeral instability. (Morgan, 1992)

With greater degrees of shoulder abduction, for example in the "apprehension" position, the inferior glenohumeral ligament (IGHL) and the inferior capsular sling come into play. (O'Connell et al, 1991; Terry, Hammon and France, 1991; Turkel et al, 1981) The IGHL originates below the sigmoid notch and courses obliquely between the antero-inferior glenoid and its humeral capsular insertion. (O'Brien et al, 1990a) O'Brien et al have described an anterior thickening of the IGHL, the anterior superior band.(O'Brien et al, 1990a) The anterior and posterior aspects of the IGHL are said to function as a cruciate construct, alternatively tightening in external or internal rotation. (O'Brien et al, 1990a; Warner et al, 1992; Warren, 1984)

When the humerus is elevated anteriorly in the sagittal plane (flexion), the posterior-inferior capsular pouch along with the rotator interval capsule come into tension. (Harryman et al, 1990; Harryman et al, 1992; O'Brien et al, 1990a; Rhee et al, 1994; Warner et al, 1992) If the humerus is internally rotated while elevated in the sagittal plane, the interval capsule slackens but the posterior inferior pouch tightens. Posterior-inferior capsular tension also limits flexion, internal rotation and horizontal adduction. (Harryman et al, 1990; Harryman et al, 1992; Rhee et al, 1994) Excessive tightness of this portion of the capsule is a well-recognized clinical entity.

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