Definition

The glenoid labrum is a densely fibrous tissue that is located along the periphery of the glenoid bone [1] (Fig. 15.1). As the outer labrum transitions from the periphery to its articulation with the glenoid, the histology changes from fibrous to a small fibrocartilaginous zone at the junction with the glenoid [2]. The labrum increases the height and width of the glenoid while also giving extra depth to the joint. This provides increased stability while still allowing great range of motion [3]. The labrum also serves as an attachment point for the long head of the biceps tendon, the glenohumeral ligaments, and the long head of the triceps tendon, forming a periarticular system of fibers that gives the shoulder joint much needed stability [4]. The vascular supply to the labrum is from the posterior humeral circumflex artery, the circumflex scapular branch of the subscapular artery, and the suprascapular artery. These arteries come from the periphery of the labrum, making the articular margins of the labrum avascular [2]. It has also been shown that the superior labrum has less vascular supply than the inferior labrum. The long head of the biceps has a variable attachment to the labrum and glenoid. Approximately 40% to 60% of the biceps tendon originates from the supraglenoid tubercle, and the remaining fibers insert into the labrum [1]. The biceps insertion into the labrum is variable but most commonly is in a more posterior position.

Tears can occur in all regions of the labrum. The most studied injury to the labrum is the superior labral anterior-posterior (SLAP) tear. Anterior dislocations of the shoulder can be associated with a disruption of the anteroinferior labrum and anterior band of the inferior glenohumeral ligament, also known as a Bankart lesion. Posterior shoulder instability may result in injury to the posterior band of the inferior glenohumeral ligament as well as the posterior labrum, or a reverse Bankart lesion. Tears can extend to involve multiple regions of the labrum and have other associated injuries. The SLAP tear and Bankart lesion are the most common and for that reason are the focus of this discussion.

The most common mechanisms for SLAP tears are forced traction on the shoulder and direct compression. Direct compression can occur in the acute traumatic setting or in the chronic setting typical in the overhead throwing athlete. Overhead throwers are predisposed to SLAP tears secondary to their adaptive anatomy. They tend to have posterior capsular contractures, loose anterior capsular structures, and a retroverted humeral head, all increasing the amount of external rotation in the shoulder. As a result of these anatomic changes, the arm goes into an extreme externally rotated position while the biceps kinks at its insertion and assumes a more vertical and posterior position. This applies a torsional force to the biceps-labral complex superiorly, resulting in a peel back mechanism on the superior labrum [5,6]. Alternatively, as throwers externally rotate in the cocking phase, the rotator cuff may impinge on the posterior-superior glenoid, causing an “internal impingement” and tearing of the labrum [7].

Snyder [8] classified SLAP tears into four types, which was further modified by Morgan and Maffet. Most physicians think that the four-class system (Fig. 15.2) is sufficient and that the additional classifications could be placed within these basic types, so it is the preferred classification.

Bankart lesions are created by episodes of anterior instability. As the humeral head moves out anteriorly and inferiorly, anterior damage can occur to the anterior-inferior labrum, glenohumeral ligaments, joint capsule, rotator cuff, and possibly neurovascular structures. It has been shown that the Bankart lesion is created about 85% to 97% of the time in anterior dislocations [9,10]. This pathologic change is thought to be an important reason for recurrent instability.

In addition to the labrum’s increasing the depth and diameter of the glenoid, the labrum and capsule also create a negative pressure that provides stability through the glenohumeral articulation. If the labrum or capsule is injured, such as in the Bankart lesion, this suction is lost, and this decreases the stability of the shoulder. Several factors may predispose patients to recurrent instability. These include fracture on the glenoid or humeral head, hyperlaxity syndromes, male gender, younger age at initial dislocation, participation in contact or overhead throwing sport, and positive correlation between number of dislocations and risk of future dislocation. Dislocations later in life increase the risk of rotator cuff injury, with tears occurring in nearly 30% of patients older than 40 years and in up to 80% of patients older than 60 years.

A patient with a SLAP tear will most commonly present with symptoms of deep-seated pain, which can be sharp or dull [11]. It is usually located deep within the center of the shoulder and can be made worse with overhead activities, pushing heavy objects, lifting, or reaching behind the back. Patients may have mechanical symptoms, such as catching, popping, or grinding with rotation of the shoulder. Many patients with a SLAP tear will also have other shoulder disease, making clinical diagnosis challenging [11].

It is essential to obtain a thorough history for trauma to evaluate for traction or compression type injuries, dislocations, and sports (e.g., baseball, football, waterskiing, tennis) they play that may predispose them to this injury. Overhead throwing athletes may suffer decreased velocity and usually complain of pain in the late cocking and early acceleration phase of throwing. They may have weakness due to pain or secondary to a paralabral cyst compressing the suprascapular nerve. Compression on the nerve at the spinoglenoid notch can cause weakness in external rotation as well as deep posterior shoulder pain.

Bankart Lesion

Symptoms of anterior instability are usually obvious as the patient states that there has been a dislocation and continues to complain of pain and instability in that shoulder. Sometimes there is not a history of overt dislocation, but instead the patient has multiple episodes of instability without a complete dislocation. The patient will complain of pain and feeling of impending dislocation with the arm in abduction and external rotation. Important historical variables include the patient’s age at first dislocation, need for formal reduction, number of recurrent instability episodes, voluntary instability, and anticipated future sports activities.

The most comfortable position for these patients is usually with the arm in adduction and internal rotation. They avoid abduction and external rotation because this is the position that led to the dislocation and it also stresses the injured labrum, inferior glenohumeral ligament, and subscapularis tendon.

Several clinical tests are designed to assist the clinician in making the SLAP tear diagnosis [12–15]. These tests are trying to do one of two things: to pinch the torn labrum between the humeral head and the glenoid, causing pain or mechanical symptoms, or to place traction on the biceps tendon (Table 15.1). The tests have had variable ranges of sensitivity and specificity between studies, and thus no single test is considered diagnostic. The most commonly performed test is the O’Brien active compression test. This has been shown to be very sensitive but has extremely poor specificity. Accurate diagnosis requires a careful history to correlate with the examination findings.