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SLAC Lesions
Diagnosis and Treatment
The superior labrum-anterior cuff, or SLAC, lesion is a recently described problem that previously had not received much attention. The lesion refers to an injury to the anterior-superior glenoid labrum that involves the insertion of the superior glenohumeral ligament and the anterior portion of the biceps tendon. This injury creates an anterior-superior instability in the shoulder, which allows the undersurface of the anterior supraspinatus tendon to contact the anterior-superior labrum and glenoid. If this contact is severe enough, it can result in a partial thickness rotator cuff tear on the articular side of the tendon. This combination of the labral and cuff injuries constitutes the SLAC lesion.
Indications
Anterior-superior labral injury with associated undersurface tearing of the anterior supraspinatus tendon. The labral injury should involve the glenoid insertion of the superior glenohumeral ligament and the anterior aspect of the biceps tendon. The attachment of the middle glenohumeral ligament may also be involved.
Contraindications
1. Normal anatomical variations of the anterior superior labrum with pathology of the rotator cuff
2. Impingement syndrome of the shoulder with labral fraying or degeneration but no history or symptoms supporting the diagnosis of instability
3. Severe degenerative joint disease of the glenohumeral joint
4. Active shoulder infection
5. Medically unstable patient
Mechanisms of Injury
Two major mechanisms have been found to cause the SLAC lesion. Repetitive overhead activity, either during work or recreation, has been found to be the cause of many of these injuries. The rest result from traumatic events, such as falls and motor vehicle accidents, which involve an anterior-superior subluxation event. In the overhead activity patients, the dominant arm is most commonly involved. For those patients involved in motor vehicle accidents, the arm on the side of the shoulder strap is most commonly affected.
Physical Examination
1. There is no single test that is diagnostic for this problem.
2. Whipple testing is almost always positive (Fig. 19–1).
3. Load and shift testing for the anterior superior labrum is usually positive.
4. Anterior-superior SLAP testing is usually positive (Fig. 19–2), but standard SLAP testing is negative. The standard SLAP test is done exactly like the anterior-superior SLAP test but the force is aimed directly superior rather than anterosuperior.
5. O’Brien’s test is usually positive.
6. Jobe’s series of instability tests can often be negative.
7. Impingement testing can be positive, but most rotator cuff tests, including the supraspinatus isolation and rotator cuff strength tests, are usually negative.
Diagnostic Tests
1. Standard radiographs are usually normal.
2. Standard magnetic resonance imaging can be negative, although most scans reveal pathology in either the cuff or the labrum.
3. Magnetic resonance arthrogram usually demonstrates both the labral and cuff pathology.
Special Considerations
It is important to remember that the SLAC lesion is primarily an instability problem. The rotator cuff tears that result from this process are different from those that occur with impingement or traumatic injury to the shoulder. The tears are undersurface tears and result from the contact of the cuff with the anterior-superior glenoid and labrum. This contact occurs due to the increased anterior-superior translation that is allowed by the instability in the shoulder. While the treatment of these rotator cuff tears is sometimes necessary, the most important aspect of treatment is the correction of the underlying instability. Treatment of the rotator cuff alone will result in failure.
The SLAC lesion is only one presentation of the wide spectrum of instability that can be seen in the shoulder. If instability occurs in a different region of the shoulder, then the resulting rotator cuff pathology will be different. The cuff will come into contact with the glenoid at a different point and cause a different type of lesion. The term internal impingement, for example, has been used to describe the situation that occurs when a posterior-superior labral/biceps avulsion allows contact to occur at the posterior-superior glenoid. Because these problems have a similar pathology, the symptoms that are encountered with SLAC lesions can be very similar to those of the other types of shoulder instability. Care must be taken to ensure that the diagnosis is correct and that all instability is addressed. Careful physical exam and arthroscopic evaluation is essential to making this diagnosis.
Preoperative Planning and Timing of Surgery
1. This lesion is not an emergent problem and should not be treated operatively until a trial of conservative treatment has failed.
2. If conservative treatment fails, then operative treatment should be undertaken in an elective fashion. The surgeon should be sure that all appropriate equipment is available and that the patient will be able to alter his daily routine to comply with the postoperative treatment regimen.
Special Instruments
1. Arthroscope and appropriate support equipment
2. Large arthroscopic cannula (at least 7 mm)
3. Arthroscopic shaver with soft-tissue blade
4. Burr for arthroscopic shaver
5. Suture anchor (we use Panalok anchor, Mitek, Johnson & Johnson, NJ) and insertion equipment
6. Suture punch or penetrating suture retriever (we use a 30 degree Suture Grasper retriever, Mitek)
7. Arthroscopic knot pusher
8. Spinal needle
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