Shoulder Lesions/LAG SIGNS

Lag Signs Are Important in Diagnosing Shoulder Lesions

By Warren Hammer, MS, DC, DABCO

Two primary ways of testing for rotator cuff ruptures is to determine whether the shoulder has enough strength to maintain a position against resistance, and by passive testing whereby the examiner attempts to determine if a passive position can be maintained in space (Lag sign).

Resistive tests are more likely to cause increased pain leading to reflex muscle weakness, even in the presence of an intact cuff.¹ Lag tests therefore may be more accurate since the arm is supported by the examiner and the pain level is decreased. Another reason this passive test may be superior to resistive testing for cuff rupture is that the influence of surrounding muscles, such as the deltoid and pectoralis major, is reduced.

A recent study² revisited the external rotation lag sign (ERLS). This test evaluates the integrity of both the supraspinatus and infraspinatus tendons. The ERLS is performed in the seated or standing position with the patient's elbow passively flexed to 90 degrees and the shoulder abducted to 20 degrees in the scapular plane, and near-maximal external rotation (minus a few degrees to avoid elastic recoil of the joint capsule or scapulothoracic joint caused by the examiner).

The examiner supports the elbow joint and holds the patient's wrist (Figure 1). The examiner then removes their hand from the wrist and asks the patient to actively maintain this position. If the patient cannot maintain original position against gravity and their arm rotates internally, the test is positive (Figure 2). The study2 concluded that this ERSL was "a useful sign for the diagnosis of isolated full thickness tears of the supraspinatus tendon." The amount of internal rotation lag for an isolated supraspinatus rupture was 7.35 degrees ± 3.12 degrees. This test should be compared with the contralateral side.

There was a strong correlation between the extension of the tear and the amount of the lag. As the lag (internal rotation) increases, there is most likely tearing of the infraspinatus and teres minor. For tears of the supraspinatus extending to superior and inferior portion of the infraspinatus, the lag was 17.76 degrees ± 9.55 degrees. If the teres minor is torn, the degree of internal rotation goes to 26.25 degrees ± 16 degrees.

The ERLS could not identify partial tears of the supraspinatus. The tests were confirmed by either arthroscopic or open surgery. The sensitivity was 56 percent and the specificity was 98 percent, meaning that if the test were negative, there was a 98 percent probability that there was not a full-thickness tear.

The ERLS test should be added to the tests recommended by the Parks, et al., study³ that found a 91 percent probability for full-thickness rotator cuff tears when there was a combination of a painful arc sign, drop-arm sign and a positive infraspinatus muscle test. For the drop-arm sign, the examiner holds the affected arm at 90 degrees of abduction (in the scapular plane) and at almost full external rotation, with the elbow flexed at 90 degrees. In this position, maintenance of the position of external rotation of the shoulder is a function primarily of the infraspinatus, but also stresses the supraspinatus. The patient is then asked to actively maintain this position as the examiner releases the wrist while supporting the elbow. The sign is positive if a lag or "drop" occurs. The magnitude of the lag is recorded to the nearest 5 degrees.

The lag sign for the subscapularis is performed with the patient's arm held in the lift-off position (behind their back, elbow flexed to 90 degrees, shoulder abducted 20 degrees, and extended 20 degrees). Examiner passively lifts the dorsum of the patient's hand away from the lumbar region until almost full internal rotation is achieved. The patient is then asked to actively maintain this position while the examiner, who is supporting the elbow, releases the patient's wrist.

If the patient cannot maintain the position and a lag toward the lumbar area occurs, then the subscapularis is ruptured. A slight lag indicates a partial tear of the cranial part of the subscapularis tendon, while an obvious drop of the hand may indicate a large tear.¹

References

1. Hertel R, Ballimer FT, Lambert SM, Gerber C. Lag signs in the diagnosis of rotator cuff rupture. J Shoulder Elbow Surg, 1996;5:307-313.
2. Castoldi F, Blonna D, Hertel R. External rotation lag sign revisited: accuracy for diagnosis of full thickness supraspinatus tear. J Shoulder Elbow Surg, 2009;18:529-534.
3. Park HB, Yokota A, Gill HS, et al. Diagnostic accuracy of clinical tests for the different degrees of subacromial impingement syndrome. J Bone Joint Surg (U.S.), 2005;87:1446-55.

Lag Signs

By Thomas Souza, DC, DACBSP

We often assume that muscle testing about the shoulder will indicate the presence of a partial tear or full rupture of the rotator cuff muscles. Logically, if there is a partial tear or full rupture, active resisted testing of the muscle should cause painful weakness with a partial tear, and perhaps painless or minimally painful  weakness with a full rupture. 

Given that rotator cuff musculature and, in particular, tendon insertion, is largely hidden by more superficial musculature, the observation of a displaced tendon or bulge of a retracted muscle tendon is not obvious.

A common testing procedure is the drop sign, in which a patient's arm is elevated to 90 degrees and the patient is asked to hold the position. Inability to hold the position indicates involvement of either the deltoid or supraspinatus. Given that the supraspinatus is more often torn, the assumption is that a tear of the supraspinatus has occurred.

An extension of this concept is to add resistance to the position. This is often referred to as the Jobe sign. With the arm at 90 degrees abduction, the examiner exerts a downward force with the patient attempting resistance. The obvious confounding factor is that this test is likely to cause pain with many shoulder conditions, and the pain is likely to cause a reflex inhibition of the muscles. The weakness, then, is more a neurologic response rather than a biomechanical inability to hold the position.

Recently, Hertel et al.¹ performed an evaluation of 100 consecutive patients. The results of those patients who went on to arthroscopic or open repair of any rotator cuff muscle/tendon were examined to determine the effectiveness of several tests in detecting a partial or full rupture. The tests incorporated into the study evaluation were:

• The Jobe sign. The shoulder is elevated to 90 degrees abduction with internal rotation. The patient maintains position with the examiner exerting a downward force on the arm (similar to the "empty can" test).

• The liftoff test. The patient is seated with the hand of their involved arm placed palm outward on the lower back. The patient is asked to lift the hand off of the back.

• The external rotation lag sign. The patient is seated. The elbow is passively flexed to 90 degrees and the shoulder is held at 20 degrees elevation in the scapular plane in a position of near maximum external rotation (i.e., maximum external rotation minus five degrees to avoid elastic recoil). The examiner supports the elbow and holds the arm in external rotation at the wrist. The patient is asked to hold the position while the examiner supports the elbow but releases the hold at the wrist. The degree of movement is estimated and is referred to as the "lag" (i.e., the difference between active and passive ROM).

• The drop sign (different than the standard drop sign). The patient is seated. The arm is held at 90 degrees elevation (in the scapular plane) and almost full external rotation with the examiner supporting the elbow and holding the arm in external rotation at the wrist. The patient is asked to hold the position while the examiner supports the elbow but releases the wrist hold. The degree to which the arm falls into internal rotation is the degree of lag.

• The internal rotation lag sign. The patient is seated. The patient is asked to bring the arm behind the back with the palm facing outward. The arm is held in near maximum internal rotation and with the hand away from the back by approximately 20 degrees of extension. The patient is asked to hold the position while the examiner supports the elbow but releases the wrist hold. If the patient is unable to hold the position, the lag sign is positive.

The biomechanical principle used in the design of the lag signs was to place the muscle/tendon in the most disadvantaged positions possible, thereby requiring full function of the muscle. The position was also designed to eliminate, as much as possible, contribution from other synergists. False negatives may occur if there is a restricted passive movement pattern. False positives may occur if the arm is held in maximum rotation or if the patient has an excessive passive range of motion.

The results of the study indicate the following:

• For rupture of the supraspinatus and infraspinatus tendons, the external rotation lag sign was less sensitive but more specific that the Jobe sign. This is probably because the Jobe sign is often painful.

• The drop sign was the least sensitive, but was as specific as the external rotation lag sign.

• Partial ruptures of the supraspinatus were not revealed with the external rotation lag sign.

• For the subscapularis, the internal rotation lag sign was as specific but more sensitive than the liftoff sign.

• Partial ruptures of the subscapularis tendon could be missed with the liftoff sign but detected with the internal rotation lag sign.

Reference

1. Hertel R, Ballmer FT, Lambert SM, Gerber CH. Lag signs in the diagnosis of rotator cuff rupture. J Shoulder Elbow Surg 1996;5:307-13.