3 Interesting Facts About Rotator Cuff Tears
In a previous post, we talked about the anatomy and assessment of the glenohumeral ligaments. Now we extend the shoulder assessment further with three interesting facts that can occur after a massive rotator cuff tear. For more detailed information, I highly recommend this book covering the diagnosis and management of massive rotator cuff tears.
1. Latissimus dorsi and pectoralis major act as humeral depressors
Most clinicians understand that without a well functioning rotator cuff, the superficial deltoid muscles can take over and lead to problems such as subacromial impingement. This occurs due to the centralizing force of the rotator cuff (FS) compared with the superior force vector of the deltoid (FD).
As evident above, if the force of the rotator cuff is not sufficient to counteract the force of the deltoid muscle, the humeral head will shift superiorly, leading to a dynamic upward glenohumeral subluxation. If the rotator cuff cannot provide sufficient humeral head depression, the body will compensate by recruiting larger muscles to provide this force. The pectoralis major, latissimus dorsi and teres major provide a large adduction force during arm abduction. These muscles cocontract during a massive tear, acting as the rotator cuff in order to stabilize and depress the humeral head. However, this cocontraction is fatiguing and inefficient, leading to pain and restriction during arm elevation in patients with rotator cuff tears. As a clinician, don’t forget to treat these muscles if you suspect a rotator cuff tear.
2. Suprascapular nerve injury can occur with supraspinatus retraction
The suprascapular nerve runs under the transverse scapular ligament to innervate the supraspinatus and infraspinatus muscles. A massive rotator cuff tear of the supraspinatus can lead to retraction of the muscle belly (it peels back and rolls away from the shoulder). As it retracts, the supraspinatus can produce a traction force on the suprascapular nerve, leading to suprascapular neuropathy. On exam, this can be seen as supraspinatus and infraspinatus muscle wasting and may be indicative of a massive rotator cuff tear. Because this is a stretch injury, surgical repair of the supraspinatus usually is sufficient to reverse the neuropathy and restore innervation to these rotator cuff muscles.
3. The humeral head can dislocate into the deltoid
During the beginning of my career, I saw a patient with a massive degenerative rotator cuff tear who had limited motion but no pain. When observing his affected shoulder, his front deltoid muscle looked massive compared to the other side. At the time, I rationalized that he probably used his front deltoid so frequently to lift his arm that it had hypertrophied. In hindsight, it was more likely a case of anterosuperior escape of the humeral head.
Anterosuperior escape occurs when the humeral head does not stay within the socket and “escapes” or dislocates through the coracoacromial arch. This usually happens following a large rotator cuff tear of the subscapularis, supraspinatus and sometimes the posterior cuff as well. On physical exam, the anterior deltoid is much larger in appearance due to the humeral head pushing into it from below. Anytime the patient lifts their arm, the humeral head rubs underneath the anterior deltoid muscle, tendon, and acromion. This constant friction can lead to erosion and fracture of the acromion, and degeneration or cyst formation of the deltoid muscle tendon leading to rupture. Anterosuperior escape is difficult and unpredictable to manage with conservative care, although physical therapy is still beneficial. Typically, patients with anterosuperior escape are candidates for reverse shoulder arthroscopy in order to allow full functional movement.