Orthopedic Teaching Cases 2023, Jan, 18 | 12:00 am

Shoulder and Elbow cases full-thickness rotator cuff tears

A 65-year-old, left-hand-dominant woman returns to clinic complaining of persistent left shoulder pain. She has a chronic, degenerative rotator cuff tear of her left shoulder and has persistent symptoms after 2 months of physical therapy, corticosteroid injections, and NSAID use. An MRI of the left shoulder is obtained, which shows a medium-sized, full-thickness tear of the supraspinatus and part of the infraspinatus with no retraction, no atrophy, and no fatty infiltration.

Which of the following widths of tears would be classified as a medium-sized rotator cuff tear?

  1. 0.5 cm

  2. 2 cm

  3. 4 cm

  4. 7 cm

  5. 10 cm

 

Discussion

The correct answer is (B). When classifying tears by size, the following classification can be used. If a tear is less than 1 cm, it is considered a small tear (Answer A). If a tear is between 1 and 3 cm, it is considered a medium tear (Answer B). If a tear is between 3 and 5 cm, it is considered a large tear (Answer C). If a tear is greater than 5 cm, it is considered a massive tear (Answers D and E). In Europe, tears that involve two or more rotator cuff tendons are also considered massive tears.

During diagnostic arthroscopy, a thick band of tissue is seen just before the insertion of the supraspinatus and infraspinatus that is running perpendicular to the direction of the muscle fibers. What is this structure called?

  1. Rotator crescent

  2. Rotator interval

  3. Rotator cable

  4. Rotator cuff

  5. Rotator bridge

 

Discussion

The correct answer is (C). This structure is a thickening of the coracohumeral ligament that starts anteriorly just posterior to the short head of the biceps tendon on the coracoid process, extends posteriorly through the edge of the avascular zone of the supraspinatus and infraspinatus, and ends at the inferior edge of the infraspinatus. One proposed function of the cable is to act like a cable in a suspension bridge, helping to evenly distribute forces on the humeral head produced by the rotator cuff (see Fig. 2–6).

 

 

 

Figure 2–6 Illustration showing the rotator cable and rotator crescent. B, rotator crescent; C, rotator cable; BT, biceps tendon; I, infraspinatus; S, supraspinatus; TM, teres minor. (Redrawn from Burkhart SS, Lo IKY. Arthroscopic rotator cuff repair. J Am Acad Orthop Surg. 2006;14(6):333–346.)

 

The rotator crescent (Answer A) is the thin tissue that exists lateral to the rotator cable medial to the attachment of the supraspinatus and infraspinatus. It is composed on the tendons of these two rotator cuff muscles (see Fig. 2–6).

The rotator interval (Answer B) is the area on the anterior shoulder bordered by the subscapularis inferiorly and the supraspinatus superiorly.

The rotator cuff (Answer D) is composed of all four rotator cuff muscles, the supraspinatus, infraspinatus, teres minor, and subscapularis.

What is the most likely shape of this patient’s rotator cuff tear?

  1. U shaped

  2. L shaped

  3. V shaped

  4. Crescent shaped

  5. Massive and immobile

 

Discussion

The correct answer is (D). Rotator cuff tears come in different shapes. Crescent-shaped tears are tears where the edge of the torn rotator cuff tendons form a crescent shape with an apex that points medially along the tension line of the rotator cuff muscles but is not retracted. Since this patient’s tear is not retracted, the tear is likely to be crescent shaped.

U-shaped tears (Answer A) look similar to crescent-shaped tears but the apex of the U extends further medially, usually to the edge of the glenoid in the sagittal plane.

An L-shaped tear (Answer B) resembles a tear that can be thought of as partially a crescent-shaped tear and partially a U-shaped tear. One leg of the L is the more mobile, less retracted, crescent-shaped tear which transitions into the other leg of the L, which is a less mobile, more retracted part of the tear which resembles a U-shaped tear.

Finally, a massive and immobile tear (Answer E) can be either U-shaped or longitudinal. These tears are greater than 5 cm in size and cannot be mobilized to the greater tuberosity.

A V-shaped tear (Answer C) is not a type of rotator cuff tear.

 

What muscles make up the anterior and posterior force-couples, respectively?

  1. Anterior: subscapularis. Posterior: supraspinatus

  2. Anterior: pectoralis major. Posterior: infraspinatus

  3. Anterior: latissimus dorsi. Posterior: infraspinatus

  4. Anterior: subscapularis. Posterior: infraspinatus and teres minor

  5. Anterior: pectoralis major. Posterior: infraspinatus and teres minor

 

Discussion

The correct answer is (D). One of the functions of the rotator cuff is to dynamically stabilize the humeral head in the glenoid, providing a fulcrum so that the shoulder can articulate properly. In order to do this, forces around the center of rotation must be equal in the transverse and coronal planes. In the transverse plane, the humeral

head is relatively unconstrained by the glenoid anteriorly and posteriorly. Any anterior and posterior forces placed on the humeral head must be balanced so that it does not sublux or dislocate in an anterior or posterior direction. This is accomplished by the subscapularis pulling the humeral head anteriorly with the same force that the infraspinatus and teres minor pull it posteriorly. All of these muscles also act to pull the humeral head medially into the concavity of the glenoid, stabilizing it in a medial-lateral dimension. When a patient has a rotator cuff tear, these force couples become uneven and can lead to instability (see Fig. 2–7).

 

 

 

Figure 2–7 A. The transverse plane force couple (left) and the coronal plane force couple (right) are disrupted by a massive rotator cuff tear involving the posterior rotator cuff, infraspinatus, and teres minor. B. An alternative pattern of disruption of the transverse plane force couple. The transverse plane force couple is disrupted by a massive tear involving the anterior rotator cuff (ie, subscapularis). D = deltoid, I = infraspinatus, O = center of rotation, S = subscapularis, TM = teres minor. (From Burkhart SS, Lo IKY. Arthroscopic rotator cuff repair. J Am Acad Orthop Surg. 2006;14(6):333–346.)

 

What muscles make up the superior and inferior force-couples, respectively?

  1. Superior: deltoid. Inferior: supraspinatus and infraspinatus

  2. Superior: trapezius. Inferior: subscapularis, infraspinatus, and teres minor

  3. Superior: deltoid. Inferior: subscapularis, infraspinatus, and teres minor

  4. Superior: deltoid. Inferior: supraspinatus, infraspinatus, and teres minor

  5. Superior: deltoid. Inferior: supraspinatus

 

Discussion

The correct answer is (C). As stated above, the rotator cuff is needed to stabilize the humeral head in the glenoid and provide a fulcrum to allow the humeral head to

rotate properly. In the coronal plane, the humeral head is relatively unconstrained by the glenoid superiorly and inferiorly, so forces on the humeral head in these directions must be balanced. This is accomplished by the combined inferior forces of the subscapularis, infraspinatus, and teres minor equaling the superior force of the deltoid. When a patient has a rotator cuff tear, these force couples can be uneven, causing instability (see Fig. 2–7 above).

 

Objectives: Did you learn...?

 

 

Classify full-thickness rotator cuff tears based on size, shape, and retraction? Identify the rotator cable and crescent?

 

Identify the muscles that compose the force couples in the transverse and coronal planes?