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Rotator Cuff of the Shoulder

 Rotator Cuff of the Shoulder


Rotator Cuff is a group of muscles surrounding the shoulder joint, it consists of 4 muscles abbreviated in the word “SITS”:

  1. Supraspinatus muscle.
  2. Infraspinatus muscle.
  3. Teres minor muscle.
  4. Subscapularis muscle.
See Also: What is SLAP Lesion?
Rotator Cuff muscles
Rotator Cuff muscles
See Also: Hawkins Test

Rotator Cuff Muscles

Supraspinatus Muscle
OriginSupraspinous fossa of scapula.
InsertionSuperior facet on greater tuberosity of humerus.
InnervationSuprascapular nerve (C4, C5 and C6) (C4,C5, C6).
Arterial SupplySuprascapular artery.
ActionInitiates and assists deltoid in abduction of arm and acts with other rotator cuff muscles.
Supraspinatus Muscle
Supraspinatus Muscle
Infraspinatus Muscle
OriginInfraspinous fossa of scapula.
InsertionMiddle facet on greater tuberosity of humerus.
InnervationSuprascapular nerve (C5 and C6) (C5, C6).
Arterial SupplySuprascapular and circumflex scapular arteries.
ActionLaterally rotate arm; helps to hold humeral head in glenoid cavity of scapula.
Infraspinatus Muscle
Infraspinatus Muscle
Teres minor muscle
OriginSuperior part of lateral border of scapula.
InsertionInferior facet on greater tuberosity of humerus.
InnervationAxillary nerve (C5 and C6) (C5, C6).
Arterial SupplySubscapular and circumflex scapular arteries.
ActionLaterally rotate the arm; and helps to hold humeral head in glenoid cavity of scapula.
Teres minor muscle
Teres minor muscle
Subscapularis muscle
OriginSubscapular fossa of scapula.
InsertionLesser tuberosity of humerus.
InnervationUpper and lower subscapular nerves (C5, C6 and C7) (C5, C6, C7).
Arterial SupplySubscapular artery.
ActionMedially rotates the arm and adducts it; and helps to hold humeral head in glenoid cavity of scapula.
Subscapularis muscle
See Also: Brachial Plexus Anatomy

Rotator Cuff Muscle Function

These muscles are referred to Glenohumeral Joint as the protectors of the shoulder since, in addition to actively moving the humerus, they fine-tune the humeral head position during arm elevation.

Rotator Cuff Muscle Functions include the following:

Assist in the rotation of the shoulder and arm:

At the G-H joint, elevation through abduction of the arm requires that the greater tuberosity of the humerus pass under the coracoacromial arch. For this to occur, the humerus must externally rotate, and the acromion must elevate. ER of the humerus is produced actively by a contraction of the infraspinatus and teres minor, and by a twisting of the joint capsule.

A force couple exists in the transverse plane between the subscapularis anteriorly and the infraspinatus and teres minor posteriorly in which cocontraction of the infraspinatus, teres minor, and subscapularis muscles both depresses and compresses the humeral head during overhead movements.

In the coronal plane, there is another force couple between the deltoid and the inferior rotator cuff muscles (infraspinatus, subscapularis, and teres minor).

With the arm fully adducted, contraction of the deltoid produces a vertical force in a superior direction, resulting in an upward translation of the humeral head relative to the glenoid. Contraction of the inferior rotator cuff muscles produces both a compressive force and a downward translation of the humerus that counterbalances the force of the deltoid, thereby stabilizing the humeral head.

Reinforce the G-H capsule:

The rotator cuff muscles, together with the coracohumeral ligament, and the LHB (often referred to as the fifth rotator cuff muscle) function as contractile ligaments. For example, firing of the rotator cuff muscles increases the tension of the middle G-H ligament when the arm is abducted to 45 degrees and externally rotated.

Control much of the active arthrokinematics of the GH joint:

Contraction of the horizontally oriented supraspinatus produces a compression force directly into the glenoid fossa. This compression force holds the humeral head securely in the glenoid cavity during its superior roll, which provides stability to the joint and also maintains a mechanically efficient fulcrum for elevation of the arm.

In the shoulder midrange position, when all of the passive restraints are lax, joint stability is achieved almost entirely by the rotator cuff. In addition, as previously mentioned, without adequate supraspinatus force, the near vertical line of force of a contracting deltoid tends to jam or impinge the humeral head superiorly against the coracoacomial arch.

Compared with most joints that have a single axis on which torques are generated, the shoulder is very different, because it has no fixed axis. As a result, each muscle activation creates a unique set of rotational moments, which necessitates precise coordination in the timing and magnitude of muscle contractions.

Jenp et al. used electromyography (EMG) to detect the most specific positions of highest activation for the individual rotator cuff muscles:

  • The greatest activation of the subscapularis was with the arm in the scapular plane at 90 degrees of elevation and neutral humeral rotation. The subscapularis has also been shown to be an effective humeral head depressor in ER, whereas it produces almost no A-P translation in abduction and ER.
  • The infraspinatus–teres minor muscles are very effective humeral head depressors with the arm in the sagittal plane and the humerus elevated to 90 degrees in the midrange of external/IR (the socalled hornblower’s position).
  • The supraspinatus could not be effectively isolated.

Rotator Cuff Footprint:

Footprint of the rotator cuff means the value of space of its insertion on the humeral head:

  1. Supraspinatus: Triangular in shape, with an average maximum medial-to-lateral length of 6.9 mm and an average maximum anteroposterior width of 12.6 mm.
  2. Infraspinatus: Trapezoidal in shape, with an average maximum medial-to-lateral length of 10.2 mm and an average maximum anteroposterior width of 32.7 mm.
  3. Teres minor: Triangular in shape, with an average maximum medial-to-lateral length of 29 mm and an average maximum width of 21 mm.
  4. Subscapularis: Comma-shaped insertion, with an average maximum medial-to-lateral length of 40 mm and an average maximum width of 20 mm.
See Also: Hornblower Sign
Rotator Cuff Footprint
Rotator Cuff Footprint

Acromiohumeral Distance AHD

The Acromiohumeral distance AHD can be measured on an anteroposterior (AP) radiograph of the shoulder joint in neutral rotation, the Rockwood view, or the outlet view (v-view).

  • The Acromiohumeral distance AHD is measured as the distance between the superior margin of the humeral head and the under surface of the acromion.
  • The reference values are as follows:
    • Mean value (in healthy individual): AHD = 1.05 cm
    • Abnormal: AHD = 7 mm

If the acromiohumeral distance is at or below the cut off value of 7 mm, it should be assumed that a complete rotator cuff tear is present.

Acromiohumeral Distance AHD

References

  1. Jenp YN, Malanga GA, Growney ES, An KN. Activation of the rotator cuff in generating isometric shoulder rotation torque. Am J Sports Med. 1996 Jul-Aug;24(4):477-85. doi: 10.1177/036354659602400412. PMID: 8827307.
  2. Turkel SJ, Panio MW, Marshall JL, Girgis FG. Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint. J Bone Joint Surg Am. 1981 Oct;63(8):1208-17. PMID: 7287791.
  3. Culham E, Peat M: Functional anatomy of the shoulder complex. J Orthop Sports Phys Ther 18:342–350, 1993.
  4. Blackburn TA, McLeod WD, White B, et al: EMG analysis of posterior rotator cuff exercises. Athl Train 25:40–45, 1990.
  5. Perry J, Glousman RE: Biomechanics of throwing. In: Nicholas JA, Hershman EB, eds. The Upper Extremity in Sports Medicine. St Louis, MO: CV Mosby, 1990:727–751.
  6. Sharkey NA, Marder RA: The rotator cuff opposes superior translation of the humeral head. Am J Sports Med 23:270–275, 1995.
  7. Sharkey NA, Marder RA, Hanson PB: The role of the rotator cuff in elevation of the arm. Trans Orthop Res Soc 18:137, 1993.
  8. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.
  9. Millers Review of Orthopaedics -7th Edition Book.

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