What is the rotator cuff of the shoulder?
Rotator Cuff is a group of muscles surrounding the shoulder joint.
Rotator cuff consists of 4 muscles abbreviated in the word “SITS”:
- Supraspinatus muscle.
- Infraspinatus muscle.
- Teres minor muscle.
- Subscapularis muscle.
See Also: What is SLAP Lesion?
|Origin||Supraspinous fossa of scapula.|
|Insertion||Superior facet on greater tuberosity of humerus.|
|Innervation||Suprascapular nerve (C4, C5 and C6) (C4,C5, C6).|
|Arterial Supply||Suprascapular artery.|
|Action||Initiates and assists deltoid in abduction of arm and acts with other rotator cuff muscles.|
|Origin||Infraspinous fossa of scapula.|
|Insertion||Middle facet on greater tuberosity of humerus.|
|Innervation||Suprascapular nerve (C5 and C6) (C5, C6).|
|Arterial Supply||Suprascapular and circumflex scapular arteries.|
|Action||Laterally rotate arm; helps to hold humeral head in glenoid cavity of scapula.|
|Teres minor muscle|
|Origin||Superior part of lateral border of scapula.|
|Insertion||Inferior facet on greater tuberosity of humerus.|
|Innervation||Axillary nerve (C5 and C6) (C5, C6).|
|Arterial Supply||Subscapular and circumflex scapular arteries.|
|Action||Laterally rotate the arm; and helps to hold humeral head in glenoid cavity of scapula.|
|Origin||Subscapular fossa of scapula.|
|Insertion||Lesser tuberosity of humerus.|
|Innervation||Upper and lower subscapular nerves (C5, C6 and C7) (C5, C6, C7).|
|Arterial Supply||Subscapular artery.|
|Action||Medially rotates the arm and adducts it; and helps to hold humeral head in glenoid cavity of scapula.|
See Also: Brachial Plexus Anatomy
The primary function of the rotator cuff is to provide dynamic stability by balancing the force couples about the glenohumeral joint in both the coronal and transverse plane.
- Coronal plane:
- The inferior rotator cuff (infraspinatus, teres minor, subscapularis) functions to balance the superior moment created by the deltoid.
- Transverse plane:
- The anterior cuff (subscapularis) functions to balance the posterior moment created by the posterior cuff (infraspinatus and teres minor).
Rotator Cuff Footprint:
Footprint of the rotator cuff means the value of space of its insertion on the humeral head:
- 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.
- 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.
- Teres minor: Triangular in shape, with an average maximum medial-to-lateral length of 29 mm and an average maximum width of 21 mm.
- Subscapularis: Comma-shaped insertion, with an average maximum medial-to-lateral length of 40 mm and an average maximum width of 20 mm.
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.