Editing Rotator cuff (section)

==Function==
The rotator cuff muscles are important in shoulder movements and in maintaining [[glenohumeral joint]] (shoulder joint) stability.<ref name=Morag2006>{{cite journal |vauthors=Morag Y, Jacobson JA, Miller B, De Maeseneer M, Girish G, Jamadar D |title=MR imaging of rotator cuff injury: what the clinician needs to know |journal=Radiographics |volume=26 |issue=4 |pages=1045–65 |year=2006 |pmid=16844931 |doi=10.1148/rg.264055087|doi-access=free }}</ref> These muscles arise from the [[scapula]] and connect to the head of the [[humerus]], forming a cuff at the shoulder joint (hence the name rotator cuff). They hold the head of the humerus in the small and shallow [[glenoid cavity|glenoid fossa]] of the scapula. The glenohumeral joint has been analogously described as a [[golf ball]] (head of the humerus) sitting on a [[golf tee]] (glenoid fossa).<ref>{{cite journal |vauthors=Khazzam M, Kane SM, Smith MJ |title=Open shoulder stabilization procedure using bone block technique for treatment of chronic glenohumeral instability associated with bony glenoid deficiency |journal=Am. J. Orthop. |volume=38 |issue=7 |pages=329–35 |year=2009 |pmid=19714273 |url=http://www.amjorthopedics.com/pdfs/038070329.pdf }}</ref>

The rotator cuff compresses the glenohumeral joint during abduction of the arm, an action known as concavity compression, in order to allow the large [[deltoid muscle]] to further elevate the arm.  In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle.  The anterior and posterior directions of the glenoid fossa are more susceptible to [[shear force]] perturbations, as the glenoid fossa is not as deep relative to the superior and inferior directions. The rotator cuff's contributions to concavity compression and stability vary according to their stiffness and the direction of the force they apply upon the joint.

In addition to stabilizing the glenohumeral joint and controlling humeral head translation, the rotator cuff muscles also perform multiple functions, including abduction, [[internal rotation]], and [[external rotation]] of the shoulder. The infraspinatus and subscapularis have significant roles in scapular plane shoulder abduction ([[scaption]]), generating forces that are two to three times greater than the force produced by the supraspinatus muscle.<ref name=Escamilla09>{{cite journal |vauthors=Escamilla RF, Yamashiro K, Paulos L, Andrews JR |title=Shoulder muscle activity and function in common shoulder rehabilitation exercises |journal=Sports Med |volume=39 |issue=8 |pages=663–85 |year=2009 |pmid=19769415 |doi=10.2165/00007256-200939080-00004 |s2cid=20017596 }}</ref> However, the supraspinatus is more effective for general shoulder abduction because of its [[moment arm]].<ref>{{cite book |last=Arend |first=C.F. |chapter=01.1 Rotator Cuff: Anatomy and Function |chapter-url=http://www.shoulderus.com/ultrasound-of-the-shoulder/rotator-cuff-anatomy-and-function/ |title=Ultrasound of the Shoulder |publisher=Master Medical Books |year=2013 |url=http://www.shoulderus.com/ |access-date=5 September 2013 |archive-date=14 October 2013 |archive-url=https://web.archive.org/web/20131014020541/http://www.shoulderus.com/ |url-status=live }} ShoulderUS.com]</ref> The anterior portion of the supraspinatus tendon is submitted to a significantly greater load and stress, and performs its main functional role.<ref>{{cite journal |vauthors=Itoi E, Berglund LJ, Grabowski JJ, Schultz FM, Growney ES, Morrey BF, An KN |title=Tensile properties of the supraspinatus tendon |journal=J. Orthop. Res. |volume=13 |issue=4 |pages=578–84 |year=1995 |pmid=7674074 |doi=10.1002/jor.1100130413 |s2cid=22224279 }}</ref>