the

The Rotator Cuff

the shoulder joint is the most mobile

joint in the body the ball and socket

configuration allows an extensive nearly

unlimited range of motion this extreme

flexibility comes at a cost however with

limited bony interaction between the

head of the humerus and the shallow cup

of the scapular glenoid the shoulder is

prone to dislocation because of the

anterior angulation of the glenoid

traumatic dislocations are usually

anterior and inferior posterior

dislocations are usually associated with

colonic tonic seizures where the

powerful muscles of the back pulled the

humerus posteriorly out of the glenoid

fossa well there are a multitude of

muscles that act on and move the arm

about the shoulder joint for powerful

muscles originating from the scapula and

attaching to the proximal humerus are

responsible for maintaining the

glenohumeral articulation and are

collectively known as the rotator cuff

before we get into the details of the

rotator cuff itself let's review some

relevant soft tissue and bony Anatomy

every skeletal muscle in the body

consists of the contracting muscle belly

with a tough but flexible fibers band at

the end known as a tendon the tendons

connect to the regional bony structures

to both anchor the muscle and transmit

the muscular force across the joint to

move the bone on the other side the

scapula is a thick flat plate like bone

that's part of the upper extremity

girdle and serves as a durable anchor

for the powerful muscles of the rotator

cuff the scapular spine is an oblique

horizontal projection or protuberance

off the backside of the scapular plate

that again serves as a sturdy anchor for

the regional musculature the acromion is

a forward projecting bony extension that

articulates with the clavicle in front

of the chest wall to provide anterior

support of the scapula itself and

finally the glenoid is the cup-like

cavity or socket that holds the ball

like extension off of the head of the

upper arm bone or humerus there are two

bony projections off of the humeral head

called the greater and lesser tuberosity

that serve as the strong bony

attachments for the tendons of the

rotator cuff remembered the rotator cuff

is primarily responsible for securing

the ball of the humeral head into the

socket of the scapular glenoid fossa and

therefore there's no need to restore the

bony thorax at this point but we'll

briefly display the thorax to clarify

and recall the relationship and

orientation of the scapula to the chest

the subscapularis muscle belly is

affixed to the undersurface of the

scapular blade and the tendon passes

under the coracoid process then attaches

to the lesser tuberosity of the humerus

its primary functions are internal

rotation of the upper arm and

stabilization of the shoulder joint

the remaining three structures of the

rotator cuff originate from the back of

the scapula beginning at the top the

relatively small muscle above the staff

that our spine is appropriately the

supraspinatus the tendon passes directly

beneath the acromion and attaches to the

greater tuberosity of the humerus

its primary functions are abduction or

raising the arm especially through the

first 15 degrees of the arc and

stabilization of the shoulder joint the

infraspinatus is a large muscle

originating from the infraspinatus fossa

below the scapular spine and similarly

attaching to the greater tuberosity its

primary functions are lateral rotation

of the upper arm and stabilization of

the shoulder joint the most inferior

member of the cuff is the teres minor

originating off the lateral border of

the scapula the tendon again attaches to

the greater tuberosity its primary

functions are similar to the

infraspinatus with lateral rotation and

stabilization of the upper arm these are

the four muscles of the rotator cuff

additional muscles secure the scapula to

the thoracic cage an axial skeleton

including the serratus anterior

originating from the outer surface of

the upper eight or nine ribs and

inserting on the front of the scapula

near its inner border will now restore

the humerus in the rotator cuff

before we show the additional muscles

that secure the scapula to the bony

thorax the rhomboids originated from the

spinous processes of vertebra c7 through

t5 and insert on the medial border of

the scapula the latissimus dorsi muscle

originates from the spinous processes of

vertebrae t7 through s3 the inferior

three to four ribs the iliac crest as

well as a variable attachment to the

inferior aspect of the scapula and

inserts on the intertubercular groove of

the humerus while the main action is to

a duct or pull down the upper arm it

also keeps the tip of the scapula close

to the rib cage

finally the trapezius originates from

the spinous processes of vertebra c7

through t12 as well as the occiput of

the skull and inserts on the scapular

spine acromion process in the lateral

third of the clavicle many other muscles

of the shoulder work on the upper and

lower arm that originate from either the

bony thorax or the scapula these include

the triceps that extends the lower arm

the biceps muscle that flexes the lower

arm the pectoralis minor and major

muscles that flex the upper arm forward

and the large deltoid muscle which

raises the upper arm especially beyond

the 15 degree mark of the supraspinatus

muscle as described previously looking

back at the rotator cuff

of the four components the supraspinatus

muscle and tendon are situated the

highest on the cup running in a tunnel

bordered by the humeral head below and

the acromion above repetitive motions

especially those involving over the head

activities such as painting carpentry

and pitching can impinge on and damage

the tendon over time

thus the supraspinatus is the most

commonly affected tendon in rotator cuff

injuries in addition to job or activity

related risk factors the anatomic shape

of the acromion is felt to predispose

certain individuals to rotator cuff

injuries as well looking from the side

the acromion has three anatomic

classifications type 1 is essentially

flat providing the maximum space for the

supraspinatus and the lowest congenital

risk for injury type 2 is curved with an

intermediate risk and type 3 is hooked

with the smallest space and therefore

highest risk of injury MRI can be used

to evaluate the rotator cuff oblique

coronal t2-weighted images through the

supraspinatus tendon show a homogeneous

dark signal if the tendon is completely

intact

areas of increased signal can represent

frein partial tear or inflammation also

known as tendinopathy where they

complete through and through hole in the

tendon showing up as a disruption in the

tendon itself in the worst case scenario

the tendon completely splits in half the

part connected to the muscle is pulled

back towards the scapula if the injury

is chronic the other powerful muscles of

the shoulder will pull the humerus

upward and fill the gap once occupied by

the supraspinatus muscle and tendon the

loss of the acromial humeral interval is

described as a high-riding shoulder and

is a plain film indicator of a chronic

rotator cuff injury

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