Anatomy of Shoulder in a Nutshell

Great mobility at the expense of stability / strength.
4 regions: Pectoral region, Back, Axilla (armpit), Arm.
The only bony articulation is at the manubrium. All others are through muscles.
Skeleton region involved: Manubrium, clavicle, scapula, and also humerus (arm bone).
Scapula: Levator scapula has origin at superior angle.

Emerging from medial border (AKA vertebral border) is the spine of the scapula which proceeds laterally and flattens out into the Acromion (highest point of shoulder).

2 concavities:

- Supraspinous fossa
- Infraspinous fossa

Both of these are filled with muscle.

On anterior surface have Coracoid process. Suprascapular notch = on superior aspect, is closed by the superior transverse scapular ligament (AKA suprascapular ligament). This turns the notch into a foramen in which structures pass through = Suprascapular nerve and over which structures travel = Suprascapular artery / vein.

Glenoid fossa: on lateral border, for the articulation with head of humerus. Beneath this fossa, have infraglenoid tubercle, and above the fossa have supraglenoid tubercle.

Humerus:

The head of the humerus is a part of a “ball and socket” joint. Where this head meets the shaft of the humerus = anatomical neck. The surgical neck = a zone beneath anatomical neck. It is here where many fractures occur.

Lesser tubercle: more anterior, smaller.
Greater tubercle: larger, seen more in posterior view.

Between these two tubercles is a sulcus = Intertubercular sulcus AKA bicepetal groove.

Deltoid tuberosity: a roughened area on the shaft of the humerous where the deltoid muscle attaches.
Radial (spiral) groove: radial nerve travels right next to the bone at this point.

Synovial joint: Fibrous capsule surrounds the joint to create a joint cavity. Lining the inside of this = synovial membrane which makes synovial fluid. Hyaline cartilage (articular cartilage) lines the ends of the bones.

Sternal Clavicular Joint: the only bony articulation of upper limb with the axial skeleton. Very uncommon to dislocate this. Held together by 3 ligaments:

Interclavicular ligament = Between the two clavicles.
Sternoclavicular ligaments = On both anterior and posterior
Costoclavicular ligament = Holds clavicle onto costal cartilage of 1^st rib.

Coracoclavicular joint: between coracoid process and clavicle.

Coracoclavicular ligament
Acromioclavicular ligament = small ligament connecting lateral end of clavicle to acromion. When this ligament is separated, have a “separated shoulder” not dislocation.
Coracoacromial ligament

Glenohumeral joint: Very flexible. No bony reinforcement on anterior aspect, just ligaments. Within the fibrous capsule, have 3 Thickenings = glenohumeral ligaments which strengthen the anterior capsule: superior / middle / inferior glenohumeral ligaments.

Coracohumeral ligament: strengthens superior aspect of capsule.

Transverse humeral ligament: strengthens the anterior capsule by bridging the greater and lesser tubercles. This covers the bicepetal groove. It also holds the long head of the biceps in place.

Coracoacromial arch: formed by coracoid and acromion. A ligament spans the gap between them which prevents superior displacement of the humerus. When head of humerus comes out of the glenoid fossa = shoulder dislocation.

The glenoid fossa has Glenoid Labrum which is a fibrocartilage ring that deepens the glenoid fossa.

Muscles that strengthen the shoulder and make up the rotator cuff:

Maintains stability and integrity of humerus in glenoid fossa.

Terres minor
Subscapularis
Infraspinatus
Supraspinatus

Bursae: allows gliding action under rotator cuff muscles. This is a sac with synovial fluid. Facilitates where tendon rubs on bone. Have bursae around different aspects of joint.

Subscapular bursae = gliding force over which subscapularis muscle glides with head of humerus, toward anterior aspect. This can communicate with the joint cavity. In Bursitis, have inflammation spreading between them.
Subacromial ( subdeltoid) bursae = just above supraspinatus muscle and beneath deltoid. Does not communicate with joint cavity.

Shoulder dislocation:

Dislocation: joint injury in which ends of bones are forced from normal positions.

Shoulder dislocation = humeral head forced from normal position in glenoid cavity of scapula.

Shoulder integrity maintained by: glenohumeral joint capsule, cartilaginous glenoid labium, rotator cuff muscles.

Most commonly dislocated joint. Most of the time (95%) it is dislocated in an anterior direction. Very rarely dislocated to superior / intrathoracic directions.

Shoulder separation: AC separation

When acromioclavicular joint separates.

6 types, most are in first 3 types.

Type I = strain of supporting ligaments without tearing
Type II = partial tearing of supporting ligaments
Type III = complete tearing of supportive ligaments

Treat with a sling and restrict activity for long recovery. Surgery not used often.

Shoulder joint replacement: not as common as knee or hip.Used to treat severe shoulder problems / painful conditions: arthritis, rotator cuff damage, avascular necrosis.

Muscles of shoulder girdle: both extrinsic and intrinsic

Extrinsic: pectoral muscles, serratus anterior plus those extrinsic back muscles that move upper limb.

Intrinsic: aka scapular = those muscles of the rotator cuff + Deltoid / teres major. Start on scapula and go to upper limb.

Spaces:

Triangular space = formed by teres minor, teres major , triceps which create boundaries.
on other side of long head of triceps: 4 sided Quadrangular space. Borders by teres minor / major, triceps, humerus. These two spaces are separted by the long head of the triceps.
Triangular interval: another triangular shape space related to teres major, long head of triceps, shaft of humerus. This is not an actual anatomical entity, but has important associations.

Movements:

Scapular movements

When reach forward = abduction / protraction.
Pulling shoulder blade back toward midline = adduction / retraction.
Elevation / depression = by levator scapula.
Upward / downward rotation = based on which way glenoid fossa is facing.

Glenohumeral movements:

Flexion / extension
Abduction / adduction = Jumping jacks
Medial rotation = lateral rotation (serving plates)
Circumduction = wind up.

Extrinsic muscles:

Anterior view = Pectoralis major (2 heads = clavicular / sternocostal), serratus anterior, pectoralis minor.

Pectoralis major: two heads attach at their sitesà inserts humerus at lateral lip of the bicepetal groove. Function = adduction of humerus and medial rotation of humerus. Innervated by medial and lateral pectoral nerves.
Pectoralis minor: origin from ribs 3,4,5 and inserts at corocoid process. Innervated mostly by medial pectoral nerve and some by lateral pectoral nerve. Function is to stabilize scapula.
Subclavius: anchors and depresses the clavicle. Innervated by nerve to subclavius.
Serratus anterior: origin is upper 8 ribs. Inserts on medial border of scapula. Innervated by long thoracic nerve. Function is to protract scapula and rotate scapula to orient the glenoid cavity upward. Holds scapula against thorax.

Winging of scapula: due to long thoracic nerve palsy. Medial borders of scapula are not held to thoracic wall.

Infraclavicular injury = surgical dissections in axilla, direct injury, incidence as high as 30% are from removing breast tissue during massectomy.
Supraclavicular injury = nerve compression as it passes through middle scalene muscle. More common in athletics.

Posterior extrinsic muscles:

Trapezius: upper, lower, and middle fibers. Upper fibers elevate the lateral end of scapula. Lower fibers will depress it. the middle fibers along with others will retract scapula. For upward rotation of glenoid fossa (along with serratus anterior). Innervated by Accessory nerve (CN XI). This cranial nerve is different in that the cell bodies are in the upper cervicle spinal cord. The nerve then goes up in to the skull and then come out again. Nerves for proprioreception emerge from C3-4.
Latissimus dorsi: innervated by thoracodorsal nerve. Origin = spinous processes, iliac crest and inserts at bicepetal groove. Involved with extension of arm, helps with adduction, medial rotation.
Levator scapulae. Innervated by dorsal scapular nerve. Rotates glenoid cavity downward.
Rhomboid major / minor. Innervated by dorsal scapular nerve also. Functions for downward rotation and retraction.

Intrinsic shoulder muscles:

Rotator cuff:

Supraspinatus. Nerve = suprascapular nerve. Attaches greater tubercle of humerus. Initiates the abduction of the arm.
Infraspinatus. Nerve = suprascapular nerve. Also attaches greater tubercle. Contributes to lateral rotation.
Teres minor. Nerve = axillary nerve. Origin = lateral border of scapula, attaches to greater tubercle. Lateral rotation.
Subscapularis. Nerve = subscapular nerve. anterior aspect. Origin = subscapular fossa, attaches lesser tubercle. Medially rotates.

All of these hold the head of the humerus in place.

Teres major: adduction of humerus. Innervated by lower subscapular nerve.

Deltoid: innervated by axillary nerve. Involved in abduction of the humerus (all 3 parts of deltoid – anterior / medial / posterior). Anterior part = medial rotation. Posterior part = lateral rotation.

Biceps brachii: musculocutaneous nerve. 2 heads. The short head takes origin from the coracoid process. Long head attaches supraglenoid tubercle. Passes under the transverse humoral ligament. Weak flexor of the glenohumeral joint. Stabilizes the capsule / joint. Goes through capsule to get to joint.

Coracobrachalis: musculocutaneous nerve. Weak flexor and adductor of glenohumeral joint. Origin = coracoid process and inserts on shaft of humerus.

Triceps: extends the elbow. 3 heads. By Radial nerve. Long head = extension of the humerus, attaches tubercle in scapula. Lateral head = adduction.

Long heads / Short heads: Refers to length of tendons.

Scapular rotation with humeral abduction:

0-30 Degrees: by supraspinatus acting at glenohumeral joint. No scapula rotaton.
30-120 Degrees: supraspinatus acts with deltoid continue abduction. Scapular rotation by trapezius and serratus anterior. Glenoid fossa faces upward.
Over 120 Degrees: humerus hits the lateral edge of the acromion and prevents further abduction, now only scapular rotation is occurring until straight up via trapezius and serratus anterior.