This section describes the shoulder and brachial plexus and their structures.

Shoulder Anatomy

• Referred to as the shoulder or pectoral girdle consisting of articulations between the clavicle, scapula, and proximal end of humerus

• Sternoclavicular articulation is the only bony link between the upper limb and the axial skeleton

• This joint helps provide static stability to upper limb reducing the need to use muscle energy to keep upper limb in its proper alignment

• This joint has the greatest range of motion of any joint in the body

• Mobility of the shoulder joint is necessary for the hand to maximize manipulation

Shoulder Layers

• BONES are the deepest layer

• JOINTS are the next layer

• LIGAMENTS follow

• MUSCLES/TENDONS are next with deltoid muscle being outer most

• ARTERIES/VEINS/NERVES throughout the shoulder

• The bones of the shoulder are held in place by muscles, tendons, and ligaments.

• Tendons are tough cords of tissue that attach the shoulder muscles to bone and assist the muscles in moving the shoulder.

• Ligaments attach shoulder bones to each other, providing stability.

Shoulder Girdle Components

• 3 Bones

• Clavicle

  • An “S” shaped bone located between the sternum and the scapula

  • It articulates medially with the manubrium of the sternum and laterally with the acromion process (roof of shoulder) of scapula

  • It forms a strut that supports the upper limb

  • It is frequently fractured and also called the collarbone

  • It is the first bone to begin ossification during development (bone formation)

  • Structures included are sternal extremity(proximal end of clavicle) and acromial extremity (lateral end of clavicle)

• Scapula

  • Is a bone of the shoulder also called shoulder blade

  • It floats in a sea of muscles and is difficult to fracture

  • It articulates with only one – the clavicle

  • There are many borders and angles that come off of the scapula but ones to remember are the following

  • Spine : posterior surface of scapula, flat and runs medial to the acromion

  • Glenoid Cavity : articulates with head of the humerus

  • Scapular Notch : is a notch on the superior border of the scapula attached to the coracoid process

  • Coracoid Process : beak like process that is the attachment site for 3 muscles and 2 ligaments

  • Acromion : A broad, flat process that articulates with the clavicle through a synovial joint

• Humerus

  • Is a bone of the arm

  • It articulates proximally with the scapula at the glenoid fossa and distally with the radius and ulna at the elbow joint

  • The head of the humerus is the smooth rounded proximal end of ulna that articulates with the glenoid cavity of the scapula to form the shoulder joint

  • The “Upper Extremity” section will discuss the humerus in more detail

http://www.kylepalmermd.com/shoulder/shoulder-full-04.htm

• 4 Articulations

  •  

  Acromioclavicular Joint

  • planar, synovial type joint between lateral portion of the clavicle and the acronium of the scapula

• Sternoclavicular Joint

  • synovial joint that connects the clavicle with the sternum

  • this joint has the range of motion, but not the form, of a ball and socket

• Glenohumeral Joint

  • ball and socket articulation between head of humerus and glenoid cavity (shoulder joint)

  • favors mobility over stability

  • depends on muscle rather than ligament for support

• Scapulothoracic Joint

  • scapula is suspended on rib cage by muscles and is highly mobile

  • scapula movements increases range of motion at the shoulder joint

  • not a true joint , but functions as a apart of the shoulder complex

  • also called scapulocostal joint

http://www.kylepalmermd.com/shoulder/shoulder-full-04.htm	http://www.jointinjury.com/shoulder/page1.htm

• 7 Ligaments

  • annular ligament : the ligament that encircles the head of the radius

  • coracoacromial ligament : the ligament that connects the coracoid process to the acromion of the scapula

  • coracoclavicular ligament : the ligament that connects the upper surface of the coracoid process to the under surface of the clavicle

  • costoclavicular ligament : a ligament that attaches the clavicle to the first rib

  • glenohumeral ligament : a ligament reinforcing the anterior wall of the capsule of the glenohumeral joint

  • interclavicular ligament : a ligament that reinforces the capsule of the sternoclavicular joint

  • sternoclavicular ligament : a ligament that reinforces the capsule of the sternoclavicular joint

The shoulder ligaments secure the joints of the shoulder. Ligaments connect bone to bone. Gives static stability and strength. Ligaments keep the joint within the normal limits of movement. The joint capsule is made by a group of ligaments that connect the humerus to the socket of the shoulder joint on the scapula
	http://www.extremities.org/patient_info/ shoulder.html

• 6 Extrinsic Muscles

  • Trapezius

    • elevates and depresses the scapula

    • rotates the scapula superiorly and retracts scapula

  • Levator Scapula

    • elevates the scapula

  • Rhomboid Major and Minor

    • retracts, elevates and rotates the scapula inferiorly

  • Serratus Anterior

    • draws the scapula forward

  • Pectoralis Minor

    • draws the scapula forward, medialward, and downward

  • Pectoralis Major

    • flexes and adducts the arm, medially rotates the arm

    • attaches trunk to humerus

http://www.jointinjury.com/shoulder/page4.htm

• Main Artery (Axillary = continuation of the subclavian to the brachial) see upper limb anatomy
• Bursa

A bursa is simply a closed space between two moving surfaces that has a small amount of lubricating fluid inside. Bursae are everywhere in the body. They occur wherever two body parts move against one another (and there is no joint to reduce the friction). Sandwiched between the rotator cuff muscle layer and the outer layer of large bulky muscles is a structure known as a bursa

• 2 Cartilages
  • Articular cartilage is the shiny white coating that covers the end of the humeral head and lines the inside surface of the glenoid. It has two purposes:
    • To provide a smooth, slick surface for easy movement
    • To be a shock absorber and protect the underlying bone
  • Fibrocartilage is the thick tissue that forms the disks of the AC and SC joints and the labrum, the ring that deepens the glenoid. Fibrocartilage has three roles:
    • To act as a cushion in shock absorption
    • To help stabilize the joint by improving the fit of the bones
    • To act as a spacer and improve contact between the articular cartilage surfaces

Brachial Plexus Anatomy

http://bms.leeds.ac.uk/humb3170/group_cweb/plexus.html

• The plexus is responsible for the motor innervations to all of the muscles of the upper limb with the exception of the trapezius and levator scapula

• It supplies all of the cutaneous innervations of the upper limb with the exception of the area of the axilla (armpit) (supplied by the intercostobrachial nerve), an area just above the point of the shoulder (supplied by supraclavicular nerves) and the dorsal scapular area which is supplied by cutaneous branches of dorsal rami.

• Brachial plexus is a somatic nerve plexus formed by intercommunications among the ventral rami of the lower four cervical nerves (C 5 - C 8) and the first thoracic nerve (T 1).

• Communicates with the sympathetic trunk by gray rami communicates that join all the roots of the plexus and are derived from the middle and inferior cervical sympathetic ganglia and the first thoracic sympathetic ganglion.

• The brachial plexus consists of successively

  1. ventral rami & trunks - in the neck

  2. divisions – usually posterior (deep) to the clavicle

  3. cords & branches – in the axilla

• Prefixed & Postfixed Brachial Plexus

  • Prefixed:

    • Occurs when the C4 ventral ramus contributes to the brachial plexus

    • Contributions from the plexus usually come from C4-C8

  • Postfixed:

    • Occurs when the T2 ventral ramus contributes to the brachial plexus

    • Contributions to the plexus usually come from C6-T2

• Segments of the brachial plexus (Mnemonic: Robert Taylor Drinks Cold Beer=Roots, Trunks, Divisions, Cords, Branches )

  • Roots

    • The ventral rami of the spinal nerves C5-T1 are referred to as the roots of the plexus

  • Trunks

Shortly after emerging from the intervertebral foramina, these 5 roots unite to form three trunks. The ventral rami of C5 & C6 unite to form the Upper Trunk. The ventral ramus of C 7 continues as the Middle Trunk. The ventral rami of C 8 & T 1 unite to form the Lower Trunk
	http://bms.leeds.ac.uk/humb3170/ group_bweb/Hannahframes.html

• Divisions

  • Each trunk splits into an anterior division and a posterior division.

  • The anterior divisions usually supply flexor muscles

  • The posterior divisions usually supply extensor muscles

• Cords

  • The anterior divisions of the upper and middle trunks unite to form the lateral cord.

  • The anterior division of the lower trunk forms the medial cord.

  • All 3 posterior divisions from each of the 3 cords all unite to form the posterior cord.

  • The cords are named according to their position relative to the axillary artery.

• Branches

  • Musculocutaneous

    • Derived from the lateral cord

    • Runs superficially (near the skin) down the front of the arm.

    • Muscle innervations = C5-7

    • Supplies the muscles which flex (bend) the arm at the elbow joint

    • Damage = weak flexion of elbow ( Bicep + Brachialis)

    • Sensory innervations = from the lateral (radial) side of the forearm

    • Damage = paraesthesia to lateral forearm

  • Ulnar

• Median

  • Derived from both the lateral and medial cords

  • Motor innervations are to most of the flexors muscles in the forearm and intrinsic muscles of the thumb

    • Motor damage can result in not being able to make OK sign with fingers and inability to oppose thumb and 5 th digits

  • Sensory innervations are from the lateral (radial) 3 & 1/2 digits ( the thumb and first 2 and 1/2 fingers)

    • Sensory damage decreases sensation on palm surface of thumb and first 3 ½ digits

    • Carpal tunnel syndrome usually presents with pain associated with wrist flexion/ extension (narrowing of carpal tunnel) and intermittent numbness

  • The median nerve is often injured by deep cuts in the forearm.

• Axillary

  • Derived from the posterior cord, nerve segment (C 5,6 )

  • Motor innervations are deltoid and teres minor muscles that act on the shoulder joint

  • Sensory innervations and deficits are just below the point of the shoulder

  • Leaves the axilla (armpit) and runs to the inferior (underside) of the shoulder joint

  • Supplies: shoulder joint, deltoid muscle, teres minor muscle, and skin to outer part of shoulder down to middle part of the arm

  • This nerve is also called circumflex nerve because it surrounds the Humerus surgical neck.

  • Motor damage can result from shoulder abduction > 90 degrees for long period of time, position with caution

• Radial

Derived from the posterior cord and nerve segment (C5-T1) § Called “Great Extensor Nerve” Sensory innervations are on the posterior forearm and dorsum of hand Supplies: all the extensors, supinator muscle, skin of posterior arm and hand, lateral hand and thumb Motor a high radial nerve injury above the elbow => cannot extend the wrist (wrist drop), thumb (hitchhike), upper arm (tricep damage) Sensory low radial nerve injury at the level of the lower forearm => no loss of motor function + only loss of sensory function

http://mywebpages.comcast.net/ wnor/clinicalconsiderations.htm

Spinal Cord to their Muscles (Anterior View)

( Posterior View)

http://www.pediatric-orthopedics.com/Treatments/Brachial_Plexus/BrachialLink/brachiallink.html

Distribution of Roots

• Spinal Segment

  • Region of spinal cord giving origin to a specific spinal nerve

• Dermatome

  • Region on the surface of the skin from which sensation is carried by cutaneous branches of a single spinal nerve

• Myotome

  • Those muscles receiving innervation from axons derived from a single spinal nerve &/or the ventral ramus of a spinal nerve

    • Predominant spinal nerve determines myotome segment

      • Anterior Compartment of the Arm: C5-6

      • Anterior Compartment of the Forearm:

        • Superficial Group: C7

        • Deep Group: C8-T1

      • Hand Muscles: C8-T1

      • Posterior Compartment of Arm: C6-7

      • Posterior Compartment of Forearm: C7-8

• Segmental Innervation

  • ventral rami of spinal nerves are distributed to the various dermatomes and myotomes of a given region such as the upper limb

Basic Study Questions

  1.  Which joint has the greatest range of motion of any joint in the body?

  2.  Identify the bones of the shoulder girdle.

  3.  What is a bursa?

  4.  What is the rotator cuff?

  5.  Which 5 spinal nerves comprise the brachial plexus?

Additional Study Questions