Upper Limb Anatomy Notes Pdf

[Blanchefle Strycker]

Theshoulder is structurally and functionally complex as it is one of the most freely moveable areas in the human body due to the articulation at the glenohumeral joint. It contains the shoulder girdle, which connects the upper limb to the axial skeleton via the sternoclavicular joint. The high range of motion of the shoulder comes at the expense of decreased stability of the joint, and it is prone to dislocation and injury.

The shoulder girdle is composed of the clavicle and the scapula, which articulates with the proximal humerus of the upper limb. Four joints are present in the shoulder: the sternoclavicular (SC), acromioclavicular (AC), and scapulothoracic joints, and glenohumeral joint.

The sternoclavicular joint is a synovial saddle joint and is the only joint that connects the upper limb to the axial skeleton. It connects the clavicle to the manubrium of the sternum and gets stabilization from the costoclavicular ligament. The acromioclavicular joint is a plane synovial joint that connects the acromion of the scapula to the clavicle. It receives stabilization primarily from the coracoclavicular ligament, and secondary stabilizers are super and inferior acromioclavicular ligaments. The scapulothoracic joint is not a true joint, but rather the articulation of the scapula gliding over the posterior thoracic cage.

The glenohumeral joint is a highly moveable ball-and-socket synovial joint that is stabilized by the rotator cuff muscles that attach to the joint capsule, as well as the tendons of the biceps and triceps brachii. The humeral head articulates with the glenoid fossa of the scapula. It is a shallow articulation, as the fossa accommodates less than one-third of the humeral head. The labrum, a fibrocartilaginous ring, attaches to the outer rim of the glenoid fossa and provides additional depth and stability securing the humeral head. A small number of fluid-filled sacs known as bursae surround the capsule and aid in mobility. These are the subacromial, subdeltoid, subscapular, and subcoracoid bursae.

All elements of the human body arise from the three primary germ layers in the young embryo: the ectoderm, endoderm, and mesoderm. Cartilage, bone (and marrow), muscles and ligaments, and connective tissue all arise from the mesoderm, which lies between the ectoderm and endoderm.

The axillary artery is the major blood vessel in the shoulder, with many of its branches supplying the area. These branches include the superior thoracic artery, thoracoacromial artery, lateral thoracic artery, subscapular artery, anterior humeral circumflex artery, and posterior humeral circumflex artery. Before becoming the axillary artery, after passing beyond the lateral edge of the first rib, the subclavian artery also includes branches that supply the area of the shoulder. The thyrocervical trunk off of the subclavian artery adds the suprascapular artery and the transverse cervical artery. The dorsal scapular artery most often branches off of the subclavian, but may sometimes branch off the transverse cervical artery.

As it contains the most mobile joint in the body, the shoulder is very susceptible to injury. Surgical interventions may be required to repair or replace bones, joints, or tendons. Techniques used include arthroscopy, total arthroplasty, and shaving down bone in cases of impingement.

Shoulder pain affects approximately 18 million Americans a year, most of which are a result of rotator cuff tears. Tears can occur from a mix of trauma, overuse, or age-related degeneration and can be asymptomatic or cause severe pain and decreased mobility. Research has shown that smoking, hypercholesterolemia, and family history all predispose to tears. Even with small full-thickness tears, conservative, non-surgical treatment is the first line and may be effective. When it is not, or with larger full-thickness tears, surgical repair is a reliable fix. Rotator cuff tendonitis/impingement presents with pain during overhead activities and results from the tendon of the supraspinatus muscle being pinched down by the acromion in most cases, which can cause inflammation around the tendon and in the fluid-filled bursae surrounding it.

The price of being the most mobile joint in the body is that the glenohumeral joint lacks stability and is subject to dislocation. Anterior dislocations are the most common as they make up 97% of all dislocations. The typical cause by a blow to an abducted, externally rotated and extended extremity. Anterior dislocation may damage the axillary nerve, causing paralysis of the deltoid and decreased cutaneous sensation over the shoulder, as well as ligament tears and fractures. Patients usually recover functionality of the axillary nerve with a reduction of the humeral head back into the glenoid fossa. Posterior dislocations are less frequent but are associated with seizures. There is more risk of rotator cuff and ligament tears with posterior dislocations than anterior. Inferior dislocations are very rare and are the result of hyperabduction. They have the highest incidence of axillary nerve and artery damage.

Adhesive capsulitis also called frozen shoulder, occurs in 2 to 5% of the population, with most patients being females and over the age of 55. The thinking is that inflammation in the area of the shoulder capsule causes initial pain as well as capsular fibrosis and adhesions that lead to a decreased range of motion in all planes. There is a strong association of adhesive capsulitis with endocrine disorders like diabetes and hypothyroidism. Treatment is conservative, with most cases resolving spontaneously. Surgical intervention is reserved for refractory cases and involves releasing the fibrotic capsule.

Like other joints with extensive use, the shoulder joint is susceptible to wear and tear degeneration of the articular cartilage within the joint. Age, female gender, obesity, anatomical factors, muscle weakness, and joint injury are predisposing factors to the development of osteoarthritis. Bone-on-bone friction causes moderate to severe pain in patients. Treatment is usually conservative, with NSAIDs being the first-line choice. Refractory osteoarthritis may need intra-articular corticosteroid injections to decrease the inflammation. Surgical intervention in the form of arthroplasty is reserved for severe cases in which pharmacotherapy is not relieving symptoms.

The upper extremity or arm is a functional unit of the upper body. It consists of three sections, the upper arm, forearm, and hand. It extends from the shoulder joint to the fingers and contains 30 bones. It also consists of many nerves, blood vessels (arteries and veins), and muscles. The nerves of the arm are supplied by one of the two major nerve plexus of the human body, the brachial plexus.

The upper extremity begins at the shoulder joint. This joint is commonly referred to as a ball-and-socket joint, although it is more correctly described as a ball-and-saucer joint. In contrast to the hip, the other ball-and-socket joint of the body, the socket is much shallower. This allows for less restriction of movement at the joint but compromises stability in the process. The elbow joint is referred to by many as a hinge joint. This is partially true but does not explain the ability to pronate and supinate the forearm at the elbow joint. The articulation of the radial head and the radial notch on the ulna allows for this motion. This creates what is called a "pivot" joint, allowing the movement of one bone on another. The wrist joint can be classified as an ellipsoidal or condyloid joint. There are also joints of the carpal bones, which are referred to as intercarpal joints. Even though they are synovial joints, they do not allow much movement. The interphalangeal joints are basic hinge joints.[1][2][3]

During the third week of development, the trilaminar embryonic disc is formed. Three layers, the endoderm, mesoderm, and ectoderm, are differentiated. The notochord is formed from mesoderm, and the overlying ectoderm becomes the neural plate. During the fourth week, the upper and lower limb buds begin to form. Muscle, bone, blood vessels, and lymphatics are all formed from the mesoderm, while the peripheral nerves are differentiated neural crest cells.

Thirty bones in total make up the structure of the upper extremity. They act as a framework for the muscle, blood vessels, nerves and lymphatics to work upon. There is one bone in the upper arm region, the humerus. The forearm contains two bones, the radius and the ulna. When picturing the upper extremity in a standard anatomical position with the palm of the hand facing forward, the radius is located laterally and the ulna medially. However, because the forearm allows rotation around a central axis, the terms radial and ulnar provide a better description when describing direction or location in the forearm, wrist, and hand. The wrist and hand contain 27 bones. There are eight carpal bones, organized into a proximal and distal row. The proximal bones, from radial (thumb side) to ulnar are the scaphoid (navicular), lunate, triquetrum, and pisiform. From radial to ulnar, the distal row consists of the trapezium, trapezoid, capitate, and hamate. There are five metacarpal bones, each associated with a group of phalanges. There are also 14 phalanx bones. Fingers two to five have a proximal, intermediate, and distal phalanx, while the thumb has only a proximal and distal phalanx. Although many bony injuries can result, the most clinically significant are injuries to the humerus and scaphoid bones. Injuries at the neck of the humerus can result in axillary nerve injury. Midshaft fractures will damage the radial nerve, and supracondylar fractures can damage the median nerve (a common mnemonic is "ARM"). Another common clinical pathology is an injury to the scaphoid. Not only is it the most commonly injured carpal bone, but it also is a common site of avascular necrosis due to its retrograde blood supply. This commonly occurs in fall on an outstretched hand (FOOSH) injuries.

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