Upper Extremity

Brachial Plexus

The brachial plexus supplies nerve innervation to most of the upper limb.  The roots of the brachial plexus start at C5 and runs through T1.  They pass through the anterior and middle scalene muscles with the subclavian artery.  There are three trunks within the brachial plexus: superior, middle and inferior.  Each trunk emerges into an anterior and posterior division.  All the posterior divisions merge to form the posterior cord.  The anterior divisions of the superior trunk and the middle trunk meet to form the lateral cord and the anterior division of the inferior trunk merge to make the medial cord.  The figure below shows the organization of the brachial plexus from the roots to the cords. 

A neuronal disease associated with the brachial plexus is "acute brachial plexus neuritis".  This disease has no known cause.  Symptoms of brachial plexus neuropathy(BPN) include severe pain around the shoulder that start at night.  This condition typically is followed by weakness in the muscles and sometimes muscle atrophy.  BPN often follows some type of event like upper respiratory infection, vaccination, or non specific trauma.

Axillary Artery

The borders of the axillary artery are the lateral bordero of the first rib and the inferior border of the teres major.  As it passes the pectoralis minor it becomes the brachial artery.  The axillary artery is divided into three parts.  The first part of the axillary artery only has one branch and that is the superior thoracic artery.  The borders of the first part of the artery are the lateral border of the first rib and the medial border of the pectoralis minor.  The second part of the artery has two branches, and those are the thoracoacromial trunk and the Lateral thoracic artery.  The third part of the axillary artery consists of three branches which are the Subscapular artery, Anterior humeral circumflex artery, and the Posterior humeral circumflex artery.  The subscapular artery has two artery branching off of it, and they are the circumflex scapular artery and the thoracodorsal artery. The figure below is a representation of the axillary artery transcending into the brachial artery as it passes the pectoralis minor.


The axillary artery can be palpated on the most inferior part of the axilla. The third part of the axillary artery can be compressed against the humerus as a necessary result of some type of trauma.  If compression is required that is more proximal, the origin can be compressed as the subclavian artery crosses the first rib.  The first part of the axillary artery can enlarge and can result in an axillary artery aneurysm.  An axillary artery aneurysm will compress the trunks of the brachial plexus, and this will cause pain and loss of sensation on certain areas of the skin that the nerves of the brachial plexus innervate.  Aneurysms occur frequently in baseball pitchers because of the rapid movement of the arm.

The acromioclavicular joint is a plane type of synovial joint.  This joint allows the acromion of the scapula to articulate with the acromion of the clavicle.  The joint capsule contains a fibrous layer that is lined with a synovial membrane.  The ligaments of the acromioclavicular joint consist of the acromioclavicular ligament, coracoclavicular ligament (as shown in figure below), conoid ligament and the trapezoid ligament.  Movements of the acromioclavicular joint consists of rotation of the acromion of the scapula on the acromion of the clavicle.  Blood is supplied to the AC joint by the thoracoacromial arteries and innervation sources are the lateral pectoral and axillary nerves.  Shown below are some of the attributes of the acromioclavicular joint. 


The acromioclavicular joint is a joint that can be easily injured if exposed to some type direct trauma.  Oftentimes, the cause of these forceful blows are sports like football, soccer, hockey  or even martial arts.  Dislocation of the acromioclavicular joint is very common due to a hard fall on the shoulder or outstretched upper limb.  A dislocation of the acromioclavicular joint is considered severe when the acromioclavicular ligament and the coracoclavicular ligament are torn . This is due to the separation of the shoulder from the clavicle and the weight of the upper limb falls.