I . Arm (Netter 448)

Often referred to as the brachium, the arm is the portion of the upper extremity located between the glenohumeral joint and the elbow joint. The information below describes, in detail, both the superficial and deep structures found within the arm

  1.1 Bony structures (Netter 392-393)
 
  1.1.1. In cross-section, the shaft of the humerus is circular superiorly and triangular inferiorly. The radial groove (also called spiral groove) can be observed posteriorly and inferiorly to the deltoid tuberosity. This groove allows passage downward for the radial nerve (between the medial and lateral heads of the triceps brachii).
 
  1.1.1 The distal end of the humerus. Study and identify the following features(Netter 407):
 
Medial and lateral epicondyles
     Coronoid fossa
     Capitulum
     Medial and lateral supracondylar ridges
 
Olecranon fossa
Radial fossa
Trochlea
    1.2. Superficial structures

  1.2.1.  The cutaneous innervation of the arm is derived from branches of the brachial plexus (Netter 450):
 - Supraclavicular nerves (cervical plexus C3 C4): sensory to the upper aspect of the shoulder
 - Superior lateral cutaneous nerve of the arm (C5 C6, a branch of axillary n.): sensory to the lower aspect of the deltoid
 - Inferior lateral cutaneous nerve of the arm (C5 C6, a branch of radial n.): sensory to the lateral aspect of the  arm, inferior to deltoid insertion
 - Medial cutaneous nerve of the arm (T1) and intercostobrachial nerves (T2): sensory in armpit  area as well as the medial arm - Posterior cutaneous nerve of the arm (C5 C6 C7 C8, a branch of the radial n.): sensory to the posterior arm
 
  1.2.2. Superficial veins
- Found in the superficial fascia of the arm (Netter 452)
- Cephalic vein: ascends lateral to biceps muscle up to the infraclavicular fossa where it pierces the clavipectoral fascia and joins the axillary vein.
- Basilic vein: ascends medial to biceps and pierces deep fascia, approximately midway up the arm and travels to the lower border of teres major where it joints the venae commitantes of the brachial artery to form the axillary vein
 
 1.2.3. Superficial lymph vessels
 - Drain superficial tissues of the upper arm into axilla.
 - Lateral arm: lymph vessels follow the cephalic vein to the infraclavicular nodes
 - Medial arm: lymph vessels follow the basilic vein to the lateral axillary nodes
 
  1.3. Compartments of the upper arm (Netter 406)

A sheath of deep fascia, called the brachial fascia, encloses the upper arm. The medial and lateral  intermuscular septae extending from the sheath attach to the medial and lateral supracondylar ridges of the humerus respectively and divide the arm into an anterior and posterior compartment. Each compartment contains its own muscles, nerves, and arterial supply.
 
 1.3.1. Anterior compartment of the arm (Netter 402-442)
 
A.  Muscles of the anterior compartment of the arm
-    Biceps brachii m. (Musculocutaneous n): Consists of a long head and short head.
- Coracobrachialis m.(Musculocutaneous n.)
-       Brachialis m.(Musculocutaneous n.):

B.  Nerve supply of the anterior compartment of the arm
  - Musculocutaneous nerve: from C5 C6 C7,  one of the two terminal branches of the lateral cord from the brachial plexus innervates the     coracobrachialis (pierces it) and the biceps and brachialis muscles
  - Median nerve: from C5 C6 C7, C8, T1, travels lateral to the brachial artery until the
  midpoint of the upper arm where it crosses over the brachial artery and continues its course medial to the artery.
 - Ulnar nerve: from C8 T1,  one of the two terminal branches of the medial cord, travels
  medially to the brachial artery until insertion of the coracobrachialis m. where it pierces the medial fascial septum and enters the posterior compartment of the arm. This nerve travels behind the medial epicondyle of the humerus.
 
C.  Brachial artery (Netter 442)
 
The brachial artery is a continuation of the axillary artery that begins at the lower border of teres major. It is the main supply to the arm and travels through the anterior compartment to the neck of the radius where it divides into the radial and ulnar arteries. Branches of the brachial artery include (Netter 405):
 - muscular branches that supply the anterior compartment,
 - nutrient artery that supplies the humerus
 - the superior and inferior ulnar collateral arteries
 - the radial collateral artery
 - the deep artery of the arm that follows the radial nerve into the spiral groove.
 
  1.3.2. Posterior compartment of the arm

A.  Muscles of the posterior Compartment of the Arm (Netter 403)
   -  Triceps m. (Radial n.): Consists of the long, lateral and medial heads
 
B.  Nerve supply of the posterior compartment of the arm (Netter 446)
 - Radial nerve: originates from the posterior cord of the brachial plexus (from C5C6C7C8T1) and travels in the posterior compartment arm, in the spiral groove of the humerus. As the radial nerve travels in the spiral groove, it is in direct contact with the humerus and is frequently damaged in humeral shaft fractures.
 
C. Arterial supply of the posterior compartment (Netter 405-403)
 - Deep artery of the arm: originates from the brachial artery and enters the posterior compartment to travel with the radial nerve through the spiral groove. It supplies the triceps muscle and provides anastomosis for the elbow joint.

II.  Elbow Joint (Netter 407)


The elbow joint is in fact formed of 3 joints:
- the humero-ulnar joint: a synovial hinge joint between the trochlea of the humerus and the trochlear notch of the ulna (movement only occurs along a transverse axis)
- the humero-radial joint: a synovial hinge joint between the capitulum of the humerus and
the head of the radius (movement only occurs along a transverse axis)
- the radio-ulnar joint: a synovial pivot joint between the head of the radius and the radial
 notch of the ulna (movement only occurs along a longitudinal axis)
 
2.1 The bony structures (Netter 407)
2.1.1. The lower aspect of the humerus has been described with the arm
2.1.2. The upper aspect of the ulna and radius. Please study and identify the following on:
 
A. the radius:
    -head
    -neck
    -tuberosity

B. the ulna:
    -olecranon
    -trochlear notch
    -radial notch of the ulna ulnar tuberosity
    -coronoid process

2.2 Capsule, ligaments, and nerve supply of the elbow joint (Netter 408)
 
2.2.1 Articular capsule
The capsule of the elbow is loose and surrounds the entire elbow complex allowing movement while providing stability. However, because the capsule is thinner posteriorly, most elbow dislocations occur in the posterior direction.
Margins of the capsule: anteriorly, the articular capsule extends from the upper margins of the coronoid and radial fossa of the humerus to the medial and lateral epicondyles of the humerus. It continues downward to attach to the coronoid process of the ulna and annular ligament surrounding the radial head. Posteriorly, the capsule extends from the olecranon fossa of the humerus to the olecranon process of the ulna and annular ligament below.
 
   2.2.2 Ligaments of the elbow

The medial and lateral collateral ligaments may be found surrounding the elbow complex, which provide additional strength and support to the articular capsule.
 
A. Medial (ulnar) collateral ligament: broad and triangular in shape, consisting of three bands
(1)  the anterior band: extends from the medial epicondyle of the humerus to the medial coronoid process,
(2)  the posterior band: extends from the medial epicondyle of the humerus to the medial olecranon
(3)  the transverse band: travels between and connects the ulnar attachments of the anterior and posterior bands.
 
B. Lateral (radial) collateral ligament: More cord-like in appearance, this ligament is found on the lateral aspect of the elbow complex where it extends from its apex, the lateral epicondyle of the humerus, to the annular ligament surrounding the radial head below.
 
   2.2.3.   Nerves Supplying the Elbow Joint:
  Branches of the median, ulnar, musculocutaneous, and radial nerves supply the elbow joint.

  2.3   Movements and muscles of the elbow joint
 
 The  humero-ulnar and humero-radial joints allow for movements flexion and extension. Flexion is normally limited by soft tissue approximation along the anterior surface of the arm and forearm extension is limited by the stretch in the anterior structures, such as brachialis and biceps brachial muscles. The upper radio-ulnar allows for pronation and supination.
 
  2.3.1. Movements at the elbow joint:
 
Movement Degrees
flexion: 140
extension: 0 (anat position)
pronation: ~ 90
supination: ~ 90

 
Note the carrying angle: when extended, the long axis of the forearm lies at a slight lateral angle to the long axis of the arm.  An angle of  about170 in males and 165 degrees in females is considered normal and is termed the "carrying angle".
 
       2.3.2 Muscles acting on the elbow joint:
 
 The muscles producing movements are:
  - Flexion: brachialis, biceps brachial, brachioradialis, pronator teres mm.
  - Extension: triceps and anconeus muscles
  - Pronation: pronator teres m. (pronator quadratus and flexor carpi radialis mm.: see later)
  - Supination: biceps brachii m. (supinator m.: see later)
 
 Note : the anconeus muscle (Netter 414) is a small, triangular muscle that originates from the posterior portion of the lateral epicondyle of the humerus and inserts into the lateral olecranon process of the ulna as well as the articular capsule. This muscle serves to assist the triceps in extending the elbow and to pull the capsule out of joint during extension.

III. Cubital fossa (Netter 416)

 The cubital fossa is a triangular-shaped depression anterior to the elbow.  Due to its contents and location, the cubital fossa is often used as a site for venipuncture.
 
  3.1 Boundaries of the cubital fossa (Netter 416-417)
 The boundaries of the cubital fossa are listed below:
    - Roof is formed by skin and fascia  and reinforced by the bicipital aponeurosis.
    - Floor is formed by the supinator m. laterally and by the brachialis muscle medially.
    - Body is triangular in shape with  the brachioradialis muscle being the lateral border, the pronator teres forming the medial border, and the base formed by an imaginary line between the two epicondyles of the humerus.

  3.2 Contents of the cubital fossa (Netter 418)

  The content of the cubital fossa is listed below from medial to lateral:
     -    Median nerve
     -   The bifurcation of the brachial artery into the ulnar and radial arteries
     -   Tendon of the biceps muscle
     -   Radial nerve and its deep branch
 
 Additional structures located in the cubital fossa are as follows (Netter 448):
       -  The bicipital aponeurosis travels through the cubital fossa to attach to the superficial fascia of the forearm. Sometimes identified as the "Grace of God" tendon, the aponeurosis covers and protects the underlying structures in the cubital fossa
       - The median cubital vein travels upward and medially in the cubital fossa and to connect the cephalic and basilic vein.
       - The lateral and medial antebrachial cutaneous nerves which supply sensory sensation to the lateral and medial forearm respectively
 
 IV. Clinical correlations.



 In the radiology CD, under the upper extremity section, under radiographs, click on "Lateral elbow", go to the clinical cases:
 -  Rheumatoid arthritis
 -  Radial head fracture
 Try to understand how these cases relate to the contents of the lecture.

V. Internet Sites.


 You will not be tested on the contents of the site as this is for illustration only. Please visit the following internet site: http://www.medmedia.com/o2/179.htm. This excellent site with fractures and dislocations of the elbow has a large variety of x-rays.

VI.  Surface Anatomy


 Please study the surface anatomy terms that are relevant to this lecture

VII. Computer Software


 Please study the laboratories 6 and 10 (dissection step 4 for the elbow) in the human anatomy 2.2 software http://edweb.library.musc.edu/haonline3/labs/upperex.htm

VIII. Conclusion.