Make sure you study and learn the origins, insertions, actions and innervation of all muscles discussed in this lecture (see appendix).

I. Bony structures

The forearm, also referred as antebrachium, is the portion of the upper exrtemity found between the elbow and the wrist. It contains two bones: laterally, the radius and medially, the ulna.

1.1 The radius (Netter 409)
The radius has a upper end, consisting of the head, neck and tuberosity,  articulating with the capitulum of the humerus and the upper end of the ulna. The lower end articulates with the scaphoid and lunate bones at the wrist (see later). The shaft of the humerus is narrow at the head and wide at the lower end. It has a sharp interosseous border on its medial aspect for the attachment of the interosseous membrane. The anterior oblique line extends from radial tuberosity to the pronator tubercle (mid shaft, lateral aspect). The distal end of the radius has a styloid process on its lateral margin. On the medial surface of the lower radial end is the ulnar notch where the head of the ulna articulates with the radius. The posterior aspect of the lower end presents a dorsal tubercle, grooved medially by tendon of the extensor pollicis longus and medially by the tendons of the extensor carpi radialis and brevis.

1.2 The ulna (Netter 409)
The ulna articulates with the humerus and the radius superiorly, and the radius inferiorly. It is separated from the bones of the wrist by an articluar disc. The upper end has two processes: the the olecranon and the coronoid.  The shaft of the ulna has a sharp lateral border for the attachment of the interosseous membrane.  The lower end also has a styloid process (medial aspect).

II. Superficial structures.


2.1 The cutaneous innervation of the forearm is derived from branches of the brachial plexus (Netter 450):
- lateral cutaneous nerve of the forearm (C5 C6 C7, a branch of the musculocutaneous n.) innervates the posterior and anterior lateral aspect of the forearm
- medial cutaneous nerve of the forearm ( C8 T1) supplies the skin of the anteriomedial  and posteromedial forearm
- posterior cutaneous nerve of the forearm  (C5 C6 C7, a branch of the radial  n.) supplies a narrow band of skin on the posterior aspect of the forearm

2.2 The superficial veins (Netter 449) lie in the superficial fascia:
- the basilic vein arises from the medial side of the dorsal arch on the posterior aspect of the hand, winds around the anterior aspect of the mid forearm, continue on the medial aspect of the cubital fossa and up on the medial side of the biceps brachii
- the cephalic vein arises from the lateral side of the dorsal arch on the posterior aspect of the hand, appears anteriorly at the mid forearm, continues on the lateral aspect of the cubital fossa and up to the lateral side of the arm
- the median cubital vein (Netter 448), when present,  is found on the upper aspect of the forearm, over the cubital fossa. It links the cephalic vein to the basilic vein. It is the site of choice for venipuncture. The median cubital vein is superficial to the brachial artery and the medial nerve. It is separated from these structures by the bicipital aponeurosis.

2.3. Superficial lymph vessels (Netter 448)
The lateral forearm drains through the lymph vessels to the infraclavicular nodes, following the path of the cephalic vein. The medial forearm drains through the lymph vessels to the axillary nodes, following the path of the basilic vein. Note that the deep drainage follows the veins accompanying the arteries of the forearm (radial, ulnar and their branches).

III. Joints and movements of the forearm (Netter 409).



The two movements taking place at the forearm, supination and pronation  have been described with the elbow. The joints involved are:
- the proximal radio-ulnar joint: a synovial uni-axial pivot joint betweeen the head of the radius and the radial notch of the ulna. Note the annular ligament encircling the head of the radius and holding it against the head of the ulna. Another significant ligament is the oblique cord. It is a slender fibrous cord extending from the lateral border of the ulnar tuberosity to the radial shaft distal to the radial tuberosity.  This structure is taut in supination and relaxed in pronation.
- the middle radio-ulnar joint is a syndesmosis type joint. It consists essentially of the interosseous membrane attaching to the shafts of the radius and ulna. This membrane serves as attachment for the muscles of the forearm
- the lower radio-ulnar joint is also a uni-axial pivot joint.   It allows the radius to roll around the distal  end of the ulna during pronation/supination.

IV. Anterior compartment of the forearm (Netter 419).


The forearm is enclosed by the deep fascia of the forearm. This one attaches posteriorly to the subcutaneous border of the ulna. The forearm is divided in 3 compartments (anterior, lateral and posterior)  by the deep fascia, the interosseous membrane and the intermuscular septa .

4.1. The anterior compartment of the forearm (Netter 416)
The anterior compartment can be divided in 3 groups:  superficial, intermediate and deep muscle groups. The muscles of the forearm can also be categorized in 3 functional groups: the pronators of the forearm, the flexors of the wrist and the long flexors of the fingers and thumb.

A. The muscles of the superficial group are (Netter 416) :
- pronator teres m.
- flexor carpi radialis m.
- palmaris longus m.
- flexor carpi ulnaris m.
Note that all the muscles are innervated by the median nerve except the flexor carpi ulnaris (ulnar nerve).

B. The intermediate layer consists of the flexor digitorum superficialis m. innervated also by the median nerve.

C. The muscles of the deep group are (Netter 418):
- flexor pollicis longus
- flexor digitorum profundus
- pronator quadratus
The median nerve (anterior interosseous branch) innervates these 3 muscles, except the medial half of the flexor digitorum profundus (ulnar nerve).

V. Clinical correlations


In the radiology CD, under the upper extremity section, under "bones and joints", click on "ulna"
go to clinical cases and study: forearm fracture and rheumatoid arthritis.
Try to understand how these case relate to the contents of the lecture.

VI. Internet sites


You will not be tested on the contents of this site as this is for illustration only. Please visit the following site: http://www.medmedia.com/orthoo/126.htm
 
VII. Surface anatomy


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

VIII. Computer Software


Please study the laboratory 7 in the human anatomy 2.2 software at:
http://edweb.library.musc.edu/haonline3/labs/l07/lo0000.htm

IX. Conclusion