Anatomy of Forearm & cubital fossa in a Nutshell

Forearm:

Between the ulna and radius = tough membrane called interosseus membrane.  Has gaps:

• Proximal
• Distal

Distal ends of radius / ulna have Styloid processes (like record needle)

Compartments:

• Flexor compartment = Anterior. Has both pronators and flexors. Origin = medial epicondyle of humerus and proximal anterior of radius / ulna.
• Extensor compartment = Posterior. Wrap around slightly to anterior side. Has both supinators and extensors. Origin = lateral epicondyle of humerus and proximal posterior radius / ulna.

Are separated by septum = lateral intermuscular septum.  Also divided by Interosseus membrane.

Muscle details:

Superficial muscles (flexors / pronators) most are innervated by median nerve.

• Pronator teres = from medial epicondyle. Inserts onto the radius. Has 2 heads, one from medial epicondyle and another form the ulna.  Pronates the forearm.  Median nerve passes through this muscle.
• Palmaris longus: takes origin from medial epicondyle→ long tendon that flares out at palm→ inserts into palmar aponeurosis which is a thick fascia in palm of hand. Acts as a flexor of the wrist.
• Flexor carpi radialis and flexor carpi ulnaris: Origin from medial ep. Radialis has attachment on base of 2^nd metacarple. This flexes the wrist and radial deviation (bend to the side , abduction).  Ulnaris has insertion on pisiform carple→ flexes wrist and adduct = ulnar deviation. Ulnaris innervated by ulnar nerve (exception).
• Flexor digitorum superficialis: origin from anterior ulna / radius and medial ep. Passes into hand and puts tendon out on to each finger→ at ends, branch into fork like structures and insert onto middle phalanx on fingers 2-4.  Will flex wrist joint, will flex MP joint, flexes PIP joint.
  

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Deep flexors:  do not attach medial epicondyle, only ulna / radius

• Flexor digitorum profundus: origin = proximal portion of ulna. Sends tendons to same fingers  / joints as flexor digitorum suferficialis.  Flexes wrist, MP, PIP joint and the DIP joint.  That furthest distal joint = at tips of fingers. Lateral half innervated by radial nerve, medial half innervated by ulnar nerve.
• Flexor pollicis longus (pollicis always refers to thumb): origin from ulna / radius→ down to the tip of the thumb→ flexes wrist, MP, IP of thumb. Median nerve.
• Pronator quadratus: Spans distal portion between ulna and radius.  Ulna acts as origin since radius is that bone which moves. Inserts onto distal radius.  Median nerve innervates.

NOTE: for exams→ written portion, watch out for pictures. 85 total questions on lab practical.  25 are histology.  Thus, 60 or so questions are anatomy proportionate to amount of time spent on portion.  Majority are “identify the tagged structure”.  Lesser amount are: what is innervation of this / this nerve has what type of fibers / etc.

Superficial extensors / supinators: all innervated by radial nerve.

• Brachioradialis: Origin from humerus. Tendon inserts radius at the styloid process.  Functions = flex the elbow joint (is an exception).  Also a partial supinator / pronator.
• Extensor carpi radialis longus: Origin from supercondyle ridge, attaches metacarple II.
• Extensor carpi radialis brevis: Origin from lateral epicondyle , inserts onto metacarple III. Both ECR’s extend and abduct = radial deviation.
• Extensor digitorum: From lateral epicondyle. Fairly large. Gives rise to tendons that cross the back of the wrist and go all the way down into the fingers.  As this muscle crosses the wrist, it is held in place by “extensor retinaculum” which is like a bracelet of dense fibrous CT that holds these tendons against the wrist. The tendons themselves stop part way down the fingers but continue as specializations that continue all the way down to finger tips.
• Extensor carpi ulnaris: From lateral epicondyle. Long tendon goes to base of metacarple V (base of little finger). extends the wrist joint and has ulnar deviation.

Deep muscles: Extensors / Supinators:  all innervated by radial nerve.

• Supinator: from lateral epicondyle and ulna→ inserts on radius to allow supination.
• Extensor indicis: origin from ulna→ inserts by long tendon onto tip of index finger.
• Snuff box muscles: common origin from radius / ulna / interosseus membrane. run together but have their own tendons.
  • Abductor pollicis longus = abducts the thumb, insertion on base of metacarple I.
  • Extensor pollicis longus: tendon goes all the way to tip of thumb to distal phalanx. Extensor for all joints in thumb.
  • Extensor pollicis brevis: tendon stops at proximal phalanx of thumb.

Cubital Fossa: riangular shaped area on the front of the elbow.

Boundaries:

• Superior boundary = between condyles
• Medial = Pronator teres
• Lateral = Brachialis
• Floor = Brachialis and supinator muscles.
• Roof = Deep fascia (including bicepital aponeurosis), this is covered by superficial fascia (fat and skin). This is where median cubital vein is found (veinipuncture).

Contents:

1. Biceps tendon
2. Passing deep to bicepital aponeurosis = median nerve and brachial artery. As brachial artery passes into cubital fossa, it branches into ulnar and radial artery branches.
3. Deep paired veins: are also called brachial, ulnar, and radial = associated with arteries.

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