Forearm

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Forearm
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Julius II
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Forearm

• The role of forearm movement is to assist the
  shoulder in the application of force and in
  controlling the placement of the hand in space.
  To allow the free manipulation of the hand the
  bulk of the forearm musculature is located
  proximally with long tendonous insertions on the
  distal bony structures.

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Muscles of the forearm

• From a functional perspective the forearm
  includes the distal humerus.
• The structures of the forearm are divided into an
  anterior and posterior compartment.
• Flexors and pronators are located in the anterior
  compartment supplied by the median nerve except
  for 11/2 exceptions which are supplied by the
  ulnar nerve. There is one other big exception
  (the brachioradialis is a forearm flexor located
  in the posterior compartment and supplied by the
  radial nerve).
• Extensors and supinators are located in the
  posterior compartment and all supplied by the
  radial nerve.

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Muscles of the forearm
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Antebeachial Fascia

• The musculature of the forearm is invested in
  fascial layers that divide the forearm into
  functional units. This fascia also forms
  structures that assist in muscular function
• Palmar aponeurosis
• Palmar carpal ligament
• Flexor retinaculum (transverse carpal ligament
  (the carpal tunnel))

Fig 6.39 p 798
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Flexor-Pronator Muscles

• The tendons of most flexors pass across the
  anterior surface of the wrist and are held in
  place by the palmar carpal ligament and the
  flexor retinaculum (transverse carpal ligament).

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Flexor-Pronator Muscles

• The flexors can be categorized into three groups
• Superficial layer
• Pronator teres
• Flexor carpi radialis
• Palmaris longus
• Flexor carpi ulnaris
• Brachioradialis
• All are attached proximally by the Common flexor
  tendon to the medial epicondyle (common flexor
  origin)
• 2. Intermediate layer Flexor digitorum
  superficialis
• 3. Deep group
• Flexor digitorum profundus
• Flexor pollicis longus
• Pronator quadratus
• Superficial and intermediate groups cross the
  elbow joint, the deep doesnt

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Muscles of the Anterior Compartment of the Arm

• Table 6.7 p 804

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Superficial layer Pronator teres

• O- 2 heads
• Humeral head from the medial supracondylar
  ridge common flexor tendon, the intermuscular
  septum and antebrachial fascia
• Ulnar head from the medial side of the coronoid
  process.
• I midway on the lateral surface of the radius
• Innervation median nerve
• Action rotates the radius on the ulna and helps
  flex the forearm, used for quick powerful
  pronation

• Table 6.7 p 804

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Superficial layer Flexor carpi radialis

• O medial epicondyle of humerus and antebrachial
  fascia
• I base of 2nd 3rd metacarpal bones
• Innervation Median nerve
• Action flexes hand at the wrist, aids in wrist
  abduction
• The radial artery pulse may be palpated just
  lateral to the tendon

• Table 6.7 p 804

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Superficial layer Palmaris longus

• O medial epicondyle of humerus by the common
  flexor tendon and antebrachial fascia
• I- Anterior aspect of the distal flexor
  retinaculum and palmer aponeurosis
• Innervation Median
• Action flexes hand at wrist and tightens
  aponeurosis
• Absent in 10, in animals this muscle operates
  the claws!

• Table 6.7 p 804

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Superficial layer Flexor carpi ulnaris

• O 2 heads
• Humeral head from medial epicondyle of humerus by
  the common flexor tendon
• Ulnar head from the medial margin of the
  olecranon and posterior border of the ulna
• I into the pisiform bone with an extension that
  attaches to the hamate hook and 5th metacarpal
  base.
• Innervation Ulnar
• Action flexes adducts hand at the wrist
• The ulnar nerve runs between the two heads as it
  moves distally. Compression at the wrist results
  in cubital tunnel syndrome. Works with the
  extensor carpi ulnaris to adduct the hand.

• Table 6.7 p 804

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The exception forearm muscle Brachioradialis

• An exceptional muscle because it violates the
  rules, technically located in the posterior
  compartment of the UE it is innervated by the
  radial but it is a forearm flexor (and quite a
  good one at that)
• O proximal 2/3rds of the lateral supracondylar
  ridge and the intermuscular septum
• I Lateral aspect of the distal radius proximal
  to the styloid process.
• Innervation Radial nerve before it divides into
  deep superficial
• Action Accessory flexor of the forearm,
  functions best when the forearm is at
  midpronation, testing causes the muscle body to
  become prominent.

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Intermediate layer Flexor digitorum superficialis

• O 2 heads
• Humeroulnar head from the medial epicondyle, the
  ulnar collateral ligament and coranoid process of
  the ulna.
• Radial head arises from the superior half of the
  anterior aspect of the radius
• I 4 tendons of insertion attach to the middle
  phalanges of the medial 4 digits.
• Innervation Median nerve
• Action flexes the proximal interphalangeal
  joints (PIP), contributes to the flexion of all
  the joints it crosses.
• At the bases of the proximal phalanges each
  tendon splits to allow the profunda tendon to
  pass through to the distal phalanx. Both sets of
  tendons share a common synovial sheath

• Table 6.7 p 804

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Deep group Flexor digitorum profundus

• O From the proximal 3/4ths of the medial and
  anterior aspects of the ulna and interosseous
  membrane
• I 4 tendons attach to the base of the distal
  phalanges of the medial 4 digits
• Innervation
• Medial ½ - Ulnar
• Lateral ½ Anterior interosseous branch of the
  Median nerve
• Action Flexion of the DIP, also assist in
  flexion of the joints its tendons cross.

• Table 6.7 p 804

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Deep GroupFlexor pollicis longus

• O Anterior aspect of the radius and adjacent
  interosseous membrane
• I Base of the distal phalanx of the thumb.
• Innervation Median
• Action Flexion of the DIP joint also flexes the
  PIP of the thumb

• Table 6.7 p 804

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Deep GroupPronator quadratus

• O Arises from the medial aspect of the anterior
  surface of the distal 1/4th of the ulna.
• I Distal 1/4th of the lateral border and
  anterior surface of the radius
• Innervation Median nerve
• Action Pronates the hand, is assisted by the
  pronator teres when power and speed are needed.

• Table 6.7 p 804

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FDS FDP

• Long flexors of the digits also flex the
  metacarpophalangeal and wrist joints.
• FDP slowly flexes the fingers FDS is recruited
  when speed and flexion against resistance are
  needed.
• Wrist flexion mechanically decreases the power
  generated by the FDP FDS, grip strength is
  increased with the wrist in a neutral position.
• The FDS flexes the middle phalanges, FDP flexes
  the distal phalanges.
• Pronator quadratus is the prime pronator assisted
  by the pronator teres the quadratus also plays a
  role in holding the radius ulna together

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The End
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Extensor Muscles
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