Anterior Forearm Muscles

• Anterior forearm muscles attachment sites, functions, and nerve supply should be identified.
• Structures that form and pass through the carpal tunnel must be labeled.

The Forearm

• The interosseous membrane divides the forearm into 2 muscle compartments.
• Muscles that act on the wrist and hand originate in the proximal forearm to maximize function and minimize bulk

Muscles of the Anterior Forearm

• Muscles of the anterior forearm may be studied in a superficial, middle, and deep layer.
• The superficial muscles consist of:
  • Pronator teres
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor carpi ulnaris
• The middle muscles consist of:
  • Flexor digitorum superficialis
• The deep muscles consist of:
  • Flexor digitorum profundus
  • Flexor pollicis longus
  • Pronator quadratus
• Many of these muscles originate from the medial epicondyle of the Humerus also known as “common flexor origin".

Pronator Teres

• Proximal attachment at the common flexor origin and coronoid process of the ulna
• Distal attachment at the mid-shaft of the radius on the lateral surface
• Innervation via the median nerve
• Action: Forearm pronation, assists with elbow flexion.

Flexor Carpi Radialis

• Proximal attachment at the common flexor origin
• Distal attachment at the base of the 2nd metacarpal
• Innervation via the median nerve
• Action: Wrist flexion and wrist abduction (radial deviation).

Palmaris Longus

• Vestigial muscle, absent on one or both sides in 15% of the population
• Proximal attachment at the common flexor origin
• Distal attachment at the palmar aponeurosis
• Innervation via the median nerve
• Action: Wrist flexion and tenses palmar aponeurosis.

Flexor Carpi Ulnaris

• Proximal attachment at the common flexor origin, olecranon process, and posterior shaft of ulna
• Distal attachment at the pisiform, hook of hamate, and base of 5th metacarpal
• Innervation via the ulnar nerve
• Action: Wrist flexion and wrist adduction (ulnar deviation).

Flexor Digitorum Superficialis

• Proximal attachment at the common flexor origin and shaft of radius
• Distal attachment: Middle phalanges of digits II, III, IV, and V
• Innervation via the median nerve
• Action: Wrist flexion, flexion of all joints in the wrist and hand except the distal interphalangeal joints

Flexor Digitorum Profundus

• Proximal attachment at the interosseous membrane and ulna (does not cross elbow)
• Distal attachment: Distal phalanges of digits II, III, IV, and V
• Innervation:
  • Medial half via the ulnar nerve
  • Lateral half via the median nerve
• Action: Wrist flexion, flexion of all joints in the wrist and hand including the distal interphalangeal joints

Flexor Pollicis Longus

• Proximal attachment: Interosseous membrane and radius (does not cross elbow)
• Distal attachment: Distal phalanx of thumb
• Innervation via the median nerve
• Action: Flexes all joints of the thumb

Pronator Quadratus

• Proximal attachment at the distal surface of ulna
• Distal attachment: Distal surface of radius
• Innervation via the median nerve
• Action: Forearm pronation

Carpal Tunnel

• Recall the concavity of the carpus due to the following bony landmarks:
  • Tubercle of the scaphoid
  • Tubercle of the trapezium
  • Pisiform
  • Hook of hamate
• Flexor retinaculum is a band of connective tissue that attaches to these bony landmarks
• This creates a space deep to the flexor retinaculum called the carpal tunnel

This lesson identifies the anterior forearm muscles attachment sites, functions, and nerve supply. It also labels structures that form and pass through the carpal tunnel. The muscles may be studied in a superficial, middle, and deep layer.