Your complete guide to the bones and muscles of the forearm.
The forearm, which is sometimes referred to as the lower arm, is the region of the human body that lies between the elbow and the wrist. As you will see, however, many of the forearm muscles actually insert further down the upper limb into the hand because they’re responsible for flexing and extending the fingers.
The forearm muscles consist of flexors, which lie in the anterior compartment of the forearm, and the extensors, which lie in the posterior compartment [1
]. The muscles of the forearm also consist of supinators, which turn the palm down, and pronators, which turn the palm up. Additionally, the brachioradialis is another forearm muscle, one which flexes the elbow.
Anatomically speaking, the term arm refers to the upper arm only, hence why forearm is a more correct term than lower arm.
The forearm anatomy consists of two elongated bones that run parallel to each other; the ulna, which lies medially; and the radius, which lies laterally. Together, these two bones form the radioulnar joint, which permits supination and pronation of the forearm.
Skin covers these bones, and most people have a higher quantity of hair on the top of their forearm (the posterior compartment) than on the underside (anterior compartment).
The ulnar and radial arteries supply blood to the forearm. The radial artery supplies blood to the posterior and lateral part of the forearm anatomy, while the ulnar artery supplies blood to the anterior and medial aspects [2
The muscles of the forearm are split into two distinct compartments; the anterior compartment, which contains the flexors; and the posterior compartment, which contains the extensors.
The radial nerve supplies the extensor muscles, which are naturally weaker than the opposing flexors, while the median nerve supplies the flexor muscles [3
The forearm muscles in the anterior compartment flex the forearm, wrist, and fingers. They also perform pronation, which is to say turning the palm down [4
]. They’re divided into three layers; superficial muscles, which lie close to the skin; deep muscles, which lie near to the bones (radius and ulnar) or internal organs; and intermediate muscles, which lie between the superficial and deep forearm muscles.
These lower arm muscles are:
• Flexor Carpi Radialis
• Flexor Carpi Ulnaris
• Pronator Teres
• Palmaris Longus
• Flexor Digitorum Superficialis
• Flexor Pollicis Longus
• Flexor Digitorum Profundus
• Pronator Quadratus
The forearm extensors function to extend the wrist and fingers and are separated into two layers; superficial and deep. While there are only 8 forearm flexor muscles, there are 12 unique forearm extensor muscles, 5 of which originate at the lateral epicondyle of the humerus.
The extensor muscles in the forearm are:
• Extensor Carpi Radialis Longus
• Extensor Carpi Radialis Brevis
• Extensor Carpi Ulnaris
• Extensor Digitorum
• Extensor Digiti Minimi (superficial)
• Brachioradialis (superficial)
• Extensor Pollicis Brevis
• Extensor Pollicis Longus (deep)
• Extensor Indicis Proprius (deep)
• Abductor Pollicis Longus (deep)
• Supinator (deep)
Proximally, at the elbow joint, the ulna articulates the humerus.
Distally, it forms a synovial pivot joint with the radius, which allows for pronation and supination. This joint is known as the radioulnar joint, and it helps to keep the ulna and radius together when we move our forearm.
The radius has more articulation points than the ulna. Proximally, at the elbow joint, it articulates with the capitulum of the humerus and the radial notch of the ulna.
Distally, the radius articulates between the carpal bones, the lunate (medially), and the scaphoid (laterally). As mentioned, the radius also articulates with the semilunar notch at the radioulnar joint.