Muscles in the Posterior Compartment of the Forearm

Finally, we will identify the muscles of the posterior compartment of the forearm. If we consider the nerve supply of the muscles of the posterior compartment of the forearm (radial), then all of the muscles supplied by that nerve should be located in that compartment. However, one of the muscles has migrated anteriorly and is best seen from that vantage point. The muscle is the brachioradialis.

brachioradialis muscle

The remainder of the muscles of the posterior compartment can be examined in three groups: 1) superficial
2) intermediate
3) deep.

For the most part, the superficial and intermediate groups arise from the lateral epicondyle of the humerus.

Muscles of the Posterior Compartment of the Forearm

Superficial group
extensor carpi radialis longus
extensor carpi radialis brevis
extensor carpi ulnaris
superficial extensor muscles of forearm
Intermediate group
extensor digitorum
extensor digiti minimi
intermediate extensor muscles of forearm
Deep group
anconeus
supinator
abductor pollicis longus
extensor pollicis brevis
extensor pollicis longus
extensor indicis
deep extensor muscles of forearm

The Extensor Expansion

Once the muscles of the posterior compartment are identified and studied, take a look at the insertions of the tendons of the extensor digitorum. They are special and deserve closer attention.
The extensor tendons insert into the phalanges by way of a special connective attachment called the extensor expansion.

Dorsal View dorsal view of extensor expansion Lateral View lateral view of extensor expansion

When the extensor digitorum muscle contracts, it pulls on the extensor expansion and this, in turn extends the interphalangeal joints. You will also notice that the lumbrical muscle inserts into the hood part of the expansion and through this attachment can also extend the interphalangeal joints. This muscle can at the same time flex the metacarpophalangeal joint. Because of these two actions, the lumbricals are called the bye bye muscles. That is the action they perform.

Nerves of the Hand Table of Muscles of the Hand

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cadaver This is copyrighted© 1999 by Wesley Norman, PhD, DSc

Muscles of the Posterior Compartment of the Forearm
Superficial group extensor carpi radialis longus extensor carpi radialis brevis extensor carpi ulnaris		Intermediate group extensor digitorum extensor digiti minimi		Deep group anconeus supinator abductor pollicis longus extensor pollicis brevis extensor pollicis longus extensor indicis

The Extensor Expansion
Once the muscles of the posterior compartment are identified and studied, take a look at the insertions of the tendons of the extensor digitorum. They are special and deserve closer attention. The extensor tendons insert into the phalanges by way of a special connective attachment called the extensor expansion.
Dorsal View		Lateral View
When the extensor digitorum muscle contracts, it pulls on the extensor expansion and this, in turn extends the interphalangeal joints. You will also notice that the lumbrical muscle inserts into the hood part of the expansion and through this attachment can also extend the interphalangeal joints. This muscle can at the same time flex the metacarpophalangeal joint. Because of these two actions, the lumbricals are called the bye bye muscles. That is the action they perform.