Extensor carpi radialis longus

Description

Muscles of the posterior forearm

Extensor carpi radialis longus lies on the lateral side of the posterior compartment of the forearm, being partly covered by brachioradialis. Approximately in the middle of the forearm, the muscle forms a flattened tendon which runs distally over the lateral surface of the radius. In the lower third of the forearm, the tendon, together with that of extensor carpi radialis brevis, is crossed by the tendons of abductor pollicis longus and extensor pollicis brevis. The tendons of extensor carpi radialis longus and brevis pass deep to the extensor retinaculum in a common synovial sheath. Together they groove the posterior surface of the styloid process of the radius.[1]

Origin

Extensor carpi radialis longus arises from the anterior part of the lower third of the lateral supracondylar ridge of the humerus and adjacent intermuscular septum. Occasionally, there may be an attachment to the lateral epicondyle by the common extensor tendon.[1]

Insertion

The tendon of the extensor carpi radialis longus attaches to the posterior surface of the base of the second metacarpal.[1]

Nerve

Extensor carpi radialis longus is supplied by the radial nerve (root value C6 and 7) from the posterior cord of the brachial plexus, which enters the muscle above the elbow. The skin over the muscle is supplied by roots C5 and C6.[1]

Artery

Radial artery[1]

Function

Working with extensor carpi ulnaris, extensors carpi radialis longus and brevis produce extension of the wrist. Working with the flexor carpi radialis, however, they will produce abduction (radial deviation) of the wrist. In addition extensor carpi radialis longus may help to flex the elbow joint.[1]

Clinical relevance

Extensor carpi radialis longus is one of the three primary wrist extensors. Extensor carpi radialis longus is most effective as a wrist extensor when the elbow is extended and when radial deviation is balanced by the primary ulnar deviator- extensor carpi ulnaris. Functionally, the wrist extensors work strongly in the action of gripping, where they have a synergistic role. The synergy of the two radial extensors and extensor carpi ulnaris is an important factor in the gripping action. By maintaining the wrist in an extended position, flexion of the wrist under the action of flexors digitorum superficialis and profundus is prevented, with the result that these muscles act on the fingers. If the wrist is then allowed to flex the flexor tendons cannot shorten sufficiently to produce effective movement at the interphalangeal joints. This therefore becomes a state of active insufficiency.

If the radial nerve is damaged a person is unable to produce an effective grip because of the paralysis of the wrist extensors. However, with the wrist splinted in extension, the tendons of flexors digitorum superficialis and profundus act on the fingers and a functional grip can be obtained.[1]

Intersection syndrome is a bursitis that occurs at the site where the abductor pollicis longus and extensor pollicis brevis tendons cross over the extensor carpi radialis tendons proximal to the extensor retinaculum. This may be due to friction at this site of crossing or it may occur from tenosynovitis of the two extensor tendons within their synovial sheath. Tenderness is found dorsally on the radial side, with swelling and crepitus a short distance proximal to the site of maximal tenderness in de Quervain's syndrome. This condition is often seen in rowers, but also in canoeists and racket sports.[2]

Assessment

Active movements[2]

  • elbow flexion/extension
  • supination/pronation
  • wrist flexion/extension

Passive movements[2]

  • as above

Resisted movements[2]

  • wrist extension
  • wrist extension and abduction
  • grip test
[3]

Palpation

  • lateral epicondyle[2]
  • when the wrist is extended and abducted against resistance, both extensors carpi radialis longus and brevis can be palpated in the upper lateral aspect of the posterior part of the forearm. The tendons, particularly longus, can be palpated in the floor of the anatomical snuff box if the same movement of extension and abduction is carried out.[1]

Special tests[2]

  • neural tension
  • cervical spine assessment
  • thoracic spine assessment
  • periscapular soft tissues

Treatment

  • Control of pain[2]
  • Soft tissue therapy[2]
  • Manual therapy - elbow and wrist[2]
  • Stretching[2]
  • Muscle strengthening[2]

See also

Elbow examination

Elbow

Wrist and hand examination

Resources

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Palastanga N, Field D, Soames R. Anatomy and human movement: structure and function. 5th ed. Edinburgh: Butterworth Heinemann/Elsevier; 2006.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 Brukner P, Khan K. Clinical sports medicine. 3rd ed. Sydney; McGraw Hill: 2006.
  3. Michael Moline.Extensor carpi radialis longus and brevis. Available from:https://www.youtube.com/results?search_query=extensor+carpi+radialis+longus+assessment [last accessed 26/6/2018]