The muscles in the posterior compartment of the forearm are collectively known as the extensor muscles. Their general function is to produce extension at the wrist and fingers, and all are innervated by the radial nerve. These muscles are further organized into two layers; deep and superficial.
The superficial layer of the posterior forearm contains seven muscles. Four of these muscles – the extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi – all originate from a common tendinous origin at the lateral epicondyle. In addition, the anconeus is situated proximally in the forearm, and is often blended with the fibres of the triceps brachii, making the distinction between the two muscles difficult.
The brachioradialis is a unique muscle in the posterior forearm, as its origin and innervation would imply that it is an extensor muscle, while in fact it is actually a flexor at the elbow. This paradoxical muscle can be best seen when the forearm is half pronated and flexing against resistance, as the radial artery and nerve are situated between the brachioradialis and the deep flexor muscles.
The brachioradialis originates from the proximal aspect of the lateral supracondylar ridge of humerus, and attaches to the distal end of the radius, just before the radial styloid process. Its main function is to flex the elbow, and it is innervated by the radial nerve.
The extensor carpi radialis muscles are located on the lateral aspect of the posterior forearm, and are responsible for both extension and abduction of the wrist. The extensor carpi radialis longus (ECRL) originates from the lateral supracondylar ridge of the humerus, while the extensor carpi radialis brevis (ECRB) originates from the lateral epicondyle. Their tendons connect to metacarpal bones II and III, and they are innervated by the radial nerve.
The extensor digitorum is the main extensor of the fingers, and can be tested by half pronating the forearm and attempting to extend the fingers against resistance. It originates from the lateral epicondyle, and splits into four tendons to connect to the extensor hood of each finger. Its main actions are extension of the digits at the interphalangeal and metacarpophalangeal joints, and it is innervated by the radial nerve (deep branch).
The extensor digiti minimi is often thought to originate from the extensor digitorum muscle, and in some people, these two muscles are fused together. This muscle lies medially to the extensor digitorum and originates from the lateral epicondyle of the humerus. Its tendon attaches to the extensor hood of the little finger, enabling extension at this joint, and it is innervated by the radial nerve (deep branch).
The extensor carpi ulnaris is situated on the medial aspect of the posterior forearm, and it is responsible for both extension and adduction of the wrist. It originates from the lateral epicondyle of the humerus, and attaches to the base of metacarpal V. Its action is extension and adduction of the wrist, and it is innervated by the radial nerve (deep branch).
The deep layer of the posterior forearm contains several muscles, including the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius.
The supinator is located on the posterior and lateral aspect of the forearm, and its main action is supination of the forearm. It originates from the lateral epicondyle of the humerus and attaches onto the proximal aspect of the radius. It is innervated by the radial nerve.
The abductor pollicis longus (APL) is located in the anterior compartment of the forearm, and its action is abduction of the thumb. It originates from the radius, interosseous membrane, and ulna, and attaches to the base of the metacarpal of the thumb. It is innervated by the posterior interosseous nerve.
The extensor pollicis brevis (EPB) is a small triangular muscle located above the APL. Its main action is extension of the thumb, and it originates from the radius, interosseous membrane, and ulna. It attaches to the base of the metacarpal of the thumb and is innervated by the posterior interosseous nerve.
The extensor pollicis longus (EPL) is located deep to the EPB and originates from the posterior surface of the ulna, interosseous membrane, and radius. Its main action is extension of the thumb, and it attaches to the base of the metacarpal of the thumb. It is also innervated by the posterior interosseous nerve.
Finally, the extensor indicis proprius is located anterior to the EPL. Its action is extension of the index finger, and it originates from the posterior surface of the ulna. The tendon attaches to the base of the proximal phalanx of the index finger, and is innervated by a branch of the posterior interosseous nerve.
Injury or damage to any of the muscles in the posterior forearm can have a range of clinical consequences. For instance, injury to the brachioradialis can result in reduced strength in the elbow flexors, leading to difficulty in performing activities that require elbow flexion. Injury to the extensor carpi radialis muscles can result in decreased abduction or extension at the wrist, leading to weakness in grip strength.
Injury to the extensor digitorum may cause difficulty extending the fingers, resulting in weakened grip strength, while injury to the extensor carpi ulnaris can cause reduced adduction and extension at the wrist. Injury to the anconeus or the deep muscles may also impair movement and weaken grip strength. Note that while anconeus is traditionally considered part of the extensor muscles, it acts as a stabilizer of the elbow and a flexor of the ulna during pronation.
Injury to any of the muscles in the posterior forearm requires rest, ice therapy, and rehabilitation exercises. In more severe cases, surgery may be required in order to restore movement and strength in the forearm.
The posterior forearm contains both superficial and deep layers of muscles. The superficial layer includes the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius. These muscles originate from the lateral epicondyle of the humerus and the posterior surface of the ulna, and attach to various parts of the radius and metacarpal bones. Collectively, they allow the forearm to flex, abduct, extend, and supinate. In addition to helping move the wrist and fingers, they play a role in lateral epicondylitis (or tennis elbow) and wrist drop.
The superficial layer of the posterior forearm contains seven muscles, four of which (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris and extensor digiti minimi) share a common tendinous origin at the lateral epicondyle. Let’s look at each muscle in more detail:
The deep muscles of the posterior forearm - the pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and the flexor digitorum superficialis - are located deep to the supinator and are responsible for flexion and pronation of the forearm, and flexion of the wrist and fingers, respectively.
The muscles of the posterior forearm are important in enabling us to perform everyday activities like writing, typing, and tying shoelaces. Damage or injury to these muscles can lead to difficulties in performing even the simplest movements. It is therefore important to maintain strength and flexibility in these muscles in order to avoid any long-term problems.
In addition to helping us move our wrist and fingers, the muscles of the posterior forearm play a role in certain clinical conditions, such as lateral epicondylitis (or tennis elbow), and wrist drop. Lateral epicondylitis is caused by repeated use of the superficial extensor muscles and straining of their common tendinous attachment to the lateral epicondyle, while wrist drop is caused by nerve injury and leads to unopposed flexion of the wrist. It is therefore important to keep these muscles healthy and functioning well in order to avoid any complications.
The muscles of the posterior forearm are complex and diverse. It is important to understand their anatomy, attachments, actions, and clinical relevance in order to properly care for them and keep them functioning optimally. By understanding the anatomy of the posterior forearm, we can take better care of our bodies and perform everyday tasks with ease.
The posterior compartment of the forearm is a thin, fusiform compartment containing both superficial and deep muscles. Superficial muscles present in the posterior compartment of the forearm include the extensor carpi radialis longus, the extensor carpi radialis brevis, the extensor digitorum, the extensor digiti minimi, and the brachioradialis.
The anconeus is situated medially and proximally in the extensor compartment of the forearm. It is blended with the fibres of the triceps brachii, and the two muscles can be indistinguishable.
The anconeus has two primary attachments. It originates from the lateral epicondyle of the humerus, and attaches to the posterior and lateral part of the olecranon. Actions of the anconeus muscle include the extension and stabilization of the elbow joint, as well as the abduction of the ulna during pronation of the forearm. Its innervation is provided by the radial nerve.
The deep compartment of the posterior forearm contains five muscles - the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius. With the exception of the supinator, these muscles act on the thumb and the index finger.
The supinator lies in the floor of the cubital fossa. It has two heads, which the deep branch of the radial nerve passes between. Its attachments originate from the lateral epicondyle of the humerus and the posterior surface of the ulna. Together, they insert into the posterior surface of the radius. The actions of the supinator include the supination of the forearm, and its innervation is provided by the radial nerve (deep branch).
The abductor pollicis longus is situated immediately distal to the supinator muscle. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox. It originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna. It attaches to the lateral side of the base of metacarpal I. The actions of the abductor pollicis longus include the abduction of the thumb. Its innervation is provided by the radial nerve (posterior interosseous branch).
The extensor pollicis brevis can be found medially and deep to the abductor pollicis longus. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox. It originates from the posterior surface of the radius and interosseous membrane. It attaches to the base of the proximal phalanx of the thumb. The actions of the extensor pollicis brevis include extension at the metacarpophalangeal and carpometacarpal joints of the thumb. Its innervation is provided by the radial nerve (posterior interosseous branch).
The extensor pollicis longus muscle has a larger muscle belly than the EPB. Its tendon travels medially to the dorsal tubercle at the wrist, using the tubercle as a 'pulley' to increase the force exerted. The tendon of the extensor pollicis longus forms the medial border of the anatomical snuffbox in the hand. It originates from the posterior surface of the ulna and interosseous membrane. It attaches to the distal phalanx of the thumb. The actions of the extensor pollicis longus include extension at all joints of the thumb- carpometacarpal, metacarpophalangeal and interphalangeal. Its innervation is provided by the radial nerve (posterior interosseous branch).
This muscle allows the index finger to be independent of the other fingers during extension. Its attachments originate from the posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus. It attaches to the extensor hood of the index finger. The actions of the extensor indicis proprius include the extension of the index finger. Its innervation is provided by the radial nerve (posterior interosseous branch).
Wrist drop is a sign of radial nerve injury that has occurred proximal to the elbow. There are two common characteristic sites of damage - axilla, injured via humeral dislocations or fractures of the proximal humerus, and the radial groove of the humerus, injured via a humeral shaft fracture. The radial nerve innervates all muscles in the extensor compartment of the forearm. In the event of a radial nerve lesion, these muscles are paralysed. The muscles that flex the wrist are innervated by the median nerve, and thus are unaffected. The tone of the flexor muscles produces unopposed flexion at the wrist joint - wrist drop.
In summary, the posterior compartment of the forearm contain both superficial and deep muscles. The anconeus, the supinator, the abductor pollicis longus, the extensor pollicis brevis, the extensor pollicis longus, and the extensor indicis proprius are all muscles of the deep compartment of the posterior forearm. The radial nerve, which is innervated by all of these muscles, can be damaged at two common sites, leading to the symptom of wrist drop.
The posterior compartment of the forearm contains several deep muscles that play an important role in the body's vital bodily functions. These muscles include the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius. This region of the forearm is susceptible to a range of different medical conditions, one of the most common of which is lateral epicondylitis.
Clinically, dysfunction of the muscles in the posterior compartment of the forearm can produce a rather telling symptom – wrist drop. Wrist drop is characterized by an inability to elevate the wrist or fingers due to the wrist extensor muscles being weakened. This condition can cause considerable disruption to an individual’s daily life, as it can interfere with the performance of fine and gross motor skills.
Lateral epicondylitis, commonly referred to as “tennis elbow”, is a condition that affects the tendons in the forearm. It is caused by overuse of the wrist extensor muscles, leading to inflammation and pain in the tendons and muscles. The condition is reported to be more common among tennis players, hence the name “tennis elbow”.
Symptoms of tennis elbow include pain and tenderness on the outside of the elbow, especially when trying to straighten the arm. People may also experience a sense of weakness in the wrist and pain when gripping or lifting things. In some cases, the pain can even extend down the forearm.
Fortunately, there are several treatment options available for treating lateral epicondylitis. The first step in treating tennis elbow is to rest the affected limb, as this allows the tendons and muscles to recover and heal. Adequate time should also be taken to stretch the muscles in the forearm in order to reduce the level of tension on the tendons.
Applying ice to the affected area is another viable treatment option, as this can help to reduce swelling and inflammation. Heat therapy, such as the use of a heating pad, can also be helpful in alleviating the pain by increasing the circulation of blood to the area. Oral medications, topical creams, and corticosteroid injections are also commonly used to treat lateral epicondylitis.
In some cases, physical therapy may be recommended to improve the flexibility and strength of the muscles in the forearm. This can help to alleviate the pressure on the tendons and prevent further injury. It is important to note that recovery times may vary, so it is important to check in with a doctor or physical therapist to ensure that the recovery is on track.
Since lateral epicondylitis is most commonly caused by repetitive use of the forearm muscles, it is important to practice proper technique when engaging in activities that could lead to injury. Using proper form when exercising is key, as this can help to reduce the risk of injury.
Wearing appropriate protective gear, such as elbow pads or wrist straps, is also important. It is important to use adequate stretching techniques before and after any type of activity to ensure that the muscles are properly warmed up. Finally, if one does experience any kind of pain or discomfort, it is important to take some time off from the activity.
The deep muscles of the posterior compartment of the forearm are important for the performance of a range of functions, from movement to control. Understanding the common pathology affecting this part of the body, such as lateral epicondylitis, and the available treatments and prevention methods is important in order to maintain good health and wellbeing. Through proper prevention and treatment measures in place, individuals can continue to exercise and participate in activities without fear of causing further injury to the posterior compartment of the forearm.
