Dominic Stone
The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. It is a type 2 muscle flap that can cover small to medium-sized elbow defects in the posterior, medial, and anterior aspects of the elbow. The FCU is the most medial of the superficial flexors and is the only muscle in the anterior compartment that is fully innervated by the ulnar nerve. The FCU is supplied by the ulnar collateral arteries along with the anterior and posterior ulnar recurrent arteries. The FCU shares a common tendon with the other wrist flexors and can be involved in various pathologies associated with them, such as medial epicondylalgia. So, is the FCU an intrinsic muscle?
| Characteristics | Values |
|---|---|
| Muscle Type | Type 2 muscle flap |
| Muscle Group | Superficial flexors of the forearm |
| Muscle Layer | First layer of the anterior compartment of the forearm |
| Muscle Innervation | Ulnar nerve |
| Muscle Artery Supply | Ulnar collateral arteries, anterior and posterior ulnar recurrent arteries, ulnar artery, inferior ulnar collateral artery |
| Muscle Function | Flexes and adducts the hand at the wrist joint |
| Muscle Tendinitis | Acute flexor carpi ulnaris tendinitis |
| Muscle Pathology | Involved in various pathologies such as medial epicondylalgia and Volkmann's contracture |
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What You'll Learn
The FCU is an extrinsic hand muscle
The flexor carpi ulnaris (FCU) is an extrinsic hand muscle. It is a type 2 muscle flap that can cover small to medium-sized elbow defects in the posterior, medial, and anterior aspects of the elbow. The FCU is situated in the forearm and is the most proximal muscle innervated by the ulnar nerve. It is supplied by branches both above and below the elbow and is involved in various pathologies associated with other wrist flexors.
The FCU is one of the extrinsic muscles of the hand and is located in the anterior compartment of the forearm. It is the most medial of the superficial flexors and, together with other muscles of the anterior forearm, flexes the hand at the wrist. The FCU shares a common tendon with the other wrist flexors and can be involved in pathologies such as medial epicondylalgia and Volkmann's contracture. The FCU is also susceptible to tendinitis, especially when performing activities that require repeated flexion and adduction of the hand, such as racquet sports.
The FCU originates with two heads: a smaller humeral head and a more extensive ulnar head. These heads are named according to the bones they attach to. The humeral head arises from the common flexor origin on the medial epicondyle of the humerus, while the ulnar head originates from the olecranon and proximal part of the posterior border of the ulna. As the muscle fibres pass towards the wrist joint, they converge on a long tendon in the distal part of the forearm.
The FCU is innervated by the ulnar nerve, with corresponding spinal nerves C8 and T1. It receives its arterial blood supply via three different routes: proximally by a branch of the posterior ulnar recurrent artery, and in the middle and distal parts by branches of the ulnar artery. An accessory supply is also present distally via the inferior ulnar collateral artery. The FCU is the only muscle in the anterior compartment fully innervated by the ulnar nerve.
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The FCU is a major wrist flexor
The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. It is the most proximal muscle innervated by the ulnar nerve. The FCU muscle is a major wrist flexor, particularly in an ulnar direction, and is supplied by branches both above and below the elbow. The FCU is the only muscle in the anterior compartment that is fully innervated by the ulnar nerve. It has a long linear origin from olecranon and the posterior border of the ulna. The FCU also has a humeral head origin from the medial epicondyle of the humerus.
The FCU is supplied by the ulnar collateral arteries along with the anterior and posterior ulnar recurrent arteries. The ulnar nerve gains access to the forearm by passing between the humeral and ulnar heads of the FCU. The FCU flexes and adducts the hand at the wrist joint. The FCU shares a common tendon with the other wrist flexors and can be involved in various pathologies associated with them, such as medial epicondylalgia. The FCU is susceptible to Volkmann's contracture, where ischemic damage compromises the FCU, leading to fibrosis and contracture. This constriction can result in deformities and impaired function in the affected limb.
The FCU has two heads: a humeral head and an ulnar head. The humeral head originates from the medial epicondyle of the humerus via the common flexor tendon. The ulnar head originates from the medial margin of the olecranon of the ulna and the upper two-thirds of the dorsal border of the ulna by an aponeurosis. Between the two heads passes the ulnar nerve and ulnar artery. The FCU inserts onto the pisiform, hook of the hamate, and base of the fifth metacarpal. The tendon of the FCU can be seen and palpated beneath the skin immediately proximal to the wrist joint.
The FCU muscle is a type 2 muscle flap that can cover small to medium-sized elbow defects in the posterior, medial, and anterior aspects of the elbow. However, its use takes away the most potent wrist flexor and ulnar deviator to the hand. The FCU tendon may develop tendinitis after overuse or misuse, especially when performing activities that require repeated flexion and adduction of the hand. Acute FCU tendinitis has been seen more frequently due to the increasing popularity of racquet sports such as tennis, baseball, and golf.
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The FCU is susceptible to tendinitis
The flexor carpi ulnaris (FCU) is a type 2 muscle flap that can cover small to medium-sized elbow defects. It is the most medial flexor muscle in the forearm's superficial compartment. The FCU is a major wrist flexor, particularly in an ulnar direction, and is supplied by branches both above and below the elbow.
Flexor carpi ulnaris tendinitis can result in a rupture of the inflamed tendon due to repetitive trauma. This can be caused by injection directly into the tendon, which is a major complication. Injection can also cause infection, although this is rare if a strict aseptic technique is followed. The injection technique is generally safe if attention is paid to the clinically relevant anatomy, especially the ulnar nerve, which is susceptible to damage at the elbow.
The FCU is also susceptible to Volkmann's contracture, where ischemic damage compromises the FCU along with other muscles, leading to fibrosis and contracture. This constriction can result in deformities and impaired function in the affected limb.
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The FCU is innervated by the ulnar nerve
The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. It is the most medial flexor muscle in the superficial compartment of the forearm. The FCU is the most proximal muscle innervated by the ulnar nerve. The ulnar nerve provides motor innervation to the FCU, controlling the flexion of the distal interphalangeal joint (DIP) of the ring and small fingers. The ulnar nerve also relays sensory information back to the central nervous system in the hand from the ulnar border of the ring finger, the small finger, and spanning the dorsal and volar aspect of the hypothenar region of the hand.
The FCU has two heads: a humeral head and an ulnar head. The humeral head originates from the medial epicondyle of the humerus via the common flexor tendon. The ulnar head originates from the medial margin of the olecranon of the ulna and the upper two-thirds of the dorsal border of the ulna by an aponeurosis. Between the two heads of the FCU passes the ulnar nerve and ulnar artery. The FCU inserts onto the pisiform, hook of the hamate, and base of the fifth metacarpal. The FCU is supplied by the ulnar collateral arteries along with the anterior and posterior ulnar recurrent arteries. The FCU flexes and adducts the hand at the wrist joint.
The ulnar nerve gains access to the forearm by passing between the humeral and ulnar heads of the FCU. The ulnar nerve and ulnar artery enter Guyon's canal, or the ulnar tunnel at the wrist, which is bordered by the transverse carpal ligament, volar carpal ligament, pisiform, and hook of the hamate. The ulnar nerve lies ulnarly and posteriorly to the ulnar artery within Guyon's canal. Ulnar nerve entrapment occurs most commonly in the cubital tunnel or the ulnar tunnel, i.e., Guyon's canal. At the cubital tunnel, compression between Osborne's ligament, defined as the fascia connecting the two heads of the FCU superficially, and the MCL of the elbow deep, can lead to symptoms of compressive neuropathy in the forearm and hand.
Ulnar nerve entrapment can manifest within the cubital tunnel, occurring between the aponeuroses of the two heads of the FCU. This scenario underscores the clinical significance of potential issues associated with ulnar nerve compression in the cubital tunnel. The FCU tendon insertion serves as a landmark in finding the ulnar nerve and ulnar artery, which are lateral to the tendon at the wrist joint. The FCU is susceptible to involvement in Volkmann's contracture, where ischemic damage compromises the FCU, along with other muscles, leading to fibrosis and contracture. This constriction can result in deformities and impaired function in the affected limb.
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The FCU is involved in Volkmann's contracture
The flexor carpi ulnaris (FCU) muscle is a type 2 muscle flap that can cover small to medium-sized elbow defects. It is one of the extrinsic muscles of the hand. The FCU is a major wrist flexor, particularly in an ulnar direction, and is supplied by branches both above and below the elbow. The FCU is also the most proximal muscle innervated by the ulnar nerve.
Volkmann's contracture is a permanent flexion contracture of the hand at the wrist, resulting in a claw-like deformity of the hand and fingers. Passive extension of the fingers is restricted and painful. It is named after Richard von Volkmann, a 19th-century German doctor who first described it in a paper on "non-Infective Ischemic conditions of various fascial compartments in the extremities".
Volkmann's contracture results from acute ischemia and necrosis of the muscle fibres of the flexor group of muscles of the forearm, especially the flexor digitorum profundus and flexor pollicis longus. The incidence of Volkmann's contracture is low, but if compartment syndrome is not treated adequately, it will occur. Most cases are severe, with virtually no muscle function and a significant nerve deficit. The condition has been classified into four grades of severity by Lipscomb, with Grade I being mild, and Grades III and IV requiring surgical intervention.
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Frequently asked questions
The full form of FCU is Flexor Carpi Ulnaris.
The FCU is a type 2 muscle flap. It is a fusiform muscle located in the anterior compartment of the forearm.
The FCU is a major wrist flexor, especially in an ulnar direction. It can also move the hand sideways.
The FCU is susceptible to Volkmann's contracture, where ischemic damage compromises the FCU along with other muscles, leading to fibrosis and contracture. It may also develop tendinitis due to overuse or misuse, especially in activities requiring repeated flexion and adduction of the hand, such as racquet sports.
The FCU receives its blood supply through three routes. Proximally, it is supplied by a branch of the posterior ulnar recurrent artery. The middle and distal parts of the muscle are supplied by branches of the ulnar artery, with an additional supply from the inferior ulnar collateral artery.
