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The lumbrical muscles are a group of four small, worm-like muscles found in each hand. They are deep muscles that originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons. Unlike other muscles, they do not attach to bone, which makes their function difficult to visualise. The lumbricals assist in metacarpophalangeal joint flexion and interphalangeal joint extension, contributing to the complex movement and dexterity of the hand. They also likely play a role in proprioception and sensory feedback in the fingers.
| Characteristics | Values |
|---|---|
| Number of Lumbrical Muscles | 4 |
| Location | Deep muscles of the hand |
| Function | Flex the metacarpophalangeal (MCP) joints and extend the proximal and distal interphalangeal (PIP and DIP) joints |
| Attachment Points | Proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions |
| Innervation | The first and second lumbricals are innervated by the median nerve; the third and fourth lumbricals are innervated by the ulnar nerve |
| Blood Supply | The superficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital arteries |
| Clinical Relevance | Can be damaged in crush injuries to the hand and is relevant in carpal tunnel syndrome |
| Role | May play a role in proprioception and sensory feedback due to the presence of many muscle spindles |
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What You'll Learn
Lumbrical muscles are involved in sensory feedback
The lumbrical muscles are a group of four small, worm-like muscles on each hand. They are deep muscles that originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons. This is unusual as they attach to tendons, not bone, making their attachment points very mobile. This means that the muscles can perform two different actions: flexion at the metacarpophalangeal joints and extension at the proximal and distal interphalangeal joints.
The lumbrical muscles have a small cross-sectional area and are relatively weak. They contain many muscle spindles and have a large fibre length, indicating that they play a role in proprioception and sensory feedback. This is important for the precision pinch movements and complex movement of the hand, such as holding a pen.
The first and second lumbricals (the most radial two) are innervated by the median nerve, while the third and fourth lumbricals (the most ulnar two) are innervated by the ulnar nerve. This is the most common innervation pattern, occurring in 50-60% of individuals. However, there is variation, with some individuals having different innervation patterns or double/absent lumbricals.
The lumbrical muscles are involved in sensory feedback due to their high number of muscle spindles. This is supported by their anatomical factors and the allocation of spindle fibres among the lumbricals. Their unique architectural properties, including a small cross-sectional area and long fibre length, indicate that they are important for fast, alternating movements and fine-tuning digit motion.
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They are responsible for complex hand movements
The lumbrical muscles are four small, worm-like muscles on each hand that are responsible for complex hand movements. They are deep muscles that originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons. Unlike most muscles, they do not attach to bone, which makes their function difficult to visualise. Instead, they have two movable attachment points, which allow them to perform two different actions: flexion at the metacarpophalangeal (MCP) joints and extension at both the proximal and distal interphalangeal (IP) joints.
The combination of these movements enables complex hand movements, such as holding a pen, and contributes to the hand's overall dexterity. The lumbricals' unique properties, including their long fibre length, indicate that they are important for fast, alternating movements and fine-tuning digit motion. They are also thought to play a role in proprioception and sensory feedback, particularly in the distal, proximal, and metacarpophalangeal joints of the fingers.
The first and second lumbricals (the most radial) are supplied by the median nerve, while the third and fourth lumbricals are supplied by the ulnar nerve. This is the most common innervation pattern, occurring in 50-60% of individuals. However, there is some variation, with 20-30% of people having the median nerve innervate only the first lumbrical, and the rest having the median nerve innervate the lateral three lumbricals.
The lumbrical muscles are also clinically relevant in certain trauma injuries, such as replantation for zone 3 amputations. Damage to the lumbrical muscles during these injuries can lead to poor functional outcomes. Additionally, the lumbrical muscles have been implicated in carpal tunnel syndrome.
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Lumbricals are weak muscles
The lumbricals are a group of four small, worm-like muscles on each hand. They are deep muscles that originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons. This is unusual as they attach to tendons rather than bone, making their attachment points quite mobile. This means the muscles are capable of two different actions: flexion at the metacarpophalangeal (MCP) joints and extension in both the proximal and distal interphalangeal (IP) joints.
The lumbricals are relatively weak muscles. They have a small cross-sectional area and weak motor function, which is only 1/10 of the interosseous muscle. Biomechanical studies have shown that the interosseous muscle is much more important for extending the PIP and IP joints. However, the high number of muscle spindles in the lumbricals suggests that they are important for proprioceptive monitoring of the fingers and sensory feedback. This is especially important for precision pinch movements.
The lumbricals' tendons pass anteriorly to the deep transverse metacarpal ligaments. From their points of origin, each of the lumbrical muscles passes distally along the radial side of the corresponding finger, extending obliquely to attach to the lateral margin of the extensor expansion of hand at the proximal phalanges of digits 2-5. The first and second lumbricals are supplied by the median nerve, while the third and fourth are supplied by the ulnar nerve.
The lumbrical muscles can be assessed by asking a patient to flex the MCP joints with the palm supine and the IP joints extended. Resistance is then applied to the palmar surface of the proximal phalanx of digits 2-5. This tests IP joint extension while maintaining MCP joint flexion. The lumbrical muscle is sometimes damaged in crush injuries to the hand and has also been shown to be relevant in carpal tunnel syndrome.
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They are involved in carpal tunnel syndrome
Lumbrical muscles are deep muscles of the hand that flex the metacarpophalangeal (MCP) joints and extend the interphalangeal joints. They are unusual in that they attach to tendons rather than bones, which gives them a high degree of mobility. This mobility allows them to perform two different actions: flexion at the MCP joints and extension at the proximal and distal interphalangeal joints. This complex movement enables the hand to perform dexterous tasks such as holding a pen.
The lumbricals have been found to be relevant in carpal tunnel syndrome (CTS), a common compression neuropathy. CTS is often idiopathic, but it is sometimes caused by the incursion of the lumbricals into the carpal tunnel during finger flexion. This incursion increases pressure on the median nerve, leading to symptoms such as numbness and pain. In some cases, this pressure can cause a snapping phenomenon at the carpal area when flexing the fingers.
The Berger test or closed fist test can be used to determine the role of the lumbricals in CTS. During this test, the patient holds a full fist for 30 to 60 seconds while keeping the wrist in a neutral position. If the patient experiences symptoms of paresthesia during the test, it indicates that the lumbricals are contributing to CTS symptoms. Lumbrical stretching can be used as a conservative treatment for CTS, especially in individuals who perform repetitive tasks or have well-developed lumbricals.
In cases of CTS resistant to conservative treatment, operative treatment is preferred. Carpal tunnel release with synovectomy is usually performed, and in some cases, resection of the lumbrical muscle may be necessary. The prognosis after operative treatment is typically good, as it is performed before irreversible pathological changes occur in the nerve.
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Lumbricals have two different functions
The lumbricals are a group of four small, worm-like muscles on each hand that do not attach to bone. Instead, they attach proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions. This unique structure gives the lumbrical muscles two distinct functions.
Firstly, the lumbricals assist in metacarpophalangeal joint flexion. This means that they help to bend the joints in the middle of the fingers, known as the metacarpophalangeal joints. This action is important for complex hand movements and contributes to the overall dexterity of the hand. For example, lumbrical muscles are used when holding a pen.
Secondly, the lumbricals contribute to interphalangeal joint extension by acting as deflexors of the proximal interphalangeal joint. In other words, they help to straighten the joints in the fingers, specifically the proximal interphalangeal joints. This function is facilitated by the lumbricals' movable attachments to tendons, which allow them to perform opposite actions. The tendons cross the metacarpophalangeal joints on the palmar side but insert at the dorsal side of the finger, enabling both flexion and extension movements.
The lumbricals' high number of muscle spindles suggests that they are important for proprioceptive monitoring of the fingers and sensory feedback. This is particularly relevant for precision pinch movements. The first and second lumbricals are typically innervated by the median nerve, while the third and fourth lumbricals are innervated by the ulnar nerve. However, there is some variation in innervation patterns among individuals.
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Frequently asked questions
Lumbricals are a group of four small, worm-like muscles on each hand. They are deep muscles that originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons.
Lumbrical muscles assist in metacarpophalangeal joint flexion and contribute to interphalangeal joint extension by acting as deflexors of the proximal interphalangeal joint. They also play a role in proprioception and sensory feedback in the fingers.
Lumbrical muscles are unique in that they do not attach to bone. Instead, they attach proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions. This gives them greater mobility, allowing them to perform complex movements and contributing to hand dexterity.
