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The extensor indicis proprius (EIP) muscle is a narrow, elongated muscle in the deep layer of the dorsal forearm. It is involved in the extension of the index finger at the metacarpophalangeal and interphalangeal joints. The EIP muscle is one of the few separate extensor muscles that enable independent finger movement. It also assists in extending the wrist and midcarpal joints. The EIP muscle has applications in tendon transfers and tendon grafting for hand injuries.
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What You'll Learn
- The extensor indicis proprius (EIP) muscle is located in the posterior deep compartment of the forearm
- The EIP muscle extends the index finger
- The EIP muscle is involved in tendon transfers
- The EIP muscle is used in tendon grafting and transplantation
- The EIP muscle is involved in the extension of the metacarpophalangeal and interphalangeal joints
The extensor indicis proprius (EIP) muscle is located in the posterior deep compartment of the forearm
The EIP muscle arises from the distal third of the dorsal part of the ulna and from the interosseous membrane. It extends inferiorly and narrows into a tendon that passes deep to the extensor retinaculum. The tendon is then invested within a tendinous sheath with the tendons of the extensor digitorum muscle. As it courses through the hand, the tendon of the EIP passes obliquely over the carpal bones and joins the ulnar side of the tendon of the extensor digitorum, opposite the head of the second metacarpal bone.
The EIP muscle is involved in tendon transfers and is commonly used in cases of extensor pollicis longus (EPL) rupture. It has also been studied for its potential use in tendon grafting and transplantation for hand injuries. In some rare cases, the EIP muscle may contain an additional muscle belly on the dorsum of the hand, known as the extensor indicis brevis manus.
The independent movement of the thumb and index finger is critical for proper hand function. The extension of these digits is predominantly performed by the separate EPL and EIP muscles, respectively.
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The EIP muscle extends the index finger
The extensor indicis proprius (EIP) muscle is a narrow, elongated muscle found in the posterior compartment of the forearm. It is involved in extending the index finger at the metacarpophalangeal and interphalangeal joints. The index finger is one of the few fingers with its own separate extensor muscle, allowing it to extend independently from the other fingers.
The EIP muscle originates mainly from the ulna, arising from the posterior two-thirds of its distal surface, distal to the extensor pollicis longus muscle. Some fibres also stem from the adjacent interosseous membrane. The EIP tendon passes deep to the extensor retinaculum and joins the ulnar side of the tendon of the extensor digitorum, which belongs to the index finger.
The EIP muscle is important for proper hand function, as it enables the independent movement of the index finger. This muscle can be palpated by applying deep pressure over the lower part of the ulna while the index finger is extended. The EIP muscle also produces a weak extension of the wrist joint as it crosses the wrist.
Variations in the EIP muscle have been observed in different populations. For example, in a study of 50 cadavers, only one out of 100 limbs was reported to have an absent EIP muscle and tendon. In some cases, the EIP muscle exhibited variations such as double tendons or an extra muscle belly. These variations may have implications for hand reconstructive surgery and tendon transfers.
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The EIP muscle is involved in tendon transfers
The extensor indicis proprius (EIP) is a narrow, elongated muscle in the deep layer of the dorsal forearm. Its tendon goes to the index finger, which it extends. Independent movement of the thumb and index finger is critical for proper hand function. The index finger has its own separate extensor, the EIP, which enables it to extend independently from other fingers.
The EIP is involved in tendon transfers, which can restore function to an extremity. Tendon transfers have been used to treat radial nerve paralysis, which results in debilitating motor dysfunction of the hand. The patient loses the ability to extend the wrist, fingers, and thumb, which are essential for a functional grasp. The transfer of the EIP from the ulnar to the radial aspect of the index MCP joint can strengthen the first dorsal interosseous muscle.
Opposition tendon transfer using the EIP to insert onto the abductor pollicis brevis (APB) is one example of a tendon transfer involving the EIP. The ring finger FDS can be split and inserted into both the EPL and the EIP, allowing concomitant thumb and index finger extension. This transfer does not violate the principle of using a single tendon to perform a single movement because concomitant thumb and index finger extension is a composite movement that is useful in precision manipulation.
During World War I, Sir Robert Jones developed a set of tendon transfers for radial nerve paralysis, which included the FCR to EIP transfer. Many modifications have been made to this plan, and as understanding of hand biomechanics and tissue healing continues to evolve, tendon transfer surgery will expand to new applications and dimensions.
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The EIP muscle is used in tendon grafting and transplantation
The extensor indicis proprius (EIP) is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm. Its primary function is to extend the index finger at the metacarpophalangeal and interphalangeal joints. The EIP is also involved in producing a weak extension of the wrist joint as it crosses it.
The EIP tendon is commonly used in tendon grafting and transplantation for hand injuries. It is the first choice for tendon grafting due to its length and diameter, and because it can be used without causing any functional deformity. The EIP tendon is often used to reconstruct thumb extension following the loss of the extensor pollicis longus (EPL) tendon function due to injury or rupture.
The EIP tendon is also used in the transposition of the extensor indicis proprius tendon, which is one of the two most common secondary reconstruction methods for the extensor pollicis longus muscle. This procedure is compared to the free intercalated palmaris longus (PL) tendon graft, which uses the palmaris longus tendon to extend the lower part of the palmar aponeurosis.
The choice between EIP tendon transposition and PL tendon grafting depends on the patient's demands. EIP tendon transposition is generally offered to the general undemanding population, while more demanding patients, such as musicians, may require the more extensive PL tendon graft procedure.
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The EIP muscle is involved in the extension of the metacarpophalangeal and interphalangeal joints
The extensor indicis proprius (EIP) muscle is a narrow, elongated muscle found in the posterior compartment of the forearm. It is involved in the extension of the metacarpophalangeal and interphalangeal joints of the index finger, allowing it to extend independently from other fingers. The index finger is one of the few fingers with its own separate extensor muscle.
The EIP muscle originates mainly from the ulna, arising from the posterior two-thirds of its distal surface, distal to the extensor pollicis longus muscle. Some fibres also stem from the adjacent interosseous membrane. It extends inferiorly and narrows into a tendon that passes deep to the extensor retinaculum. The tendon is invested within a tendinous sheath with the tendons of the extensor digitorum muscle.
As the EIP muscle crosses the wrist, it produces a weak extension of this joint. It assists in extending the wrist and midcarpal joints. The EIP muscle is also involved in tendon transfers and is commonly used in tendon grafting and transplantation for hand injuries.
The EIP muscle is important for proper hand function, allowing independent movement of the index finger. It is situated in the deep extensor compartment of the forearm, medial to the extensor pollicis longus and lateral to the extensor carpi ulnaris. The EIP muscle can be palpated by applying deep pressure over the lower part of the ulna while the index finger is extended.
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Frequently asked questions
The extensor indicis proprius (EIP) muscle is a narrow, elongated muscle found in the posterior compartment of the forearm.
The EIP muscle is involved in the extension of the index finger at the metacarpophalangeal and interphalangeal joints.
The EIP muscle is located in the deep extensor compartment of the forearm, medial to the extensor pollicis longus and lateral to the extensor carpi ulnaris.
The main function of the EIP muscle is to extend the index finger, which can move independently from other fingers due to having its own separate extensor muscle.
The EIP muscle tendon is commonly used for tendon grafting and transplantation in hand injury management. It is also utilized in tendon transfers, particularly in cases of extensor pollicis longus (EPL) rupture.
