Logan Steele
The human hand is a complex system of muscles, tendons, and joints that work together to allow for a wide range of movements and dexterity. One of the key muscles involved in finger flexion is the flexor digitorum profundus (FDP), which is responsible for flexing the distal phalanges of the medial four digits, including the index finger. This muscle is unique in its ability to flex the distal interphalangeal (DIP) joints of the second to fifth fingers. The independence of the FDP for the index finger allows for a greater range of motion and dexterity in the hand. However, this complexity also makes the FDP susceptible to various injuries and conditions, such as quadrigia and jersey finger, which can impact the finger's range of motion and gripping strength.
| Characteristics | Values |
|---|---|
| Muscle name | Flexor digitorum profundus (FDP) |
| Other names | Flexor digitorum communis profundus |
| Location | Forearm |
| Function | Flexes the fingers |
| Primary action | Bends the index, middle, ring, and small fingers |
| Assists in flexing | Wrist |
| Joints | MCP, DIP, PIP |
| Tendon | Flexor digitorum superficialis (FDS) |
| Conditions | Quadrigia, Jersey finger, Volar compartment syndrome, Carpal tunnel syndrome |
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What You'll Learn
The flexor digitorum profundus (FDP) muscle
The FDP muscle is a component of the deep flexor compartment of the forearm, which also includes the flexor pollicis longus and pronator quadratus muscles. The FDP muscle originates from four locations: the superior three-quarters of the anterior surface of the ulna, the adjacent interosseous membrane, the coronoid process of the ulna, and the aponeurosis of the flexor carpi ulnaris muscle. The muscle then travels toward the hand, where it divides into four tendons that attach to the palmar surfaces of the distal phalanges of digits 2-5.
The FDP muscle is innervated by both the ulnar and median nerves. The medial half of the muscle, which flexes the 4th and 5th digits, is supplied by the ulnar nerve, while the lateral half, which flexes the 2nd and 3rd digits, is supplied by the median nerve's anterior interosseous branch. The FDP muscle is crucial for hand gripping strength and plays a significant role in establishing and maintaining a strong grip.
Injuries to the FDP muscle can result in conditions such as quadrigia and jersey finger. Quadrigia occurs when the FDP tendons to the medial 3 digits fuse with the FDP tendon to the index finger, resulting in the patient's inability to make a full fist and a weak grasp. Jersey finger is a rupture of the FDP tendon close to the base of the distal phalanx, affecting the 4th digit in most cases. These conditions can arise from FDP tendon adhesion, scarring, or rupture and repair, highlighting the importance of the FDP muscle in finger and hand function.
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The flexor digitorum superficialis (FDS) muscle
The FDS arises from the medial epicondyle, which is an elbow bone, and is positioned between the palmaris longus and flexor carpi ulnaris muscles. As it courses down the forearm, it separates into two planes of muscular fibres: the superficial and deep planes. The superficial plane divides further to supply tendons for the middle and ring fingers, while the deep plane provides muscular support for the tendon of the ring finger before dividing to supply tendons for the index and little fingers.
The FDS has four independent muscle bellies, from which four tendons arise. These tendons pass deep through the transverse carpal ligament, contributing to the nine tendons found in the carpal tunnel. The FDS tendon inserts onto the middle phalangeal bases of the second to fifth fingers, with the independence of each finger's FDS allowing for skilled hand movements such as using chopsticks.
The primary function of the FDS is to flex the middle joint of each finger, excluding the thumb. It is important to distinguish the FDS from the FDP, as the latter has a common muscle belly for the middle, ring, and small fingers, resulting in the simultaneous bending of these fingers. In contrast, the FDS enables independent finger movements, such as bending the tip of one finger without affecting the others.
Injuries to the FDS, such as belly or tendon rupture, are considered rare but have been documented in case reports. One such injury is Carpal Tunnel Syndrome (CTS), which can cause intermittent numbness and discomfort in the wrist, palm, thumb, index, and middle fingers. Treatment options for CTS include surgical release of the carpal tunnel or non-operative interventions like steroid injections or wrist splinting.
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Carpal tunnel syndrome
The flexor digitorum profundus (FDP) is a muscle in the forearm that flexes the fingers. It is the only muscle that can flex the distal phalanges of the medial 4 digits at the DIP joints. The FDP also assists in flexing the hand and is the main gripping muscle.
The treatment for carpal tunnel syndrome ranges from non-invasive treatments to surgery. Non-invasive treatments include splinting the hand to restrict wrist movement and ease nerve compression, anti-inflammatory medication to reduce swelling, and hand therapy or exercises to improve ergonomics and nerve function. Surgery may be recommended to directly address the compression on the nerves in the carpal tunnel.
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Quadrigia
The flexor digitorum profundus (FDP) is a muscle in the forearm that flexes the fingers. It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. The FDP forms the deep layer of the ventral forearm muscles together with the flexor pollicis longus (FPL) and pronator quadratus. The FDP is the only muscle that can flex the distal phalanges of the medial 4 digits at the DIP joints.
The FDP tendons to the 5th, 4th, and 3rd fingers have a common muscle belly, but there is a separate belly for the index finger. This allows for the independent movement of the index finger. However, in some cases, the FDP tendons to the 3 medial digits may fuse with the FDP tendon to the index finger. This condition is known as Quadrigia.
The condition can also occur following adhesion or scarring of the FDP after rupture and repair. Treatment for Quadrigia may vary depending on the underlying cause and severity of the condition. In some cases, surgery may be required to correct the fused tendons and restore independent movement to the fingers.
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Jersey finger
The name 'Jersey finger' comes from football athletes who grip the jersey of an opposing player who is trying to get away. As the player tries to free themselves, the finger gets unexpectedly straightened as it is still trying to flex and grip. This creates a tug of war, where the tendon is being pulled in two directions, which can result in the tendon separating from its bone insertion at the fingertip. Sometimes, a piece of the bone is also torn away. While this example is classic, other sports and activities, such as rock climbing, can also lead to a jersey finger.
The classification system of a jersey finger injury is based on the level of tendon retraction and the presence or absence of a fracture. The injury can be classified as one of five types, with Type I being the most severe and Type III being the most favourable. Type I occurs when the FDP tendon retracts to the palm at the lumbrical origin, while Type III involves little to no retraction of the tendon. The treatment for a jersey finger injury depends on the specifics of the injury, with surgery being the most common form of treatment.
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Frequently asked questions
The flexor digitorum profundus (FDP) is the muscle that flexes the index finger.
The FDP forms the deep layer of the ventral forearm muscles along with the flexor pollicis longus (FPL) and pronator quadratus.
The FDP is the main gripping muscle and acts optimally when the wrist is extended. It is the only muscle that can flex the distal phalanges of the medial 4 digits at the DIP joints.
Injury to the FDP can lead to conditions such as quadrigia and jersey finger, resulting in decreased hand function and weakness in finger flexion.
Symptoms of an FDP injury include difficulty performing tasks requiring finger dexterity, such as using chopsticks, and the inability to make a full fist or perform an "OK" sign with the thumb.
