Imagine your hand has undergone a major accident and it is difficult for you to move your fingers. Do you know the reason for this? It is because your flexor digitorum profundus (FDM) and flexor digitorum superficialis (FDS) muscles of your fingers have been damaged.
Table of Contents
Flexor Digitorum Profundus
The flexor digitorum profundus is situated on the exterior side of the forearm also known as the extrinsic hand muscle (EHM) that is responsible for flexing the joints of four fingers index, middle, ring, and pinky finger. Its nucleus lies in the deep volar compartment of the forearm and arises from the ulna of the forearm.
The flexor digitorum profundus is a muscle of (wrist) midcarpal, (knuckles) metacarpophalangeal, and (proximal end of fingers ) interphalangeal joints of index, middle, ring, and little fingers.
The tendons of the flexor digitorum profundus merge with the base of the distal phalanges of index, middle ring, and pinky fingers. While the tendons of the index finger separates from the middle, ring and little fingers partially attached flexor digitorum profundus tendons because they go through the carpal tunnel.
Function of Flexor Digitorum Profundus
We often marvel at the creation of our bodies. All the organs are devoted to working in a disciplined manner. We are amazed at how our fingers can have a grip on any object!
It is because the flexor digitorum profundus originates at or below the wrist joint, therefore the contraction of muscles produces mass action movement in all four digits which results in a powerful grip.
It aids in full flexing of fingers at interphalangeal joints and metacarpophalangeal joints because the flexor digitorum profundus muscle inserts into the dorsal extensor of the proximal phalanges
Blood Supply and Lymphatic
The flexor Digitorum profundus is supplied through anterior interosseous artery(a branch of the common interosseous artery) accompanied by the palmar interosseous artery(a branch of the median nerve). These interosseous arteries together branches out flexor digitorum profundus muscles and flexor pollicis longer muscles
Flexor digitorum profundus is associated with the upper limb or forearm lymphatic system consisting of superficial and deep lymphatic vessels.
The superficial vessel around the basilic vein goes to the cubital lymph nodes and the cephalic vein goes to the axillary lymph nodes. Some of the deep lymphatic vessels also drain lymph from flexor digitorum profundus which terminates into the humeral axillary lymph nodes
Nerves
The lateral part of flexor digitorum profundus associated with the index and middle finger is innervated by the median nerve, and the medial part i.e. ring and little finger is supplied by the ulnar nerve
Muscles
Along with flexor pollicis longus and pronator quadratus, the flexor digitorum profundus muscle forms a deep layer of the ventral forearm muscles. The decussation of the flexor digitorum profundus tendons and flexor digitorum superficialis tendons occur at Camper chiasm.
Clinical Significance
Jersey Finger
The most common injury of flexor digitorum profundus is “Jersey Finger”. It is caused by rupturing the tendons of flexor digitorum profundus at its point to the attachment to the distal phalanx. It is also known as the “rugby finger”.
This injury can occur if a player catches hold of another player’s jersey with a tip of the fingers while the player is running or playing. This results in hyperextension at the tip of the finger and the proximal portion of the finger is flexed.
The “Jersey finger” can partially or completely rupture FDP tendons depending upon the severity of the injury. 75%of the time ring finger is commonly associated with a jersey finger injury. The traumatic accident is not associated only with football, any other athletic game can cause a jersey finger injury.
Flexor Digitorum Superficialis
It is the largest muscle of the anterior compartment of the forearm. As the name suggests this muscle is found in the superficial layer of the forearm. It courses distally towards the wrist where it splits into four different tendons. As they are superficial in nature they can be easily spotted on the distal part of the forearm
Origin and Insertion
It is divided into two heads
Humeroulnar head – It originates from the medial epicondyle humerus bone via the common flexor tendons
Radial head- it arises from the upper two-thirds of the anterior of the radius. It extends to the distal forearm.
Here the muscles are generally arranged superficially in the strata form.
What is the relation of flexor digitorum profundus to flexor digitorum superficialis ?
As mentioned earlier, flexor digitorum superficialis lies in the anterior compartment of the forearm which is superficial to flexor digitorum profundus.
In simple words, the superficialis splits into two to pave way for profundus to pass, the superficialis split tendon then reunites deep to the tendon of profundus around which it forms a loop
Blood supply
The two heads of superficialis form a muscular arch through which the median nerve and ulna artery pass.
The primary arterial blood supply to the superficialis receive blood from the ulna artery and its posterior surface receive blood from the median artery
Function
The main function of the superficialis is flexion of the digits 2-5 at the proximal interphalangeal and metacarpophalangeal joints. They have independent muscle slips for all four digits which results in individual flexing of the fingers at the interphalangeal joints. It also helps in flexion of the wrist
Clinical Significance
Carpal Syndrome
Carpal syndrome is a condition that causes numbness, tingling or prickling, and pain in the thumb, index and middle finger, and in the median portion of the ring finger. It is mainly caused due to compression of the median nerve as it passes through the carpal tunnel. This median nerve is also accompanied by flexor digitorum profundus, flexor digitorum superficialis, and flexor pollicis longus.
Carpal syndrome is mostly caused by the reduction of the space around the median nerve. It could be selling due to injury, inflammation, or neoplasm.
It is not common for aberrant muscle belly arising from flexor digitorum superficialis to compress the median nerve and cause Carpal syndrome.
