Anatomy of Flexor Digitorum Profundus

 

ANATOMY OF FLEXOR DIGITORUM PROFUNDUS

The flexor digitorum profundus (FDP) is a muscle in the forearm that flexes the fingers.
The flexor digitorum profundus muscle lies in the deep compartment of the forearm.

ORIGIN

• The FDP muscle arises from the upper 3/4 of the volar and medial surfaces of the ulna as well as the interosseous membrane and deep fascia of the forearm.

INSERTION

• The tendons of the FDP muscle are inserted into the base of the distal phalanges (2, 3, 4, 5) of the fingers.

Flexor Digitorum Profundus Tendon
– inserted into the distal phalanx.
Flexor Digitorum Superficialis Tendon
– inserted into the middle phalanx.

Decussation with the FDS at Camper’s Chiasma

INNERVATION
The FDP muscle is innervated by:

• Lateral part: anterior interosseous branch of median nerve.
• Medial part: ulnar nerve.

FUNCTION

• The FDP muscle is a flexor of all joints of the four medial fingers and specifically works on the DIP.
• The lumbrical muscles in the palm of the hand arise from the tendons of the flexor digitorum profundus and are inserted into the dorsal extensor expansions on the backs of the proximal phalanges of the fingers.

Disruption of the flexor digitorum profundus tendon distal to the lumbrical origin by amputation or rupture of the tendon can cause lumbrical plus finger.

Lumbrical plus finger is a paradoxical extension of the IP joint when attempting finger flexion.

The flexor digitorum profundus tendons to the long, ring and small finger have a common muscle belly and this my cause a condition know as quadrigia.
They may also be interconnected to the separate tendon that runs to the index finger.
These tendons will not be able to move independently.
If one tendon gets shorter, the other tendons will not have full excursion (quadrigia).

CAUSES OF QUADRIGIA
• Usually results from adhesion or scarring of the flexor digitorum profundus tendons.
• Can also result from over tightening or distal advancement of the tendon after rupture and repair.
• May also be seen after amputation with suturing of the profundus tendon to the extensor tendons

The condition results in a weak grasp in the remaining fingers.
The patient will not be able to make a full fist.
If one tendon is shortened the others will not shorten and there will be loss of flexion in the other digits.

COMPARTMENT SYNDROME OF THE FOREARM

Four Compartments of the Forearm
1. DORSAL COMPARTMENT
2. HENRY’S MOBILE WAD COMPARTMENT
3. SUPERFICIAL VOLAR COMPARTMENT
4. COMPARTMENT DEEP VOLAR COMPARTMENT

DEEP VOLAR COMPARTMENT

Muscles within the compartment:
* Flexor Digitorum Profundus
* Flexor Pollicis Longus
* Pronator Quadratus
(distal third of the forearm)

Clinical Presentation of Volar Compartment Syndrome

* Pain with passive extension of fingers / wrist
* Tenderness over volar aspect of forearm
* Flexion posture of the fingers
* Weakness of finger / wrist flexion

FASCIOTOMY

Fasciotomy of the Forearm Volar compartments, superficial and deep, must be released through an ample incision when involved.

1. Skin Incision
2. Release of superficial volar compartment
3. Release of deep volar compartment

Median nerve

• The median nerve branches as it courses through the forearm.
• The median nerve descends between the flexor digitorum superficialis and the flexor digitorum profundus proximally.
• The nerve then becomes superficial distally and is located between the flexor carpi radialis and the the palmaris longus.
• Here the nerve can become easily injured or blocked by anesthesia.

Anterior Interosseous nerve

• About half way down the forearm the anterior interosseous nerve exits from the dorsal lateral aspect of the median nerve.
• The anterior interosseous nerve is purely motor.
• All the muscles in front of the forearm are supplied by the median nerve except the medial half of the flexor digitorum profundus.

The Anterior Interosseous nerve gives branches to three muscles:

• pronator quadratus
• lateral half of the flexor digitorum profundus
• flexor pollicis longus

The patient will be unable to give the OK sign due to paralysis of the flexor pollicis longus and the flexor digitorum profundus muscles.