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In human anatomy, the annular ligaments of the fingers, often referred to as A pulleys, are the annular part of the fibrous sheathes of the fingers.Four or five such annular pulleys, together with three cruciate pulleys, form a fibro-osseous tunnel on the palmar aspect of the hand through which passes the deep and superficial flexor tendons.
It contains tendons of the flexor digitorum superficialis and the flexor digitorum profundus, but not the flexor pollicis longus. [ 2 ] The sheath which surrounds the flexor digitorum extends downward about halfway along the metacarpal bones , where it ends in blind diverticula around the tendons to the index , middle , and ring fingers .
The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor, used, for instance, for pointing. The extensors are situated within 6 separate compartments.
The capsule, extensor tendon, and skin are very thin and lax dorsally, allowing for both phalanx bones to flex more than 100° until the base of the middle phalanx makes contact with the condylar notch of the proximal phalanx. [1] At the level of the PIP joint the extensor mechanism splits into three bands.
The absence of the tendon of the extensor digitorum communis to the little finger is associated with the thicker type 3r juncturae tendinum in the fourth intermetacarpal space. [3] Hirai et al. reported type 1 junturae tendinum between the extensor digiti minimi and the extensor digitorum communis to the ring finger in 6% of the specimens. [1]
The vincula brevia (short), which are two in number in each finger, and consist of triangular bands of fibers, one connecting the tendon of the flexor digitorum superficialis to the front of the first interphalangeal joint and head of the first phalanx, and the other the tendon of the flexor digitorum profundus to the front of the second ...
These tendons, along with those of flexor digitorum profundus, are enclosed by a common flexor sheath. The tendons attach to the anterior margins on the bases of the intermediate phalanges of the four fingers. These tendons have a split (Camper's Chiasm) at the end of them through which the tendons of flexor digitorum profundus pass.
Flexor digitorum profundus originates in the upper 3/4 of the anterior and medial surfaces of the ulna, interosseous membrane and deep fascia of the forearm. The muscle fans out into four tendons (one to each of the second to fifth fingers) to the palmar base of the distal phalanx. [3]