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The distal interphalangeal joint is one of two joints within the four fingers and four lesser toes. Found between the second and third phalanges — the phalanges being the three bones in each finger and toe — it is the first joint in from the tips of the fingers and toes. Compared to the proximal interphalangeal joint, the second joint in from the tips of the fingers and toes, the distal joint is slightly smaller and exhibits a narrower range of motion.
In the hand, the distal interphalangeal joint is found roughly an inch below the fingertip, just beyond the fingernail. In anatomy, distal is a term of relative location, referring to a structure that is farthest from the trunk of the body versus one that is nearest the body, or proximal. As the thumb has only two phalanges rather than three, there is no distinction between a proximal and distal interphalangeal joint in this digit.
At this articulation, a synovial hinge joint, possible movements are a small degree of flexion and extension, or the bending and straightening of the fingers. The flexor digitorum profundus is the muscle responsible for flexion of the distal interphalangeal joint. Found deep in the palm side of the forearm, it is located on the pinky side of the arm above the ulna bone. It is considered an extrinsic flexor of the hand, meaning that the body of the muscle is situated in the forearm, with only its tendon penetrating the hand. Contraction of this muscle allows about 80 degrees of flexion in the distal joint, whereas the proximal joint enjoys about 100 degrees of flexion.
Distal interphalangeal joint extension is similarly initiated by an extrinsic muscle of the hand, the extensor digitorum. It is centrally located in the posterior compartment of the forearm with tendons running through the back of the hand to the middle and distal, or second and third, phalanges. The degree of extension permitted here is relatively restricted by the presence of very strong ligaments, the palmar and collateral ligaments, which stabilize the joint and keep it from hyperextending.
In the foot, a similar joint is found between the middle and distal phalanges of each of the four smaller toes. The big toe, like the thumb, has two phalanges and therefore only one interphalangeal joint. Also a ginglymoid or synovial hinge joint, the distal interphalangeal articulation of the foot allows no movement other than flexion and extension, with extension limited by the presence of plantar and collateral ligaments. The muscle that flexes this joint is the flexor digitorum longus, an extrinsic toe flexor found in the posterior compartment of the lower leg on the medial or tibial side. Extension of this joint is provided by the extensor digitorum longus, situated in the anterior compartment of the lower leg with four tendons inserting on the four distal phalanges.
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