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Types of Interphalangeal Joints

The phalanges (singular phalanx) are the bones of the fingers and toes. The name comes from an ancient word for soldiers standing in formation--side by side and several rows deep. The arrangement of the finger bones apparently suggested to someone rows of solders. There are basically three types of phalanges: finger bones, thumb bones and toe bones. The joints between phalanges are called interphalangeal joints.

  1. Finger Bone Joints

    • Fingers have three phalanges. Starting from the hand, the three phalanges are the proximal, medial and distal. Therefore there are two interphalangeal joints: the Proximal/Medial joint (PMJ) and the Medial/Distal Joint (MDJ). They are similar in that they move in the same plane (that the finger is pointing in) and can flex (move forward from a resting position) much further than they can extend (move in the other direction). The PMJ can flex more than 90 degrees but the MJD can flex little more than 45 degrees--and that only if the PMJ is flexed. The PMJ can almost never extend past the resting position (finger straight) but the MJD can often extend slightly beyond the resting position. The first joint (the knuckle) is not called an interphalangeal joint because it is not between two phalanges--it is between a phalanx and a metacarpal (hand bone).

    Thumb Bone Joints

    • The thumb has only two phalanges, but they are much more mobile than the phalanges of the fingers. The only interphalangeal joint of the thumb can only move in a plane like the phalanges of the fingers, but the large proximal phalanx of the thumb has a phalanx/metacarpal joint that allows it to point the thumb in a much wider range of direction than is available to the fingers. One demonstration of this increased range of motion is the fact that the thumb can easily touch its tip to the tips of the fingers, and none of the fingers can even come close to doing this. The interphalangeal joint cannot flex quite 90 degrees, but it doesn't need to because the proximal phalanx can bring into so many positions. The interphalangeal joint of the thumb can, however, easily extend to 45 degrees.

    Toe Bone Joints

    • The toes are built on the same general model as the fingers. The big toe has two phalanges and all the rest have three. All the toes are much shorter and much less flexible than the fingers. Toes move in a single plane except for some lateral movement of the big toe in some people. There is the same number of interphalangeal joints in a foot as in a hand--nine--but they cause fewer problems because they see much less action.

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