Phalanges of the hand
The phalanges are the terminal bones of the upper limb. There are fourteen in total, with each finger having three; a proximal, middle and distal phalanx, with the exception of the thumb, which only has two; a proximal and a distal phalanx.
There are five proximal phalanges which correspond to each of the five fingers. Like the metacarpal bones, the proximal phalanges have a proximal base with a transverse oval articular facet which connects them to their subsequent metacarpal bones respectfully. Their shafts are long and are flat on their palmar aspect. They are convex both dorsally and transversally and also have sharpened medial and lateral borders in order for the fibrous tendon sheaths of the flexor muscles to attach. Distally, the trochlea or phalangeal head has an articular surface that links the proximal phalanges to the middle phalanges and in the case of the thumb, to its distal phalanx.
There are four middle phalanges which correspond to the index finger, the middle finger, the ring finger and the little finger. They have a proximal base and a distal head which is separated by a much shorter shaft than that of the proximal phalanges. The base of a proximal phalanx has a medial and lateral facet that surrounds a midline groove that is smooth and is coherent with the distal head of the proximal phalanx. Distally, the heads of the middle phalanges articulate with the bases of the distal phalanges.
There are five distal phalanges, including that of the thumb. Each of them is tapered distally and has a wider proximal base that articulates with the middle phalanges or the proximal phalanx in the case of the thumb. Distally, the surfaces of the distal phalanges are rough, especially on their palmar aspect where the tendon of the flexor digitorum profundus inserts. Dorsally, a rough spade-shaped plate that faces in the palmar direction can be seen and is known as the tuberosity of the distal phalanx.
Mallet finger is a term used to describe a dislocated fracture of the extended distal phalanx of a finger and is commonly seen is sports such as volleyball or baseball. In this situation, the force of impact disconnects the distal phalanx from the middle phalanx and in some cases the tendon that attaches to it is also ruptured.
When this happens, the flexor digitorum profundus tendon may also avulse small or large bone fragments with it. Damage risk to the tendon is increased when it undergoes violent traction as the distal phalanx is flexed.