Overview
The forepaw of the dog has five digits. Digits II to V each have a proximal, a middle and a distal phalanx (phalanx proximalis, media et distalis); digit I (the dewclaw) has only a proximal and a distal phalanx. The dog stands on its digits (digitigrade stance): the phalanges of digits III and IV are the longest and carry most of the load, under the digital pads.
Key features
- Proximal phalanx: the longest; articulates with the head of the metacarpal bone. Two proximal sesamoid bones lie on the palmar side of each metacarpophalangeal joint, in the tendon of the interosseous muscle, and a small dorsal sesamoid sits on its dorsal side.
- Middle phalanx: shorter, with a proximal base and a distal head.
- Distal phalanx: carries the claw. Its ungual crest (crista unguicularis) overlaps the base of the claw and its unguicular process (processus unguicularis) forms the core of the claw. Elastic dorsal ligaments keep the distal phalanx raised when the digital flexor muscles relax.
Clinical relevance
- Subungual tumours (squamous cell carcinoma, melanoma) destroy the distal phalanx; treatment is amputation of the digit.
- Sesamoid disease: fragmentation of the proximal sesamoid bones, especially the second and seventh of the forepaw, is common in Rottweilers and other large breeds and often incidental on radiographs.
- Dewclaw injuries: torn or overgrown dewclaw claws are frequent because they do not wear down on the ground.
In this model the phalanges and proximal sesamoid bones come from a CT scan of another dog (Scan the World), scaled and posed in a standing position.