Overview
Cattle bear weight on two main digits, III (medial) and IV (lateral), each with three phalanges: proximal, middle and distal. Digits II and V are the dewclaws (accessory digits), on the palmar side of the fetlock; they contain one or two small bones that do not articulate with the rest of the skeleton. The joints of each digit are the metacarpophalangeal (fetlock), the proximal interphalangeal (pastern) and the distal interphalangeal joint, the last inside the claw. In the thoracic limb the medial claw is usually slightly larger than the lateral.
Phalanges
- Proximal phalanx (phalanx proximalis): the longest; articulates with one condyle of the metacarpus and with the proximal sesamoid bones.
- Middle phalanx (phalanx media): shorter; its distal end lies partly inside the claw.
- Distal phalanx (phalanx distalis): entirely enclosed in the claw, whose shape it mirrors. It has a parietal surface under the horn wall, a solear surface over the sole, an axial surface facing the interdigital space, the dorsal extensor process for the tendon of the digital extensor, and the flexor tubercle on the solear surface for the tendon of the deep digital flexor.
Sesamoid bones
- Proximal sesamoid bones (ossa sesamoidea proximalia): four per limb, two on the palmar side of each fetlock.
- Distal sesamoid bone (os sesamoideum distale): one per digit, palmar to the distal interphalangeal joint; the tendon of the deep digital flexor passes over it to the flexor tubercle.
Clinical relevance
- Fractures of the distal phalanx: mainly affect the medial claw of the thoracic limb, sometimes in both forefeet. They are treated by gluing a block onto the sound claw to unload the injured one.
- Septic pedal osteitis and septic distal interphalangeal arthritis: complications of claw lesions such as sole ulcer, white line disease or toe necrosis, when infection reaches the bone or the joint. They may require resection of the affected tissue or amputation of the digit.
- Toe necrosis: affects the tip of the distal phalanx.