Overview
The tarsus (ossa tarsi) is the group of short bones of the hock, between the tibia proximally and the metatarsus distally. Cattle have five tarsal bones, because several of them are fused; laterally the malleolar bone, the distal remnant of the fibula, is added to them. A feature of ruminants is that the talus has two trochleae, a proximal and a distal one, so that besides the tarsocrural joint the proximal intertarsal joint also allows some flexion.
Bones
- Talus: medial in the proximal row. Its proximal trochlea fits the cochlea of the tibia; its distal trochlea articulates with the centroquartal bone.
- Calcaneus: lateral in the proximal row. Its tuber (tuber calcanei) forms the point of the hock and receives the common calcaneal tendon (gastrocnemius and superficial digital flexor, among others), which extends the tarsus. The sustentaculum tali guides the tendon of the deep digital flexor medially.
- Malleolar bone (os malleolare): between the distal end of the tibia and the calcaneus, on the lateral side.
- Centroquartal bone (os centroquartale): fusion of the central and fourth tarsal bones; it spans the whole width of the tarsus below the talus and calcaneus.
- Fused second and third tarsal bone (os tarsale II et III): a single bone in the distal row.
- First tarsal bone (os tarsale I): small, on the plantaromedial side of the distal row.
Clinical relevance
- Hock lesions: hair loss, wounds and swellings on the lateral side of the tarsus, over the calcaneal tuber and the malleolar bone, in dairy cows housed in cubicles or on hard or abrasive floors with little bedding. They can be complicated by bursitis and infection of the periarticular tissues.
- Septic tarsocrural arthritis: in calves with navel infection and, in adults, from wounds or extension of hock lesions.
- Rupture of the gastrocnemius or the common calcaneal tendon: in cows that slip or become recumbent; the hock drops towards the ground.
- Spastic paresis: not a lesion of the tarsus but a neuromuscular disorder of young cattle in which spastic contraction of the gastrocnemius holds the hock overextended, with the limb straight and swung caudally.