Bone spavin is osteoarthritis, or the final phase of degenerative joint disease (DJD), in
the lower three hock joints. It usually affects the two lowest joints of the hock (the
tarsometatarsal and the distal intertarsal joints), with the third joint, the proximal
intertarsal, being the least likely to develop bone spavin (Fig. 1). The condition is
most commonly seen in teenage to elderly horses, although it can also occur in
younger horses less commonly.
Causes of Bone Spavin
• Cartilage compression
Excessive compression can cause, over time, the cartilage between the upper and
lower surfaces of the lower tarsal bones to become compressed and eroded. The joint
spaces then become smaller and new bone growth may occur.
• Uneven loading
Uneven loading causes excessive compression of the cartilage and bone on one side,
and strain in the joint capsule and supporting ligaments on the other side. When the
joint is repeatedly overloaded, exostoses, or ‘bone spurs’, occur. Strain of the
supporting ligaments can cause exostosis around the joint as well.