Hock Bone Cyst

9 y.o. warmblood jumper with acute onset, moderate, left hind limb lameness and large tibiotarsal joint (hock) effusion. Horse improved for 1 week then became toe-touching lame on left hind limb. Digital radiographs of the left hock showed no significant abnormalities. Horse improved significantly when local anesthetic injected into left tibiotarsal joint, or with peroneal/tibial nerve blocks. No improvement when horse blocked from foot to distal intertarsal joint. Nuclear scintigraphy (bone scan) performed: intense uptake of radioisotope at the level of the intertarsal joints or talus), and also had increased uptake in the distal left tibia, at the level of the tibiotarsal joint.

Recommended MRI of left hock: there was a fairly large, centrally located talus bone cyst in the distal end of the talus, which appears to communicate with the proximal intertarsal joint. STIR MRI showed intense signal surrouding a large area around this cyst, and the T2-Weighted MRI showed abnormal architecture of the bone suggestive of stress fracture, or severe bony inflammation, propagating through this cyst. The distal subchondral plate of the cyst is not apparent, so it must involve the proximal intertarsal joint. The proximal suspensory ligament was within normal limits.