The hock (tarsus) is a complex of joints of the lower rear limb of the horse. It is composed of six bones (tarsal bones) that comprise four different joints. The uppermost or most proximal joint (tarsocrural) has the widest range of motion. The other three joints are less mobile (low motion joints) but do experience torsional forces that affect the overall health of the hock. Bone spavin usually affects the two most distal lower joints of the hock [distal intertarsal (DIT) and tarsometatarsal (TMT) joints].
What is bone spavin?
Bone spavin is a common, often painful condition of the two most distal joints of the hock (DIT and TMT); it is also called true spavin or jack spavin and is a manifestation of osteoarthritis or degenerative joint disease. The lameness associated with bone spavin usually has a slow onset with progressively worsening clinical signs.
What causes bone spavin?
Bone spavin usually occurs in mature or older horses that are asked to work excessively off the hind limbs. Repeated compression and rotation of the bones (as with high speed stops and turns) and excessive tension on the ligaments and tendons is a prominent component of the whole disease process. Multiple repetitive traumatic insults (“use trauma”) to the hock as associated with day to day training, activities, and competition of these horses is a common factor in the pathogenesis of osteoarthritis.
Although some horses do not have observable changes that can be detected or measured, they still suffer from pain in the hock. When this is the case, the term blind or occult spavin is instituted. These horses display the clinical signs of bone spavin (such as pain and/or a reluctance to perform or a reluctance to perform at the previous level), but not all of the documentable changes are necessarily seen. Conformation of the horse is also a factor in the development of bone spavin. Horses with sickle hocks (increased angle of flexion) or cow hocks (hocks close together and almost touching with the toe pointing outward) have increased stress on the bony structures of the joint. Bone spavin can also occur in conjunction with fractures, infectious joint disease, metabolic bone disease, and developmental bone diseases of young horses.
How is bone spavin diagnosed?
Bone spavin can be diagnosed by a veterinarian by assessing the history of the horse (age, breed and use of horse), performing a physical exam (joint effusion or swelling, heat, pain on palpation of the joint), performing a lameness exam (hock flexion, trotting and circling the horse on a hard surface, intraarticular anesthesia (joint blocks), and radiographs. Radiography of the hock may reveal periarticular osteophytes (bony proliferation in proximity with joint spaces), bone lysis (decreased density of bone), and/or bone remodeling (increased density of tarsal bones). Nuclear scintigraphy (bone scan) can also be performed which may reveal "hot" spots indicative of joint/bone injury. Not all of these procedures are necessary to diagnose bone spavin. Consideration is given to the owner’s wishes to either invest in the diagnosis or to invest in treatment. Although some horses do not have observable changes that can be detected or measured, they still suffer from pain in the hock; when this is the case, the term blind or occult spavin is instituted. These horses display the clinical signs of bone spavin (such as pain and/or a reluctance to perform or a reluctance to perform at the previous level), but not all of the documentable changes are necessarily seen.
Treatment of bone spavin can be divided into three main types: conservative, medical, and surgical. Conservative and medical treatments focus on reduction of inflammation with or without protection of the joint cartilage, while surgical treatment involves arthrodesis (joint fusion), or tendon cutting. The goal of any treatment for bone...