Equine Hock Arthritis

Figure 1

The radiograph above (Figure 1) is of a horse's hock or tarsus. This view is also known as the "Lateral" view or side view. The equine hock joint is made up of 4 individual joints which are labelled above. The bottom two joints are also known as the distal hock joints and include the distal inter-tarsal joint (DIT) and the tarsal metatarsal joint (TMT). When "injecting" hocks, these are the most common joints treated and are often referred to as the "upper and lower hock joints". Degenerative joint disease (DJD) or osteo-arthritis is most common in the distal hock joints and  often results in poor performance plus/minus lameness. Bog spavin is the term that refers to increased joint fluid within the tibiotarsal joint. This is the "high motion" joint of the hock and is NOT commonly injected with "hock injections". However if increased fluid is noted, a radiographic exam is definitely indicated prior to instituting a treatment plan. Generally speaking, arthritis of the distal hock joints is more acceptable and can be managed with intra-articular therapies. However, arthritis of the tibiotarsal joint and/or the proximal inter-tarsal joint is more concerning and is reason for concern when predicting future performance.

Figure 2

In Figure 2 and 3, there are radiographic changes that indicate osteo-arthritis of the tarsal metatarsal joint space. These changes were noted during a prepurchase exam of a 5 year old horse. The horse was sound during the exam and did NOT respond to hock/stifle flexion. The million dollar question is what to recommend to the buyer based on these findings. In my clinical experience, most horses with these changes will eventually need intervention via intra-articular cortisone injections. I believe that horses with these changes are MORE likely to need hock injections than those with "normal" radiographs. However, these findings are not necessarily a negative prognostic indicator with regards to the horse's future performance. 

With management, i.e, hock injections, these horses can compete at the highest level and succeed!  As such, these findings do NOT constitute a FAILING grade during the prepurchase exam however the buyer needs to be prepared for the strong likelihood of routine "maintenance". This can easily result in hundreds to thousands of dollars per year that should be considered into the price of the horse. 

Figure 3