Severe Cartilage Degeneration in a Horse

A 12 year-old show jumper mare presented to PHD veterinary services for the history of recurring forelimb lameness. In the past 2 years, the mare had the left front coffin joint treated with corticosteroids and hyaluronic acid every 6 months. However, the most recent treatment with intra-articular corticosteroids did not result in resolution of the lameness. On presentation, the mare was a grade 3/5 lame in the left front. The lameness was most evident when trotting on firm ground and in a circle to the right. The mare was NOT positive to hoof tester exam and was mildly positive to lower limb flexion. The coffin joint was "blocked" with carbocain and the mare's lameness improved by >85%. Radiographic exam of the left front foot only revealed evidence of mild osteoarthritis of the coffin joint.  (Figure 1).

Figure 1

Due to the following factors: 1) a history of poor response to intra-articular therapy, 2) a positive response to blocking the coffin joint, and 3) minimal data via the radiographic exam, it was recommended that the distal forelimb of this mare be evaluated via magnetic resonance imaging (MRI).  The MRI exam requires general anesthesia and generally costs between $1800-$2000; however the information gathered from an MRI exam is far superior than any other type of diagnostic exam! As such, I strongly recommend considering an MRI exam in cases that the CAUSE for the lameness has not been determined and a reasonable attempt has been made to treat and/or diagnose the problem. Figures 2-4 includes several images from the MRI exam involving this show jumper mare. A small, blue circle is included in each image to high light the large articular cartilage and subchondral bone defect that was discovered through the MRI study. In each image, the lesion appears as a small black circle at the surface of the bone. In addition to this finding, the MRI study noted additional evidence of chronic degeneration of the coffin joint. The full extent of the degeneration and the cartilage damage was NOT evident in the radiographic exam!!

Figure 2

Figure 3

Figure 4

Although the prognosis was poor for return to soundness, the mare was treated aggressively with various regenerative therapies and extended rest. Unfortunately, the mare remained significantly lame and it was determined that humane euthanasia was the best option due to the relentless foot pain. A post-mortom exam was performed and a very large area of abnormal cartilage loss (blue circle in Figure 5) was noted that corresponded to the MRI findings. This case represents yet another exam of the importance for getting an answer as to WHAT is causing the problem such that a prognosis can be provided followed by a proper course of action.

Figure 5

In the state of Florida, the most sensitive MRI for imaging in horses is ONLY available at the University of Florida's College of Veterinary Medicine. In addition, the board certified radiologists at the Veterinary College of Veterinary Medicine are especially well trained for the evaluation of MRI studies in horses! For more information about their services please go to:

http://largeanimal.vethospitals.ufl.edu/services/diagnostic-imaging/

High Ring Bone!!

The radiographic image below is of the right hind pastern of a 4 year old mare that presented for a prepurchase exam. The mare had only been under saddle for 6 months. During the active exam, the mare cross-cantered when lunged to the left. In addition, the pastern area was "thicker" when compared to the opposite hind limb and the mare was moderately positive to flexion of the limb in question. Due to the suspicion of a significant problem, the right hind pastern was radiographed. The yellow arrows highlight new bone growth along the edges of the pastern joint. The bone growth or osteophytes are large and proliferative. These findings are indicative of advanced osteo-arthritis of the pastern joint otherwise known as "high ring bone". 

Figure 1

In Figure 2, the same osteophytes are noted as the course around the front of the pastern joint. The yellow arrows point to the osteophytes or irregular "white" structures along the edge of the pastern joint. 

Figure 2

Figure 3 and 4 are radiographs of a normal pastern joint. There are no osteophytes noted along the margins of the pastern joint. Notice in Figure 4 the smooth, curved border of the normal pastern joint. Interestingly, the pastern imaged in Figures 3 and 4 was radiographed because it palpated "thicker" than the opposite limb. Fortunately, there was no evidence of pastern arthritis. 

Figure 3

Figure 4

 In Figure 5 there is significant new bone growth or osteophyte development along the margins of the coffin joint. This is known as "low ring bone". Generally speaking, "high" or "low" ring bone is a significant finding during a prepurchase exam. Low ring bone is more common in draft breed horses. In addition, varying degrees of coffin joint arthritis, in active sport horses, is more common than pastern arthritis.

Figure 5

 High ring bone or pastern arthritis should be a concerning finding in any horse that is expected to carry a rider. Medical management of pastern osteoarthritis is limited to intra-articular treatment with cortisone or regenerative therapies. Unfortunately, the degeneration of the joint progresses rapidly and commonly results in chronic lameness. Surgical management involves fusion of the joint either with hardware or chemicals.