Extensor Process Fracture in a Horse

A teen-age gelding presnted for the complaint of forelimb lameness. The gelding had been purchased approximately 6 months prior and the prepurchase exam performed did NOT include a radiographic exam. The gelding was mildly lame in a straight line however the lameness was significantly worse when lunged in a small circle. Through a series of nerve blocks it was determined that the lameness was originating from the foot and a radiographic study was performed. The radiographic images in Figure 1-3 are lateral views of the foot in question. Two abnormalities are noted by the yellow and blue arrows in Figure 2. The blue arrow corresponds to a chip fracture of the extensor process of the coffin bone and the yellow lines correspond to extensive mineralization of the cartilage of the foot (side bone).

Figure 1

Figure 2

 In Figure 3, the extensor process chip fracture is magnified. It is likely that this chip fracture was present at the time of purchase and would have been discovered had the client opted for a radiographic exam of the forelimb feet.  In my opinion, this radiographic finding would have been reason enough the FAIL the horse at the time of prepurchase exam.  In addition to the extensor chip fracture, moderate "side bone" development is evident in the lateral view and the dorsal-palmar view (Figure 4). Typically, side-bone does not present a clinical problem however does consist of an abnormal finding and in this horse the side bone is more pronounced along the inside versus the outside of the foot. The asymmetry of the side-bone may be more clinically relevant that bilateral side-bone that is symmetrical.

Figure 3

Figure 4

The horse was treated with intra-articular corticosteroid and is approximately 75% improved with respect to lameness. The long term prognosis for this horse is guarded due to fracture of the extensor process of the coffin bone. This case represents yet another example of the need for at least foot radiographs at the time of prepurchase exam.

Stifle OCD!!

A yearling thoroughbred presented for sudden lameness and swelling around the stifle joint. The filly had been purchased several months prior from a select thoroughbred sale and repository radiographs were performed at the time of purchase. At the time of purchase, the filly was sound, there was no effusion of the stifle joint and there were no obvious radiographic changes noted in either stifle joint. When the filly presented for lameness, the stifle radiographs were repeated. Close inspection of the lateral trochlear ridge suggested irregular contours (yellow arrows inside blue box, Figure 2) of the trochlear ridge along the mid body region (Figure 1 and 2, blue box). Based on the radiographs alone, the filly was treated with intra-articular Hylartin and forced stall rest for 30 days.

Figure 1

Figure 2

Unfortunately, the filly remained lame after 30 days of stall rest and a follow-up exam included an ultrasound evaluation of the stifle joint. The ultrasound exam revealed significant changes along the lateral trochlear ridge which were not fully appreciated on the radiographic exam. In Figure 3, the lateral and medial trochlear ridge are displayed. The bony surfaces of the trochlear ridges appear as a bright white lines and the cartilage as  thin black lines that follow the contour of the bony surface. Any disruption of the bony surface/cartilage will appear as a mix of disrupted white lines and black pockets. In Figure 3, the image on the left is of the lateral trochlear ridge and there is clearly disrupted bone and cartilage along the bony surface.

Figure 3

In Figure 4, the lateral trochlear ridge is imaged in a longitudinal plane to assess the length of the defect. Irregular bone/cartilage appears to extend for several centimeters along the length of the trochlear ridge (yellow lines). The filly was referred for arthroscopic exam and a large bone/cartilage defect was identified on the lateral trochlear ridge consistent with a osteochondritis dissecans or OCD lesion.

Figure 4

Osteochondritis dissecans is defined as a disorder that results in cracks in the articular cartilage and underlying subchondral bone. The "cracks" and cartilage separation result due to lack of blood flow to the region resulting in avascular necrosis of the tissues involved.  This condition is considered in part a hereditary disorder AND nutritional.  Unfortunately OCD lesions are common in young horses that were bred for sport such as racing thoroughbreds, performance quarter horses, and warm blood breeds.  Some cases of OCD can be managed with surgical intervention however the OCD lesion in this filly's stifle was so large that there was no hope for soundness. This case is a good example of the benefit of multiple imaging modalities in diagnosing the source of lameness in the equine stifle.