The Prevalence of degenerative radiographic findings in the small tarsal joints of two-year-old warmblood stallions and the development of these findings over five to sixteen months

For the equine veterinarian, it is often difficult to interpret degenerative radiographic changes in the small tarsal joints of clinically healthy young horses on sales or prepurchase radiographs. The aim of this study was to expand the knowledge in this area by investigating the prevalence and progression of degenerative radiographic findings of the small tarsal joints in a homogenous population of young horses. For this purpose, the first part of the study comprised the radiographic examination of 292 two-year-old, clinically healthy and untrained Warmblood stallions to determine the prevalence of radiographic degenerative changes in the small tarsal joints. The second part of the study assessed the development of such degenerative changes over five to sixteen months. This time period is relevant for the public sale or stallion approval preparation of the horses. Follow-up radiographs of 77 stallions with degenerative changes were taken and evaluated to monitor the development of these changes over time. A standardized evaluation of the radiographs was guaranteed by a detailed evaluation scheme and three experienced and specifically qualified investigators. Our hypotheses were: a. Degenerative radiologic findings in the small tarsal joints have a high prevalence even in young and clinically healthy horses, b. Such radiologic changes can be dynamic over a short period of time. In the first part of the study, 22.6% of the stallions showed radiologic changes consistent with degenerative joint disease. There were osteophytes in the distal intertarsal and/or tarsometatarsal joint in 15.4%, areas of reduced radiopacity in the central tarsal or third tarsal bone in 6.5%, narrowing of the joint space of the distal intertarsal and/or tarsometatarsal joint in 0.3%, and sclerosis at the distal intertarsal joint in 0.7% of the horses. Dorsoproximal spurs at the third metatarsal bone were observed in 27.4% of horses; this was the most common radiologic finding. However, this finding alone did not result in the radiologic diagnosis of degenerative joint disease. In part two of the study, there was a tendency for progression of the findings “spur at third metatarsal bone” and “osteophytes at distal intertarsal and/or tarsometatarsal joint” over time. The finding “areas of reduced radiopacity in the central tarsal or third tarsal bone” appeared to be regressive over time. While the progression of spurs and osteophytes was expected as described in the literature, there was an unexpected regressive dynamic of areas of reduced radiopacity in the small tarsal bones. In the literature, these changes have been interpreted as lytic areas and as a sign of degenerative joint disease. A regression of bone lysis secondary to degenerative joint disease is not described in the literature and seems not plausible. However, it is possible that such areas of reduced radiopacity in the small tarsal bones are due to a delayed increase in bone density in young horses – such areas could really be regressive due to the significant potential for bone remodelling, especially in young animals. Results of our study confirm the high prevalence of degenerative radiographic changes of the small tarsal joints even in young, untrained and clinically healthy Warmblood stallions. However, areas of reduced radiopacity in the small tarsal bones can be regressive over a short period of time and should be evaluated cautiously concerning the radiologic diagnosis of degenerative joint disease