Lesions of the caudal aspect of the femoral condyles in foals: 20 cases (1980-1990)
Authors: Hance S. R. , Schneider R. K. , Embertson R. M. , Bramlage L. R. , Wicks J. R. 
Published: December 2023

Medical records and radiographs were reviewed from 20 foals with caudal femoral condylar lesions. Osseous lesions were classified radiographically into 3 categories. Type-I lesions were characterized by a discrete area of radiolucency within the subchondral bone of the caudal aspect of a femoral condyle and were associated with septic arthritis and osteomyelitis. Type-II lesions had localized, osseous irregularities involving < 50% of the femoral condyle. Type-III lesions had widespread irregularities involving a large area of the condyle, and in 5 foals with type-III lesions, there was a thin osseous fragment displaced from the condyle and free in the femorotibial joint pouch.

Foals with type-I and -III lesions were severely lame and often required assistance to stand. Foals with type-II lesions were not as lame, but lameness was evident at the trot and was exacerbated by flexion of the affected stifle. Cytologic evaluation of the synovial fluid from foals with type-I lesions was compatible with septic arthritis, whereas synovial fluid from foals with type-II and -III lesions was not septic.

Surgical exploration and debridement were performed in 4 foals. Two foals with type-II lesions are currently performing athletically. The remaining 2 foals, in which surgery was performed, had type-III lesions; both of those foals were euthanatized at surgery because of the severity of the lesions. Follow-up information was available in 5 foals that did not have surgery. Two foals with type-I lesions and 1 foal with a type-III lesion were sound 1 year after diagnosis. One foal with a type-II lesion had residual lameness that prevented performance, and 1 foal with a type-III lesion was salvaged for breeding.

Eleven foals were euthanatized and available for postmortem examination. Gross examination of the joints in foals with type-I lesions revealed a subchondral bone defect with intact articular cartilage in 3 of 4 foals examined. In 1 foal with a type-II lesion, a gross examination was performed, which revealed a focal indentation of the articular cartilage and on cross section had a retained cartilaginous core. Postmortem examination of 4 foals with type-III lesions revealed a large, denuded area with a shell-like cartilage fragment free within the joint. Two additional foals within this same group had marked irregularity of the articular cartilage with deep reticulation in the articular surface. In 2 of 3 foals examined with type-I lesions, histologic examination revealed suppurative osteomyelitis. The third foal in this group had changes compatible with focal ischemia. Two of 3 foals examined with type-III lesions had ischemic changes.

Type-I lesions represent focal epiphyseal osteomyelitis and septic arthritis. The cause of type-II and -III lesions is speculative, but there appeared to be a disruption or delay in endochondral ossification. These lesions may be caused by osteochondrosis or may result from some vascular insult that is not currently well-defined.