Bilateral nonossifying fibromas in the proximal tibiae of a yearling Thoroughbred filly.

This research case study examines a yearling Thoroughbred filly that exhibited signs of musculoskeletal distress and was eventually diagnosed with an exceedingly rare form of bone tumor called nonossifying fibromas in both of her upper tibia bones, which is an unprecedented case in veterinary medicine.

Introduction and Background

• The paper begins by providing a brief background on musculoskeletal neoplasia (tumors) in horses, noting that they are rare, and when they do occur, they mostly affect the axial skeleton (the head and spine), rather than the appendicular skeleton (the limb bones).
• The authors point out that nonossifying fibroma, the specific type of bone tumor found in the horse under study, is infrequent in domestic animals but typical in humans.
• The aim of the paper was to describe the features and diagnostic process of bilateral (occurring on both sides) nonossifying fibromas in the upper tibias of a yearling Thoroughbred filly—something that has never before been documented in veterinary literature.

Case Details and History

• The filly was first brought to attention due to kyphosis (curvature of the spine causing a hunchback) and a stiff, stilted gait of over three months’ duration.
• Despite healthy appetite, the horse had a poor bodily condition and had trouble rising to her feet, often standing with one hindfoot elevated and moving in a bunny-hopping pattern at a canter.
• The authors note that the horse’s health did slightly improve with a seven-day course of phenylbutazone, a nonsteroidal anti-inflammatory drug commonly used in horses.

Clinical Examination

• Upon examination, the filly displayed signs of general dullness and disinterest, appeared malnourished and had a rough coat.
• In addition to clear kyphosis, lateral scoliosis (sideways curvature) was also evident in the spine.
• The researchers observed considerable swelling in both knee joints, and stiffness and decreased flexion range in the hind limbs.
• No abnormalities of the bone structure could be detected physically, and the horse displayed no neurological deficits.

Imaging and Diagnosis

• X-rays of the lumbar spine showed no abnormalities.
• However, X-rays of both kneecaps revealed areas of irregular radiolucency (lesser density than surrounding bone, indicating a potential pathological process) as well as sclerosis (hardening) in the upper tibia growth plates, mostly towards the inside.
• These lesions extended towards the articulating surfaces of the tibias but did not include the epiphyseal plates, the area of growing tissue near the ends of long bones.
• In the right knee, there was also evidence of fragmentation in the intercondylar eminence area, a projection of bone between the two lower leg bones at the knee joint.