A phalangeal fusion defect and osteochondrosis dissecans with subluxation of the distal interphalangeal joints in a foal.

This study investigates a case of a Standardbred filly with a fusion defect in her hindlimbs, osteochondrosis dissecans in her forelimbs, and subluxation in all of her distal interphalangeal joints. Observed complications included lameness, irregularities and lucency of subchondral bone, loss of proximal interphalangeal joint spaces, and articular cartilage erosion. The foal was ultimately euthanised.

Research Details

• This research is centred on a Standardbred filly, a young female horse of a breed used primarily for harness racing. The filly displayed multiple physical anomalies, particularly in the form of a fusion defect in the proximal and middle phalanges, the finger bones, of its hindlimbs; osteochondrosis dissecans, a joint condition where cracks form in the articular cartilage and underlying subchondral bone, in the distal interphalangeal joints, the upper joint of its forelimbs; and subluxation, a partial dislocation, in all four of its distal interphalangeal joints.
• Lameness, an impairment that affects the animal’s ability to move, was the first noticeable sign of this condition. It manifested at the age of one week in the left forelimb, then progressed over time to impact all four limbs by the time the filly was five weeks old.

Radiographic and Necropsy Findings

• Radiographs, also known as X-rays, of the forelimbs presented subluxation in the distal interphalangeal joints, along with irregularities and lucency, an area of increased radiographic brightness, in the subchondral bone, the layer of bone just below the cartilage.
• Radiographic examination of the distal, or lower, hindlimbs showed joint space loss in the proximal interphalangeal joints and fusion of the proximal and middle phalanges.
• The filly was eventually euthanised. Following this, a necropsy was conducted – an autopsy for animals. This revealed focal, or concentrated, areas of erosion in the articular cartilage of the distal interphalangeal joints in both forelimbs. Moreover, the proximal and middle phalanges in the hindlimbs were found to be fused.
• A histopathological examination, which uses a microscope to study diseased tissue, of the right foreleg’s distal interphalangeal joint showed further signs of degeneration, including loss of articular cartilage and degenerative changes in the exposed subchondral bone.