Radiographic/morphologic investigation of a radiolucent crescent within the flexor central eminence of the navicular bone in thoroughbreds.

This research investigates the cause behind the appearance of a previously identified radiolucent crescent, or a part that appears dark or transparent on x-rays, in the flexor cortex of a particular bone in thoroughbreds. The study utilizes advanced radiography and CT scans to analyze the navicular bones of 24 such horses, with certain bones also undergoing microradiography and histologic examination.

Methods

• The study was carried out on the forelimb navicular bones of 24 thoroughbred horses, resulting in a total of 48 bones being investigated.
• Advanced methods of examination were utilized including in-depth radiography, x-ray computed tomography (CT), microradiography and histologic examinations.
• Out of the 48 samples, 25 were also evaluated using microradiography and histologic examinations. Additionally, five of these 25 bones had been labeled in vivo with fluorochrome markers.

Findings

• A major observation was a line of compacted cancellous bone that was parallel and a few millimeters deep to the flexor cortex in the area of the flexor central eminence. This was visualized using CT in 42 of the 48 navicular bones and by microradiography in 23 of the 25 navicular bones investigated.
• Variable degrees of compaction were observed in the cancellous bone between the flexor cortex and the reinforcement line.
• High-detail skyline radiographic projections and reconstructed CT images indicated a crescent-shaped lucency (a transparent or ‘light’ area) within the flexor central eminence of the flexor cortex. This specifically occurred in the bones where the reinforcement line was identified, but the cancellous bone between the reinforcement line and the flexor cortex had not been compacted.

Conclusion

• The radiolucent crescent seen in the flexor central eminence of the navicular bone on certain projections was not caused by the concave defect or synovial fossa of the flexor central eminence overlying the flexor cortex, as was previously described.
• This implies that the previous supposition about the radiolucent crescent’s origin was incorrect, indicating the need for further research and understanding in this area.