Radiographic abnormalities of the thoracolumbar spinous processes do not differ between yearling and trained Thoroughbred horses without perceived back pain

Objective: The purpose of this prospective study was to investigate the prevalence and severity of radiographic abnormalities of the interspinous spaces (ISSs) in the thoracolumbar vertebral column of unbroken yearlings and to compare these findings with a group of older trained Thoroughbred horses without perceived back pain. Animals: Yearlings (n = 47) and trained horses (55); 102 total. Procedures: Each horse underwent a digital radiographic study of the thoracolumbar vertebral column (T7-L3) and each space graded for narrowing of the ISSs, increased opacity, radiolucency, and modeling of the cranial and caudal margins of 2 contiguous dorsal spinous processes (DSPs). This generated both an individual anatomical space score for each space and a total score for each horse for subsequent comparison. Statistical analysis of the results was then undertaken. Results: Narrowing and impingement were detected in a third of the examined ISSs, while DSP increased opacity, radiolucencies, and modeling were found in over half of the yearlings. The median total score per horse was 33 (0 to 96) in the yearlings and 30 (0 to 101) in trained horses, indicating no significant difference in radiographic abnormalities (P = .91). Likewise, the median total score per anatomical space was 112 (25 to 259) and 127.5 (24 to 284) in the yearlings and trained horses (P = .83). No differences were found between the groups for number of radiographic abnormalities, scores, and total score. Clinical relevance: This study reported the incidence of DSP radiographic abnormalities in Thoroughbred horses. The absence of difference in occurrence between yearlings and older horses supported a developmental rather than acquired etiology.