Influence of head and neck position on radiographic measurement of intervertebral distances between thoracic dorsal spinous processes in clinically sound horses.

Reasons for performing study: Reductions in distances between dorsal spinous processes on radiographs are used as criteria for the diagnosis of impingement of the thoracic dorsal spinous processes in horses but are potentially altered by spine motion and different head and neck positions.

Objectives: To determine the influence of head and neck positions on intervertebral distances between dorsal spinous processes on radiographs of thoracic spines of clinically sound horses.

Methods: Lateral-lateral radiographs were obtained from 23 horses in 3 head and neck positions. The width of the thoracic dorsal spinous processes and intervertebral distances between adjacent thoracic dorsal spinous processes were measured at points perpendicular to a tangent between the dorsal spinous processes and the caudal extremity of the thoracic vertebrae.

Results: A low head and neck position increased intervertebral distances between adjacent thoracic dorsal spinous processes from the 8th to 15th dorsal spinous processes whereas a high head and neck position had the opposite effect (P < 0.05). Overall, intervertebral distances between adjacent thoracic dorsal spinous processes decreased from cranial to caudal in intermediate head and neck positions (P < 0.01). The 12th thoracic dorsal spinous process was readily identifiable due to its significant difference to the narrower cranial and broader caudal dorsal spinous process (P < 0.05).

Conclusions: The head and neck position influences the distances between the dorsal spinous processes of the vertebrae of equine thoracic spine on radiography.

Potential relevance: The measuring system reported here offers potential to improve and standardise radiographic evaluation of thoracic dorsal spinous processes.