Ultrasound diagnosis of interference between costovertebral joint injuries and the eighth cervical nerve

Summary Background Equine cervicothoracobrachial syndrome (CTBS) has been shown as a cause of proximal forelimb lameness and dyskinesia in horses. Because of close anatomical relationships, arthropathies of the first costovertebral joint (CVJ1) may interfere with the ventral ramus of the eighth cervical nerve (C8N), the major root of the brachial plexus (BP). Objectives To describe the ultrasonographic technique to image CVJ1 and C8N in field practice, to provide normal ultrasonographic images and present abnormalities seen in horses presenting a CTBS. Study design The presentation is based on clinical cases referred for non‐blockable lameness or athletic difficulties. Methods A regular 5–10 MHz macroconvex (curvilinear) ultrasound probe is used to examine CVBJ1 and CTJ1. After adequate preparation of the area, the forelimb is moved caudally to facilitate access to the two parts of the CVJ1: the costovertebral‐body joint, CVBJ1 (between the costal head of the first rib—R1 and costal foveas of the C7 and T1 vertebral bodies), and the costotransverse joint, CTJ1 (between R1 costal tuberculum and T1 transverse process). Results Abnormalities identified in clinical cases include arthropathy of CVBJ1 and fracture of the costal head interfering with the cranial fibres of C8N. CTJ1 conditions include peri‐articular osteophytes, capsulitis, capsular enthesopathies and hypogenesis of R1 in contact with the caudal fibres of C8N or the BP itself. Main limitations Deep bone lesions cannot be imaged with ultrasonography; interference between CTJ1 and the ventral ramus of the first thoracic spinal nerve are hidden by the first rib. Conclusion Ultrasonography is presently the only imaging technique providing detailed discrimination of the soft tissues including nerves in the cervicothoracic area. The procedure can be done in the field on the standing horse. It provides an essential contribution to the understanding and management of many unexplained lameness in horses.