History
A 5-year-old 500-kg Appaloosa stallion was referred to the Auburn University Large Animal Teaching Hospital for an evaluation following a possible neck injury. Around 5 weeks prior to presentation, the stallion was seen with his head under the fence in the pasture. That evening, he had an abnormal posture (neck stretched out) and a dull mentation. He was treated with oral methocarbamol, 10 mg/kg, q 24 h for 5 days, which improved his attitude but did not resolve the abnormal posture.
On referral presentation, the physical examination findings were within normal limits, with 1 notable exception. The stallion was very sensitive to palpation over the poll and seemed uncomfortable lowering his head to graze. This was evident from his abnormal posture, as he extended one forelimb forward and the other back and lowered his head without extending his cervical spine. Lateral cervical spine flexions did not elicit any pain response, and he had a full range of motion. Neurological examination, including gait analysis and cranial nerve exam, was within normal limits. Radiographs of the cranial cervical spine were obtained (Figure 1).
Lateral radiographs of the cranial cervical spine of a 5-year-old stallion with a 5-week history of abnormal neck posture.
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Lateral radiographs of the cranial cervical spine of a 5-year-old stallion with a 5-week history of abnormal neck posture.
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Lateral radiographs of the cranial cervical spine of a 5-year-old stallion with a 5-week history of abnormal neck posture.
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Radiographic Findings and Interpretation
A complete, minimally displaced fracture was identified at the cranial dorsal aspect of C1 (atlas; Figure 2). Oblique (dorsolateral 45° to ventromedial) radiographs were obtained to compare the right and left wings and localized the fracture to the right side (Figure 3). This fracture involved the lateral aspect of the dorsal arch of C1 and extended through the lateral foramen and articular fovea on the right side. No other abnormalities were identified.
The same images as in Figure 1. A minimally displaced wing fracture of the atlas is depicted (arrow).
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
The same images as in Figure 1. A minimally displaced wing fracture of the atlas is depicted (arrow).
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
The same images as in Figure 1. A minimally displaced wing fracture of the atlas is depicted (arrow).
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Oblique cervical spine radiographs, highlighting the left (A) and right (B) wings of the atlas, revealing the location of the fracture to be the right wing (arrow).
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Oblique cervical spine radiographs, highlighting the left (A) and right (B) wings of the atlas, revealing the location of the fracture to be the right wing (arrow).
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Oblique cervical spine radiographs, highlighting the left (A) and right (B) wings of the atlas, revealing the location of the fracture to be the right wing (arrow).
Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.07.0281
Treatment and Outcome
The stallion was discharged with instructions to be fed from a shoulder height (such that he would not have to lower his head) and rest for 3 months. The owner was instructed to turn the stallion out in a dry lot and provide hay nets to discourage grazing on the ground and stretching out his neck. The breeding of mares was discouraged.
At the 90-day recheck, the stallion was more comfortable and able to graze with normal posture. He was still sensitive to deep palpation of the poll area, but this was improved from the initial presentation. Oblique (dorsolateral 45° to ventromedial) radiographs of the cranial cervical spine were obtained. These revealed rounding of the edges of the fracture, with the presence of a gap between the bone fragments indicating a lack of primary union and osseous callus formation. However, as the clinical signs were improved and no crepitus was palpable, this was suspected to be a fibrous union given the time duration between radiographs. The atlanto-occipital joint appeared within normal limits. The owner was advised to slowly bring the horse back into ridden work but to continue to monitor for any signs of stiffness or neck pain. The breeding season had discontinued at this time.
Comments
Cervical vertebral fractures are relatively common, particularly in young horses. They are caused by trauma and result in a range of clinical signs including pain on palpation of the area. Resultant damage to the CNS, for example due to fracture fragment displacement into the vertebral canal, can cause a range of neurological signs from minor deficits to recumbency or sudden death. Fractures of the atlantal arches, including portions of the atlantal wings, occur occasionally.1 The size of the vertebral canal in this region makes spinal cord compression less likely, and thus fractures in this region do not usually cause neurological deficits. The stallion in this report had a history of trauma, a normal neurological examination, and pain upon palpation of the poll, localizing the injury to the cranial cervical area. The pain the stallion experienced when lowering his head was likely due to distraction of the fracture by the cervical musculature.
Based on the presenting clinical signs, an important differential diagnosis in this case was cranial nuchal bursitis (“poll evil”). Usually, the cranial nuchal bursa is not apparent on cranial cervical radiographs; however, in disease it is evident as a soft tissue opacity dorsal to the first and second cervical vertebrae.2 Occasionally, radiographic evidence of mineralization is present within the bursa. If radiography was not available in this case, ultrasonography of the poll aiming to identify fluid distension of the bursa would have been useful. Ultrasound of C1 would have likely identified the fracture due to its displacement.
The complex anatomy of the cervical vertebrae can make radiographic interpretation challenging. The fracture was barely visible on the lateral projection but was clearly identified on the oblique projections, highlighting the importance of obtaining oblique radiographs if a suspicion for fracture exists. It was unclear from the radiographs whether the fracture line extended into the atlanto-occipital joint, which would have caused concern for the development of degenerative joint disease. CT examination of the area would have allowed for confirmation of articular involvement and a more complete understanding of the fracture but was not pursued by the client, as the treatment plan was not likely to change. As there were no signs of degeneration on the follow-up radiographs, clinically significant articular involvement was thought to be unlikely.
The stallion in this report responded to conservative management. Occasionally, chronic fractures of the atlas can result in proliferative fracture callus, which can cause spinal cord compression if it extends into the vertebral canal.3 Treatment involves removal of the fracture callus via dorsal laminectomy.3 The laterality of the fracture in this report made it unlikely that callus formation would result in spinal cord compression, though removal could be considered if the stallion did not respond to conservative management or neurological signs developed.
Horses that present with signs of cranial cervical pain should undergo radiography. If soft tissue changes consistent with cranial nuchal bursitis are not identified, oblique radiographs of the cervical spine may be useful for identifying fractures in this region.
Acknowledgments
The authors thank Thea Partin for her help with this case.
References
- 1. ↑
Nixon AJ. Fractures of the Vertebrae. Equine Fracture Repair. 2nd ed. John Wiley & Sons Inc; 2019:734–69.
- 2. ↑
García-López JM, Jenei T, Chope K, Bubeck KA. Diagnosis and management of cranial and caudal nuchal bursitis in four horses. J Am Vet Med Assoc. 2010;237(7):823–829. doi:10.2460/javma.237.7.823
- 3. ↑
Nixon AJ, Stashak TS. Laminectomy for relief of atlantoaxial subluxation in four horses. J Am Vet Med Assoc. 1988;193(6):677–682.
