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Retrospective radiographic myelogram measurements and long-term outcomes in horses undergoing cervical interbody fusion surgery: 22 cases

Devon England 1, Lauren Newsom 1, Constance White 2, Erica McKenzie 1

Background
Cervical vertebral myelopathy (CVM) is a common cause of spinal ataxia in horses, typically resulting from spinal cord compression within the cervical vertebral canal. Radiographic myelography is frequently used for diagnosis and surgical planning, with dorsal contrast column reduction (DCCR) and dural diameter reduction (DDR) being two common measurement criteria. However, these methods may yield conflicting results. The study aimed to assess the correlation between DCCR and DDR, their association with selected surgical sites, the occurrence of articular process joint (APJ) atrophy postoperatively, and long-term surgical outcomes.

Methods
This retrospective study included 22 horses that underwent cervical interbody fusion surgery between 2008 and 2022. Preoperative myelograms in neutral, flexed, and extended positions were independently assessed by three masked observers using established DCCR and DDR measurement methods. Radiographic outcomes were compared to surgical site selection. A subset of horses with follow-up imaging (>18 months post-surgery) was evaluated for APJ changes by a blinded radiologist. Complications and long-term clinical outcomes were also documented.

Results
DCCR was unremarkable at nearly all articulations, while DDR met abnormal criteria at over 50% of sites in flexion. Neither measure reliably distinguished operated from non-operated sites, except at C6-7 in neutral and extended positions. DCCR and DDR were poorly correlated at most sites. Postoperative complications were frequent, particularly right laryngeal hemiplegia. In follow-up imaging, reduced APJ opacity was common at operated sites, but no consistent decrease in APJ height or area ratios was observed. Long-term outcomes varied: some horses showed improvement and returned to activity, while others had persistent neurologic deficits or complications.

Limitations
The study’s retrospective design limited control over variables. The relatively small sample size, especially for long-term follow-up, and potential interobserver variability in measurements may affect generalizability. The study did not include histopathologic confirmation of spinal cord compression and excluded assessment of the C7-T1 junction.

Conclusions
DCCR and DDR were inconsistent predictors of surgical site selection, with only C6-7 measurements showing some predictive value. These measures often provided conflicting classifications and were poorly correlated. Despite frequent complications, some horses experienced long-term improvement. Radiographic evidence of APJ remodeling was variable, with no consistent pattern of postoperative atrophy. The findings suggest a need for improved diagnostic criteria to guide surgical decision-making in CVM.

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