"The Circle" Predicts Extent of Fusion for Surgical Correction of Cervical Spinal Kyphotic Deformities: Proof of Concept.

Background: Correction of kyphotic deformities of the spine is a common problem faced by spine surgeons. Unfortunately, there are no clear published guidelines available regarding the extent of spinal fusion required to achieve and maintain lasting deformity correction. We aim to share a set of novel radiographic parameters ("the Circle") that can be used as a guideline for determining the extent of fusion required in surgical correction of spinal kyphotic deformity.

Methods: A Google forms survey was distributed among spine surgeons and trainees to evaluate differences in recommended extent of posterior-approach fusions for cervical spinal kyphotic deformities before and after introduction to the Circle. Extent of fusion before and after use of the Circle were qualitatively and quantitatively analyzed. Data were anonymized and stored in a secure database.

Results: Twenty-seven neurosurgical attendings (n = 14), residents (n = 9), and fellows (n = 3) responded to the survey. Variance between predicted upper and lower instrumented vertebrae, and length of construct, was statistically significantly decreased after application of the Circle in almost all cases. Respondents rated the ease of use of the Circle an average of 4.2 out of 5 (5 = the most ease). The majority of participants (92 [6%]; n = 25 of 27) stated that they would or would likely use the Circle as a radiographic tool in the surgical planning for correction of cervical spinal kyphotic deformities in the future.

Conclusions: The Circle is a novel set of radiographic parameters that may be used to educate and guide surgical plans and extent of fusion when aiming to correct spinal kyphotic deformities.