• Zabiullah Bajouri, Sagar Telang, Zoe Fresquez, Michael Kim, Zachary Gilbert, Trevor Pickering, Zorica Buser, Raymond J Hah, Jeffrey C Wang, and Ram Kiran Alluri.
• Department of Neurological Surgery, Keck School of Medicine USC, Los Angeles, CA.
• Spine. 2023 Jun 15; 48 (12): 859866859-866.

Study DesignRetrospective cross-sectional review of a large database.ObjectiveLittle is known regarding extension K-lines for treatment of cervical myelopathy. Therefore, this study seeks to examine differences between K-lines drawn in neutral and extension.Summary Of Background DataThe modified K-line is a radiological tool used in surgical planning of the cervical spine. As posterior cervical decompression and fusion often results in patients being fused in a more lordotic position than the preoperative neutral radiograph, a K-line measured in the extension position may offer better utility for these patients.Materials And MethodsTotal of 97 patients were selected with T2-weighted, upright cervical magnetic resonance imaging taken in neutral and extension. For each patient, the K-line was drawn at the mid-sagittal position for both neutral and extension. The distance from the most posterior portion of each disk (between C2 and C7) to the K-line was measured in neutral and extension and the difference was calculated. Paired t test was used to assess significant differences.ResultsAcross all levels between C2 and C7 there was an increase in the distance between the dorsal aspect of the disk and K-line when comparing neutral and extension radiographs. The average change in difference (extension minus neutral) at each cervical spinal level was 0.9 mm (C2-C3), 2.5 mm (C3-C4), 2.6 mm (C4-C5), 2.0 mm (C5-C6), and 0.9 mm (C6-C7). A paired t test showed that the K-line increase from neutral to extension was statistically significant across all disk levels ( P <0.001).ConclusionWhen positioned in extension, patients experience a significant increase in distance from the dorsal aspect of a disk to the K-line compared to when positioned in neutral, especially between C3 and C6. This is clinically relevant for surgeons considering a posterior cervical decompression and fusion in patients with a negative modified K-line on preoperative magnetic resonance imaging, as these patients may have enough cervical cord drift back when fused in an extended position, maximizing likelihood of improving postoperative DSM functional outcomes.Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.

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