Jun Jae Shin, Sun Joon Yoo, Se Jun Park, Dong Kyu Kim, Hyun Jun Jang, Bong Ju Moon, Kyung Hyun Kim, Jeong Yoon Park, Sung Uk Kuh, Dong Kyu Chin, Keun Su Kim, Yong Eun Cho, Chang Kyu Lee, Dong Ah Shin, Seong Yi, Keung Nyun Kim, Joongkyum Shin, Yoon Ha
Neurospine 2025;22(4):937-948. Published online December 31, 2025
Objective To evaluate the clinical significance of a negative K-line in the neck flexion position (FK-line [-]), which indicates that cervical ossification of the posterior longitudinal ligament (OPLL) crosses the K-line during flexion, and to compare surgical outcomes between laminoplasty (LP) and laminectomy with fusion (LF) for multilevel FK-line (-) cervical OPLL.
Methods A total of 349 patients with multiple cervical OPLL who underwent posterior decompression surgery (LP or LF) with a minimum of 2 years of follow-up were stratified by FK-line status. Clinical and radiological parameters were compared between the FK-line (+) and FK-line (-) groups. Subgroup analysis of FK-line (-) patients evaluated the efficacy of LP versus LF. Multivariate regression identified predictors of neurological recovery.
Results Patients with FK-line (-) OPLL exhibited a smaller FK-line distance, more kyphotic alignment, greater cervical flexion, and lower recovery ratios compared to those with FK-line (+). In the FK-line (-) subgroup, LF achieved a significantly greater increase in FK-line distance, better correction of the flexion angle, and more neurological recovery than LP. Multivariate analyses identified postoperative FK-line distance, C2–7 flexion angle, and preoperative dynamic extension reserve as independent predictors of neurological outcomes.
Conclusion FK-line status reflects the sagittal cord position and predicts surgical outcomes in cervical OPLL. In FK-line (-) patients, LF provides better neurological recovery and more effective posterior cord shift and kyphotic alignment correction than LP. Incorporating FK-line assessment to guide surgical planning could improve individualized treatment outcomes for multilevel OPLL.
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A Commentary on “Flexion K-Line Status Predicts Surgical Strategy in Multilevel Cervical Ossification of the Posterior Longitudinal Ligament: A Multicenter Comparison of Laminoplasty and Laminectomy With Fusion” John H. Chi Neurospine.2025; 22(4): 951. CrossRef
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Jun Jae Shin, Sun Joon Yoo, Dong Kyu Kim, Hyun Jun Jang, Bong Ju Moon, Kyung Hyun Kim, Jeong Yoon Park, Sung Uk Kuh, Dong Kyu Chin, Keun Su Kim, Yong Eun Cho, Won Joo Jeong, Tae Woo Kim, Chang Kyu Lee, Dong Ah Shin, Seong Yi, Keung Nyun Kim, Joongkyum Shin, Yoon Ha
Neurospine 2025;22(2):337-348. Published online June 30, 2025
Objective To evaluate the impact of the K-line and canal-occupying ratio (COR) on surgical outcomes in patients with multilevel cervical ossification of the posterior longitudinal ligament (OPLL).
Methods Patients with cervical myelopathy due to multilevel OPLL who underwent decompression surgery (anterior or posterior) from 2013 to 2022, with 2-year minimum follow-up, were enrolled. Radiological evaluations included K-line, COR, OPLL type/level, and cervical parameters (C2 slope [C2S], T1 slope [T1S], K-line tilt). Clinical outcomes included Japanese Orthopaedic Association (JOA) score and neck-pain visual analogue scale. Patients were categorized by K-line status (+/-) and COR (<50% or ≥50%).
Results Among 575 patients, JOA recovery was significantly better in the K-line (+) and in low COR (<50%). In high COR (≥50%), K-line (-) was associated with poorer recovery. In low COR, outcomes were similar regardless of K-line. Anterior decompression with fusion (ADF) yielded the best outcomes. Laminoplasty (LP) was optimal for COR ≥50% and/or K-line (+), while laminectomy with fusion (LF) was better for COR ≥50% and K-line (-). In high COR, K-line was influenced by cervical alignment, C2S, and T1S, while in low COR, it was mainly affected by COR percentage.
Conclusion Combining K-line and COR is essential for surgical planning in multilevel OPLL. When COR is high, K-line plays a significant role in predicting neurological recovery. ADF led to superior recovery, whereas for patients with K-line (-) and high COR, LF offered better results than LP. Cervical parameters at high COR influence the K-line more.
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Objective The study compared the morphometric changes of the cervical spinal cord using dynamic magnetic resonance imaging (MRI) in patients with cervical spondylotic myelopathy (CSM) and assessed the correlation with kinematic changes, cord cross-sectional area (CSA), and high signal intensity (SI) on T2-weighted imaging (T2WI).
Methods Patients with CSM were evaluated through dynamic MRI for sagittal and axial CSA changes of the cervical cord, cerebrospinal fluid (CSF) reserve ratio, degree of cord impingement, cord compression rate, range of motion (ROM), and severity of SI on T2WI. The degree of cord impingement was evaluated using the Muhle grading system. Clinical outcomes were assessed using Japanese Orthopaedic Association scoring and Nurick grade.
Results The study included 191 patients (113 males) with a mean age of 55.34 ± 12.09 years. The lowest sagittal CSF reserve ratio and cord occupation rate were observed during extension. Cord impingement and SI change were more prevalent in extension-positioned MRI. There was no difference between ROM on dynamic radiographs and dynamic MRI. Preoperative cervical ROM was greater in patients with intensely high SI change.
Conclusion Dynamic MRI is useful for evaluating neck movement. Patients with high SI had greater ROM before surgery but worse outcomes after. Neck extension exacerbated cervical stenosis and cord compression compared to flexion, and cervical spinal motion contributed to the severity of CSM. Cervical spinal motion should be carefully evaluated, particularly in hyperextension, to prevent worsening of CSM.
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Objective This multicenter study compared radiological parameters and clinical outcomes between surgical and nonsurgical management and investigated treatment characteristics associated with the successful management of unstable atlas fractures.
Methods We retrospectively evaluated 53 consecutive patients with unstable atlas fracture who underwent halo-vest immobilization (HVI) or surgical fixation. Clinical outcomes were assessed using neck visual analogue scale and disability index. The radiological assessment included total lateral mass displacement (LMD) and the anterior atlantodental interval (AADI).
Results Thirty-two patients underwent surgical fixation and 21 received HVI (mean follow-up, 24.9 months). In the surgical fixation, but not in the HVI, LMD, and AADI showed statistically significant improvements at the last follow-up. The osseous healing rate and time-to-healing were 100% and 14.3 weeks with surgical fixation, compared with 71.43% and 20.0 weeks with HVI, respectively. Patients treated with HVI showed poorer neck pain and neck disability outcomes than those who received surgical treatment. LMD showed an association with osseous healing outcomes in nonoperative management. Clinical outcomes and osseous healing showed no significant differences according to Dickman’s classification of transverse atlantal ligament injuries.
Conclusion Surgical internal fixation had a higher fusion rate, shorter fracture healing time, more favorable clinical outcomes, and a more significant reduction in LMD and AADI compared to nonoperative management. The pitfalls of external immobilization are inadequate maintenance and a lower probability of reducing fractured lateral masses. Stabilization by surgical reduction with interconnected fixation proved to be a more practical management strategy than nonoperative treatment for unstable atlas fractures.
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