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
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” Yutaro Kanda Neurospine.2025; 22(4): 949. 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 Spinal stenosis is a prevalent condition; however, the optimal surgical treatment for central lumbar stenosis remains controversial. This study compared the clinical outcomes and radiological parameters of 3 surgical methods: unilateral laminectomy bilateral decompression with unilateral biportal endoscopy (ULBD-UBE), conventional subtotal laminectomy (STL), and minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF).
Methods This retrospective study included 86 patients, divided into ULBD-UBE (n=34), STL (n=24), and MIS-TLIF (n=28) groups. We evaluated demographics and perioperative factors and assessed clinical outcomes using the visual analogue scale (VAS), Oswestry Disability Index (ODI), and neurogenic intermittent claudication (NIC). Radiological parameters assessed included lumbar lordosis, L4S1 Cobb angle (L4S1), T12S1 Cobb angle (T12S1), increased cross-sectional dural area (CSA), dynamic angulation (DA), dynamic slip (DS), and development of postoperative instability.
Results The ULBD-UBE group showed a significantly shorter hospital stay duration and operation time and reduced blood loss than the other groups (p<0.001). ULBD-UBE group showed a trend towards greater VAS and ODI improvement at 1 month and postoperative NIC symptom relief. Radiologically, MIS-TLIF group exhibited lower postoperative DA and DS (p<0.001), indicating higher postoperative stability. Postoperative instability was lower in the ULBD-UBE group (2.9%) than in the STL group (16.7%) and similar to the MIS-TLIF group (0.0%) (p=0.028). The CSA was highest in the MIS-TLIF group (295.5%) compared to that in the other groups (ULBD-UBE, 216.3%; STL, 245.2%) (p<0.001).
Conclusion Compared to other procedures, ULBD-UBE is a safe, effective, and viable surgical procedure for treating lumbar central stenosis.
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Neurospine 2023;20(4):1272-1280. Published online December 31, 2023
Objective Although adult spinal deformity (ASD) surgery aims to restore and maintain alignment, proximal junctional kyphosis (PJK) may occur. While existing scoring systems predict PJK, they predominantly offer a generalized 3-tier risk classification, limiting their utility for nuanced treatment decisions. This study seeks to establish a personalized risk calculator for PJK, aiming to enhance treatment planning precision.
Methods Patient data for ASD were sourced from the Korean spinal deformity database. PJK was defined a proximal junctional angle (PJA) of ≥ 20° at the final follow-up, or an increase in PJA of ≥ 10° compared to the preoperative values. Multivariable analysis was performed to identify independent variables. Subsequently, 5 machine learning models were created to predict individualized PJK risk post-ASD surgery. The most efficacious model was deployed as an online and interactive calculator.
Results From a pool of 201 patients, 49 (24.4%) exhibited PJK during the follow-up period. Through multivariable analysis, postoperative PJA, body mass index, and deformity type emerged as independent predictors for PJK. When testing machine learning models using study results and previously reported variables as hyperparameters, the random forest model exhibited the highest accuracy, reaching 83%, with an area under the receiver operating characteristics curve of 0.76. This model has been launched as a freely accessible tool at: (https://snuspine.shinyapps.io/PJKafterASD/).
Conclusion An online calculator, founded on the random forest model, has been developed to gauge the risk of PJK following ASD surgery. This may be a useful clinical tool for surgeons, allowing them to better predict PJK probabilities and refine subsequent therapeutic strategies.
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