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.

Minimally invasive surgery-transforaminal lumbar interbody fusion (MIS-TLIF) is widely adopted for the treatment of lumbar degenerative disease. Expandable cages are now increasingly used in MIS-TLIF to facilitate disc height restoration in narrow spaces. Despite theoretical advantages, the clinical and radiologic outcomes of expandable cage compared to static cage remain controversial. This retrospective study analyzed 151 patients who underwent single-level lumbar MIS-TLIF performed by a single surgeon at a single institution, with more than 1-year follow-up. Static cages were exclusively used from May 2022 to March 2023 (n = 76), and expandable cages from April 2023 to March 2024 (n = 75). The primary outcomes were radiological disc height and lordotic angles. The expandable cage group demonstrated significantly greater postoperative disc height restoration compared to the static cage group at both immediate postoperative periods (10.3 ± 1.2 mm vs. 9.5 ± 1.5 mm, P = 0.003) and at 1-year follow-ups (9.6 ± 1.4 mm vs. 9.0 ± 1.6 mm, P = 0.028). There were no significant differences between the groups in lordotic angles, fusion rates, and clinical outcomes. Various complications were also comparable, other than the incidence of cage subsidence > 3 mm, which was higher in the expandable cage group (14.7% vs. 3.9%, P = 0.047). Expandable cages in MIS-TLIF demonstrated superior disc height restoration compared to static cages, which were maintained throughout a 1-year follow-up period despite the relatively higher subsidence rate. No significant differences were observed in terms of lordotic angle restoration, clinical outcomes, or fusion rates.

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.

Objective: To evaluate long-term bone quality changes within the fusion construct (FC) after 2- to 3-level lumbar fusion using computed tomography (CT)-derived Hounsfield units (HUs).Methods: Among 520 screened patients, 222 who underwent 2- to 3-level posterior lumbar interbody fusion met the inclusion criteria. HU values were measured on CT scans preoperatively, at 1-year postoperative, and at final follow-up. The percentage change in HU (HU [final–pre]%) was calculated for each vertebral level.Results: At the final follow-up, the FC demonstrated a significant decline in HU compared to preoperative values (median [10th–90th percentile], 132.0 [86.5–220.4]; 95% confidence interval [CI], 116.0–142.5 vs. 124.5 [71.0– 210.0]; 109.8–135.1; HU (final–pre)%: -11.0 [-62.0 to 48.5]; -19.9 to -6.1; p<0.001). In contrast, HU increased significantly at the uppermost instrumented vertebra (HU (final–pre)%: median [10th–90th percentile], 28.3 [-19.9 to 102.9]; 95% CI, 21.1–36.4; p<0.001), likely reflecting increased mechanical demands. Subgroup analysis revealed a more pronounced decline in HU in patients with longer follow-up durations, particularly in the FC group (p=0.003).Conclusion: CT-derived HU revealed progressive trabecular bone loss within FC over time after lumbar fusion. In patients with longer postoperative intervals, clinicians should remain aware of the potential weakening of the FC, which has important implications when considering implant removal or planning revision surgery.

Kim D, et al. Brain Tumor Res Treat. 2021 Oct;9:e17. https://doi.org/10.14791/btrt.2021.9.e17