Evaluating the predictive value of K-line conversion in surgical outcomes for K-line negative cervical ossification of the posterior longitudinal ligament (OPLL): laminectomy with fusion versus laminoplasty.

Background context: Laminectomy with fusion (LF) and laminoplasty are common treatments for K-line negative cervical ossification of the posterior longitudinal ligament (OPLL). However, the clinical significance of postoperative K-line conversion from negative to positive remains unclear.

Purpose: To determine whether converting a K-line from negative to positive improves surgical outcomes in patients with cervical OPLL by comparing LF and laminoplasty.

Study design/setting: Retrospective cohort study.

Patient sample: Patients with cervical myelopathy due to K-line negative OPLL who underwent LF or laminoplasty, with ≥1 year of follow-up.

Outcome measures: Primary outcomes included neck and arm pain visual analog scale (VAS) scores, neck disability index (NDI), Japanese Orthopedic Association (JOA) score, JOA recovery rate, and radiographic parameters (C2-C7 lordosis, modified K-line interval).

Methods: We compared radiographic and clinical outcomes between the 2 groups.

Results: Among 85 patients with K-line-negative OPLL (39 LF, 46 laminoplasty), postoperative K-line conversion occurred significantly more frequently in the LF group (56.4% vs. 16.8%; p<.001). Although laminoplasty better preserved cervical range of motion and reduced neck pain, LF provided superior neurologic outcomes, as indicated by higher final JOA scores and recovery rates. Patients who achieved K-line conversion had significantly higher rates of favorable clinical outcomes compared to those who did not (58.1% vs. 27.7%; p=.019). Multivariate regression analyses further demonstrated that K-line conversion independently predicted favorable clinical outcomes (odds ratio [OR]: 3.900; p=.023), and LF was significantly associated with a higher likelihood of K-line conversion compared to laminoplasty (OR: 3.683; p=.033).

Conclusion: In patients with K-line-negative cervical OPLL, postoperative conversion to K-line-positive status is significantly associated with improved neurological outcomes. Although laminoplasty provides advantages regarding neck pain relief and motion preservation, LF more reliably facilitates K-line conversion and suppresses kyphosis, leading to superior clinical outcomes. Careful preoperative evaluation of cervical alignment, combined with surgical strategies aimed at promoting K-line conversion, may optimize surgical results.

Level of evidence: III.