In Reply: Changes in the Cervical Range of Motion and Clinical Outcomes After Laminectomy With Fusion for Ossification of the Posterior Longitudinal Ligament: Impact of K-Line and OPLL Subtypes

To the Editor: We thank Dr Abudayeh and Dr Fishchenko for their thoughtful and erudite letter regarding our recent article examining the impact of K-line status and ossification of the posterior longitudinal ligament (OPLL) subtype on clinical outcomes after posterior cervical laminectomy with fusion.1 Their biomechanical interpretation offers a valuable theoretical framework that substantially enriches the discussion of our findings.2 We wholeheartedly concur with their central thesis that posterior fusion functions as a “biomechanical equalizer.” By effectively immobilizing the operated segments and eliminating dynamic cord compression, laminectomy with fusion may neutralize the motion-dependent disadvantages traditionally associated with K-line (−) alignment or continuous-type OPLL. This explains why, in our cohort, we observed homogeneous neurological recovery across morphological subgroups despite the well-established prognostic value of these classifications in motion-preserving procedures such as laminoplasty.3,4 Their insight reinforces a critical principle in cervical OPLL surgery: the predictive value of preoperative radiographic parameters is inherently procedure-specific. Building on the complexity of the mechanism and their compelling framework, we wish to propose several avenues for future inquiry that may further advance this discourse: The question of long-term trade-offs. Although fusion homogenizes short-term outcomes, does this come at the cost of accelerated adjacent segment degeneration or progression of OPLL at unfused levels over extended follow-up? Does residual segmental motion following fusion interact with specific OPLL subtypes in a clinically meaningful way? For instance, in patients with mixed or continuous type OPLL, even when fusion is performed, if the instrumented segments fail to encompass all levels subject to abnormal mechanical stress, the preserved micro-motion may precipitate dural sac abrasion or irritation. Furthermore, although it is now generally accepted that fusion surgery reduces the likelihood of OPLL progression, several studies suggests that continuous type and mixed type OPLL have been found to progress at a faster rate compared with segmental type.5-7 The inherent tendency toward heterotopic ossification of the spinal ligaments in OPLL patients raises an additional concern: does the concentration of mechanical stress at levels adjacent to the fusion construct paradoxically accelerate OPLL progression or contribute to new-onset spinal stenosis at those segments?8,9 Future studies should integrate OPLL subtype classification with selection strategies for the upper and lower instrumented vertebrae, thereby elucidating whether K-line status or OPLL subtype influences the incidence of symptomatic adjacent segment disease requiring reoperation—a question that our current data set is unable to address. The refinement of surgical decision-making. We endorse their view that K-line and OPLL subtype should not be abandoned in preoperative planning but rather reweighted according to the intended procedure. In selecting between laminoplasty and fusion, these factors retain decisive importance. At our medical center, we have accumulated a substantial cohort of patients from Northern China, who typically present with functional deterioration and restricted activities of daily living due to recent disease progression. Benefiting from the efficiency and accessibility of the Chinese healthcare system, these patients can generally undergo surgical intervention within 1 to 2 weeks of acute neurological deterioration. This expedited surgical timing may contribute to differences in both early and long-term postoperative outcomes compared with studies from other countries, where health care system constraints may delay intervention. We fully concur with the concerns raised in the letter: our study lacks comparison with other surgical techniques and our findings are specific to patients undergoing posterior laminectomy with instrumented fusion. Accordingly, these results should not be generalized to motion-preserving posterior procedures such as laminoplasty or laminectomy alone. Furthermore, patients who were candidates for anterior approaches were excluded from our cohort during patient selection; therefore, our conclusions cannot serve as a basis for decision making between anterior and posterior surgical strategies. We are grateful that their correspondence has clarified an essential distinction: the absence of outcome differences in our study reflects the equalizing effect of the procedure, not the irrelevance of established classifications. This perspective ensures that our findings are interpreted correctly and applied judiciously in clinical practice.