Could Spinal Cord-Canal Mismatch Compromise Clinical Success of Cervical Disc Replacement in Cervical Myelopathy?

We sincerely thank the authors for their thoughtful and insightful comments on our article. ¹ We appreciate their acknowledgment of the clinical importance of spinal cord–canal mismatch (SCCM) in the setting of cervical disc replacement (CDR), as well as their constructive observations, which provide valuable context and help to further clarify our findings.

First, we agree that global spinal cord occupation ratio (SCOR) measurements obtained at C3 and C7 may not fully capture focal or segment-specific compression at the index level. Our rationale for using these standardized levels was to provide a reproducible and pragmatic assessment of overall canal reserve while minimizing measurement variability.^2,3 Nonetheless, as highlighted by the authors, local canal compromise and level-specific SCCM may exert distinct biomechanical and biological effects on the spinal cord. Future investigations incorporating index-level SCOR, maximum canal compromise, and compression morphology may offer more granular insights into the relationship between focal SCCM and postoperative neurological recovery following CDR.

Second, we agree that variations in prosthesis design may affect postoperative spinal cord mechanics, particularly in patients with limited canal reserve. In the present study, implant selection was determined by surgeon preference and device availability, which precluded meaningful stratified analyses based on prosthesis type. Future comparative studies exploring the relationship between SCCM and prosthesis-specific biomechanics may help identify implant designs that are more suitable for patients with reduced canal reserve.

Finally, we appreciate the authors’ emphasis on the biological and adaptive mechanisms underlying spinal cord tolerance to canal mismatch. Variations in neural plasticity, microvascular perfusion, and chronic compression adaptation may indeed explain the heterogeneous clinical responses observed among patients with similar degrees of SCCM. Advanced imaging techniques, such as perfusion MRI and diffusion tensor imaging (DTI), ⁴ combined with neurophysiological assessments, may help elucidate these mechanisms and refine risk stratification in future studies.

In summary, we thank the authors for their insightful commentary. We agree that larger, prospective, multicenter studies incorporating level-specific imaging, dynamic assessments, implant-specific analyses, and longer follow-up are needed to further define the role of SCCM in motion-preserving cervical surgery. We hope that our study, together with this scholarly exchange, stimulates continued investigation into optimizing patient selection and outcomes for CDR in cervical myelopathy.