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

To the Editor,

We read with great interest the recent article by Wang et al. ¹ entitled “Could Spinal Cord–Canal Mismatch Compromise Clinical Success of Cervical Disc Replacement in Cervical Myelopathy?” published in Global Spine Journal. The authors should be commended for addressing an important and understudied topic, namely the impact of spinal cord–canal mismatch (SCCM) on outcomes following cervical disc replacement (CDR) in patients with cervical myelopathy. Their use of patient-reported outcome measures (PROMs), global rating of change, and minimal clinically important difference (MCID) provides a clinically meaningful framework for evaluating surgical success. The finding that SCCM, as measured by the spinal cord occupation ratio (SCOR), does not adversely affect short-to mid-term outcomes after CDR is particularly noteworthy, as it may help refine patient selection criteria and alleviate concerns regarding the use of motion-preserving surgery in this population.

Nevertheless, several points merit further discussion. First, global SCOR measurements at C3 and C7 may not accurately reflect focal cord compression at the index surgical level. Naghdi et al. ² reported that greater maximum canal compromise is associated with increased fatty infiltration and greater asymmetry of the deep extensor cervical muscles in patients with DCM. However, the relationship between segment-specific SCCM, local canal compromise, and postoperative outcomes remains poorly understood. Future research should explore level-specific cord–canal mismatch, anterior vs posterior compression patterns, and their differential effects on neurological recovery after CDR.

Second, cervical disc prostheses differ substantially in constraint, center of rotation, height restoration, and motion patterns.^3,4 These biomechanical characteristics may influence postoperative spinal cord mechanics, especially in patients with limited canal reserve. Comparative analyses stratified by implant design could clarify whether certain prostheses are more suitable for patients with SCCM and help refine device selection strategies.

Finally, the biological and adaptive mechanisms underlying spinal cord tolerance to canal mismatch remain poorly understood. Differences in cord plasticity, microvascular perfusion, and chronic compression adaptation^5,6 may explain why some patients with pronounced SCCM experience favorable outcomes while others do not. Translational studies combining advanced imaging and neurophysiological assessments may provide valuable mechanistic insights.

In conclusion, Wang et al provide an important contribution by demonstrating that SCCM may not compromise early to mid-term clinical outcomes following CDR for cervical myelopathy. Larger, multicenter prospective studies with longer follow-up, dynamic imaging, and comprehensive neurological assessment will be essential to validate these findings and to further elucidate the role of SCCM in motion-preserving cervical surgery.