In Reply: Surgery on the C3-4 Level and the Presence of Ligamentum Flavum Hypertrophy Increases the Risk of 30-Day Reoperation Rate After Anterior Cervical Discectomy and Fusion

To the Editor: First, we would like to express our gratitude to the editor for the opportunity to respond to the letter by Dr Goel.1 We sincerely appreciate Dr Goel's interest in our recent publication on the distinct characteristics of the C3-4 level in anterior cervical discectomy and fusion surgery.2 In our study, we proposed that the degeneration process is primarily driven by mechanical loading, with the highest stress occurring at the C5-6 level due to gravitational forces. Consequently, degeneration and spondylosis initially develop at C5-6 and subsequently progress to adjacent levels, leading to compensatory hypermobility at C3-4. Our findings support this hypothesis, as patients with C3-4 involvement exhibited baseline characteristics such as older age, more prevalent ligamentum flavum hypertrophy, and a higher incidence of cord signal changes compared with those without C3-4 pathology. In the letter of Dr Goel, he posited that atlantoaxial instability is associated with assimilation of the atlas, C2-3 fusion, several subaxial spinal alterations, buckling of the posterior longitudinal ligament and ligamentum flavum, and central or axial atlantoaxial dislocation. He suggested that atlantoaxial instability may be the primary factor underlying these degenerative changes. Although both our perspective and Goel's view recognize the high cervical region as a critical site of instability, the background behind the explanation of the degenerative process seems the opposite. Our study characterizes C3-4 instability as the “result” of long-standing spondylosis and rigidity of the lower cervical spine, whereas Dr Goel proposes that atlantoaxial instability is the “trigger” of many cervical spinal disease. Despite these differing viewpoints, both studies share a common goal: identifying the most unstable segment. Our study aimed to highlight the unique characteristics of C3-4 anterior cervical discectomy and fusion and emphasize the intrinsic instability of this level. We believe that continued research will contribute to a more comprehensive understanding of cervical spine pathology and inform future surgical strategies.