Impact of Posterior Cord Compression From Ligamentum Flavum on Clinical Outcomes Following ACDF or CDR

Retrospective cohort study. To determine the impact of hypertrophied ligamentum flavum (HLF) on outcomes following anterior cervical discectomy and fusion (ACDF) and cervical disc replacement (CDR). HLF contributes to spinal cord compression in cervical myelopathy. While ACDF's effectiveness in decompressing HLF is debated and severe HLF may worsen its outcomes, CDR's role with HLF is unclear. A retrospective study was performed on patients following 1- or 2-level ACDF or CDR for cervical myelopathy or myeloradiculopathy. Patients with cervical deformity, fracture, or OPLL were excluded. HLF was dichotomized as non-HLF and HLF based on previously reported HLF grading. The HLF group was then categorized into "severe" and "mild" cases. PROMs included neck disability index (NDI), numerical rating scale (NRS) for neck and arm, and SF-12 PCS. Multivariable linear mixed-effects models (LMMs) were used for longitudinal outcome assessments, including three-way interaction term among postoperative time, ACDF or CDR, and HLF. IPTW-adjusted LMM was utilized to compare outcomes in patients with HLF between ACDF and CDR. A total of 240 patients were assessed, of whom 228 met the inclusion criteria, with 160 ACDF and 68 CDR. Both groups experienced significant improvements in NDI, NRS neck, and arm over time [ F(5, 835.67) =70.03, P <0.001]. HLF status did not significantly influence these outcomes in both ACDF and CDR cohorts [ F(5, 835.68) =0.65, P =0.66]. Subgroup analyses by the existence of radiculopathy and the number of surgical levels revealed no significant impact of HLF. IPTW-adjusted comparisons in HLF patients with balanced-cohort showed no significant difference in NDI trajectories between ACDF and CDR [ F(5, 472.19) =1.30, P =0.26]. CDR can be offered to carefully selected patients with mild HLF, challenging the traditional view that excludes them from arthroplasty, with significant improvements in patient-reported outcomes.