Spine (Phila Pa 1976). 2026;51(19):1363-1373
Posterior compression from the ligamentum flavum can complicate the choice between cervical fusion and motion-preserving surgery when an anterior procedure is otherwise being considered. Pezzi and colleagues investigate whether this imaging finding modifies patient-reported recovery after one- or two-level anterior cervical discectomy and fusion or cervical disc replacement. Their retrospective analysis suggests that mild ligamentum flavum involvement need not automatically exclude arthroplasty in carefully selected patients. The distinction between mild and severe disease is essential, however, because the study contains very few arthroplasty patients with severe posterior compression and cannot establish equivalent neurological safety across the full spectrum of cervical myelopathy.
Objective
To assess whether hypertrophied ligamentum flavum influences longitudinal clinical outcomes after anterior cervical discectomy and fusion (ACDF) or cervical disc replacement (CDR), and to compare these procedures among patients with posterior ligamentum flavum involvement.
Methods
This single-center retrospective study reviewed adults aged 18 years or older treated between April 2017 and August 2024. The final cohort comprised 228 patients undergoing one- or two-level ACDF (160 patients) or CDR (68 patients) for degenerative cervical myelopathy or myeloradiculopathy. Preoperative MRI and patient-reported outcomes with at least six months of follow-up were required. Cervical deformity, fracture and ossification of the posterior longitudinal ligament were excluded.
MRI findings were classified using a three-grade system for cord compression by ligamentum flavum. Grade 0 indicated no buckling or hypertrophy; grade 1 represented mild buckling; grade 2 combined buckling and hypertrophy. Grades 1 and 2 were grouped as hypertrophied ligamentum flavum, although this grouping encompasses different structural patterns and severities.
Outcomes included the Neck Disability Index (NDI), neck and arm pain ratings, and the SF-12 physical component score. Mixed-effects models assessed recovery over time. Comparisons within the ligamentum-flavum subgroup also used inverse-probability-of-treatment weighting, followed by additional adjustment for persistent imbalance. Postoperative MRI was available in a subset of 86 patients.
Main results
Median clinical follow-up was 18.9 months. Disability and pain improved after both procedures. The interaction between ligamentum flavum status, procedure and time was not statistically significant for NDI or neck and arm pain. Among the 127 patients classified as having ligamentum flavum involvement, the weighted analysis likewise found no significant difference in NDI trajectories between ACDF and CDR (P=.26).
The composition of this subgroup is crucial: 101 patients underwent ACDF and only 26 underwent CDR. Of the CDR patients with ligamentum flavum involvement, 24 had grade 1 findings and only two had grade 2 findings. The corresponding ACDF counts were 70 and 31. The evidence concerning arthroplasty therefore relates predominantly to mild disease.
The SF-12 physical component analysis differed from the disability and pain results: a significant interaction was reported, with selected timepoint comparisons favoring patients with ligamentum flavum involvement. This secondary finding should not be interpreted as showing that posterior compression improves recovery.
In the MRI subset, canal measurements improved after both procedures. Apparent differences in ligamentum flavum thickness change were no longer significant after baseline adjustment. The imaging findings therefore do not demonstrate that one procedure reliably reverses posterior ligament hypertrophy better than the other.
Interpretation
The decision informed by this study is whether mild posterior ligamentum flavum involvement should, by itself, rule out CDR in a patient otherwise selected for an anterior procedure. The results support a more nuanced assessment of severity rather than a binary exclusion based on the presence of any posterior buckling.
The relevant technical assessment remains anatomical: the severity and distribution of compression on MRI, the available canal space, and the features that made a patient suitable for motion preservation. The study does not validate a threshold of ligament thickness for choosing CDR, prescribe a disc height or implant design, or test an anterior-versus-posterior decompression algorithm. In particular, favorable patient-reported recovery does not establish that anterior surgery adequately treats every substantial posterior compressive lesion.
Limitations
Treatment allocation was not randomized. CDR patients were substantially younger and healthier and had less severe posterior compression. Importantly, weighting did not fully balance the groups: standardized differences for age and comorbidity remained above 0.5 before further model adjustment. Residual confounding is therefore a central concern, despite the adjusted analyses.
Only two CDR patients had severe grade 2 findings, precluding a dependable conclusion for that subgroup. Nonsignificant differences do not establish equivalence. Outcomes focused on disability, pain and physical health rather than a dedicated neurological myelopathy scale, so similar NDI trajectories should not be equated with identical spinal cord recovery or long-term neurological safety.
Postoperative MRI was available for only 62 ACDF and 24 CDR patients, was obtained at variable intervals, and was assessed by a single reviewer. Imaging selection and measurement bias may affect the radiographic conclusions. Long-term or dynamic assessment was insufficient to determine whether persistent posterior compression later progresses or becomes symptomatic.
Clinical takeaway
Mild ligamentum flavum buckling need not be treated as an automatic contraindication to cervical arthroplasty in carefully selected adults with one- or two-level degenerative myelopathy or myeloradiculopathy. This is a cautious selection message, not an endorsement of CDR for severe posterior compression or proof of equivalence to ACDF. The degree of compression and the complete clinical and anatomical context remain decisive.