Risk Factors for Persistent Neurological Deterioration After Biportal Endoscopic Posterior Decompression for Multilevel Cervical Myelopathy: The “Structural Mismatch” Concept

Objective: This study aimed to evaluate clinical outcomes and identify risk factors for persistent neurological deterioration (PND) following unilateral biportal endoscopic (UBE) posterior decompression for multilevel degenerative cervical myelopathy (DCM).Methods: We retrospectively analyzed 39 patients with multilevel DCM, including ossification of the posterior longitudinal ligament, who underwent selective UBE decompression involving 3 or fewer segments. All patients were followed for at least 1 year. Delayed neurological deterioration (DND) was defined as new or worsening myelopathic symptoms after initial postoperative improvement and was classified as transient neurological deterioration or PND. Clinical outcomes, including the Japanese Orthopaedic Association (JOA) score and visual analogue scale score; radiological outcomes, including cervical alignment, range of motion, and adjacent border stenosis; and surgical technique, categorized as lamina-preserving or laminectomy-based, were evaluated. Multivariable Firth penalized logistic regression was used to identify independent contributors to PND.Results: At 1 year, JOA scores improved significantly, from 12.8 to 15.4 (p<0.001), and cervical alignment was maintained. DND occurred in 43.6% of patients, with 30.8% classified as PND. Multivariable analysis identified 3 factors independently associated with PND: residual stenosis at both the cranial and caudal borders (adjusted odds ratio [aOR], 21.4), use of lamina-preserving techniques (aOR, 7.44), and lower preoperative JOA score (aOR, 0.34).Conclusion: Although selective UBE decompression provides effective, motion-preserving cervical decompression, PND was strongly associated with insufficient decompression at border levels and the use of lamina-preserving techniques in patients with severe myelopathy. These findings support the “structural mismatch” concept as a potential mechanism underlying clinical failure. To reduce the risk of PND, surgeons should ensure extended decompression at border levels and consider laminectomy-based techniques rather than lamina-preserving approaches in high-risk patients.