Cervical Ossification of Ligamentum Flavum: Elaborating an Underappreciated but Occasional Contributor to Myeloradiculopathy in Aging Population Based on Synthesis of Individual Participant Data

Purpose Cervical ossification of ligamentum flavum (COLF) is a rare clinical entity which can occasionally contribute to severe myeloradiculopathy. Many orthopedists are unfamiliar with or underestimate this pathology. Therefore, a comprehensive research is obligatory to reappraise the epidemiological, radiological, clinical and histopathological characteristics of COLF-myeloradiculopathy based on synthesis of individual patient data. Methods Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, PubMed, EMBASE, Scopus and Web of Science databases were searched for studies discussing COLF-myeloradiculopathy from the inception to December 2020. Results A total of 94 cases from 54 studies were identified. The annual publications demonstrated a steady increase, and most reports were from Japan and China. The mean age was 58.76±13.39 years and nearly 60% of cases occurred in the 55-64 and 65-74 years age group. The male-female ratio was 1.4:1. Most cases belonged to East Asian population (60.64%). COLF predominately appeared in the lower cervical and cervicothoracic spine (76.60%) and mainly affected C4-5 (23.29%) and C5-6 (21.23%). Single-segment type ossification accounted for 62.76 and 45.45% of ossification lesions distributed bilaterally. The majority of COLF (81.1%) were spontaneous, and motor disturbance (76.4%), spinal ataxia (62.5%) and sensory disturbance (58.9%) were the most common manifestations. Histopathologically, it's a metaplastic process of endochondral ossification with the formation of mature lamellar bone which was distinguished from calcification of ligamentum flavum. About 21.28% of concurrent COLF and COPLL cases were identified as a separated group, with unique characteristics. Conclusion COLF is an underappreciated but potentially growing pathogeny of myeloradiculopathy in aging population, though its distinct epidemiological, radiological, clinical and histopathological features are not fully supported by current evidence. However, our findings will provide several referential data for future researches to shed light on COLF.