Analysis of the Variables Affecting the Incidence, Location, and Severity of Cage Subsidence Following Anterior Cervical Discectomy and Fusion Operation

BACKGROUND: For surgical management of degenerative cervical spine disease with myeloradiculopathy, stand-alone cages are frequently used in 1- and 2-level anterior cervical discectomy and fusion (ACDF) operations with a paucity of literature on factors influencing cage subsidence. The aim of this study was to analyze the variables affecting the incidence, location, and severity of cage subsidence.

METHODS: Retrospective review of prospectively collected data of 77 patients (95 levels) undergoing ACDF surgery was conducted. Variables analyzed were age, gender, sagittal alignment, maximum disc height (superior, inferior, and procedure levels), cage size, shape, location, degree of subsidence (minor <2 mm, mild 2-4 mm, moderate 5-7.5 mm, severe >7.5 mm) and location of subsidence.

RESULTS: The incidence of cage subsidence was 34% (32 levels), and 91% were minor or mild. Significantly lower mean maximum height of the inferior disc compared to the nonsubsidence group (5.17 versus 5.96; P = 0.0025) was recorded. Significantly greater incidence of subsidence (40%) was recorded in patients with abnormal cervical spine alignment (focal or diffuse kyphosis) versus 18% with normal alignment (P = 0.02). Greater incidence of subsidence was recorded with more anterior positioned cages (52%; p=0.01). No statistical significance was found for age, gender, superior disc height, or cage shape/size.

CONCLUSIONS: Greater incidence of cage subsidence is significantly associated with a lower maximum disc height of the disc below the operated level (<5.5 mm), abnormal sagittal alignment, and more anteriorly positioned cages. We found that the vast majority of cage subsidence was focal, minor to mild, without having any immediate or late clinical implications in terms of need for revision surgery.