Sagittal geometry of the middle and lower cervical endplates

Abstract

Purpose: Construct subsidence is a relatively common complication following anterior cervical fusion. Its occurrence has been revealed to be closely related to endplate-implant contact interface. But current literature focusing on the anatomy of cervical endplate is very scarce. The purpose of this morphometric study was to analyse the sagittal geometry, especially the concavity and slope, of vertebral endplates from C3 to C7 by employing data from CT scans.

Methods: Reformatted CT scans of 97 individuals were analyzed and endplate concavity depth, endplate concavity apex location, as well as endplate slope were measured in midsagittal plane. Those specific parameters were compared among different age and gender groups. Meanwhile, comparison between superior and inferior endplate of each vertebra was also performed.

Results: Age and gender did not influence endplate concavity depth, endplate concavity apex location, or endplate slope significantly (P > 0.05). Endplate concavity depths of superior endplates (range 0.9-1.2 mm) were significantly smaller than those of inferior endplates (range 2.1-2.7 mm). Endplate concavity apex was always located in the posterior half of the endplate, with the superior one ranged from 56 to 67% and the inferior one 52 to 57%. Average endplate slopes of superior endplates were between 4.5° and 9.0°, and average inferior endplate slopes ranged from 4.5° to 7.5°. Among all measured segments, C5 had the largest endplate slope values, while C7 the least.

Conclusions: Superior endplate is more flat than its inferior counterpart in middle and lower cervical spine, and the concavity apex is always located in the posterior half of the endplate. Endplate slope is correlated with cervical curvature, greater slope implying more significant lordosis. These sagittal endplate geometrical parameters should be taken into consideration when investigating implant subsidence following anterior cervical fusion.

Fig. 1

Landmarks in midsagittal plane: A anterior rim of endplate; P posterior rim of endplate; C_a the concavity apex in midsagittal plane; C’ projective point of C_a on AP

Fig. 2

Landmarks in midsagittal plane: A anterior rim of endplate, P posterior rim of endplate, S superior rim of the anterior wall of vertebral body, I inferior rim of the anterior wall of vertebral body

Fig. 3

Schematic illustration of the measurement of superior endplate slope: first locate vertebral landmarks including anterior (A), posterior (P), superior (S), and inferior (I) rim of vertebral body, then connect points A, P as well as S, I, measure the angle formed by the AP and SI line, then subtract that value from 90°