Morphological studies of cartilage endplates in subaxial cervical region.

Purpose: The aim of this study was to provide morphological data of endplates for the redesign of cervical artificial disc for use in the middle and lower cervical spine (C3-C7).

Methods: Reformatted CT scans of 73 individuals were analysed. The shapes of superior endplates (SEPs) and inferior endplates (IEPs) were classified as either flat or arced. The curvature radius of the IEP and sagittal disc angle were measured in the mid-sagittal plane. The maximum transverse diameter (MTD) of the SEPs and IEP was measured in the coronal plane.

Results: The majority of SEPs were flat (79.5 % at C7 and 91.8-95.9 % at C3-C6). Almost all (98.6-100 %) IEPs were arced. The curvature radius has a gradually increasing trend from C3 to C6 (P < 0.05, mean 29.26 mm). There were significant differences at C3-C7 in the average sagittal disc angles (5.80°, 6.92°, 7.51°, and 8.82°, respectively; P < 0.05; mean 7.26°), the average MTDs of the SEPs (13.64, 14.42, 15.03, and 16.74 mm, respectively, P < 0.05; mean 14.96 mm) and the average MTD of the IEPs (16.77, 17.67, 19.15, and 21.66 mm, respectively; P < 0.05; mean 18.81 mm).

Conclusion: The majority of SEPs were flat, while almost all IEPs were curved. The curvature radius of IEPs has a gradually increasing trend from C3 to C6. The average sagittal disc angles, MTDs of the SEPs and IEPs significantly increased from C3 to C7. Based on the above, the current cervical artificial disc design does not sufficiently match the morphology of cervical endplates (CEPs). This mismatch may lead to some postoperative complications of cervical disc arthroplasty.