Biomechanical effects of uncinate process excision in cervical disc arthroplasty

Studies on the role of uncinate process have been limited to responses of the intact spine and patient's outcomes, and procedures to perform the excision. The aim of this study was to determine the role of uncinate process on the biomechanical response at the index and adjacent levels in three artificial discs used in cervical disc arthroplasty.

A validated finite element model of cervical spine was used. Flexion, extension, and lateral moments and follower load were applied to Bryan, Mobi-C, and Prestige LP artificial discs at C5-C6 level with and without uncinate process. Ranges of motion at index level and adjacent caudal and cranial segments, intradiscal pressures at adjacent segments, and facet loads at index level and adjacent segments were obtained. Data were normalized with respect to the preservation of uncinate process.

Uncinate process removal increased motions up to 27% at index and decreased up to 10% at adjacent levels, decreased disc pressures up to 14% at adjacent segments, decreased facet loads at adjacent segments up to 14%, while at index level, change in loads depended on mode and arthroplasty, with Mobi-C responding with up to 51% increase and Bryan disc up to 11% decrease, while Prestige LP increased loads by 17% in extension and decreased by 9%% in lateral bending.

As surgical selection is based on morphology and surgeon's experience, the present computational findings provide quantitative information for an optimal choice of the device and procedure, while further studies (in vitro/clinical) would be required.