Background: The biomechanics of the cervical spine after anterior cervical discectomy with fusion (ACDF), and in particular changes in its global mobility, are phenomena that have not yet been sufficiently studied. Consequently, their effect on the eventual result of treatment is not fully understood. The aim of this study was to assess changes in global and segmental mobility of the cervical spine after ACDF.

Methods: 28 patients who underwent ACDF for cervical spondylosis were examined. The study was divided into two stages: preoperative and postoperative. Range of motion (ROM) was analysed based on X-ray AP, lateral and functional images: C1-C7, C1-C2, C2-C7, C1-C4, C4-C7, and segments adjacent to the stabilisation. The patients were divided into groups depending on the length of spondylodesis and the occurrence of adjacent segment degeneration (ASDeg).

Results: A statistically significant difference was found in the total ROM of C2-C7, C1-C7 and C4-C7 after ACDF. The ROM of C2-C7 decreased by 23%, of C1-C7 by 20%, and of C4-C7 by 38%. These changes occurred by reducing the extension ROM C2-C7 by 33%, C1-C7 by 31%, and C4-C7 by 12%. There was a statistically significant (31%) reduction in total ROM in the segment above ACDF, a 41% reduction in extension ROM of this level in the non-ASDeg group, and a 73% increase in the segmental extension ROM above ACDF in patients with ASDeg.

Conclusions: ACDF reduces the total ROM of the cervical spine in the sagittal plane. This change occurs by reducing the neck extension, and its severity depends on the length of the spondylodesis. In patients without ASDeg after ACDF, the mobility of the level above the stabilisation decreases. The occurrence of ASDeg is associated with a higher postoperative ROM of the segment located above the spondylodesis.