Relationship of Adult Cervical Spinous Processes to Vertebral Midline for Cervical Disc Replacement

Study DesignRetrospective Cohort.ObjectivesAccurate, midline artificial disc placement is crucial when performing cervical disc replacement (CDR). Although cervical spinous processes (SPs) are considered midline structures, clinical experience has often shown noticeable deviation at times. This study aims to quantitatively characterize this known observation to better understand the utility of SPs as midline indicators during CDR.MethodsPatients who underwent anterior cervical discectomy and fusion with preoperative cervical spine computerized tomography (CT) scans were retrospectively identified, excluding those with previously surgically altered spines. Angular and lateral SP deviations from C3-C7 were collected from these CTs. Statistical analysis was conducted using one-way ANOVA with post-hoc testing using Tukey's test.ResultsThe average angular SP deviations at C3-C7 were 2.94 ± 2.06 degrees, 3.52 ± 2.19 degrees, 3.50 ± 2.13 degrees, 4.31 ± 2.15 degrees, and 3.53 ± 2.86 degrees, respectively. The average lateral SP deviations at C3-C7 relative to vertebral body widths were 5.43%, 6.10%, 6.14%, 8.17%, and 7.52%, respectively. Angular deviation at C6 was greater than C3 (p = 0.009). Relative lateral deviation at C6 was greater than at C3 (p = 0.027). Neither angular nor lateral deviation differed by sex at any level (p > 0.05 for all).ConclusionsGiven significant variation in cervical SP deviation between patients and by level, surgeons should hesitate to solely rely on them for determining vertebral midline during CDR. The C6 and C7 SPs especially should be used cautiously as they show relatively higher magnitudes and variations of deviation. However, the C3-C5 SPs may be of use if viewed in conjunction with other radiographic landmarks, such as the uncinate processes or medial borders of the pedicles.