Does Position of Pedicle Screws Correlate With Adjacent Segment Degeneration? An Average 6-Year Follow-Up...

Study DesignRetrospective case serie.ObjectivesAssess the correlation between pedicle screw (PS) position of the first instrumented vertebra (FIV) with proximal adjacent segment degeneration (ASD) development or progression.MethodsPatients ≥55 years who have undergone lumbar fusion with a minimum 2-year follow-up were included. Radiographic PS position was assessed by the angle between the first PS and the upper vertebral endplate (VE) and by the PS tip-VE distance. Radiographic parameters of ASD included: disc height, disc angle, and vertebral listhesis. ASD magnetic resonance imaging (MRI) parameters included: disc degeneration and lumbar stenosis. ROC curve analysis was performed to identify the best cut-off points in correlation with lumbar stenosis.ResultsForty-eight patients were included with an average follow-up of 6 years. All 48 included patients developed some degree of ASD whether on radiographic or MRI parameters. PS tip-VE distance and PS-VE angle were both positively correlated with: (1) Delta (Δ) lumbar stenosis; (2) Δ Disc degeneration; and (3) Δ Disc height. ROC curve analysis correlating PS tip-VE distance and PS-VE angle with an increase in the canal stenosis severity ≥2° resulted in a cut-off point of 36% and 9.5°, respectively.ConclusionsThe cranial orientation (PS-VE angle) of the pedicle screw in the first instrumented vertebra, along with a shorter pedicle screw tip-vertebral endplate distance (PS tip-VE), positively correlated with ASD progression at an average 6-year follow-up. Protective values against lumbar stenosis were identified as a PS tip-VE distance ≥36% of the first instrumented vertebra height and a PS-VE angle ≤9.5° relative to the upper vertebral endplate.