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

STUDY DESIGN

Retrospective case serie.

OBJECTIVES

Assess the correlation between pedicle screw (PS) position of the first instrumented vertebra (FIV) with proximal adjacent segment degeneration (ASD) development or progression.

METHODS

Patients ≥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.

RESULTS

Forty-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.

CONCLUSIONS

The 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.