The positioning of pedicle screws in the first instrumented lumbar vertebra influences the reoperation rate due to the development of adjacent segment disease

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INTRODUCTION: Adjacent Segment Disease (ASD) is a significant concern following lumbar arthrodesis, particularly in patients aged 55 and older. While various risk factors for ASD have been investigated, modifiable surgical factors related to pedicle screw (PS) positioning remain underexplored. OBJECTIVES: This study aims to specifically evaluate the correlation between PS positioning and reoperation rates due to ASD in elderly patients undergoing lumbar arthrodesis, identifying specific surgical parameters that could mitigate the risk of ASD. METHODS: We conducted a retrospective analysis of 48 patients aged 55 and older who underwent posterior lumbar arthrodesis from May 2013 to May 2021. Patients had 2 to 4 segments fused between L2 and S1 and a minimum follow-up of 2 years. We assessed PS positioning parameters, including the angle between the first PS and the upper vertebral endplate (VE) and the PS tip-VE distance, using logistic regression to analyze associations with reoperation rates. ROC curve analysis was performed to identify optimal cut-off points. RESULTS: Out of the 48 patients, 7 (14.6%) required reoperations for ASD, with an average follow-up of 6.5 years. A greater PS tip-VE distance was significantly associated with a lower probability of reoperation (OR: 0.68; p = 0.001), while a higher PS-VE angle correlated with an increased risk (OR: 1.48; p = 0.001). Critical cut-off values identified included a PS tip-VE distance of ≥ 7.5% (sensitivity: 90.63%) and a PS-VE angle of ≥ 10° (sensitivity: 75.00%). CONCLUSIONS: Our findings indicate that optimizing pedicle screw positioning-specifically maintaining a PS tip-VE distance of at least 7.5% and a PS-VE angle below 10°-can significantly reduce reoperation rates due to ASD in patients over 55. Implementing these specific parameters in surgical practice may lead to improved patient outcomes and reduced incidence of ASD-related interventions.

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