Comparison of Thoracolumbar Interfascial Plane-to-Skin Distances at Different Lumbar Levels and Positions Under Ultrasonography

Background: This study aimed to determine the optimal lumbar level and patient position for performing the thoracolumbar interfascial plane (TLIP) block by evaluating the distance between the thoracolumbar interfascial plane and the skin using ultrasound guidance. Additionally, we explored the influence of body mass index (BMI) on this distance. Materials and Methods: Eighty patients aged 18 to 65 years undergoing upper lumbar region surgery were evaluated. The thoracolumbar interfascial plane-to-skin distance was measured at L1 and L3 levels in three po-sitions: sitting, lateral, and prone, using a high-frequency ultrasound probe. Measurements were conducted without needle insertion, ensuring clarity and accuracy. Patient demographics, including age and body mass index (BMI), were recorded and analyzed to assess their impact on these measurements. Results: The thoracolumbar interfascial plane was significantly closer to the skin at the L1 level compared to L3 across all positions (p<0.01). Among the positions, the prone position provided the closest plane-to-skin dis-tance and the clearest ultrasound image, allowing better visualization of anatomical landmarks. Conversely, the sitting position produced the poorest image quality and was the least comfortable for patients. Furthermore, a moderate positive correlation was found between BMI and the thoracolumbar plane-to-skin Conclusions: Our findings suggest that the L1 level and prone position are optimal for TLIP block application, offering clearer imaging and easier block administration. For obese patients, the prone position is particularly advantageous as it reduces the skin-to-plane distance, potentially minimizing procedural difficulty and compli-cation risks. These insights contribute to the optimization of TLIP block techniques, especially in patient popu-lations with higher BMI. Further studies are recommended to confirm these findings and expand clinical appli-cations.