How does the needle trajectory for L4 and L5 compare to T10-L3 levels?

The needle trajectory for L4 and L5 levels compared to T10-L3 levels is contralateral and wider due to the anatomical considerations and positioning of the lumbar vertebrae in relation to the spinal canal and exiting nerve roots. At the lumbar levels, the intervertebral foramina are larger, and the spinal canal is more spacious, allowing for a wider approach. Also, the need to reach the lateral aspect of the intervertebral disc or the epidural space at the lower lumbar levels often requires a contralateral approach to avoid injury to nearby structures.

In contrast, at higher levels such as T10 to L3, the needle trajectory tends to be more ipsilateral and narrower because the anatomical structures, including the spinal cord and its protective dural sheath, are positioned differently. The closer proximity of the spinal cord at these thoracic and upper lumbar levels necessitates a more cautious approach. Understanding the reason behind choosing contralateral and wider trajectories at L4 and L5 serves to highlight the differences in anatomy and access that must be navigated during procedures like epidural or spinal injections.