Objective: To analyze the mechanisms of iatrogenic L5 nerve root injury during L5-S1 percutaneous interlaminar endoscopic discectomy (PEID) based on three clinical cases.

Methods: We retrospectively reviewed three patients who developed L5 nerve root deficits following L5-S1 PEID. Preoperative imaging and intraoperative maneuvers were analyzed to identify anatomical risk factors and technical errors leading to neural compromise.

Results: Analysis revealed that iatrogenic injury resulted from a "dynamic-on-static" compression mechanism. Pre-existing stenosis in the L4/5 lateral recess, L5 posterior vertebral osteophytes, or L5/S1 foraminal exit entrapment pre-tensioned the L5 root. Subsequent intraoperative retraction of the dural sac exacerbated this tension, leading to nerve insult. Furthermore, during right-sided approaches, the ergonomic bias of the surgeon (left hand holding the scope, right hand operating) often caused the working cannula to tilt cephalad, resulting in direct mechanical impingement of the L5 root by the cannula or instruments.

Conclusion: The L5 nerve root is highly vulnerable during L5-S1 PEID, particularly when the root’s course is compromised by pre-existing bony or ligamentous stenosis. Preoperative evaluation of the L4-S1 trajectory is critical. If high nerve tension is anticipated or encountered, surgeons should avoid excessive dural retraction and consider transitioning to Unilateral Biportal Endoscopy (UBE) to minimize neural manipulation.