Prolapse of veebral disc between L5-S1 will affect which nerve root
Since most disc herniations occur posterolaterally, the root that gets compressed is actually the root that exits the foramen below the herniated disc. So, a disc protrusion at L4/L5 will compress the L5 root, and a protrusion at L5/S1 will compress the S1 root . Ref - sciencedirect.com
L4
L5
S1
S2
General anatomy