Lumbar Disc Herniation: This is the most common cause of low back pain radiating to one leg, typically due to a herniated disc compressing a nerve root, leading to pain, numbness, and weakness in the affected leg.

Lumbar Spondylosis: Degenerative changes in the lumbar spine can cause pain and stiffness, which may radiate to the legs due to nerve root compression or foraminal stenosis.
Lumbar Spinal Stenosis: Narrowing of the lumbar spinal canal can compress the spinal cord or nerve roots, leading to pain, numbness, and weakness in the legs, especially with walking or standing.
Piriformis Syndrome: Compression of the sciatic nerve by the piriformis muscle can cause pain, numbness, and tingling in the buttock and leg.
Sacroiliac Joint Dysfunction: Inflammation or dysfunction of the sacroiliac joint can cause low back pain that radiates to the leg, especially with weight-bearing activities.

Cauda Equina Syndrome: A serious condition where the nerves in the spinal canal are compressed, leading to severe pain, numbness, and weakness in the legs, as well as bowel and bladder dysfunction. Prompt recognition and treatment are crucial to prevent permanent damage.
Spinal Infection (e.g., Abscess or Osteomyelitis): Infections of the spine can cause severe back pain, fever, and neurological deficits, requiring urgent medical attention.
Spinal Tumor: Tumors in the spine can cause back pain, numbness, and weakness in the legs, and may be life-threatening if not diagnosed and treated promptly.

Arachnoiditis: Inflammation of the arachnoid membrane surrounding the spinal cord, which can cause severe pain, numbness, and weakness in the legs.
Tarlov Cyst: A rare condition where a cyst forms in the nerve roots of the spine, causing pain, numbness, and weakness in the legs.
Lumbar Spinal Epidural Lipomatosis: A rare condition where excess fat accumulates in the spinal canal, compressing the spinal cord or nerve roots and causing pain, numbness, and weakness in the legs.