Lumbar Disc Herniation: This is the most common cause of low back pain radiating down the leg, especially if the pain is accompanied by numbness, tingling, or weakness. The herniated disc can compress or irritate the nerve roots, leading to radicular symptoms.

Lumbar Spondylosis: Degenerative changes in the lumbar spine can lead to foraminal stenosis, causing nerve root compression and resulting in radiating pain down the leg.
Lumbar Spinal Stenosis: Narrowing of the lumbar spinal canal can compress the nerve roots, leading to pain, numbness, and weakness in the legs.
Piriformis Syndrome: The piriformis muscle can compress the sciatic nerve, causing pain, numbness, and tingling in the leg.
Sacroiliac Joint Dysfunction: Inflammation or dysfunction of the sacroiliac joint can refer pain to the leg, especially if the pain is accompanied by buttock pain.

Cauda Equina Syndrome: A serious condition where the nerve roots in the lumbar spine are compressed, leading to severe pain, numbness, and weakness in the legs, as well as bowel and bladder dysfunction. Prompt diagnosis and treatment are crucial to prevent permanent damage.
Spinal Infection (e.g., Abscess or Osteomyelitis): Infections in the spine can cause severe pain, fever, and neurological deficits. Early diagnosis and treatment are essential to prevent serious complications.
Spinal Tumor: Tumors in the spine can compress nerve roots, leading to pain, numbness, and weakness in the legs. Prompt diagnosis and treatment are critical to prevent neurological deterioration.

Tarlov Cyst: A rare condition where a cyst forms in the nerve root sleeve, causing compression and leading to pain, numbness, and weakness in the leg.
Arachnoiditis: Inflammation of the arachnoid membrane surrounding the nerve roots, leading to pain, numbness, and weakness in the legs.
Neurogenic Claudication: A rare condition where the nerve roots are compressed, leading to pain, numbness, and weakness in the legs, especially with walking or standing.