Musculoskeletal strain: This is the most common cause of acute low back pain, often resulting from lifting, bending, or sudden movement. The sharp nature of the pain and its localization to one side are consistent with a strain or pull of the muscles or ligaments in the lower back.

Lumbar disc herniation: A herniated disc can cause sharp, localized pain, especially if it compresses or irritates nearby nerves. The pain can be unilateral and is often exacerbated by certain movements or positions.
Degenerative disc disease: This condition involves the wear and tear of the spinal discs and can lead to sharp pains, especially with movement or after periods of rest.
Sacroiliitis: Inflammation of the sacroiliac joint can cause sharp pain on one side of the lower back, which may radiate to the buttock or thigh.

Kidney stone: A stone in the left ureter can cause severe, sharp pain that radiates from the flank to the groin. This condition requires urgent medical attention.
Abdominal aortic aneurysm: Although less common, a ruptured abdominal aortic aneurysm can present with severe back pain, often described as sharp or tearing, and is a medical emergency.
Pyelonephritis or kidney infection: An infection of the kidney can cause severe, sharp flank pain, which may radiate to the lower back.
Osteoporotic vertebral fracture: Especially in older adults or those with known osteoporosis, a vertebral fracture can cause sudden, severe back pain.

Spinal tumor: Tumors of the spine, whether primary or metastatic, can cause localized pain, which may be sharp and is often constant, worsening over time.
Inflammatory spondyloarthropathies: Conditions like ankylosing spondylitis can cause chronic back pain and stiffness, but acute episodes of sharp pain can occur.
Osteonecrosis of the spine: Also known as Kummell's disease, this condition involves the collapse of a vertebral body due to avascular necrosis and can cause sharp back pain.