The flank is the area on the sides of the body between the lower rib and hip bone, including the front and back aspects of the torso. It is commonly referred to as the side. Pain can radiate to the back or flank because of a problem in any of the nearby organs, or it may arise due to a neuromuscular condition.

Kidney Stones

Kidney stones, or renal calculi, are small deposits of crystals that form in the urine. They are usually made of calcium oxalate crystals but sometimes consist of other types of crystals, according to The Merck Manuals Online Medical Library. Very small stones can pass through the urinary tract unnoticed. Larger stones can cause severe pain when moving through the ureters or if they cause obstruction. When the stone is in the upper ureter or kidney, pain is felt on the involved side in the mid back, and radiates to the flank and abdomen. Other symptoms include sweating, nausea and vomiting. Some patients observe blood in their urine and may also notice a stone.

Shingles

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Shingles, also called herpes zoster, can occur in anyone who has had the chickenpox virus. The painful rash is a reactivation of the virus that has been dormant within certain nerve roots. People over 50, or those with weak immune systems, are at increased risk of developing shingles. The condition often begins with burning, tingling and pain on one side of the body, often on the flank. The pain is typically present two or three days before the rash appears. The shingles rash consists of very painful clusters of blisters on reddened skin. Tiny vesicles of the rash ooze and form crusts. Shingles rashes usually resolve in two to four weeks. Some individuals go on to experience post herpetic neuralgia, a painful condition that usually clears up in one to three months, according to FamilyDoctor.org.

Spinal Compression Fracture

A compression fracture of the spine is the collapse of a vertebral bone. Sometimes these fractures cause no symptoms or may only produce pain during certain activities, such as walking. This is especially true if the fractures have a slow onset. If they occur suddenly, pain is felt in the mid to lower back, flanks or abdominal area. Osteoporosis is the most common cause of compression fractures, according to MedlinePlus. Trauma and tumors are additional causes.