Tennis elbow can affect the outside of the elbow (lateral tennis elbow) or the inside (medial tennis elbow). Lateral tennis elbow is the most common muscular problem in the upper limb. Studies suggest one to three percent of the adult population is affected each year.

Some patients have no idea what caused the problem. Other report work-related or sports activities as the problem. The number of people with tennis elbow may continue to increase as adults work long hours at repetitive tasks or at the computer keyboard. Numbers may also increase as Americans try to stay in shape with exercise like tennis that can bring on tendonitis.