Tendons attach muscles to bones. The elbow has a humerus and two bones in the forearm (ulna and radius). The inner and outer bulges of the elbow form the epicondyle of the upper humerus. The tendons of the forearm muscles, which are responsible for stretching and flexing the wrist. Adhere to these bulges. inflammation of the outer tendon It's medically known as lateral epicondylitis, commonly known as “tennis elbow,” because the problem is often caused by playing tennis or similar repetitive movements. (for wrist flexion) medial epicondylitis or “golfer's elbow”