The biceps muscle attaches to the radial tuberosity, which is a small hump on the side of one of the two bones of the forearm (the radius) near the elbow joint. The biceps muscle bends the elbow bringing the hand in toward the body. This muscle also helps to twist the forearm, turning the hand palm up, the motion you use to tighten a screw with a screwdriver.

Injury to the biceps tendon can happen when the arm, bent at the elbow, is forced to straighten. With this injury, the tendon is typically pulled from its attachment point on the forearm near the elbow joint. This is an unusual injury, affecting only 1 to 2 people per 100,000 each year.

The biceps works in conjunction with other muscles that cross the elbow joint. If the biceps tendon ruptures or detaches from the bone, these other muscles make it possible to bend the elbow and twist the forearm. However, strength is reduced. Tests have compared the strength of people with a normal healthy arm and those who have injured their biceps tendons. Results show that the injured arm has a loss of 30% to 40% of its strength, mainly in twisting the forearm.

Diagnosis begins by reviewing the events of the injury to determine how the injury occurred. During examination the doctor looks for:

• Swelling in the front of the elbow
• Weakness bending the elbow
• Weakness twisting the forearm against resistance (screwdriver motion)
• Visible bruising
• A gap created by shortening of the biceps tendon on the front of the elbow

Although X-rays do not typically show biceps tendon rupture abnormalities, they are obtained to make sure there are no other problems. Other tests may include ultrasound or an MRI (magnetic resonance imaging) of the elbow to get an image of the disruption.

The typical person with this injury is a male age 30 years or older. Females very rarely experience this injury. Biceps tendon rupture is equally likely to occur in the dominant arm or the nondominant arm and is usually related to lifting a heavy weight. Smoking and corticosteroid use increase the risk of experiencing this injury. It is believed that smoking alters nutrition to the tendon. Biceps tendon ruptures are not usually associated with other medical conditions.

As the tendon disconnects, there is often the sensation of or the sound of a "pop" in the elbow. Some swelling in the front of the elbow is likely. There is weakness when bending the elbow. The biceps muscle and tendon can recoil and shorten, creating a firm swelling in the upper arm and a gap that can often be felt. Following injury, there may not be much pain at rest. Pain is usually felt when using the arm forcefully.

Nonsurgical treatment may be considered initially, especially if there are reasons not to perform surgery and lesson urgent need to restore full strength in the arm.