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Ligaments are strong, fibrous tissues that typically connect bones to other bones. The ligaments in the thumb help keep the bones in proper position while allowing for motion in the joints.

• Sprains occur when the ligament is stretched beyond its limit, which can also cause small, incomplete tears in the fibers that make up the ligament. The ligament, however, remains intact. These incomplete tears are commonly known as partial-thickness tears.
• Ligaments can also be torn completely — either in the middle of the ligament or at the end(s) of the ligament, where it can pull off the bone(s). These complete tears are commonly known as full-thickness tears.

In this illustration, the ulnar collateral ligament of the thumb is completely torn, also known as a full-thickness tear

Grades of Thumb Sprains

Sprains are graded based on the degree of injury to the ligament:

• Grade 1 sprain (mild). The ligament is stretched, but not torn.
• Grade 2 sprain (moderate). The ligament is partially torn. This type of injury may involve some loss of function.
• Grade 3 sprain (severe). The ligament is completely torn in the middle or is pulled off its attachment to the bone. These are significant injuries that require medical or surgical care. If the ligament tears away from the bone, it may take a small chip of the bone with it. This is called an avulsion fracture.

Injury to the Ulnar Collateral Ligament of the Thumb

The ulnar collateral ligament (UCL) of the thumb is a strong band of tissue running along the inside of the metacarpophalangeal (MCP) joint, which is where the thumb meets the palm. This ligament keeps your thumb stable, especially when you pinch and grasp things.

A thumb UCL injury is commonly called “skier’s thumb,” because falling on the ski slopes with your hand strapped to a ski pole is a common cause of this injury.

The ligament can also be injured more gradually, over time, from repetitive grasping or twisting activities. This type of chronic injury is known as “gamekeeper’s thumb" because originally, it was most commonly a work-related injury seen among Scottish gamekeepers (workers who manage wildlife and areas of land used for hunting).

The ulnar collateral ligament can tear in different ways. For example, it may be:

• Pulled off its attachment at the base of the first bone (the proximal phalanx) in the thumb
• Pulled off the metacarpal bone, where it originates
• Torn through its middle, though this is less common

Any strong force that bends the thumb backward and away from the palm of the hand can stretch or tear the ulnar collateral ligament. This most often occurs by falling onto an outstretched hand.

Sprained thumbs are also common in skiers and in athletes who participate in sports that involve catching and throwing a ball, such as football, baseball, softball, and basketball.

• Depending on the severity of the sprain, you may or may not experience pain at the time of the injury.
• You may have bruising, tenderness, and swelling around the base of your thumb, near the palm.
• If the ulnar collateral ligament is completely torn, the end of the ruptured ligament may cause a lump or swelling on the inside of the thumb. Your thumb joint may also feel loose or unstable. You may have difficulty grasping items between your thumb and index finger.

Clinical photo of an unstable thumb. This patient has a complete tear of the ulnar collateral ligament.

Reproduced and adapted from JF Sarwark, ed: Essentials of Musculoskeletal Care, ed 4. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2010.

It is important for your doctor to evaluate even a mild thumb sprain if it does not improve quickly. Proper and prompt diagnosis and treatment of a thumb injury is necessary to avoid long-term complications, including chronic pain, instability, and arthritis.

Physical Examination

Your doctor will:

• Ask how and when your injury occurred
• Ask you to describe your symptoms.
• Carefully exam your thumb and hand. To help determine whether the ulnar collateral ligament is partially or completely torn, your doctor will move your thumb in different positions to test the stability of the MCP joint. If the joint is loose and unstable, it is an indication that the ligament may be completely torn.

Imaging Tests

X-rays. X-rays provide images of dense structures, such as bone. Your doctor may order X-rays of your thumb and hand to ensure that you do not have an avulsion fracture or any broken bones. They may take an X-ray of your uninjured thumb to compare it to the injured thumb.

Your doctor may also order special type of X-ray, called a stress X-ray. During this test, your doctor will apply tension to your thumb while it is being X-rayed to learn more about the stability of the MCP joint. If the test causes pain, you may be given an injection of a local anesthetic.

During a stress X-ray, the doctor applies tension to the thumb to test the stability of the MCP joint.

Reproduced from JF Sarwark, ed: Essentials of Musculoskeletal Care, ed 4. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2010.

Stress X-ray showing an unstable MCP joint. The abnormal opening of the joint (arrow) is a sign that the ulnar collateral ligament is completely torn.

Reproduced from TR Johnson, LS Steinbach (eds.): Essentials of Musculoskeletal Imaging. Rosemont, IL. American Academy of Orthopaedic Surgeons, 2004, p. 378.

Other imaging tests. If more information is needed, your doctor may order a magnetic resonance imaging (MRI) scan or an ultrasound. These tests can help your doctor learn more about the severity of your injury and make decisions about your treatment and return to activity.

Treatment for a sprained thumb depends on the severity of the injury.

Home Care

Mild thumb sprains will usually improve with home treatment that includes the RICE protocol:

• Rest. Try not to use your hand for at least 48 hours.
• Ice.  Apply ice immediately after the injury to keep the swelling down. Use cold packs for 20 minutes at a time, several times a day. Do not apply ice directly on the skin.
• Compression. Wear an elastic compression bandage to reduce swelling. Do not make the bandage too tight, as this could cut off blood flow to the thumb.
• Elevation. As often as possible, rest with your hand raised up higher than your heart.

Additionally, nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen, can help reduce pain and swelling. If, however, pain and swelling continue for more than 48 hours, see a doctor.

Nonsurgical Treatment

For a moderate sprain, your doctor will probably immobilize your thumb joint with a bandage, thumb spica cast, or splint until it heals. To ease pain and swelling, you can apply a cold pack to your thumb twice a day for 2 to 3 days after the injury. Do not apply ice directly on your skin.

Depending on the severity of the injury, you may be instructed to wear the splint or cast at all times. It is important that you avoid applying any pressure or resistance to your thumb until your doctor says it is OK to do so.

For a partial tear, wearing a thumb spica cast for a period of time will allow the ligament to heal.

Reproduced from The Sports Medicine Field Manual. Rosemont IL. American Academy of Orthopaedic Surgeons, 2015.

Because immobilization may cause some stiffness in your thumb joint, your doctor may recommend some stretching exercises to help you regain full range of motion.

Surgical Treatment

For a severe sprain or tear, you may need surgery to restore the stability of your thumb joint and help you regain function. Surgery involves reconnecting the ligament to the bone and/or repairing the avulsion fracture using a pin, screw, or special bone anchor.

After surgery, you may have to wear a short arm cast or a splint for 6 to 12 weeks to protect the thumb ligament while it heals.

When diagnosed and treated properly, most thumb sprains will heal well with no complications. However, ignoring a sprained thumb with the hope that it will heal on its own may lead to long-term problems, including:

• Chronic instability
• Weakness
• Arthritis

If these late complications develop, you may need surgery to rebuild the ligament using tissue from your upper arm. If there is significant arthritis, you may need a joint fusion procedure to address both the arthritis and the instability of the MCP joint.