Extensor Tendon Injury

Overview

Extensor tendons run along the back of the hand and fingers and connect the muscles of the forearm to the bones of the fingers and thumb. When these muscles contract, the tendons pull on the bones to straighten the digits. Because they lie just under the skin on the back of the hand, extensor tendons are easily injured by cuts, scrapes, crush injuries, bites, or a forceful bending of a fingertip.

Extensor tendon injuries are common and range from a small tear at the fingertip to a complete laceration that severs the tendon. Even though these tendons are close to the surface and may seem like a minor problem, a torn extensor tendon can leave a finger unable to straighten fully. Two well-known patterns are mallet finger, where the tip droops, and boutonniere deformity, where the middle joint bends down and the fingertip points up. Prompt, proper treatment usually restores good function.

Symptoms

The hallmark of an extensor tendon injury is the inability to fully straighten one or more finger joints. Symptoms depend on where along the tendon the damage occurs.

• Difficulty or inability to straighten a finger or thumb
• A drooping fingertip that will not lift (mallet finger)
• Pain, swelling, and tenderness over the back of the finger or hand
• A visible cut or wound over a tendon
• Weakness when trying to extend the digit

Some injuries, especially those caused by a closed jamming force rather than a cut, may have little more than mild swelling at first, which is why a finger that cannot straighten after a minor injury should still be checked.

Causes

Extensor tendons can be injured in several ways:

• Lacerations: A cut from a knife, glass, or sharp object on the back of the hand or finger can partly or fully sever a tendon.
• Jamming injuries: A ball or object striking the tip of an extended finger can tear the tendon at the fingertip, causing mallet finger.
• Crush and avulsion injuries: Heavy objects or machinery can damage the tendon and nearby tissue.
• Bites and infections: Human or animal bites over a knuckle can cut a tendon and introduce infection.
• Underlying disease: Conditions such as rheumatoid arthritis can weaken tendons and cause them to rupture with little force.

Risk Factors

• Work or hobbies involving sharp tools, knives, or glass
• Contact and ball sports that can jam the fingers
• Rheumatoid arthritis or other inflammatory joint disease
• Previous hand injury or surgery
• Punching injuries that strike a hard surface or another person's teeth

Diagnosis

A clinician diagnoses an extensor tendon injury by examining the hand and asking the person to straighten each finger joint individually. Loss of active extension at a specific joint points to the injured part of the tendon.

• Physical examination: Testing each joint's ability to straighten and inspecting any wound.
• X-rays: Used to look for an associated fracture or a small bone fragment pulled off by the tendon (common in mallet finger).
• Wound exploration: For cuts, the clinician may examine the tendon directly, sometimes in an operating room, to see how much is torn.

Treatment

Treatment depends on the location and cause of the injury and whether the tendon is partly or fully torn.

• Splinting: Closed injuries such as mallet finger are often treated by holding the affected joint straight in a splint continuously for several weeks, which allows the tendon to heal.
• Surgical repair: Cut tendons usually need to be stitched back together. Bites and contaminated wounds are cleaned thoroughly, and antibiotics may be given.
• Hand therapy: After healing or surgery, guided exercises and protective splinting restore motion and strength while preventing stiffness.

Following the splinting schedule exactly is critical, because removing a mallet finger splint too soon can undo healing and require starting over.

Prevention

• Use guards and proper technique when handling knives, saws, and glass
• Wear protective gloves for tasks with a high risk of cuts
• Use appropriate finger protection in ball and contact sports
• Seek prompt care for any hand wound, especially over a knuckle
• Treat underlying conditions such as rheumatoid arthritis that weaken tendons

When to See a Doctor

See a doctor promptly if you cannot fully straighten a finger after an injury, if a fingertip droops and will not lift, or if you have a cut over the back of a finger or hand. Seek urgent care for any bite wound over a knuckle, a wound that will not stop bleeding, signs of infection such as spreading redness, warmth, pus, or fever, or numbness in the finger, as these may need surgery or antibiotics without delay.

Related Topics

Frequently Asked Questions

References

1. American Society for Surgery of the Hand (ASSH). Extensor Tendon Injuries.
2. American Academy of Orthopaedic Surgeons (AAOS). Hand and finger injuries.
3. MedlinePlus, U.S. National Library of Medicine. Tendon injury.
4. OrthoInfo, American Academy of Orthopaedic Surgeons.