Extensor Tendon Injury

How extensor tendons work

Extensor muscles in the forearm send long tendons over the back of the wrist and hand. Over the fingers, they flatten into a complex hood that straightens each joint. These tendons are thin, lie directly under the skin, and are easily injured. Surgeons divide them into zones by location, from the fingertip (zone 1) to the forearm, because treatment and outcome differ by zone.

Types of extensor tendon injury

Mallet finger (zone 1)

The tendon at the fingertip tears or pulls off a small piece of bone, often when a ball strikes the end of the finger ("baseball finger") or when tucking in a bed sheet. The fingertip droops and cannot be actively straightened. See mallet finger.

Boutonniere injury (zone 3)

The central slip of the tendon over the middle joint tears from a jamming injury, dislocation or cut. Initially the joint is swollen and weak to straighten. Over 2 to 3 weeks, the middle joint bends while the end joint hyperextends, forming a boutonniere deformity. Early splinting prevents this.

Cuts on the back of the hand (zones 4 to 7)

Knife, glass and saw injuries can divide tendons over the fingers, hand or wrist (see tendon laceration). Cuts on the palm side damage the tendons that bend the fingers instead: see flexor tendon injury. A cut over a knuckle from a punch ("fight bite") can damage the tendon and seed bacteria into the joint.

Sagittal band injury

Damage to the band holding the tendon centered over the knuckle lets the tendon slip to one side ("boxer's knuckle"), causing painful snapping and difficulty straightening the finger.

Rupture without a cut

• rheumatoid arthritis: inflamed tissue and bone spurs at the wrist wear through tendons, typically of the little and ring fingers
• after a wrist fracture: the thumb extensor tendon can rupture weeks later

Symptoms

• inability to straighten a finger, thumb or the wrist fully on your own
• the joint can be straightened passively with the other hand
• pain, swelling and bruising over the back of the finger or hand
• a drooping fingertip (mallet finger)
• a gap or cut over the tendon

Diagnosis

A doctor or hand surgeon examines each joint's ability to straighten against resistance and compares with the other hand. Special tests check the central slip at the middle joint. X-rays show fractures or avulsed bone fragments. Ultrasound or MRI may help in unclear cases. Every cut on the back of the hand should be explored to look for partial tendon injury.

Treatment

Mallet finger

• A splint holding the end joint straight, worn continuously for 6 to 8 weeks, then at night for a further few weeks.
• The finger must not be allowed to bend even once during this time, or healing restarts. Change the splint carefully with the fingertip supported flat on a table.
• Surgery is used for a large bone fragment with joint misalignment, or when splinting is not possible.

Boutonniere injury

• Splinting the middle joint straight for about 6 weeks while keeping the end joint mobile.
• Surgery for associated fractures, open injuries or late deformity.

Cuts and ruptures

• Most complete lacerations need surgical repair by a hand surgeon, ideally within days.
• Partial cuts of less than about half the tendon width may be splinted.
• Ruptures from arthritis need tendon transfer or grafting, plus treatment of the arthritis.

After surgery or splinting

A hand therapist guides a structured program, sometimes starting gentle controlled movement within days to prevent stiffness and adhesions. Full use often returns in 3 months, but strength and stiffness may take longer.

Complications

• residual droop or loss of full extension
• stiffness, especially of the middle joint
• swan-neck or boutonniere deformities
• tendon rupture after repair
• infection, especially after fight bites
• skin irritation from splints

Frequently asked questions

What is an extensor tendon injury?

It is damage to one of the tendons on the back of the hand, fingers or wrist that straighten the fingers and thumb. It can be caused by a cut, a jammed finger, or wear from arthritis. The main sign is being unable to fully straighten a joint.

How long does a mallet finger take to heal?

The splint must be worn continuously for 6 to 8 weeks, then at night for a few more weeks. Most people regain good function, although a slight droop of a few degrees can remain.

Does an extensor tendon injury need surgery?

Not always. Most mallet fingers and closed boutonniere injuries heal with splinting. Complete tendon cuts usually need surgical repair, as do injuries with displaced bone fragments or failed splinting.

Can I straighten my finger if the tendon is cut?

Usually not on your own. With a cut or ruptured extensor tendon, you cannot actively straighten the joint, although you can push it straight with your other hand. See a doctor within 24 hours for any cut on the back of the hand with this problem.