Boutonniere Deformity

How boutonniere deformity happens

The extensor tendon on the back of each finger splits into three parts at the middle joint. The central slip inserts into the middle bone and straightens the middle (PIP) joint. Two lateral bands run along the sides to the tip.

When the central slip tears, the middle joint can no longer straighten. Over days to weeks, the lateral bands slide down toward the palm side of the joint. The joint then pokes up through the gap like a button through a buttonhole, which is where the French name comes from. Displaced lateral bands now pull the end joint backward into hyperextension.

Causes

• Jammed finger: a forceful bend of the middle joint while it is trying to straighten, common in ball sports.
• Volar PIP dislocation of the middle joint.
• Cuts over the back of the middle joint that divide the tendon.
• Burns to the back of the finger.
• Rheumatoid arthritis: chronic inflammation (synovitis) of the PIP joint stretches and weakens the central slip, causing deformity without an injury.
• Osteoarthritis occasionally.

Symptoms

• pain and swelling over the back of the middle joint
• inability to fully straighten the middle joint actively, though someone else may be able to straighten it passively early on
• the fingertip bending backward and difficulty bending the end joint
• the deformity often not obvious at first and appearing 10 to 21 days after injury

Because early signs are subtle, a "jammed finger" with tenderness over the back of the middle joint should be checked.

Related finger deformities

Diagnosis

A doctor examines the finger and may perform the Elson test: the finger is bent 90 degrees at the middle joint over the edge of a table, and you try to straighten the middle bone against resistance. With a central slip tear, the end joint becomes rigid and extends. A local anesthetic block may be used if pain limits the exam. X-rays check for a fracture fragment or dislocation.

Treatment

Splinting (most injuries)

• A splint holds the middle joint fully straight while leaving the end joint free.
• Wear it full-time for about 6 weeks, then often at night for another 2 to 4 weeks.
• Bend the end joint actively several times a day; this pulls the lateral bands back into position.
• The splint must not be removed and the middle joint must not be allowed to bend during this time, or healing restarts.

A hand therapist usually supervises splinting and exercises.

Surgery

• Open injuries: cut tendons are repaired surgically.
• Fracture fragments: a large or displaced piece of bone attached to the tendon may need fixation.
• Chronic deformity: if splinting fails or the deformity is fixed, tendon reconstruction or release procedures can help, though results are less predictable. In arthritis, joint fusion or replacement may be options.

Outlook

Most acute boutonniere injuries treated early with splinting recover good function, though some stiffness or a small loss of full extension is common. Chronic, untreated deformities become stiff and are harder to correct, which is why early diagnosis matters.

Frequently asked questions

Can boutonniere deformity heal without surgery?

Yes, most acute closed injuries heal well with a splint holding the middle joint straight full-time for about 6 weeks, plus exercises for the end joint. Surgery is mainly needed for cuts, displaced fractures or deformities that fail splinting.

How long do you wear a splint for boutonniere deformity?

Usually full-time for about 6 weeks, followed by night splinting for a further 2 to 4 weeks. Removing the splint and letting the middle joint bend during the full-time period can disrupt healing.

What happens if boutonniere deformity is not treated?

The tendon heals in a lengthened position, the lateral bands stay displaced, and the joints become stiff. The finger may stay permanently bent at the middle joint with a hyperextended tip, reducing grip and fine movements. Late correction is more difficult.

Is a jammed finger a boutonniere injury?

Not always, but a jammed finger with pain and swelling over the back of the middle joint can hide a central slip tear. If you cannot fully straighten the middle joint yourself, or it starts to bend over the next few weeks, see a doctor.