Boutonniere deformity is a finger injury that prevents the ability to fully straighten one or more fingers. It is characterized by an abnormal posture of the finger joints, resulting from damage to the extensor mechanism. This configuration significantly limits hand function and makes gripping or grasping difficult. The term is derived from the French word for “buttonhole,” describing how the underlying structures become displaced.
The Mechanics of the Deformity
The characteristic posture is caused by a disruption of the extensor tendon apparatus on the back of the finger. The extensor tendon splits into three bands over the middle joint, with the middle slip known as the central slip. When the central slip tears or ruptures, it can no longer pull the finger straight at the proximal interphalangeal (PIP) joint (the middle knuckle).
The PIP joint is pulled into a bent position by the deeper flexor tendons. The two remaining lateral bands shift out of their normal position toward the palm side of the joint. This displacement prevents them from straightening the PIP joint and instead causes them to hyperextend the distal interphalangeal (DIP) joint. This imbalance creates the signature appearance: the middle joint is bent down, and the fingertip is bent backward. If untreated, the soft tissues contract, making the deformity fixed and difficult to correct.
Recognizing the Signs and Underlying Causes
The most obvious sign is the distinct physical change in the finger’s resting position, though symptoms can manifest over time. Initially, a person may notice pain and swelling over the middle finger joint following an injury. A decreased ability to actively straighten the middle joint is a primary indicator, but the full deformity might not develop until a week or two after the initial trauma.
The two main causes are acute trauma and chronic inflammatory conditions. Traumatic injuries often involve a forceful blow to the back of a bent finger, a laceration that severs the tendon, or a joint dislocation. This directly damages the central slip, creating a tear that resembles a buttonhole.
The other major cause is a rheumatologic disease, most commonly Rheumatoid Arthritis. Chronic inflammation gradually weakens and destroys the soft tissues, causing the central slip to stretch or rupture without a traumatic event. This leads to a slow, progressive development as the tendons shift out of position. Recognizing the difference between sudden traumatic onset and gradual arthritic onset guides the urgency and type of treatment required.
Non-Surgical Management Strategies
Non-surgical treatment is the preferred initial approach, particularly when the injury is acute or the deformity is flexible. The goal of conservative management is to allow the torn central slip tendon to heal without tension, achieved through continuous splinting of the affected finger.
The splint keeps the PIP joint in full extension, typically lasting six to eight weeks. The splint must allow the DIP joint to move freely. Keeping the fingertip joint mobile prevents stiffness and encourages the lateral bands to glide back into their correct position.
During splinting, the patient performs gentle exercises, flexing the DIP joint many times daily while the PIP joint remains immobilized. Following the initial healing phase, a hand therapist introduces a gradual exercise program to regain motion in the middle joint. Early intervention is important, as conservative treatment is less effective if the deformity has been present for more than three weeks and has begun to stiffen.
When Surgery is Necessary
Surgery becomes necessary when conservative management fails, or when the initial injury is too severe for the tendon to heal on its own. Indications include a completely severed central slip, a large bone fragment displaced from the tendon’s attachment site, or a chronic deformity that has become fixed and rigid.
Surgical Procedures
The operation aims to reconstruct the extensor mechanism by tightening the central slip and repositioning the displaced lateral bands back to the top of the PIP joint. For long-standing deformities where the joint has become arthritic or severely contracted, the surgeon may perform a joint fusion. Fusion permanently locks the PIP joint in a slightly bent, functional position, or the surgeon may perform a joint replacement (arthroplasty).
Following surgery, a protective splint is worn for several weeks to guard the repaired structures. Post-operative recovery involves extensive hand therapy lasting three to six months. The long-term prognosis depends on the severity of the initial injury and adherence to the rehabilitation program, which restores flexibility and strength to the finger.