Boutonniere deformity, sometimes called buttonhole deformity, is a common hand injury resulting in the abnormal positioning of a finger. This condition occurs when the finger’s extensor mechanism is damaged, preventing the finger from straightening properly. It is a specific tendon injury that can significantly affect a person’s ability to use the affected finger normally.
How the Deformity Affects the Finger Joint
The characteristic appearance of this deformity results from a mechanical imbalance between the three small joints in the finger. The key anatomical structures involved are the Proximal Interphalangeal (PIP) joint (the middle knuckle) and the Distal Interphalangeal (DIP) joint (the joint closest to the fingertip). A normal finger’s movement is governed by a balance of flexor and extensor tendons.
The deformity begins with the disruption of the central slip tendon, a portion of the extensor tendon that attaches to the base of the middle phalanx at the PIP joint. When this central slip is torn or stretched, it can no longer exert the force needed to extend or straighten the middle joint. This failure causes the PIP joint to drop into a flexed, or bent inward, position.
Once the central slip is compromised, the remaining lateral bands of the extensor mechanism shift position, slipping downward towards the palm. This downward shift transforms them from structures that extend the PIP joint into structures that increase its flexion. The head of the proximal phalanx, the bone just above the middle joint, may then protrude through the separated tendon elements, creating the “buttonhole” appearance.
As the central slip fails, tension shifts, causing an excessive pull on the DIP joint. Since the central slip is no longer functioning, the full extensor force is redirected to the terminal tendon, which attaches at the fingertip joint. This unopposed force hyperextends the DIP joint, causing the fingertip to curl backward. The combination of the middle joint being bent and the fingertip joint being hyperextended creates the unique posture defining the Boutonniere deformity.
What Causes the Injury
The disruption of the central slip tendon generally results from two main categories: acute trauma or chronic disease. Acute trauma is the most frequent cause, typically occurring when the finger is forcefully impacted while the PIP joint is bent. This type of injury often happens during sports, such as when a ball forcefully jams the finger, or from a fall.
A direct laceration or cut to the back of the middle joint can also sever the central slip, leading to an immediate onset of the deformity. A severe finger dislocation at the PIP joint can also stretch or tear the tendon away from the bone. In acute cases, the injury may be immediately apparent or the characteristic posture may develop gradually over several weeks.
Beyond sudden injury, the deformity can develop slowly due to chronic inflammatory conditions, most notably Rheumatoid Arthritis (RA). Constant inflammation within the PIP joint capsule can weaken and eventually destroy the tendon and surrounding soft tissues. This gradual deterioration compromises the structural integrity of the extensor mechanism.
Diagnosis is primarily clinical, meaning a healthcare provider assesses the characteristic posture and range of motion. X-rays are typically performed to ensure there are no underlying bone issues, such as a fracture or an avulsion of the tendon from the bone. Early and accurate diagnosis is important because the condition may not be fully apparent until weeks after the initial injury.
Treatment and Recovery Options
Prompt intervention is important for achieving a satisfactory recovery. For most recent injuries without a complete tendon tear or joint dislocation, non-surgical treatment is the preferred initial approach. The primary non-surgical intervention is continuous splinting of the affected finger.
Splinting is designed to hold the PIP joint in a completely straight position while allowing the DIP joint to move freely. Keeping the middle joint straight relieves tension on the injured central slip, allowing the tendon ends to heal. This conservative treatment typically requires the splint to be worn full-time for a continuous period, often lasting six weeks or more.
After the initial period of splinting, physical therapy is often necessary to restore full range of motion, as the joint can become stiff from immobilization. A hand therapist guides the patient through specific exercises to prevent recurrence while gradually increasing the strength and flexibility of the finger. Successful non-surgical treatment relies heavily on strict adherence to the splinting protocol.
Surgical intervention becomes necessary if the central slip is fully severed, a large piece of bone is avulsed with the tendon, or the deformity is chronic and fixed. For chronic deformities where tissues have contracted and scarred, surgery may involve reconstructing the tendon.
In severe, long-standing cases, the PIP joint may be fused to permanently fix it in a functional position. Even with successful treatment, some patients may experience residual stiffness, and a full recovery can take several months.