Boutonniere Deformity

Etiology

Injury to the extensor tendon is the chief etiology for this flexion deformity of the PIP joint. The extensor tendon is disrupted and the lateral aspects of the tendon separate. The head of the proximal phalanx subsequently projects through the disrupted tendon elements. This deformity obtained its name presumably due to its appearance to a buttonhole on surgical exploration.[5] Football and basketball-related injuries are the most common sources of sports-related boutonniere deformities.

Epidemiology

While jam-injuries represent a heterogeneous group of trauma-related injuries, central slip injuries and subsequent development of boutonniere deformities constitute a well-known sequela of jam-injuries. [6] Up to half or 50% of patients with rheumatoid arthritis develop a boutonniere deformity in at least one digit. [7]

Pathophysiology

A boutonniere deformity results when the triangular ligament and the central slip of the extensor tendon of a digit are disrupted. This disruption of the ligament and tendon will cause the lateral bands to displace volarly. This results in forced flexion of the finger, and subsequent limitation of the DIP joint to extend. Over time, the oblique retinacular ligament gradually contracts. This ligament contracture will gradually worsen the hyperextension deformity of the joint. [8] The pathophysiology is different if it is secondary to rheumatoid arthritis (RA) or a burn injury. In the setting of inflammatory arthritides such as RA, inflammatory cells collect in the synovial fluid of the joint which forms a layer of fibrous tissue. This leads to bony erosion and damage to cartilage and ligaments. The joints gradually deform which leads to loss of function and pain.

History and Physical

A thorough history and physical should be obtained to determine the mechanism of injury to the affected digit. Treatment options vary depending on etiology and early identification of injury can prevent long-term complications and deformities from these injuries. A deformity can take several weeks to manifest. In the setting of a laceration injury, the area needs to be thoroughly cleaned and examined in a “bloodless field” for tendon integrity. [9] In the setting of "jam injuries," a central slip injury is oftentimes occult. The "Elson test" can be performed to assess tendon integrity, and involves the following steps [6]:

• The patient places his affected finger over the edge of a surface such as a table. The digits are placed in a flexed position along the surface edge at the level of the PIP joint.
• The examiner applies pressure to the digit at the level of the middle phalanx.
• The patient is instructed to extend the finger at the PIP joint(opposite to the vector of pressure).
• A positive test is confirmed when the DIP is noted to hyperextend at the DIP joint.

If rheumatoid arthritis causes a boutonniere deformity, a thorough history should include the duration of symptoms, medications (both previous and current), level of pain, and degree of disability.[10]

Evaluation

Radiographs are indicated to determine if there are any associated fractures. It is also important to identify any cortical disruption of the bones that attach to the central slip of the tendon. Lateral radiographs can be used to determine the degree of hyperextension.

Treatment / Management

The goal of treatment is to regain full range of motion of the affected finger. Treatment options include both surgical and nonsurgical modalities. Splinting is a nonsurgical treatment and involves immobilizing the affected joint to allow for PIP flexion(straightening) to occur. This also allows the tendon to heal and not continue to volarly separate. Splints are usually maintained for 3 to 6 weeks depending on the patient’s age and severity of the injury. [11] Patients will often be instructed to wear the splint at night for several more weeks. Management should also include exercises to improve the strength and flexibility of the affected digit. If the injury is a result of sports activity, the affected area may be taped or further splinted for protection on activity resumption. Surgical correction can be employed if the tendon is severed or if there is a significant bone fragment displaced from its normal position of function. [12] It may also be an option if it does not improve with conservative measures, such as splinting. If a large avulsion is present, surgical fixation with a wire or screw is used to correct for the extensor injury. The deformity becomes more difficult to correct if the deformity has been left untreated for greater than three weeks.

The treatment options for a boutonniere deformity if it represents a chronic sequela of rheumatoid arthritis. The classes of medications to treat rheumatoid arthritis are disease-modifying anti-rheumatic drugs (DMARDs), biologic response modifiers, glucocorticoids, nonsteroidal anti-inflammatory medications (NSAIDs), and analgesics. DMARDs are used to delay the progression of rheumatoid arthritis. DMARDs have different mechanisms of action and are often used in combination therapy. Although the mechanism of action varies, they have a similar impact on the disease process. Biologic response modifiers are genetically engineered and work by interrupting a patient’s immune system signals that are responsible for tissue damage. Most of these medications attempt to interfere with the activity of tumor necrosis factor. Glucocorticoids are used to reduce inflammation and also to curb the autoimmune activity. They are often used in conjunction with DMARDs. NSAIDs can aid with pain control, swelling, and inflammation, but do not affect slowing the disease process. Analgesics are used to control pain only. 

If nonsurgical measures are unsuccessful, surgical joint replacement may be necessary. Joint fusion is another surgical procedure that involves fusing the two joint surfaces of the affected digit together. The benefits of joint fusion are pain improvement, increased the stability of the joint, and prevention of worsening joint deformity. After surgery, patients are instructed to wear a splint or brace for several weeks to keep the proximal interphalangeal joint straight. [7] Physical or occupational therapy often follows splinting.

Differential Diagnosis

• Dislocation of the PIP joint. Classically this is traumatic in etiology and the deformity is often more pronounced.
• Skin contracture at the proximal finger from burn injury.
• Less common causes of contractures from other pathologies (Hansen's disease, epidermolysis bullosa, etc).

Prognosis

Preventing progression to a boutonniere deformity is the chief goal of good treatment outcomes. Serial digital casting has been shown to be moderately successful. [11] Depending on severity of the injury, a complete recovery with relation to range of motion is infrequently seen. [11]

Complications

Complications with or without treatment include [13]:

• Chronic joint stiffness
• Reinjury/redislocation
• Post-traumatic arthritis
• Chronic swelling
• Decreased range of motion