Swan neck deformity
Typical finger appearance of a swan neck deformity

Definition

A swan neck deformity is defined as an alteration in the alignment of two joints at the proximal and distal phalanges of the finger conferring a typical swan neck shape.

Hyperextension of the proximal phalangeal joint and flexion of the distal inter-phalangeal joint in swan neck deformity

Pathology

A swan neck deformity consists in a permanent hyperextension of the proximal inter-phalangeal (PIP) joint and a flexion of the distal inter-phalangeal (DIP) joint. This is the consequence of the volar plate becoming loose following ongoing disease or injury. In chronic medical conditions a prolonged inflammation weakens the PIP joints. This causes excessive pressure on the volar plate, which over time relaxes, causing the PIP to bend into a hyperextension. This in turn forces the flexion of the DIP joint in the opposite plane. The changes of the DIP and PIP joints lead to the development of a swan neck deformity of the finger. A swan neck deformity can follow a forced traumatic hyperextension of the PIP joint with the consequent rupture of the volar plate. If damage of the extensor tendon occurs at the DIP joint the condition is named mallet finger.

Classification

Fractures of the humerus shaft can display various patterns: transverse, oblique, spiral, and comminuted. In addition they are differentiated depending on whether the fracture is displaced or undisplaced, relative to the loss of bone alignment and closed or open fracture. The AO (Arbeitsgemeinschaft für Osteosynthesefragen) Foundation, an international organisation founded in Switzerland, focussing on research and education for the management of orthopaedic injuries), is one of most used systems available to characterise humerus shaft fractures. According to the AO humerus shaft fractures are divided into their level of comminution:

Type A - No comminution

Type B - Presence of butterfly fragment (wedge-shaped fragment of bone

Type C - Comminution

Rheumatoid arthritis affects fingers joints possibly leading to swan neck deformity

Causes

A swan neck deformity can arise from medical conditions involving chronic inflammation and neurological degenerative diseases that immobilise the patients' limbs and fingers. It also occurs following a traumatic event to the fingers. The most common causes are:

Rheumatoid arthritis

Neurological disorders: Parkinson’s disease, cerebral palsy, stroke

Hand/finger injury

In rugby players finger injuries are at high risk to occur when catching the ball

Risk factors

In addition to chronic conditions mentioned above, a swan neck deformity is found amongst players of ball games such as:

Baseball

Basketball

Netball

Football

Rugby

Daily activities

Alterations of the thumb with a swan neck deformity

Symptoms

The symptoms arising from a swan neck deformity are:

Typical finger deformity

Localised pain (sudden and acute in traumatic injuries)

Swelling around the PIP joint

Hyperextension of the PIP joint under passive movement

Flexion of the DIP joint

The examiner measures the angle of each finger joint to determine an pathological changes

Diagnosis

The medical examination begins with the history of existing conditions and/or the mechanisms of injury leading to swan neck deformity. Physical investigation is usually sufficient for the diagnosis and includes:

Detection of finger deformity

Palpation to the PIP and DIP joints

Assessing changes in range of movement of the finger phalanges, both passively and actively

X-rays are taken to determine the condition of the joints, evaluate finger misalignment and possible finger fractures.

Treatment

A splint can be used to straighten the finger joints for conservative therapy

Nonoperative treatment

Management of the swan neck deformity is normally achieved conservatively if no fractures are present. Choice of conservative versus surgical therapy also depends on the joint stiffness. In milder cases of swan neck deformity when the PIP joint maintains flexibility, conservative treatment includes the use of a specially designed splint similar to a double ring, which realigns the finger and prevents hyperextension of the PIP joint. This is kept for up to 6 weeks and is combined with physical therapy to gain joint mobility.

X-rays showing examples of surgical joint fusion in the ring finger and joint replacement of the index in an arthritic hand

Surgical treatment

Surgery is employed in case of joint stiffness, when the rupture of the extensor tendon is associated with a joint misalignment, or with the presence of a phalange fracture.

Soft tissue repair: consists in the reconstruction of soft tissue (skin, tendons and ligaments) to realign the PIP joint.

PIP joint replacement or arthroplasty: if the PIP joint is severely compromised and stiff, it is replaced with an artificial implant following the excision of both extremities of the phalanges forming the PIP joint.

PIP/DIP joint fusion: fusion of the phalanges can be performed as an alternative to internal fixation. This usually involves the DIP joint but can also be performed at the PIP joint keeping it in a bent position.

Fracture fixation: internal fixation of the bony fragment with screws and wires is a common approach to repair the fractures of the phalanges associated with extensor tendon rupture.

Complications

The most common complications following either conservative or surgical treatment of mallet finger include:

Skin damage due to prolonged splinting

Stiffness at the DIP joint

Infection following surgery

Stretching exercises in rehabilitation therapy

Rehabilitation

In conservative management, a physical or occupational therapist recommends exercises to achieve joint mobility and muscle strength of the finger affected by swan neck deformity.

Following surgery a splint is worn for approximately 3 weeks and physical therapy commence after 3-6 after surgery for a period up to 6 months. Medications are also recommended to reduce pain and swelling. Additional rehabilitative therapy includes: 

Administration of NSAIDs

Joint mobilisation

Stretches for finger alignment

Electrotherapy

Activity modification advice

The use of finger splint can prevent finger injuries at the DIP and PIN joints during sport

Prevention

The main goal for preventing swan neck deformity is to seek medical advice as soon as the deformity begins. With a suited physiotherapy program the patient is able to maintain a close to normal finger anatomy and function. The risk of recurrent injuries to the PIP and DIP joints is reduced by protecting the hand during physical activities using: 

Finger splinting

Finger taping