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.
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.
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:
Neurological disorders: Parkinson’s disease, cerebral palsy, stroke
In addition to chronic conditions mentioned above, a swan neck deformity is found amongst players of ball games such as:
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 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.
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.
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.
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
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
Stretches for finger alignment
Activity modification advice
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: