A swan neck deformity is characterized by two prominent features: 1) flexion of the distal interphalangeal (DIP) joint and 2) hyperextension of the proximal interphalangeal (PIP) joint. In other words, the joint closest to the fingernail is bent towards the palm, whereas the middle finger joint is bent away from the palm. The finger's resulting shape looks like a swan's neck, which is how the condition got its name.
Swan neck deformity often begins to develop after an injury to the extensor mechanisms, typically within the central slip. The extensor mechanism is often injured by a laceration, a direct blow to the finger's tip, or inflammation of the finger joints due to rheumatoid arthritis. If left untreated, swan neck deformity can reduce the hand and fingers' functionality and limit a person's ability to engage in occupations.
To assess swan neck deformity, occupational therapists often visually observe for signs of swelling and palpate to look for signs of effusion or tenderness at both the DIP and PIP joints. The affected finger may have a reduced range of motion because of increased stiffness and possible joint fixation. Therapists may also assess using joint and ligament tests, observing slippage of the later bands dorsally during active flexion, often noticing a "snapping" sensation.
Depending on the severity of swan neck deformity, various treatment methods are available. Combining hand therapy for passive stretching with a corrective splint may improve both DIP and PIP joints' functionality. Other splints, such as an extension blocking splint called the Oval-8, could help correct the PIP joint's hyperextension. For more severe cases of swan neck deformity, surgery may be required. Visit an occupational therapist who specializes in hand therapy to ensure that rehabilitation promotes healing and enables participation in meaningful activities.
Reference: Lane R, Nallamothu SV. Swan-Neck Deformity. StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK525970/