Swan Neck Deformity: Pathophysiology, Classification, and Contemporary Management Strategies — A Narrative Review

Swan neck deformity (SND) is a complex digital deformity characterized by hyperextension of the proximal interphalangeal (PIP) joint associated with flexion of the distal interphalangeal (DIP) joint. Although classically associated with rheumatoid arthritis, SND may also arise from traumatic injuries, neurological disorders, connective tissue diseases, congenital abnormalities, and chronic tendon imbalance. The deformity represents a multifactorial disruption of the intricate biomechanical equilibrium between intrinsic and extrinsic tendon systems, ligamentous stabilizers, and articular structures of the finger. Progressive alteration of these relationships may lead to pain, stiffness, impaired dexterity, diminished grip strength, and substantial functional disability. The pathogenesis of SND involves several mechanisms, including volar plate laxity, intrinsic muscle tightness, terminal extensor tendon dysfunction, dorsal migration of the lateral bands, and chronic synovitis. Understanding the underlying etiology and stage of deformity is essential for establishing an appropriate treatment strategy. Multiple classification systems have been proposed, with the Nalebuff classification remaining the most widely used in clinical practice because of its therapeutic implications. Management ranges from conservative interventions, such as splinting and hand therapy, to a broad spectrum of surgical procedures aimed at restoring extensor balance and joint stability. Surgical options include flexor digitorum superficialis tenodesis, lateral band translocation, central slip reconstruction, volar plate advancement, intrinsic release, arthroplasty, and arthrodesis. Selection of treatment depends on deformity flexibility, joint integrity, patient functional demands, and associated systemic disease. Recent advances in hand surgery have improved understanding of extensor mechanism biomechanics and facilitated the development of individualized reconstructive approaches. Nevertheless, treatment outcomes remain variable, particularly in advanced deformities associated with inflammatory arthropathies. This narrative review summarizes current evidence regarding the anatomy, biomechanics, pathophysiology, classification, clinical evaluation, and modern management of swan neck deformity, with emphasis on surgical decision-making and contemporary reconstructive techniques.