Arch Hand Microsurg.  2023 Mar;28(1):1-15. 10.12790/ahm.22.0038.

Swan neck deformity: a review of its causes and treatment options

• Ha C
• Lim CK
• Lee JK
• Han SH
• Park JW

• KMID: 2540025
• DOI: http://doi.org/10.12790/ahm.22.0038

Abstract

Swan neck deformity is characterized by hyperextension of the proximal interphalangeal joint and limited extension of the distal interphalangeal joint, showing the shape of a swan’s neck. The deformity can occur either acutely or chronically. A common acute cause of this deformity is trauma, and a common chronic cause is a secondary deformity due to rheumatoid arthritis. The treatment of swan neck deformity tends to depend on the knowledge and experience of the physician because the number of cases that hand surgeons can experience is limited, and there are no clear guidelines on treatment options. This review introduces the known causes of swan neck deformity and its treatment options. For swan neck deformity, the cause of the deformity, the elapsed time, the stage of the deformity, the biomechanical relationship between adjacent joints, and the functional limitations and needs of the patients must be considered when determining the treatment method. Based on these considerations, an appropriate choice should be made between nonsurgical and surgical treatment. The patients should receive a full explanation before treatment that an optimal outcome is not always guaranteed. The treatment process requires full understanding and cooperation from the patient.

Keyword

Swan neck deformity; Mallet finger; Rheumatoid arthritis; Proximal interphalangeal joint; Distal interphalangeal joint

Figure

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  Fig. 1. (A) Schematic drawing and (B) clinical photograph of swan neck deformity.

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  Fig. 2. The extensor tendon mechanism, in (A) dorsal and (B) lateral views.

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  Fig. 3. Positive Finochietto-Bunnell test in swan neck deformity of the finger with intrinsic muscle contracture. (A) When the proximal phalanx is in the extension position, it is impossible to flex the proximal interphalangeal joint. (B) However, flexion of the metacarpophalangeal joint allows proximal interphalangeal joint flexion.

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  Fig. 4. (A) Schematic drawing of modified tenodermodesis. (B) A 32-year-old man, injured 4 years ago, noted a painful dorsal bump and a 45° extension lag (arrow) in the distal interphalangeal joint (DIPJ). (C) After the Z-shaped skin incision, the subsequent extensor tendon was exposed over the DIPJ. (D) An elongated extensor tendon, including the joint capsule, was incised. (E) The dorsal osteophyte was trimmed with osteotomy. (F) After inserting a transaxial Kirschner wire (K-wire) in a fully extended DIPJ, the extensor tendon was repaired. (G, H) The redundant skin was incised, followed by separated skin sutures. The skin suture, tendon suture, and K-wire were sequentially removed at 2, 4, and 6 weeks. (I) Three months later, the deformity had improved.

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  Fig. 5. Volar plate direct repair. (A, B) A 37-year-old man with a 70° hyperextension of the proximal interphalangeal joint (PIPJ) and 40° flexion contracture of the distal interphalangeal joint 3 months after an initial volar plate avulsion injury in the left small finger. (C) A Bruner-style lazy S-shaped incision was made over the PIPJ. (D) Between the flexor tendons, the injured volar plate was exposed. (E–G) After drilling, Mitek Micro QuickAnchor (DePuy Mitek Inc., Raynham, MA, USA) was inserted into the middle phalanx base, and the volar plate was sutured. (H) Photograph after the volar plate procedure was done. (I, J) At the final clinical follow-up, the finger showed an improved range of motion.

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  Fig. 6. Flexor digitorum superficialis tenodesis; A2 pulley technique. (A) A Bruner-style lazy S-shaped incision at the volar side of the proximal interphalangeal joint and a transverse incision at the volar side of the metacarpophalangeal joint were made. (B, C) The radial slip of the flexor digitorum superficialis was identified through a metacarpophalangeal joint incision and transected from the metacarpophalangeal joint level. (D, E) The flexor digitorum superficialis slip was attached to the A2 pulley and knotted.

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  Fig. 7. Flexor digitorum superficialis tenodesis; bone hole technique. (A, B) A 36-year-old man with 50° hyperextension of the proximal interphalangeal joint (PIPJ) and 30° flexion contracture of the distal interphalangeal joint 10 years after an initial chronic mallet finger injury to the right middle finger. (C) With a Bruner-style lazy S-shaped incision at the volar side of the PIPJ. (D) The radial side slip of flexor digitorum superficialis was transected from the proximal phalanx level, and the injured volar plate was exposed. (E, F) A 2-mm bone hole was made 1 cm proximal to the joint line through the proximal phalanx neck, and the harvested slip was knotted again through the hole. (G, H) An additional Mitek Micro QuickAnchor (DePuy Mitek Inc., Raynham, MA, USA) was inserted into the middle phalanx base, and the volar plate was repaired. (I) Photograph after flexor digitorum superficialis tenodesis and volar plate augmentation were done. (J, K) At the final clinical follow-up, the finger showed an improved range of motion.

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  Fig. 8. Oblique retinaculum ligament reconstruction. (A) A schematic drawing shows the concept of oblique retinaculum ligament reconstruction. (B, C) Swan neck deformity occurred after replantation surgery of the right index and middle finger amputation at the middle phalanx level. (D, E) The extensor digitorum longus tendons of the contralateral foot were harvested to reconstruct new ligaments. (F, G) The distal end was fixed using the pull-out technique. (H, I) A 2-mm bone hole was made in the shaft of the proximal phalanx. The proximal end of the tendon is inserted through the tunnel and fixed after graft tension adjustment. (J, K) At the final clinical follow-up, the finger showed an improved range of motion.

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