An Unusual Case of Swan Neck Deformity in a Child.

Supplemental Digital Content is available in the text.

Sir:

Swan neck deformity (SND) is a well-recognized clinical entity characterized by proximal interphalangeal (PIP) joint hyperextension with associated distal interphalangeal joint flexion. The causes may be classified into 3 groups based on mechanisms: dominance of intrinsic muscles, hyperactivity of the extrinsic muscles, or mixed etiology.[1]

SND in the pediatric population is rare and is generally associated with neurologic disorders like cerebral palsy and usually secondary to chronic imbalances in the mechanical dynamics of the hand. For example, in mallet finger deformity, the distal interphalangeal is fixed in flexion, and there is relaxation of the lateral band. Over time, the PIP is hyperextended due to the pull from the extrinsic extensors on the middle phalanx and the weakened supporting structures around the PIP.[2]

We present an unusual case of a 9-year-old boy with an acute onset deformity of the long finger of his right hand 1 week in duration that consisted of deformity and disabling pain necessitating hospitalization. He was otherwise healthy without any comorbidity or any prior hand traumas. Physical examination showed the characteristic features of SND. He was unable to make a fist and also had a peculiar involuntary radioulnar fasciculation of this finger (See Video , which demonstrates swan neck deformity and fasciculation, http://links.lww.com/PRSGO/A119). It was also apparent that his ring finger was beginning to demonstrate early SND changes. Bunnell testing showed no evidence of intrinsic muscle tightness. His laboratory results, which included a sedimentation rate, were unremarkable.

There was enhancement of the extensor digitorum communis muscle belly in the proximal forearm but no abnormality in the hand on magnetic resonance imaging. In the operating room, this area was biopsied, a central slip tenotomy of the third finger was performed, and the PIP joint was pinned in 10 degrees of flexion. His postoperative course was unremarkable. His pain resolved, and he regained functionality of his hand.

To our knowledge, there is no reported case in the pediatric or adult literature of acute, painful SND in an otherwise healthy person. Interestingly, biopsy of the area that enhanced on magnetic resonance imaging was negative for any pathology that could account for his presentation.

The underlying pathomechanics causing the features of SND have also been well reported in the literature. For example, with rheumatoid arthritis, Welsh and Hastings[3] described the causes as either from synovitis involving the PIP or metacarpophalangeal joint and described the progression of the disease as beginning with a mobile joint that later progresses to a snapping state and then becomes fixed.

The differential diagnosis should guide differential management. Many different surgical options with their technical variations have been described such as sublimis tenodesis.[4,5] We concluded that our patient had an idiopathic over pull by the proximal extensor digitorum communis. Despite the idiopathic etiology, surgery was curative, and interestingly, the early SND changes in the ring finger also resolved.

This case highlights four clinical features that are important to emphasize: acute, painful, associated with fasciculation, and occurred in a child. Our goal is to bring awareness that such an entity does exist and may be managed with surgery.

See video, Supplemental Digital Content 1, which demonstrates swan neck deformity and fasciculation, http://links.lww.com/PRSGO/A119.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article. The Article Processing Charge was paid for by the authors.