History
Upon presentation, a careful patient history should be obtained to determine the etiology of the boutonnière (buttonhole) deformity (BD). If the deformity is of traumatic origin, it is important to determine when the causative incident occurred to provide insight into the timeline of the deformity’s progression. If the deformity is chronic, it is worthwhile to discuss the functional limitations the patient is experiencing. Such a discussion will be relevant in arriving at an appropriate management strategy.
Physical Examination
In the evaluation of a patient with a potential BD (see the image below), a general extremity examination should be conducted. The examiner should take note of any deformity or muscle atrophy, assess the patient for tenderness, and conduct an adequate neurovascular examination to ensure that peripheral sensation and motor function are intact.
Boutonnière deformity. Image courtesy of David Bozentka, MD, University of Pennsylvania School of Medicine, published by Medscape (Late Reconstruction of Flexor and Extensor Tendon Injuries at http://www.medscape.com/viewarticle/717388).
In the context of a suspected BD, there are two special tests that help identify the presence of an injury to the extensor mechanism, as follows:
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Elson test
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Boyes test
The Elson test is conducted by fixing the proximal interphalangeal (PIP) joint at 90° of flexion and asking the patient to extend the affected digit. A patient with an intact central slip will demonstrate PIP extension strength, but, most notably, if the PIP joint is rigidly held at 90°, the patient will be unable to extend the distal interphalangeal (DIP) joint. Conversely, a patient with a central slip injury will exhibit an inability to extend at the PIP joint; however, this patient will exhibit additional extension force at the DIP joint. [10]
Alternatively, the Boyes test is conducted by extending the PIP joint and asking the patient to flex the DIP joint. If the extensor mechanism is intact, the patient will be able to flex the DIP joint. However, if an extensor mechanism injury has led to contracted lateral bands, as may be seen in a subacute or chronic BD, the patient will be unable to actively flex the DIP joint. [11]
It is important to distinguish a BD from a so-called pseudoboutonniere deformity. [12]
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Lateral view of relevant finger anatomy.
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Normal lateral band location, dorsal to axis of rotation of proximal interphalangeal joint.
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After central slip disruption, lateral bands migrate volar to axis of rotation of proximal interphalangeal joint.
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Boutonnière deformity. Image courtesy of David Bozentka, MD, University of Pennsylvania School of Medicine, published by Medscape (Late Reconstruction of Flexor and Extensor Tendon Injuries at http://www.medscape.com/viewarticle/717388).
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Radiographic evidence of boutonnière deformities. Image courtesy of Radiopaedia.org; case by Dr Aditya Shetty (http://radiopaedia.org/cases/rheumatoid-arthritis-13).
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Bunnell safety-pin splint.
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Boutonnière deformity.
