Boutonniere deformity is a deformed position of the fingers or toes, in which the joint nearest the knuckle (the proximal interphalangeal joint, or PIP) is permanently bent toward the palm while the farthest joint (the distal interphalangeal joint, or DIP) is bent back away (PIP flexion with DIP hyperextension). Causes include injury, inflammatory conditions like rheumatoid arthritis, and genetic conditions like Ehlers-Danlos syndrome. Pathophysiology
This flexion deformity of the proximal interphalangeal joint is due to interruption of the central slip of the extensor tendon such that the lateral slips separate and the head of the proximal phalanx pops through the gap like a finger through a button hole (thus the name, from French boutonnière "button hole"). The distal joint is subsequently drawn into hyperextension because the two peripheral slips of the extensor tendon are stretched by the head of the proximal phalanx (note that the two peripheral slips are inserted into the distal phalanx, while the proximal slip is inserted into the middle phalanx). This deformity makes it difficult or impossible to extend the proximal interphalangeal joint. Diagnosis
Stages
Mild extension lag, passively correctable
Moderate extension lag, passively correctable
Mild flexion contracture
Advanced flexion contractureHigher numbers indicate a more severe problem and greater likelihood of a poor outcome. Treatment
Usually treated with a splint placing the proximal interphalangeal joint in extension for 4–6 weeks. Occasionally surgery is needed when splinting is unsuccessful. See also
Swan neck deformity
Z-deformity

References
Further reading
Coons, Matthew S.; Green, Steven M. (August 1995). "Boutonniere deformity". Hand Clinics. 11 (3): 387–402. doi:10.1016/S0749-0712(21)00060-3. PMID 7559817. Souter, William A. (October 1974).
The risk is greater when the mother is small or when the infant is of large weight. Risk of injury to the lower brachial plexus results from traction on an abducted arm, as with an infant being pulled from the birth canal by an extended arm above the head or with someone catching themselves by a branch as they fall from a tree. Lower brachial plexus injuries should be distinguished from upper brachial plexus injuries, which can also result from birth trauma but give a different syndrome of weakness known as Erbs palsy. Other trauma, such as motorcycle accidents, that have similar spinal cord injuries to C8 and T1, also show the same symptoms of Klumpkes paralysis. Diagnosis
Electromyography and nerve conduction velocity testing can help to diagnose the location and severity of the lesion. Otherwise, the diagnosis is one made clinically after a thorough neurologic exam. Treatment
Treatment effectiveness varies depending on the initial severity of the injury. Physiotherapy is used to increase strength of muscle and improve muscle functions. Electrical modalities such as electric nerve stimulation can also be used.Occupational therapy to provide exercises and coping mechanisms to improve the patients ability to perform activities of daily living. Goals of therapy are to improve tactile sensation, proprioception, and range of motion.Acute treatment of a severe injury will involve repositioning and splinting or casting of the extremity. Epidemiology
Klumpke Palsy is listed as a rare disease by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH).