History
A felon presents as pain and swelling to the fingertip. It is generally on the volar aspect and usually does not extend proximally past the distal interphalangeal joint(DIP).
Penetrating trauma often precedes a felon. Wooden splinters, thorns, glass, repeated fingersticks in diabetics or minor cuts are common predisposing causes, yet no history of penetrating trauma is discovered in approximately 50% of patients. Infection also may spread from a paronychia. [4]
The infection often begins as cellulitis, which is initially confined by the tough fibrous septa that course throughout the pad. At this stage, patients may report pain, redness, and swelling.
If resolution does not occur, abscess formation is accompanied by progression of swelling and intense throbbing pain. There is usually not significant pain with range of motion at the DIP joint.
Physical
A felon is characterized by a fingertip pad that is erythematous, tensely swollen, and very tender to palpation. There may be an associated puncture wound or paronychia.
Usually, due to the septae, the infection is usually contained to the pulp of the fingertip. If the infection has spread to the flexor tendon sheath, bone or joint, spreading of the infection may be visible. [4] The point of maximal fluctuance may be on the volar aspect, raadial or ulnar surfaces.
Causes
Staphylococcus aureus is the most common cause of a felon and is often methicillin-resistant (MRSA). [5, 6, 7, 3]
Streptococcal specias are one of the other leading causes of a felon.
Gram-negative organisms have been reported in immunosuppressed patients. Lancet-induced trauma from fingertip blood glucose measurements have been implicated as an etiology.
Eikenella corrodens has been reported in persons with diabetes who bite their fingernails. [5, 8, 9]
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Differential diagnosis for a felon includes herpetic whitlow.
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A paronychia can progress to a felon if left untreated.
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Drainage of pus from under perionychium in a paronychia.
