Diagnostic Criteria for a Felon
A felon is diagnosed clinically by identifying a painful, tense abscess of the distal pulp space of the fingertip, characterized by severe throbbing pain, swelling, and erythema localized to the volar pad of the distal phalanx. 1, 2
Clinical Presentation
The diagnosis of a felon is primarily clinical and based on the following key features:
Severe, throbbing pain in the fingertip that is disproportionate to the visible findings, often described as extremely painful due to the limited space for swelling within the complex fibrous septa system of the pulp space 3, 2
Tense swelling and erythema localized to the volar (palmar) aspect of the distal phalanx, specifically affecting the pulp space of the fingertip 1, 3
Fluctuance on palpation when an abscess has formed, indicating accumulation of pus in the pulp space 2
Tenderness that is exquisite and localized to the fingertip pulp 4
Essential Physical Examination Findings
Knowledge of anatomy and correct physical examination technique are essential when assessing a patient suspected of having a felon. 1
Key examination components include:
Inspection for swelling, erythema, and any signs of extension beyond the distal phalanx 1
Palpation to assess for fluctuance, which indicates abscess formation requiring surgical drainage 2
Assessment for complications including signs of flexor tendon sheath infection (pain with passive extension, fusiform swelling of the entire digit, tenderness along the flexor tendon sheath), osteomyelitis, or septic arthritis of the distal interphalangeal joint 1, 5
Evaluation for lymphangitis (red streaking up the arm) or systemic signs of infection 5
Anatomical Considerations
Understanding the anatomy is critical for diagnosis:
The pulp space contains a complex system of fibrous septa that compartmentalize the area, limiting swelling and creating high pressure within a confined space 3
This anatomical arrangement can lead to digital compartment syndrome if not adequately drained 2
If the septa are destroyed by infection, spread into the bone (osteomyelitis) or flexor tendon sheath is possible, representing a complicated felon 3, 1
Differentiation from Paronychia
It is essential to distinguish a felon from paronychia:
Paronychia involves infection of the proximal or lateral nail folds (dorsal localization), whereas a felon affects the volar fingertip pulp space 3, 2
Some patients may present with both conditions simultaneously 5
Risk Factors and Special Populations
Consider the following factors that may alter presentation or treatment intensity:
Immunosuppressive states (including immunosuppressed patients, those on chronic steroids) 4, 5
Cardiac valve prosthesis recipients 5
These conditions warrant more aggressive evaluation and may require antibiotic coverage even after surgical drainage 5
Staging for Treatment Decisions
The stage of infection determines management:
Early felon (cellulitis without abscess formation): may respond to antibiotics alone with close follow-up 2
Established felon (abscess present with fluctuance): requires surgical incision and drainage 2, 5
Complicated felon (with signs of osteomyelitis, septic arthritis, or flexor tendon sheath involvement): requires more extensive surgical intervention and antibiotic therapy 1, 5
Common Pitfalls
Delaying diagnosis and treatment can result in significant limitation of hand function or even require partial amputation of the digit 1
Misdiagnosing as a "minor" infection when inadequate treatment can have long-term implications for both the individual and society 4
Treating with antibiotics alone when an abscess has formed; antibiotics should never replace adequate incision and drainage once an abscess is present 4
Failing to elevate the extremity and remove constricting jewelry or clothing as part of initial management 4