My index finger is painful and swollen; how should I evaluate and manage it?

Evaluation and Management of Painful, Swollen Index Finger

Start with plain radiographs (posteroanterior, lateral, and oblique views) to exclude fracture, septic arthritis, and osteomyelitis, then proceed to ultrasound if infection is suspected or MRI if soft tissue pathology needs further characterization. 1

Initial Clinical Assessment

Your immediate priority is distinguishing infection from inflammatory or traumatic causes, as infection requires urgent intervention to prevent irreversible functional loss. 2

Key history elements to obtain:

• Mechanism of injury (penetrating trauma, bite, or spontaneous onset) 3
• Timing and progression (acute versus chronic) 4, 5
• Fever or systemic symptoms suggesting infection 1, 5
• Morning stiffness or bilateral joint involvement suggesting inflammatory arthritis 4, 5

Critical physical examination findings:

• Erythema, warmth, and tenderness suggesting infection 1, 5, 2
• Fusiform swelling with pain on passive extension (Kanavel signs for pyogenic flexor tenosynovitis) 6
• Joint effusion suggesting septic arthritis 1
• Localized bony tenderness suggesting fracture 1
• Multiple joint involvement suggesting rheumatoid arthritis 4

Imaging Algorithm

Step 1: Plain Radiographs (Always First)

Obtain three-view radiographs immediately (posteroanterior, lateral, and oblique) to identify: 1

• Fractures or dislocations 1
• Soft tissue swelling, joint effusion, or gas in tissues 1
• Erosions suggesting chronic osteomyelitis or inflammatory arthritis 1
• Foreign bodies 1

Important caveat: Early acute osteomyelitis (<14 days) may show only soft tissue swelling on radiographs, so normal films do not exclude infection. 1

Step 2: Advanced Imaging Based on Clinical Suspicion

If infection is suspected (erythema, warmth, fever, or systemic symptoms):

• Ultrasound is the next appropriate study to differentiate abscess from cellulitis/phlegmon and to identify joint effusions. 4, 7
• Ultrasound can guide aspiration for culture, which is essential for diagnosis and antibiotic selection. 1, 7
• Do not delay aspiration to obtain advanced imaging if septic arthritis is suspected—aspirate immediately, even with normal radiographs. 1
• MRI with IV contrast may be obtained after aspiration to stage the extent of infection, identify abscesses, or evaluate for osteomyelitis in chronic cases. 1, 7
• CT with IV contrast can assess soft tissue compartments and guide surgical debridement but is generally reserved for complex cases. 1

If soft tissue pathology is suspected (tendinopathy, ligament injury, or ganglion cyst):

• MRI without IV contrast is usually appropriate to evaluate tendons, ligaments, bone marrow, and articular cartilage. 1, 4
• Ultrasound is effective for examining flexor and extensor tendons, tendon sheaths, and can guide therapeutic injections. 4, 5

If inflammatory arthritis is suspected (morning stiffness, bilateral involvement, multiple joints):

• MRI with IV contrast is particularly useful to identify active synovitis, inflammatory tenosynovitis, and bone marrow edema (osteitis), which predicts disease progression in rheumatoid arthritis. 4
• Ultrasound with power Doppler can detect active synovitis and small erosions. 4

Laboratory Testing

If infection is suspected:

• Joint aspiration with cell count, Gram stain, and culture is mandatory. 1
• Blood cultures if systemic symptoms are present. 2

If inflammatory arthritis is suspected:

• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) 4
• Rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) 4
• Antinuclear antibody (ANA) if connective tissue disease is suspected 4

Initial Management

For suspected infection:

• Immediate surgical consultation for drainage if abscess or pyogenic flexor tenosynovitis is present—delay causes irreversible tendon and joint destruction. 2
• Empiric IV antibiotics covering Staphylococcus aureus and Streptococcus (adjust based on culture results). 2

For non-infectious causes:

• Relative rest and activity modification 5
• Cryotherapy (10-minute periods with melting ice water through wet towel) 5
• NSAIDs for short-term pain relief (2-3 weeks maximum; topical NSAIDs have fewer systemic side effects) 5, 8
• Splinting if pain impedes function 4

Critical Pitfalls to Avoid

• Do not delay aspiration or surgical drainage to obtain MRI or CT if infection is suspected—tissue viability depends on prompt intervention. 1, 3, 2
• Do not dismiss infection based on normal radiographs alone—early osteomyelitis and septic arthritis may have normal or minimal findings. 1
• Do not overlook pyogenic flexor tenosynovitis—this is a surgical emergency requiring immediate drainage to prevent permanent loss of finger function. 2, 6
• Radiographic soft tissue thickness differentiating volar from dorsal swelling ≥7 mm at the proximal phalanx level has 82% positive predictive value for pyogenic flexor tenosynovitis. 6