What is the diagnosis and first step in management for a finger injury with a distal phalanx stuck in a flexed position, unable to actively extend but can passively extend, with swelling, tenderness, and dip?

Mallet Finger: Extensor Tendon Rupture at DIP Joint

This is a mallet finger injury—an extensor tendon disruption at the distal interphalangeal (DIP) joint—and the first step is obtaining a standard 3-view radiograph of the affected finger to differentiate between a tendinous injury versus a bony avulsion fracture, as this distinction determines whether conservative splinting alone is sufficient or if surgical intervention is required. 1, 2

Clinical Diagnosis

The presentation is pathognomonic for mallet finger:

• Inability to actively extend the DIP joint with the distal phalanx held in flexion 3, 4
• Preserved passive extension of the DIP joint (distinguishes this from joint dislocation or arthritis) 3, 4
• Swelling and tenderness at the DIP joint from the acute injury 3
• Mechanism of injury (tucking sheet under mattress) represents an axial load with forced flexion—classic for mallet finger 4

First Step: Radiographic Evaluation

Obtain a 3-view radiograph of the injured finger immediately (posteroanterior, lateral, and oblique views) 1, 2. This is critical because:

• Radiographs differentiate tendinous from bony mallet finger, which have different treatment implications 2
• Bony avulsion fractures involving ≥1/3 of the articular surface require surgical referral 2, 4
• Palmar subluxation of the distal phalanx or interfragmentary gap >3mm indicates need for operative fixation 1, 2
• Standard radiographs are sufficient for diagnosis—advanced imaging (MRI/CT) is not indicated for routine mallet finger 2

Immediate Management While Awaiting Imaging

• Splint the DIP joint in the position found (do NOT attempt to straighten manually before proper evaluation) 2
• Apply ice-water mixture for 10-20 minutes with a thin towel barrier to reduce swelling 2
• Avoid heat application which can worsen swelling 2

Treatment Algorithm Based on Radiographic Findings

For Tendinous Mallet Finger (No Fracture):

• Continuous DIP joint splinting in slight hyperextension (0-5 degrees) for 6-8 weeks full-time 2, 4, 5
• Uninterrupted immobilization is critical—even brief splint removal restarts the healing timeline 2
• Begin active PIP and MCP joint exercises immediately while keeping DIP splinted to prevent stiffness 2
• Overnight splinting for additional 4-6 weeks after starting mobilization 6

For Bony Mallet Finger (Avulsion Fracture):

• Fracture <1/3 articular surface without subluxation: Treat conservatively with DIP splinting in neutral (0 degrees) for 6-8 weeks 2, 4
• Fracture ≥1/3 articular surface OR palmar subluxation OR >3mm interfragmentary gap: Immediate orthopedic/hand surgery referral for operative fixation 1, 2, 4

Critical Pitfalls to Avoid

• Do not delay radiographs—clinical examination alone cannot reliably exclude fractures requiring surgery 1, 2
• Do not allow any splint removal during the initial 6-8 week period—this is the most common cause of treatment failure 2
• Do not ignore volar subluxation on lateral radiographs—this is an absolute surgical indication even with small fracture fragments 1, 2, 4
• Left untreated, mallet finger progresses to chronic deformity, swan-neck deformity, and DIP osteoarthritis 4, 5

Expected Outcomes

With appropriate conservative management for tendinous injuries, excellent to good results are achieved in >90% of cases when patient compliance with continuous splinting is maintained 6, 4. Surgical intervention for appropriate indications (large fracture fragments with subluxation) prevents chronic functional loss and joint instability 4, 7.