What is the appropriate assessment and treatment approach for an adult patient with a thumb injury, considering their overall health, medical history, and potential pre-existing conditions such as diabetes or rheumatoid arthritis?

Assessment of Thumb Injuries

Begin with standard three-view radiography (PA, lateral, and oblique) as the initial imaging for any suspected thumb injury, as this detects most fractures and dislocations, though clinical examination with specific provocative tests guides the overall diagnostic approach. 1, 2

Initial Clinical Assessment

History Taking - Key Elements

• Mechanism of injury (blunt trauma, penetrating injury, hyperextension, or repetitive use) to guide differential diagnosis 1, 3
• Pain characteristics: location (interphalangeal joint, metacarpophalangeal joint, or carpometacarpal/thumb base), timing (with use vs. rest), and severity 1
• Functional limitations: opposition, retroposition, palmar abduction, and radial abduction—these account for up to 50% of overall hand function 3
• Pre-existing conditions: diabetes, rheumatoid arthritis, osteoarthritis, or prior hand injuries increase risk and alter management 1
• Occupational/recreational exposures: repetitive or forceful thumb movements predispose to cumulative trauma disorders 3

Physical Examination - Specific Maneuvers

• Inspect for: Heberden nodes (DIP joint), Bouchard nodes (PIP joint), bony enlargement, deformity, subluxation, or soft tissue swelling 1
• Palpate for: point tenderness over specific joints, ligaments (ulnar/radial collateral), or tendon sheaths 4
• Lever test (preferred): Grasp the first metacarpal just distal to the basal joint and shuck back and forth in radial/ulnar directions—this has the highest sensitivity for thumb base osteoarthritis and best reproduces presenting pain 5
• Grind test: Has high specificity but lowest sensitivity and highest false-negative rate for basal joint arthritis—less diagnostically useful 5
• Assess for: ligamentous instability at the metacarpophalangeal and carpometacarpal joints, particularly ulnar collateral ligament (gamekeeper's/skier's thumb) 4

Imaging Strategy

Initial Radiography

• Standard three-view examination (PA, lateral, oblique) is necessary—two views alone are inadequate for detecting thumb fractures 1, 2
• Ensure complete coverage: Hand radiographs must include all metacarpals, phalanges of all five digits including the complete thumb ray, and carpometacarpal joints 2
• Order specificity: Specify "hand" or "thumb" on imaging orders to guarantee complete first ray coverage 2
• Radiographs detect: fractures (Bennett, Rolando, phalangeal), dislocations, bony avulsions (mallet injuries), and osteoarthritic changes (joint space narrowing, osteophytes, subchondral sclerosis/cysts) 1

Advanced Imaging - When Initial Radiographs Are Negative or Equivocal

• MRI without IV contrast is the preferred advanced modality for evaluating tendon injuries, ligamentous injuries, and occult fractures with sensitivity of 28-85% for extensor hood injuries 1, 6
• CT without IV contrast is useful when radiographs are equivocal for fractures, particularly for complex articular injuries requiring surgical planning, but cannot evaluate ligamentous injuries 1
• Ultrasound or MRI may be indicated if diagnostic uncertainty exists or to rule out alternative pathology (e.g., trigger thumb, de Quervain's tenosynovitis) 7
• Avoid routine imaging for clinically obvious conditions like trigger thumb unless alternative pathology is suspected 7

Specific Injury Patterns and Management Considerations

Fractures

• Bennett and Rolando fractures (metacarpal base): Require assessment of articular involvement and displacement on radiographs 4
• Operative indications: >2mm articular step-off, coronally oriented fracture line, die-punch depression, or >3 articular fragments 1
• Mallet injuries: Radiographs assess for bony avulsion; surgery indicated if >1/3 articular surface involved, palmar displacement of distal phalanx, or interfragmentary gap >3mm 1

Ligamentous Injuries

• Ulnar/radial collateral ligament tears: Common in athletes; MRI is ideal for surgical planning if operative repair considered 6, 4
• Clinical stress testing under local anesthesia may be needed to assess instability 4

Thumb Base Osteoarthritis

• Clinical diagnosis in adults >40 years with typical features: pain on usage, mild morning stiffness, targeting DIP, PIP, or thumb base joints 1
• Radiographic confirmation: PA view of both hands shows joint space narrowing, osteophytes, subchondral sclerosis/cysts; erosive changes indicate erosive OA subtype 1
• Functional assessment: Use validated outcome measures as impairment may be as severe as rheumatoid arthritis 1
• Conservative management first: NSAIDs, splinting, activity modification 1
• Surgery (trapeziectomy, interposition arthroplasty, arthrodesis) is effective for severe refractory cases; avoid combined procedures as they offer no advantage but higher complication rates 1

Tendon Injuries

• Radiographs first to detect fracture fragments that may require open reduction and internal fixation 1
• MRI for surgical planning if tendon repair anticipated 6
• Trigger thumb: Primarily clinical diagnosis; imaging only if diagnostic uncertainty 7

Special Population Considerations

Diabetes

• Increased risk of stiffness, delayed healing, and infection—lower threshold for specialist referral 1

Rheumatoid Arthritis

• Differentiate from osteoarthritis: RA targets MCP and PIP joints more than DIP; consider inflammatory markers if diagnostic uncertainty 1

Erosive Osteoarthritis

• Abrupt onset, marked pain, inflammatory signs (swelling, erythema), mildly elevated CRP, worse prognosis—requires more aggressive management 1

Common Pitfalls

• Relying on two-view radiographs alone—inadequate for thumb fracture detection 1, 2
• Using grind test exclusively—high false-negative rate; lever test is superior 5
• Delaying imaging in equivocal cases—leads to functional impairment; proceed to CT or MRI rather than casting and waiting 10-14 days 1
• Ordering "finger" instead of "hand" or "thumb" radiographs—may miss carpometacarpal pathology 2
• Assuming all thumb base pain is osteoarthritis—consider psoriatic arthritis (targets DIP/single ray), gout, or hemochromatosis in differential 1