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Upper Extremities

16 Fingers & Thumb

Anatomy & Pathology

Key Anatomical Structures

  • Phalanges: The fingers (digits 2–5) each contain three phalanges — proximal, middle, and distal.
    The thumb (digit 1) has only two phalanges — proximal and distal.
    Each phalanx includes a base (proximal end), body (shaft), and head (distal end).
    The phalanges articulate with each other to form interphalangeal (IP) joints.
  • Metacarpals: The metacarpal bones form the palm and articulate distally with the phalanges at the metacarpophalangeal (MCP) joints. The first metacarpal (of the thumb) is short and thick, forming a saddle (sellar) joint at its base with the trapezium.
    This articulation allows the thumb’s wide range of motion, including opposition.
  • Joints and Articulations:
    • Distal interphalangeal (DIP) – hinge joint, flexion and extension.
    • Proximal interphalangeal (PIP) – hinge joint, flexion and extension.
    • Metacarpophalangeal (MCP) – ellipsoidal joint, flexion, extension, abduction, adduction, circumduction.
    • Carpometacarpal (CMC) of thumb – saddle joint, flexion, extension, abduction, adduction, rotation, and opposition.

Common Pathologies

  • Fractures:
    • Tuft fracture – crush injury to distal phalanx; seen on lateral projection.
    • Mallet finger – avulsion of distal phalanx extensor tendon; may show small bone fragment at DIP joint.
    • Boxer’s fracture – transverse fracture of 5th metacarpal neck (may extend into proximal phalanx region).
    • Bennett’s fracture – fracture-dislocation at base of first metacarpal involving CMC joint.
  • PIP or MCP dislocation – visible misalignment or overlapping joint surfaces.
  • Soft-Tissue and Ligamentous Injuries:
    • Gamekeeper’s (Skier’s) thumb – ulnar collateral ligament tear at first MCP joint.
    • Tendon avulsion injuries – require lateral and oblique projections for assessment of alignment.
  • Arthritis and Degenerative Change:
    • Osteoarthritis – joint-space narrowing, osteophytes at DIP and PIP joints.
    • Rheumatoid arthritis – erosion and joint deformity, often beginning at MCPs.
  • Congenital or Developmental Variants:
    • Polydactyly – extra digits.
    • Syndactyly – fused digits.
      Both may require oblique or lateral views for full evaluation prior to surgical correction.
  • Foreign Bodies: Splinters, glass, or metal fragments may be radiopaque or radiolucent.
    Exposure note: Lower kVp improves soft-tissue contrast when searching for low-density material.

Routine Projections (ARRT Required)

Finger — PA

CR Location & Positioning

  • SID: 40″
  • Patient position: Seated at table, forearm on tabletop.
  • Adjustments: Pronate hand; spread digits; keep the finger of interest flat with phalanges parallel to IR. Center PIP to IR.
  • CR: Perpendicular to PIP joint.
  • Pt. Instructions: “Hold very still—don’t let the fingertip lift.”
  • Exposure: Small focal spot; ~55–60 kVp, no grid.

Evaluation Criteria

  • Coverage: Entire digit from fingertip through distal 1/3 of the adjacent metacarpal.
  • Rotation checks: Equal concavity on both sides of phalangeal shafts; equal soft tissue on both sides.
  • Motion checks: Crisp cortical margins and trabeculae.
  • Technique checks: Open IP & MCP joints (phalanges parallel); no artifacts/rings.
  • Clinical aim: Baseline alignment, subtle avulsions, joint space evaluation.

Finger — PA Oblique

CR Location & Positioning

  • SID: 40″
  • Patient position: Seated; forearm on table.
  • Adjustments:
    • 2nd–3rd digits: rotate the hand medially (internally) from pronation until the affected finger rests at a 45° angle on a radiolucent wedge, keeping the phalanges parallel to the IR.
    • 4th–5th digits: rotate the hand laterally (externally) to achieve the same 45° oblique, keeping the digit of interest closest to the image receptor to reduce magnification and improve detail.
  • CR: Perpendicular to PIP.
  • Pt. Instructions: “Stay relaxed; don’t let the finger roll.”
  • Exposure: Small focal spot; ~55–60 kVp, no grid.

Evaluation Criteria

  • Coverage: Entire digit + distal 1/3 of metacarpal.
  • Rotation checks: 45° rotation—C+oncavity on elevated cortex; Because equal concavity of the shafts of the phalanges and equal soft-tissue margins indicate no rotation, if the concavity is greater on one side, the finger was rotated toward that side. No overlap from adjacent digits at proximal phalanx/MCP.
  • Motion checks: Sharp edges, no blur.
  • Technique checks: Open IP & MCP joints (phalanges parallel); proper collimation.
  • Clinical aim: Oblique fracture planes, corner avulsions, joint margins.

Finger — Lateral

CR Location & Positioning

  • SID: 40″
  • Patient position: Seated; forearm on table.
  • Adjustments:
    • 2nd–3rd digits: lateromedial lateral (radial side down).
    • 4th–5th digits: mediolateral lateral (ulnar side down).
    • Flex/secure other digits; keep digit of interest true lateral with phalanges parallel to IR; center PIP.
  • CR: Perpendicular to PIP.
  • Pt. Instructions: “Hold the fist tight; keep the finger straight.”
  • Exposure: Small focal spot; ~55–60 kVp, no grid.

Evaluation Criteria

  • Coverage: Entire digit; include MCP.
  • Rotation checks: Fingernail in profile; double cortical (concave anterior surface) appearance; no overlap of adjacent digits at proximal phalanx/MCP.
  • Motion checks: Sharp trabeculae along distal tuft.
  • Technique checks: Open IP joints; correct collimation.
  • Clinical aim: Displacement/angulation assessment in the true sagittal plane.

Thumb — AP

CR Location & Positioning

  • SID: 40″
  • Patient position: Seated; arm internally rotated.
  • Adjustments: Extreme medial rotation; retract other digits; lay thumb flat AP with phalanges parallel to IR; include trapezium; center 1st MCP.
  • CR: Perpendicular to 1st MCP.
  • Pt. Instructions: “Keep the palm out of the way; don’t lift the thumb.”
  • Exposure: Small focal spot; ~55–60 kVp, no grid.

Evaluation Criteria

  • Coverage: Distal tip through entire 1st metacarpal and trapezium.
  • Rotation checks: Equal concavity on both sides of proximal phalanx & metacarpal; equal soft tissue.
  • Motion checks: Crisp cortex of 1st metacarpal base & trapezium.
  • Technique checks: Open IP & MCP joints; minimal palm soft-tissue overlap on mid-1st metacarpal.
  • Clinical aim: True AP reduces OID (vs PA), optimizes CMC/MCP assessment.

Thumb — PA Oblique

CR Location & Positioning

  • SID: 40″
  • Patient position: Seated; hand pronated.
  • Adjustments: Abduct thumb; slight ulnar deviation positions thumb in PA oblique; keep thumb phalanges parallel to IR; center 1st MCP; include trapezium.
  • CR: Perpendicular to 1st MCP.
  • Pt. Instructions: “Don’t press the thumb down; let it rest.”
  • Exposure: Small focal spot; ~55–60 kVp.

Evaluation Criteria

  • Coverage: Distal tip through trapezium.
  • Rotation checks: Proper oblique—concavity on elevated cortex of proximal phalanx; appropriate soft-tissue contour.
  • Motion checks: Sharp margins.
  • Technique checks: Open IP & MCP; correct collimation.
  • Clinical aim: Routine view for injuries when AP isn’t feasible.

Thumb — Lateral (true lateral)

CR Location & Positioning

  • SID: 40″
  • Patient position: Seated; hand in natural arch.
  • Adjustments: Flex fingers or use sponge to roll thumb into true lateral; keep phalanges parallel to IR; center 1st MCP; include trapezium.
  • CR: Perpendicular to 1st MCP.
  • Pt. Instructions: “Hold this arch; keep the thumbnail perfectly sideways.”
  • Exposure: Small focal spot; ~55–60 kVp.

Evaluation Criteria

  • Coverage: Distal tip through trapezium.
  • Rotation checks: Thumbnail in profile; anterior cortex concavity; true lateral shaft; no overlap of other digits.
  • Motion checks: Sharp trabeculae at 1st metacarpal base.
  • Technique checks: Open IP & MCP; correct collimation.
  • Clinical aim: Displacement/angulation of 1st ray, Bennett/Rolando fracture alignment.

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Hows & Whys of Finger & Thumb Radiography

Anatomy

  • Which digit has only two phalanges?
    The 1st digit (thumb)—proximal and distal only.
  • What type of joints are the IP joints?
    Synovial hinge joints (flexion/extension).
  • What type of joints are the MCP joints?
    Synovial condyloid joints (flexion/extension, ab/adduction, circumduction).
  • What type of joint is the 1st CMC?
    A saddle joint (wide ROM—opposition).

Positioning 

  • Why center the CR to the PIP for fingers?
    To align the narrow joint space with the central ray and keep IP joint spaces open across the digit.
  • Why keep the phalanges parallel to the IR for all finger/thumb views?
    To open IP/MCP joints and prevent foreshortening.
  • Why use a 45° foam wedge for the PA oblique finger?
    The wedge holds the digit at 45° while keeping phalanges parallel, so the joints remain open.
  • Why choose lateromedial for 2nd–3rd and mediolateral for 4th–5th digit laterals?
    Those approaches minimize OID and make a true lateral easier to hold.
  • Why perform the thumb in AP rather than PA when possible?
    AP reduces OID and magnification of the 1st metacarpal/CMC region and improves detail of the trapezium.
  • Why must the trapezium be included on all thumb projections?
    It articulates with the 1st metacarpal (CMC)—critical for Bennett/Rolando and CMC pathology.
  • Why retract or tape the other fingers for lateral finger/thumb views?
    To avoid superimposition over the proximal phalanx/MCP and preserve joint visibility.

Technique & Image Evaluation 

  • On a PA finger, how can you tell there was no rotation?
    Equal concavity on both cortices of the phalanges and equal soft tissue on both sides.
  • On a PA finger, how do you know the phalanges were parallel to the IR?
    Open IP and MCP joint spaces across the digit.
  • On a PA oblique finger, how do you know you achieved a true 45°?
    Concavity is more pronounced on the elevated cortex; no adjacent digit overlap at the proximal phalanx/MCP.
  • On a lateral finger, how do you confirm a true lateral?
    The fingernail is in profile, the anterior cortex is concave, and adjacent digits do not overlap the proximal phalanx/MCP.
  • On an AP thumb, how do you confirm true AP and reduced OID?
    Equal concavity on both sides of the proximal phalanx & metacarpal, sharp 1st metacarpal base/trapezium detail, and open IP & MCP.
  • On a thumb lateral, how do you know rotation is correct?
    Thumbnail in profile, shaft true lateral, open IP/MCP, and trapezium included without overlap from other digits.
  • What indicates the phalanges weren’t parallel (any view)?
    Closed IP spaces and foreshortened phalanges.
  • What indicates motion?
    Loss of fine trabecular detail at the distal tuft/phalangeal cortices.

Clinical Applications

  • Which views best assess displacement in phalangeal or metacarpal neck fractures?
    Lateral views (true sagittal assessment).
  • Which view best evaluates suspected Bennett or Rolando fractures?
    AP and lateral thumb with trapezium included for CMC alignment.
  • When is a PA oblique thumb useful?
    When AP is uncomfortable/impractical; it still profiles the 1st ray while maintaining joint visibility.

 

 

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Radiographic Procedures Review Guide Copyright © 2025 by Carla M. Allen and Taylor M. Otto is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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