A posterior-anterior (PA) hand X-ray provides a detailed view of the bones, joints, and soft tissues of the hand. Below are the key features visible in a normal PA hand radiograph:

1. Positioning and View

• The hand is palm-down on the X-ray detector.

• Fingers are slightly spread to avoid overlap of bony structures.

• The wrist and forearm are included to capture the full anatomy.

2. Normal Anatomy

Bones:

1. Phalanges (Fingers):

   • Each finger has three phalanges (proximal, middle, distal), except the thumb, which has two.

   • The bones are smooth, without fractures, cortical interruptions, or deformities.

2. Metacarpals (Palm):

   • Five long bones extending from the wrist to the fingers.

   • Appear straight and evenly spaced, with visible heads, shafts, and bases.

3. Carpal Bones (Wrist):

   • Eight small bones in two rows:

     • Proximal row: Scaphoid, lunate, triquetrum, pisiform.

     • Distal row: Trapezium, trapezoid, capitate, hamate.

   • These bones are well-aligned and articulate properly with adjacent bones.

Joints:

• Interphalangeal Joints (IPJ): Between phalanges.

• Metacarpophalangeal Joints (MCPJ): Between metacarpals and phalanges.

• Carpometacarpal Joints (CMCJ): Between metacarpals and carpal bones.

• Joint spaces are uniform, with no narrowing, subluxation, or dislocation.

Soft Tissues:

• Outlines of soft tissue are visible and symmetrical.

• No signs of swelling, masses, or foreign bodies.

3. Radiographic Characteristics

• Bone Density: The bones are uniformly dense, without signs of osteoporosis (reduced density) or sclerosis (increased density).

• Cortical Continuity: The outer edges (cortex) of bones are smooth and intact.

• Joint Alignment: Proper alignment of all joints, with no evidence of displacement.

• Soft Tissue Shadows: Normal soft tissue shadows are present, with no calcifications or abnormalities.

A hand X-ray showing rheumatoid arthritis (RA) reflects the chronic inflammatory process that primarily affects the joints. Below are the key radiographic findings and their clinical implications:

1. Key Radiographic Features

Joints:

• Joint Space Narrowing:

  • Symmetrical narrowing of the joint spaces due to cartilage destruction.

  • Commonly affects the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints.

Bone Changes:

• Deformities:

  • Late-stage changes, including subluxations (partial dislocations) and ulnar deviation of the fingers.

  • Severe cases show "boutonnière deformity" (flexion at PIP, hyperextension at DIP) or "swan-neck deformity" (hyperextension at PIP, flexion at DIP).

Soft Tissues:

• Swelling:

  • Diffuse or localized soft tissue swelling around affected joints, reflecting synovial hypertrophy or effusion.

• Loss of Soft Tissue Mass:

  • Chronic RA may cause muscle atrophy and thinning of soft tissues.

• Overlap of soft tissue at fingers

2. Common Locations Affected

• MCP Joints:

  • Frequent site of joint erosions and swelling.

• PIP Joints:

  • Involved early in disease progression.

• Wrist Joints:

  • Carpal bones may show loss of definition and erosion.

• Ulna Styloid Process:

  • Often eroded due to inflammation.

3. Progression Stages on X-ray

• Early RA:

  • Joint swelling and periarticular osteopenia without major erosions.

• Moderate RA:

  • Narrowing joint spaces and early marginal erosions.

• Severe RA:

  • Advanced erosions, deformities (e.g., ulnar deviation), and ankylosis (fusion of joints).