A hand X-ray (radiograph) is a foundational diagnostic tool providing a rapid, non-invasive look at the hand’s internal structures. The image is created by passing radiation through the hand; dense materials like bones block the radiation and appear white, while less dense soft tissues appear in shades of gray to black. This technique is routinely employed to diagnose acute injuries like fractures, evaluate chronic conditions such as arthritis, and identify foreign objects. Interpreting a normal hand X-ray requires understanding how the intricate anatomy is translated onto a two-dimensional image.
Standard Views and Positioning
A single X-ray view is insufficient to fully visualize the hand’s three-dimensional complexity. Therefore, a standard hand X-ray series typically includes three distinct projections for a comprehensive assessment.
The Posteroanterior (PA) view is the most common, taken with the palm flat against the detector plate. This projection offers the best visualization of overall bone alignment and joint spaces.
The Oblique view is obtained by rotating the hand approximately 45 degrees. This view is useful for separating superimposed structures, helping detect subtle fractures (especially in the metacarpals), and providing a clearer look at joint surfaces.
The Lateral view is taken with the hand positioned 90 degrees from the PA view, often in a “karate chop” stance. This projection is primarily used to assess the displacement or angulation of detected fractures and to localize foreign bodies within the soft tissues.
The Bony Landscape (Anatomical Components)
A normal hand is composed of 27 individual bones, grouped into three regions: the digits, the palm, and the wrist. The fingers contain fourteen long bones known as the phalanges. Each finger (except the thumb) has three phalanges—proximal, intermediate, and distal—while the thumb has only a proximal and a distal phalanx.
The five bones of the palm are the metacarpals, numbered one through five starting with the thumb side. Each metacarpal has a base connecting to the wrist, a shaft, and a head that forms the knuckle joint with the proximal phalanx.
The wrist region (carpus) contains eight small, irregularly shaped carpal bones, organized into two rows: a proximal row and a distal row.
- The proximal row includes the scaphoid, lunate, triquetrum, and pisiform bones.
- The distal row consists of the trapezium, trapezoid, capitate, and hamate bones.
Defining “Normal” (Joints, Alignment, and Texture)
A radiograph is considered normal when the bones, joints, and surrounding soft tissues meet specific criteria for structural integrity and proper relationship. Alignment is the first criterion; the bones should form smooth, continuous arcs and columns without abrupt breaks or steps. On the PA view, imaginary lines drawn through the carpal bones and down the metacarpal shafts must be uninterrupted and congruent.
The joint spaces between articulating bones should appear uniform in width and clearly visible, representing healthy, non-calcified cartilage. For example, the space between the carpal bones and the metacarpals should measure between one and two millimeters. A reduction in this uniform space often indicates cartilage loss (e.g., arthritis), while widening may suggest a ligamentous injury or dislocation.
The internal structure, or bone texture, is also examined, differentiating the dense outer shell (cortex) from the inner, spongy trabecular bone. A normal cortex appears as a smooth, distinct white line, with the internal trabecular pattern appearing as fine, interconnected lines. There should be no evidence of abnormal features like erosions, cysts, or areas of increased or decreased bone density. The soft tissues surrounding the bony structures should appear as faint, even shadows without significant swelling or unexpected calcifications.