Wrist and hand x-ray projections
The standard wrist and hand radiographs projections includes posteroanterior, oblique, and lateral views [3,4].
- Posteroanterior (PA) projection: The best for visualizing and inspecting bone alignment, the joint spaces of the carpal bones and the distal radioulnar joint. This projection is obtained with the shoulder abducted 90°, the elbow flexed at 90°, and the forearm in a pronated position, with the palm facing down [5].
- Lateral projection: The essential view to assess the alignment of the radius, lunate, and capitate. This projection is obtained with the elbow flexed at 90° and adducted against the trunk. The forearm should be in a mid-prone position, with the fingers and metacarpals superimposed [5,6].
- Oblique projection: It is an important view to evaluate the scaphoid tuberosity, scaphotrapeziotrapezoidal joint and trapeziometacarpal articulation. This projection is obtained like the PA view, but with the wrist and hand rotated laterally 45° from the pronated position [5,6].
Additional projections may be necessary when initial radiographs are normal but a fracture is still suspected. For instance, a PA view with ulnar deviation is useful for detecting potentially hidden scaphoid fractures [5].
Systematic wrist and hand radiographs approach
- Bone alignment
Evaluating the alignment of the carpal bones, metacarpals, and phalanges is crucial [7]. The carpal alignment is guided by four key principles:
- Gilula three carpal arcs: Gilula’s arcs are evaluated in wrist PA radiographs. Any disruption suggests a ligamentous injury or fracture [8].
- Rule of the spaces: the joint space between the carpal bones carpal bones should be consistent (1-2 mm) [9].
- Rule of the parallelism: the articular surfaces of the adjacent carpal bones should be parallel to each other [9].
- Lateral carpal alignment: In the lateral wrist projection, the longitudinal axes of the third metacarpal, lunate, capitate and radius should be aligned. Any deviation indicates carpal instability [8].
The rules of spaces and parallelism apply not only to carpal alignment but also to the metacarpophalangeal and interphalangeal joints.
- Subluxation: refers to an insufficient joint surface contact in these joints and is commonly seen in conditions such as rheumatoid arthritis, psoriatic arthritis, and osteoarthritis [10].
- Cortical integrity
The cortex should appear continuous. Any interruption or disruption of the cortical outline may indicate a fracture. Fractures of the scaphoid and triquetrum are the most common fractures of the carpal bones [11,12].
When a fracture is identified, it is crucial to assess various factors, including the fracture morphology (e.g., transverse, oblique, or spiral), location, intra-articular extension, impaction, displacement, angulation, and any associated fractures or soft tissue injuries [13].
A potential differential diagnosis for a fracture includes vascular lines, which may mimic cortical irregularities but are, in fact, a normal anatomical feature [11,12].
- Trabecular patterns
Alterations on trabecular patterns could indicate a bone lesion. Besides, subtle increase in density could suggest a minor fracture [14].
- Joint abnormalities
Cartilage is radiolucent; however, the cartilage can be assessed by evaluating the preservation of joint space width. Potential joint pathological findings include joint space narrowing and the presence of erosions [10].
- Loss of joint space: Asymmetric joint loss is commonly associated with osteoarthritis, whereas symmetrical joint loss is typically linked to inflammatory arthropathies, such as rheumatoid and psoriatic arthritis [10].
- Erosions: Marginal erosions are characteristic of rheumatoid and psoriatic arthritis; central erosions are typical of erosive osteoarthritis; and periarticular erosions are commonly observed in gout [10].
- Abnormalities in the surrounding soft tissues
Soft tissue abnormalities in the hand and wrist include a wide range of conditions, from normal variants to cystic lesions, post-traumatic changes, inflammatory and infectious disorders, vascular anomalies, metabolic issues, and other miscellaneous conditions [15].
Soft tissue abnormalities are often key in assessing arthropathies, especially inflammatory or depositional arthritis. Symmetrical soft tissue swelling around a joint suggests synovitis, and swelling may appear focal, diffuse, symmetric, asymmetric, or lumpy-bumpy [10].
Critical standard diagnostic measurements
- Bone mineralization
Osteoporosis is a systemic metabolic disorder characterized by a decline in bone quality and mass, leading to increased bone fragility and an increased risk of fracture [16].
The main radiographic finding in osteoporosis is thinning of the cortex. Bone mineralization can be assessed through a measurement on hand and wrist radiographs by calculating a ratio. This ratio is derived from the transverse diameter of the trabecular bone of the second or third metacarpal shaft, divided by the maximum diameter of the respective metacarpal shaft. A ratio less than 0.5 is considered normal, while a ratio greater than 0.5 indicates a subjective reduction in bone mineral density [17].
- Radial inclination and height
Radial inclination and radial height are key measurements in the evaluation and treatment of distal radius fractures. A decrease in either the radial inclination angle or radial height may indicate a radial fracture. [18].
- Radial inclination: Angle between the articular surface of the radius and a line perpendicular to the diaphysis. Normal: 21º-25º [18].
- Radial height: Distance between two lines perpendicular to the radial shaft: a line passing through the styloid process of the radius and a line parallel and adjacent to the distal articular surface of the ulna. Normal: 8 to 14 mm [18].
- Ulnar variance
Ulnar variance is measured by drawing a line along the distal articular surface of the radius and determining the distance to the distal surface of the ulna [19]:
- Neutral: The radial and ulnar surfaces are at the same level.
- Negative: The ulna is more than 2.5 mm proximal to the radius articular surface.
- Positive: The ulna is more than 2.5 mm distal to the radius articular surface.
Ulnar variance is unaffected by the length of the ulnar styloid process. Accurate measurement requires a true PA view, as supination or pronation alters the apparent lengths of the radius and ulna. If the ulnar styloid process overlaps the head, ulnar variance cannot be measured reliably [19].
- Scapholunate and capitolunate angles
When carpal instability is suspected, the scapholunate and capitolunate angles should be measured. These angles can only be assessed on a neutral lateral wrist radiograph [8]:
- Scapholunate angle: Determined by a line drawn along the long axis of the scaphoid and another along the mechanical axis of the lunate. The normal range is 30° to 60°;
- Capitolunate angle: Determined by the same lunate axis line compared to the long axis of the capitate. The normal range is 0° to 30°.
Any deviation from the normal ranges for these angles suggests carpal instability [8].
Normal anatomical variants
Recognizing normal anatomic variations, such as accessory ossicles, epiphyseal spurs, and persistent ulnar styloid ossicles, is crucial to prevent misdiagnosing these structures as fractures or degenerative changes, thereby avoiding unnecessary investigations and treatments that may harm the patient [20].
