Residency · Residency · Diagnostic Radiology

Systematic Approach to Trauma Radiography

Overview

Principles

Radiographs remain the first-line imaging for most extremity and axial skeletal trauma. A systematic search pattern prevents satisfaction of search errors. A minimum of two orthogonal views should be obtained, and the images should include the joints above and below the injury. Adequacy assessment should be performed before interpretation, confirming proper exposure, positioning, and inclusion of all relevant anatomy.

ABCDs Framework

The ABCDs framework provides a structured approach to radiograph interpretation. A stands for alignment, encompassing joint congruity, anatomic relationships, and displacement. B stands for bones, referring to cortical integrity, trabecular pattern, and periosteal reaction. C stands for cartilage and joint spaces, assessing symmetry, widening, and narrowing. D stands for soft tissues, including swelling, fat pad displacement, and foreign bodies.

Adequacy Assessment

General Principles

Every radiograph should be checked for correct patient identification and laterality markers. A minimum of two views at 90 degrees (AP and lateral) is standard. The entire bone and adjacent joints should be included, and exposure should be adequate, with cortical margins visible and soft tissues evaluable.

Specific Regional Considerations

For the cervical spine lateral, the image must visualize C1 through the C7-T1 junction, with a swimmer's view obtained if needed. For the chest, the PA view is preferred over AP for accurate cardiac size assessment, and the lateral view is essential for the retrosternal and retrocardiac regions. For the pelvis, the AP view should be centered on the symphysis with both hips included, and the iliac wings, sacrum, and pubic rami should be assessed.

Commonly Missed Fractures

Upper Extremity

Scaphoid fractures present with tenderness in the anatomic snuffbox, but initial radiographs are negative in 15-20% of cases. Dedicated scaphoid views should be obtained, and MRI is the gold standard if radiographs are negative and clinical suspicion persists. Radial head fractures are often subtle, and the posterior fat pad sign (sail sign) is the key indirect finding; elevation of the anterior fat pad is also significant in the trauma setting. Posterior shoulder dislocations are identified by the lightbulb sign on the AP view (an internally rotated humeral head), the rim sign, and the reverse Hill-Sachs (trough) lesion. Hook of hamate fractures are often missed on standard views and require the carpal tunnel view or CT for diagnosis.

Lower Extremity

Posterior malleolus fractures are seen on the lateral ankle view and frequently accompany bimalleolar fractures, creating a trimalleolar injury pattern. Lisfranc injuries are identified by widening of the space between the first and second metatarsal bases on the AP foot view and the fleck sign (an avulsion at the base of the second metatarsal); weight-bearing views are critical for diagnosis. Calcaneal fractures produce a decreased Bohler angle (less than 20 degrees), are often bilateral, and are associated with lumbar burst fractures from a fall-from-height mechanism. Tibial plateau fractures may produce a lipohemarthrosis (fat-fluid level on cross-table lateral view), and subtle depression may require CT for definitive evaluation.

Axial Skeleton

C2 fractures include odontoid (dens) fractures (Types I through III) and hangman fractures (bilateral pars interarticularis fractures); the open-mouth odontoid view is essential. Thoracolumbar junction fractures are the most common traumatic spine fractures, occurring at T11 through L2, and alignment should be checked on the lateral view.

Fracture Description

Key Descriptors

A fracture should be described by its location (bone, segment such as proximal, mid-shaft, or distal, and whether it is intra-articular or extra-articular), its type (transverse, oblique, spiral, comminuted, segmental, avulsion, or compression), the degree and direction of displacement (as a percentage of shaft width or in millimeters), the angulation (direction of the apex, such as apex volar or apex lateral, measured in degrees), any shortening (overlap of fracture fragments), and rotation (assessed clinically and on imaging). Gas in the soft tissues suggests an open fracture.

Pediatric-Specific Fracture Patterns

The Salter-Harris classification grades growth plate injuries from Types I through V. Type I is a fracture through the physis only, which may be radiographically occult. Type II passes through the physis and metaphysis and is the most common type. Type III passes through the physis and epiphysis, making it intra-articular. Type IV crosses the metaphysis, physis, and epiphysis. Type V is a crush injury to the physis. A torus (buckle) fracture involves compression of one cortex and is stable. A greenstick fracture breaks one cortex while bending the other. A plastic (bowing) deformity produces deformation without a discrete fracture line.

Soft Tissue Signs

Fat Pad Signs

The elbow posterior fat pad is abnormal when visible and indicates an intra-articular effusion, which in the setting of trauma represents a hemarthrosis and an occult fracture. The elbow anterior fat pad is normal when it appears as a thin triangle, but elevation producing the "sail sign" is pathologic. A suprapatellar effusion causes distension of the suprapatellar bursa, and a lipohemarthrosis on cross-table lateral view indicates an intra-articular fracture. The pronator quadratus fat pad becomes obscured in distal radius fractures.

Other Soft Tissue Findings

Prevertebral soft tissue swelling in the cervical spine (greater than 7 mm at C2 or greater than 22 mm at C6) suggests hemorrhage or fracture. Joint effusion should be compared asymmetrically with the contralateral side. Subcutaneous emphysema, or gas in the soft tissues, indicates an open fracture or penetrating injury.

<image>A radiograph panel showing commonly missed fractures: (1) AP and scaphoid view of the wrist with a subtle waist fracture of the scaphoid (arrow). (2) Lateral elbow radiograph demonstrating a posterior fat pad sign (sail sign, arrow) with a subtle radial head fracture. (3) AP ankle radiograph with a bimalleolar fracture and the lateral view revealing an associated posterior malleolar fracture making it trimalleolar. (4) AP foot radiograph showing widening of the first-second intermetatarsal space with a fleck sign at the base of the second metatarsal (Lisfranc injury). Each panel is labeled with the diagnosis.</image>

<image>An illustration of the Salter-Harris classification of pediatric growth plate fractures. Five diagrams of a long bone (distal femur) showing Types I through V. Type I: fracture through the physis only. Type II: fracture through the physis extending into the metaphysis (Thurston-Holland fragment). Type III: fracture through the physis extending into the epiphysis. Type IV: fracture crossing the metaphysis, physis, and epiphysis. Type V: crush injury to the physis (depicted with compression arrows). Each type is labeled with its prognosis (Type V worst prognosis for growth disturbance).</image>

<image>A lateral elbow radiograph annotated to show the anterior and posterior fat pads. The normal anterior fat pad is shown as a thin line along the anterior humerus. The abnormal elevated anterior fat pad (sail sign) and the visible posterior fat pad are highlighted with arrows, indicating an intra-articular effusion. A subtle radial head fracture line is shown with a magnified inset. The coronoid process and olecranon are labeled for orientation.</image>

Clinical Pearls

The posterior fat pad sign on a lateral elbow radiograph in the setting of trauma indicates an occult fracture until proven otherwise, most commonly a radial head fracture in adults. Weight-bearing views should always be obtained for suspected Lisfranc injuries, as non-weight-bearing radiographs may appear normal. A fall from height should prompt evaluation of both calcanei and the thoracolumbar spine due to the axial loading mechanism. In pediatric patients, Salter-Harris Type II is the most common growth plate fracture, while Types III and IV are intra-articular and typically require surgical fixation. Fractures should be described systematically using location, type, displacement, angulation, and involvement of the articular surface, as this standardized approach ensures clear communication with orthopedic surgeons. Satisfaction of search is the most common perceptual error in trauma radiography, and the entire systematic review should always be completed even after identifying an obvious fracture.

References

• Helms CA. Fundamentals of Skeletal Radiology. 5th ed. Elsevier, 2020
• Rogers LF. Radiology of Skeletal Trauma. 3rd ed. Churchill Livingstone, 2002
• ACR Appropriateness Criteria: Acute Trauma to the Foot, Ankle, Knee, Hip, Shoulder, Elbow, Wrist (multiple documents)
• Porrino J, et al. "Commonly Missed Fractures." Radiologic Clinics of North America, 2019

Read this lecture as Markdown