Basic principles and fracture characteristics
To correctly evaluate any skeletal injury, the two-view rule is applied. At least two radiographs must be obtained in mutually perpendicular planes (e.g., anteroposterior and lateral). A single view is categorically insufficient, as many nondisplaced oblique (oblique) fractures may only be visualized at a specific angle.
The injury pattern heavily depends on the patient's age. The pediatric skeleton has high elasticity, so children's bones tend to deform rather than break completely. In adults, complete fractures predominate, where the fracture line extends through both cortices. It is important to understand that conventional radiographs often underestimate injury severity: a fracture appearing incomplete on X-ray frequently turns out to be complete on CT or MRI.
When describing trauma, radiologists consider:
- Orientation: transverse, oblique, or spiral lines (this affects stability and the choice of reduction method).
- Location: relative to the diaphysis, metaphysis, or epiphysis.
- Fragment displacement: distraction (separation), impaction, or angulation. Impacted fractures (e.g., of the femoral neck) appear on a radiograph not as a dark line, but as a hyperdense (bright) band due to the superposition of bone structures.
Intra-articular, comminuted, and occult injuries
Involvement of the joint in the fracture line generally worsens the prognosis and requires a specific surgical approach. Small periarticular fragments are of great significance—most commonly avulsion fractures (avulsions) at capsule or ligament attachment sites. A classic example is the Segond fracture of the knee, which is a strong predictor of an anterior cruciate ligament tear.
An indirect sign of intra-articular trauma is lipohaemarthrosis (identified on a horizontal-beam lateral radiograph). However, the absence of an effusion does not guarantee joint integrity: if the capsule ruptures, fluid may simply escape into the surrounding soft tissues.
If clinical symptoms are pronounced while standard radiographs are normal, occult fractures (occult fractures) are suspected. In such cases, MRI is indicated. Occult incomplete fractures are stable, but require axial load restriction to prevent further displacement.
Bone bruises and special types of fractures
A bone bruise (bone bruising) consists of trabecular microfractures occurring from joint surface overload. This pattern is invisible on X-rays and is detected only on MRI (in STIR sequences). Focal bruising of the lateral femoral condyle is closely associated with ACL injury, and in the long term, bone bruises lead to degeneration of the adjacent cartilage.
Fractures occurring without high-energy acute trauma are classified separately:
- Insufficiency: occur under normal load on pathologically weakened bone (typical of femoral neck osteoporosis in elderly women).
- Pathological: occur in the zone of a local defect (tumor, metastasis, myeloma).
- Stress: develop in healthy bone due to extreme repetitive loading. In early stages, X-rays may not show a fracture line, revealing only periosteal reaction or sclerosis later.
Specific patterns of upper extremity, wrist, and calcaneal trauma
Classic distal radius fractures are differentiated by the direction of displacement on the lateral view: a Colles' fracture is characterized by dorsal displacement, while a Smith's fracture features volar displacement.
Among the carpal bones, the scaphoid (scaphoid) is injured most frequently. Three views are obtained for its visualization (including an oblique view to "elongate" the bone). Due to its blood supply pattern (vessels run from the distal pole to the proximal), proximal fractures carry a high risk of nonunion and avascular necrosis (AVN).
In calcaneal injuries, an axial view and CT are mandatory to assess the articular facets. The most critical radiological criterion is Böhler's angle (normally 30°). Its reduction indicates the need for surgical reconstruction of bone height. Small avulsion fragments of the anterior process of the calcaneus must be differentiated from an accessory ossicle—the Os calcaneus secundarius—which has smooth, rounded margins.
Briefly: answers to topical questions
What indirect radiological signs indicate an intra-articular injury?
Indirect radiological signs of an intra-articular injury include soft tissue changes and the presence of specific fluids within the joint cavity. These include:
- Lipohaemarthrosis (lipohaemarthrosis) — the presence of fat droplets in the joint during haemarthrosis.
- Joint effusion (joint effusion) — an accumulation of fluid stretching the capsule.
- Fat pad sign (fat pad sign) — elevation of fat pads due to effusion or hematoma (especially the posterior fat pad, posterior fat pad, the visibility of which is always pathological).
The absence of these signs does not exclude trauma, as capsular rupture may allow fluid to extravasate into surrounding tissues.
What projections are required for adequate radiological visualization of the scaphoid bone?
For adequate radiological visualization of the scaphoid bone (scaphoid), three main projections are standard, along with supplementary views.
- Posteroanterior view (PA view) — the baseline straight projection.
- Lateral view (lateral view) — the standard projection for assessing carpal structures.
- Oblique view (oblique view) — allows visual "elongation" of the bone and isolates it from overlapping shadows of other bones.
- Second posteroanterior view — performed with the wrist in ulnar deviation (ulnar deviation), with or without X-ray tube angulation (tube angulation).
- Special oblique view (forehand oblique) — further improves visualization.
What types of bone fragment displacement are distinguished in traumatology and diagnostic imaging?
In traumatology and diagnostic imaging, the following main types of bone fragment displacement (dislocatio) are distinguished:
- Transverse displacement / displacement in width (dislocatio ad latus / ad latum) — fragments diverge sideways relative to the cross-section.
- Axial displacement / angular displacement (dislocatio ad axin / ad angulum) — an angle forms between the axes of the fragments.
- Displacement along the length (dislocatio ad longitudinem) — movement along the long axis of the bone. Includes displacement with shortening/overriding (cum contractione), with lengthening/distraction (per extensionem / diastasis), and impaction.
- Rotational displacement / peripheral displacement (dislocatio ad periferium / periphericum) — rotation of a fragment around its longitudinal axis.
What classifications of pelvic and pelvic ring fractures exist?
Sources indicate that many different pelvic fracture classifications have been proposed to predict the severity of consequences. In particular, pelvic ring injury classifications based on the mechanism of trauma include:
- Anteroposterior compression (AP Compression) — includes types ranging from AP type 1 (stable ring) to AP type 3 (complete instability with ligamentous disruption).
- Lateral compression (Lateral Compression, LC) — the most common pattern, including types from LC type 1 (oblique/comminuted fractures) to LC type 2 and LC type 2a (internal rotation of the innominate bone).
Also, specific types are distinguished: avulsion (avulsion fractures), pathological (pathological fractures), and insufficiency fractures (insufficiency fractures).
Class and exam questions
Why is a single radiograph insufficient when a fracture is suspected?
Many oblique or spiral fractures without significant displacement are not visible in the anteroposterior projection. Taking at least two views at right angles is a mandatory rule to avoid diagnostic errors.
What does widening of the medial ankle joint space indicate?
On the anteroposterior radiograph, this sign reliably indicates a concomitant rupture of the deltoid ligament, which frequently accompanies fibular fractures.
How to distinguish an impacted fracture on a radiograph?
Unlike the classic dark (radiolucent) line, an impacted fracture appears as an abnormal light (hyperdense) line of sclerosis due to bone compaction and the overlap of bone fragments.
What is the risk of a proximal scaphoid fracture?
Due to the retrograde blood supply to the proximal pole, such injuries are frequently complicated by avascular necrosis and prolonged non-union of the fragments.
What else to study on this topic
- Specific features of oblique projections for the scaphoid
- Specific ankle fractures in adolescents: Tillaux and triplane
- CT patterns and reconstruction of comminuted fractures
- Differential diagnosis of accessory foot bones and avulsion fractures
- Measurement of Böhler's angle and evaluation of subtalar joint congruence
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