Application in traumatology: assessment of knee ligaments
Standard radiography for knee ligament injury is often uninformative and can show only indirect signs, such as local widening of the joint space (medial or lateral). To objectively assess the degree of joint instability, comparative stress radiographs are performed.
Depending on the suspected injury zone, different stress vectors are applied:
- Collateral ligaments: images with maximum shank deviation are used. To assess the tibial collateral ligament, a valgus stress is applied (aimed at opening the medial joint space). For the fibular collateral ligament, a varus stress is applied (opens the lateral space).
- Cruciate ligaments: the examination is performed with anteroposterior displacement in the Lachman test position.
It is important to consider the role of the muscular system. Muscle atrophy frequently develops following trauma and can clinically simulate grade I–II anteromedial instability even with intact ligaments. Active stabilizers (muscles) can partially or fully compensate for the deficit of passive structures (ligaments and menisci).
Critical pre-hospital rule: any attempts to determine joint instability using stress tests are strictly contraindicated prior to initial radiographic examination, as this may worsen the condition in the presence of an undiagnosed fracture.
Diagnosis of occult hip fractures
In displaced trochanteric and femoral neck fractures, the diagnosis is usually obvious: the leg is non-weight-bearing, externally rotated, the «heel pad» sign is present, and the fracture line is clearly visible on standard images.
However, the diagnosis of impacted or «stress» fractures presents a serious challenge. With such injuries, weight-bearing capacity may be preserved, and typical limb positioning changes are absent. Standard radiographs may not show obvious bone tissue defects.
In complex cases, to confirm the diagnosis, stress radiographs in the anteroposterior projection are ordered. Images are taken in two positions:
- Adduction of the leg.
- Abduction of the leg.
If the diagnosis remains doubtful, additional methods are used: CT, MRI with 3D reconstruction, or evaluation of follow-up images in dynamics after 10–14 days (when bone resorption becomes visually distinguishable at the fracture site).
Dynamic airway fluoroscopy
Real-time functional assessment (rapid pulsed fluoroscopy, Fluoroscopy) is extremely demanded in pediatrics and pulmonology to differentiate the causes of obstruction and changes in lung radiolucency.
Main clinical scenarios:
- Foreign body aspiration: Organic objects (e.g., nuts) or plastic are often radiolucent. They can create a ball-valve mechanism, leading to local or diffuse hyperlucency. During functional fluoroscopy, the obstructed and overinflated lung does not change volume during the respiratory cycle, and the mediastinum characteristically shifts toward the healthy (contralateral) side on expiration.
- Tracheomalacia: Dynamic examination allows visualization of tracheal wall collapse on expiration.
- Vascular ring or sling (Vascular ring or sling): Functional assessment using a barium suspension (Barium swallow) in a strict lateral projection reveals abnormal vascular impressions on the contrast column during esophageal distension.
Although thin-slice CT has largely replaced older vascular ring imaging methods, functional fluoroscopy remains the method of choice for dynamic assessment of intermittent obstruction. This is especially important when adjusting non-invasive ventilation parameters, as it avoids high cumulative radiation exposure from repeated CT scans.
To memorize collateral ligament tests: «VALgus — pushes INward» (opens the inner/medial space), «VARus — tears OUTward» (opens the outer/lateral space).
Class and exam questions
Can functional ligament tests be performed immediately after trauma?
No, this is an absolute contraindication. Prior to performing a plain radiography and ruling out fractures, any stress tests are strictly prohibited.
What is the value of fluoroscopy in suspected bronchial foreign body?
If the foreign body is not visible on the image (radiolucent), fluoroscopy allows visualization of the valve mechanism in dynamics: the affected lung does not collapse during respiration, and the mediastinum shifts toward the healthy side on expiration.
Why take a follow-up image in suspected impacted hip fracture after 2 weeks?
After 10–14 days, bone resorption occurs in the area of the occult fracture, making the fracture line clearly visible on follow-up radiographs.
What else to study on this topic
- Features of the radiological pattern of pleural empyema and the possibilities of ultrasound navigation.
- Congenital bronchopulmonary foregut malformations (CPAMs) and pulmonary sequestration.
- Assessment of pulmonary status: criteria and scoring system for pulmonary function tests.
- Complications of button battery aspiration and timelines for emergency intervention.
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