Fractures of the lateral tibial condyle
Computed tomography (CT) plays a crucial role in surgical planning and diagnosis of lateral condyle fractures. The method allows for accurate visualization of the number of bone fragments and measurement of the degree of depression (downward displacement of fragments).
- Surgical criterion: the key indicator for surgery is articular surface depression of more than 10 mm. It is measured vertically from the lowest point of the intact medial condyle to the deepest displaced fragment of the lateral condyle.
- Radiological signs of occult injuries: in subtle injuries, three signs should be sought:
- Blurring or loss of definition of the cortical margin of the lateral condyle.
- Areas of subchondral sclerosis beneath the condyle resulting from impaction of subcortical trabeculae.
- Lateral displacement of the bone margin. Normally, an imaginary vertical line transitions smoothly from the outer margin of the femoral condyle to the margin of the tibial plateau. In a displaced fracture, this contour is interrupted.
Small bone fragments and avulsion injuries
The detection of small bone shadows around the knee should not be dismissed as benign bone chips. As a rule, these are avulsion fractures caused by massive force at the attachment sites of ligaments and tendons.
- Anterior cruciate ligament (ACL) avulsion: most typical in adolescents, in whom the ligament is stronger than its bony attachment site. On the anteroposterior radiograph, the intercondylar eminence fragment (anterior tibial eminence) is seen in the center of the joint space, and on the lateral view, in the anterior half of the joint. To assess displacement, the Meyers and McKeever classification is used (from Type I with minimal displacement to Types III and IV with rotation and comminution).
- Segond fracture (Segond fracture): a small bone fragment at the superolateral margin of the tibia, often overlapping the fibular head. It occurs via a varus mechanism due to tension of the lateral capsular ligament. This is a 100% indicator of severe trauma—an ACL and medial meniscus tear.
- Fibular head avulsion: the so-called arcuate sign (arcuate sign). It indicates a catastrophic injury to the posterolateral corner structures (fibular collateral ligament, arcuate ligament, and biceps femoris tendon). Missing this injury guarantees the patient chronic instability.
Patellar injuries: fractures and dislocations
Patellar fractures are most commonly the result of direct impact or a sudden contraction of the quadriceps femoris muscle. Their visualization depends on the orientation of the fracture plane.
- Transverse fractures: account for up to 60% of cases and are clearly visible on the lateral projection.
- Vertical (15%) and comminuted fractures: difficult to distinguish on a standard anteroposterior view due to superposition of the femoral shadow. When clinically suspected, an axial projection (skyline view) with a flexed knee is mandatory.
- Bipartite patella (bipartite patella): a normal variant that is easily mistaken for a fracture. Unlike an injury, the anomalous fragment has sclerotic (dense) margins, exceeds the size of the defect in the main bone, and is always localized in the superolateral quadrant.
- Patellar dislocation: often reduces spontaneously before radiography. Signs of a previous dislocation may include an avulsion fragment of the medial patellofemoral ligament or an osteochondral fragment of the lateral femoral condyle. Unlike an ACL avulsion, in a dislocation, the bone fragment is seen far from the center of the joint and frequently in only one projection.
Assessment of adjacent joints: ankle
When examining patients with lower extremity injuries, it is important to remember the biomechanics of adjacent joints. The ankle is viewed as a unified ring of bones and ligaments.
- Stability: an injury is stable only with a single isolated disruption of this ring. The combination of two or more injuries (e.g., of the lateral malleolus and syndesmosis) renders the injury unstable, requiring surgery.
- Ankle mortise projection (mortice view): performed with 10 degrees of internal rotation of the foot. Unlike the standard anteroposterior view, it isolates the fibular shadow from the talus, making it easy to identify widening of the lateral clear space and lateral malleolus fractures.
Rule of the axial projection: if clinical findings strongly suggest a patellar fracture or dislocation, but the anteroposterior radiograph shows no pathology, obtain a view with a flexed knee (skyline view).
Class and exam questions
How to radiographically distinguish an ACL avulsion from a fragment in a patellar dislocation?
In an anterior cruciate ligament avulsion, the bone fragment is located strictly in the center of the joint space on both projections. In a patellar dislocation, the fragment is displaced peripherally and is often visualized in only one plane.
What is the main danger of an avulsion fracture of the fibular head?
This fracture indicates destruction of the posterolateral corner ligaments and is associated with a cruciate ligament tear in 90% of cases. Without timely surgery, the patient will develop chronic posterolateral knee instability.
How not to confuse a patellar fracture with a bipartite patella?
The fragment of a bipartite patella is always located in the superolateral quadrant, has clear sclerotic margins, and its size is typically larger than the visualized defect in the main bone.
What else to study on this topic
- Meyers and McKeever classification of intercondylar eminence fractures
- Anatomy and imaging of the posterolateral corner of the knee joint
- Biomechanics of the ankle joint: the bone ring concept
- Technique for performing axial projections of the patella (skyline, sunrise views)
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