and Claudio Chillemi2
(1)
Sapienza University of Rome, Latina, Italy
(2)
Latina, Italy
Tibial Tubercle Avulsions
In teenager, especially during jumping sports, it is frequent to see tibial tubercle fractures.
The OSs is one of the predisposing conditions, but with the absence of previous symptoms, it is not indicative for diagnosis. Radiographs are helpful for the diagnosis and correct staging according to the Ogden classification of tibial tubercle fractures.
Tibial Plateau Fractures
Tibial plateau fractures, also known as bumper fractures, are caused by axial loading, lateral, or twisting injuries. These fractures are associated with soft tissue involvement such as ACL on collateral ligament injuries that can compromise the articular stability resulting in posttraumatic osteoarthritis degeneration. The fractures are classified on the basis of condyles involvement and by the presence of articular surface depression. Three classification methods are identified: Schatzker, OTA/AO, and Hold. Schatzker and OTA/AO are the most used. Depression fractures are most common in older patients and split fractures in younger.
Radiography: Radiography exam is sufficiently accurate in the detection of tibial plateau fractures; however, nondepressed fractures can be overlooked. AP projection, cross table lateral, sunrise view, and oblique views are recommended if this fracture is suspected. In case of severe fractures, cross table lateral and AP may be the only choice. In such cases, the presence of lipohemarthrosis can suggest articular surface impairment.
CT: CT scans have a key role in confirming and assessing complex fractures, in particular the relationship between bone fragments and anatomic structures, or assessing the involvement of articular surface with precision. For a clear image, the thickness of the scan needs to be 1 mm or less, allowing MPR reconstruction. It is possible that some fractures will be undetected with the use of only axial reconstruction images; however coronal and sagittal reconstructions may avoid this problem.
MRI: The level of usefulness of MRIs in tibial plateau fracture management is still being studied. MRI is better in visualizing fracture patterns as well as full tissue injuries like meniscal injuries and certain ligament injuries than CT scans except in cases where the fracture was comminuted.
Trochlear Dysplasia
Trochlear dysplasia is defined as the anomalous morphology of the trochlea which is straight proximally with decreased concavity distally. The variant is considered as a developmental anomaly even because it often affects both knees. In some, severe, cases the trochlear surface develops into a convex shape because of prevalent hypoplasia of the medial condyle. This condition leads to loss of patellar tracking on the trochlea during the knee flexion and must be assessed on images.
Figure 1
Trochlear dysplasia: Sagittal T1-weighted image shows medial condyle hypoplasia (arrows) as trochlear type 3 according to Dejour classification
Radiographs and CT
On lateral films, a normal trochlea presents sulcus crossing the anterior surfaces of the condyles also known as “the crossing sign”; instead if there is medial hypoplasia, it is possible to appreciate the “double contour sign” that is an abnormal double line of the anterior surfaces of the condyles. According to Dejour classification, we may consider four morphologic types of trochlear dysplasia: (1)“V” shape of the trochlea but less deep (sulcus angle of more than 150°), (2) flattened trochlea, (3) asymmetric oblique trochlea for medial condyle hypoplasia (Fig. 1), and (4) asymmetric oblique trochlea with vertical link between medial and lateral condyles (cliff pattern).
MRI: Axial and sagittal planes may be used for trochlear morphology evaluation suitably when an axial radiogram is not available. In particular, some trochlear measures may be performed on MRI, and its variation may be assessed also during quadriceps contraction, with GRE images at suitable signal to time ratio, and the knee is 20° flexed.
Lateral trochlear inclination: For this measure the axial image with most salient trochlea is selected, and two lines are drawn on the subchondral bone of the trochlea lateral facet and behind the femoral condyles; the angle formed must be an inclination of more than 11°.
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