chapter 6: Dysplasias

TROCHLEAR DYSPLASIAS

Hypoplasia of the Medial Condyle

This is frequently associated with hypoplasia of the medial patellar facet. However, dysplasias of both sides of the medial compartment are not always linked. With this particular dysplasia, CT or MRI may be particularly helpful.

This deformity will often appear only in the first 30 degrees of knee flexion, because it is primarily a deformity of the proximal portion of the trochlea. The trochlea progressively deepens as it approaches the intercondylar notch. Therefore, the use of views taken in more than 30 degrees of flexion may result in a true hypoplasia being missed. Hypoplasia primarily affects the width of the medial condyle, but it may affect simply the height. The latter abnormality is more difficult to separate from a rotational malposition. Both types of medial hypoplasia are important in the various forms of patellar instability and chondromalacia.

Aplasia of the Medial Trochlea

This is a rare abnormality in which the proximal trochlea appears on the axial view or tomographic slice as an oblique slope running posteriorly from lateral to medial (Fig. 6.16). The patella usually consists of a single facet.

 

        

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