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Dysplasia

Dysplasia means 'abnormal formation' so that a body part is abnormal in shape as a consequence. In the knee world it most commonly refers to the groove in which the kneecap rides ('trochlear dysplasia') but may be used in relation to other structures.

Trochlear dysplasia

The trochlea is said to be dysplastic when it has lost itscongruence with the patella, ie the patella no longer snugs comfortably into the trochlear groove. The trochlea may be flattened or even convex instead of concave.

Patellar dysplasia

The patella may not develop at all (aplasia), or be very small (hypoplasia) overly large (hyperplasia). The patella may also form in two (bipartite) or more fragments, and look on X-ray like a fracture.

There are several syndromes associated with small patellae, where there are other concurrent abnormalities, eg of the genitals, kidneys, nails.