When we see Patella Dislocation the next thing we need to do is assess for an underlying abnormality that can lead to dislocation.
There are three structural abnormalities that can predispose to Patella Dislocation.
- Lateralisation of the Tibial Tuberosity
- Patella Alta
- Trochlear Dysplasia
Today’s post is on Trochlear dysplasia
- The medial and lateral trochlear facets form a cup in which the patella sits and restrict lateral subluxation of the patella.
- Trochlear Dysplasia is abnormal development of the Lateral Trochlear facet.
- This results in a shallower cup to varying degrees ( see image below).
- The lateral trochlear facet can become relatively flat or even convex.
There are so many measurements for trochlear dysplasia.
If your referring surgeon has a preference for a particular one, thats the one you need to give them.
If there is no preference or the referral is from a non orthopod, use this…
Where you do the measurement varies in different articles.
- 3cm above joint line
- First slice where you see full cartilage cover of lateral facet.
Even a small change in where its measured can make a difference in the angle.
In the image below the angle of the lateral facet changes depending on where you measure.
We use the first slice where you see full cartilage cover of lateral facet as this is where the patella first engages with the trochlear.
Measure the angle between a line along the lateral trochlear facet ( Pink line) and a line drawn parallel to the posterior femoral condyles ( Yellow line).
