Relationships Between the Joints of the Knee
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Knee anatomy.
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Basic MRI.
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Let's talk about the skeleton.
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We've got the patella, which has extreme variability.
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The perfect patella fits very nicely into the femur or trochlea.
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It's got a lateral facet covered by cartilage.
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It's got an apex and it's got a slightly undulated medial facet.
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The medial and lateral facet are almost the same size.
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The medial facet may be a little bit shorter in this direction than the lateral
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facet, and that's okay, but it shouldn't be terribly shorter.
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In other words, it shouldn't look like this.
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That's a variation known as the Wiberg three
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variation of patella and is a risk factor for this location.
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More on that when we talk about the patella.
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Then we've got an area of the patella that is uncovered.
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In other words, there's no cartilage covering it.
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That's the odd patellar facet.
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In front of the patella is the prepatellar plate.
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It is critical that you analyze not only
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the size of the patella, too small, pebble patella, too big, patella magna,
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the size of the facets. But more importantly, the shape and relationship
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of this structure and its conformity to the trochlea of the femur.
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In other words, how do these fit together?
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Do they fit together like a jigsaw puzzle?
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Is this deep enough or is it too shallow?
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Is this too big for the structure that's meant to hold it?
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So one of your jobs is to analyze
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the relationships between bones, not just the bone itself.
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Let's look at another area where relationships really matter.
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In fact, relationships matter in everything.
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But here's our femur and our tibia.
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The femorotibial conformity, an alignment.
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In other words, does the femoral condyle sit properly along the vertical axis
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of the tibia or is it drifting over as occurs in osteoarthritis?
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Does the curvature of the femoral condyle fit in the concavity of the tibia?
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Does it accommodate it or is it flattened?
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Sometimes you'll even see dysplasias of the femur.
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One example would be discoid meniscus where the femoral condyle is flattened
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and sometimes the fibular head is overgrown or hypertrophy,
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as part of the anomaly.
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You should be looking at the tibial notch,
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whether it's too big or too small,
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for notch dysplasia can be a cause of ACL deficiency and or insufficiency.
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And then back to the fibular head again.
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Not too many abnormalities or anomalies of the fibular head.
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But we said that the fibular head can be big in patients with discoid meniscus.
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There's also an accessory bone, which this patient does not have, called the fabella.
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It is located in a tendinous structure and it will get its own vignette.
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It is located posteriorly. Conformity, the relationship of one bone to another.
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Bone-size dysplasias,
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such as that occurring in the patella or the femoral notch of the knee. These are all
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relevant in assessing the basic skeletal anatomy of the knee.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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