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Now we're gonna discuss extensor mechanism disruption.

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And common causes are things like patella fracture,

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quadriceps tear, and patella tendon tear.

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So here we have our lateral projection,

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and through the patella we see a

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complete transverse lucency.

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And so this represents a minimally displaced

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patella fracture.

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They can also become distracted

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because of the forces of the extensor mechanism

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with quadriceps attaching to the cephalad fragment

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and patella tendon attaching to the inferior fragment.

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So if the sleeve in which the patella exists, that is

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the extensor mechanism becomes disrupted,

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then you can get this distraction.

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So one way to think about the patella bone is

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that it is a sesamoid within the quadriceps tendon

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that then becomes the patella tendon.

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And so as it resides in this sleeve here,

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you can have a fracture

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but not necessarily have a displaced fragment if the soft

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tissue envelope surrounding it is maintained.

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However, if there is also disruption of

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that soft tissue envelope

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or if there's this complete fracture

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and then the extensor mechanism forces are greater than

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that, it can then pull the fragment apart.

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Here we have two companion cases

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of extensor mechanism injuries.

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So in the one case here we have a lower set patella,

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or what's known as a patella baja

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or patella infra prominent soft tissue swelling over the

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quadriceps region of the extensor mechanism.

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And MRI demonstrates a complete disruption of

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that quadriceps tendon allowing for that

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inferior translation of the patellar bone.

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So with quadriceps tendon rupture, the mechanism can be

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eccentric overload to the extensor mechanism,

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typically from foot planted knee.

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Partially flexed position could also be from jumping,

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squatting, or tumbling.

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Traumatic is usually in the younger patient.

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The appearance is that it can tear almost the entire

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quadriceps, but sparing the vast intermedius.

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That is that more central portion may present

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with this patella Baja

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or inferiorly positioned patella

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seeing an undulating patella tendon.

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Uh, now that it's become redundant,

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there are some associations with decreased vascularity such

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as diabetes, inflammatory arthropathy such

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as rheumatoid arthritis and lupus, other chronic steroid use

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or even regional injections, uh, into that area.

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So here on the MRI tendon is normally low signal intensity.

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We see fluid signal filling a gap

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or an interval here with a malpositioned

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Inferiorly migrated patella

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and undulation of the patella tendon.

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Now with patella tendon rupture, we tend to get, uh,

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patella alta, but here it's like a super alta.

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In this case the patella is retracted cephalad,

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there's prominent soft tissue swelling anteriorly,

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there may be some residual bone fragments.

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And on MRI this confirms that a complete disruption,

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although pretty diagnostic on the radiograph

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and the elevation of patella,

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but can also look at concomitant injuries in the cartilage.

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So in this case here, there's a central trochlear defect.

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So here are two other examples

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of patella tendon rupture on CT

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and MRI that are not as dramatic as the previous one.

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This case on ct, we can identify

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that there's pre patellar soft tissue edema.

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The extensor mechanism shows that the quadriceps tendon,

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we can see the fat planes around the quadriceps maintained,

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but the patellar tendon has this undulating configuration.

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And now we've lost

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to peric tendonous fat planes in the region here

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in association with a little bit of patellar malpositioning.

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An example of a tendon rupture on CT on MRI.

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In this other case here we see some pre patella soft tissue

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edema, undulation of the patella tendon,

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and then near the patella inferior pole there is this area

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of discontinuity.

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So again, diagnostic for patella tendon rupture.