Patellar Instability - What and How to Measure

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In this video, I give some insights into patellar instability measurements. I do not cover the basics on how to measure the indexes and cut-off values, as there is plenty of information in the internet. I cover patella alta, trochlear dysplasia and TTTG TT-TG tibial tuberosity trochlear groove distance and give some points to consider when performing these measurements.
One of my Patreons, Matas, suggested the topic of this video. Thanks for that. If you want to suggest video topics, consider becoming a Patreon yourself! ( / agten )
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References:
www.thieme-con... (Imaging of Individual Anatomical Risk Factors for
Patellar Instability by Tobias J. Dietrich, MD et al.)

[@markusschmid6315]

Great video:-)!When you measure the depth of the trochlear groove, do you measure to the bone or the cartilage?

[@DrChristophAgten]

In the original paper by Pfirrmann they measured the bony contours, but different from what I have shown in the video. They measured hight of the lateral and medial facets together, divided by and then subtracted the height of the trochlear groove. This was done 3 cm above joint line Why 3 cm? You have to m measure somewhere 😂. The depth is different when measuring cartilage or bone. Cartilage in the centre of the trochlea is thicker and aggravates any dysplasias as shown here online.boneandjoint.org.uk/doi/full/10.1302/0301-620X.88B5.16866 So it is not really evidence based to measure to the cartilage, but probably clinically more relevant. But I use it only if not sure from eyeballing. 3 cm above joint is random anyways as it does not take patient size into consideration. So take it with a little bit of salt 😂🙈

[@DrChristophAgten]

radsource.us/trochlear-dysplasia/ Very good discussion about measurements, so the way I measure is the Charlie method.

[@prashantrdgmc]

Thanks a ton doctor! Which is the most accepted and sensitive & specific measurement to determine PFI?

[@DrChristophAgten]

can't tell you, really, I guess there are also regional differences and different "schools" etc

[@DrrGCH]

Caton-Deschamps for patella alta for ortho surgeons

[@samikshyasingh2385]

My both the knees suffering from Severe trochlear dysplasia with shallow trochlear groove. Dr. Suggesting for surgery. Is it necessary to go for surgery?

[@dr.halaalzayat1651]

Excellent as usual Dr Agten You make difficult topics easy Thank you

[@svenrachor3018]

Hallo Christoph, vielen Dank für die tollen Videos! Ich halte die ganzen Indices wie Insall-Salvati und ähnliche für faktisch wertlos, da sie keine Rückschlüsse darüber zulassen, wie groß die artikulierende femoropatellare Kontaktfläche bei Kniestreckung ist. Man könnte diese jedoch mühelos im sagittalen Bild ausmessen. Je kleiner die Kontaktfläche, desto geringer die Führung (wobei bei gestrecktem Knie die Stabilisierung ja hauptsächlich über den medialen Kapsel-Band-Apparat funktioniert). Letztlich hilft es oft mit den Zuweisern zu sprechen und heraus zu finden welche Ausmessungen gewünscht sind.

[@DrChristophAgten]

Hi Sven. Genau, man kann viel messen wenn der Tag lang ist. Oft halt damit man in Studien irgendwas messen und "Statistik" machen kann

[@dagourdis]

great video! cheers from mexico!

[@Deepikaaniket]

what is the Dicom viewer software you are using sir?

[@DrChristophAgten]

Different ones

[@mohammedarifhossain3293]

which software you are using here????

[@Sheikisspear]

Increase in cut off value means ? Like if thenormal ratio for IS is 1.2. We should add 0.09 to 0.13 to that ratio if done through mri?

[@JSieberer77]

Just FYI, the knee in the CT scan for TT-TG is not 100% aligned, causing measurement error (0.8 mm per degree(Yao et al. ?2014?)) so you are likely about 4-5 mm off, hard to say without a coronal slice.

[@JSieberer77]

Long knee-axis to scanner axis

[@dilipmundhada5875]

I think by mistake initially you said if it is below 3 cm. And it should be 3 mm for shallow groove at 6.32 minutes in video

[@geniussaiyan3608]

Thanks bros😊😊

[@SharonKirchberg]

I have Gemodificeerde Insal Salvati ratio: 1.8 what does this mean i have a lot of pain

[@РульныйДядька]

Thank you

[@陈俊-m4p]

which software do you use? how to overlap two CT images together?

[@DrChristophAgten]

Do you mean for recording?

[@陈俊-m4p]

@@DrChristophAgten about how to put two CT images in one image

[@DrChristophAgten]

What do you mean?

[@mnoufalmcmc47]

in most viewers, you can copy or cut the line (graphics) from one slice and paste it wherever you want.

[@tugrulokur8108]

which program do you use to measure @@DrChristophAgten

[@juonasre]

Is there any recommendation regarding the ideal degree of knee flexion for measuring the TTTG distance? Since the distance changes in an inversely proportional manner to the degree of knee flexion, this can potentially lead to clinically significant variations in measurement.

[@zainullah1367]

U don’t know anything