TT-TG distance is a measurement, derived from CT or MRI scans, which gives an indication of the sideways alignment of the groove in which the kneecap slides compared to the attachment point of its tendon on the tibia.

Page updated March 2024 by Dr Sheila Strover (Clinical Editor)

TT-TG distance

TG = trochlear groove, and for the measurement it is identified via the scans at its deepest point. TT = tibial tubercle, where the patellar tendon attaches.

 

How to measure TT-TG distance

Two imaging 'slices' from different levels (one at the TG level and the other at the TT level) are overlaid within the computer software to measure this distance.

 

TT-TG distance

The TT-TG distance is the distance measured from side to side, as if you dropped a 'plumb line' down from the deepest part of the groove.

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What is the normal TT-TG Distance?

The TT-TG distance is normally about 9mm, and if it´s more than 15-20mm then that means that the alignment of the groove with the tendon attachment is poor, tending to pull the kneecap over to the outer side.

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Why is the TT-TG measurement important?

Increased TT-TG distance is often noted in patients with patellofemoral pain syndrome.

The finding implies that the poor alignment of the the tendon to the groove is stressing the patella. Calculation of the TT-TG distance is a normal part of the evaluation of a person with a painful or unstable kneecap.

 

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Forum discussions

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Synonyms: 
Tibial tubercle - trochlear groove distance
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Dr Sheila Strover (Editor)
BSc (Hons), MB BCh, MBA

See biography...


Relevant material -


Video and paper -

Dr Lars Blønd2017 - The J-Sign - by Dr Lars Blønd (Knee Surgeon)

2017 - TT-TG distance - by Dr Lars Blønd (Knee Surgeon)


 

Peer-reviewed paper -


 

eBook on patellar instability

eBook - Factors contributing to an Unstable Patella

Authored by Dr Lars Blønd (Knee Surgeon). Free to download.