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 January 2024 by Dr Sheila Strover (Clinical Editor)

TT-TG distance

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

TT-TG distance

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


Why is the TT-TG measurement important?

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

Back to top


How to measure 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.

Back to top


What is the normal TT-TG Distance?

It 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.

Back to top


Back to top


Forum discussions

Back to top


Peer-reviewed papers

  • Tibial Tubercle-Trochlear Groove Distance Is a Reliable and Accurate Indicator of Patellofemoral Instability

    Citation: Vairo GL, Moya-Angeler J, Siorta MA, Anderson AH, Sherbondy PS. Tibial Tubercle-Trochlear Groove Distance Is a Reliable and Accurate Indicator of Patellofemoral Instability. Clin Orthop Relat Res. 2019 Jun;477(6):1450-1458. doi: 10.1097/CORR.0000000000000711. PMID: 31094842; PMCID: PMC6554121.


    " Authors "found a TT-TG distance of 13 mm to be the best cutoff value to use for PFI diagnosis"...and "...accuracy of the MRI-based TT-TG distance as an indicator of PFI risk to be less than that reported for CT scan"

Back to top


Tibial tubercle - trochlear groove distance

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.