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)
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.
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.
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.
- Re: Mpfl reconstruction for chronic pain
Discussion with patient regarding options for a maltracking patella.
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.
Relevant material -
Video and paper -
Peer-reviewed paper -
- 2016 - First time patellar dislocation in children – risk factors Authors: Askenberger M et al. - and summarised by Dr Sheila Strover (Clinical Editor)
- 2015 - Current Concepts for Patellar Dislocation Authors: Petri M et al. - and summarised by Dr Sheila Strover (Clinical Editor)