Tibial tuberosity to trochlear groove distance (TT-TG distance)

Last revised by Henry Knipe on 20 Oct 2023

The tibial tuberosity to trochlear groove (TT-TG) distance is used to guide the treatment of patellofemoral instability. It can be accurately measured on both CT and MRI although MRI measurements are consistently shorter 6.

TT-TG and TT-PCL have similar reliability and sensitivity/specificity, however, TT-TG has greater diagnostic accuracy 4,5.

Superimpose axial images of:

  • femoral condyles

  • tibial tuberosity

Draw a line along the posterior femoral condyles, and then draw the following lines perpendicular to this line:

  • bisecting the tibial tuberosity (TT)

  • bisecting the trochlear groove sulcus (TG)

  • measure the distance between TT and TG = TT-TG distance

The following measurements are generally accepted:

  • normal: <15 mm

  • borderline: 15-20 mm

  • abnormal: >20 mm

When measuring on MRI, a reduction of 3 mm has been suggested 6.

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