What is an abnormal TT-TG distance?
Tibial tubercle–trochlear groove distance There is a degree of variability in the literature about what is considered an abnormally high TT-TG. TT-TG distance of more than 20 mm is believed to be nearly always associated with patellar instability [27].
How do you measure TTTG?
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.
What is Trochlear dysplasia knee?
This condition is called trochlear dysplasia. When an individual has a flat or dome-shaped trochlea, the patella loses stability and can track to the outside of the knee as the knee bends. Individuals with trochlear dysplasia are much more likely to dislocate the patella compared to individuals with a normal trochlea.
What is Mpfl knee?
The medial patellofemoral ligament is a part of the complex network of soft tissues that stabilize the knee. The MPFL attaches the inside part of the patella (kneecap) to the long bone of the thigh, also called the femur.
What is TTTG in knee?
The TT-TG distance represents the radiographic measurement of the quadriceps vector, which represents a lateral force displacement on the patella during knee motion. It is > 20 mm in patients with recurrent patellar dislocations, as compared with 13 mm in control subjects.
Is patella an index?
The Insall-Salvati ratio or index is the ratio of the patella tendon length to the length of the patella and is used to determine patellar height.
What is the normal distance between TT and TG?
Method. bisecting the trochlear groove sulcus (TG) measure the distance between TT and TG = TT-TG distance A distance of <15 mm is considered normal, 15-20 mm is considered borderline and a distance >20 mm is considered abnormal. The distance has been shown to be slightly less when measured on MRI than CT 1.
Is there a normal TT-TG value for children?
Recurrent patellar instability, however, frequently affects children, but normal and pathological TT-TG values have not been established for pediatric patients.
How is patellar translation ( TT-TG ) distance calculated?
Patellar translation (TT-TG distance) is an analysis performed by overlapping or superimposing axial images of the femoral condyles and tibial tuberosity. The measurements are used to quantify patellar instability.
How big is the TT-TG on a CT scan?
These TT-TG distances are smaller than previously described using CT scan. In one early study using CT scans, Dejour, et al., 1 found that average TT-TG distance in repeated dislocators was greater than or equal to 20 mm, compared with 12-13 mm in controls.
