What is tibial tubercle Trochlear groove distance?

Using MRI in a recent series of cases, Dr. Sherbondy and Ashley Anderson, MD, Penn State sports medicine orthopaedics fellow, found average TT-TG distances of 12-13 mm in patients with repeated patellar dislocation (n=30), compared to 9-10 mm in normal controls without dislocation (n=38) (Figure).

What is normal TT-TG distance?

Normal range of the TT-TG distance value varies among studies from 9.4 ± 0.6 mm to 13.6 ± 8.8 mm;4,5,6,7,8) and most of these studies were performed in Europeans or North Americans. The conclusion of these studies is that patients with patellar instability have higher TT-TG distances.

What is tibial tubercle Trochlear groove?

Tibial tubercle-trochlear groove (TT-TG) distance is a measurement generally made on CT scans that is commonly used to quantify the risk of patellofemoral instability (PFI); however, its interrater reliability and accuracy as an indicator of PFI in patients is poorly characterized.

What is the Trochlear groove?

The patella rests in a groove on top of the femur called the trochlear groove. When you bend and straighten your knee, the patella moves back and forth inside this groove. A slippery substance called articular cartilage covers the ends of the femur, trochlear groove, and the underside of the patella.

How is tibial tuberosity measured?

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

  1. bisecting the tibial tuberosity (TT)
  2. bisecting the trochlear groove sulcus (TG)
  3. measure the distance between TT and TG = TT-TG distance.

What is patellar instability?

Patellar instability occurs when the kneecap moves outside of this groove. There are two types of patellar instability. The first is known as a traumatic patellar dislocation. This is most often the result of an injury to the knee. In a patellar dislocation, the patella gets pushed completely out of the groove.

How is TT-TG calculated?

Where is the tibial tuberosity?

The tibial tuberosity or tubercle is an elevation of the anterior aspect of the tibia. At full skeletal maturity, it is approximately 3 cm distal to the proximal tibial articulating surface. It serves as an attachment for the patella tendon, acting as a lever to extend the knee joint.

How is TTTG distance calculated?

Patellar translation can be measured using the tibial-tuberosity to trochlear groove distance (TT-TG distance) by calculating the transverse length between the trochlear groove on the femoral and tibial tuberosity on axial images. The measurements are used to quantify patellar instability.

What is the tibial tubercle trochlear groove distance?

Background: The tibial tubercle-trochlear groove (TT-TG) distance is a useful tool in guiding surgical management for patients with recurrent lateral patellar instability. Current recommendations for tibial tubercle transfer are based on TT-TG distance thresholds derived from adult populations.

How is patellar translation of trochlear groove measured?

Patellar translation can be measured using the tibial-tuberosity to trochlear groove distance (TT-TG distance) by calculating the transverse length between the trochlear groove on the femoral and tibial tuberosity on axial images. The measurements are used to quantify patellar instability.

Can a TT-TG be performed on a tibial tubercle?

Dr. Sherbondy adds, “With a high TT-TG distance, it might be helpful to perform a tibial tubercle osteotomy. With other types of pathology, a medial patellofemoral ligament reconstruction (MPFL) may be adequate to address the problem.” Dejour H, Walch G, Nove-Josserand L, Guier C. 1994.

What is the normal patellar TG translation distance?

normal: <15 mm. borderline: 15-20 mm. abnormal: >20 mm. The distance has been shown to be slightly less when measured on MRI than CT 1.