TTTG stands for Tibial Tuberosity-Trochlear Groove distance, a measurement used to assess the alignment of the knee joint and evaluate the risk of patellar (kneecap) instability.
Understanding TTTG
The TTTG distance measures the lateral (outward) displacement of the tibial tuberosity (the bony bump on the front of your shinbone where the patellar tendon attaches) relative to the trochlear groove (the groove on the thighbone where the kneecap sits). A higher TTTG distance indicates that the tibial tuberosity is positioned further laterally than normal, which can lead to increased stress on the patellofemoral joint (the joint between the kneecap and thighbone) and a greater chance of patellar dislocation.
Clinical Significance
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Patellar Instability: TTTG distance is a crucial factor in evaluating patients with recurrent patellar dislocations or subluxations (partial dislocations). An increased TTTG distance is a strong predictor of future instability.
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Surgical Planning: Surgeons use TTTG measurements to plan corrective surgeries for patellar instability. These surgeries aim to realign the patellar tendon by moving the tibial tuberosity medially (inward), thereby reducing the lateral pull on the kneecap.
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Diagnosis: It helps in diagnosing malalignment syndromes of the knee.
Measurement Techniques
TTTG distance is typically measured using:
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Computed Tomography (CT) scans: This is the gold standard for accurate TTTG measurement. CT scans provide detailed cross-sectional images of the knee joint, allowing precise measurement of the distance between the tibial tuberosity and the trochlear groove.
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Magnetic Resonance Imaging (MRI): MRI can also be used, although it may be slightly less accurate than CT for bony landmarks. However, MRI offers the advantage of visualizing soft tissues, such as ligaments and cartilage, which can provide additional information about knee joint stability.
Normal Values
The normal TTTG distance is generally considered to be less than 20mm. A TTTG distance greater than 20mm is often associated with patellar instability. However, normal values can vary slightly depending on the measurement technique and the specific population being studied. Some studies use 15 mm as the upper limit of normal. The exact threshold used depends on several factors and should be interpreted by a medical professional.
TTTG in Surgical Correction
If a high TTTG distance is identified as a contributing factor to patellar instability, a surgical procedure called a tibial tubercle osteotomy (TTO) may be performed. This procedure involves cutting the tibial tuberosity and moving it medially to reduce the TTTG distance and improve patellar tracking. The TTTG measurement is used to determine the amount of medialization needed to achieve optimal alignment.
In summary, the Tibial Tuberosity-Trochlear Groove (TTTG) distance is a valuable measurement in assessing patellar instability and guiding surgical planning.
