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Patellar instability-CT

Patellar Instability (TT - TG measurement)  Case Submitted by Dr Ayush Goel

Risk factors for patellar instability :
1. Trochlear dysplasia, 
2. High positioning of the patella (aka patella alta)
3. Lateralization of the tibial tuberosity (measured as distance between the tibial tubercle and the trochlear groove or the TT-TG distance )

Normal TT-TG is less than 15mm
Borderline 15 - 20
Abnormal > 20mm

The images show measurement of TT-TG distance.

Method : A tangential is drawn joining the posterior margins of femoral condyles. A line is drawn passing through the deepest point in trochlear groove (femoral sulcus), which is perpendicular to the tangential drawn initially.
Now either we can use superimposition or simple scrolling down to reach the tibial tuberosity. Another line is drawn perpendicular to the tangential drawn initially, this 3rd line should pass through the mid point of tibial tuberosity.

Patellar instability-CT Reviewed by Sumer Sethi on Monday, May 20, 2013 Rating: 5

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