Insall-Salvati ratio - normal patella
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Sagittal images demonstrating how to measure the Insall-Salvati ratio.
A patella baja ( or patella infera) is an abnormally low lying patella, which is associated with restricted range of motion, crepitations and retropatellar pain.
The traditional number used to TL:PL is < 1.2 (between 0.8 and 1.2), although more recent literature 2 suggests that the true range of normal is more forgiving - up to 0.74 to 1.50.
Patellar length (PL) is the greatest pole - pole lenghth
Patellar tendon length (TL) is defined as the length of the post surface of the tendon from the lower pole of patella to its insertion on the tibia.