The Insall-Salvati Ratio is the ratio of the length of the patellar tendon to the length of the patella, when measured on an X-ray or MRI with the knees bent to 30 degrees.
The normal ratio is 0.75 - 1.50. Higher ratios suggest that the patella is abnormally high.
A brief overview.
The kneecap or patella is part of a chain of structures.