From the Research
The Insall-Salvati ratio is the most reliable method for measuring patellar height, with a normal ratio ranging from 0.8 to 1.2, and it should be calculated by dividing the length of the patellar tendon by the greatest diagonal length of the patella itself, as supported by the most recent study 1. The Insall-Salvati ratio is a crucial measurement in assessing patellar height on lateral knee radiographs.
- The normal ratio is approximately 1.0, with a range of 0.8 to 1.2 considered normal.
- To calculate it, divide the length of the patellar tendon (measured from the lower pole of the patella to its insertion on the tibial tuberosity) by the greatest diagonal length of the patella itself.
- A ratio greater than 1.2 indicates patella alta (high-riding patella), while a ratio less than 0.8 suggests patella baja (low-riding patella). This measurement is clinically important because abnormal patellar height can contribute to various knee pathologies, including patellar instability, chondromalacia patella, and patellofemoral pain syndrome. When evaluating knee pain or instability, the Insall-Salvati ratio provides objective data to help determine if patellar height is contributing to the patient's symptoms. The measurement should be taken with the knee in slight flexion (30 degrees) for the most accurate assessment, as full extension or excessive flexion can alter the apparent patellar position, as noted in studies 2, 3, 4, 5. Recent advancements in artificial intelligence have enabled fully automated measurement of the Insall-Salvati ratio, which can enhance the accuracy and efficiency of diagnosing patellar height abnormalities 1.