Modified Insall-Salvati ratio
Citation, DOI & article data
The modified Insall-Salvati ratio or index is another technique to assess patellar height.
It was proposed to avoid mismeasurement due to the variable shape of the inferior patella pole 2, however, the Insall-Salvati ratio has been demonstrated to be more reproducible 3.
The modified Insall-Salvati ratio is applied on a lateral 30° flexed knee radiograph like the Insall-Salvati ratio but is measured differently:
- A: distance from the inferior margin of the patellar articular surface (as opposed to the lower pole of the patella itself) to the patellar tendon insertion
- B: length of the patellar articular surface
Modified Insall-Salvati ratio = A/B
- normal: 1.25 (range 1.2-2.1) 2
patella alta: >2
- at this cut-off, 3% of normal knees will be classified as patella alta 3
- 1. Grelsamer RP, Meadows S. The modified Insall-Salvati ratio for assessment of patellar height. Clin. Orthop. Relat. Res. 1992; (282): 170-6. Pubmed citation
- 2. W. Norman Scott. Insall & Scott Surgery of the Knee E-Book. (2011) ISBN: 9781455727896
- 3. Mark D. Miller, Stephen R. Thompson. DeLee and Drez's Orthopaedic Sports Medicine E-Book. (2009) ISBN: 9781437721713