Insal-Salvati index is used for

a-length of patellar ligament b-length of patella INSAL-SALVATI index=a/b Normal range is 0.8 -1.2 If ratio increases it suggests patella is at a higher level-PATELLA ALTA If ratio decreases it suggests patella is at a lower level -PATELLA BAHA ref:apley's 9th edition pg no.565