Insall-Salvati Ratio

Introduction[edit | edit source]

Insall–Salvati (IS) ratio is used in measuring the patellar height to detect patellar height abnormalities such as patella alta and patella baja. It is the ratio of the length of the patellar tendon to the maximum length of patella.[1][2]

Insall-Salvati ratio. A:Patellar tendon length . B: Maximum length of the patella

Method[edit | edit source]

IS ratio done by measuring the patellar tendon length (from the inferior pole of the patella to tibial tuberosity) to maximum length of patella (the distance between the superior and inferior poles of the patella) ratio.[1]

IS ratio is measured with the knee flexed 30 degrees, to provide the right tension on the patellar tendon for right measurement.[3] It is commonly measured by knee X-ray, Lateral view or MRI, sagittal plane.The normal range is between 0.8 and 1.2, with patella baja <0.8 and patella alta >1.2.[2]

The modified IS ratio was proposed to decrease the measurement errors in IS ratio resulting from measuring unusual patellar shapes,[4] but a study by Fleur V. Verhulst et al, concluded that Insall–Salvati ratio has better intra- and inter-observer reliability than the modified Insall–Salvati ratio. It is the ratio between the patellar tendon length (from the inferior pole of the patella to the tibial tuberosity) and the articular surface length of the patella.[1]

A value of modified IS of 2 is indicative of patella alta.[4]

Clinical significance[edit | edit source]

Anterior knee pain is from the most common problems presenting in the Orthopedic clinic which can be attributed to patella alta or patella baja.[5]

Patella alta or high riding patella leads to increased patellar instability due decreased contact between the patella and the trochlea in knee extension and the first degrees of knee flexion.[6] Patella alta is associated with recurrent patellar subluxation, PFPS, chondromalacia patella, Osgood–Schlatter’s Disease, Sinding-Larsen-Johansson Disease and patellar tendonitis.

Patella baja or low riding patella can be a sign of quadriceps tendon rupture, neuromusucalr disorder or achondroplasia.[5]

References[edit | edit source]

  1. 1.0 1.1 1.2 Verhulst FV, van Sambeeck JD, Olthuis GS, van der Ree J, Koëter S. Patellar height measurements: Insall–Salvati ratio is most reliable method. Knee Surgery, Sports Traumatology, Arthroscopy. 2019 May 14:1-7.
  2. 2.0 2.1 Giovagnorio F, Olive M, Casinelli A, Maggini E, Presicci C, Tominaj C, Ricci P. Comparative US-MRI evaluation of the Insall–Salvati index. La radiologia medica. 2017 Oct 1;122(10):761-5.
  3. Anagnostakos K, Lorbach O, Reiter S, Kohn D. Comparison of five patellar height measurement methods in 90 knee flexion. International orthopaedics. 2011 Dec 1;35(12):1791-7.
  4. 4.0 4.1 Grelsamer RP, Meadows S. The modified Insall-Salvati ratio for assessment of patellar height. Clinical orthopaedics and related research. 1992 Sep(282):170-6.
  5. 5.0 5.1 Althani S, Shahi A, Tan TL, Al-Belooshi A. Position of the Patella among Emirati Adult Knees. Is Insall-Salvati Ratio Applicable to Middle-Easterners?. Archives of Bone and Joint Surgery. 2016 Apr;4(2):137.
  6. Biedert RM, Tscholl PM. Patella alta: a comprehensive review of current knowledge. Am J Orthop. 2017 Nov;46(06):290-300.