Blackburne-Peel Ratio

Original Editor - Fitim Cami Top Contributors - Kim Jackson, Lilian Ashraf, Fitim Cami and Daphne Jackson


Patella alta or high riding patella is a risk factor for patellar instability and pain.[1]

Many imaging modalities are used to measure the height of the patella including Blackburne-Peel ratio, Insall-Salvati ratio, the Caton-Deschamps ratio, modified Insall-Salvati ratio and patellotrochlear index. [1]


Blackburne-Peel ratio compares the distance of the articular cartilage surface of the patella to a line drawn from the tibial plateau to the inferior pole of patella. [2]


  • A lateral radiograph of the knee with 30 degrees of flexion is obtained, and a horizontal line at the level of the tibial plateau is drawn.
  • Measurement (B): a perpendicular line is drawn vertically from the horizontal line of the tibial plateau to the inferior aspect of the patellar articular surface.
  • Measurement (A): a line is made along the patella articular surface.
  • A/B is a measure of patella height
     Normal value = ratio of 0.8.
     Patella alta = ratio >1.0 [3]


Seil et al and Berg et al, found Blackburne-Peel ratio to be most reliable on computed radiography.

To fully assess the patellofemoral anatomic morphology using the Blackburne-Peel ratio both conventional radiographs and a scan should be done.[1]


  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. 2020 Mar;28(3):869-75.
  2. Wolfe S, Varacallo M, Kahwaji CI. Patellar Instability.
  3. Syed A. Ali, Robert Helmer and Michael R. Terk; Patella Alta: Lack of Correlation Between Patellotrochlear Cartilage Congruence and Commonly Used Patellar Height Ratios; AJR November 2009 vol. 193 no. 5 1361-1366. (Level of evidence: B)