Blackburne-Peel ratio

Last revised by Henry Knipe on 1 Mar 2020

The Blackburne-Peel ratio is an alternative to Insall-Salvati ratio and is used to assess patellar height including patella alta and baja

The Blackburne-Peel ratio has higher interobserver reliability compared to the Insall-Salvati ratio and can also be used when the tibial tuberosity is abnormal (e.g. Osgood-Schlatter disease, osteotomy) as it does not rely on this landmark 3,4.

A lateral radiograph of the knee with 30° of flexion is obtained, and a horizontal line at the level of the tibial plateau is drawn. Perpendicular to this line (i.e. vertically) two measurements are made:

  • A: along the patellar articular surface
  • B: distance between the horizontal line and the inferior aspect of the patellar articular surface

B/A is a measure of patellar height

  • patella baja: <0.5
  • normal: 0.8
  • patella alta: >1.0 

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Cases and figures

  • Figure 1: Blackburne-Peel ratio
    Drag here to reorder.
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