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Defining radiographic incidence and progression of knee osteoarthritis: suggested modifications of the Kellgren and Lawrence scale
  1. David T Felson1,
  2. Jingbo Niu1,
  3. Ali Guermazi1,
  4. Burton Sack1,
  5. Piran Aliabadi2
  1. 1Clinical Epidemiology Research and Training Unit and the Department of Radiology, Boston University School of Medicine, Boston, Massachusetts, USA
  2. 2Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts, USA
  1. Correspondence to David T Felson, Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, 715 Albany Street, A203, Boston, MA 02118, USA; dfelson{at}

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In the 1950s, Kellgren and Lawrence carried out the first large-scale epidemiological studies of osteoarthritis. Obtaining x-rays on multiple subjects from the populations of various communities in England, they defined a grading scale for osteoarthritis that is still widely used and called by their names, the Kellgren and Lawrence (K&L) scale.1 This osteophyte-based scale is used in most large and small-scale clinical and epidemiological studies to define whether osteoarthritis is present or absent on the radiograph.

Unfortunately, neither Kellgren and Lawrence nor subsequent users of their scale were consistent in how they described each of their grades. Importantly, for grade 2, which usually defines whether osteoarthritis is present, it has been labelled as ‘definite osteophyte’ to ‘definite osteophyte with possible narrowing of the joint space’. As noted by Schiphof and colleagues,2 3 as investigators have come up with various descriptions of K&L grade 2, each of these studies may have identified a somewhat different group of persons with radiographic knee osteoarthritis.

With the emergence of large longitudinal studies of osteoarthritis have come questions about how to define new-onset disease and progressive disease, questions that the K&L scale was never designed to address. Even so, many studies, especially large epidemiological investigations, have used the K&L scale to identify knees with new-onset disease or progressive disease. In the Framingham and Rotterdam Studies,4 5 for example, investigators have defined new-onset disease as the emergence of K&L grade 2 disease in knees that had previously been graded as either K&L grades 0 or 1. Rotterdam Study investigators have alternatively used as disease incidence the new onset of K&L grade 1 in knees previously graded as grade 0.5 Progression of extant disease has also been characterised using K&L grades with progression by one grade or more often listed as one criterion …

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  • Funding This study was supported by NIH AR47785 and by NIH AR 51568.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.