The KL grading system is the most widely accepted assessment tool for quantifying the degree of knee osteoarthritis found on X-ray. Knowing this grading system is of increasing importance today, as some insurance carriers are requiring documentation of KL grade 2 or higher knee osteoarthritis on X-ray to approve certain treatments such as viscosupplementation injections. Viscosupplementation, or hyaluronic acid injections, are gel-like injections for the knee that provide lubrication and pain relief for patients with knee arthritis.

KL grade 1 changes include no obvious joint space narrowing with small osteophytes present, grade 2 changes include definite osteophytes with possible joint space narrowing, grade 3 changes include multiple osteophytes, moderate joint space narrowing, subchondral sclerosis, and possible bony deformity, and grade 4 changes include large osteophytes, severe joint space narrowing, subchondral sclerosis, and definite bony deformity.

There are several flaws in the KL grading system, however. The KL system relies on the formation of osteophytes occurring before joint space narrowing, although generally the opposite occurs. Also, several studies have examined arthroscopic findings in patients with early articular degeneration compared with KL grade and concluded that the KL system can significantly underestimate the degree of osteoarthritis in the knee.

Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).


  1. Kijowski R, Blankenbaker D, Stanton P, Fine J, De Smet A. Arthroscopic validation of radiographic grading scales of osteoarthritis of the tibiofemoral joint. AJR Am J Roentgenol. 2006;187:794-799.
  2. Pai V, et al. Kellgren and Lawrence system for classification of osteoarthritis of knee. Accessed on August 15, 2017. 

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