The Kellgren-Lawrence (KL) grading system is a widely accepted method used by healthcare professionals to classify the severity of osteoarthritis (OA) based on findings from X-ray images. It allows doctors to categorize the progression of the condition, aiding in diagnosis and understanding the extent of joint degeneration. The classification was initially developed in 1957 by British rheumatologist Jonas H. Kellgren and epidemiologist John S. Lawrence, and later adopted by the World Health Organization in 1961 as a radiological definition for OA, particularly for epidemiological studies.
How the Grade is Determined
Radiologists and doctors examine specific features on an X-ray to assign a Kellgren-Lawrence grade. These features reflect the changes in the joint as osteoarthritis progresses. One such indicator is the presence of osteophytes, which are bony outgrowths or spurs that form around the joint margins.
Another significant feature is joint space narrowing, which refers to the reduction in the space between the bones in a joint. This narrowing occurs due to the loss and thinning of articular cartilage, the smooth tissue that covers the ends of bones and allows them to glide past each other. As cartilage wears away, the bones move closer together, and this reduction in space is visible on an X-ray.
Subchondral sclerosis is also assessed, appearing as an area of increased bone density or hardening directly beneath the cartilage. This change in bone structure is thought to be a reaction to increased stress on the bone as the protective cartilage layer diminishes. Sometimes, subchondral cysts, which are small, fluid-filled sacs within the bone, can also be observed beneath the joint surface. In more severe instances, the actual shape of the bone ends within the joint may undergo alteration or deformity.
The Kellgren-Lawrence Grades Explained
The Kellgren-Lawrence system categorizes osteoarthritis into five distinct grades, from 0 to 4, each representing increasing severity of radiographic findings.
Grade 0 signifies no radiographic signs of osteoarthritis. This indicates a healthy joint without any visible degenerative changes typically associated with OA.
Grade 1 is classified as “doubtful” osteoarthritis. At this stage, there might be minute osteophyte formation, often described as possible osteophytic lipping, and only doubtful narrowing of the joint space. The changes are subtle and may be difficult to definitively identify as OA.
Grade 2 represents “mild” osteoarthritis, where definite osteophyte formation is visible, and there is possible narrowing of the joint space. This grade is often the point at which a definitive clinical diagnosis of osteoarthritis is made, as the radiographic signs become more apparent.
Grade 3 indicates “moderate” osteoarthritis. At this stage, multiple osteophytes are present, along with definite narrowing of the joint space. Some subchondral sclerosis, or hardening of the bone beneath the cartilage, is also observed, and there might be possible deformity of the bone ends.
Grade 4 denotes “severe” osteoarthritis, representing end-stage disease. X-rays at this grade show large osteophytes, marked narrowing of the joint space, often leading to bone-on-bone contact. There is also severe subchondral sclerosis and definite deformity of the bone ends.
Relationship Between Grade and Patient Symptoms
While the Kellgren-Lawrence grading system provides a standardized measure of structural changes in the joint, it does not always directly correlate with a person’s experience of pain, stiffness, or functional limitation. The KL scale assesses physical alterations visible on X-ray, not pain sensation. Some individuals may present with a high Kellgren-Lawrence grade, such as Grade 3 or 4, showing significant radiographic changes, yet experience minimal or no symptoms. Conversely, other individuals might report considerable pain and functional limitations even with a low KL grade, like Grade 1 or 2, where radiographic evidence of OA is subtle or mild.
This disconnect highlights that pain perception is complex and influenced by many factors. The grade serves as an important diagnostic tool, helping healthcare providers understand the anatomical extent of osteoarthritis. However, treatment and management strategies are primarily guided by the individual patient’s symptoms, their level of pain, and how the condition impacts their daily life and functional abilities. The radiographic grade assists in shaping the overall approach to care, but personalized treatment plans focus on improving the patient’s quality of life rather than solely addressing X-ray findings.