Osteoarthritis can be mainly classified into two. They are primary and secondary. The criterion for this classification is based on the different types of risk factors. Primary OA is mainly due to age where the reason for cartilage breakdown is not known or maybe due to genetics. Secondary OA is due to direct injury through sports or trauma, stress, inflammation, or other metabolic diseases. In this case, the cause may localize.

OA grading

Grading is the process of classifying the disease based on its extent or severity. OA has been graded into 5 from grade 0 to grade 4

Stage numberCondition

This was proposed by Kellgren and Lawrence and it is known as KL grading. The five grades have been proposed based on radiographic analysis of subjects. This was accepted as a standard measure by WHO in 1961. The grading has been done based on the narrowing of joint space and the formation of osteophytes.

  • grade 0 (normal): no changes in knee x-ray
  • grade 1 (minor): minimalistic joint space narrowing with possible osteophyte lipping
  • grade 2 (mild): definite osteophytes and  joint space narrowing
  • grade 3 (moderate): multiple osteophytes, definite narrowing of joint space and some sclerosis and possible deformity of bone ends
  • grade 4 (severe): large osteophytes, marked narrowing of joint space, severe sclerosis and definite deformity of bone ends

Grade 0

Grade 0 is considered normal. The subject will not exhibit any features for OA. The x-ray image from this grade is taken as a standard and the other grades are compared with this grade.

Credit:- Häggström, M (2014). “Medical gallery of Mikael Häggström 2014“. WikiJournal of Medicine 1 (2). doi:10.15347/wjm/2014.008. ISSN 2002-4436. Creative Commons CC0 1.0 Universal Public Domain Dedication
X-ray of a healthy knee 
Credit:- Häggström, M (2014). “Medical gallery of Mikael Häggström 2014“. WikiJournal of Medicine 1 (2). doi:10.15347/wjm/2014.008. ISSN 2002-4436. Creative Commons CC0 1.0 Universal Public Domain Dedication
This is the joint space which is observed in healthy patients.

Grade 1

Grade 1 is known as the minor. It can be considered as the initial grade. The joint space has just started to decrease. Osteophyte refers to excess bone growth. It is also known as bone spurs since spur refers to kind to sharp material. This bone growth can be observed as sharp spikes. Here there is very minimal growth of excess bone. Bone spurs occur only at the bones adjacent to the joint. There will be very minor loss of cartilage but this does not contribute to the narrowing of the joint space. Subject in this stage is not confirmed with osteoarthritis. However, subjects having any of the risk factors become more prone to the disease

Grade 2

Grade 2 is known as mild. In this grade, the narrowing of the joint space is more and is visible through the x-ray. There will be also more formation of osteophytes. This grade can be considered as the precursor to many complications like bone dislocation and rubbing. None of these complications are seen in this grade but these complications are soon to occur. The subject in this grade is confirmed with osteoarthritis. Special care has to be taken by those in this grade and through proper medications, they can prevent those further complications.

Grade 3

Grade 3 is known as moderate. Obvious damage occurs to the cartilage and the joint space narrows even at a faster rate. Swelling of the joints starts to occur in this stage. Erosion of cartilage becomes prominent in this stage. The joints become rougher due to spurs leading to stiffness. Inflammation occurs at regular intervals. Subjects can experience popping sounds from the knee.

Grade 4

Grade 4 is known as severe. It is the worst and highest grade of all. The changes become prominent and occur at larger scales. There will be no gap literally meaning the joint is absent. The bones start to rub over each other causing pain. The joint becomes stiff like a rock. The cartilage wears down and maximum growth of osteophyte is seen. Various cytokines are released at cartilage resulting in further death. Life would be dreadful for those in this grade. The arrow in the given X-ray indicates the bones are touching each other and there is no gap in between them.

Grade 4 osteoarthritis
Courtesy: – James Heilman, MD Osteoarthritis of the left knee. Note the osteophytes, narrowing of
 the joint space (arrow), and increased subchondral bone density (arrow). the joint space (arrow), and increased subchondral bone density (arrow). Creative Commons Attribution-Share Alike 3.0