This article deals with some of the concepts related to the progression of osteoarthritis. These statements were given by prominent researchers and resulted in a debate between two prominent groups of researchers against each other. All of these took place actively in the 19th century where the publications of research scholars were opposed to that of the scholars in the other group.

William Bauer told that mechanical trauma can result in OA directly or indirectly. By the 20th century ideologies were majorly split into two ‘inflammation’ and ‘no inflammation’. Henry Fuller and Robert Todd suggested that OA occurred due to disruption to nutrients required for knee development and doesn’t occur through inflammation. On the other hand, Garrod and others stated that OA is partly degenerative and partly inflammative. Hence the study for OA continued under these two domains and each group of scientists trying to prove the other is false. But this situation can be compared to two sides of a coin where both the situations cannot be neglected. Hence both the domains of OA cannot be neglected.

Some others say that OA is a neurogenic immune homeostatic disorder. Garrod in 1988 stated that OA is associated with lesions in CNS in a peculiar manner. CNS refers to the central nervous system which constitutes the brain and spinal cord. The brain is the mastermind of the body which generates electrochemical signals to simulate several neurons in the body. The spinal cord is known as a warehouse of reflexes. Reflex is an involuntary (cannot be controlled by conscience) rapid sequence of actions. Reflex can be best explained by several experiments.

When someone comes to hit you; you will either duck or catch his hand spontaneously and this is known as a reflex and the spinal cord or vertebral column is responsible for this.

The reflex of the knee is tested by the doctor who takes a rubber mallet and taps it on the knee and what interestingly happens is that the knee starts to retract and the patient can feel the pain. In case of OA or any knee-related diseases, the patient cannot experience any pain and hence the doctor understands that there is some abnormality in the knee. Hence we can understand that there is a connection between the knee’s ability and CNS and an interruption in this connection can lead to knee diseases.

We have to understand that this is a basic relation and there are other complex associations between them and require more complex methods like electrophysiology and pharmacology to understand them. Later it was proposed that changes in the sympathetic nervous system can also lead to OA.

The sympathetic nervous system is a part of the autonomic nervous system. This can be correlated to the word ‘increase’. The sympathetic nervous system works in response to stimuli like emotions and increases some parameters of the human body like heart rate, eye dilation, blood sugar, blood pressure, etc. this proposal paved the way for using micro-circuitry to correct it.

There is also another field on which the world is divided into two namely ‘nociceptive’ and ‘neuropathic’ where nociceptive refers to pain resulted due to receptors. These are present at target and send signals to the brain via the spine more or less like the reflex. On the other hand neuropathic refers to the condition where pain occurs due to nerves. The following table shows the difference between these two. 

Receptor-mediated painNerve mediated pain
Doesn’t affect nervesAffects the nerves
Due to painful stimuliDue to inflammation

However, some of the debate topics have not been resolved even till now but a lot of research articles about the progression of the disease and its underlying phenomena have been published. This is one of the cases in which a debate has done some good to the field of science!



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



Osteoarthritis is the most well-known type of joint pain, influencing a huge number of individuals in the world. It occurs as a result of the wearing down of the cartilage that cushions the ends of your bone over time. It is a complex disease that integrates biomechanics and biochemistry associated with the knee. This is the standard way of defining OA which will be difficult to understand. Hence let us try to understand what OA is. The best way is by splitting the word and analyzing it part by part

Osteo- bone

Arth- joint                        

It is- inflammation    

Knee, Old, Care, Injury, Pain, Knee Pain
x-ray of the osteoarthritic knee joint


As mentioned earlier, the unit of bone is called osteon and any word ending with itis refers to inflammation. Also, arthro term refers to joints in general. Hence the combination of the terms corresponds to inflammation of bones in the joint. This rather sounds simplified. The previous definition had complex terms like biomechanics and biochemistry. Biomechanics refers to the study of movement in living beings. Biochemistry refers to the study of the reactions occurring in living things. So in short, osteoarthritis is such a disease that results in inflammation of joints that occur due to wearing down of the bones surrounding the joint hence affecting the movement and chemical reactions which used to occur properly during normal conditions.

Osteoarthritis can occur in any joint in the human body like elbows, hips, knees, etc. Since our primary focus is on the knee, we will take a deep dive into it. In view of its expectancy and the tolerance that goes with sickness in the knee osteoarthritis represents more prevalence with daily activities like climbing steps and walking when compared to other diseases. Osteoarthritis is the most standardized reason for total knee replacement. As a result of the frequency of this disease especially in middle-aged people, osteoarthritis can act as an extensive barrier towards work and can lead to early retirement.

Coining of OA

Many say that the term osteoarthritis was coined by the British physician John Kent Spender but it was Richard Von Volkmann who tried to separate it from rheumatoid arthritis. The other names which were offered to this disease were ‘chronical rheumatism’

‘senile arthritis’

‘hypertrophic arthritis’

‘arthritis deformans’.

Effect of age

Osteoarthritis can affect people of any age group but it majorly affects old age people. National Library of Medicine suggests that people with an age greater than 70 have more risk to get osteoarthritis. The reason lies in the definition of osteoarthritis. The definition says that disease occurs due to the wearing down of bones. So the bones don’t get worn down the next instant a baby is born. Every process requires time to occur. A mother has to wait for a minimum of 9 months to give birth to a healthy baby. A student must wait for 4 years to get a degree from college. Similarly, it takes time for the bones in the knee to get worn down.

This disease has always troubled old aged people in their lives. Living with osteoarthritis is dreadful. Even climbing the stairs will be a difficult task for them. Hence it is worth knowing about the disease.



The knee joint is one of the biggest and most important joints in the lower part of the body. The knee plays an important role in distributing the body weight throughout the body. It is worth studying about this joint.

The knee joint is the tibiofemoral synovial hinge joint. This seems a bit complex. This can be easily understood by splitting each term.

  • Tibio- tibia bone
  • Femoral- femur bone
  • Synovial- freely movable joint
  • Hinge- swinging motion

We can consider the knee joint as a castle with the patellar bone as a castle wall protecting it from the front, the femur from top, tibia and fibula from bottom and muscles aiding these bones. In general, the massive structures protect the joint from mechanical damage like banging the knee onto a hard surface etc…

                      the detailed structure of knee joint.
                   Credit:- OpenStax College Anatomy & Physiology, Connexions Web site., Jun 19, 2013

The above diagram shows the complete parts of the knee joint. There are some terms that were not explained earlier. Bursa can be compared to a tin of oil or any other lubricant and structurally is like a sac containing fluid to reduce friction. Friction is      

A physical quantity develops when two things come in contact and the lubricant is the one that provides a medium between the two objects thus reducing friction.

Here are the anatomical terms and their meaning:-

  • Anterior-front
  • Posterior-back
  • Supra-upper
  • Infra-lower
  • Cruciate-cross shape
  • Pre-before

The fat pad is the one present beneath the knee bone and acts as a cushion for the joint. Ligaments are the primary elements of the knee joint which connect bone to bone.

There are two types of ligaments namely ACL and PCL. They connect the tibia to the femur as mentioned earlier through the term tibiofemoral. ACL is medial (present more close to centre) than PCL and PCL are lateral (present far from the centre).

NOTE:-Understanding these structures are very important as an imbalance in each structure can lead to a disorder.

The knee is the largest known joint in the human body which performs very complex functions. The various functions are:-

  1. It bears the weight load and prevents the lower legs to take in all the weight.
  2. Acts as a supportive agent to the body.
  3. Provides motion but is limited.
  4. Coordination of the movement of upper and lower legs
  5. Fat present in knee acts as thermal insulator
  6. Bursa reduces friction between the bones
  7. Synovial fluid acts as medium for bones to articulate with.

As mentioned earlier motion is a key aspect amongst the functions of the knee. The following table shows the various movements exhibited directly or indirectly using the knee.

Knee movements are of two types- primary and secondary.

FlexionDecreasing the angle
ExtensionIncreasing the angle
Medial rotationRotating towards centre
Lateral rotationRotating away from centre
AdductionMoving towards middle
AbductionMoving away from the middle
Anterio-posterior displacementFront and back movement

Flexion, extension, medial and lateral rotations constitute the primary movements. Adduction, abduction and anterio-posterior displacement constitute secondary movements. Hence all these movements can be offered by the knee. In addition to that knee joint also has sensory receptors and produce proprioreceptic information about the position of knee.

The ligaments contribute more towards the stability of the joint as compared to other elements.  The several structures inside the knee must perform perfectly so that the knee functions properly as a whole. The knee joint is hinge type and hence it is more vulnerable to injury (stretching beyond the limit leads to injury). In case of injury, the damaged cells start to heal when the stress is removed but there is a chance of losing their functions as there is a chance of them getting replaced with scars.

It is absolutely worth knowing about the structure and function of the knee joint and how they help to carry ourselves on.