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What is arthritis?

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Before I start my article on Arthritis, I would like to give you a brief idea on the Musculoskeletal system of our body which is responsible for-

1] Mobility i.e. the ability to move our body;

2] Protection to inner organs of the body.

The musculoskeletal system can be likened to that of frame of a building for eg. the columns and the pillars which support the walls, the doors, and the windows of a room.

Similarly, the bones, the ligaments, muscle, etc., form a sort of protective structure which shields the internal organs such as the lungs and heart[the rib cage], the liver, kidney bladder, etc.,[ the abdomen and pelvis], the brain, eyes, etc.[the skull] and so on and so forth.

Just like the damage which occurs in the structure of a building can weaken and shorten its life, so does the damage of the parts of our skeletal system can lead to crippling, pain and shortening of our life span.

In my 35 years of medical practice, I have come across patients having different forms of joint disease, preferably known as ARTHRITIS.

What is arthritis?

The word arthritis is derived from two words-“arthron”-meaning joint in Greek and “itis”- meaning inflammation. So, arthritis simply means inflammation of joints.

What is a joint?

There are about 206 bones in our body. These bones are held together by various structures like the muscle, ligaments, tendons, cartilage, etc. to form a joint. So, a joint is two or more bones held together by these structures to allow movement.  Depending on different sites like the hands, legs neck, etc. they are named as wrist, elbow, knee, etc.

The different types of joint in our body are:-

1] Hinge Joints:-

eg. elbow, knee, small joints of  fingers

2] Ball and Socket Joints:-

eg. shoulder and hip joints

3]Pivot Joints:-

eg. spine

4] Cartilaginous Joints:-

eg. Ribs with the central Breast bone[sternum]

5] Fibrous Joints:-

eg. wrist, ankle, skull.

Before we dig into different types of arthritis, we should understand the structure of a normal joint. The picture shown below is a cross-section of a typical joint that explains the different structures involved in the making of a normal joint.

Different parts of a normal human joint

The table given below shows the function of the major joint parts shown in the picture above:-

Serial No.


Parts of JointsWhat it ContainsHow it WorksWhat Happens with Age
1Joint CartilageProtein[chondroitin sulfate, keratin] and water-there is no blood supplyActs as a shock absorberWater reduces, so does shock absorbing property
2Synovial FluidViscous LiquidLubricates the JointReduces in quantity
3Intraarticular DiscMostly protein. Gets oxygen from synovial fluidActs as a shock absorberShrinks
4Joint CapsuleFibrous structure containing nerves, blood, and lymphatic vesselsConnects bones, encompasses the jointShrinks
5Synovial MembraneContains 2 types of cells:-


Type A

Type B

Lines the joint capsule.


Type A cells remove particulate matter;

Type B cells secrete synovial fluid

Thickens and degenerates
6LigamentsSame as a joint capsule but thickerStabilizes the jointShrinks
7MuscleBundles of cells called MyofibrilsHelps in the movement of the joint by contracting and relaxingShrinks
8TendonThe thickened end part of muscleAttaches muscle to boneRemains unchanged
9BursaHollow sacs containing a small amount of synovial fluidHelps tendon and muscle move smoothly during joint movementShrinks

When we speak about Arthritis, we are usually referring to the pain in single or multiple joints and their surrounding tissues.

Different types of arthritis

So, depending on the type of structure involved, we have about 8 types of major arthritis.

Table 1 below defines the different types of arthritis and the body part/s involved:-

Table 2

The most common arthritis that is encountered is Rheumatoid and Osteoarthritis. The picture shown below shows what happens in these 2 types of arthritis:-

Picture showing difference between rheumatoid and osteoarthritis
Rheumatoid and Osteoarthritis[click on the picture to enlarge]

We will now see how the bones and joints get affected due to different joint diseases. Take a look-

Different types of arthritis of foot
Arthritis of joints of toes of the foot- RA-Rheumatoid PSA-Psoriatic OA-Osteoarthritis RED color shows part of a joint and bone affected

We shall learn more about arthritis and its management in my subsequent articles.

My next post will be a detailed study of OSTEOARTHRITIS its types, signs and symptoms.

Hope this brief introductory post has helped you understand what is arthritis.

Your suggestions and comments on this article are welcome.