Cause Osteoarthritis is complex and multifactorial. It is a result of problems that deriving from the morphology of the cartilage and the mechanical properties of it, as well as changes in the biochemistry of the area.

Few factors that are described as causes of OA are

Anatomical abnormalities

Trauma (either major fractures or microfractures as result of repeated low degree trauma)

Loss of joint stability

Abnormal loading due to alteration of the weight bearing axis

Meniscal surgery (medial meniscectomy almost doubles the incidence of OA)

Altered kinetics of the knee

Gait modification.

Repetitive increase load in a particular area of the knee

Inflammatory factors (increase of them)

Increase of activities of the immune system in the joint environment

Metabolic disorders

Obesity.

In females if they have 6 or more pregnancies.

Vitamin D deficiency (about 2.5 times more OA)

and so on.

All mechanical problems influence the Proteoglycans and all inflammatory problems increase the Proteolytic Enzymes.

Obesity is found to increase the Leptin within the joint which is influencing the chondrocytes.

These are part of the Causes leading to Osteoarthritis and mentioned here in brief.

Yes, the etiology of OA is of a multiple origin while the pathogenesis follows one and the same path which is plainly a  progressive  degeneration of the articular cartilage with secondary changes in all structures of the joint. Joint instability and  deformation follow these changes. 

Meanwhile, I still wonder why the English literature uses the term "osteoarthritis" which is a denomination for an inflammatory process, and is in my opinion incorrect. As we see from the above presented list of causes, inflammatory factors are rare with OA.  "Osteoarthrosis" corresponds better to the nature of this pathology being widely used in German, Russian, French and other literatures. 

I agree about the ending - itis instead of - osis is not representing the "truth", but this is the habit of a language.

“By the end of the 20th century the term “osteoarthritis”, derived from the Greek (bone+joint+inflammation) was corrected  to “osteoarthosis” (bone+joint+affection).” This is written by John Kirkup in his excellent book “An illustrated history of hip joint surgery” (2014). That means that some British orthopaedic surgeons gradually accept the term “osteoarthrosis”.

 Of course tradition is something important but somewhat inert. 

Dear Panayot.

Etymology of the wording is correctly and precisely demonstrated by your report and the term of arthrosis than arthritis can be heard in meeting although it is not the common ground of discussion and mainly the patients have to be educated as they cannot follow the term. So unfortunately although you are right the ending of -itis is still used as the most common one.

We are talking about an osteoarthrosis?

The pathophysiology of knee OA depends on its etiology: traumatic, dysplastic, idiopathic. In the first case the injury as a trigger leads to anatomical changes in the bone, meniscus, ligaments. In the absence of appropriate treatment leads to the progression of the damaged tissue, changes of cartilage, subchondral bone perfusion.

In the second case dysplasia of bone, forming the knee, patellar dislocation with age leads to severe disturbance of biomechanics, changes in the structure of cartilage, para-articular tissues. In the future, changes to the cellular structure of the subchondral bone, progressing change cartilage, bone

 Idiopathic osteoarthritis as a result of violations of metabolic processes, increase in body mass index, hormonal disorders, osteoporosis, impaired blood flow and changes the structure of the subchondral bone changes the biomechanics of the knee joint, disrupted the structure of cartilage, bone.

Start may be different, but the situation is further repeated: the progressive degeneration of the articular cartilage with secondary changes in all structures of the joint.

Whereas I agree with  my colleagues, I think we also have to reconsider the simple conclusion that degeneration of articular cartilage leads to secondary changes in all strutures of the joint.  In animal models with spontaneous OA, as opposed to the surgical and/or mechanical models, bone changes precede the changes in articular cartilage.  Moreover, if we move forward to consider OA as a metabolic disease than if follows that potentially all tissues could be affected at the same time which would make more sense.  As the modifications of one tissue over the other may be leading the disregulation of the affected joint, than an array of possibility could be proposed.  Hence, I believe we have to move away from the simple approach of a cartilage-borned disease leading to secondary changes to all other tissues to a disease affecting simulteneously all tissues.

Dr. Lajeunesse, you are right to some extent  that the degeneration of cartilage is associated with changes in the subchondral plate and disturbed nutrients supply to cartilage from the bone. But do not forget that disturbance in synovial fluid supply is very important too.  Under secondary changes I understand the changes in ligaments, and menisci, joint instability, asymmetrical loading and deformity, osteophytes formation, further bony changes. 

I believe that the following factors are the most important factors in aetiopathogenesis of knee OA is multifactorial:

1. Strength of the articular cartilage (Genetic, Nutritional, Metabolic)

2. Strength of  the subchondral bone (Osteoporosis, Nutritional, Metabolic)

3. Increase load on the cartilage and subchondral bone (Obesity, Mechanical)

4. Quality of synovial fluid

I agree with all the previous considerations but I like to add that mechanical (biomechanical) factors also contribute to the primary OA of the knee.

In this particular, quadriceps muscle strength and stretching is a important cause of mechanical overload of knee joint and may lead to degenerative changes in the cartilage, starting the process.

Yes, perhaps, but far less frequently than other causes, which were mentioned.

Much less !!!!

Need to mention - Meniscal root tears, Valgus/Varus alignment and perhaps also Trochlear Dysplasia - are all factors that can be dealt with surgically and not only prevent, but also reverse the arthritic changes