Three Theories of Osteoarthritis: It's not just "Wear and Tear."

Todd Lloyd
August 10, 2022

A 2013 narrative review from the American Academy of orthopedic surgery outlines three theories of osteoarthritis that go beyond the normal wear and tear that we always tell our patients.

Osteoarthritis is the most common type of arthritis that we experience as we grow older. Osteoarthritis is also known as degenerative joint disease, or degenerative disc disease in the spine. When you have osteoarthritis, you tend to have stiffness more than pain. Osteoarthritis will make you stiffer in the morning, and you will experience better movement in your arthritic joints as you warm up, and as the day goes on.

It's common to see osteoarthritis in patients who have suffered the chronic effects of a whiplash injury. Osteoarthritis, or DJD, is also very common in the low back. Most people in their 40s will tell you that stiffness in the low back and neck creeps up on you over time. Many people who work with their hands will also experience a growing stiffness in their thumbs where the thumb attaches to the wrist. Sometimes this can be painful. Also, if you've ever had a knee injury, and that injury was a decade ago or more, you might have osteoarthritis in your knee that was injured but not the one that was not injured.

Local biomechanical factors contribute to osteoarthritis

This is the classic wear and tear part of osteoarthritis. Your body weight increases loadbearing on the joints in your body. This distributes forces across your knees. Your knees will bear the brunt of three times your body weight while walking, six times your body weight while climbing stairs. This causes an increase wear and tear on your cartilage. If you are obese your body mass increases more than your muscle mass. Therefore, you have a higher ratio of body weight to muscle mass. This makes you fatigue earlier if you were obese, which leads to decrease shock attenuation and increase loathing rate on your joints. Carrying extra weight also influences your skeletal alignment, such as a varus deformity of your knee, or your upper back posture.

This wear and tear aspect of arthritis can also be caused by muscle weaknesses or muscle imbalances from inactivity or old injuries.

Effects of Mechanobiology at a Cellular Level

With increases of loadbearing, especially in obese people, changes happen on a cellular level in your joints. Mechanoreceptors on chondrocytes in your cartilage activate "mitogen-activated protein kinase." This is a secondary messenger for cells, and they release inflammatory signals.

This local inflammatory response will trigger cartilage wear. The inflammation causes matrix synthesis inhibition, and cartilage degeneration.

Systemic Theories linking Osteoarthritis to Obesity

Obesity will cause a low-grade inflammatory state throughout your whole body. Osteoarthritis actually has an inflammatory component and it is related to immunomodulatory and pro-inflammatory mediators. These mediators are actually derived from adipose tissue, your fat cells.

People who are obese have excessive amounts of "white adipose tissue." Traditionally white adipose tissue was thought as an excess energy depot, but it is also a powerful endocrine organ that secretes pro-inflammatory and immune regulatory cytokines. This endocrine activity is directly related to the amount of white adipose tissue mass that you have.

Adipocytokines and Adipokines appear in higher concentrations in the obese. Higher amounts of adipokines are known to have significant effects on the musculoskeletal system, and are associated with elevated inflammatory markers in the blood. Bone and cartilage are affected by these inflammatory chemicals.

The pro-inflammatory state caused by obesity is considered to be an underlying cause of metabolic syndrome. Metabolic syndrome is a cluster of conditions including obesity, hypertension, insulin resistance, and atherogenic dyslipidemia. These characteristics share common mediators, mechanisms, and pathways. Osteoarthritis should be considered a part of this syndrome.

The Takeaway from this study is that in order to treat, mitigate the effects of, and prevent osteoarthritis, you have to watch your weight, eat an anti-inflammatory diet, and continue exercising in a way that supports and stabilizes your musculoskeletal system.

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