I have been asked many times over the years why you get osteoarthritis in one knee (or hip or finger). If osteoarthritis is a disease of old age why does one joint wear out when others are fine. After all your joints are the same age!
A quick knee joint anatomy lesson. In a knee there is two pads of cartilage called the meniscus (different from the articular cartilage that covers the joint) and these can tear.
This is a normal knee on X-ray. The black space between the thigh bone and the shin is where the meniscus are. Cartilage cannot be seen on X-ray but if there is osteoarthritis the joint space will get narrower.
Why you get osteoarthritis in one knee really goes back to the causes of osteoarthritis. I believe THE major cause of osteoarthritis is trauma to the joint.
This can be a big trauma that you will probably remember. A significant trauma will strain the tendons and muscles and sprain the ligaments around the joint. Traumas that cause significant damage often have a rotational component to them which will tear at the meniscus and damaging it.
If that happens studies have shown that that you are much more likely to get osteoarthritis later in life and explains why you get osteoarthritis in one knee.
This two year study used MRI scans to determine whether if you damaged the meniscus whether the articular cartilage was affected.
Background: The relation between knee meniscal structural damage and cartilage degradation is plausible but not yet clearly proven.
Objectives: To quantitate the cartilage volume changes in knee osteoarthritis using magnetic resonance imaging (MRI), and determine whether meniscal alteration predicts cartilage volume loss over time.
Methods: 32 patients meeting ACR criteria for symptomatic knee osteoarthritis were studied. MRI knee acquisitions were done every six months for two years. The cartilage volumes of different knee regions were measured. Three indices of structural change in the medial and lateral menisci were evaluated—degeneration, tear, and extrusion—using a semiquantitative scale.
Put in plain English they took some people who had had damaged their meniscus and, using MRI scans every 6 months, they measured how much articular cartilage the person had. They discovered that the articular cartilage decreased over this two year period and that the more severe the meniscus damage the greater the loss of articular cartilage. They concluded that
“Meniscal tear and extrusion appear to be associated with progression of symptomatic knee osteoarthritis.”
I believe osteoarthritis will also occur if you have had a lesser trauma or repetitive trauma as the meniscus will still be damaged. The osteoarthritis simply takes longer to show itself- sometimes 20, 30 or 40 years.
When we fell out of that tree as a kid or hurt our knee playing soccer and we limped for a few day that was the start of osteoarthritis. The trauma was so not bad that we were given any therapy but the small amount of damage was done. As the study showed the smaller the damage to the meniscus that longer the symptoms took to occur so the many years before we start with getting those familiar aches and pains.
I hope that has answered why you get osteoarthritis in one knee but now you have it I am afraid you can’t cure it. However knee osteoarthritis can be successfully managed and you can find out how on my free course, Pain Management for Osteoarthritis.