Parts start failing at 40
What are you all doing to your knees?
Rad tech here: most people who have this phenomenon have arthritic knees from being fat. Internet disclaimer: I DIDN’T SAY ALL. But a huge number of people get to 30s or 40s and are overweight or have been for a significant part of their life and have worn out their knees at an early age. Then they come to get xrays with “idiopathic” knee pain.
From a technical perspective, what part gets “worn out” when you see the scans? Is it cartilage, ligaments, tendons, or something else?
As other people have said it’s somewhat all of the above, though the biggest and most visible on xray is the narrowing of the joint space from deterioration of the cartilage. This causes arthritis, and also calcification of the joint which is also all worsened with age and varying bone density which can change based on things like ancestry, gender, habits (drug use/smoking) or medical conditions.
Edit: I also forgot to mention that occupation can make a big difference here. Being overweight AND having a job that is strenuous on the knees (construction/manual labor/heavy lifting) is a bad combo which can lead to joint deterioration and premature joint replacement as well.
