She didn’t make a video and then hit the “instant global internet fame button” it’s just luck of the draw. Maybe consider limiting your nieces’ access to the internet because hawk tuah isn’t even the 10th worst thing they can find on youtube. It seems more to me that your siblings probably told you it was fine and you’re bitter they didn’t immediately stop your nieces from saying it.
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.
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.
Before sleeping. It also always makes me think of this song