Arthritis. Causes heaps of pain and reduced mobility which brings a whole lot of other medical complications. Hips replacement are super common past a certain age.
Osteoarthritis (or specifically, osteoarthrosis), not rheumatoid arthritis (swelling of the areas around the joint due to immunoresponse), it's when the cartilage on the femural head wears out so its just bone on bone. Doctors can inject hyaluronic acid for temporary lubrication but a replacement is pretty much the only long term treatment.