Type of arthritis beginning in middle age with erosion of bone where bones meet at the joint?

The type of Arthritis you're describing is likely rheumatoid arthritis (RA). It typically begins in middle age and is characterized by the inflammation of the synovial membrane, leading to joint erosion and damage where bones meet. RA can cause pain, stiffness, and swelling in the joints and may also affect other systems in the body. Early diagnosis and treatment are crucial to manage symptoms and slow disease progression.