My husband was injured at work while lifting a piece of steel. He had a fractured ankle and his left knee was more swollen than I thought was possible. While we were in the emergency room, the doctor said that he had fluid on his knee and that they needed to aspirate it through a needle. When they started pulling fluid off his knee, it was somewhat pinkish at first but then became bloody looking.
The doctor diagnosed him as having traumatic hemarthrosis due to his injuries. His knee was extremely swollen and looked deformed from all of the fluid. He was referred to an orthopedic surgeon who performed a synovectomy.
He is still in physical therapy but doing much better.