acquired adult flatfoot

Hi, I've recently been diagnosed by an ankle ortho here in the USA that I have tibialis posterior dysfunction and there's swelling and arch collapse on that foot. He says the tendon's not torn. How can I progressively rehab it? Physical therapy gave me some namby-pamby geriatric exercises and the ortho only offered surgery for pain relief-no more athletics. It's an old injury(10 years maybe). Can I get it together again? The right arch is flat on the ground in weightbearing and the foot and calf are painful in walking. Forget about running.