HOUSTON-Thomas Shelton Powers, M.D., has purchased the assets of Durham Medical Associates. The group practice of 12 physicians filed for Chapter 11 bankruptcy reorganization last year. Powers is the former owner of Oakland, Calif.-based Medicus Medical Group, an emergency physicians contract management firm that was sold to Coastal Healthcare Group two years ago. Durham has signed an exclusive contract with Humana Health Plans for enrollees within a five-mile radius of the clinic. It also plans to expand with three to five additional satellite offices, said Terry Goss, the clinic's executive director.