About General Surgical Associates General Surgical Associates, Inc. (formerly Charles H. Cook, M.D., Inc.) has served the Lancaster community since 1975. Charles H. Cook, M.D. founded the practice and practiced solo for 24 years. Jeffrey K. Yenchar, M.D. joined Dr. Cook in practice in 1999. They practiced together for five years before recruiting David J. Robertson, M.D., F.A.C.S. in 2004 as a third surgeon. Dr. Cook then retired from General Surgical Associates in December 2004. In 2009 a fourth surgeon, Margaret S. Sawyer, M.D. M.B.A, joined the practice.