Our Physicians

The Arthritis Center has a dedicated staff of professionals that are experts in Rheumatoid Arthritis and related autoimmune diseases:

Karen Rendt-Zagar, MD

Karen E. Zagar, MD is a native of Pennsylvania, where she attended college (majoring in mathematics and chemistry at Clarion State College) and attended medical school (University of Pennsylvania in Philadelphia). She remained at the Hospital of the University of Pennsylvania for her internship and residency in Internal Medicine. She did her fellowship in Rheumatology at Duke University in Durham, North Carolina.

Dr Zagar joined our staff in 2005.  Prior to that, she spent six years on the staff of the Department of Rheumatic and Immunologic Diseases at the Cleveland Clinic Foundation in Cleveland, Ohio. There she served as the Fellowship Education Program Director to train physicians specializing in Rheumatology. She was also a member of the Center for Vasculitis Care and Research, headed by Dr. Gary Hoffman, and has participated in numerous clinical trials related to osteoarthritis, rheumatoid arthritis, and vasculitis.

Dr. Zagar is board certified in both Internal Medicine and Rheumatology, and she is a fellow in the American College of Rheumatology. Dr Zagar is currently Principal Investigator for all research trials and studies performed at Arthritis Center.

Dr. Zagar and her family enjoy numerous outdoor activities, particularly sailing, biking, and gardening. She also plays flute and classical piano.

Tatiana Nagibina, MD

Dr. Nagibina received her medical degree from Minsk State Medical Institute (former USSR). She completed her internship and residence in Internal medicine at The Chicago Medical School as well as fellowship in Rheumatology at the University of Illinois at Chicago.

Before joining our staff in 2011, Dr. Nagibina spent 10 years serving patients in Pinellas County providing Rheumatological care.

Dr. Nagibina is board certified in Internal medicine and Rheumatology and she is a fellow of the American College of Rheumatology.

Dr. Nagibina enjoys travel, theater, and museums.

Elaine Greifenstein, MD

Dr. Greifenstein attended college at Youngstown State University and medical school at Northeastern Ohio Universities College of Medicine.  She completed an Internal Medicine residency at the NEOUCOM Affiliated Hospitals in Canton, Ohio and a Rheumatology fellowship at the University of Pittsburgh in Pittsburgh, Pennsylvania.

 Before joining our staff in 2020, Dr. Greifenstein spent 20 years practicing Rheumatology and teaching medical students and medical residents in western Pennsylvania and northeast Ohio.

 Dr. Greifenstein is board certified in Internal Medicine and Rheumatology.  She is also a fellow of the American College of Rheumatology.

 She is an enthusiastic Pittsburgh Steelers and Pittsburgh Penguins fan.  She also loves hiking, reading and board games.