With Karin's stem cell transplant came the risk of rejection of the stem cells by the body, much like there is with an organ transplant. The resulting graft versus host disease can me life threatening or mild.
Luckily, Karin suffered rather minor symptoms. The steroid prednisone, which she was prescribed for its anti-inflammatory properties, ultimately led to osteonecrosis (bone death), a known side effect of the drug. This, in turn, led her to need a hip replacement.