This study is intended to compare the proximal migration of the tantalum design (TM) with a cemented cup used in conjunction with bone allografting in cases with major bone loss. A group of patients with good periacetabular bone stock are included to analyse the differences between the tantalum and titanium design regarding risk of loosening and differences in clinical outcome measures. Radiostereometry (RSA) is used to accurately measure migration and rotation of the revision cups.