The study aims to describe bone apposition and fixation of the Trident and Trident II Tritatnium acetabular system in patients 1 year status post total hip replacement. We will be studying this by comparing magnetic resonance imaging (MRI)s taken 1 year s/p total hip replacement with a Trident II cup with MRI's taken of patients with the Trident Cup who had MRIs done at 1 year post-op.

Inclusion Criteria:

1. Patients who had a primary total hip replacement with a Stryker Trident II acetabular cup that have one year or more follow up.
2. Patients that are willing able able to have an MRI at their one year follow up visit.
3. Patients entered into the CORRe database (our HSS institutional joint replacement registry).

Exclusion Criteria:

1. Patients who have not been consented as part of the CORRe database.
2. Patients who are unable or refuse to have an MRI at their 1 year follow up.