Inclusion Criteria:

• Patients who understand the conditions of the study and are willing to participate in a single two-hour visit to the clinical site.
• Patients who are male and female, 30 years of age or older.
• Patients with a pre-primary THR diagnosis of osteoarthritis or avascular necrosis.
• Patients with a 32mm or 36mm diameter THR bearing.
• For Group 1, Patients who have had a single or first episode of dislocation beyond 6 weeks following their primary THR.
• For Group 1, Patients who have had a single episode or multiple episodes of dislocation following their primary THR, but have not been revised.
• For the Group 2, Patients who are beyond 1 year post-operative following their primary THR and have had no incidence of hip dislocation following their primary THR.
• For the Group 2, Patients who are asymptomatic based upon their pain, feeling of "popping out", and range of motion in the primary THR hip.
• Patients who have been deemed eligible for the study as determined by a blinded radiograph reviewer.
• Patients who have consented to participate in the study.

Exclusion Criteria:

• Patients who aren’t able to clearly describe the activity in which their dislocation occurred (applicable to "dislocator group").
• Patients with a lipped polyethylene liner.
• Patients who are reluctant to flex as far forward as possible during the seated x-ray with their legs abducted.
• Patients with abductor insufficiency.
• Patients whose index hip is short by >5mm, or have offset reduced by >10mm in comparison to the contralateral side as measured on radiographs.
• For the Group 1, Patients who had a spinal fusion or spinal surgery post-dislocation.
• For the Group 2, Patients with evidence of hip joint instability (e.g., pain, feeling of "popping out", and limited range of motion, ball and socket joint laxity) of the joint.
• Patients who have a neurological disorders which may interfere or adversely affect gait or weight bearing (e.g., Parkinson’s, muscular dystrophy, multiple sclerosis).
• Patients who have cerebral dysfunction (e.g., stroke).
• Patients who have a medical history of femoral neck fracture, hip fracture.
• Patients who have a medical history of rheumatoid arthritis.
• Patients who are a known drug or alcohol abuser, or have a psychological disorder.
• Patients who are currently involved in any personal injury litigation, medical-legal or worker’s compensations claims.
• Patients who are unable to provide informed consent.
• Patients who are unable to comply with all the required study procedures.

FINAL EXCLUSIONS - following consent to participate in the study:

• If the subject isn’t flexed enough in the picture taken by radiology to achieve the positioning specified in the Imaging Protocol, or if the subject answers to being "apprehensive" or "significantly apprehensive" in the flexed seated position on the Apprehension Questionnaire
• A combined anteversion5 (CT measured supine cup anteversion + stem anteversion to the posterior condyles) that is outside of the range of 25 – 50.