This is a multi-center, randomized study to compare blood and urine cobalt, chromium, and titanium ion levels of a metal-on-metal articular bearing coupled with two different head sizes to that of a conventional metal-on-polyethylene bearing.

Inclusion Criteria:

• Undergoing cementless primary total hip replacement
• Receiving acetabular cup of 52mm or greater
• Preoperative level of function and pain same as for conventional hip replacement
• Likelihood of obtaining relief of pain and improved function
• Full skeletal maturity
• Ability to follow instructions
• Good general health
• Willing to return for follow-up evaluations
• X-ray evaluation confirming the presence of NIDJD
• Femoral and acetabular bone stock that is sufficient, regarding strength and shape, and suitable to receive the implants

Exclusion Criteria:

• Age less than 40 years or greater than 80 years at time of surgery
• Patients templated to receive an acetabular component smaller than 52mm in diameter
• Presence of a previous prosthetic hip replacement device in the hip joint to be operated
• Previous girdlestone procedure or surgical fusion of the hip to be operated
• Acute femoral neck fracture
• Above knee amputation of the contralateral and/or ipsilateral leg
• Patients with a diagnosis of inflammatory degenerative arthritis
• Skeletally immature
• Evidence of active infections that may spread to other areas of the body
• The presence of a highly communicable disease that may limit follow-up
• Presence of known active metastatic or neoplastic disease
• Significant neurologic or musculoskeletal disorders or disease that may adversely affect gait or weightbearing
• Any previous hip surgery or conditions that may interfere with the total hip replacement's survival or outcome
• Any patient believed to be unwilling or unable to comply with a rehabilitation program for a cementless total hip replacement or indicates difficulty to return for follow-up
• Patient is know to be pregnant, a prisoner, mentally incompetent, and/or alcohol or drug abuser
• Any patient who qualifies for inclusion in the study but refuses consent to participate in the study
• Any steroid therapy, local or systemic, within three months prior to surgery
• Patient requiring structural bone grafts in order to support the prosthetic components or to shape the bone to receive the implants
• Patient has known allergies to metal, e.g., jewelry
• Any patient not meeting all radiographic and clinical parameters for inclusion