This project is designed to use MRI to evaluate pre- and post-arthroplasty hips; the specific aims of this project are three-fold. First, the investigators intend to compare the amount of muscle atrophy and tendon damage that occurs around the hip between two commonly-used operative approaches: the direct-anterior approach and the posterior approach. Second, the investigators aim to provide baseline data on the amount of muscle atrophy and tendon damage that should reasonably be expected to occur with both of these approaches. Third, the investigators will document the degree of recovery of the periprosthetic soft tissues post-surgery in both patient groups.

The investigators first hypothesis is that the posterior approach will demonstrate significantly more damage to the abductors, piriformis, and short external rotators than the direct anterior approach, which will demonstrate minimal soft tissue damage. The investigators second hypothesis is that both surgical approaches will cause some degree of baseline muscle damage and atrophy, in a predictable pattern. The investigators third hypothesis is that each of the surgical approaches inherently cause some degree of soft tissue damage, and that the periprosthetic soft tissues that are incised during the surgical exposure will recover in a predictable pattern which is consistent but unique within each group

Inclusion Criteria:

1. Patients undergoing elective, primary total hip arthroplasty
2. Use of Cementless Total Hip components
3. Preoperative diagnosis of degenerative joint disease secondary to osteoarthritis

Exclusion Criteria:

1. Prior surgery on the affected hip
2. No implanted medical devices or metallic debris in the patient which will preclude use of MRI
3. patients must be able to participate in standard post-arthroplasty rehabilitation protocols.

Patients undergoing Total Hip arthroplasty by one of the two fellowship trained arthroplasty surgeons.