Patient presents with complaints of chronic left hip pain, stiffness, and functional limitation consistent with osteoarthritis.  Symptoms include significant pain with weight-bearing activities, limited range of motion impacting mobility, and morning stiffness.  The patient reports a history of conservative management including physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs), and corticosteroid injections, which have provided insufficient relief.  Physical examination reveals decreased left hip flexion, internal and external rotation, and abduction.  Radiographic imaging confirms severe degenerative changes in the left hip joint characterized by joint space narrowing, osteophytes, and subchondral sclerosis.  Diagnosis of primary osteoarthritis of the left hip is confirmed.  After discussion of risks and benefits, including infection, dislocation, leg length discrepancy, and the need for potential revision surgery, the patient has elected to proceed with a left total hip arthroplasty (THA).  Surgical plan includes a posterior approach left total hip replacement.  Preoperative optimization, including medical clearance and bloodwork, is scheduled.  Postoperative care will include pain management, physical therapy, and monitoring for complications such as deep vein thrombosis and infection.  ICD-10 code M16.11, primary osteoarthritis left hip, and CPT code 27130, total hip arthroplasty, are appropriate for this case.  Medical necessity for the left THA is documented based on failed conservative treatment and significant impact on quality of life.  This procedure is deemed medically necessary to alleviate pain, improve function, and restore mobility.