A Comparative Study of In-vivo Wear Between 28 mm and 40 mm Metal Heads

Inclusion Criteria: 1. Male and non pregnant female patients between 18-75 years of age. 2. Patients requiring uncemented primary total hip arthroplasty (THA), suitable for the use of the Symax stem 3. Patients with a diagnosis of osteoarthritis (OA), rheumatoid arthritis (RA), avascular necrosis (AVN) or post-traumatic arthritis (TA). 4. Patients who understand the conditions of the study and are willing and able to comply with the post-operative scheduled clinical and radiographic evaluations and the prescribed rehabilitation 5. Patients who signed the specific Informed Consent Form prior to surgery Exclusion Criteria: 1. Patients who require revision of a previously implanted THA 2. Patients who had a THA on contra-lateral side within the last 1 year. 3. Patients who had a THA on contralateral side more than 1 year ago and the rehabilitation period outcome was considered unsatisfactory or not good. (Patients with contra-lateral THA \> 1 year ago with good outcome (Harris Hip Score \> 85) can be included in the study). 4. Patients who will need lower limb joint replacement for another joint within one year. 5. Bilaterally operated patient. 6. Patients who have had a prior procedure of acetabular osteotomy. 7. Patients with active or suspected infection. 8. Patients with malignancy - active malignancy 9. Patients with a diagnosed systemic disease that would affect the subject's welfare or overall outcome of the study (i.e. severe osteoporosis, Paget's disease, renal osteodystrophy) or is immunologically suppressed, or receiving steroids in excess of physiologic dose requirements. 10. The patient has a neuromuscular or neurosensory deficit which would limit the ability to assess the performance of the device or the patient has a neurological deficit which interferes with the patient's ability to limit weight bearing or places an extreme load on the implant during the healing period. 11. Female patients planning a pregnancy during the course of the study. 12. Patients with systemic or metabolic disorders leading to progressive bone deterioration. 13. Patients, who as judged by the surgeon, are mentally incompetent or are unlikely to be compliant with the prescribed post-operative routine and follow-up evaluation schedule. 14. Patients with other severe concurrent joint involvements which can affect their outcome. 15. Patients with other concurrent illnesses which are likely to affect their outcome such as sickle cell anaemia, systemic lupus erythematosus, psoriasis, Insulin dependent Type I diabetes or renal disease requiring dialysis. 16. Surgeries to be performed with navigation and/or robot-assisted instruments. 17. Patient with a known sensitivity to device materials.