A Multi-Centre Study in Patients Undergoing Total Hip Arthroplasty With the Smith+Nephew CATALYSTEM™ Primary Hip System

Inclusion Criteria: 1. a. Subject needing primary THA due to end stage degenerative joint disease (primary diagnosis of osteoarthritis), avascular necrosis, post-traumatic arthritis, inflammatory arthritis, or congenital hip dysplasia. OR 1. b. Subject has undergone primary THA with the S+N CATALYSTEM™ Primary Hip stem in the past 12 months for end stage degenerative joint disease (primary diagnosis of osteoarthritis), avascular necrosis, post-traumatic arthritis, inflammatory arthritis, or congenital hip dysplasia and all the following conditions have been met for the appropriate timepoint: * Preoperative Patient Reported Outcome Measures (PROMs): * Hip Disability and Osteoarthritis Outcome Score Junior (HOOS, JR.) * European Quality of Life (EuroQol) Five-dimensional Five-level (EQ-5D-5L), and * Radiographs have been obtained: ° Anterior Posterior (AP) Pelvis * AP Hip\*, and * Lateral\*\* * 6-Weeks ° PROMs (HOOS, JR., and EQ-5D-5L), and * Radiographs (AP Pelvis, AP Hip\*, and Lateral\*\*) have been obtained or these can be collected prospectively in window per schedule of events, and * 1-Year ° PROMs (HOOS, JR., and EQ-5D-5L), and ° Radiographs (AP Pelvis, AP Hip\*, and Lateral\*\*) have been obtained or these can be collected prospectively in window per schedule of events 2\. Subject agrees to consent and to follow the prospective study visit schedule by signing the Independent Review Board (IRB)/Independent Ethics Committee (IEC) approved Informed Consent Form (ICF). 3\. Subject is eighteen to eighty (18-80) years old (inclusive). 4\. Subject can read, understand, and communicate responses to the PROMs. footnote: \*For the AP Hip radiograph, sites MUST ensure that positioning (standing AP Hip vs. supine AP Hip) is consistent across all study visits for an individual subject (i.e. if subject had standing AP Hip at pre-op then collect standing AP Hip at all visits for that subject). \*\* Lateral radiograph is to include any one of the following, but for standardization, sites MUST ensure consistency across all study visits for an individual subject: Cross-Table Lateral (CTL) or Frog-lateral or lateral femoral/Lowenstein (i.e. if subject had frog-leg lateral at pre- op then collect frog-leg lateral at all visits for that subject). Exclusion Criteria: Any one (1) of the following criteria will disqualify a potential subject from participation in the study: 1. Subject has conditions that would eliminate or tend to eliminate adequate implant support or prevent the use of an appropriately-sized implant, e.g.: * Blood supply limitations * Insufficient quantity or quality of bone support e.g., osteoporosis, or metabolic disorders which may impair bone formation, and or osteomalacia * Mental or neurological conditions which may tend to impair the patient's ability or willingness to restrict activities; or impairing or precluding cooperation with post-operative protocols including mental illness, drug or alcohol abuse. * Physical conditions or activities which tend to place extreme loads on implants and may impair short and long-term satisfactory results of the implant, e.g., Charcot joints, muscle deficiencies, multiple joint disabilities, etc. * Infections or other conditions which may lead to increased bone resorption * Skeletal immaturity 2. Subject has a Body Mass Index (BMI) \>/= 45 at time of surgery. 3. Subject has a known allergy to one or more components of the study device. 4. Any subject that meets the definition of a Vulnerable Subject per ISO 14155 Section 3.55 (i.e., individuals who are unable to fully understand all aspects of the investigation that are relevant to the decision to participate, or who could be manipulated or unduly influenced as a result of a compromised position, expectation of benefits or fear of retaliatory response). 5. Subject is entered in another drug, biologic, or device study or has been treated with an investigational product 30 days prior to the surgery date. 6. Subject is known to be at risk for lost to follow-up, or failure to return for scheduled visits. 7. Women who are pregnant or nursing. 8. Subject has participated previously in this clinical trial and has been withdrawn. 9. Subject has an active infection - systemic or at the site of intended surgery. 10. Subject had a contralateral (opposite) hip replacement that was implanted less than 3 months prior to consent, is scheduled for a simultaneous contralateral hip implant, or plans to have their contralateral hip implanted within 3 months following this study-specific implant (known as 'staged bilateral THA'). 11. Subject with a medical or physical condition that, in the opinion of the Investigator, would preclude safe subject participation in the study.