This is a randomized control trial that will investigate whether a collared hip replacement implant provides greater stability compared to a collarless option. Stability will be measured by implant migration with radiostereometric analysis (RSA) imaging. Secondary objectives will be to compare function, quality of life and cost between the two implant types. We will also compare between two different surgical approaches, the direct anterior and direct lateral.

Total hip arthroplasty (THA) is a procedure that has been demonstrated to provide excellent patient satisfaction and improve quality of life while being cost effective. The number of THA's conducted worldwide is expected to continue to grow; in some projections to grow exponentially. However, the environment for health care continues to evolve. Patients continue to demand higher activity levels, decreased recovery times, and greater patient autonomy. Health care economics are increasingly influencing clinical decision making. Bundled health care payments and more stringent evaluations are becoming the norm. Changes in care pathways based on patient input as well as due to health care economics are our new reality.

These two pervasive forces of change have led to a variety of care challenges and thought leaders have proposed solutions to these challenges. One solution that has responded to both changing patient expectations in their THA experience as well as the economic pressures has been rapid recovery pathways. An increase in rapid recovery care pathways and the growing prevalence of outpatient surgery and surgi-centers has enabled patients to increase their autonomy as well as decrease their time away from activities that are important to them such as employment. Rapid recovery care pathways also provide substantial cost savings by diminishing or eliminating inpatient care as well as enabling improved bed management options.

To facilitate rapid recovery programs, a variety of surgical changes have been made. Improved peri-operative care, decreased muscle trauma, improved hemostasis, and multi-modal analgesia have all made positive impacts. The increasing adaptation of the Direct Anterior Approach (DAA) relative to the Direct Lateral Approach (DLA) can be seen as a response to the need for rapid recovery programs as DAA has been demonstrated to enable earlier function and is thought to result in better patient outcomes, less pain, and shorter recovery times. Orthopaedic industry partners have also supported this change in practice by providing improved instrumentation and technologies to potentiate this minimal invasive surgical approach. A key change is the increasing use of implants that facilitate muscle sparing approaches: femoral components that do no require straight femoral reamers as well as broaches and implants with design features such as an angled lateral shoulder, abbreviated stem lengths, easy to control stem tips, and stems that do not require aggressive impaction to create intimate cortical contact. The Corail both has these features that potentiate surgery as well as excellent survivorship on registry and prospective studies.

In addition to the design features that potentiate minimally invasive implantation, the Corail stem has two main designs - the collared and collarless versions. Without question, the collar provides improved axial stability, and it has also been shown to provide improved rotational stability. It is unclear if this stability enables improved early function by providing the patient the sense that their implant is more stable immediately after surgery. Clinicians also appreciate the ability to more precisely control leg length during THA by ensuring the appropriate leg length is maintained when the collar abuts the calcar. The collar is felt to enable greater initial stability to the hip and provide the surgeon with greater confidence that the patient can embark on a rapid recovery care pathway.

However, not all surgeons are as supportive of implants that have a collar nor are they supportive of implants that have a collar, and highlight a lack of literature that is able to demonstrate the benefits. A lack of literature makes it a challenge for surgeons to adopt the change in philosophy. The purpose of this study is to examine the role of surgical approach and implant design on activity and implant fixation following THA.

Inclusion Criteria:

• unilateral hip osteoarthritis
• primary total hip arthroplasty

Exclusion Criteria:

• symptomatic osteoarthritis in the contralateral hip
• bilateral total hip arthroplasty
• revision arthroplasty
• cognitive defects/neuromuscular disorders
• inability to understand English (questionnaires are only provided in English)
• live more than 100km from London, Ontario
• BMI greater than 40

Participants will be blinded to which group they have been assigned to until the final study visit at which point study personnel will reveal the group allocation.