The primary objective of this study is to determine whether the Corin Optimised Positioning System (Corin, U.K.) reduces the rate of hip dislocation at one-year post-operatively compared with standard templating in patients undergoing total hip replacement.

The secondary objectives of this study are to determine whether the Corin Optimised Positioning System (Corin, U.K.) improves functional outcomes, reduces length of hospital stay, and reduces leg length discrepancy compared with standard templating in patients undergoing total hip replacement.

Osteoarthritis (OA) is the most common joint disease worldwide affecting an estimated 10% of males and 18% of females over 60 years of age. The resultant pain and loss of function can be debilitating and in developed countries represents a large socioeconomic burden, costing between 1% and 2.5% of gross domestic product, which currently stands at over £1.5 trillion. Total hip replacement (THR) is an effective treatment for end-stage hip arthritis; however, demand for the procedure is growing rapidly, fuelled by an ageing population and the obesity epidemic. In fact, rates of THR are predicted to rise 174% between 2005 and 2030. The current commissioning environment in developed countries means that investment in iterative improvements of existing THR implant designs are unlikely to yield either significant benefits to patients or be supported by health funders. The two principle issues that concern surgeons and patients are the longevity of implants and the ability of new technologies to minimise complications such as dislocation and infection. The James-Lind Priorities Setting Partnership, an internationally recognised patient-driven organisation, has recently identified these pre-operative and intra-operative factors as targets for improving outcome following hip and knee replacement.

One of the largest costs to healthcare providers following THR is dislocation. Although the dislocation rate reported in Joint Registries is between 1 and 3% we know that this significantly underestimates the true problem, as the majority of dislocation events are managed with closed reduction and do not result in revision surgery. It is estimated that dislocation is an order of magnitude more common than reported in Registry data. Literature estimates indicate a true dislocation prevalence of 3 to 15%. The cost of dislocation is significant as the problem is often recurrent, resulting in multiple hospital admissions. The resulting average cost for each patient who suffers a THR dislocation is around £30,000.

The factors that influence dislocation are poorly understood. Conventional surgical wisdom dictates that placing a cup in the Lewinneck 'safe zone' reduces both instability and wear. A recent study of 9784 primary THRs, however, demonstrated that 58% of patients who suffered a dislocation had implants judged to be in a safe position. This has led to suggestions that the idea of one generic 'safe zone' may be misleading; instead, there is a unique optimum position to place a cup in each patient undergoing THR, based on the unique and complex interaction of the spine and pelvis of the individual. Thus, in some patients, whilst the acetabular cup appears well positioned by conventional measures, pelvic tilt and spinal position mean that the cup is placed in a position of instability during some activities.

The Corin Optimised Positioning System (OPS) is a novel platform, designed to enable delivery of the prosthetic acetabular cup into an optimised position for every patient undergoing THR. It comprises two stages: pre-operative planning and intra-operative guidance. Pre-operatively, patients undergo dynamic imaging (computed tomography scanning and X-ray films). The information gained about the relative movements of a patient's spine, pelvis and hips are used to create a personalized physiological profile. This enables calculation of the optimized acetabular cup orientation for each individual. A unique physical guide (which falls under the definition of a custom-made device in the Medical Device Directive) is then created for each patient to fit precisely into the acetabular fossa, for use intra-operatively. Intra-operatively, the Corin OPS uses laser alignment to aid the surgeon in aligning the acetabular cup in the calculated optimised orientation. One laser is affixed to an immovable pelvic screw; the other is attached to the reverse of the acetabular cup. The target orientation of the cup is achieved when the two lasers are aligned.

The aim of this trial is to assess the efficacy of the use of the Corin Optimised Positioning System in reducing post-operative hip dislocation in patients undergoing total hip arthroplasty by comparing it with current standard templating in total hip arthroplasty. All total hip implants/components used in the study will be produced by Corin for uniformity and have the required approvals. There is currently no evidence that this novel approach to templating has an effect on dislocation rate. This project aims to provide evidence that this new technique can improve outcomes for patients and have the potential to reduce the need for complex, expensive revision surgery.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the trial
• Diagnosed with hip OA, post-traumatic OA, inflammatory arthropathy, avascular necrosis, or congenital or developmental hip disease, avascular necrosis of the hip
• Listed for total hip arthroplasty at one of participating centres
• Participant is fit to undergo total hip arthroplasty based on consultant anaesthetist review
• In the Investigator's opinion, is able and willing to comply with all trial requirements
• Willing to allow his or her General Practitioner and consultant, if appropriate, to be notified of participation in the trial
• Female participants of child bearing potential must be willing to ensure that they use effective contraception during the trial

Exclusion Criteria:

• Inability to provide informed consent
• Previous surgery to the ipsilateral hip
• Significant co-morbidities that would make follow up difficult or uncomfortable
• Scheduled elective surgery or other procedures requiring general anaesthesia during the trial
• Pregnancy

De-identified individual participant data for all primary and secondary outcome measures will be made available.

Data will be available within 6 months of study completion

Data access requests will be reviewed by the trial steering committee. Requestors will be required to sign a data access agreement

Participants: participants in both arms will undergo total hip replacement while under general anaesthetic. Participants will not be aware of the templating method used during the total hip replacement due to the general anaesthetic, therefore will remain blinded. Wounds and dressings will be the same for both study arms. Participants in the two study arms will undergo the same pre- and post-operative imaging to prevent unmasking.

Outcomes assessors examine patients from 3 months post-operatively. There is no risk they will know which arm the patient is in, as they will not have access to the study database.