The Hip Arthroplasty Positioning Improvement Study

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.