Title: Comorbidity as a predictor of referral to, and outcome from, surgery in primary care patients with newly diagnosed osteoarthritis in the hip: a population-based cohort study
Funder: Department of Health and Social Care

Abstract: Background There is increasing demand for hip joint replacement surgery in the growing number of elderly and very elderly people in the UK. This demand is associated with an increasing level of comorbidity which can constrain the benefits of surgery and increase the intra-operative and post surgery risks. There is scant knowledge of the influence of pre-existing comorbidity/ies on benefits and risks from surgery and hence decision-making by patients, clinicians and health policy makers lacks an evidence base. There is the additional concern that patients who may benefit substantially from surgery either self-preclude or are recommended to avoid/defer surgery based on an over-pessimistic view of risks and benefits Aims and Objectives The overall aim is to improve decision making for hip joint replacement surgery by more robust information on risk and benefits in the presence of common comorbidities. There are a number of specific objectives to be addressed: 1. Within UK primary care, in patients newly identified as having hip osteoarthritis, does comorbidity predict the likelihood of and the lag till receiving hip replacement surgery? a. If there is a relationship, what is its size and how much of a contribution does it make to joint surgery? Further we will explore how consistent is this relationship. b. How do the different approaches to assessing comorbidity compare in their impact on the above in order to best advise what is the optimal approach in this clinical situation? 2. In those UK primary care patients newly identified as having hip osteoarthritis who then receive surgery, what is the relationship between the pre-surgical markers of comorbidity and surgical outcomes including a. Early post-operative mortality b. Intra-operative complication(s) c. Short term complications in the post-operative period d. Length of stay e. Patient reported outcomes (PROMs) f. Longer term serious morbidities and death Plan of Investigation The research will take advantage of the existence of a dataset of over subjects identified with any form of arthritis from CPRD, with linked HES data on hospital admissions, available to the applicants. The estimated 40,000 patients over the age of 65 within theis existing dataset with newly coded GP diagnosis of hip osteoarthritis (based on READ codes) will then have their CPRD record interrogated to ascertain levels of baseline comorbidity using a number of different approaches based on the likelihood of appropriate data being available. These include the Charlson index, prescribing history, number of GP visits and also specific comorbidity mentions. The outcomes to be investigated will be: 1. the time from GP recording of hip osteoarthritis in CPRD to the date of hip replacement surgery in HES 2. in those undergoing surgery the development of key outcomes, including PROM reported to HES. Outcome Assessment For the purposes of analysis, the cohort will be stratified into those referred and not referred for surgery during the period of observation. The primary analysis will therefore be the proportion referred for surgery, and the delay in referral, in relation to the different measures of comorbidity. The secondary analysis will examine the relationship between baseline comorbidity and surgical outcomes. This analysis, therefore restricted to those patients who had an arthroplasty, using the different data sets available would examine the outcomes referred to in 2a-f above. Potential Patient Benefits A number of benefits could derive from this research: 1 Robust information on risks and benefits of hip joint replacement in patients with comorbidity/ies that can better inform decision making for patients, their carers and clinicians 2 Robust information on current practice to highlight inequalities in decision making that can inform health care policy and practice in this area

Lay abstract: Hip joint replacement surgery is a very effective treatment, bringing pain relief and improved function to 80000 UK patients with hip osteoarthritis each year. No surgery is without risk and the risks during and immediately following surgery are increased in the elderly especially those with significant other health conditions. The decision whether or not to have an operation is harder when there are other such health problems. Patients, their carers and health care professionals have concerns about the possible increased risk and how this should be weighed against the benefits from having an operation. There are, however, no hard data to best advise patients. We don t know how much other ill health issues influence patients and their general practitioners in making the decision to seek surgery. As a consequence we don t know if the right decision is made. What is the size of the problem of patients who are being operated who would have been better advised to avoid surgery? Possibly more relevant is the reverse question: who is not operated because of concerns about their other health problems where the evidence suggests there would have been an overall benefit to health? The proposed research will use a very large general practice database of patients identified as having hip osteoarthritis. Using the same database the research will investigate the levels of other existing health problems at the time of the hip problem and analyse how they informed the decision for any subsequent joint surgery. Those who received surgery will also be followed up using both general practice and hospital data sources to determine if their pre-existing other health conditions actually did affect the risks and outcomes from surgery. The goal of the research is to provide the information to better support decision making for patients and those who advise them.

Research activity codes: 7.3 MANAGEMENT AND DECISION MAKING
Health categories: MUSCULOSKELETAL