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Cost-effectiveness of a model consultation to support self-management in patients with osteoarthritis

Abstract Objectives The aim of this study was to estimate the cost-effectiveness of a model OA consultation for OA to support self-management compared with usual care. Methods An incremental cost–utility analysis using patient responses to the three-level EuroQoL-5D (EQ-5D) questionnaire was undertaken from a UK National Health Service perspective alongside a two-arm cluster-randomized controlled trial. Uncertainty was explored through the use of cost-effectiveness acceptability curves. Results Differences in health outcomes between the model OA consultation and usual care arms were not statistically significant. On average, visits to the orthopaedic surgeon were lower in the model OA consultation arm by −0.28 (95% CI: −0.55, −0.06). The cost–utility analysis indicated that the model OA consultation was associated with a non-significant incremental cost of £−13.11 (95% CI: −81.09 to 54.85) and an incremental quality adjusted life year (QALY) of −0.003 (95% CI: −0.03 to 0.02), with a 44% chance of being cost-effective at a threshold of £20 000 per QALY gained. The percentage of participants who took time off and the associated productivity cost were lower in the model OA consultation arm. Conclusion Implementing National Institute for Health and Care Excellence guidelines using a model OA consultation in primary care does not appear to lead to increased costs, but health outcomes remain very similar to usual care. Even though the intervention seems to reduce the demand for orthopaedic surgery, overall it is unlikely to be cost-effective.


Introduction
OA is most prevalent in older people and is known to adversely affect quality of life [13]. Estimates from the United States of America (USA) suggest that 12.4 million adults over the age of 65 years are living with this condition and around 2.9 million people have a disabling form of OA. A report by the Royal College of General Practitioners indicates that about 1 million adults consult with symptoms of OA in a year and it is one of the main reasons why people seek medical care [46]. The total healthcare cost of OA has been estimated at £1 billion in the UK [5]. Therefore OA places a considerable burden on scarce healthcare resources. The proportion of older people in the population has been increasing over time [7], and with this ageing population, it is expected that the prevalence of conditions such as OA will rise. A number of published guidelines have been developed to aid the treatment and management of OA [812]. In the UK, for example, the National Institute for Health and Care Excellence (NICE) recommend that patients with OA should be offered core treatments when they first present in primary care. These include education and access to information, advice on local muscle strengthening exercise and general aerobic fitness, and if appropriate, advice on losing weight [12]. However, there is a gap between the care that is recommended and that which patients actually receive, and the core aspects of assessment and management of OA currently delivered in primary care do not meet the recommendations of these guidelines [13,14]. Therefore, measures need to be put in place to ensure that resources are used optimally. Consequently, there was a need to develop a practical approach that could potentially support selfmanagement of OA and also aid the implementation of the core NICE guidelines for OA. This led to the development of a model OA consultation [15] for older patients presenting with peripheral joint pain, and training for health care professionals to support its delivery. The model OA consultation integrated core recommendations from NICE and consisted of an OA guidebook written by patients and health professionals for patients, an enhanced initial consultation with a general practitioner (GP), and subsequent follow-up with a practice nurse (up to four consultations) in a dedicated nurse-led OA clinic. In addition a practice e-template was developed to record quality measures of care derived from a systematic review of quality indicators for OA [15,16]. The Management of OsteoArthritis in Consultations (MOSAICS) trial compared the model OA consultation with usual care over a 12-month period. This paper reports the economic evaluation alongside the MOSAICS trial to assess the cost-effectiveness of the model OA consultation compared with usual care in patients who consult with OA.

Methods
The economic evaluation was conducted alongside a twoarm prospective pragmatic cluster randomized controlled trial in eight general practices in Cheshire, Shropshire and Staffordshire, UK. The protocol has been previously published [15]. The eight practices were randomized to receive either the model OA consultation or usual care (control). Additional details of the intervention can be found in the supplementary data, section on the model OA consultation and supplementary Fig. S1, available at Rheumatology online. The trial on which the present study is based was approved by the North West 1 Research Ethics Committee, Cheshire (REC reference: 10/H1017/ 76) and was monitored by an Independent Trial Steering Committee and Data Monitoring Committee (Trial registration number ISRCTN06984617); no additional ethical approval was required for this study.
The primary outcome measure for the trial was the 12-item Short Form (SF-12) physical component score [17]. The health economic analysis initially took the form of a costconsequence analysis where a description of all the important results relating to costs and consequences [(clinical outcomes, EuroQoL-5D (EQ-5D), Short Form Six Dimension (SF-6D), ICEpop CAPability measure for Adults (ICECAP-A)] were reported. Subsequently, an incremental costutility analysis using the quality adjusted life year (QALY) as an outcome measure was undertaken from a UK National Health Service (NHS) perspective.

Resource use and costs
Information on resource use and time off work due to joint problems was collected from the postal MOSAICS consultation questionnaires completed by participants at 6 and 12 months' follow-up. NHS costs included primary and secondary care contacts, investigations, medication and contacts with other health care professionals such as physiotherapists and occupational therapists. Questions on participant's personal expenditure focused on private health care use and over-the-counter treatments [15].
In order to value resource use, unit costs were obtained from standard sources such as the Unit Costs of Health and Social Care [18], the British National Formulary [19] and NHS Reference Costs [20] and applied to resource use data. Due to the lack of nationally representative unit cost estimates for private health care, this care was costed as the NHS equivalent. To obtain the cost of the model OA consultation, information on the resources used to deliver the intervention was obtained from patient records collected throughout the trial. To generate the intervention cost, we obtained records collected as part of the intervention. These records showed that the average number of times that trial participants actually saw their nurse from available records was 2.3. We therefore made the assumption that everyone in the intervention arm who actually saw the nurse did so at least 2.3 times. GP costs were not included as part of the intervention since all participants, irrespective of trial intervention arm received usual care. Costs associated with over-the-counter medication were based on participant responses to the postal questionnaires. Unit costs of the resource use items are presented in supplementary Table S1, available at Rheumatology online, and are in 201213 prices.

Health and quality of life outcomes
All participants completed the three-level version of the EQ-5D questionnaire [21] at baseline, 3, 6 and 12 months. EQ-5D index scores were generated using the UK value set [22] to calculate QALYs over the 12-month period, which was used in the base case analysis. (The QALY is an outcome measure that takes into account both the quality and quantity of life associated https://academic.oup.com/rheumatology with an intervention). Participants also completed the SF-12 questionnaire [17], which was used to generate SF-6D scores [23], and the ICECAP-A questionnaire at baseline, 3, 6 and 12 months. The ICECAP-A is a measure of capability for adults, which aims to capture an individual's freedom to function in five key areas of their life: attachment, autonomy, enjoyment, stability and achievement [24].

Statistical analysis
Descriptive statistics were used to summarize the main health economic outcomes (EQ-5D, SF-6D and ICECAP-A). The costutility analysis was focused on determining the difference in costs and QALYs between the model OA consultation and usual care arms. To ensure all eligible participants were included in the study, missing EQ-5D, SF-6D, ICECAP-A and costs were imputed using multiple imputation methodology [25]. An imputation model was fitted and included 25 imputed datasets. Using EQ-5D scores, QALYs over a 12-month time period were calculated for each study participant with the area under the curve method [26]. Imbalances in baseline utility (EQ-5D) scores between the model OA consultation and usual care arms were controlled for using a multiple linear regression approach [27]. Mean costs associated with each trial arm were estimated, and due to the skewed nature of the costs, the difference in mean costs and 95% CIs were calculated using non-parametric bootstrapping [28]. Net monetary benefit (ÁE Â ÁC) was also estimated for each participant. This is defined as the change in effectiveness/QALYs (ÁE) multiplied by the cost-effectiveness threshold () minus the change in cost (ÁC) [29]. The threshold value () used for the estimation of net benefits was £20 000 per QALY.
The base case took the form of a costutility analysis from a NHS perspective and was conducted using multilevel linear modelling (as participants are clustered within GP practices), a method that has been recommended for the economic evaluation of cluster trials [30]. The dependent variables were net monetary benefits, costs, QALYs and cost of work absence. Independent variables included gender and baseline EQ-5D. Model estimates of the difference in costs, QALYs and net monetary benefits were used to derive an incremental cost per QALY gained and an incremental net monetary benefit.
Uncertainty was explored through the use of cost-effectiveness planes and cost-effectiveness acceptability curves; these plot the probability that the intervention is cost-effective against willingness to pay threshold values [31]. All analyses were carried out in Stata 12, Realcom and Microsoft Excel [3234]. Discounting was not required as the follow-up period was 12 months.

Sensitivity analysis
The sensitivity analysis had two main foci. The first was to explore uncertainties in the trial-based data by using QALYs generated from the SF-6D to obtain cost-effectiveness estimates. The second was to explore broader societal costs through the inclusion of private health care costs, for example, over-the-counter medication costs and private health care utilization costs as well as productivity costs. The human capital approach [35], was used to estimate productivity costs using data collected on employment status at every time point and days off work due to health. The average wage for each respondent was identified using UK Standard Occupational Classification coding and annual earnings data for each job type [36].

Results
A total of 525 participants across the eight randomized practices were recruited to the cluster trial. Of these, 288 participants were in the practices randomized to the model OA consultation arm and 237 in practices randomized to the usual care arm. The mean (S.D.) age across all patients was 67.3 years (10.4) and 59.5% were female. Follow-up rates at 6 and 12 months were 424 (81%) and 384 (73%), respectively, in the intervention and control arms. A total of 305 (58.1%) participants provided complete EQ-5D data at all time points.

Resource use
Primary care visits were generally higher in the usual care arm. Although the differences were not statistically significant, participants in the usual care arm had more visits to both the GP and the nurse. There was no significant difference in secondary care visits between trial arms with the exception of visits to the orthopaedic surgeon, which was significantly higher in the usual care arm. Approximately 65% of participants in the usual care arm had prescribed medication as compared with 59% in the model OA consultation arm (Table 1).

Health outcomes
Mean EQ-5D and SF-6D scores increased at all time points over the 12-month period in both the intervention and usual care arms indicating an improvement in health status over time. Although these scores were higher in the usual care arm, the differences were not statistically significant. When total QALYs were estimated, the usual care arm was associated with marginally higher overall QALYs (in respect to both the EQ-5D and SF-6D). Also, the results for the between-group differences in ICECAP-A showed similarly that the usual care arm showed slightly higher average levels of capability across follow-up (Table 2). EQ-5D scores were generally lower than SF-6D scores at all times.

Costs
Overall NHS and health care costs were also higher in the usual care group compared with the model OA consultation arm. However, these differences were not statistically significant (Table 3). Table 3 also gives a breakdown of costs for each intervention. Use of primary and secondary care, including visits to the orthopaedic surgeon, was greater in the usual care arm leading to higher costs.

Cost-effectiveness
Estimates from the regression model show that the intervention was associated with a lower cost (P = 0.705) and fewer QALYs (P = 0.786) (Table 4). At a willingness to pay threshold of £20 000 per QALY, the model OA consultation was associated with a 44% chance of being costeffective (Fig. 1).

Sensitivity analysis
When broader health care costs were used, the intervention was still less costly (P = 0.768) and less effective (P = 0.786) than the usual care arm (Table 5). Costutility analysis with QALYs generated from the SF-6D yielded similar results to the base case analysis, that is, the intervention was less costly (P = 0.705) and less effective (P = 0.187) than the usual care (Table 5). A total of 136 participants were in full-time employment at baseline. Of these, 40 participants, 20 in each trial arm, took time off over the 12-month period. Those in the intervention arm had fewer mean days off work than those in the usual care arm (P = 0.364). The associated productivity-related cost was lower in the intervention arm, but the difference was not statistically significant (Table 5).

Summary of main findings
This study sought to assess the cost-effectiveness of the model OA consultation for the implementation of NICE guidelines and support for self-management of OA in primary care. Our results reveal that there was a general increase in health status across the whole population as measured by the EQ-5D and SF-6D over the 12-month period, and although scores were slightly higher in the usual care arm, the difference was not statistically significant. SF-6D scores were higher than EQ-5D scores, a result which was in line with a previous study [37]. With the exception of visits to the orthopaedic surgeon, which was higher in the usual care group, there were no significant differences in all other secondary care resource use items between the trial arms. Participants in the usual care arm also reported more time off work compared with the intervention arm. The finding that the intervention may lead to reduced referrals and less time off work suggests a possible avenue for future research to identify individual patients who might benefit from the approach. The model OA consultation was less expensive than usual care and although this was not statistically significant, one might argue that the exclusion of the cost of training resulted in this lower cost. However, it should be noted that there are difficulties associated with the estimation of a per patient training cost within economic evaluation studies and also training received would be used for a large number of patients over a number of years, resulting in a low mean cost per patient.
The costutility analysis showed that the model OA consultation was less costly but less effective than usual care. Even though these differences are not statistically    significant, the established approach that is used in health economics is to conduct a cost-effectiveness analysis, focusing on the joint estimation of costs and outcomes [38]. At a cost-effectiveness threshold of £20 000 per QALY, the probability of the model OA consultation being cost-effective was low at 44%.
Strengths and weaknesses of the study A major strength of this study is that it is the first to consider the cost-effectiveness of the model OA consultation for the implementation of NICE guidelines and support for self-management of OA in primary care. Second, the study considered cost-effectiveness in a population consulting with peripheral joint pain and OA in primary care. Much of the cost-effectiveness studies for OA are based on studies of knee OA and, as such, our study considered a population where evidence of cost-effectiveness is lacking. Third, this study considered multiple outcomes and also considered outcomes broader than just healthrelated quality of life, which distinguishes it from other health economic evaluations, which consider a single outcome measure. This study also has some limitations. First is the fact that the main outcome for the health economic analysis was the three-level EQ-5D, which may not be sensitive to changes in this disease area [39]. The fivelevel version of the EQ-5D [40] is now available and this is likely to be more sensitive to change. Second, the difficulty associated with the estimation of a per-patient training cost led to the exclusion of this cost from the analysis.
Meaning of the study Implementing NICE guidelines using a model OA consultation in primary care may not lead to increased costs. Although the intervention may support some people with OA to remain in work and reduce the demand for orthopaedic surgery, overall it is unlikely to be cost-effective.