Background
Traditional systematic reviewing methods tend to focus on measurement and reporting of programme effectiveness, or cost effectiveness in the case of health economic literature. Findings often show mixed results and do not provide a clear indication of why the invention worked under a certain setting. The realist research question is often summarised as “What works for whom, under what circumstances, how and why?” Programme theories are developed that make assumptions about how interventions work in practice. These programme theories are then tested against empirical evidence to populate a theoretical framework. The empirical evidence will support, contradict, or lead to modification of the programme theories through a highly iterative process. With regards to complex social interventions, realist review methods can provide a rich, detailed understanding of the intervention itself, which can be utilised during planning and implementation stages. The aim of this review is to inform the development of a novel multidisciplinary intervention for rehabilitation after hip fracture in the elderly, as part of a larger feasibility trial.

Methods
An ongoing realist review of multidisciplinary rehabilitation packages after hip fracture in the elderly will be used as a case study to show this method's application. Programme theories of behavioural economics (eg, welfare judgments, expected utility gains, and choice architecture) and theories relating to additional costs (eg, due to setting, delivery team, staff training, and additional resources such as time, equipment, or technology) with implications for cost effectiveness were developed as part of the Fracture in the Elderly Multidisciplinary Rehabilitation (FEMuR) realist review. Medline, Embase, AMED, CINAHL, Cochrane Library, and PEDro were searched for studies including the population (elderly adults with proximal hip fracture), intervention (multidisciplinary rehabilitation), and outcomes of interest (mortality, pain, functional status, quality of life, health utility, health service use, costs, patients' experiences). Identified references were transferred to bibliographic software (Endnote) and duplicates removed. References were included if they involved the population of interest, used any type of rehabilitation programme to support re-enablement after proximal hip fracture, and contained any elements of the developed programme theories. With regards to economic evidence, references were excluded if they were not full economic assessments or cost comparative studies. After independent screening by two reviewers and discussion of discrepancies, the full articles were then categorised independently by two reviewers on the basis of their conceptual richness into three categories: rich, thick, and thin. Any discrepancies were resolved by discussion. Data were then extracted until a particular programme theory reached saturation, whereby the inclusion of further references does not add anything new to the understanding of the theory.

Findings
11 294 references were screened after de-duplication. 620 were included for categorisation. Of these, 20 economic articles were categorised as thin and six as thick. Thick articles discussed implications of setting and delivery team with regards to costs and cost analyses. Thin articles reported economic analyses; however, no explicit programme theories were apparent. None contained elements of behavioural economic theories.

Interpretation
The inclusion of health economic programme theories in the FEMuR realist review provides insight into economic mechanisms and contextual factors of multidisciplinary rehabilitation of hip fracture in the elderly, which has previously not been explored. This finding is of particular importance because previous research recommendations from National Institute for Health and Care Excellence guidance relevant to hip fracture rehabilitation interventions specifically highlight the need for evidence of cost effectiveness.