Comorbidity and functional outcomes after hip fracture: an umbrella review protocol : JBI Evidence Synthesis

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Comorbidity and functional outcomes after hip fracture: an umbrella review protocol

Nguyen, David1; Lightfoot, David2; Journeay, W. Shane3,4,5

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JBI Evidence Synthesis 21(5):p 1001-1008, May 2023. | DOI: 10.11124/JBIES-22-00110
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Osteoporotic hip fractures are on the rise and represent a major medical event in the aging population. Approximately 310,000 people were hospitalized for hip fracture in the United States in 2003 and one-third of hip-fracture patients go on to receive a hip replacement.1,2 Although multifactorial, a significant contributor to hip fracture is a decline in bone mineral density, which puts elderly people at an exponentially higher likelihood of suffering a hip fracture.3 There is also evidence that elderly individuals who have had a hip fracture are at increased risk of both short- and long-term excess all-cause mortality regardless of their sex.4 Furthermore, patients who have suffered a hip fracture are at an increased risk of poor functional recovery, which may be influenced by a host of factors, including age, functional status at baseline, and comorbid conditions. Overall, the functional impact on the individual after hip fracture can be devastating, with 40% of patients unable to ambulate after 1 year and 60% of patients having difficulty with at least 1 activity of daily living.5 Therefore, it is essential that patients with hip fractures receive appropriate rehabilitation, as failure to do so leads to increased health care costs, decreased survival, and reduced function.6

Recovery after a hip fracture is crucial in facilitating the optimization of function and improving quality of life. However, patients who have suffered a hip fracture seldom present without other comorbid conditions. In fact, 1 study showed that out of 19,682 hip-fracture patients, 14% of the young (18 to 39 years) and 45% of the middle aged (40 to 65 years) patients had at least 1 comorbidity.7 When examining the effect of comorbidity on the elderly, one can expect that many patients will exhibit frailty and be burdened with increased medical complexity and associated disability.8 Not only do elderly patients tend to have more comorbidities at the time of fracture, but an observational study also found that all comorbidities increased in elderly patients who suffered a hip fracture between 1986 and 2005.9 One study found that after a hip fracture, patients with 3 or more impaired organ systems had an 8-fold increased risk of being discharged to a nursing home compared to patients with 2 or fewer organ-system impairments.10 This highlights the burden of comorbidity complicating hip-fracture management. To quantify the degree of comorbid illness, indices such as the Charlson Comorbidity Index have been developed.11 These indices and the association of comorbidity have been studied in the context of mortality and recovering ambulation after hip fracture;8,12 however, the association of comorbidities with functional outcomes is less clearly understood.

Comorbidities can interfere with regaining functional ability, such as ambulation, and lead to challenging recovery and rehabilitation efforts.7 Insight on prognostic factors, such as medical comorbidities on functional outcomes, are valuable in directing patient care. Functional outcomes scores are often used to track patient recovery. Two of the most widely used scores are the Functional Independence Measure (FIM)13,14 and the Barthel index (BI),15 which inform clinicians on the level of disability patients experience carrying out activities of daily living. Although both scores are similar, a study examining stroke rehabilitation found that the FIM is more commonly used in North America while the BI has been used more frequently in Europe.16 Notwithstanding, both functional measures are routinely collected for the purposes of measuring functional outcomes and have implications affecting hospital resource provision as well as policies for the population at large.17 One study that examined the BI as a proxy for recovering activities of daily living after hip fracture found that recovery was related to comorbidities and cognitive status.18 Another study concluded that a high comorbidity score could indicate clinical instability and, thus, would prevent hip-fracture patients from benefiting from and engaging in sustained rehabilitation.19 Therefore, the role of comorbidity on functional recovery is nuanced and warrants further research.

As hip fractures are so common, a number of systematic reviews examining functional outcomes have been conducted. A study by Kabboord et al.20 reported a comprehensive approach to comorbidity and functional outcome after hip fracture and stroke. They included studies that used valid scales of comorbidity and reported on functional outcome <6 months from the acute event. They reported a modest association between comorbidity and functional outcome. One limitation of this study was the inclusion of patients who had a hip fracture and patients recovering from stroke. While the authors report that this enabled them to study the impact of comorbidity broadly, it led to limitations in their analysis as the functional outcomes after stroke and hip fracture are often quite different.

Van der Sijp et al.21 examined long-term functional outcomes in patients with a proximal femur fracture. They evaluated 23 factors identified in 31 studies for functional prognostic value and concluded age, comorbidity, cognition, and pre-fracture function were supported by substantial evidence. Among the studies included, they indicated a wide variety of approaches in assessing comorbidity as well as functional outcomes. It is because of the range of outcomes in the literature among largely observational data that they suggested further work is required on prognostic factors after hip fracture.

In a systematic review by Xu et al.22 the authors identified multiple predictors of poor functional outcomes, including hand-grip strength and frailty, which were reported as the most important. They also included the presence of comorbidities as a predictor of poor functional outcomes in 8/8 studies included their review. In this review, it was not clear how these primary studies measured comorbidity burden or what functional outcomes were reported.

In another study examining prognostic factors of functional outcome after hip fracture, Sheehan et al.23 grouped some of the identified factors as comorbidities. They then assigned 2 factors of cognition and anemia a weak evidence level and Parkinson’s disease an inconclusive evidence level for functional prognostication.

An umbrella review is a suitable study design to provide insight into the role of comorbidity on functional outcomes after a hip fracture as it provides an opportunity to synthesize evidence from systematic reviews. An umbrella review will highlight the evidence base surrounding the association of comorbidity and functional outcome and identify where prior research is consistent or contradictory, as well as allow exploration into the reasons for such findings.24 A preliminary search of the literature has revealed existing systematic reviews that examined the association of comorbidity with functional outcome in the setting of hip fracture.8,20–22 This umbrella review aims to collate all relevant systematic reviews that report on the association of comorbidity with functional outcomes in the hip-fracture population. Conclusions drawn from an umbrella review may lead to informing practices in rehabilitative settings, directing resources towards patients with increased medical complexity, and further understanding the association between prognostic factors and functional recovery through future studies. At present, based on our preliminary screening of the literature in PubMed and Google Scholar, and a search of registered systematic review databases such as PROSPERO, there are currently no umbrella reviews or published protocols examining the association of comorbidities with functional outcomes after hip fracture.

The objective of this umbrella review is to examine the association of comorbidity with functional outcome after hip fracture.

Review question

What is the association of comorbidity with functional outcomes after hip fracture?

Inclusion criteria


This umbrella review will include systematic reviews reporting on adult (≥18 years old) patients who have suffered a hip fracture.

Phenomena of interest

The exposure of interest is the burden of comorbidity in patients. Comorbidity scores such as the Charlson Comorbidity Index,11 and lists of comorbidities will be included as indicators of comorbidity burden. It is recognized that comorbidity may range from none to multiple comorbidities or low to high comorbidity burden as indicated by a score or scale.


The outcome of interest is measures of functional outcome after hip fracture. Specific functional outcome measures of interest include, but are not limited to, the FIM and BI as well as reported indicators of ambulation. The FIM is a standardized indicator of function, and such data can be readily obtained from rehabilitation reporting systems13,14; it can also be used as a clinical marker to reflect progression in self-care, transfers, and mobility. Similarly, the BI also represents a global measure of function across a number of domains, including activities of daily living and mobility.15 Furthermore, we plan to include all outcomes related to ambulation, which can be determined in many ways, including formal distance and timed tests, or included as a dichotomous outcome after hip fracture, such as the restoration of independent ambulation or inability to ambulate. As there is considerable debate about whether mortality is a functional outcome, and given that we are most interested in daily function and mobility, we will not examine mortality after hip fracture in this review.

Types of studies

Systematic reviews that include cohort studies, published at any time, reporting on comorbidity and functional outcomes (eg, FIM, BI, ambulation) after hip fracture will be included in this review. Studies will be considered systematic reviews if the authors use a clear and reproducible methodology, including a description of the search strategy and defined eligibility criteria to select primary studies and synthesis of results.25 We will include systematic reviews of quantitative primary studies that include cohort studies with or without a meta-analysis. We will not include qualitative syntheses in this review.

The following will be excluded: study protocols, papers that are not a systematic review, narrative reviews, papers not reporting on comorbidities, and papers not reporting on functional outcomes.


The JBI methodology for umbrella reviews will be followed.24,26 The results of the search will be reported and presented as a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) diagram.27 This protocol has been registered in PROSPERO (CRD42021272502).

Search strategy

A health science librarian (DL), will conduct the literature search. The following keywords will be used: “hip fracture,” “femur,” “comorbidity(ies),” “chronic disease” (see Appendix I). Applicable filters will be applied, including systematic review publications published at any time.

MEDLINE (Ovid), Embase, and the Cochrane Database of Systematic Reviews will be searched using indexed words and keywords appearing in the title, abstract, and author-supplied keywords. Reference lists for each of the included studies will be searched for additional eligible works.

The purpose of this review is to identify all systematic reviews, including cohort studies of functional outcomes after hip fracture. A librarian from Library Services at Unity Health Toronto (DL) will assist in the development and conduct of the search to identify all systematic reviews of hip fractures and comorbidities for screening. Systematic reviews will be identified using the Scottish Inter-professional Guidelines Networks’ validated filter.

The number of results will be calculated using EndNote Online (Clarivate Analytics, PA, USA) as well as the automatic deduplication function in Covidence (Veritas Health Innovation, Melbourne, Australia). Papers published in languages other than English will be excluded due to limited language and translation resources for this review.

Study selection

Once the references are imported into Covidence, 2 independent reviewers will screen the titles and abstracts against the eligibility criteria. Where there is uncertainty or disagreement regarding the appropriateness of a study, the reference will be included for full-text review. The full texts of potentially eligible articles will then be assessed against the eligibility criteria by the same 2 reviewers. Disagreements at this stage will be resolved by discussion amongst the 2 reviewers, or with a third reviewer if consensus cannot be reached.

Assessment of methodological quality

The retrieved systematic reviews will be assessed for quality by 2 independent reviewers. Quality assessment will be performed using the JBI critical appraisal checklist for systematic reviews and research syntheses.24,26 Eleven criteria on the JBI checklist will be assessed and assigned a result (ie, yes/no/other specific response) applicable to the criteria. The result from the JBI appraisal will be used to classify each review into high, moderate, low, or critically low quality. The JBI checklist will yield a score that will be classified as follows: 0–3 points = critically low quality; 4–6 points = low quality; 7–9 points = moderate quality; 10-11 points = high quality. The overall quality of the systematic review will not be used for inclusion/exclusion purposes for this umbrella review. Instead, it will be used to guide interpretations of the umbrella review results and inform limitations. Any disagreements between the 2 reviewers will be resolved by discussion or, if a consensus cannot be reached, with a third reviewer. The results of this quality assessment will be presented in tabular format and included in the results section of the umbrella review manuscript.

Data extraction

A data extraction table will be developed and piloted using 2 to 3 articles to minimize potential error. Based on the pilot results, adjustments will be made before proceeding to the full data extraction phase. Data extraction will be performed by 2 independent reviewers on the selected systematic review articles. The following study characteristics will be collected: citation information, objectives/type of review, participant details, setting and context, date range/number of databases searched, publication date range of studies included in the review used to inform functional outcome, number/type/country of origin of studies included in each review, instrument used to appraise the primary studies and quality rating, outcomes reported that are relevant to the review question, method of synthesis/analysis used to synthesize the evidence, and additional comments on the included studies.25

Results of the included reviews, including comorbidity measures, functional outcomes, quantitative data on heterogeneity, as well as result of meta-analysis (if conducted), will be extracted.

Comorbidity scores, such as the Charlson Comorbidity Index,11 and lists of comorbidities will be included as indicators of comorbidity burden as reported in each included review. We will further classify comorbidities as None, <5 or >5 if reported as lists or quantified. Specific functional outcome measures of interest include, but are not limited to, FIM and BI as well as reported indicators of ambulation. The FIM and BI are quantitative scores and will be reported as is (with range) in the source paper. Indicators of ambulation will be reported in the systematic review with the anticipated outcomes, including independence with ambulation (dichotomous) or details reported on the ambulation evaluation (eg, distance walked in a 2-minute walk test). Any disagreements will be resolved through discussion. If consensus cannot be achieved, a third reviewer will be consulted to reach a conclusion. The data will be presented in tabular format.

Data synthesis

We will provide a summary of the quality of each included review using the JBI checklist. A summary of the extracted data will be presented in tabular format and a narrative synthesis will be performed on the collected systematic reviews that meet the inclusion criteria. Any research studies that are included in multiple systematic reviews (ie, a study captured by more than one included systematic review) will be identified and clearly stated.


This research was funded by a Providence Healthcare Foundation Research Grant awarded to WSJ for fracture rehabilitation research. The funder did not have a role in the development of the protocol or conduct of this research.

WSJ is the JD Irving Endowed Chair in Occupational Medicine at Dalhousie Medicine New Brunswick, Dalhousie University.

Author contributions

DN and WSJ were involved in the conception and development of the research plan and protocol, reviewing the literature and writing and reviewing of the protocol. DL contributed to the refinement of the search strategy and protocol development.

Appendix I: Search strategy



Search Query Results retrieved
1 exp hip fracture/ 25,820
2 ((fragility or femur or femoral) adj2 fracture:).mp. 37,678
3 exp Osteoporotic Fractures/ 6558
4 (Femur* or femoral or hip*).tw. [textword] 497,995
5 3 and 4 2549
6 1 or 2 or 5 52,193
7 exp Comorbidity/ 118,832
8 (comorbid: or co-morbid: or co morbid:).af. [all fields for major concept] 279,755
9 (coexisting or co-existing or co existing).ti,ab,kf. 32,029
10 (Preexisting or pre-existing or pre existing).ti,ab,kf. 62,538
11 Chronic Disease/ 270,238
12 (chronic disease* or chronic illness*).ti,ab,kf. 89,375
13 7 or 8 or 9 or 10 or 11 or 12 690,527
14 6 and 13 3275
15 Meta-Analysis as Topic/ [SIGN validated filter for systematic reviews] 20,233
16 meta analy$.tw. 208,915
17 metaanaly$.tw. 2305
18 Meta-Analysis/ 140,446
19 (systematic adj (review$1 or overview$1)).tw. 214,883
20 exp Review Literature as Topic/ 17,582
21 or/15-20 359,265
22 cochrane.ab. 102,041
23 embase.ab. 114,356
24 (psychlit or psyclit).ab. 915
25 (psychinfo or psycinfo).ab. 43,969
26 (cinahl or cinhal).ab. 34,613
27 science citation index.ab. 3350
28 bids.ab. 574
29 cancerlit.ab. 635
30 or/22-29 184,805
31 reference list$.ab. 19,697
32 bibliograph$.ab. 19,817
33 hand-search$.ab. 7579
34 relevant journals.ab. 1250
35 manual search$.ab. 5014
36 or/31-35 47,860
37 selection criteria.ab. 32,526
38 data extraction.ab. 25,254
39 37 or 38 55,337
40 Review/ 2,849,602
41 39 and 40 30,436
42 Comment/ 925,042
43 Letter/ 1,148,968
44 Editorial/ 578,281
45 animal/ 6,903,917
46 human/ 19,629,934
47 45 not (45 and 46) 4,844,580
48 or/42-44,47 6,763,282
49 21 or 30 or 36 or 41 430,081
50 49 not 48 408,725
51 14 and 50 101


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comorbidity; functional outcomes; hip fracture; rehabilitation; systematic review

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