With social development and medical advances, the average life expectancy is increasing significantly, which leads to an accelerating population aging process. It is predicted that approximately 17% of the global population is expected to be over 65 years old by 2050 (1). The growing demand for surgery among older patients is driven by a combination of increased life expectancy and improved surgical safety (2). The bone mass and muscle mass of the organism start to decrease significantly from approximately fifty years of age, and they can interact with each other through paracrine and endocrine signals (3). Osteoporosis, muscle atrophy, and many other reasons have put the older persons at high risk for fractures (4, 5). Hip fractures have become a worldwide public health threat, with data indicating that the 1-year mortality rate after hip fracture surgery may exceed 20% (6). It is estimated that by 2050, the population of hip fractures is predicted to reach 4.5 million worldwide, and nearly 30% will occur in China (7). Due to the unsatisfactory quality of life and inevitable complications associated with conservative treatment, surgery is now mostly preferred when the physical condition of the patient is compatible with the surgical indications. Risk stratification of geriatric patients appears to be necessary regardless of therapeutic measures.

It has long been widely accepted that advancing age is an increasing risk contributor to undesirable postoperative outcomes. However, the emerging perspective holds that frailty (age-related impairment of physical reserves and resilience) seems to be a better predictor of complication occurrence and increased mortality in comparison to age (8, 9). Frailty is characterized by a multi-dimensional and dynamic condition of increased vulnerability and decreased resistance to stress in the older persons as a result of reduced physiological reserves. Current perspectives suggest that a combination of chronic inflammatory responses, nutritional and metabolic imbalances, oxidative stress, and changes in hormone levels are involved in the development of frailty (10–12). Frailty often affects multiple systems, such as the neuromuscular, endocrine, and immune systems (13). In a weakened state, a relatively small stimulus can cause an increased probability of a series of negative clinical events. Frailty assessment can reflect the ability of older adults to regulate the internal environmental stability and resist stress. Therefore, early identification of frailty has become an essential component of health promotion in geriatric aging.

Now-a-days, a modest but growing number of clinical studies have researched the association between frailty and undesirable outcomes in geriatric hip fracture patients. However, these findings are not convincing owing to small samples and inconsistent results, and there has not been a meta-analysis to systematically and quantitatively synthesize the results of multiple independent studies. Hence, we perform the systematic review and meta-analysis to assess the status of frailty assessment in clinical practice. Our objectives were to assess the predictive value of frailty for adverse outcomes among geriatric hip fracture patients (death, complications, adverse discharge destination, and prolonged length of hospital stays).

The concept of frailty was first introduced by the Federal Conference on Aging in the United States and usually refers to the dynamic process of declining multisystem function (25). There are various methods for frailty evaluation, but the uniform standard has not been identified. Among the articles we included, various assessment tools derived from Frailty Index, Frailty Phenotype, and Clinical Frailty Scale were mainly included. Most focused on several aspects such as endurance, fatigue, mobility, and disease. Hip fracture is a relatively serious type of fracture and can be even the last fracture of an individual's life. A possible reason for this is the increased risk of infection (Respiratory and urinary systems) and reduced cardiac function associated with prolonged bed rest (26).

Now-a-days, more researchers have focused on frailty screening in clinical practice. In a meta-analysis of 2,278 participants, the researchers evaluated that the frailty phenotype could be a valuable risk assessment tool for preoperative screening (27). Similarly, the results of our meta-analysis were consistent with the previous study, indicating that frailty evaluation should be applied to aged patients. Our study reconfirmed the predictive role of frailty on poor outcomes after a fracture. Hence, frailty can be considered as an intermediate step from self-care to disability. Early identification of frailty and prevention of frail elders toward disability will play an immensely prominent role in healthy aging.

In our meta-analysis, frail older were at a higher risk to suffer complications and prolonged hospital stays. In the study of the association between frailty and postoperative complications, I² was 77.4% and we found that I² was 0.0% in the respective subgroups. We considered that the reason was probably partly since the frailty assessment tool in Choi's study was Hip-MFS and the adjusted OR referred to the increased risk along with per 1 point increase in Hip-MFS. The hip fracture could be strong stress for elders. Weak physical conditions were more likely to lose stability under the impact of stress (13). In addition, frailty was associated with both short-term mortality and long-term mortality. In the study of the relationship between frailty and long-term mortality, we did subgroup analyses based on the region of the experiment and the type of study design. The results showed that frailty was a stronger predictor of mortality in the European and American studies and prospective studies. Although frail elders had no significant risk higher in adverse discharge destination in our research results. The study of Chan et al. had shown that seniors with higher frail scores were more likely to experience an adverse discharge destination (discharge to long-term care or death) (17). However, there was no significant difference in Thorne's study. One of the reasons may be that patients who previously lived in a nursing home and death were not included (23). Moreover, the number of studies and sample size were both small, and more research was required in the future to explore the predictive value of frailty on discharge destination.

Previous meta-analyses have demonstrated the relationship between frailty and surgical outcomes (27–29), but there are fewer pooled analyses on the specific population of hip fracture patients. Therefore, our study is dedicated to enriching this field of research. In our research, we have discovered that frailty might be a good predictor of adverse outcomes in aged hip fracture patients. Frail seniors are more vulnerable to suffer undesirable complications, increased mortality, and prolonged hospitalization. There are several limitations in our study which should be taken into consideration. First, not all articles are at a high level of quality. Low-quality (<7 scores) studies are also included in the analysis to access the results of larger samples and more studies. There may be comparability issues with the included studies. One of the conditions for evaluating cohort studies as comparable can be understood as whether the experiment is corrected for important confounding factors. We evaluated all articles, but inevitably, the poor comparability of the included articles leads to compromised veracity of the merged effects worth. Confounding factors in the article can have an impact on the study results. Therefore, we combined the adjusted ORs and confidence intervals for the analysis whenever possible, which would reduce the effect of confounding factors to some extent. Second, the measures of frailty assessment in the included 11 studies are inconsistent, contributing to the obvious heterogeneity across our studies. Third, only 2 studies are involved to explore the impact of frailty on discharge destination and prolonged hospitalization, which may affect the reliability of the conclusions. Additionally, the differences in study design might be a source of heterogeneity. Frailty is a non-specific state in which the organism is less responsive to internal and external environmental stressors. The gold standard on the assessment of debilitation has not yet been established. Differences in frailty assessment tools do account for a significant amount of heterogeneity, but we believe the results of this study are still informative. At last, prospective studies have stronger arguments and higher reliability than retrospective studies. However, the included 11 articles only involve 4 prospective studies.

Our study is not only intended to highlight the relationship between frailty and poor outcomes, but also to raise awareness of the importance of early identification and prevention of frailty. The prevalence of frailty in elders is currently high and is anticipated to increase further as global aging accelerates. According to statistics, the incidence of frailty among community-dwelling seniors fluctuated from 14.9 to 31.9%, which will vary with assessment tools (30). The prevalence of frailty in hospitalized geriatric patients is higher (31). A study data has shown that the likelihood of falling is 1.8 times higher for the frail than for the healthy elders (5). Concerning the strengths and implications of the study, our study suggests a significant correlation between preoperative frailty status and poor prognosis in aged hip fracture patients. Frailty seems to be more reflective of the physical condition of older individuals compared to age. The application of frailty assessment to geriatric patients is something that should be widely implemented in future clinical practice, and caring for frail geriatric patients and providing some early interventions may reverse the occurrence of poor outcomes. Current interventions for frailty include the following: exercise, nutritional supplementation, enhanced treatment of existing conditions, and medical injury reduction. We propose that there is a strong causal relationship between the events of frailty, falls, fractures, and the occurrence of postoperative adverse outcomes. Focusing on the frailty status of older adults will be important to promote healthy aging.

In summary, frailty, fall, fractures, and the increased risk of complications and mortality combine to constitute a series of causal associations that will have a serious threat to the health of older adults. In future medical practice, frailty has the potential to be an effective tool for risk stratification of aged patients and thus guide disease prevention and treatment.

This meta-analysis was conducted mainly to explore the impact of frailty on poor outcomes in hip fracture patients. We conclude that frailty is a good predictor for adverse complications, increased mortality, and prolonged hospitalization.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

YS and ZW retrieved the literature and independently evaluated the potentially eligible studies. They respectively extracted relevant data from the included articles and conducted the meta-analysis. HH provided assistance in the data analysis process. When disagreements arose, they discussed and consulted with the corresponding author (PZ) to reach a consensus. YS wrote this manuscript under the supervision and assistance of PZ. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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