Functioning of Elder Muscle; Understanding Recovery

Overview

As people get older, the amount of skeletal muscle in the body can decrease. When the amount of this muscle in the body gets very low, there is an increased risk of falling, and not only is recovery to any injury slower, but more complications can be experienced following surgery, and patients may end up being more dependent on the help of others for meeting daily activities. However, it is not clear whether it is simply the amount of muscle that is in the body that is important for health, or whether it is the ability of muscle to function properly which is important. This research study is looking at the way muscles of frail older people function; not just how strong they are, but the amount of fats and protein that there are in muscle cells, and how the genes in the muscles are being expressed (genes being a collection of chemical information that carry the instructions for making the proteins a cell will need to function). We will also investigate whether recovery from hip fracture is impacted by the amount of muscle that there is in the body, and/or the functioning of this muscle.

Sarcopenia is the age-associated loss of skeletal muscle mass, muscle quality and strength, and is a contributive factor to frailty in older individuals. Meta-analyses suggest that individuals with sarcopenia appear to be at greater risk of hospitalisation (all cause), falls and fracture, with hip fracture following a fall being both a serious consequence of sarcopenia, as well as a risk factor for frailty syndrome. The short and longer term outcomes for patients who have a hip fracture following a fall are poor (post-operative complications, increased length of hospital stay, and increased mortality risk, institutionalisation and dependency, respectively), and these are understood to be largely due to the underlying vulnerability (frailty) of the people who sustain hip fractures, with poor recovery being compounded by the reduced muscle strength and low muscle mass common in those who are frail. As a consequence of research on the physiology of ageing muscles and sarcopenia, increasingly there is the possibility that novel agents (such as anabolic agents) could help to alleviate the frailty state in these patients and hence improve shorter and longer term outcomes. However, before novel interventions can be applied to patients with frailty and sarcopenia, such as those sustaining a hip fracture following a fall, an understanding of how the muscles of these patients are functioning at the cellular level, both in the injured and uninjured state is needed; which metabolic pathways are active and which are inactive, those which are enhanced and those which are impaired, so that treatments that are appropriate for the specific metabolic state of these patients can be selected. In recent years there have been advances in the understanding of the cellular physiology of the muscles of older people. However, few of the research studies carried out to date have analysed muscle collected from individuals who are as frail as the patients who present with hip fractures, or probed the metabolic changes which occur in the muscle following injury in this cohort. Findings from cross-sectional investigations on the healthy older person and prospective studies which try and mimic the muscle wasting seen in sarcopenia (using immobilisation or bed rest protocols) could prove useful in this endeavour. However, it is possible that results from these studies may not be generalizable to those who are frail (who may have other clinical problems and take multiple medications) and it is important that deep phenotyping of muscle from these patients is undertaken to address this knowledge gap. Across the whole study, including a cohort subset, a range of people with frailty, including those with cognitive impairment will be studied. Those with dementia or severe cognitive impairment tend to be those who are most frail and represent a high proportion of patients admitted with a hip fracture. If such patients are excluded, there is a risk of only observing muscle metabolic and histological changes seen in milder levels of frailty, which may not provide a comprehensive picture of sarcopenia. This is a frequent criticism and limitation of previous studies carried out in this field. Participants will be older individuals admitted to Nottingham University Hospital (UK) with a fractured hip sustained following a fall. In all participants, a muscle sample will be taken from their injured leg during the surgical repair to their hip, with the option for a muscle biopsy to be taken, whilst in theatre, from their uninjured leg using the Bergstrom technique. These samples will be analysed for intramyocellular lipid content and messenger ribonucleic acid (mRNA) expression of 384 gene targets spanning a number of cellular functions. In the week following surgery, measurements of thigh muscle thickness (Ultrasound imaging) and hand grip strength will be made, and an optional assessment of whole body muscle mass using the D3-creatine method will be offered. After discharge from hospital, patient-related outcomes measures will be obtained from medical notes and Three months after surgery, a set of questionnaires will be sent to the participant or their carer to complete. These will assess current mobility, dependency and wellbeing.