Skeletal muscle is the amplest tissue within the anatomy in adults, in keeping with the Davis law (the corollary to the Wolff law for bone), muscles are generally remarkably plastic, with the flexibility to achieve or lose tissue playing on several factors. Muscle depletion commonly occurs with aging, chronic disease, and disuse, but may go unrecognized by clinicians .
Sarcopenia, first proposed by Irwin Rosenberg in 1989, is characterized by a progressive loss of muscle mass and is related to chronic disease. It reduces muscle strength and performance .
Sarcopenia—broadly defined as a significant loss of muscle mass and function—is increasingly identified as a crucial independent risk factor for varied adverse outcomes. These negative outcomes include physical disability, osteoporosis, fractures, prolonged hospital stay and re-admission. Subsequent, operational definitions also incorporate functional criteria (e.g., low muscle strength measured by hand grip strength) [2, 3].
In cirrhotic patients, it was reported that loss of rectus femoris muscle cross-sectional area (CSA) was encountered due to increased protein turnover and an imbalance between muscle protein synthesis and protein degradation. From a conceptual point of view, muscle mass assessment in these patients may help detect at-risk patients and predict the patient outcome. Furthermore, monitoring muscle mass may allow physicians to successfully identify patients who would benefit the foremost from tailored nutritional interventions [4, 5].
The diagnostic criteria for sarcopenia don't seem to be yet uniform. The diagnostic index for sarcopenia includes muscle mass, muscle strength (usually reflected by hand grip strength) and physical performance (usually reflected by gait speed) [2, 6].
Because muscle mass is considered to be one of the most important parameters for grading sarcopenia, its measurement techniques have received widespread concerns. The mostly used are Dual-energy X-ray absorptiometry (DXA) and bio-electrical impedance analysis (BIA). Computed tomography (CT) and magnetic resonance imaging (MRI) are nominated as the gold standard for assessing muscle mass because they clearly show the tissue structure. However, Ultrasound, being convenient and pocket-friendly, is usually recommended. Although the literature and guidelines suggest that the gold standard for muscle mass testing is CT or MRI, these two methods have some limitations, they're time-consuming expensive, and need specialized equipment, also CT has ionizing radiation hazards, because of these limitations, the employment of CT and MRI as a measuring tool for the muscle mass within the elderly has not yet peaked [7, 8].
When the target sarcopenic population is expected to be frail, elderly, and immobile, the imaging technique must be easily accessible, both geographically and physically, cheap, simple and can be done along the bedside, thus, rendering ultrasound a clearly better option than the previously mentioned modalities, specifically, as it offers a non-invasive, portable, and safe imaging technique, whilst having the extra benefits of maintaining image clarity, being widely utilized in medicine, familiar to clinicians, reliable and simply interpreted by the lay sonographer [9, 10].
However, several questions remain. First, should (or can) sarcopenia be diagnosed in single or composite anatomic sites, and second, which site or sites should be used? the selection of site, especially if only one peripheral site is employed, should otherwise be an appropriate surrogate marker of broader muscle mass, particularly appendicular muscle mass (ASM) or total muscle mass (TMM). However, evidence that ultrasound can accurately predict whole-body muscle mass is insufficient and it must be considered that not all peripheral muscles decline alike. As such, prediction equations for TMM (and ASM) from ultrasound-derived sites need further validation [11,12,13].
Measurement of the (quadriceps) rectus femoris (RF) cross-sectional area (CSA) is widely used as a marker for muscle size in clinical research. The rationale for these measures can be explained by its tolerability by participants, easily accessible position, simple method in acquiring its location accurately, and robust association with functional strength .
With ultrasound increasingly used as a good and valid muscle-imaging tool in liver cirrhosis, ultrasound based measurements cut-off points are progressively needed for both sexes, to assess the condition of an individual’s muscle, as well as help early and accurate detection of sarcopenia, this might help distinguish those at greater risk and aid in targeted treatment programs .
Few studies have focused on the importance of assessing upper limb muscles using ultrasound. For a far better understanding of the biceps muscle thickness (MT), cross-sectional area (CSA) and fat thickness (FT) measured by ultrasound in sarcopenic patients, a comparative analysis was performed between FT, MT, CSA of biceps, muscle mass, grip strength against the severity of sarcopenia .
The muscle thickness of the forearm was also significantly correlated to the grip strength . Positive correlations between CSA of the biceps brachii and SMI or grip strength were observed in both genders.
Therefore, there's an urgent need for a customary and uniform measurement of sarcopenia. Ultrasound is universally accustomed diagnose and follow-up within the clinic. It can distinguish muscle tissue from subcutaneous fat and show the thickness and cross-sectional area of muscle. It's a convenient, reliable and non-radiative technique, and might be performed at the bedside for those that cannot cooperate with DXA, CT or MRI. Compared with the above methods, the appliance of ultrasound is more common, and lots of people are more willing to just accept the ultrasound examination, which contains a great prospect within the application for sarcopenia. It's been got wind as a good method to assess muscle mass within the elderly .
The Foundation for the National Institutes of Health Sarcopenia Project  recommends specific cutoff points to spot populations with functional limitations related to sarcopenia. These evidence-based criteria recognize measures of low muscle strength (i.e., grip strength < 26 kg for men and < 16 kg for women) and low lean body mass (i.e., appendicular lean mass adjusted for body mass index [BMI; weight in kilograms divided by the square of height in meters] < 0.789 for men and < 0.512 for women) . These criteria were validated as predictive of future mobility impairment with a 3-year clinical follow-up , and this definition of muscle weakness appears to be a treatable symptom of sarcopenia .
The purpose of this study was to validate the utilization of ultrasound measurement as a measure of muscle mass and predictor of sarcopenia in liver cirrhosis patients and its relevance conventional prognostic scores for liver cirrhosis, like (MELD) scores similarly as detecting its effect on morbidity and mortality.