Sarcopenia and Bone Mineral Density Relation in Hip Fracture Patients

Introduction

Sarcopenia is a progressive and common skeletal muscle disorder, that causes progressive loss of age-related muscle strength and mass, associated with an increased likelihood of outcomes such as falls, fractures, physical disability, and death. Estimates place the overall prevalence of sarcopenia in older adults at approximately 10-40%. Osteoporosis and sarcopenia, prevalent conditions of advanced age, have comparable etiologies and risk factors. The co-occurrence of these illnesses amplifies the incidence of falls, fractures, and mortality. While EWGSOP2 and AWGS guidelines recommend using validated technologies like bioimpedance analysis, dual X-ray absorptiometry (DXA), computed tomography and magnetic resonance imaging for evaluating sarcopenia, these may not be feasible in certain clinical situations. The International Society of Physical and Rehabilitation Medicine (ISPRM) has suggested a different algorithm to diagnose sarcopenia by measuring anterior thigh muscle thickness using ultrasound (US). This method is easy to obtain, does not involve radiation, and is less expensive.

The study uses the sonographic thigh adjustment ratio (STAR) to look into the link between sarcopenia and bone mineral density (BMD) in people who have had a hip fracture. Additionally, the study explores the association between sociodemographic factors, laboratory results, comorbidities, and these measurements.

1. Material and Method

2.1. Study Design and Population

An observational cross-sectional study was conducted on hip fracture patients attending the orthopedic clinics of a tertiary hospital in Kastamonu, Turkey. The study was approved by the local Institutional Review Board (2024-KAEK-26- 01, February 7th, 2024). Written informed consent was obtained from all participants. Subjects were consecutively recruited during the first 24 hours of hospital stay from May to November 2023. Sarcopenia was diagnosed using the ISarcoPRM algorithm, which considers low grip strength and low STAR values. Inclusion criteria included the detection of low muscle strength with a hand dynamometer and patients scheduled for hip fracture surgery. Exclusion criteria included terminal disease, acute or chronic neuromuscular disease, and traumatic or pathological hip fracture.

2.2 Handgrip strength

Handgrip strength was measured using a Jamar dynamometer (Baseline Hydraulic Hand dynamometer, Irvington, NY) with participants performing two trials with both hands. The highest value obtained was used for analysis. Cut-off values for Turkish people were <22 kg for women and <32 kg for men.

2.3. Laboratory Data

The Kastamonu Research and Training Hospital Laboratory Service, a medical laboratory service with Turkey Accreditation System accreditation, performed laboratory analyses on-site. Total protein, albumin, and 25-OH-vitamin D3 (25[OH]D) levels were collected. The normal range for total protein is 6.6-8.3 g/dl, for albumin, it is 3.5-5.2 g/dl, and for 25[OH]D levels: deficient (<20 ng/dl), insufficient (20-30 ng/dl), or normal (>30 ng/dl).

2.4. Dual Energy X-ray Absorptiometry (DXA)

Non-fracture proximal femur neck BMD (g/cm2) and T-scores were obtained using the same DXA (Stratos DR (DMS) Mauguio, France). The World Health Organization (WHO) categorizes patients based on their lumbar spine, femoral neck, and/or total hip bone mineral density (BMD). Patients are classified as normal if their T score exceeds -1 standard deviation (SD), as osteopenic if it falls between -2.5 SD and -1 SD, and as osteoporotic if it equals or falls below - 2.5 SD. As only a small number of subjects presented with osteoporosis, "severe" osteopenia (-2.5 SD<T score ≤-2.0 SD) was added to the classification in our population.

2.5. Muscle Ultrasound(US) Measurements

Evaluation with the US (Mylab 25Gold, Esaote, Genova, Italy) was planned to be performed by the same clinicians using a 5-15 MHz linear probe in B mode, with the technique reported in previous studies. The thickness of the anterior thigh muscles was assessed in the non-fractured limb, between the anterior superior iliac spine and the proximal end of the patella with the patient lying in the supine position and the US probe placed perpendicularly with slight pressure. Once the muscle tissue was identified, the distance was measured between the femoral cortex and the most superficial muscle fascia (7). Measurements were obtained on two separate occasions by two different clinicians. The average value of a set of four consecutive measurements was calculated to assess the STAR value.

2.6. Sarcopenia Diagnosis

Sarcopenia was diagnosed according to the ISarcoPRM algorithm using low grip strength (< 22 kg for females and <32 kg for males) with low STAR values (<1 for females and <1.4 for males). The chair stand test, which is also recommended as a power and performance test to assess anterior thigh muscle function is unsuitable for this study's population with hip fractures. The STAR value was utilized to confirm the diagnosis. It is calculated by dividing the anterior thigh muscle thickness (mm) by the body mass value (kg/m2). According to prior research, the study used the established sonographic thigh adjustment ratio values of 1.0 for female patients and 1.4 for male subjects.

2.7. Statistical Analyses

Statistical analyses were performed with the SPSS v22 (SPSS Inc., Chicago, IL, USA) package. Quantitative data were summarized by mean ± standard deviation and median (minimum-maximum), while qualitative data were depicted as frequency and percentage. The Shapiro-Wilk test was performed to assess the normal distribution of the data, while the Levene test tested the homogeneity of variances. Two-sided independent t-tests were used to compare the mean for observations between sarcopenic and normal patients. Linear regressions and the Pearson coefficient were used to investigate associations and examine the relationship between parametric variables. Spearman's rho was used to investigate associations between nonparametric variables.