Participants were recruited from orthopedic patients who visited Nishi-Isahaya Hospital and voluntarily enrolled in this observational study. Written informed consent forms were available in Japanese to ensure complete understanding, and all participants provided written informed consent before examinations. This study was approved by the Ethics Committee of Tokyo Professional University of Health Sciences (project registration number: TPU-23-029).
The study sample included 109 older outpatients ≥ 65 years of age with orthopedic diseases. Our power analysis showed that the sample size was sufficient for our statistical analyzes (G*Power ver. 3.1. Test family [chi-square test], statistical test [goodness-of-fit test: contingency tables], effect size = 0.40, alpha error = 0.05, 1-beta error = 0.80, total sample size = 81). G*Power was designed as a general standalone power analysis program for statistical tests commonly used in social and behavioral research.13 All participants had sufficient cognitive function to complete the questionnaire and were asked if they had any comorbidities (heart disease, lung disease, stroke, or diabetes mellitus). Data on the diagnoses of musculoskeletal disorders (such as osteoarthritis, rheumatoid arthritis, and fractures) were collected. Pain sites (shoulder, elbow, wrist, finger, hip, knee, ankle, foot, upper back pain, middle back pain, and lower back pain) were recorded, but the severity of pain has not been assessed.
Height (m) and weight (kg) were measured with the participants wearing light clothing and no shoes. Body mass index (BMI) was calculated by dividing weight by height squared (kg/m2). Muscle mass was measured by bioelectrical impedance analysis (BIA) using InBody 430 (InBody Japan Inc., Tokyo, Japan). The BIA method requires participants to step onto a platform and remain in the standing position for approximately 30 seconds. Appendicular skeletal muscle mass index (AMI) was calculated as the sum of the muscle mass of the four limbs. Absolute appendicular muscle mass was converted to AMI, which was calculated by dividing the absolute appendicular muscle mass by the square of height in meters squared (kg/m2).
The grip strength of the dominant hand was measured using a Jamar hydraulic hand dynamometer (Jafayette Instrument Company, Inc., Jafayette, IN, USA). The best performance from two attempts was accepted. Walking speed was calculated as the time required for participants to complete a distance of 10-m at their usual pace (usual walking speed; average of two trials). Participants were classified as having sarcopenia based on their muscle mass, muscle strength, and physical performance. The classification was based on the recommendations of the Asian Working Group for Sarcopenia (AWGS).14 These recommendations define sarcopenia as age > 60 years, low handgrip strength (< 28 kg and 18 kg in men and women, respectively) and/or slow walking speed (< 1.0 m/s), and low AMI (< 7.0 kg/m2 and 5.7 kg/m2 in men and women, respectively). “Sarcopenia” was defined as the presence of low muscle mass, low muscle strength or poor physical performance, while “severe sarcopenia” was defined the presence of all three conditions. “Non-sarcopenia” was defined as absence of low muscle strength, low muscle mass, and poor physical performance.
We used the Tokyo Metropolitan Institute of Gerontology Index of Competence (TMIG-IC) to measure participants’ high-functional capacity.15 We used the TMIG-IC because it was developed for older Japanese individuals and has been widely used in the Japan community.15 The TMIG-IC is a 13-item multidimensional scale consisting of three subscales: IADL (five items), Intellectual activity (four items), and Social roles (four items) (Fig. 1). The answer for each item was either ‘‘yes’’ (able to do, 1 point) or ‘‘no’’ (unable to do, 0 points); the maximum score was 13 points. The IADL subscale scores range from 0 to 5 points, the intellectual activity subscale scores range from 0 to 4 points, and social role subscale scores range from 0 to 4 points; higher scores reflected higher skill levels. A score of one or more below the total scores on these subscales indicated the presence of disability in the given domain. A score of 4/5 or less on the IADL or 3/4 or less on intellectual activity or social roles was considered to indicate disability in this subscale.16
Statistical Analysis
We used the Shapiro–Wilk test for normality. Comparisons of variables among the severe sarcopenia, sarcopenia, and non-sarcopenia groups were performed using one-way way ANOVA for continuous variables or Fisher’s exact test for categorical variables. The association between sarcopenia and disability was assessed using logistic regression analysis adjusted for age, sex, BMI and comorbidities. The Hosmer–Lemeshow test was used to assess the difference between the observed and predicted prevalence in the logistic regression analysis. Odds ratios (OR) and 95% confidence intervals (CIs) were calculated. Statistical significance was set at P < 0.05. All statistical analyses were performed using IBM SPSS Statistics, version 27 (IBM Corp., Armonk, NY, USA).