Ethics
The study protocol conformed to the ethics guidelines of the Declaration of Helsinki, as reflected in prior approval given by the institutional review board of Munakata Suikokai General Hospital. Informed consent from patients was obtained using an opt-out approach.
Patients
We did a cross-sectional study and assessed 100 ambulatory patients when they came to our hospital (Munakata Suikoukai General Hospital, Japan) for osteoporosis treatment between January 2018 and December 2018. We summarized inclusion and exclusion criteria in Table1. According to the Japanese Society for Bone and Mineral Research, we diagnosed osteoporosis and osteopenia [10].
Diagnosis of sarcopenia
We assessed sarcopenia according to the Asian Working Group for Sarcopenia guidelines [14]. 1) Cutoff values for handgrip strength are <26 kg for men and <18 kg for women. The cutoff value for walking speed is the usual gait speed of <0.8 m/s. Patients with either grip strength or walking speed less than the cutoff value are suspected to have sarcopenia. 2) In cases of suspected sarcopenia, the next-step is to evaluate muscle mass. Cutoff values for skeletal muscle mass index (SMI) are 7.0 kg/m2 for men and 5.7 kg/m2 for women measured by bioimpedance analysis. 3) Patients with less than the muscle mass cutoff are diagnosed with sarcopenia.
Outcome measures
Bone mineral density
Areal BMD of the posterior-anterior lumbar spine was measured by dual-energy x-ray absorptiometry using a Hologic QDR 4500A densitometer (Hologic, Waltham, MA). All scans of an individual subject were performed using the same densitometer. Quality control measurements were performed daily with a Hologic anthropomorphic spine phantom.
Isometric knee extension strength
Isometric knee extension strength on the dominant side was measured at discharge using a manual muscle strength monitor (Mobie; Sakai Medical Co., Ltd.) [11]. Patients sat on the edge of a bed with their feet not touching the floor and with their arms crossed in front of their body. The highest value of three assessments was used in the analysis.
Evaluation of Pain
Low back pain, pain from the buttocks to lower limbs, and numbness of the buttocks to lower limbs were evaluated using a Visual Analogue Scale (VAS) with 100 being an extreme amount of pain and 0 no pain.
Spinal Alignment
The patient was radiographed at the clavicle position [12]. LL, PI, PT, and sacral slope (SS) were measured from various lumbar spine lateral views (Figure1). We defined adult spinal deformity as PT>30 degrees, based on the SRS-Schwab classification [9].
Disease-specific QOL Measure for Patients with Low Back Pain
The Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) was designed for the assessment of disease specific QOL and for low back pain and lumbar spinal disease. It is a disease-specific tool that contains 25 items tapping into five subscales: low back pain (four items), lumbar function (six items), walking ability (five items), social function (four items), and mental health (seven items). The score for each subscale ranges from 0 to 100, with higher scores indicating better condition. The JOABPEQ is used in Japan and other countries, and its reliability has been proven [12]. Recently, the JOABPEQ is used to assess low back pain patients and can be used to assess other lumbar spine disorders such as lumbar canal stenosis, lumbar disc herniation, and neuropathic pain in a low back pain patient (12).
Statistical analysis
All the statistical analysis were performed by JMP Version 14.0 statistical software (SAS Institute Inc., Cary, NC, USA), with P < 0.05 considered statistically significant in all cases. Differences in patient characteristics at the time of visit and JOABPEQ results between the sarcopenia and non-sarcopenia groups were evaluated by the Willcoxon rank-sum test. QOL is affected by age, history of vertebral fracture and adult spinal deformity, so we used analysis of covariance to adjust these factors. Pearson correlation coefficient was used to determine the correlation between SMI and spinal alignment parameters or the JOABPEQ. The Pearson correlation coefficient measures the strength of the linear relationship [15,16]. It ranges from -1 to 1. The correlation coefficient value may be expressed from very weak to very strong in increments of 0.2. 0 to 0.19 is considered very weak, either positive or negative, and 0.8 to 1.0 is considered very strong. A multivariate Cox regression analysis with stepwise variable selection was used to identify independent variables associated with low back pain in the JOABPEQ. All data are expressed as either median, (interquartile range [IQR]), range, or average, standard error.