Introduction: Sarcopenia, the condition of decreased muscle mass as well as muscle strength, is reported to be risk factors for mortality and disability. On the other hands, the condition of decreased muscle strength, but retention of muscle mass is called Dynapenia and has received attention in recent years. Dynapenia is also highly associated with the risk of physical dysfunction and mortality. However, whether muscle mass or muscle strength affects clinical outcomes, including bone mass, bone turnover, fractures, spinal sagittal alignment, and LBP, is not fully understood. To clarify these clinical questions, in the current study, we aimed to elucidate the prevalence and characteristics of Sarcopenia and Dynapenia in patients with osteoporosis.
Methods: In this cross-sectional observational study, 279 patients with osteoporosis (45 men and 234 women;) aged >65 years (mean age: 74.8 years) were included. Skeletal muscle mass index (SMI) and grip strength were recorded in all patients. According to previous reports, patients were categorised into four groups: normal, pre-Sarcopenia, Dynapenia, and Sarcopenia. Age, number of vertebral fractures, bone mineral density (BMD), spinal sagittal alignment parameters, and low back pain (LBP) scores including Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ) and Oswestry Disability Index (ODI), were compared between the groups. Additionally, the correlation between SMI or grip strength and measurements were evaluated.
Results: The prevalence of pre-Sarcopenia, Dynapenia, and Sarcopenia were 14.4%, 30.2%, and 14.0%, respectively. The mean age in the pre-Sarcopenia, Dynapenia, and Sarcopenia groups was higher than those in the Normal group. Several LBP scores in the Sarcopenia and Dynapenia groups, showing decreased muscle strength were worse than those in Normal group. BMD in the pre-Sarcopenia and Sarcopenia groups, showing decreased muscle mass, were lower than those in Normal group, especially in women. In addition, BMD had weak positive correlations with SMI or grip strength. On the other hands, several LBP scores and several spinal sagittal alignment parameters had weak correlations with grip strength, but not SMI.
Discussion: More than 50% of patients with osteoporosis showed decreased muscle mass and/or muscle strength. Additionally, BMD might be associated with grip strength or skeletal muscle mass. On the other hands, LBP and spinal sagittal alignment might be associated with grip strength, but not skeletal muscle mass. When treating for the LBP and spinal sagittal alignment, we should focus on muscle strength rather than skeletal muscle mass.