The Effect Of Sarcopenia On Bone Quality Assessed By Trabecular Bone Score (TBS)

Objective:Aging is associated with a number of structural and functional changes that can result in frailty,disability and death.The typical features of aging in the musculoskeletal system are a gradual deterioration of bone(osteoporosis)and a progressive decline in muscle mass and strength(sarcopenia).As the general population is aging worldwild,the incidence of osteoporosis and sarcopenia increasing rapidly.Osteoporosis and sarcopenia can result in adverse outcomes such as physical disability,poor quality of life,escalated costs of health care,and increased mortality,therefore pose a major clinical and public health burden.Many studies have provided evidence of a link between sarcopenia and osteoporotic fracture,but the majority of existing studies focus on the association between sarcopenia and bone mineral density(BMD),few have assessed the effect of sarcopenia on bone quality.The definition of osteoporosis implies a decrease in bone mass and a deterioration of bone architecture.However,its operational definition is limited to the assessment of BMD with a reference standard at the femoral neck.The evaluation of BMD as a prognostic tool lacks sensitivity to predict fracture over most reasonable assumptions.Trabecular bone score(TBS)is a new and non-invasive medical imaging technique that has been recently suggested to provide a measure of bone quality.It reflects an index of bone texture derived from the analysis of two-dimensional lumbar spine bone densitometry images,and it captures a component of fracture risk that is independent of BMD.The aim of our study is to investigate the association between sarcopenia and TBS,and the effect of muscle mass and hand grip strength on TBS.Methods:1.The clinical characteristics such as age,body weight,height,waist circumference,hip circumference,smoking,drinking and age of menopause were recorded.The level of fasting blood glucose,glycated hemoglobin,triglyceride,total cholesterol,high-density lipoprotein cholesterol and low-density lipoprotein cholesterol were also measured in the study subjects.2.The Hologic dual-energy X-ray absorptiometry(DXA)scanner was used to measure BMD at lumbar spine(LS),femoral neck(FN)and total hip(TH),total fat mass(FM),and total lean mass(LM).BMD for spine reflected the combined BMD of L1-L4.DXA can give regional measures for the limbs,and limb lean tissue mass(appendicular)can be used as a good proxy for muscle mass.Appendicular lean mass(aLM)was calculated as the sum of lean mass in the arms and legs.As absolute muscle mass correlates with height,the relative appendicular skeletal muscle mass(RASM)was was calculated as appendicular lean mass divided by height squared(aLM/height^2,kg/m^2).Percentage fat mass(PFM)was defined as the ratio of total body fat mass divided by body weight.All TBS measurements were performed through TBS iNsight(R) software using lumbar spine DXA files.The Jamar hydraulic hand dynamometer was used to assess muscle strength.Gait speed were determined by a timed 4-meter walk and participants were instructed at usual paces.Walking speed was calculated as the average of two usual-walking-pace attempts.Those walked slower than 0.8 meter/second were defined as slow walking speed.3.Descriptive data for the subject characteristics were shown as the mean±standard deviation or n(%).The association between body compositions,Handgrip strength and BMDs or TBS was determined using Pearson’s correlation analysis.We further applied multiple linear regression models for TBS and BMD analyses,using age,BMI,RASM,and Handgrip strength data.4.According to the European Working Group on Sarcopenia in Older people(EWGSOP),subjects were divided into 3 groups:control group,pre-sarcopenia group(characterized only by low muscle mass),sarcopenia group(defined by low muscle mass plus either low muscle strength or low physical performance).One-way ANOVA with Tukey post hoc analysis was performed to compare LM,aLM,RASM,Handgrip strength,BMD and TBS among control,presarcopenia and sarcopenia groups.Results:1.We presented unadjusted and adjusted correlation coefficients between body compositions,handgrip strength and BMDs or TBS.After adjustment for age and BMI,TBS correlated positively with LM,aLM,RASM in both sexes and with handgrip strength in women.2.After adjustment for age and BMI,BMDs at lumbar spine,femoral neck,and total hip correlated positively with RASM in men.No significant correlation was observed between BMD and RASM in women.Handgrip strength correlated positively with BMDs in women,but not in men.3.In the multiple linear regression model adjusted for age and BMI,both in men and women,RASM only associated positively with TBS(β＝0.347 in men,β＝0.462 in women,all P<0.001),no significant correlation was observed between RASM and BMDs.Interestingly,in women,handgrip strength showed the positive associations with both all evaluated BMDs and TBS,which were not observed in men.4.Regarding the significant relationship between muscle and BMD,bone quality.We further performed subgroup analyses by stages of sarcopenia such as presarcopenia,sarcopenia.Women with sarcopenia had lower TBS and BMDs at the sites evaluated.Men with sarcopenia also had lower BMDs only at femur neck and total hip.There was no significant difference in lumbar spine BMD and TBS among men with and without sarcopenia.Conclusion:1.After adjustment for age and BMI,BMDs correlated positively with RASM in men and handgrip strength in women.2.After adjustment for age and BMI,TBS correlated positively with RASM in both sexes and with handgrip strength in women.3.Women with sarcopenia had lower TBS and BMDs.