Association between low lean mass and low bone mineral density in 653 women with hip fracture: does the definition of low lean mass matter?
OBJECTIVE
Loss of both muscle and bone mass results in fragility fractures with increased risk of disability, poor quality of life, and death. Our aim was to assess the association between low appendicular lean mass (aLM) defined according to different criteria and low bone mineral density (BMD) in hip-fracture women.


METHODS
Six hundred fifty-three women admitted to our rehabilitation hospital underwent dual energy X-ray absorptiometry 19.1 ± 4.1 (mean ± SD) days after hip-fracture occurrence. Low aLM was identified according to either Baumgartner's definition (aLM/height2less than two standard deviations below the mean of the young reference group) or FNIH criteria: aLM <15.02 kg, or aLM adjusted for body mass index (BMI) <0.512. Low BMD was diagnosed with a T-score <-2.5 at the unfractured femoral neck.


RESULTS
Using Baumgartner's definition, the association between low aLM/height2and low BMD was significant: χ2(1, n = 653) = 8.52 (p = 0.004), but it was erased by adjustments for age and fat mass. Using the FNIH definition the association between low aLM and low BMD was significant: χ2(1, n = 653) = 42.5 (p < 0.001), and it was confirmed after adjustment for age and fat mass (p < 0.001). With the FNIH definition based on aLM/BMI ratio the association between low aLM/BMI ratio and low BMD was nonsignificant: χ2(1, n = 653) = 0.003 (p = 0.957).


CONCLUSIONS
The association between low aLM and low BMD in women with hip fracture dramatically depends on the adopted definition of low aLM. FNIH threshold for aLM (<15.02 kg) emerges as a useful tool to capture women with damage of the muscle-bone unit.
Division of Physical and Rehabilitation Medicine, Osteoporosis Research Center, Presidio Sanitario San Camillo, Fondazione Opera San Camillo, Strada Santa Margherita 136, 10131, Turin, Italy. Marco.di.monaco@alice.it.|Department of Culture, Politics, and Society, University of Turin, Lungodora Siena 100, 10100, Turin, Italy. Marco.di.monaco@alice.it.
Marco
http://orcid.org/0000-0002-9519-608X
M
Di Monaco
Division of Physical and Rehabilitation Medicine, Osteoporosis Research Center, Presidio Sanitario San Camillo, Fondazione Opera San Camillo, Strada Santa Margherita 136, 10131, Turin, Italy.|Department of Culture, Politics, and Society, University of Turin, Lungodora Siena 100, 10100, Turin, Italy.
Carlotta
C
Castiglioni
Division of Physical and Rehabilitation Medicine, Osteoporosis Research Center, Presidio Sanitario San Camillo, Fondazione Opera San Camillo, Strada Santa Margherita 136, 10131, Turin, Italy.|Department of Culture, Politics, and Society, University of Turin, Lungodora Siena 100, 10100, Turin, Italy.
Roberto
R
Di Monaco
Division of Physical and Rehabilitation Medicine, Osteoporosis Research Center, Presidio Sanitario San Camillo, Fondazione Opera San Camillo, Strada Santa Margherita 136, 10131, Turin, Italy.|Department of Culture, Politics, and Society, University of Turin, Lungodora Siena 100, 10100, Turin, Italy.
Rosa
R
Tappero
D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D015992:Body Mass Index; D015519:Bone Density / Q000502:physiology*; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging / Q000473:pathology; D006620:Hip Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D016015:Logistic Models; D010384:Pelvic Bones; D011788:Quality of Life; D013851:Thinness / Q000503:physiopathology
Body composition; Dual energy X-ray absorptiometry; Hip fracture; Osteoporosis; Sarcopenia