Impact of biomechanical loading on bone mineral density explored in weight-bearing and non-weight-bearing bones of people living with HIV: An observational study

Abstract Background Bone demineralization in people living with HIV (PLWH) could be ameliorated by biomechanical loading of the musculoskeletal system which exerts an osteogenic stimulus. Therefore, we determined whether the bone mineral density (BMD) varied in weight-bearing and non-weight-bearing bones in PLWH, and its relationship with some risk factors (age, body mass index-BMI, duration of HIV, and height) of bone loss Method A cross-sectional observational study of 503 people living with HIV (PLWH) selected by convenience sampling at Enugu State University Teaching Hospital, Nigeria, was conducted from September 2015 to September 2016. The BMD of toe or weight-bearing (BMD toe ) and thumb or non-weight-bearing (BMD thumb ) bones were measured with Xrite 331C densitometer and compared using independent t-test. Impact of the risk factors of bone loss and their relationships with the BMD were compared across the sexes using multivariate, and univariate regression analyses, at p < 0.05,two-tailed. Result The 352 HAART-experienced participants comprised of females(265/75.2%), males(62/17.6%) and others(25/7.1%) without gender specificity. Their demographics were: mean age = 37.2 ± 9.79years, BMI = 25.6 ± 5.06kg/m 2 and duration of HAART-exposure = 4.54 ± 3.51 years. The BMD toe (-0.16 ± 0.65g/cm 3 ) was higher(p < 0.05) than BMD thumb (-0.93 ± 0.44g/cm 3 ), and differed across BMI classes(p = 0.000003;d = 0.998) unlike BMD thumb , and was accounted for in post hoc analysis by normal weight versus underweight BMI classes(p = < 0.001). BMD toe was positively correlated with height (r = 0.13,r 2 = 0.0169;p < 0.05), and males were taller than females (p < 0.001). Females accounted for 90%(9/10) cases of osteopenia and 71.43% (5/7) osteoporosis. Males were older(p = 0.002) while females had greater BMI(p = 0.02), lower median BMD toe (p = 0.005) and BMD thumb (p = 0.005). Conclusion Significant BMD variations across BMI classes in weight-bearing unlike non-weight-bearing bones is explained by biomechanical loading. Higher BMD in weight-bearing bones(toe), and lower BMD toe in underweight BMI class (implying sub-optimal loading) suggest a role for osteogenic stimulus and fat metabolism in bone loss. Females being younger/heavier should have greater loading and osteogenic stimulus reinforced by lesser age-related BMD changes. Males being taller should have greater bone marrow adipose tissues that promote osteogenesis through paracrine mechanisms. Greater height and BMD in males than females are explained by sexual dimorphism in skeletal length and density. The greater BMD observed in the females’ weight-bearing than non-weight-bearing bones implies that loading also ameliorates the females’ physiological tendencies towards lower BMD.