Secular decline in limb bone strength among South African Africans during the 19th and 20th centuries

Abstract

ObjectivesSouth African Africans have been reported to have experienced negative or null secular trends in stature and other measures of skeletal structure across the 19th and 20th centuries, presumably due to poor living conditions during a time of intensifying racial discrimination. Here, we investigate whether any secular trend is apparent in limb bone strength during the same period.Materials and MethodsCadaver‐derived skeletons (n = 221) were analyzed from female and male South African Africans who were born between 1839 and 1970, lived in and around Johannesburg, and died between 1925 and 1991 when they were 17–90 years of age. For each skeleton, a humerus and femur were scanned using computed tomography, and mid‐diaphyseal cross‐sectional geometric properties were calculated and scaled according to body size.ResultsIn general linear mixed models accounting for sex, age at death, and skeletal element, year of birth was a significant (p < .05) negative predictor of size‐standardized mid‐diaphyseal cortical area (a proxy for resistance to axial loading) and polar moment of area (a proxy for resistance to bending and torsion), indicating a temporal trend toward diminishing limb bone strength. No significant interactions were detected between year of birth and age at death, suggesting that the decline in limb bone strength was mainly due to changes in skeletal maturation rather than severity of age‐related bone loss.DiscussionLimb bone strength is thus potentially another feature of the skeletal biology of South African Africans that was compromised by poor living conditions during the 19th and 20th centuries.

Variation, sexual dimorphism, and enlargement of the frontal sinus with age in adult South Africans

“…A previous CT study of the long bones (humerus and femur) of this individual show notable cortical bone thinning consistent with advanced osteoporosis (Wallace et al, 2020) (Figure 5). The mid‐diaphyseal cross‐sectional geometric properties of total subperiosteal area (mm 2 ) and cortical area (mm 2 ) for the humerus and femur of this individual and the other South Africans from the Dart Collection were calculated by Wallace et al (2020) from DICOM files using the BoneJ plugin (Doube et al, 2010) for ImageJ software (NIH, Bethesda, MD). A comparison of cortical to total subperiosteal area (percent cortical area) provides an indication of relative cortical thickness or the cross‐sectional internal resistance of a bone to compression and tension (Wainwright et al, 1976).…”

“…Similarly, the overall cross‐sectional area of the humerus of this individual is moderately large in comparison to values for the entire combined sex sample, whereas her percent cortical area is notably low (Table 6 and Figure 6) The total subperiosteal and cortical areas of the femur of this particular individual are 474.4 mm 2 and 243.7 mm 2 respectively, and the femoral percent cortical area is 51.4. The corresponding averages recorded by Wallace et al (2020): Table 1) for a small sample ( n = 4) of females ≥80 years of age are 495.0 mm 2 and 253.0 mm 2 . As such, this particular individual possesses a femur that is but exiguously smaller than average for her group in overall cross‐sectional area, and also small in cortical area.…”

“…The total subperiosteal and cortical areas of the humerus of this particular individual are 286.1 mm 2 and 126.6 mm 2 , and the percent cortical area is 44.2. The corresponding averages recorded by Wallace et al (2020: Table 1) for a small sample ( n = 4) of females ≥80 years of age are 271.0 mm 2 and 133.0 mm 2 . As such, this particular individual possesses a humerus that is larger than average for her age group in overall cross‐sectional area, but small in cortical area.…”

“…Nevertheless, it is perhaps instructive to examine the distribution of sinus volumes among the populations examined by these studies in order to discern whether any geographic trends might be discerned that are not affected by methodological differences. F I G U R E 6 The combined sex South African sample distributions of total subperiosteal area and percent cortical area for the humerus and femur (data recorded by Wallace et al, 2020). The 80 year-old female values are indicated by the yellow bars.…”

“…T A B L E 6 Long bone cortical properties of the 80 year-old female in relation to the black South African sample recorded byWallace et al (2020).…”