Limb bone bilateral asymmetry: variability and commonality among modern humans

Abstract

Humans demonstrate species-wide bilateral asymmetry in long bone dimensions. Previous studies have documented greater right-biases in upper limb bone dimensionsdespecially in length and diaphyseal breadthdas well as more asymmetry in the upper limb when compared with the lower limb. Some studies have reported left-bias in lower limb bone dimensions, which, combined with the contralateral asymmetry in upper limbs, has been termed ''crossed symmetry.'' The examination of sexual dimorphism and population variation in asymmetry has been limited.This study re-examines these topics in a large, geographically and temporally diverse sample of 780 Holocene adult humans. Fourteen bilateral measures were taken, including maximum lengths, articular and peri-articular breadths, and diaphyseal breadths of the femur, tibia, humerus, and radius. Dimensions were converted into percentage directional (%DA) and absolute (%AA) asymmetries. Results reveal that average diaphyseal breadths in both the upper and lower limbs have the greatest absolute and directional asymmetry among all populations, with lower asymmetry evident in maximum lengths or articular dimensions. Upper limb bones demonstrate a systematic right-bias in all dimensions, while lower limb elements have biases closer to zero %DA, but with slight left-bias in diaphyseal breadths and femoral length. Crossed symmetry exists within individuals between similar dimensions of the upper and lower limbs. Females have more asymmetric and right-biased upper limb maximum lengths, while males have greater humeral diaphyseal and head breadth %DAs. The lower limb demonstrates little sexual dimorphism in asymmetry. Industrial groups exhibit relatively less asymmetry than pre-industrial humans and less dimorphism in asymmetry. A mixture of influences from both genetic and behavioral factors is implicated as the source of these patterns.

Are the Left and Right Proximal Femurs Symmetric?

“…This limitation was mitigated by using a systematic method and high-resolution pictures (degree of error \ 1 mm), and by using a projection that is used clinically (AP). Additionally, the measured asymmetry of the femoral head in this study falls within that reported in the literature (Table 8) [3,21,28,45].…”

“…The investigators who have examined symmetry have studied bone properties and cortex thickness [28,32,36,40], with few studying dimensions [3,28]. The clinical impact of asymmetry is subtle, as the assumption of symmetry is pervasive.…”

“…Absolute differences were obtained by subtracting the result of the smaller of the specimens (left or right) from the result of the larger. Percent absolute asymmetry or percent difference was determined using the following documented method: percent asymmetry = (maximum À minimum)/(average of maximum and minimum) 9 100 [3]. This variable was used to define the magnitude of asymmetry.…”

“…proximal femoral dimensions such as the femoral head diameter have a small sample size [28] or do not take into account age, gender, or arthritic deformities [3].…”

Asymptomatic parental mosaicism for osteogenesis imperfecta associated with a new splice site mutation in COL1A2

“…We report normal bone morphology in the mosaic father, evaluated by DXA scan and HR‐pQCT. The asymmetry in body composition with slightly reduced size of left‐sided extremities in the father is unlikely to result from the OI mosaicism as this phenomenon may be due to a number of factors 19 and is not a distinctive feature of OI.…”