Factor structure of morphometric variables measured on six metacarpal bones

Bilateral symmetry of the human metacarpal: implications for sample size calculations

OBJECTIVE

The aim of this study was to assess the three-dimensional mechanical symmetry of the human second metacarpal and provide sample size estimates for future mechanical intervention studies of the metacarpal.

DESIGN

Bone densitometry and digital image analysis were used to assess the morphometric, geometric and densitometric symmetry of the second human metacarpal.

BACKGROUND

An assessment of the left-right mechanical symmetry of the human metacarpal is important in considering the suitability of using the contralateral metacarpal as a control and in providing sample size calculations for future studies involving a mechanical intervention to the metacarpal such as implantation of a metacarpophalangeal prosthesis.

METHODS

Metaphyseal sectional areas, diaphyseal cortical sectional areas, second moments of area, average periosteal and medullary radii and bone densities were measured at nine transverse levels for each of seven pairs of index metacarpals using computed tomography and bone densitometry. Polar Fourier regression was used to assess the morphometry of sectional periosteal and endosteal boundaries. Differences between clinically important left-right parameters were assessed.

RESULTS

Mean differences between clinically important left-right parameters were small (<3%) and similar to the degree of experimental precision. There were strong significant left-right correlations for the morphometric, geometric and densitometric parameters considered, indicating a high degree of bilateral mechanical symmetry.

CONCLUSIONS

The contralateral bone is a suitable control for mechanical intervention studies of the human metacarpal, and the use of bilateral pairing results in an important reduction in sample size.

RELEVANCE

Responses to mechanical interventions on the human metacarpal, such as implantation of a metacarpophalangeal prosthesis, are generally unknown. The degree of left-right mechanical symmetry in the human metacarpal provides a measure of the advantage of using paired design studies to address these questions.

Evidence on major gene control of cortical index in pedigree data from Middle Dalmatia, Croatia

It was recently reported that the inheritance of the metacarpal cortical index (CI) in the Chuvashian population can be described in terms of a major gene (MG) model. By applying transmission probability tests, the hypothesis was accepted that not only baseline level of CI but also its sex-specific dependence on age were under control of the same putative large-effect gene. Using a pedigree sample from the population of the islands of Middle Dalmatia, Croatia (847 observed individuals in 278 pedigrees), data are presented to support the above findings. The following hypotheses were accepted: (i) inheritance of baseline CI in the Croatian population can be attributed to the effect of a MG responsible for about 42% of the variation; (ii) the same MG takes part in the control of the dependence of CI on age, particularly the age at onset of involutive bone changes (inflection point), and of the rate of decrease in CI with age (slope coefficient). Issues related to the assortative mating effect on CI and the determination of the most parsimonious model are discussed.