Second metacarpal cross-sectional geometry: Rehabilitating a circular argument

Area of Science:

• Human Biology
• Bioarchaeology
• Forensic Anthropology

Background:

• Radiogrammetry of the second metacarpal is used to assess bone growth, aging, asymmetry, and osteoporosis risk.
• Current methods use algebraic models (circular or elliptical) on radiographic images.

Purpose of the Study:

• To test the accuracy of circular and elliptical radiogrammetric models against actual bone measurements.
• To derive new equations to correct for systematic bias in radiogrammetric analysis.

Main Methods:

• Analysis of 356 second metacarpals from an archaeological sample.
• Comparison of geometric variations measured directly versus estimated by circular and elliptical models.
• Development of reduced major axis regression equations to adjust for radiogrammetric error.

Main Results:

• Both circular and elliptical models significantly overestimate actual bone measurements, including total area, cortical area, and bending rigidity.
• The elliptical model showed a greater degree of systematic bias compared to the circular model.
• Newly derived regression equations successfully corrected for radiogrammetric bias, showing no significant difference between actual and predicted values in a validation sample.

Conclusions:

• Standard radiogrammetric models introduce significant bias in estimating metacarpal dimensions and rigidity.
• The accuracy of these models is influenced by sample composition and shape variation.
• The derived regression equations provide a method to adjust for radiogrammetric error, enhancing the reliability of bone analysis.