Bone Mass (von Döbeln–Rocha anthropometric estimate)

Why use it

In full anthropometric profiling, bone is the compartment that cannot be reached by skinfolds or girths. This equation provides it from two caliper measurements, allowing the fractionation of body mass to be completed without imaging.

About

Estimates the mass of the skeleton from stature and two bone breadths — the biestyloid diameter at the wrist and the bicondylar diameter at the femur — measured with a sliding caliper. Its purpose is to close the four-component anthropometric model, in which body mass is partitioned into fat, muscle, bone and residual; it exists so that the residual can be computed, not as a measure of bone health.

When to use

• Completing a four- or five-component anthropometric fractionation of body mass
• Sports and kinanthropometric profiling where the skeletal compartment is required
• Research settings where DXA is unavailable and a bone estimate is needed for modelling

Formula

Pearls & pitfalls

• Measure the diameters with a sliding caliper, firmly enough to compress the soft tissue onto bone: under-pressure is the commonest source of error and inflates the estimate.
• The biestyloid diameter is taken across the radial and ulnar styloid processes with the wrist in slight flexion; the bicondylar femur across the epicondyles with the knee flexed to 90 degrees.
• Skeletal mass is a comparatively stable compartment in adults, so a large change between two sessions in one person means a measurement problem, not a physiological one.
• The equation is scaled to stature squared, so an error in height propagates more strongly than an error in either diameter.

Next steps

If the clinical question is bone health, mineral density or fracture risk, this estimate does not answer it — request DXA densitometry. If the question is body-composition fractionation, carry the result into the residual calculation along with fat mass and muscle mass.

Evidence

Von Döbeln proposed estimating skeletal mass from stature and bone breadths in 1964; Rocha published the modified coefficients in 1975, and that form is the one carried into the kinanthropometric literature and used to complete four-component fractionation. The method has never been validated against DXA to the standard of the fat and muscle compartments, which is why it is presented here as a modelling estimate only.

References

1. von Döbeln W. Anthropometric determination of fat-free body weight. Acta Med Scand. 1964;165(1):37-40. — link
2. Rocha MSL. Peso ósseo do brasileiro de ambos os sexos de 17 a 25 anos. Arq Anat Antropol. 1975;1:445-451. — link
3. Martin AD, Drinkwater DT. Variability in the measures of body fat: assumptions or technique? Sports Med. 1991;11(5):277-288. — link
4. Kanis JA, et al. Diagnosis of osteoporosis and assessment of fracture risk. Lancet. 2002;359(9321):1929-1936. — link