Factor of Risk for Fracture - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 133

Select Activity or Event of Interest
(e.g. fall impact, lifting a heavy load)

Determine Applied Load: Determine Failure Load

Depends on:
• Specific Activity
•

Depends on:
• Bone Mineral Density
•

External Forces Bone Size & Shape

• Anthropometry (e.g.

height and weight)

• Microarchitecture

• Damage Accumulation
• • Muscle Forces

•

Degree of Mineralization

Soft Tissue Padding or
Attenuation

Loading Direction
• Loading Mode (e.g.
bending, torsion,
compression)

•

• Loading Rate

Φ < 1

,
No Fracture

If

Calculate Factor of Risk:

Applied Load

Φ =

1 ,
Fracture

Φ≥

If

Failure Load

Fig. 1 Schematic of the process for determining the factor of risk. The applied load and failure
load should both be representative of the same activity or event, giving the factor of risk specific
to that activity or event. Determinants of applied load and failure load are noted. Theoretically, if
accurately determined, the factor of risk will indicate whether fracture will occur

height and weight. In addition, relatively few loading conditions have been studied
using factor of risk. For example, studies of wrist fractures have used only a
forward fall with loading on the outstretched hand; studies of vertebral fractures
have examined standing and forward flexion with and without lifting a weight; and
the majority of studies of hip fractures have examined a single sideways fall
condition. There is a need to examine a greater variety of loading conditions to
study the full spectrum of activities and situations that may lead to fractures.

1.2 Estimating Whole Bone Strength in Vivo

The denominator of factor of risk, bone failure load or strength, may be determined
in several ways. Generally, human cadaveric specimens are measured with one or