The Journal of Bone and Joint Surgery, Vol 72, Issue 5 689-700, Copyright © 1990 by Journal of Bone and Joint Surgery, Inc
The use of quantitative computed tomography to estimate risk of fracture of the hip from falls
JC Lotz and WC Hayes
Department of Orthopaedic Surgery, Charles A. Dana Research Institute, Beth Israel Hospital, Boston, Massachusetts 02115.
We conducted an in vitro investigation of the loads and energies needed to
fracture the proximal part of the femur in twelve fresh cadavera under
loading conditions simulating one particular type of fall. The fracture
loads ranged from 778 to 4,040 newtons and the work to fracture, from five
to fifty-one joules. We also investigated the relationship between the
fracture loads and several potential indices of bone strength, which were
measured non-invasively at the subcapital, basic-cervical, and
intertrochanteric regions with quantitative computed tomography. A very
high positive correlation with the fracture load resulted from use of an
intertrochanteric index--the product of the average trabecular
computed-tomography number and the total cross-sectional area of the bone
(R2 = 0.93, standard error of estimate = 295 newtons, and p less than
0.00001). We expect the use of this parameter to result in improved
assessments of the degree of osteoporosis and of the component of risk of
fracture of the hip that is associated with bone strength. However, the
measured work to fracture for the isolated femur was an order of magnitude
smaller than estimates of the energy available during a typical fall (about
450 joules), suggesting that energy absorbed during falling and impact,
rather than bone strength, may be the dominant factors in the biomechanics
of fracture of the hip.
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