Mechanical properties, density and quantitative CT scan data of trabecular bone with and without metastases
Introduction
With over 1.2 million new cases of cancer each year in the United States alone and at least 7–27% of cancer patients expected to have bone metastases (Michaeli et al., 1999; Greenlee et al., 2001), pathologic fracture is a serious problem. However, current guidelines for assessing risk of pathologic fracture are inadequate (Cheng et al., 1980; Hipp et al., 1992; Keene et al., 1986). A better understanding of the effect of metastases on bone mechanical properties may help improve fracture risk assessment.
Metastatic lesions cause bone destruction through disruption of the bone remodeling sequence (Kanis, 1995; Orr et al., 1995). Increased turnover, an imbalance between resorption and deposition, and even an uncoupling of bone formation and resorption can occur. These processes result in pathologic changes in bone density and mechanical properties.
The density of trabecular bone has been related to the mechanical properties and quantitative computed tomography (QCT) data of bone without metastatic disease (Ciarelli et al., 1991; Keyak et al., 1994). If similar relationships can be found for trabecular bone with metastases, these relationships may form the foundation for clinically useful technologies for assessing the risk of pathologic fracture. However, little work has been done to evaluate the effect of tumors on trabecular bone. Von Stechow et al. (2003) showed that both trabecular bone with metastases and osteoporotic trabecular bone can be modeled using constitutive relations for porous foams. Hipp et al. (1992) noted significant degradation of the elastic modulus of trabecular bone with metastases but could not determine whether the relationships between mechanical properties and density differ with metastatic involvement.
To improve our understanding of the effect of metastases on trabecular bone and to evaluate the potential for using QCT to evaluate bone with metastatic lesions, this study identified and compared relationships between the mechanical properties, apparent ash density (ρash), and QCT data of trabecular bone with and without metastases.
Section snippets
Methods
Twelve distal femora were obtained: four had lytic and/or blastic metastases (group L); four had no metastases but were from donors who died from breast, prostate, or lung cancer (group NL); and four were from donors with no cancer (group NC) (Table 1, Fig. 1). Specimens were stored at −15°C when not in use. Each specimen was cut transversely 5–7 cm proximal to the distal end of the femoral condyles. The transverse plane was defined as the plane perpendicular to the proximal–distal line of the
Results
After reviewing the test data for accidental yielding and/or failure during nondestructive testing, 49 cubes were available for determining E, 50 for Sy, and 52 for Su (Table 2). E, Sy, Su, ρash and ρQCT were not significantly different between groups (E, p⩾0.97; Sy, p=0.44; Su, p=0.35; ρash, p=0.07; ρQCT, p=0.06). However, the differences for ρash and ρQCT were only marginally insignificant, and statistical power was low (0.36 and 0.38, respectively).
Strong power relationships that did not
Discussion
Metastases may alter the mechanical properties of trabecular bone by reducing the amount of bone, i.e. by reducing ρash, by changing the microarchitecture of the trabecular bone (Fig. 1), and/or by altering the composition of the bone tissue. This study has shown that metastatic disease does not significantly alter the relationships between the mechanical properties (E, Sy and Su) and ρash of distal femoral trabecular bone. ρash alone accounted for 79% and 88% of the variance in E and Su,
Acknowledgements
This work was funded by The Whitaker Foundation grant WF-25978 and by NIH grant 1R21CA79568-01.
References (12)
- et al.
Relationships between material properties and CT scan data of cortical bone with and without metastatic lesions
Medical Engineering and Physics
(2003) - et al.
Nonoperative management of femoral, humeral, and acetabular metastases in patients with breast carcinoma
Cancer
(1980) - et al.
Evaluation of orthogonal mechanical properties and density of human trabecular bone from the major metaphyseal regions with materials testing and computed tomography
Journal of Orthopaedic Research
(1991) - et al.
Cancer statistics, 2001
CA A Cancer Journal for Clinicians
(2001) - et al.
Mechanical properties of trabecular bone within and adjacent to osseous metastases
Journal of Bone and Mineral Research
(1992) Bone and cancerpathophysiology and treatment of metastases
Bone
(1995)