Optimizing Fracture Management: Correlating the Physical and Mechanical Properties of Bone to Computed Tomography to Generate an Estimate of Bone Quality

Non-invasive estimates of bone quality are of great interest as they could potentially improve the diagnosis and treatments for bone disorders, such as osteoporosis, and could aid in preoperative planning of surgical interventions, improving patient outcomes in orthopaedic trauma.

Quantitative computed tomography (QCT) is currently being investigated as a method of estimating structural bone mineral content (sBMC) and, thus, bone quality. However, the reported correlations between QCT and sBMC have been variable and the relationships reported between sBMC and the apparent elastic modulus (E*) of bone have been even more variable.

A series of investigations are presented, relating QCT, sBMC, apparent density (ρ_APP) and the E* of bone. These studies were performed with the ultimate objective of determining the appropriateness of QCT as a predictor of the E* of bone and whether the E* of bone could be predicted from information regarding the sBMC and ρ_APP.

The repeatability of the CT scanner and the protocol for scanner calibration were studied to determine the optimal method for calibrating QCT scans. It was determined that the repeatability of the scanner was excellent and that the optimal method for scanner calibration was to image the standards in a volume of water equivalent to the soft tissue volume of the patient. However, as scans in air are easier to facilitate, an experimental protocol was developed to determine a relationship between the amount of soft tissue and the required correction to apply to the values of the calibration performed in air.

A linear trend was observed between the BMC determined from the QCT (BMC_HU) and the sBMC from ashing (R² = 0.49). No relationship was observed between the BMC_HU and the E* (R² < 0.10). A strong correlation was observed between the sBMC and the ρ_APP (R² = 0.97), as well as between the BMC and E* and the ρ_APP and the E* (R² = 0.71 and 0.77, respectively). However, there was still a relatively large amount of variation in the E* that was not explained by these relationships. It was concluded that parameters other than the sBMC and ρ_APP, such as the micro-architecture, need to be included in future studies for a better estimation of bone quality.

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Year

Entry

1966

Weaver JK, Chalmers J. Cancellous bone: its strength and changes with aging and an evaluation of some methods for measuring its mineral content, I: age changes in cancellous bone. J Bone Joint Surg. March 1966;48A(2):289-298.

1985

Cann CE, Genant HK, Kolb FO, Ettinger B. Quantitative computed tomography for prediction of vertebral fracture risk. Bone. 1985;6(1):1-7.

1988

Ashman RB, Rho JY. Elastic modulus of trabecular bone material. J Biomech. 1988;21(3):177-181.

1991

Snyder SM, Schneider E. Estimation of mechanical properties of cortical bone by computed tomography. J Orthop Res. May 1991;9(3):422-431.

1998

Jiang Y, Zhao J, Augat P, Ouyang X, Lu Y, Majumdar S, Genant HK. Trabecular bone mineral and calculated structure of human bone specimens scanned by peripheral quantitative computed tomography: relation to biomechanical properties. J Bone Miner Res. November 1998;13(11):1783-1790.