• Rong-Sen Yang, Huei-Jeng Lin, Poon-Ung Chieng, Tang-Kue Liu, and Keh-Sung Tsai.
• Department of Orthopedics, National Taiwan University, Taiwan, Republic of China.
• Spine. 2005 Oct 15; 30 (20): 228822922288-92.

ObjectiveTo investigate the effects of biologic age, as well as chronologic age, on the vertebral ultimate load (strength) and risk score of vertebral fracture (Phi) between the genders.Summary Of Background DataPrevious studies have shown a good correlation between the biomechanical strength of vertebral bodies and measured bone mineral parameters, whereas other factors also contribute to the bone strength and risk of fractures. Combining multiple factors into a single assessment may provide more comprehensive and individualized estimations of the fracture risk. In this study, we applied the measured bone mineral content (BMC) and bone projection area of the second through the fourth lumbar vertebrae (L2-L4) to assess the biomechanical strength of lumbar vertebrae. In addition, we used the body segment model to estimate the load of the L3 vertebral body during a bending-forward activity, to then estimate the risk score (Phi) of vertebral compression fracture in healthy Chinese volunteers in Taiwan, and to analyze the effects of gender and age on the risk score (Phi).MethodsA total of 611 females and 235 males aged 22-80 years were included in this study. The anteroposterior BMC and projection area of lumbar spine were measured by a Norland XR-26 dual energy radiograph absorptiometer (Norland Corp., Ft. Atkinson, WI). The estimated ultimate strength (L) of lumbar spine was calculated from the regression equation using anteroposterior lumbar BMC and bone area according to Bassman et al (Paper presented at: 39th Annual Meeting of Orthopedic Research Society; February 1993; San Francisco, CA). The estimated spinal load (F) for a person bending over with back horizontal, either with hand free (F0), lifting a 20 kg weight (F20), or a 30 kg weight (F30), was calculated from a force diagram according to William and Lissner. Risk score (Phi) was defined as the quotient of F/L.ResultsThe results showed an age-related decrease of bone mineral density (P < 0.001) in both genders corrected for weight and height. Using the multiple linear regression analysis and analysis of covariance, Phi for F0, F20, and F30 increased significantly, with increasing age only in females (P < 0.0001), especially after menopause, but not in males. The Phi of postmenopausal females was significantly larger than those of younger females (i.e., F0 (Phi) 0.533 +/- 0.075 vs. 0.458 +/- 0.064, P < 0.001; F20 (Phi) 0.903 +/- 0.101 vs. 0.789 +/- 0.080, P < 0.001; and F30 (Phi) 1.087 +/- 0.117 vs. 0.954 +/- 0.090, respectively, P < 0.001). In females, the ultimate load of the spine and Phi began to decrease to a significant level since the fifth decade, whereas in the males, the similar trends occurred since the sixth decade. Comparing both genders, the F0 (Phi) was slightly yet significantly larger in the young males (< 50 years) than the premenopausal females with similar ages (P < 0.001), but older females had higher F0 (Phi) values than males older than 60 years. Moreover, the Phi increased more prominently in the postmenopausal females with the weight lifted. As a result, both F20 (Phi) and F30 (Phi) were significantly larger in females older than 50 years as compared to males with the similar ages (P < 0.001).ConclusionsOur findings emphasize the importance of Phi, which considers BMC, bone size, body weight, body height, and weight lifted, for evaluating a more individualized risk of spine fracture in elderly men and postmenopausal women. The Phi increased more prominently with lifting weight and increased with aging only in the early postmenopausal females. The study showed that a combination of bone mass and anthropometric parameters provides a more individualized assessment of fracture risk than bone mineral density alone.

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