**7. Significance of accurately assessing hip fracture risk**

The aim of accurately assessing hip fracture risk is to identify patients at high risk of hip fracture and to start intime prevention and protection measures to reduce the number of hip fractures. These measures are accepted by the patients only after they are accurately diagnosed with the high fracture risk. Also, accurate assessment of hip fracture risk is the prerequisite step before starting a therapy. For example, during the process of osteoporosis treatment, it is required to monitor the change of fracture risk and subsequently track the effectiveness of the therapy. By knowing the risk of fracture, people can improve their bone health and change their environment to reduce the likelihood of the fall.

Patients diagnosed with high fracture risk may consider the following prevention measurements:

	- Muscle-strengthening exercises [76]
	- Practicing balance exercises [77]
	- Increasing the lower extremity joint function [32]
	- Obtaining maximum vision correction [6, 78]

Protection measurements must be provided to patients with high fracture risk, for example:

	- Trying to fall forward or backward not from sides

India, China, Indonesia, and the Philippines. It is notable that in Europe, the majority of countries are categorized as high or moderate risk. Low risk is identified only in Croatia and

**Figure 5.** Estimated number of hip fractures by sex in the year 1990 and the number expected in 2025 and 2050 by region assuming no increase in age- and sex-specific rates, a 1% annual increase worldwide, or no increase in North America and northern Europe but an increase in age- and sex-specific incidence elsewhere of 2, 3, or 4%. (ROW is rest of world)

Hip fracture incidence rates are known to increase exponentially with age in both men and women for the most regions of the world [71–74]. The increasing rate of hip fracture in the elderly is mainly associated with their slower reflex response and the inability to effectively use their arms to reduce the energy of the fall and low bone density of the proximal femur [44, 45]. Epidemiological studies show that the number of hip fractures will rise from 1.66 million in 1990 to 4.5–21.3 million by 2050 (**Figure 5**) depending on the underlying assumptions about

The aim of accurately assessing hip fracture risk is to identify patients at high risk of hip fracture and to start intime prevention and protection measures to reduce the number of hip fractures. These measures are accepted by the patients only after they are accurately diagnosed with the high fracture risk. Also, accurate assessment of hip fracture risk is the prerequisite step before starting a therapy. For example, during the process of osteoporosis treatment, it is required to monitor the change of fracture risk and subsequently track the effectiveness of the therapy. By knowing the risk of fracture, people can improve their bone health and change

age- and gender-specific incidence trends [9, 25, 51, 75].

their environment to reduce the likelihood of the fall.

**7. Significance of accurately assessing hip fracture risk**

Romania [10].

[25] (reproduced with permission).

74 Total Hip Replacement - An Overview

	- Consuming a calcium-rich diet that provides about 1000 mg (milligrams) daily for men and women up to age 50 [88]. Women over age 50 and men over age 70 should increase their intake to 1200 mg daily from a combination of foods and supplements.
	- Obtaining 600 **IU** (international units = 0.025 μg) of vitamin D daily up to age 70 [88]. Men and women over age 70 should increase their uptake to 800 **IU** daily.
	- 5–15 min' exposure to sunlight 4–6 times per week [89].

### **8. Bone fracture criterion and hip fracture risk measurement**

From biomechanics point of view, assessment of hip fracture under stance loading or lateral impact force has been performed using three criteria: factor of safety (FOS) [90], risk factor (RF) [70], and fracture risk index (FRI) [91]. In this section, a review is performed on previously adopted bone fracture criteria in both 2D and 3D FE models.

**References**

[1] Shao CJ, Hsieh YH, Tsai CH, Lai KA. A nationwide seven-year trend of hip fractures in

Hip Fracture: Anatomy, Causes, and Consequences http://dx.doi.org/10.5772/intechopen.75946 77

[2] Green C, Molony D, Fitzpatrick C, ORourke K. Age-specific incidence of hip fracture in

[3] Gronskag AB, Forsmo S, Romundstad P, Langhammer A, Schei B. Incidence and seasonal variation in hip fracture incidence among elderly women in Norway. The HUNT

[4] Alvarez-Nebreda ML, Jimenez AB, Rodriguez P, Serra JA. Epidemiology of hip fracture

[5] Wilson RT, Chase GA, Chrischilles EA, Wallace RB. Hip fracture risk among communitydwelling elderly people in the United States: A prospective study of physical, cognitive, and socioeconomic indicators. American Journal of Public Health. 2006;**96**:1210-1218 [6] Marks R, Allegrante JP, Ronald MacKenzie C, Lane JM. Hip fractures among the elderly:

[7] Testi D, Viceconti M, Baruffaldi F, Cappello A. Risk of fracture in elderly patients: A new predictive index based on bone mineral density and finite element analysis. Computer

[8] Greenspan SL, Myers ER, Kiel DP, Parker RA, Hayes WC, Resnick NM. Fall direction, bone mineral density, and function: Risk factors for hip fracture in frail nursing home

[9] Cooper C, Campion G, LJ MI. Hip fractures in the elderly: A world-wide projection.

[10] Kanis JA, Oden A, McCloskey EV, Johansson H, Wahl DA, Cooper C. A systematic review of hip fracture incidence and probability of fracture worldwide. Osteoporosis

[11] Nasiri Sarvi M, Luo Y. Sideways fall-induced impact force and its effect on hip fracture

[12] Nasiri M, Luo Y. Study of sex differences in the association between hip fracture risk and body parameters by DXA-based biomechanical modeling. Bone. 2016;**90**:90, 98 [13] Nasiri Sarvi M, Luo Y. A two-level subject-specific biomechanical model for improving

[14] Luo Y, Nasiri Sarvi M. A subject-specific inverse-dynamics approach for estimating joint stiffness in sideways fall. International Journal of Experimental and Computational

[15] Nasiri Sarvi M. Assessment of hip fracture risk by a two-level subject-specific biomechanical model. Ph.D. thesis. Canada: Mechanical Engineering, University of Manitoba;

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Keyak et al. [90] assessed FOS under two loading conditions: one representing loading during the stance phase of gait and the other simulating the impact from a fall. Their study was based on a 3D FE model generated from CT data of the patient. They calculated FOS to compare the actual element strength with the applied von Mises stress.

Schileo et al. [92] applied maximum principle strain, von Mises stress, and maximum principle stress criteria to calculate risk factor and to predict fracture location of the femur. RF compares the applied stress/strain with the yield one to predict the bone fracture. Lotz et al. [93, 94] also used von Mises stress yield criterion for the cortical bone and crushing-cracking stress criterion for the trabecular bone. The performance of nine stress- and strain-based failure theories in assessment of hip fracture is investigated by Keyak and Rossi [95]. They evaluated the distortion energy (DE), maximum normal stress, maximum normal strain, maximum shear strain, maximum shear stress, Coulomb-Mohr, modified Mohr, Hoffman, and strainbased Hoffman failure theories, using CT-based FE models of the femur [95].

The abovementioned fracture risk measurements are all derived from CT images. The most recent DXA-based fracture risk criterion is proposed by Luo et al. [91]. They calculated the averaged FRI as a ratio between the effective stress (von Mises stress) by applied forces and the allowable stress (yield stress) of the bone over a region of interest (ROI). FRI is a local fracture risk measurement, while FOS and RF are global ones.
