**3. Methods – Assessing the probability of injury**

In this section graphical presentation of risk of injury presented. Envelops pertaining to risk free and high risk injury needs to be established. Based on the data compiled here, and by others [14] the succeeding curves have been developed to establish the amount of existing risk associated with various types of cervical spinal loading. The first set of curves in Figure 5 illustrate the tolerance of tensile loads of 5 different human body types, (mannequins were used to test and extract data for each of these body types), based on the amount of time the load is applied. The Hybrid III Family of Mannequins is a well established group used for testing the effects of various types of loading on different sized bodies. Within this family are five mannequins: (i) A 3 Year Old, (ii) a 6 Year Old, (iii) a Small Adult, (iv) a Midsize Adult and (v) a Large Adult. Table 3 displays the characteristics of each particular mannequin.

**Figure 5.** Tension Loading of Five Different Body Types Retrieved from Dummy Data [13]

No height is given for the 3 and 6 year old mannequins because their development was based largely in part on estimates and approximations. This remains a difficult parameter to analyze because so little data exists on the effects of accidents on children. Figure 5 displays the Axial Tension (Newtons) Tolerance of the mannequins with respect to time (milliseconds).

Anything above each individual curve in Figure 5 indicates the potential for significant neck injury due to tension loading, while anything below indicates that significant neck injury due to loading is highly unlikely. Compression and shear data was analyzed and compiled in a similar fashion, to develop the curves in Figures 6 and 7, respectively. Anything above each individual curve indicates the potential for significant neck injury due to compression loading, while anything below means that significant neck injury due to loading is highly unlikely.

**Figure 6.** Compression Loading on the Neck [13]

120 Injury and Skeletal Biomechanics

mannequin.

(milliseconds).

0

1000

2000

3000

4000

5000

6000

mechanisms that cause occipito-atlantoaxial injuries. Transverse ligament rupture has been seen to occur at a load of 824 N, with anterior shear of the atlas [5]. Odontoid fractures reportedly occur at 1510 ± 420 N of shear force [4]. Additional, higher tolerances have been

In this section graphical presentation of risk of injury presented. Envelops pertaining to risk free and high risk injury needs to be established. Based on the data compiled here, and by others [14] the succeeding curves have been developed to establish the amount of existing risk associated with various types of cervical spinal loading. The first set of curves in Figure 5 illustrate the tolerance of tensile loads of 5 different human body types, (mannequins were used to test and extract data for each of these body types), based on the amount of time the load is applied. The Hybrid III Family of Mannequins is a well established group used for testing the effects of various types of loading on different sized bodies. Within this family are five mannequins: (i) A 3 Year Old, (ii) a 6 Year Old, (iii) a Small Adult, (iv) a Midsize Adult and (v) a Large Adult. Table 3 displays the characteristics of each particular

> **Axial Neck Tension Loading (N) as a Function of Time Load Applied (ms)**

> > 3 Yr Old 6 Yr Old Small Adult Mid Size Adult Large Adult

reported up to 5500 ± 2500 N when the shear force is applied at the chest [2].

**Figure 5.** Tension Loading of Five Different Body Types Retrieved from Dummy Data [13]

0 10 20 30 40 50 60 70

No height is given for the 3 and 6 year old mannequins because their development was based largely in part on estimates and approximations. This remains a difficult parameter to analyze because so little data exists on the effects of accidents on children. Figure 5 displays the Axial Tension (Newtons) Tolerance of the mannequins with respect to time

**3. Methods – Assessing the probability of injury** 

**Figure 7.** Shear Neck Loading Data [13]

Each of the curves for compression, tension and shear loading were analyzed. From these curves, specific data points were extrapolated and both standard deviations and standard error for each point were calculated. The extrapolated data for compression, tension and shear loading are illustrated in Figures 8, 9, and 10 respectively.

Cervical Spinal Injuries and Risk Assessment 123

3YrOld 6YrOld SmallAdult MidSize LargeMale

Similarly, a moderate injury refers to AIS 2-5 and an unsurvivable injury, to AIS 6. These three scenarios were plotted for compression, tension and shear loading for the five different

**Shear Extrapolated Data**

With the assistance of an Excel Add-In called RiskAmp, numerous Monte Carlo Simulations were set up to study the probability of the five different dummy types being exposed to various compressive, tensile and shear forces. Because of their reliance on repeated computation of random or pseudo-random numbers, these methods tend to be used when it is unfeasible or impossible to compute an exact result with a deterministic algorithm [22]. Applied forces were randomly generated for 1000 simulations. The simulation means and standard deviations were studied. Ranges of force values known to produce responses in the 3 "Injury Zones" were tested against the simulation means to determine the probability

0 10 20 30 40 50 60

The risk of injury of being exposed to a force that would place the dummy in each of the three previously discussed injury zones (No Injury Likely, Moderate Injury Likely and

Axial loading, whether tension or compression, can pose a significant risk of injury as seen by the ISO-13232 (Figure 11) testing and analysis procedures [23]. Figure 12 shows the axial neck force time responses as measured in a laboratory head impact test and computer simulation. In figure 12, it can be seen that after only 5 milliseconds, the largest compressive force is exerted on the neck of the rider. After only 15 milliseconds, the rider is then exposed to the highest tensile forces; a direct result of the neck rebounding from compression. And

of exposure to the varying degrees of compressive, tensile and shear forces.

Unsurvivable Injury Likely) were developed thereafter.

body types previously mentioned.

**Figure 10.** Extrapolated Data for Shear Loading

**4. Probability of risk** 

**5. Results** 

**Figure 8.** Extrapolated Compression Loading Data

From the standard deviations, ranges of loading were developed for each of the following three scenarios: (i) no injury or minor injury will occur, (ii) A moderate injury is likely to occur and (iii) an unsurvivable injury is likely to occur. For the purposes of comparison, no/minor injury in this analysis refers to an injury that rates from 0 to 1 on the AIS scale. Similarly, a moderate injury refers to AIS 2-5 and an unsurvivable injury, to AIS 6. These three scenarios were plotted for compression, tension and shear loading for the five different body types previously mentioned.

**Figure 10.** Extrapolated Data for Shear Loading
