A semiautomatic segmentation approach to biometric measurement of the talus bone of sedentary women and ballerinas using CT images

A Toshiba Aquilion CT system (Toshiba Medical Systems, Tochigi, Japan) was used to acquire talus bone data. Parameters for scanning were detector collimation 65 X 0.5–4 × 0.5 mm; slice thickness 0.5 mm, 100 mA, 120 kV, spatial resolution 512 × 512, and radiometric resolution 16 bit. In the scanning process, we minimized radiation exposure and optimized resolution [16]. After approval by the institutional ethics committee of Konya Clinical Research Institution (document No. 004; January 08, 2010), we selected 5 volunteer semiprofessional ballerinas and 5 sedentary women volunteers without a sports history. We obtained written informed consent for their participation. Ten feet (5 left and 5 right) of ballerinas and 10 feet of sedentary women (5 left and 5 right) were scanned. We obtained 20 images in all. The imaging procedures were conducted according to the Declaration of Helsinki [18] and to the standards of the Turkish Ministry of Health. We processed 1050 slices. We identified the health status of the volunteer ballerinas and sedentary women according to standards of Turkish Ministry of Health. All had normal health status. The general flow chart of the present study is shown in Figure 1.

Figure 1

Each of the 5 ballerinas was 18 years old and average (SD) shoe size, height, and weight were 37.2 (1.2), 166.8 cm (6.2), 49.2 kg (1.2) respectively. We attempted to match the selection of sedentary women with the ballerinas so that they had similar height, shoe size, and weight (18 years, 36.8 (1.2), 163 cm (10), and 50.4 kg (3.6) respectively). MDCT images were obtained from the Ankara Ataturk Training and Research Hospital and Selcuk University, Faculty of Medicine. Digital Imaging and Communications in Medicine was the standard for the management of medical imaging information. The medical images were stored “DICOM” format.

To avoid motion artefacts, feet were immobilized during scanning. Preprocessing consisted of median and mean filtering steps for noise removal. Following this step, segmentation was used to split bone tissue from other tissues. A region growing method [19] was applied and the required seed point was defined interactively by using Hounsfield units in the range of 32900-40000. Obtaining some noisy data after segmentation is unavoidable. Therefore, results achieved in the present study consisted of some noisy data, but this noise was reduced by filtering, and 3D talus models were created using 3D-Doctor (Able Software Corp, Lexington, MA, USA).

We made biometric measurements of 3D talus bone models in the present study. The measurement method is shown in Figure 2 showing head and posterior process measurements of the talus. The distances between head and posterior process were measured manually on the 3D talus bone models. We analyzed measurements using SPSS Statistics for Windows, version 21 (IBM Corp, Armonk, NY, USA) and calculated descriptive variables including mean, standard deviation, and variance. A two-tailed t test was used to examine differences.

Figure 2

A 3D-Reconstruction of a ballerina’s foot skeleton is shown in Figure 3, showing the location of the talus bone.

Figure 3

Talus bone measurements are shown in Table 1. Descriptive statistics are shown in Table 2. The mean talus bone length of ballerinas was 3.37 cm (SD 0.12; range 3.11 to 3.52). The talus bone length of sedentary women was 3.29 cm (SD 0.16; range 3.04 to 3.65), and tended to be shorter than that of ballerinas, although the difference was not significant (P = 0.08, t test). The power of the two-tailed test with α 0.050 was just 0.22 and therefore below the desired power of 0.80. We found less variation in the feet of ballerinas than in sedentary women.

Table 1

Talus bone measurements of ballerinas and sedentary women

Table 2

Descriptive statistics for the talus bones of ballerinas and sedentary women

The volumetric calculations for ballerinas and sedentary women are shown in Table 3. The mean volume of the talus bones from the ballerinas was 24.8 cm³ (SD 0.83) and significantly smaller than the mean volume of talus bones from the sedentary women, which was 26.9 cm³ (SD 1.25) (P < 0.001; t = 4.38, 18 degrees of freedom. Difference 2.082. Two-tailed confidence interval (95%) for difference of means: 1.084 to 3.080). We found less variation in the feet of ballerinas than in sedentary women. Deviations outside the normal range may be used to determine deformation of talus bone.

Table 3

Talus bone volumes

The measurements between the head and posterior process found that ballerinas and sedentary women and have a slightly different talus bone size, that tended to be longer in ballerinas. While the variation between right and left talus bones was small for ballerinas, it was higher for sedentary women. Our study was insufficiently powered to determine whether a difference actually exists. Therefore, the lack of a significant difference should be interpreted cautiously.

While the talus bone length of ballerinas was tended to be longer, the volumetric size was significantly smaller than it was in sedentary women. The feet of the ballerinas retained a similar shape and size. Whereas feet of sedentary women have been shaped according to their daily activities and use, and their feet are therefore irregular [20].

The talus bone length of female and male Egyptian volunteers were different [20] and could be used to determine sex for forensic purposes. Female and male talus bone lengths of north Italian volunteers between 19 and 70 years old were measured and showed that talus bone length is a reliable measurement for determining sex [21].

Early recognition of foot deformation could increase the professional life of ballerinas through protective measures. Talus bone length measurement has been used to observe deformities [16, 22]. The talus bone lengths of 49 Malaysian women were measured using CT images. Biological and environmental factors were found to determine the shape and size of talus bone [22]. We chose ballerinas and sedentary women in the present study to determine whether study of the talus bone might be a useful for anticipating occupational injuries in ballerinas. Deviations outside of the similar normal range of talus bone size in ballerinas might indicate deformation. A limitation of this study was the small number of participants, which lead to it being underpowered for length and other measurements.

In constructed 3D models, talus bone volume was found to be significantly smaller in ballerinas than in sedentary women. The feet of ballerinas retain similar shape and size, whereas the feet of the sedentary women appear more irregular than those of ballerinas, and are probably shaped according to their various activities of daily use. Deviation outside of the similar normal range of talus bone size in ballerinas may be used to determine deformation of talus bone. We recommend the ankles of ballerinas be examined periodically. Data from the biometric and MDCT 3D reconstructive methods used in this study may contribute to knowledge in orthopedics and digital image processing.