Age estimation from acetabulum and femoral head using digital image processing techniques

Abstract

The personal identification of human skeletal remains is of great importance, with age at death being one of the key parameters. The hip joint, which includes the acetabulum and femoral head, is a crucial part of skeletal remains. The acetabulum, in particular, is one of the most well-preserved skeletal elements. Percent porosity and area ratio can provide insights into the age of the bone. Traditionally, age estimation of bones has been conducted by experts, but sending bone samples to specialists has its limitations. Nowadays, image processing techniques are widely used, making it much easier to send images for expert analysis. This research employs image processing techniques to assist in estimating the age of bones, using images of the acetabulum and femoral head from the Thai population. Samples were collected from 167 skeletons, comprising 59 females aged 26 to 100 years and 108 males aged 26 to 97 years. The skeleton donations were made between 2011 and 2019. Color images were converted to grayscale, with pixel values ranging from 0 to 255. Dark gray pixels with values below a certain threshold were classified as porous pixels, while light gray pixels with values above the threshold were classified as bone pixels. Percent porosity of the acetabular fossa was calculated from acetabulum images, and percent porosity of the fovea capitis was calculated from femoral head images. Area ratios were also determined. The area ratio of the acetabulum was calculated as the ratio of the acetabular fossa area to the total acetabulum area. The area ratio of the femoral head was calculated as the ratio of the fovea capitis area to the total femoral head area. The interrelationships between these two main variables and age were analyzed using statistical methods. At a confidence level of 90% or a significance level of α = 0.10, a relationship exists between percent porosity and estimated age in males. The estimated age equation for the left side of the male acetabulum is A = 2.2776P – 25.2553 (R² = 0.3317), where A represents the estimated age and P represents percent porosity. There is also a relationship between area ratio and estimated age in the femoral head for both females and males, on both the left and right sides. For the right side of the female femoral head, the estimated age equation is A = 2.6049R + 33.7348 (R² = 0.2023), where A is the estimated age and R is the area ratio. The errors for percent porosity to estimated age equations range from 0 to 16 years, with average errors between 5 and 9 years. For area ratio to estimated age equations, errors range from 0 to 36 years, with average errors between 8 and 17 years. A significant challenge in this process is the cleanliness of the bones, as it directly affects pixel values, leading to potential inaccuracies.