Effect of hot water maceration, rehydration, and soft tissue presence on 3D geometry of bone

Abstract

Purpose: In forensic medicine, maceration is often essential for examining bone surfaces, serving purposes such as identifying cut marks, making geometric measurements, and determining the victim's age. While hot water maceration removes soft tissue effectively, it is known to cause bone surface shrinkage. This raises the question of whether this effect is permanent or if it can be partially reversed through rehydration, considering the presence of soft tissue.

Methods: Computed tomography (CT) scans were conducted on the radii of 20 paired human anatomic forearm specimens. Subsequently, the radii were extracted, macerated in 60 °C water, CT-scanned in an air environment, rehydrated, re-implanted into the forearms, and CT-scanned again.

Results: Maceration resulted in a mean shrinkage of 0.12 mm on the outer bone surface. This shrinkage was nearly fully recoverable for the diaphysis after rehydration and accounting for soft tissue surrounding the bone. In contrast, the epiphysis showed permanent shrinkage, likely due to the loss of small bone fragments. Analysis of the inner bone surface indicated a smaller effect, but with significant standard deviations, especially for the epiphysis, possibly related to the less well-defined nature of the inner bone surface.

Conclusion: The epiphyseal surface of hot water-macerated bone will, on average, be approximately 0.15 mm deflated and cannot retain the original surface. On the other hand, the diaphyseal surface is less affected and can be nearly completely restored after rehydration and accounting for soft tissue surrounding the bone.

Keywords: 3D model; Bone; Computed tomography; Dimensional accuracy; Forensic anthropology; Maceration; Rehydration.

Fig. 1

Study overview: Native forearms were initially scanned with CT, the distal radius was extracted with a modified Henry approach, macerated at 60 °C in water for two weeks, scanned with CT in air environment, re-hydrated and implanted, and another CT scan was performed. Determination of the effects of maceration, re-hydration + soft tissue (ST) presence, and the combined effects was performed as indicated with arrows

Fig. 2

Image processing: CT image series were segmented with a manually determined threshold for the epiphysis and diaphysis and merged into a single bone mask. This mask was filled to obtain the outer bone surface. The inner bone surface was obtained as the subtraction of the filled and segmented bone mask

Fig. 3

Image registration: The wedge inside the radius which simulates a dorsally inclined Colles’ fracture, was removed. A three-point registration was carried out using the Lister tubercle, the peak of the styloid processus and the most proximal part of the margo interosseus (indicated by the green dots). Subsequently, a global registration was performed to ensure perfect alignment of the epiphysis and diaphysis. Exemplary plots of 3D dimensional deviation are shown for the effect of maceration, rehydration + soft tissue (ST) presence, and the combined effect, for the epiphysis and diaphysis separately. Only for maceration, also the whole distal radius was analyzed. The displayed legend is valid for all plots and given in mm

Fig. 4

Dimensional deviation of 3D bone models for the outer bone surface following maceration (left), rehydration with re-implantation + soft tissue (ST) presence (middle), and combined effects (right). Probability density functions are shown with histograms and corresponding boxplots (outliers are not plotted, for better visibility due to a large number of data points (∼100,000))

Fig. 5

Dimensional deviation of 3D bone models for the inner bone surface following maceration (left), rehydration with re-implantation + soft tissue (ST) presence (middle), and combined effects (right). Probability density functions are shown with histograms and corresponding boxplots (outliers are not plotted, for better visibility due to a large number of data points (∼100.000))