Reconstruction of full femora from partial bone fragments for anthropological analyses using statistical shape modeling

Lars C Ebert; Dana Rahbani; Marcel Lüthi; Michael J Thali; Angi M Christensen; Barbara Fliss

doi:10.1016/j.forsciint.2022.111196

Reconstruction of full femora from partial bone fragments for anthropological analyses using statistical shape modeling

Forensic Sci Int. 2022 Mar:332:111196. doi: 10.1016/j.forsciint.2022.111196. Epub 2022 Jan 29.

Authors

Lars C Ebert¹, Dana Rahbani², Marcel Lüthi², Michael J Thali³, Angi M Christensen⁴, Barbara Fliss⁵

Affiliations

¹ 3D Center Zurich, Zurich Institute of Forensic Medicine, University of Zurich, Zurich, Switzerland. Electronic address: lars.ebert@irm.uzh.ch.
² Department of Mathematics and Computer Science, University of Basel, Basel, Switzerland.
³ Zurich Institute of Forensic Medicine, University of Zurich, Zurich, Switzerland.
⁴ Laboratory Division, Federal Bureau of Investigation (FBI), Quantico, VA, USA.
⁵ Institute of Forensic Medicine, University Hospital of Mainz, Mainz, Germany.

PMID: 35123259
DOI: 10.1016/j.forsciint.2022.111196

Abstract

Objectives: Due to taphonomic processes such as burial, fire, or animal activity, bones are often found incomplete, which can pose problematic for establishing the biological profile of the deceased using anthropological methods. The aim of this study is to test the feasibility of using statistical shape modeling (SSM) to reconstruct full femora from simulated partial femora and determine the accuracy of the reconstruction. Moreover, we assess the accuracy of sex estimation and the degree of stature error added based on the reconstructed femur using different anthropological methods.

Methods: A total of 42 (28 female, 14 female) 3D models of left femora extracted from computed tomography (CT) scans were used. We performed a leave-one-out cross-validation (LOOCV) where 41 bones were used to build the SSM and one bone was used for testing. This bone was cut in 1 cm steps proximally, distally and from both ends up to 10 cm, reconstructed using SSM, and tested using the methods established by Stewart and Purkait (2005), Trotter and Gleser (1952), as well as a method based on SSM. with landmarks being automatically identified.

Results: The error induced by reconstructing the femur to the length measurements was low, which translated into useful stature estimations (single sided cuts up to 10 cm: 0.4-1.1%, double sided<2% for cuts shorter than 6 cm). Using Purkaits method for sex estimation on reconstructed bones looked promising as well (single sided: 90.5% when compared to applying Purkaits method on the original bone, double sided 78.6% (10 cm cut) to 97.6% (1-3 cm cuts)) Using SSM for sex classification looked promising as well (single sided cut: 81-85.7%, double sided cut: 59.5-85.3%) CONCLUSION: SSM can be used to reconstruct fragmented femora. These reconstructions can be used for sex and stature estimations, at the cost of lower accuracy. Using SSM might give investigators an additional tool to gain information about the biological profile of a deceased in cases where the fragmentation of a femur does not allow for using other anthropological methods.

Keywords: Anthropology; Bone reconstruction; Computed tomography; Femur; Sex estimation; Statue estimation.