Traumatology of the superior thyroid horns in suicidal hanging--an injury analysis

It appears still questionable whether fractures to the superior thyroid horns can be used for forensic reconstruction purposes regarding the functional mechanism causing compression of the neck soft tissues. Localisations and types of such fractures were documented in 118 cases of superior thyroid horn fractures caused by suicidal hanging. The placement of the ligature was above the larynx in 109 cases and in the remaining nine cases across the thyroid cartilage. As a secondary parameter the degree of ossification of thyroid cartilages and superior horns was used. Bone densities of typical cases (equidensities) were measured radiologically. Additionally, dummy tests were performed focused on two extreme shapes of superior thyroid horns to assess stress peaks using resin dummies and polarised light. Such peaks were located in the lower thirds of the horns close to their bases. With the larynx still cartilaginous, the base appears a typical location for fractures caused by suicidal hanging. An ossification pattern defined as "type 1" showed broad and osseous superior thyroid horns. If ossification was homogenous, fractures were located at the sites of maximum mechanical stress. In case of inhomogenous ossification, being the more common mode, the horn bases were more resistant to pressure and bending so that no fractures occurred. They were instead located at the sites of the greatest differences in density and distributed in an apparent random pattern. Narrow and deep insertions of the superior thyroid horns at the back surface of the upper thirds of the thyroid cartilages (posterior aspects) were classified as "type 2" ossification. Upon flexion, the long horns came into contact with the upper edges of the dorsal aspect creating a torque. Further flexion from an increasing impact by the ligature extended the long lever arm causing the base of the upper thyroid horn being broadly torn out of the dorsal aspect. The results suggest that localisations of fractures to the superior thyroid horns in connection with ossification patterns may be helpful for the reconstruction in suicidal hanging regarding the mechanics of the ligature in relation to its position around the neck.