Hyoid-laryngeal fractures in hanging: where was the knot in the noose?

Introduction

Hanging is a form of ligature strangulation in which the force applied to the neck is derived from the gravitational drag of the weight of the body. ¹ Death by hanging is usually rapid, ^2,3 and due to asphyxia, cardiac inhibition, or obstruction of cerebral arterial flow or venous drainage. ⁴ The rapid nature of death by hanging makes it a commonly used method of suicide.

A furrow is the ligature mark on the skin, which in the case of hanging is usually localized above the larynx. Depending on the type of noose, the groove on the neck produced by the pressure of the noose may be deep; the skin shrunken, dry, brown or leather-like. ⁵ Hanging has been classified as either typical or atypical, depending on the position of the knot in the noose. If a knot is present on the occipital region, it is designated as a typical or otherwise as an atypical hanging. ⁶

The hyoid bone and laryngeal cartilage make an anatomic and functional unit, which is relatively strong, connected both to each other and to the skull base, and providing the force transmission from one structure to another. ⁷ The frequency and distribution of an inner neck injury due to hanging might indicate the mechanism of these organs being injured in relation to the hanging type or the position of the ligature knot.

The aims of this study were to determine the frequency of hyoid-laryngeal fractures in hanging in relation to the position of the ligature knot, to reconstruct the location of the ligature knot in cases of hanging when the furrow is not detectable on the skin and to identify the possible mechanism of neck structure injuries.

Materials and methods

A retrospective autopsy study over a 12-year period included selected cases of suicidal hanging; only cases of standing and full suspension, i.e. complete hanging, without a drop effect. We did not analyse incomplete hangings in kneeling, sitting, lying or other positions. The cases were determined to be suicides through police investigations, the specific circumstances of death, suicide notes, previous suicide attempts, anamnestic or medical data about the presence of mental disorders and/or other various medical conditions such as suicidal motivation, etc. There was no question of foul play in any case included in the study.

The initial hypothesis was that the distribution and mechanism of the injury's origin was related to the position of the ligature knot. Hangings were divided topographically according to where the ligature knot may have been present, into anterior, left-anterior, left, left-posterior, posterior, right-posterior, right and right-anterior. The boundaries of these topographic regions were projections of the middle part of the lower jaw body, lower jaw angles and mastoid processes, as well as external occipital protuberance and the middle position of the occipital superior curved line. In some cases, the noose was present and there was no need to make a reconstruction of the ligature knot position. In cases without the ligature present around the neck of the deceased, the location and course of the ligature were determined by measuring the distance of the skin ligature mark in relation to six fixed positions, including top of the chin, lower jaw angles, ear lobe tragus and occipital protuberance. The position of the ligature knot was determined according to the location and course of the ligature mark, as well as its depth and width. In our institute, this is the standard technique for external examination in cases of hanging. In cases where the precise position of the ligature knot could not be reconstructed, the subjects were excluded from the study.

The sample was analysed in regard to gender and age of the deceased, position of the knot (eight of them), and presence or absence of a fracture of the throat skeleton (greater horn of hyoid bone or superior horn of thyroid cartilage), as well as injury to the cervical spine. The data obtained were analysed using Pearson's χ ² test, the Mann–Whitney test, binary logistic regression and Spearman's correlation coefficient for estimating relationships, since all variables show non-parametric distribution (which was tested with the Kolmogorov–Smirnov test for normal distribution). A P value < 0.05 was considered significant, and < 0.01 highly significant.

Results

A total of 557 deceased fulfilled the criteria: 413 men and 144 women, with an average age of 52.4 ± 17.8 years (range 9–94 years). Of these, 319 (248 men and 71 women) had hyoid-laryngeal fractures: either the hyoid bone and/or thyroid cartilage; their average age was 54.3 ± 16.5 years. The average age in cases where hyoid-laryngeal fractures were absent (238 subjects) was 49.9 ± 19.2 years.

The sample distribution in regard to age and the presence of a fracture of the throat skeleton is shown in Table 1. The sample's distribution in regard to the type of hanging and presence and type of hyoid-laryngeal fractures is shown in Table 2. The sample also included 18 deceased who had cervical spine injuries: 10 men and eight women, with an average age of 51.3 ± 18.3 years (range 39–88 years). Twelve of them did not have throat skeleton fractures, and six of them had fractures of the greater horn of hyoid bone; one also had a fracture of the superior horn of the thyroid cartilage. In seven of them, the ligature knot position was anterior; it was right-anterior in four, left-anterior in two, right in two and right-posterior in two, and the position of the knot was posterior in one case.

In our sample, the male:female ratio was 2.9:1 (χ ² = 126.275, P < 0.01). In 57.3% of the observed cases, some type of hyoid-laryngeal fracture was present, including 15.1% solely with a hyoid bone fracture, 26% solely with a thyroid cartilage fracture and 16.2% with both types of injuries at the same time. Persons who had hyoid-laryngeal fractures were predominantly older than those without hyoid bone or thyroid cartilage fractures (z = 2.876, P < 0.01).

Discussion

Various reports of the frequency of solid neck structure fractures can be found in the literature: Betz and Eisenmenger ⁸ established it in 67% of cases; Feigin ⁹ found at least a single fracture of the throat skeleton in 9.5% of the examined cases; Uzun et al. ¹⁰ established 59.9% fracture-determined cases in hanging; Suarez-Penaranda et al. ¹¹ did in 75.3% cases of the observed sample; Azmak ¹² did in 76.7% of all investigated cases; Luke ¹³ did in 25.0% and James and Silcocks ¹⁴ did in 36.0% of the observed sample. Discrepancy between the frequencies of injuries of the hyoid bone and laryngeal cartilages, reported by different authors, could probably be ascribed to the lack of a common autopsy method. Most hyoid-laryngeal fractures are masked by soft tissues. False palpatory diagnostics may result from the considerable mobility of the horn, caused by its elastic junction, or anomalies and alternations of the hyoid–larynx complex. ^15,16 There is a necessity for careful preparation of the hyoid bone and laryngeal cartilages and removal of all soft tissue to reveal every hyoid-laryngeal injury. The technique performed in each case of hanging in our institution implied all soft and solid neck structure dissection and preparations in layers, as well as their thorough examination. In our sample, the bleeding around the fracture was found in every observed subject, which proved the premortem nature of the trauma. ^16,17

In our sample, some form of hyoid-laryngeal fracture was significantly more frequently present in persons older than 30 years (χ ² = 3.911, P < 0.05). In other words, the frequency of hyoid-laryngeal fractures rises in individuals over 30 years of age. This could be explained by the ossification of these structures by ageing. ^18,19

The strength of neck compression in hanging depends on many factors, including body position in the loop. In complete hanging, the loop is tightened by the whole body weight. In incomplete hanging, some of the body weight rests on the floor, thus decreasing the strain of the ligature. The more the segments of the body are supported, the less is the strain on the ligature. The head, torso and upper extremities comprise nearly 60% of the total body weight. ²⁰ Therefore, the tension of the ligature in these positions of hanging will always be significantly higher than in sitting and lying positions. According to Khokhlov, ²⁰ the so-called vulnerability coefficient of hyoid bone/thyroid cartilage shows the highest index in complete hangings of the body: 1.75, though in the other positions it is less: 0.88 in the standing position, 0.63 in kneeling, 0.33 in sitting and 0.25 in the prone position. The frequencies of hyoid-laryngeal fractures strongly correlate with body position in hangings. That is why we considered only the cases of complete hangings and hangings in the standing position.

Strangulation marks in hangings are unevenly pronounced around the neck of the deceased and are evidence of different pressure applied to various neck surfaces. Examination of any segment of the loop encircling the neck shows that two equivalent forces, directed at some angle to each other, are applied to its end. ²¹ The result of these forces, the so-called P value according to Khokhlov, ²¹ is equilibrated by the resilience of the neck tissues and is directed as normal towards the curve of the ligature. In hanging, more characteristic is the oblique position of the loop, so a hanging ligature-mark ellipse with a variable radius of curvature is formed and thus explains changes in the P value along the loop and irregularity in the groove expression. ²¹ Therefore, the depth and direction of the furrow, i.e. the ligature mark on the skin of the neck, if there is one, could indicate the position of the knot in the noose. We used these to make a reconstruction of the knot position in the deceased in the cases where the noose was left at the scene.

As statistical analysis has shown that hyoid-laryngeal fractures appear significantly more often in persons older than 30 years, we only considered that part of the sample for further analysis of a total of 491 deceased – 358 men and 133 women (gender ratio 2.7:1) (Table 2).

There is no statistically significant difference in fracture frequencies of the left and right greater horn of the hyoid bone in relation to eight different positions of the ligature knot (χ ² = 10.830, df = 7, P > 0.05 and χ ² = 11.722, df = 7, P > 0.05, respectively). This implies that a fracture of the greater horn of the hyoid bone is a weak predictor of ligature knot position. On the other hand, fracture frequencies of the left and right superior horn of the thyroid cartilage show a statistically significant difference in relation to the ligature knot position (χ ² = 16.409, df = 7, P < 0.05 and χ ² = 15.078, df = 7, P < 0.05, respectively). Furthermore, a sophisticated statistical analysis, binary logistic regression, showed that the fractures of the left superior horn of the thyroid cartilage occurred significantly more often when the knot position was on the left side of the neck, as well as in the left-posterior and posterior position, and then again that fractures of the right superior horn of the thyroid cartilage were found significantly more often in cases when the knot position was in the right-posterior and posterior position (λ = 0.978, P < 0.01), all in persons older than 30 years.

The absence of any form of hyoid-laryngeal fractures in cases of hanging in persons older than 30 years indicates that the knot position was anterior, but then the presence of either hyoid bone or thyroid cartilage fracture indicates that the knot position could be posterior (χ ² = 28.749, df = 7, P < 0.01; λ = 0.953, P < 0.01). Inner structure neck injuries can be caused in two ways: directly, at the location of the ligature's highest compression, which occurs at the side opposite the position of the knot, or indirectly, because of the neck structures being too stretched, which is most detectable in the area surrounding the position of the ligature knot. The fact that a hyoid bone fracture does not indicate the knot position in persons older than 30 years could imply that direct pressure is more important for fracture development, and that it could also depend on the contact area of the ligature and the neck skin – the thinner the ligature, the higher the applied ligature pressure (per square unit of skin area). It could be hypothesized that superior horns of thyroid cartilage get fractured due to neck stretching on the same side of the ligature knot position, and it does not depend on ligature thickness, but on the weight of the body or body part resting on the ligature: the force could propagate across anatomic neck structures and the throat skeleton, as they form a physiological unit, and then indirectly to the side opposite to the knot.

Our study suggested that the absence of hyoid-laryngeal fractures indicates an anterior knot position in persons older than 30 years. This way, it can be assumed that the force is evenly and symmetrically transferred to lateral parts of the neck, and significantly less to the anterior part, i.e. to the hyoid-laryngeal protrusion. It seems that the knot of the noose located in the chin area neither presses the hyoid bone directly nor significantly stretches the throat skeleton, particularly the thyroid cartilages. On the other hand, in the anterior type of hanging, the highest pressure position is on the posterior side of the neck, and therefore preparation of the soft tissue of the posterior side of the neck would be worthwhile in order to establish an anterior ligature knot position. An anterior knot position could also be signified by an eventual injury of the cervical part of the spinal column. However, this could not be statistically proven because of the small number of subjects with this type of injury.

It can be concluded that fractures of the throat skeleton were very common in cases of standing and full suspension suicidal hangings, especially in persons older than 30 years – around 60% of the cases. In such cases, a fracture of the superior horn of the thyroid cartilage could indicate an ipsilateral position of the knot in the noose. The mechanism of the appearance of these fractures could be the overstretching of the neck during hanging. According to our results, the absence of hyoid-laryngeal fractures could indicate an anterior position of the ligature knot. An anterior subluxation of the cervical vertebrae could indicate an anterior position of the knot as well. On the other hand, our study showed that hyoid bone fractures were not reliable in the reconstruction of the ligature knot position in such cases. These data apply to cases of standing and full suspension suicidal hangings, and not to incomplete hangings in kneeling, seating, prone or other positions. Further investigations concerning the width of the hanging ligature could be more informative in locating knot position in cases of hanging.

Our results pointed to the possibility of reconstructing the location of the ligature knot when the loop furrow is not detectable on the neck skin in cases of standing and full suspension, i.e. complete suicidal hanging, according to hyoid-laryngeal fractures. The derived data would be useful for cases where the ligature was removed from the body of the deceased shortly after the hanging, where the noose is unavailable and in cases where the ligature mark has faded, such as with soft ligatures removed promptly or in decomposed bodies.