Biomechanics and injury risk of a headbutt

Force and velocity of impact during upper limb strikes in combat sports: a systematic review and meta-analysis

Upper limb strikes are frequent movements in combat sports and self-defence systems, in which numerous types of strikes can be applied. Therefore, the aim of this systematic review and meta-analysis was to summarise and compare the mechanical consequences of different types of upper limb strikes among various sports disciplines. A literature search was conducted in Scopus and Web of Science, with the following search formula: (impact force) AND (strike) AND (taekwondo) OR (karate) OR (self-defence) OR (combat sport) OR (boxing). The search resulted in 28 studies describing 9 kinds of strikes, where straight punches and reverse punches have larger mean impact forces than the kung fu punch (p < 0.001) and that a palm strike had a lower strike velocity (p < 0.001) than a reverse punch, straight punch, or junzuki punch. The highest recorded mean force was found for a straight punch (3427 N). Athletes in mixed martial arts, trainers of self-defence or tactical coaches can expect that straight punches and reverse punches should be performed at high speeds (over 10 m/s) and provide similar or larger impacts than other upper limb strikes; therefore, those punches should favour a combat athlete to win a competition or succeed in self-defence.

Injury pattern and the biomechanical assessment of skull fracture risk in blows with a rubber mallet

Acts of violence often result in blunt force trauma. On behalf of the court, forensic experts not only have to assess injuries in terms of morphology or severity, but they also have to give statements regarding the risk of potential fatal injuries. We describe a case of domestic violence where a man hit the head of his wife using a rubber mallet. His wife sustained extensive and multiple parietal scalp lacerations and avulsions with exposure of the cranial bone. A CCT revealed neither skull fractures nor intracranial injuries. Biomechanical measurements were performed using a bowling ball and an animal head representing head surrogates. In comparison to steel hammer impacts we hypothesized longer contact durations and lower maximum contact forces in blows with a rubber mallet. However, contact durations in the magnitude of 3ms do not confirm our hypothesis. The contact forces calculated based on mallet and animal head accelerations were between 2.97kN and 4.68kN. These force values are rather below the parietal fracture thresholds, explaining the absence of parietal skull fractures in the case presented. Moreover, the relatively low Young's modulus comes along with a deformation of the rubber mallet and a decrease in contact pressure. In summary, contact times could be reliably estimated, while contact forces remained largely uncertain.

Pedestrian hit by a car impacted metal pole: reconstructing the head load

Fatal head injuries are frequently seen in pedestrians hit by motorized vehicles. In our case, the pedestrian sustained a devastating head injury with skull splitting in the mediosagittal plane. A car collided with a traffic sign causing a bending of the pole. The metal pole hit a man standing close beside it; the man had a head injury severity that is more commonly due to falling objects than due to traffic accidents. Assuming a head mass of 5 kg, simplified calculations yield maximum contact forces of ca. 36 kN exceeding mean parietal fracture forces which are in the order of magnitude of 12.5 kN. The influences of the effective body mass and the horizontal distance between the pole and the pedestrian on maximum contact forces are investigated. High contact forces in our case can be mainly explained by the comparably high impact velocity and by a partial mass transfer of the total car mass to the pole.

Maxillofacial fractures and craniocerebral injuries - stress propagation from face to neurocranium in a finite element analysis

Background

Severe facial trauma is often associated with intracerebral injuries. So it seemed to be of interest to study stress propagation from face to neurocranium after a fistlike impact on the facial skull in a finite element analysis.

Methods

A finite element model of the human skull without mandible consisting of nearly 740,000 tetrahedrons was built. Fistlike impacts on the infraorbital rim, the nasoorbitoethmoid region, and the supraorbital arch were simulated and stress propagations were depicted in a time-dependent display.

Results

Finite element simulation revealed von Mises stresses beyond the yield criterion of facial bone at the site of impacts and propagation of stresses in considerable amount towards skull base in the scenario of the fistlike impact on the infraorbital rim and on the nasoorbitoethmoid region. When impact was given on the supraorbital arch stresses seemed to be absorbed.

Conclusions

As patients presenting with facial fractures have a risk for craniocerebral injuries attention should be paid to this and the indication for a CT-scan should be put widely. Efforts have to be made to generate more precise finite element models for a better comprehension of craniofacial and brain injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13049-015-0117-z) contains supplementary material, which is available to authorized users.