You Go Out, Your Arms Go Up
Jonathan Lifshitz, PhD
Director, Translational Neurotrauma Research Program, BARROW Neurological Institute at Phoenix Children’s Hospital
Associate Professor, Department of Child Health, University of Arizona College of Medicine-Phoenix
Joshua A. Beitchman, MBS
Graduate Research Assistant, Translational Neurotrauma Research Program, BARROW Neurological Institute at Phoenix Children’s Hospital
Medical Student, University of Texas Health San Antonio Long School of Medicine
A child receives a hit to the head and falls to the ground. They may not be crying in pain or unconscious, but their arms are held postured in an unnatural position. Why are they reaching upwards or defensively guarding? Observers are aghast, confused, and worried.
This event and those like it are indicative of the Fencing Response, which identify moderate traumatic brain injury or concussion. Upon impact, if direct or indirect forces of injury transmit to the brainstem, then an individual’s forearms are held flexed or extended (typically into the air) for a period lasting up to several seconds. One expression of the posture resembles a fencer’s en guarde stance, thereby earning the name Fencing Response. Reports of the fencing response include all genders, ages, and activities, including organized sport, domestic violence, non-accidental trauma, automobile accidents, violent assaults, and self-inflicted injury.
The Fencing Response originates from motor reflexes in the brainstem. Concussive forces can be transmitted to the vestibular nuclei (lateral vestibular nucleus (LVN); aka Deiter’s nucleus) and mechanically activate primitive reflexes, normally reserved for correcting balance. The motor output arises from vestibular activation of motor nuclei in the anterior column of the spine. The classic reflex is observed as contraction of the upper limb muscles in an extended or flexed position – described as the Fencing Response as illustrated in Figure 1. The same events can activate other muscle groups in the face, neck, abdomen, and lower limbs, but the observation is less overt.
Schematic illustration of the fencing response during a knockout. A. The individual receives a punch or sudden force to the head. B. After the traumatic blow to the head, the unresponsive individual immediately exhibits posturing of the arms (and likely the legs). C. During prostration, the rigidity of the extended and flexed arms is retained for several seconds as flaccidity gradually returns. Photograph. Still frame from a video showing the Fencing Response.
The Fencing Response is used by health care professionals as an overt, visual indicator of moderate injury forces applied to the brainstem and midbrain. This aids in real-time concussion identification and classification for individuals of all ages and in all situations. Observing the Fencing Response should initiate immediate medical attention and adopted concussion protocols. If injury forces were sufficient to elicit the Fencing Response, then the likelihood exists for injury to surrounding areas that could impact breathing, cardiovascular function, alertness, and other brainstem function.
By developing clear and objective indicators of brain injury, such as the Fencing Response, patients can receive immediate medical care and thereby be positioned for optimal outcome. The concussed individual may not be aware of the events of their own injury, its severity, or potential neurological consequences. The Fencing Response removes subjectivity from the evaluation. While a positive Fencing Response, even observed by the lay public, represents a concussion requiring medical attention, an impact to the head without eliciting a Fencing Response may be severe enough to require medical attention. All head impacts require an evaluation from individuals with specialized training on the subject.
Ongoing research at BARROW Neurological Institute at Phoenix Children’s Hospital continues to develop knowledge and tools for early identification of concussion. Our scientists reproduced the Fencing Response in animal models to identify performance based rehabilitation metrics from the molecular to the behavioral level. Ultimately, our scientists work towards biomarkers, like the Fencing Response, that assist our clinicians with diagnostic, prognostic, and therapeutic decision making for our patients.
In sum, the Fencing Response is a diagnostic biomarker identified primarily as forearm posturing that indicates a concussion of moderate severity. Knowledge of this tool can speed access to care for concussed individuals. The clinical and translational research that accompanies the Fencing Response helps to improve the recovery from the acute and chronic effects of concussion for patients of all ages.