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Concussion Mechanics: Exploring How Impact Location Influences Concussion Symptoms.
Many factors affect the mechanics of a concussion. Some of the most important questions are:
How fast were you moving?
Did you hit your head directly?
How much force was transferred from the impact to your brain?
Was it a straight-line impact, or was rotation involved?
Did you see the impact coming, or was it a surprise?
Many mechanical factors can determine whether a concussion is sustained, but does the location of the impact matter for the symptoms someone experiences after a concussion?
This blog post will outline which symptoms can be traced back to impact location and which symptoms are likely driven by non-mechanical factors.
A Reminder of the Mechanisms of a Concussion (or Mild Traumatic Brain Injury).
The definition of a concussion, as defined by the International Conference on Concussion in Sport, is “a traumatic brain injury caused by a direct blow to the head, neck or body resulting in an impulsive force being transmitted to the brain that occurs in sports and exercise-related activities.” (Patricios et al., 2023)
This impact has a force translated from the body, head, or neck into the brain, causing shearing forces and metabolic changes within the brain cells, leading to a functional brain injury.
Some key factors to remember from this definition are:
You do not need to be hit in the head to sustain a concussion.
There must be sufficient force to the head, neck, or body to transmit to the brain.
There may be additional injuries to the head and neck alongside the brain injury.
Now that we remember what causes a concussion let’s dive into whether impact location means anything and what symptoms a person may experience.
There is Some Theoretical Importance of Impact Location, but it Does Not Seem to Translate to Sport-related Concussions.
Depending on the activity, there can be a variety of different injury mechanisms that lead to a concussion. However, one thing they all have in common is a shearing or “over-stretching” effect on the brain’s neurons, which impairs their function.
Depending on what brain areas experience this shearing effect, there can be different symptoms associated with the development of a concussion. For example, in a research study by Danielli et al. (2023), they listed some of the most injured brain areas and some associated symptoms.
BRAIN AREA
FUNCTION
SYMPTOMS
Amygdala
Emotional processing, motivation
Headache, fogginess, sadness, nervousness, more emotional, trouble sleeping, etc
Hippocampus
Memory and learning
Feeling foggy, difficulty remembering, etc
Inferior parietal lobe
Visuospatial navigation, sound perception and memory, decision-making
Headache, dizziness, balance problems, light and noise sensitivity, etc
Visual cortex
Processing visual information
Nausea, vomiting, sensitivity to light, blurry vision, etc
Unfortunately, while we can start to predict what brain structures are causing what symptoms, there is not much evidence on how different impacts affect those brain structures.
There have been some studies based on computer modeling of concussions that suggest there are different brain regions that are more or less impacted by various types of injuries, but that does not seem to translate to real-world applications.
In the study mentioned above, Elkin et al. 2018 used a computer model to see how variables associated with a tackle in football could affect the different strains on the brain tissues. They found that approximately one-third of the brain strain came from the location of the impact, with just over half of the brain strain coming from the speed of the incoming player. This suggests that impact location could play a role in which brain regions become the most injured and, subsequently, what symptoms patients experience.
Unfortunately, when we translate and apply that computer model to sports, it does not have as much significance as we first thought.
A research study looked at the concussion mechanics and injury severity to see if impact force and location mattered for a patient’s symptom profile in youth football players. They found no link between head acceleration, peak rotational acceleration, or number of impacts before the injury and a patient’s concussion symptom burden and recovery. Additionally, there was no link between impact location and the presence of any single concussion symptom(s) (Rowson et al., 2017).
Impact Location Appears to Matter More for Concussion Risk Rather Than Symptom Profile.
Unlike the symptom profile, the location of the impact does appear to increase or decrease the likelihood of sustaining a concussion.
However, it is good to remember that you can sustain a concussion with an impact to any part of the head or body; there are just some locations that may require less force.
When looking at impacts during a football season, most concussions resulted from players colliding with the front of the head (44.7%) and side of the head (22.3%).
In addition, players who sustained concussions from impacts to the top of the head were significantly more likely to lose consciousness than those who suffered concussions by being impacted in different parts of the head (Zachary et al., 2014).
The idea that the impact kinetics matters more than the location of the impact was further strengthened by Beckwith et al. in 2018, who ran computer models on the impacts that caused concussions in athletes. They found that linear acceleration of impact was more closely related to the diagnosed concussion than any intracranial measures (other than estimated changes in intracranial pressure).
The One Place Impact Location Does Matter: The Neck.
While it doesn’t seem that brain-specific symptoms are predictable based on the location of the impact, symptoms coming from the neck (cervical spine) are more predictable.
When you are hit in the head or body, physics tells us that different body parts will move at different speeds because of differences in momentum. Your head and body are different weights. Therefore, if you are hit in the head, your head will move, your body will stay still, and vice versa.
There is a great video that shows this principle below:
Depending on the angle of impact and the rotation of the neck, some structures will experience more stress and strain than others. Because each concussive impact can be unique, it is a good idea to have an in-depth discussion with your healthcare provider about the exact injury mechanism so they can get an idea about what structures were likely the most strained.
Here is an example:
A hockey player was checked into the boards from behind, and when they hit the boards, their cervical spine went into hyperextension (too far backward) and right rotation.
In this instance, we would expect to see muscular injuries from the overstretching of neck muscles in the front left side of the neck and compression injuries to the joints and other structures in the back-right side of the neck.
Based on this information, this player would likely have pinching neck pain on the right side when looking up or rotating to the right (from compression of the injured joints) and a headache radiating from the neck around the left eye and forehead (pain spreading from the injured muscles).
The picture above details the referral pattern for the sternocleidomastoid muscle (SCM). When muscles are injured (usually from overstretching), their pain pattern is predictable based on the muscle. For the SCM, we see pain primarily in the back of the head, around the eye, and in the forehead on the same side.
The referral patterns of neck muscles are a significant contributor to post-concussion headaches that are seen in most concussion patients.
For more information on post-concussion headaches and how to treat them, please see our other blog post here.
The neck and its connection to the eyes
The second way that a neck injury can predictably cause specific concussion symptoms is the neck’s relationship to the eyes through a group of muscles called the suboccipitals.
The suboccipital muscles can help to coordinate neck and eye movements, and in some people, they can be the cause of dizziness, balance issues, visual tracking problems, blurry vision, and eye fatigue.
Because of their location, the suboccipital muscles can also be injured depending on the rotation and position of the neck during the concussive impact. Common complaints with suboccipital injury or dysfunction are a one-sided headache in the temple region and difficulty with eye tracking or balance, especially when the head is rotated to one side.
In the real world, patients with suboccipital dysfunction may have trouble with activities like reading, driving, working on a computer, and other visually demanding tasks that require the coordination of both the neck and eyes for proper function.
In conclusion, there is little evidence that location impact matters for developing specific concussion symptoms.
There is evidence that the risk of concussion can depend on impact metrics such as speed of impact, impact location, rotational force, etc. Still, there is no ability to predict what symptoms develop after that.
The neck is an area where symptoms correlate better with impact location. Depending on what structures are strained or sprained, there will be a different set of symptoms that are likely to present. It is not an exact science, but there is some biomechanical plausibility.
Overall, it is best to give your healthcare provider as much detail about your concussion injury as possible. Even, if we cannot perfectly predict the symptoms that may develop, it can still inform what tests to conduct and what symptoms to watch for.
References
Patricios JS, Schneider KJ, Dvorak J, et alConsensus statement on concussion in sport: the 6th International Conference on Concussion in Sport–Amsterdam, October 2022British Journal of Sports Medicine 2023;57:695-711.
Danielli E, Simard N, DeMatteo CA, Kumbhare D, Ulmer S, Noseworthy MD. A review of brain regions and associated post-concussion symptoms. Front Neurol. 2023 Aug 3;14:1136367. doi: 10.3389/fneur.2023.1136367. PMID: 37602240; PMCID: PMC10435092.
Elkin BS, Gabler LF, Panzer MB, Siegmund GP. Brain tissue strains vary with head impact location: A possible explanation for increased concussion risk in struck versus striking football players. Clin Biomech (Bristol, Avon). 2019 Apr;64:49-57. doi: 10.1016/j.clinbiomech.2018.03.021. Epub 2018 Mar 29. PMID: 29625747.
Rowson S, Duma SM, Stemper BD, Shah A, Mihalik JP, Harezlak J, Riggen LD, Giza CC, DiFiori JP, Brooks A, Guskiewicz K, Campbell D, McGinty G, Svoboda SJ, Cameron KL, Broglio SP, McAllister TW, McCrea M. Correlation of Concussion Symptom Profile with Head Impact Biomechanics: A Case for Individual-Specific Injury Tolerance. J Neurotrauma. 2018 Feb 15;35(4):681-690. doi: 10.1089/neu.2017.5169. Epub 2018 Jan 19. PMID: 29132269.
Zachary Y. Kerr, Christy L. Collins, Jason P. Mihalik, Stephen W. Marshall, Kevin M. Guskiewicz, R. Dawn Comstock; Impact Locations and Concussion Outcomes in High School Football Player-to-Player Collisions. Pediatrics September 2014; 134 (3): 489–496. 10.1542/peds.2014-0770
Morin M, Langevin P, Fait P. Cervical Spine Involvement in Mild Traumatic Brain Injury: A Review. J Sports Med (Hindawi Publ Corp). 2016;2016:1590161. doi: 10.1155/2016/1590161. Epub 2016 Jul 26. PMID: 27529079; PMCID: PMC4977400.
Beckwith JG, Zhao W, Ji S, Ajamil AG, Bolander RP, Chu JJ, McAllister TW, Crisco JJ, Duma SM, Rowson S, Broglio SP, Guskiewicz KM, Mihalik JP, Anderson S, Schnebel B, Gunnar Brolinson P, Collins MW, Greenwald RM. Estimated Brain Tissue Response Following Impacts Associated With and Without Diagnosed Concussion. Ann Biomed Eng. 2018 Jun;46(6):819-830. doi: 10.1007/s10439-018-1999-5. Epub 2018 Feb 22. PMID: 29470745; PMCID: PMC5935583.
Dr. Steven Murray is a chiropractor located in downtown Toronto, Canada at Back in Balance clinic with an active living and rehabilitation-based practice. He has a special interest in working with all people of all athletic abilities to reach their fitness and wellness goals. Dr. Murray completed his undergraduate and Master’s degree in Exercise physiology at McGill University. He also completed his Doctor of Chiropractic degree at Canadian Memorial Chiropractic College. Dr. Murray treats a variety of spine related conditions, but also has a special interest in treatment of acute and chronic concussions, along with running- related injuries. In practice, he uses his previous experience in research to provide patients with the most up-to-date evidence-based treatment, so his patients receive a proven treatment plan that is tailored to their specific needs.