Researchers analyzing more than three million patients in Ontario found that even a concussion can leave permanent impairments to driving, increasing the risk of a crash far more than conditions such as sleep apnea or epilepsy.
Study: Concussion and risk of subsequent traffic accident: retrospective cohort analysis in Ontario, Canada. Image credit: Southworks/Shutterstock.com
Concussion, a form of mild traumatic brain injury, can significantly increase the risk of a subsequent motor vehicle crash, according to a new study published in BMJ Open.
Understanding concussions and driving
Road traffic accidents are a major cause of morbidity and mortality worldwide. Certain medical conditions, such as epilepsy, sleep apnea, or substance use disorder, that cause cognitive and functional impairments can potentially increase the risk of a motor vehicle crash.
Thoughtful counseling and medical care for people living with these conditions can potentially reduce traffic accidents and save lives. In some countries, policies mandate that clinicians provide safety warnings to patients who are medically unfit to drive due to functional deficits.
A concussion is a type of mild traumatic brain injury caused by a direct blow to the head. The condition is associated with temporary deficits in function after which the affected individual recovers. Symptoms sometimes last for weeks, including headaches, insomnia, dizziness, amnesia, fatigue, confusion, irritability, depression, delayed reaction time, and difficulty concentrating.
Although most people recover without long-term effects, there is still uncertainty about whether recovery is complete and whether there is no ongoing damage. Another difficulty is that one concussion can predispose patients to another concussion with further neurological consequences.
Given the potential association of concussion with neurocognitive and functional deficits, the current study aimed to investigate whether a prior concussion increases the risk of a subsequent traffic accident.
A total of 3,037,028 patients were analyzed, including 425,158 with concussion and 2,611,870 with ankle sprain (active controls). The risk of motor vehicle accidents requiring emergency medical care was compared between patients with concussion and ankle sprain.
Concussions increase the risk of a crash
The study identified a total of 200,603 patients with a concussion or ankle sprain who suffered a subsequent traffic accident during a 10-year follow-up period. This estimate equated to an absolute risk of 1 in 15 patients.
The risk of a car accident was 49% higher in patients with concussions compared to those with ankle sprains. The risk was particularly high in the first month after concussion, showing an approximately sixfold increase compared to controls.
Other factors significantly associated with an increased risk of a post-concussion traffic accident were younger age, male sex, rural home location, lower socioeconomic status, late-night driving, and alcohol abuse diagnosis.
A separate analysis that included patients with more than one concussion revealed a 73% higher risk of a traffic accident after a single concussion. 114% higher risk after two concussions. and a 124% higher risk after three strokes. However, such a strong dose-response relationship was not observed in patients with multiple ankle sprains.
Artificial intelligence (XGBoost) models were applied to adjust for potential confounders and confirmed that concussed patients still had an approximately 40% higher crash risk compared to controls, supporting the robustness of the association. “Negative control” analyzes for unrelated medical emergencies such as conjunctivitis and kidney stones showed no excess risk. Furthermore, they reported that the observed relationship between concussion and crash risk was specific and not general across all medical conditions.
Implications for safer driving
The study reveals that concussion significantly increases the risk of a subsequent motor vehicle crash, particularly during the first few weeks after a concussion. The risk is greatest after two or more concussions.
Previous simulation studies suggest that concussion is associated with specific neurological impairments that may result in reduced vehicle control, changes in driving skills, or persistent driving impairments. A study of adults reported an association between mild traumatic brain injury and abnormal driving behaviors. These impairments may contribute to the risk of a car accident.
The magnitude of concussion-related crash risk observed in the study is significantly higher than previously estimated risks associated with sleep apnea or uncontrolled epilepsy, warranting a safety warning from clinicians.
Overall, the findings of the current study suggest that current mitigation efforts are insufficient. Since driving has become an essential part of modern life, clinicians should advise concussed patients to be cautious about the increased risk of a traffic accident.
Post-concussion risks can also be reduced by effective symptom care, such as treating headaches, sleep disorders, depression, and substance abuse. Other risk mitigation strategies include temporarily reducing exposure to traffic by avoiding high-speed, long-distance road trips or late-night driving. Campaigns that raise awareness about concussion-related traffic accidents can also protect the patient and the community.
Since the causality of the observed associations could not be determined, it is possible that factors that predispose patients to concussion may also predispose patients to car accident. This possibility of reverse causation highlights that concussion is not necessarily the cause of a subsequent crash and that prioritizing concussion treatment may not necessarily improve road safety.
The presence of potential confounders makes it difficult to identify the mechanisms underlying the association between past concussion and future risk of a traffic accident. Additionally, each concussion is unique in anatomy, energy, angularity, and severity. Therefore, average risks may not apply to individual patients.
Since a concussion is often associated with impaired attention, delayed reactions, transient confusion, mood disturbances, cardiac arrhythmia, memory deficits, and sleep difficulties, future research is needed to assess neurocognitive deficits after concussion.
