Sport-Related Concussion and Lower Extremity Injury
In this blog, I will be discussing the primary research I am conducting for my PhD studies at the University of Nevada, Las Vegas. It has been a bit since I last posted, so I figured it would be best to provide an update of what I have been doing all semester, so I hope you enjoy! (One caveat, I’m not going to reference any literature in this piece, this will be based strictly off my knowledge of the current research. I recently submitted a literature review on this topic for peer-review with the expectation of publication in the near future. I will certainly share this heavily referenced text once that process is complete). Before I get into the nitty gritty of this post, I’d like to start with a cliff notes version of the crux of my dissertation research, which will be followed by a more in-depth analysis.
Sport-related concussions (SRCs) are now classified as a major public health crisis affecting athletes across all major sporting levels. Injury surveillance data has recently determined that compared to their non-concussed counterparts, athletes who sustain a SRC are at greater risk for lower extremity injury well beyond the resolution of traditional SRC assessment batteries. This may in part be attributed to subtle cognitive and neuromuscular deficits that are exposed during dynamic sporting tasks. However, the current literature has yet to elucidate the biomechanical movement patterns of sport-specific activities (i.e. jump-landing) post-SRC. Examination of lower extremity biomechanics after a concussive event may offer objective analysis to provide a rationale for the association between SRC and lower extremity injury risk. Therefore, the purpose of my research is to examine jump-landing biomechanics in adolescent and collegiate athletes with and without a history of SRC.
Our knowledge of SRCs have come a long way in the past few decades. Initially viewed as a lack of “mental toughness”, we are now starting to understand the short- and long-term ramifications of this injury. Millions of athletes per year will sustain a SRC across all sporting levels. While (US) football receives most of the media attention, sports such as soccer, ice hockey, and lacrosse also pose significant risk for a concussive injury. While the risk of subsequent SRCs are significantly (up to 6x) higher following a first concussive event, what many do not know is that these same athletes are at a much greater risk for a lower extremity injury (i.e., anterior cruciate ligament (ACL) tears, ankle sprains, hamstring strains, etc.) for reasons that are largely unknown at this point. Specially, concussed athletes across sporting levels (high school, collegiate, and professional) are at an approximately 1.5 – 4 times greater risk for the aforementioned injuries when compared to athletes who have not sustained a SRC. But here’s where it gets really interesting: The risk of lower extremity injuries post-SRC extends well beyond the resolution of traditional SRC reporting measures – in some cases up to a year after the initial concussive event. In order to best understand the SRC complexity, practitioners must first understand the common assessment batteries administered following such an event. Following this, I discuss why these measures may lack the precision to adequately detect an at-risk athlete for further injury, particularly to the lower extremity.
The three most common ways to assess a SRC are as follows: symptom reporting, neurocognitive evaluation, and balance / sway measures. However, there are issues with all three in terms of returning an athlete back to the field. Bearing in mind that I value all of these tools as part of a multifactorial approach to SRC assessment, it is my goal to develop methods in conjunction with these tools to mitigate further injury after a SRC. Let’s discuss.
Symptom Reporting: With symptom reporting, many athletes (especially adolescents) are unaware of the most common signs following a sustained SRC. There have been numerous studies published on the lack of SRC knowledge at the youth level and it continues to be a big problem (If interested, I can provide a few posters from the CDC HEADS UP program to share with your team!). Another issue is that some athletes will attempt to hide their symptoms in order to stay on the field, there’s a reason why approximately 50% of all SRC are believed to go unreported. This is typically the case in male contact sports, as the literature indicates that female athletes are much more likely to report a suspected SRC. What we must understand is that not every SRC is obvious. Some athletes will experience a headache that can be easily passed off as just the nature of contact sports. Others will demonstrate obvious signs such as postural imbalances, dizziness, or loss of consciousness. The main takeaway with symptom reporting is that education for athletes, parents, and coaches is an absolute must at the start of every season. Even more important is re-education throughout the year, which can be as simple as impromptu quizzes at the end of a training session.
Neurocognitive Evaluation: Neurocognitive exams can be administered with a paper-and-pencil or computerized testing module. These test batteries evaluate various neurocognitive performance indices such as verbal memory, visual memory, reaction time, and visual motor processing speed, and impulse control. While neurocognitive testing has demonstrated superior sensitivity and specificity for determination of a sustained SRC, there a few limitations that must be considered. First, there are issues with athletes “sandbagging” the baseline exam, especially those at the collegiate and professional levels. These athletes are aware of the ramifications of their baseline score, a poor score at the start makes it that much easier to surpass if a SRC were to occur mid-season. This limitation is more directed toward the paper-and-pencil exams, as the computerized modules are typically equipped with validity benchmarks. When an athlete is subjected to neurocognitive testing post-SRC, they are often administered multiple (3-5) exams within a very short time period, potentially inducing practice effects. Essentially what this means is that athletes may score higher on these exams just because they are more familiar with the test itself and may learn testing strategies to score higher. When these exams are administered to non-concussed control athletes over the same time period, baseline scores are typically surpassed. Therefore the question becomes, should concussed athletes be required to best their baseline scores in order to be cleared to play?
The last thing I want to discuss is the administration of these neurocognitive exams. Athletes are seated in a quiet room alone to minimize any distractions – almost the exact opposite of their dynamic sporting environment. This situation begs the question of the generalizability of the results given the conditions. During training and competition, athletes are required to interpret task relevant (e.g., opposition and teammate position) and irrelevant (e.g., crowd noise) environmental cues while performing complex motor tasks. Further, these tests do not account for mental or physical fatigue. An athlete may perform to “baseline” during a computerized exam, but do they demonstrate this same performance in the 4th quarter?
Balance / Sway Measures: The two most common balance and sway measures post-SRC are the Balance Error Scoring System (BESS) and Sensory Organization Test (SOT).
The BESS test is subjectively scored by the clinician as the athlete completes various stances on two surface conditions (flat and foam) with their eyes closed. Error scores are calculated (e.g., opening eyes, lifting hand off hip) for each stance condition over the course of 20 second trials. Despite athletes typically requiring a greater recovery time, BESS data has demonstrated impaired postural control up to 3-5 days post-SRC. However, recent review papers on the BESS has demonstrated inadequate reliability in a clinical setting (< 0.75), and this may be attributed to the subjective nature of the test (e.g., different clinicians analyzing the same athlete over an acute time frame) and the aforementioned practice effects from repeated testing.
On the other hand, the SOT produces objective balance scores utilizing dynamic posturography under six different stance conditions. Sensory deprivations under certain conditions allow the SOT to determine visual, vestibular and / or proprioceptive impairments. Not surprisingly, the SOT has demonstrated superior sensitivity and reliability, when compared to the BESS. Reviews of SOT data have demonstrated balance impairments up to 10 days following a SRC. However, researchers question the practicality of the SOT, again due to its analysis of static posture not representative of dynamic sporting movements. Additionally, the SOT is a very expensive tool, excluding many concussed athletes from access to this type of analysis.
So you have stated the issues…what are the solutions?
To reiterate, I believe the above-mentioned assessment tools have great clinical utility and should absolutely be implemented prior to- and post-SRC. My concern lies in the ability of these tools to translate into a dynamic sporting environment that poses a potentially heightened risk for a lower body injury post-SRC. However, recent gait analysis in concussed athletes has demonstrated locomotor deficits that extend beyond the resolution traditional SRC management tools. Post-SRC, adolescent and collegiate athletes have demonstrated slower walking speeds, greater frontal plane instability, and decreased cognitive performance as the gait task becomes increasingly difficult (e.g., performing a dual motor and/or cognitive task). Studies have also obstacle avoidance strategies during gait that suggest deficiencies in executive functioning, spatial awareness, and information processing. It is recommended that gait analysis be included within a SRC assessment protocol, but more research is warranted to determine best practices in sport. Perhaps it is best to have the athlete perform various walking tasks (i.e., forward, backward, and tandem) while implementing a cognitive task (i.e., reciting the months backwards or counting by threes).
This now brings me to my current research. Specifically, I am examining jump-landing biomechanics in adolescent and collegiate athletes with and without a history of SRC. My (current) first study is in the adolescent population. Thus far, our data has shown landing mechanics that would suggest a greater risk of injury to the lower body in those who have sustained a previous SRC. Post-SRC, athletes are demonstrating greater ground reaction forces and loading rates, increased knee valgus angles, and less sagittal knee ROM during various landing tasks. A large sample size is necessary before making any definitive conclusions, but if these patterns hold with a larger n, it may start to provide a biomechanical explanation as to why athletes are at greater risk for a lower body injury post-SRC. It has been suggested that subtle cognitive and neuromuscular impairments linger well after an athlete has been cleared for sporting participation. Biomechanical analysis of dynamic, complex movement tasks may help reveal these abnormalities that are not detected by our traditional reporting measures. The goal moving forward with these studies is to incorporate cognitive stressors during the jump-landing maneuvers to make the analysis more sport-specific. With the tools and the assistance of my current research, it is the hope that we will be able to further advance and develop appropriate lower body movement screenings that will be quintessential to any SRC toolbox. Stay tuned!
(Adolescent landing biomechanics from my first concussion study)
Thanks for reading!