College athletes are almost twice as likely to experience acute lower extremity musculoskeletal injury after concussion. These findings are in line with previously published data that professional European soccer players are at increased risk of musculoskeletal injury after concussion (20). The previously published data demonstrated that the risk of subsequent injury during the 12-month follow-up period was approximately two times greater in the athletes with concussion compared with that in nonconcussed athletes. Although this study was the first to highlight the association between concussion and musculoskeletal injury rates, the applicability of the findings was limited to European soccer players. We believe that our investigation constitutes the first published report of the acute lower extremity injury rates after concussion in collegiate athletes participating in a variety of sports. Furthermore, a key limitation to the previous research was the disparity of concussion management protocols. Because teams came from a wide variety of professional soccer clubs across Europe, concussion diagnostic criteria likely differed. Our study assessed athletes from the same institution operating under the same concussion management policy, limiting the effect of disparate concussion diagnostic criteria.
Several potential explanations exist for the increased injury rates after concussion. The time away from training due to concussion may have led to increased musculoskeletal injury risk after return to activity. We believe that this is an unlikely reason for increased rates of musculoskeletal injuries after concussion. Our findings are similar to those reported by Nordström et al. (20), in that we found increased rates of musculoskeletal injury for up to 365 d after concussion. Another potential explanation for increased musculoskeletal injury rates in athletes with concussion is that the athletes with concussion are more prone to injury in general as compared with other athletes. Although a possible contributor to increased musculoskeletal injury risk, our data showed similar injury rates between the group with concussion and the control group before athletes in the group with concussion sustained a concussion. This is in contrast to a previous report that observed athletes with concussion were more prone to injury before their concussion (20). Further long-term prospective investigation is needed to allow for better understanding of the effect of injury-prone athletes when investigating musculoskeletal injury rates after concussion.
It is important to note this study did not directly investigate possible mechanisms for the increased musculoskeletal injury rates. Future research should seek to identify the specific causes of increased musculoskeletal injury rates after concussion. In line with similar investigations (20,2420,24), we propose several possible mechanisms in the following section to begin the discussion of future research in this area.
Previously published literature regarding functional movement after concussion may provide insight into the underlying cause of the increased musculoskeletal injury rates. Deficits have been noted in gait after concussion, both acutely (3,21,223,21,223,21,22) and beyond an athlete’s return to activity (4,15,22,234,15,22,234,15,22,234,15,22,23). After concussion, athletes display more conservative gait strategies (2–5,21,222–5,21,222–5,21,222–5,21,222–5,21,222–5,21,22) and deficits in dynamic balance (2,3,10,21,222,3,10,21,222,3,10,21,222,3,10,21,222,3,10,21,22). These dynamic balance deficits after return to activity after concussion are not dissimilar to neuromuscular and postural control deficits noted in prospective lower extremity injury risk factor analyses. Previous research of healthy individuals demonstrated that postural (26) and neuromuscular control deficits can increase the risk of sustaining noncontact lower extremity injuries (30). In addition, females who displayed abnormally large side-to-side dynamic balance differences and individuals with trunk neuromuscular control deficiencies are at increased risk of lower extremity musculoskeletal injury (26,3026,30). This is important to note because as the previously described gait studies show, there are alterations in trunk positioning and velocity after concussion. These abnormal trunk biomechanics may increase an individual’s risk of sustaining an injury after concussion.
Disrupted cortical pathways after concussion may also plausibly explain increased acute lower extremity musculoskeletal injury rates after concussion (6,13,14,276,13,14,276,13,14,276,13,14,27). Researchers have demonstrated lower intracortical facilitation (27), lower maximal voluntary muscle activation (27), increased intracortical inhibition (6), increased motor-evoked potential latency, and decreased motor-evoked potential amplitude (13,1413,14). Similarly, individuals with chronic ankle instability have higher resting motor thresholds than individuals without chronic ankle instability and self-report more disability during activity (25). These findings suggest that reduced cortical excitability may be associated with functional disability. Although still a hypothesis, reduced cortical excitability observed after concussion may contribute to overall reductions in function ability. The brain’s ability to effectively control and coordinate movement after concussion may be impaired. In a dynamic athletic setting, any disruption of the cortical pathways to the musculoskeletal system has the potential to negatively affect movement. Although it has yet to be directly investigated, we hypothesize that these disrupted cortical pathways may increase the interval between reaction and movement time. This increased latent period has the potential to increase musculoskeletal injury risk during the cognitively and physically challenging demands of high-level athletics. Cortical changes are fairly subtle and only detectable with sophisticated laboratory equipment. The current means of assessing static balance may not be sensitive enough to detect all impairments. In addition, these cortical changes may not affect simple static balance or standard gait but may become more pronounced during physically and cognitively challenging athletic tasks.
These data, along with our findings of increased lower extremity musculoskeletal injury rates after concussion, provide compelling evidence that deficiencies after concussion may be uniquely measured beyond standard neurocognitive, static balance, and symptom reporting deficits. Importantly, the underlying mechanism for these lingering balance deficits must be explored further. If our current measures of balance after concussion are not sensitive enough to detect deficits, more functional balance assessments should be identified. To our knowledge, researchers have yet to explore any functional movement deficiencies that may be present during sport-related activity after concussion such as cutting and jumping. Understanding the changes in neuromuscular control and functional movement during sport-related activities may provide the scientific basis for explaining the increased musculoskeletal injury rates we observed after concussion. Future research should explore lower extremity biomechanical outcomes during functional movement after concussion in addition to true functional reaction time measures.
There were several limitations to our research. Our sample size was relatively small. We believe that this is the reason we did not observe significant differences in injury rates within the 90- and 180-d window between the group with concussion and the control group after concussion and in the 90-d before-with-after-injury comparison within the group with concussion. The confidence intervals included in Tables 2 and 3 indicate the clinical significance of our findings in the absence of statistically significant findings. Our data collection was completed retrospectively on the basis of recorded notes of injuries; thus, we relied on the accuracy of clinicians reporting the injury information. Electronic medical records have some inherent limitations and have the potential to be unreliable. To help combat this potential issue, we used a standardized data collection form and strict operational definitions for abstracting injury data. All our data came from a single institution whose clinicians follow the same standardized injury-reporting protocols. Some lower extremity injuries experienced by those who sustained a concussion may have increased their risk of subsequent lower extremity injury. Although this is certainly possible, we believe that this is an unlikely explanation for within- and between-group differences because our groups had similar injury rates before the concussion. Concussions may have gone unreported in our sample, possibly affecting our outcomes. In addition, the results of our findings cannot be extrapolated to include athletes of other age groups (e.g., professional, high school, or youth) or skill levels. Future research should investigate these other cohorts to identify musculoskeletal injury rates after concussion.
College athletes are at increased risk of acute lower extremity musculoskeletal injury for up to 365 d after concussion. Future research should explore the underlying causes of the increased risk.
We thank Dr. Kevin Carneiro, Dr. Marshall Ney, and Tyler Powell for their efforts in assisting with data collection.
None of the authors have any conflicts to disclose, nor did they receive funding to conduct this study.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:© 2015 American College of Sports Medicine
MUSCULOSKELETAL INJURY RISK; POSTCONCUSSION DEFICITS; CONCUSSION; INJURY; COLLEGE ATHLETICS