Concussion significantly increases the risk of subsequent injury in the lower limb, particularly among athletes returning to play after such an event. This essay explores the epidemiological evidence, biomechanical and neurological mechanisms, timeframes of elevated risk, and implications for injury prevention.
Epidemiological Evidence
Recent studies consistently show a heightened incidence of lower limb injury following concussion, with risks elevated both among amateur and professional athletes. For example, collegiate athletes demonstrated a 58% greater risk of lower extremity musculoskeletal injury post-concussion. This added risk may remain for months up to a year, especially pronounced within the first 90 days after return to play. A large-scale analysis of soldiers found a 38–45% greater hazard for lower extremity injury among those who had sustained concussion compared with matched non-concussed controls
The consistency of increased risk across populations—high school, collegiate, professional athletes, and military personnel—supports the generalizability of this association. Additionally, a history of multiple concussions is correlated with an even higher risk of future musculoskeletal injuries in the lower limb.
Neuromechanical Explanations
The mechanism underlying this increased risk appears to be related to persistent neuromuscular control deficits following concussion. While standard concussion protocols focus on symptom resolution, individuals may continue to experience subtle motor abnormalities despite feeling symptom-free. Studies examining post-concussion athletes found altered movement patterns, such as greater knee valgus and increased knee internal rotation during jump-cut maneuvers—both implicated in higher injury risk, such as ACL tears
Changes in lower limb stiffness during landing, delayed muscle activation, and disruptions in motor planning are commonly observed in post-concussion athletes. These neuromuscular disturbances may result from lingering impairment of central nervous system processing, affecting joint position sense, balance, and coordination.
Biomechanical Changes and Injury Risk
Biomechanical studies highlight that many post-concussion athletes display atypical gait and landing mechanics, which can predispose them to non-contact injuries such as sprains, strains, and tears. For example, increased dynamic knee valgus is strongly associated with non-contact ACL injuries. Inadequate neuromuscular control may undermine the protective mechanism during rapid direction changes or load absorption, commonly required in many sports.
These alterations are not necessarily detected by routine return-to-play evaluations, which may depend heavily on subjective symptom reporting and basic balance testing. Consequently, some athletes are cleared for play while still harboring deficits that increase lower limb injury risk.
Duration of Increased Risk
While the pattern is clear, the duration of elevated injury risk is still debated. Some research indicates risk persists for up to one year, with the highest vulnerability within the first three months following concussion. However, as neuromuscular function gradually improves, this heightened risk may diminish. Sub-analysis indicates college athletes are less likely to experience increased lower extremity injury risk at one year post-concussion compared to immediately after return to play.
Such findings have critical implications for post-concussion management in athletes. Continuous evaluation and gradual reintroduction to full activity may help minimize the window of heightened risk.
Mechanistic Theories
Several mechanistic theories seek to explain the link between concussion and lower limb injury risk:
- Central Sensory Deficits: Concussive injuries can disrupt integration of sensory inputs needed for coordinated movement, balance, and agility, increasing susceptibility to missteps or awkward landings.
- Motor Planning Disruption: Subtle deficits in executive motor control can delay muscle activation or alter movement strategies during sport-specific tasks.
- Delayed Reaction Time: Even after apparent clinical recovery, cognitive and motor reaction times may remain slowed, hampering athletic responses to unpredictable situations and thus increasing injury risk.
- Psychological Factors: Anxiety about re-injury or decreased confidence in movement ability may also alter biomechanics in the lower limb.
- Insufficient Rehabilitation: Rapid clearance and return to play without comprehensive neuromuscular and functional assessments may leave athletes vulnerable.
Implications for Clinical Management
Given the evidence, clinicians should recognize that symptom resolution does not necessarily equate to full physiological recovery post-concussion. Consideration of underlying neuromuscular deficits is essential. Standard concussion tests may miss subtle deficits in coordination, proprioception, and muscle firing patterns crucial for safe athletic movement.
Actual injury rates after concussion suggest the need for more robust clearance protocols, possibly including validated neuromuscular testing, gait and movement analysis, and continued monitoring post-return to play. Moreover, periodic re-evaluation may catch lingering deficits that predispose athletes to injury.
Future Directions
Ongoing research should further explore:
- Quantifying the time course of motor recovery and injury risk after concussion.
- Expanding biomechanical and neuromuscular assessment protocols for return-to-play decision-making
- Developing specific rehabilitation programs aimed at restoring neuromuscular control and reducing lower extremity injury risk.
- Investigating individualized recovery paths, given variation in concussion effects, and tailoring intervention strategies accordingly.
Concussion acts as an important risk factor for subsequent lower limb injury, particularly in the months immediately following return to play. Elevated risk may be attributed to lingering neuromuscular and biomechanical deficits, not always detectable via standard clinical evaluation. Integrating neuromuscular assessment and targeted rehabilitation into concussion protocols—and recognizing the need for extended vigilance—can help reduce injury rates and safeguard athlete health. The observed association underscores the importance of holistic concussion management beyond symptom resolution, highlighting a new facet of injury prevention in sports medicine