Reaction Time at the Time of Unrestricted Return to Activity Following Concussion and the Subsequent Risk of Acute Lower Extremity Musculoskeletal Injury

Abstract Text: Context: Emerging evidence suggests that athletes and military service members are at increased risk for acute lower extremity musculoskeletal injury (LEMSKI) following concussion; however, no prospective studies have examined the association between deficits at the time of unrestricted return-to-activity (URTA) after concussion and the subsequent risk of acute LEMSKI. Emerging evidence suggests that deficits in reaction time following concussion may be associated with this increased risk of LEMSKI. The purpose of this study was to determine if reaction time, assessed through computerized neurocognitive assessments administered at the time of URTA, was associated with acute LEMSKI risk within the subsequent 12-months.

Methods: A prospective cohort study was conducted to examine the association between computerized neurocognitive assessments of reaction time, administered at the time of URTA following concussion, and the subsequent risk of acute LEMSKI among military service academy cadets enrolled in the Concussion Assessment, Research and Education (CARE) Consortium at a single site. From August 2015 to May 2018, 325 incident cases of concussion were observed among cadets (198 Male, 127 Female). Active injury surveillance within the cohort was conducted for 12-months following URTA to identify any incident cases of acute LEMSKI. Acute LEMSKI was defined as any acute injury (i.e., fracture, strain, sprain) to the foot, ankle, lower leg, knee, thigh, or hip, as the result of a single traumatic event documented by a medical provider in the cadet’s medical record. Reaction time was measured at the time of URTA using the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT) reaction time composite score. For analysis, reaction time was examined as a continuous variable and as a categorical variable (tertiles) to optimize model fit and interpretation. Other potential risk factors considered included sex, pre-concussion baseline reaction time, level of sport participation, and LEMSKI history. The primary outcome of interest was time from URTA following concussion to incident LEMSKI during the subsequent 12-months. Kaplan-Meier survival estimates were calculated by group (fastest tertile, middle tertile, slowest tertile) for reaction time at the time of URTA. Univariate and multivariable Cox proportional-hazards regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (95%CI) for reaction time and other potential risk factors for acute LEMSKI during the follow-up period.

Results: The cohort consisted of 325 participants, of which 198 were males (61.9%) with an average age of 20.1±1.6 years, height of 174.7±9.9cm, and mass of 76.6±14.9kg. Of the 325 participants who sustained an incident concussion, 75 (23.1%) experienced an acute LEMSKI during the 12-month surveillance period after URTA. Kaplan-Meier survival estimates for acute LEMSKI by tertile for reaction time measured at the time of URTA revealed significant differences. In the univariate model, participants in slowest tertile for reaction time were nearly twice as likely (HR=1.95, 95%CI: 1.11-3.42, p=0.020) to sustain an acute LEMSKI during the 12-month follow-up period when compared to those in the fastest tertile. Participants in the middle tertile for reaction time were 19% more likely (HR=1.19, 95%CI: 0.63-2.25, p=0.594) to sustain an acute LEMSKI during the follow-up period when compared to those in the fastest tertile; however, this was not statistically significant. In the multivariable model, adjusted for sex, pre-concussion baseline reaction time, level of sport participation, and LEMSKI history, those in the slowest tertile for reaction time were still twice as likely (HR=2.01, 95%CI: 1.04-3.87, p=0.037) to sustain an acute LEMSKI during the surveillance period compared to those in the fastest tertile. Sport level and LEMSKI history remained independent risk factors for LEMSKI in the multivariable model.

Conclusions: Participants who were in the slowest tertile for reaction time, measured at the time of URTA following concussion, were twice as likely to sustain an acute LEMSKI within the first 12-months after URTA when compared to those in the fastest tertile. We observed a dose-dependent relationship between reaction time at URTA and the subsequent risk of LEMSKI. Further investigation into the deficits that may contribute to the increased risk of LEMSKI following concussion, and whether interventions can mitigate these risks, appears to be warranted.

Keywords: Concussion, mTBI, Lower Extremity, Injury, Reaction Time, Recovery, Military