Concussion in Professional Football: Reconstruction of Game Impacts and Injuries

OBJECTIVE: Concussion in professional football was studied with respect to impact types and injury biomechanics. A combination of video surveillance and laboratory reconstruction of game impacts was used to evaluate concussion biomechanics. METHODS: Between 1996 and 2001, videotapes of concussions and significant head impacts were collected from National Football League games. There were clear views of the direction and location of the helmet impact for 182 cases. In 31 cases, the speed of impact could be determined with analysis of multiple videos. Those cases were reconstructed in laboratory tests using helmeted Hybrid III dummies and the same impact velocity, direction, and head kinematics as in the game. Translational and rotational accelerations were measured, to define concussion biomechanics. Several studies were performed to ensure the accuracy and reproducibility of the video analysis and laboratory methods used. RESULTS: Concussed players experienced head impacts of 9.3 +/- 1.9 m/s (20.8 +/- 4.2 miles/h). There was a rapid change in head velocity of 7.2 +/- 1.8 m/s (16.1 +/- 4.0 miles/h), which was significantly greater than that for uninjured struck players (5.0 +/- 1.1 m/s, 11.2 +/- 2.5 miles/h; t = 2.9, P < 0.005) or striking players (4.0 +/- 1.2 m/s, 8.9 +/- 2.7 miles/h; t = 7.6, P < 0.001). The peak head acceleration in concussion was 98 +/- 28 g with a 15-millisecond half-sine duration, which was statistically greater than the 60 +/- 24 g for uninjured struck players (t = 3.1, P < 0.005). Concussion was primarily related to translational acceleration resulting from impacts on the facemask or side, or falls on the back of the helmet. Concussion could be assessed with the severity index or head injury criterion (the conventional measures of head injury risk). Nominal tolerance levels for concussion were a severity index of 300 and a head injury criterion of 250. CONCLUSION: Concussion occurs with considerable head impact velocity and velocity changes in professional football. Current National Operating Committee on Standards for Athletic Equipment standards primarily address impacts to the periphery and crown of the helmet, whereas players are experiencing injuries in impacts to the facemask, side, and back of the helmet. New tests are needed to assess the performance of helmets in reducing concussion risks involving high-velocity and long-duration injury biomechanics.