Concussion in professional football: location and direction of helmet impacts-Part 2.

Objective: National Football League game video was analyzed for the typical locations of severe helmet impacts in professional football. By use of selected cases that were reconstructed in laboratory tests and reported previously, the magnitude and direction of force causing concussion was determined for these locations.

Methods: Multiple video views were obtained for 182 severe helmet impacts that occurred between 1996 and 2001. From a top view, the helmet was divided into 45-degree quadrants with 0 degrees eyes forward. From a side view, it was divided into seven equal levels, four (+Q1 to +Q4) above the head center of gravity and three below (-Q1 to -Q3). The initial helmet contact was located in these regions. Thirty-one impacts were reconstructed with helmeted Hybrid III dummies involving 25 concussions. Measurement of head translational and rotational acceleration was used to determine the average and +/-1 standard deviation in responses, with impacts reflected to the right side.

Results: From video, the majority (71%) of impact is to the helmet shell primarily from a striking player's helmet, arm, or shoulder pad to the side (45-135 degrees) or from ground contact to the back (135-180 degrees). Most impacts were high on the helmet at +Q2 to +Q4. The remainder (29%) were primarily from helmet contact on the facemask at an oblique frontal angle (0-45 degrees) and -Q3 to +Q1 height. From reconstructions, concussion occurred with the lowest peak head acceleration in facemask impacts at 78 +/- 18 g versus an average 107 to 117 g for impacts on other quadrants (t = 2.90, P < 0.005). There was a significantly higher head acceleration for concussed versus nonconcussed players (t = 2.85, P < 0.05). The vector of peak force was essentially horizontal for facemask impacts and downward at 12 to 27 degrees for impacts to the helmet side and back. Concussion in professional football involves four typical conditions, as follows: A, 0- to 45-degree quadrant, -Q3 to +Q3 level, peak force 49 +/- 18 degrees from front and horizontal; B, 45- to 90-degree quadrant, -Q2 to +Q3 level, peak force 73 +/- 12 degrees and horizontal; C, 90- to 135-degree quadrant, +Q1 to +Q4 level, peak force 97 +/- 9 degrees and 12 degrees downward; and D, 135- to 180-degree quadrant, +Q1 to +Q4 level, peak force 157 +/- 1 degrees and 27 degrees downward. Concussed players averaged 3.6 +/- 2.7 initial signs and symptoms. The most common were headaches, dizziness, immediate recall problems, and difficulty with information processing.

Conclusion: The location, direction, and severity of helmet impacts causing concussion in the National Football League have been defined from analysis of game video and laboratory reconstruction. These conditions define the circumstances in which helmets need to reduce head injury risks in professional football.