Biomechanics of hyperextension injuries to the cervical spine in football.

The biomechanics of cervical spine hyperextension injuries in football players were assessed by using quasi-static-free body analyses. Three situations, i.e., "cases," corresponding to the loading conditions created by three different helmet designs, were examined with the following assumptions: (1) the helmet rim is cut high enough posteriorly so that it does not impinge upon the posterior cervical spine, (2) the helmet rim impacts at the level of the fourth cervical vertebra, and (3) the posterior rim of the helmet strikes the shoulder pads. The results of the analyses suggest that the most dangerous hyperextension situation is Case 1 which leads to high forces and possibly serious injury to the upper cervical spine. The impact of the posterior rim of the helmet at the fourth cervical vertebra (Case 2) significantly reduces these forces. This finding directly conflicts with the so-called "guillotine" mechanism of injury. The impact of the posterior rim of the helmet on the shoulder pads (Case 3) creates the least hazardous loading conditions.