Changes in the centre of mass and moment of inertia of a headform induced by a hockey helmet and face shield.

A study of the hockey helmet and face shield as potential contributors to cervical spinal cord trauma (burst vertebral fractures and cord injury) was undertaken. The main concern was whether the alteration in the location of the c of m or in the mass moment of inertia (Icm) of a player's head, induced by a helmet and face shield, would predispose him to a hyperflexion neck posture. The c of m and Icm of a bare Hodgson-WSU humanoid headform (H) were first determined and then the same measures were made with a helmet (H + h) and with a helmet and face shield (H+h+f). Of the nine different helmet and face shields evaluated none caused the c of m to move more than 6mm from that of H. Measurements made on minor hockey players aged 8 to 15 years indicated that the proportion of maximum isometric neck strength required to hold the head in the typical skating posture while wearing a helmet and face shield ranged from 8% to 12%. It seems unlikely that this would predispose to the hyperflexion neck posture. The Icm of H+h increased by 68% and of H+h+f by 89% from that of H and when translated to a pivot point on the neck (C7-T1) the change in I was 30% for H+h and 41% for H+h+f. The effect on the neck of such an increase in I could lead to strain on the neck ligaments and musculature but would not account for a burst fracture of a vertebrae. Thus, in and of themselves, the helmet and face shield do not appreciably alter the dynamics of the neck thereby predisposing the wearer to increased neck injury risk.