Context: The Guardian Cap provides a soft covering intended to mitigate energy transfer to the head during football contact. Yet how well it attenuates impacts remains unknown.
Objective: To evaluate the changes in the Gadd Severity Index (GSI) and linear acceleration during drop tests on helmeted headforms with or without Guardian Caps.
Design: Crossover study.
Setting: Laboratory.
Patients or other participants: Nine new football helmets sent directly from the manufacturer.
Intervention(s): We dropped the helmets at 3 velocities on 6 helmet locations (front, side, right front boss, top, rear right boss, and rear) as prescribed by the National Operating Committee on Standards for Athletic Equipment. Helmets were tested with facemasks in place but no Guardian Cap and then retested with the facemasks in place and the Guardian Cap affixed.
Main outcome measure(s): The GSI scores and linear accelerations measured in g forces.
Results: For the GSI, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .005) but not at the low (F3.23,16.15 = 0.84, P = .50) or medium (F10,50 = 1.29, P = .26) velocities. Similarly for linear accelerations, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .002, ω2 = 0.05) but not at the low (F10,50 = 0.49, P = .89, ω2 < 0.01, 1-β = 0.16) or medium (F5.20,26.01 = 2.43, P = .06, ω2 < 0.01, 1-β = 0.68) velocities.
Conclusions: The Guardian Cap failed to significantly improve the helmets' ability to mitigate impact forces at most locations. Limited evidence indicates how a reduction in GSI would provide clinically relevant benefits beyond reducing the risk of skull fracture or a similar catastrophic event.
Keywords: Gadd Severity Index; Guardian Cap; peak acceleration; traumatic brain injuries.