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Comparing head impact kinematics simultaneously measured using 6 different sensors in a human cadaver model

Objective To compare head kinematics measurements obtained from 6 different head impact sensors utilizing different methods of sensor-to-head fixation. Design Free-drop impacts (total n = 54) were performed at 3.5 and 5.5 m/s onto to the front, back, side, and top of 2 elderly human cadaveric head-neck specimens: a helmeted (Riddell Revolution Speed) male specimen was dropped onto a NOCSAE testing pad; an un-helmeted female specimen was dropped onto a framed sample of field turf. The specimens were instrumented with an intracranial reference sensor surgically mounted at the approximate head center-of-mass by a rigidly-fixed custom standoff pad, an intra-oral test sensor rigidly fixed to the upper teeth/hard palate by a custom orthodontic appliance, and 4 commercially available head impact sensing systems: X-Patch, Vector mouth guard, HITS (helmeted condition only), and G-Force Tracker (affixed to helmet interior or head band depending on helmet status). Peak linear and rotational head accelerations (PLA and PRA) were compared between each sensor and the intracranial reference sensor using intraclass correlation coefficients (ICC [2, 1]). Results Agreement with reference PLA and PRA values differed between sensors, with the greatest agreement observed for the rigidly affixed intraoral sensor (ICC = 0.921, PLA; ICC = 0.810, PRA). Agreement for PLA and PRA, respectively, was: for X-Patch, ICC = 0.638, ICC = 0.155; for Vector mouth guard, ICC = 0.775, ICC = 0.480; for HITS, ICC = 0.662 (PLA only); for G-Force Tracker, ICC = 0.364 (PLA only). Discussion Head kinematics measurements during free-drop testing differed among sensors using different approaches of fixation to the head. There was greater agreement with intracranial reference PLA and PRA values for a rigidly affixed intraoral sensor utilizing an orthodontic appliance than for commercially available sensors incorporated into athletic equipment or otherwise non-rigidly affixed to the head. Measurement error attributable to non-rigid sensor-head coupling could potentially be reduced by incorporating an impact sensor into an orthodontic appliance in future research.