Head impacts, both concussive and sub-concussive, are common in sports and can lead to adverse side effects. Since head kinematics are thought to correlate with brain injury, the implementation of protective headgear aimed to mitigate kinematics of the head during impacts. While fatal brain injuries have been reduced, concussions and other long-term effects of repetitive head impacts are still prevalent in football players at all levels. Physical surrogate models of the human head and neck are often used to assess impact severity in sports and infer the risk of brain injury, and in helmet certifications to explore the efficacy of helmets. The surrogate models can be instrumented with accelerometers to measure resultant head kinematics. Since the neck is thought to partially govern head kinematics during impact, the surrogate necks must demonstrate several performance characteristics to produce accurate results. Commercially available necks have acceptable repeatability and reproducibility, but they were not developed for the direct, multiplane loading in sports. As such, a novel prototype surrogate neck was developed for omni-directional direct head impacts. The objective of this work was to assess the repeatability and reproducibility of the neck.

Three copies of the prototype surrogate neck and one Hybrid III neck were attached to the same Hybrid III head and repeatedly impacted at 3.5 m/s using a pendulum impactor. Both the helmeted and the unhelmeted head were impacted at the front and the front boss locations. The within-neck coefficient of variation (CVW) of the prototype surrogate neck kinematics for all impact conditions was 10% or less, which satisfies standard requirements for surrogates and is comparable to work on several standardized surrogate models. While differences between the three prototype surrogate necks were generally statistically significant, the normalized absolute differences between the neck copies were usually less than 10% and less than 20% in all cases except one. Most head and neck certifications for current standardized models provide corridors that allow a range of ±10% on mean peak kinematics to be considered within specification - the normalized absolute differences of the prototype surrogate neck kinematics fall within that range. Further, the normalized absolute differences for other neck models were similar to what was calculated for the prototype surrogate neck. The reproducibility coefficient of variation (CVB) values for the prototype surrogate necks were less than 15% for all kinematics and usually 10% or less, which is considered acceptable and is comparable to the reproducibility of commercially available surrogate models.

The prototype surrogate neck had CVW values equivalent to the Hybrid III, but definitive conclusions cannot be made as to whether the kinematics differ. The Hybrid III kinematics were significantly different from the prototype surrogate neck kinematics for unprotected impacts, and the normalized absolute differences were greater than the differences calculated between the three copies of the prototype surrogate neck. In contrast, the helmeted impacts resulted in kinematics that were less significantly different between the Hybrid III and the prototype surrogate neck, with the normalized absolute differences commensurate in magnitude for the Hybrid III comparison and the prototype surrogate neck reproducibility assessment. However, the Hybrid III neck almost always had kinematics consistently greater than or less than all three of the prototype surrogate necks. Thus, the signs on the kinematics allow observation of actual differences between necks.

In summary, the prototype surrogate neck fit to a Hybrid III head and subject to multi-directional direct head impacts resulted in repeatable and reproducible kinematics. Although more testing is needed to quantify differences between the prototype surrogate neck and the Hybrid III, the prototype surrogate neck may be an effective tool for sports impact assessments.