Effectiveness of the Kato Collar for Limiting Head and Neck Loading from Helmet-to-Helmet Impacts

Guardian Athletics

Introduction

Limiting head and neck injuries is an important concern in American football.⁴ While football helmets have significantly reduced the risk of serious head injury, concussions remain an ongoing issue.⁶ Furthermore, helmets provide limited protection for neck or other whiplash-type injuries.¹¹ Cervical collars originally were developed to lower the risk of stingers (burners), which are caused by excessive head and neck motion leading to brachial plexus injury.^8,10 Cervical collars have been found to reduce head-neck range of motion, neck loads, and head acceleration under simulated helmet-to-helmet impacts.¹⁷ These findings suggest that cervical collars could assist with preventing concussion in addition to reducing neck injury risk.⁵ Furthermore, since cervical collars are placed on the shoulder pads, they can respond to whiplash-type injury mechanisms in which head and neck loading occurs from an initial impact to the torso.

Despite their potential benefits, cervical collars have been criticized for restricting the athlete's active head and neck motion, causing them discomfort and hindering their ability to visualize the field. The Kato Collar (Guardian Athletics, Mankato, MN) was developed to overcome this limitation by minimizing impact-induced passive head motion while permitting full active range of motion. Taken together, it is plausible that cervical collars, in particular the Kato Collar, could provide added protection beyond the helmet to mitigate the risk of stingers, concussion, and other head and neck injuries. However, research into cervical collars has been limited to only a handful of studies.^2,8,10,17 Thus, the purpose of this study was to assess the ability of the Kato Collar to mitigate head and neck forces due to helmet impacts. Part I compared the Kato Collar to standard football equipment (no cervical collar), while Part II investigated the Kato Collar against two other commercial collars. It was hypothesized that the Kato Collar would reduce head displacement and head impact severity compared to no collar and that it would perform better than other commercial collars, particularly for front impacts.

Methods

Part I

Helmet-to-helmet impacts were simulated with a pneumatic linear impactor. Impact speeds of 5, 6, and 7 m/s were selected to represent typical football impacts.¹⁵ A male 50th percentile Hybrid III head, neck, and torso was equipped with standard football shoulder pads and helmet. The Kato Collar was attached to the shoulder pads per manufacturer directions. The headform was instrumented with a three-axis accelerometer and three-axis angular rate sensor sampled at 20 kHz. The dummy was placed in an upright posture and fixed to a linear trolley to allow movement after impact. Impacts were delivered to the front, front boss, and side of the helmet, with and without the Kato Collar (Figure 1). Three trials were recorded for the front and front boss conditions, while one trial was executed for the side condition. Head response was evaluated by calculating peak resultant linear acceleration, Severity Index (SI)⁷, and head displacement after impact. Neck response was evaluated by estimating peak neck forces at the occipital condyle via inverse dynamics.²⁰

Figure 1. Front, front boss, and side head impact locations. The impactor setup shown was used for Study 1. The Kato Collar is visible in the left and center images.

Figure 2. Axes used to describe head and neck response in both studies. The x-axis pointed anterior, the y-axis pointed rightward, and z-axis pointed down.

Part II

A pneumatic linear impactor was used to deliver helmet impacts at 3 and 5 m/s (Figure 3), representing low and average football impact speeds, respectively.¹⁵ A medium-sized 50th percentile NOCSAE headform and custom neckform¹² were fitted with standard football shoulder pads and helmet. The headform was instrumented with three accelerometers and sampled at 20 kHz. Four collar conditions were tested: no collar, Kato Collar, Douglas Butterfly Restrictor, and Kerr Collar. Each collar was attached to the shoulder pads per manufacturer directions. The torso was positioned upright for each impact. Front, front boss, and side impact locations were tested. Three trials were conducted for each condition for a total of 72 trials. The following metrics were computed: peak resultant linear acceleration, Head Injury Criterion (HIC)¹⁴, and head displacement.

Figure 3. Pneumatic linear impactor used for testing in Study 2. From Jeffries et al.¹²

Results

Results are discussed below for impact speeds of 3, 5, and 7 m/s. All data can be found in Tables 1 and 2 at the end of the paper.

Comparison to No Collar

For front impacts, the addition of the Kato Collar reduced head displacement, peak linear acceleration, SI, and HIC at all speeds (Figure 4). It also reduced anterior-posterior and resultant upper neck force at both tested speeds.

For front boss impacts, the Kato Collar reduced head displacement at all speeds, peak linear acceleration at 3 and 5 m/s (Study 2), and HIC at 5 m/s. The Kato Collar reduced axial neck force at 7 m/s but not other neck force parameters.

For side impacts, the Kato collar was particularly effective at 7 m/s, reducing all head and neck response parameters. The Kato Collar also reduced peak linear acceleration at 3 m/s and head displacement at 5 m/s.

Figure 4. Effect of the Kato Collar for front impact, compared to no collar. The Kato Collar reduced key head and neck response parameters for all tested speeds.

Comparison to Other Collars

For front impacts, the Kato Collar outperformed the other collars (Figure 5). Except for similar reductions by all three collars in 3 m/s peak linear acceleration, the Kato Collar reduced head displacement, peak linear acceleration, and HIC more than the other tested collars.

For front boss impacts, the Kato Collar produced the largest reductions in head displacements. For peak linear acceleration and HIC, it performed better than the Kerr Collar but was not as effective as the Douglas Butterfly Restrictor (Figure 6).

For side impacts, collar performance depended on metric and speed. At 3 m/s, the Kerr Collar managed head displacement and HIC best, while the Kato Collar produced the largest reductions in peak linear acceleration. At 5 m/s, the Kato and Kerr collars similarly reduced head displacement, whereas the Butterfly Restrictor performed best for peak linear acceleration and HIC.

Figure 5. Load limiting capabilities of the Kato Collar compared to the Kerr Collar and the Douglas Butterfly Restrictor for 5 m/s front impacts. The Kato Collar performed the best of the three devices for all measures.

Figure 6. Load limiting capabilities of the Kato Collar compared to the Kerr Collar and the Douglas Butterfly Restrictor for 5 m/s front boss impacts. Across 3 and 5 m/s speeds, the Kato Collar performed best for head displacement while the Douglas Butterfly Restrictor performed best for peak linear acceleration and Head Injury Criterion.

Discussion

Cervical collars were developed to limit excessive head extension and lateral flexion from football impacts. Excessive passive motion in these directions has been associated with burner/stingers^18,19 and concussions.¹ The Kato Collar limited passive head displacement across all tested impact speeds and locations, suggesting it reduces burner/stinger risk. Likewise, peak linear acceleration, SI, and HIC, measures associated with concussion risk, were reduced by adding the Kato Collar. This was particularly apparent for front impacts but also occurred under other impact conditions. Taken together these data suggest that the Kato Collar provides added neurological injury protection beyond the helmet.

It is important that restricting head loading does not lead to concomitant increases in loading at other body segments, notably the neck. Indeed, this was not evident in the present study. This concurs with the work of Rowson et al.,¹⁷ in which they determined that neck load reduction correlated with head and neck motion restriction. They hypothesized that the cervical collar acted to transmit load to the shoulders and away from the neck. The Kato Collar limited head motion better than other collars, which suggests it also best reduces neck loads, although this has not been examined directly.

The Kato Collar was particularly effective for impacts to the front of the helmet, in which it reduced HIC by over 30%. It outperformed all examined collars for these impacts. This would be especially relevant to linemen and other positions, who experience a high percentage of impacts to the front of the helmet and are most at risk for stingers.^3,9 The Kato Collar also provided significant load reduction for side impacts at 7 m/s. However, it had mixed efficacy for front boss and low-speed side impacts, similar to the other collars examined. This agrees with previous studies of commercial neck collars, which found that they had limited ability to manage side impacts.^8,10,17 As side impacts have been implicated in football head injuries,¹³ future work should address improvements to the Kato Collar's management of these motions.

Several limitations of the present study should be noted. The study was performed on older versions of the Kato Collar and should be updated to reflect the latest model. This study did not examine head rotation, which has been implicated for concussion risk.¹⁶ Finally, this study did not incorporate the typical football tackle/block posture, in which the torso is tilted forward, the head is up (extension), and the shoulders are raised. We expect that this posture would reveal greater reductions in head and neck loads based on previous research¹⁷, but it must be tested directly.

In summary, the Kato Collar reduced head and neck loading in response to simulated football helmet-to-helmet impacts. It limited head displacement better than other commercial cervical collars without producing concomitant increases in estimated neck forces. The Kato Collar is promising technology for improving head and neck injury protection beyond the helmet.

Data Tables

Table 1. Head and neck response to simulated helmet-to-helmet impacts with and without the Kato Collar (Part I)

Impact Location	Metric	5 m/s		6 m/s		7 m/s
		No Collar	Kato Collar	No Collar	Kato Collar	No Collar	Kato Collar
Front	d (cm)	10.4	8.1	10.8	8.9	11.6	9.5
	PLA (G)	59	55	82	79	114	103
	SI	162	149	283	226	449	307
	Fx (N)	2644	2447	3646	3531	5037	4554
	Fy (N)	324	233	236	278	216	290
	Fz (N)	865	1155	1158	1028	1358	1238
	Fr (N)	2802	2717	3835	3690	5221	4729

d: head displacement, PLA: peak resultant linear head acceleration, SI: Severity Index, F_x: anterior neck force, F_y: lateral neck force, F_z: axial neck force, F_r: resultant neck force

Table 2. Head response to simulated helmet-to-helmet impacts with commercial neck collars compared to no collar (Part II)

Impact Location	Impact Speed	Metric	No Collar	Kato	Kerr	Butterfly
Front	3 m/s	d (cm)	27.96	20.01	25.90	22.2
		PLA (G)	79	78	77	78
		HIC	115	73	119	116
	5 m/s	d (cm)	33.31	23.94	27.5	28.38
		PLA (G)	184	166	179	181
		HIC	509	334	433	345

d: head displacement, PLA: peak resultant linear head acceleration, HIC: Head Injury Criterion, Butterfly: Douglas Butterfly Restrictor

References

1. Broglio SP, Sosnoff JJ, Shin S, He X, Alcaraz C, Zimmerman J. Head impacts during high school football: a biomechanical assessment. J Athl Train. 2009;44(4):342-349.
2. Caravaggi P, Leardini A, Belvedere C, Siegler S. A novel Cervical Spine Protection device for reducing neck injuries in contact sports: design concepts and preliminary in vivo testing. Sports Biomechanics. July 2018:1-13.
3. Crisco JJ, Fiore R, Beckwith JG, et al. Frequency and location of head impact exposures in individual collegiate football players. J Athl Train. 2010;45(6):549-559.
4. Dick R, Ferrara MS, Agel J, et al. Descriptive epidemiology of collegiate men's football injuries: National Collegiate Athletic Association Injury Surveillance System, 1988-1989 through 2003-2004. J Athl Train. 2007;42(2):221-233.
5. Fernandes FAO, de Sousa RJA. Head injury predictors in sports trauma--a state-of-the-art review. Proc Inst Mech Eng H. 2015;229(8):592-608.
6. Funk JR, Jadischke R, Bailey A, et al. Laboratory Reconstructions of Concussive Helmet-to-Helmet Impacts in the National Football League. Ann Biomed Eng. 2020;52(1):45–15.
7. Gadd CW. Use of Weighted-Impulse Criterion for Estimating Injury Hazard. Vol 1. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International; 1966.
8. Gorden JA, Straub SJ, Swanik CB, Swanik KA. Effects of Football Collars on Cervical Hyperextension and Lateral Flexion. J Athl Train. 2003;38(3):209-215.
9. Green J, Zuckerman SL, Dalton SL, Djoko A, Folger D, Kerr ZY. A 6-year surveillance study of "Stingers" in NCAA American Football. Res Sports Med. 2017;25(1):26-36.
10. Hovis WD, Limbird TJ. An evaluation of cervical orthoses in limiting hyperextension and lateral flexion in football. Med Sci Sports Exerc. 1994;26(7):872-876.
11. Jadischke R, Viano DC, McCarthy J, King AI. Concussion with primary impact to the chest and the potential role of neck tension. BMJ Open Sport Exerc Med. 2018;4(1):e000362-e000367.
12. Jeffries L, Zerpa C, Przysucha E, Sanzo P, Carlson S. The use of a pneumatic horizontal impact system for helmet testing. Journal of Safety Engineering.
13. Lessley DJ, Kent RW, Funk JR, et al. Video Analysis of Reported Concussion Events in the National Football League During the 2015-2016 and 2016-2017 Seasons. Am J Sports Med. 2018;46(14):3502-3510.
14. Newman JA, Shewchenko N. A Proposed New Biomechanical Head Injury Assessment Function - the Maximum Power Index. STAPP. 2000;1:2000–01–SC16.
15. Pellman EJ, Viano DC, Tucker AM, Casson IR, Waeckerle JF. Concussion in professional football: reconstruction of game impacts and injuries. Neurosurgery. 2003;53(4):799–812–discussion812–4.
16. Rowson S, Duma SM, Beckwith JG, et al. Rotational head kinematics in football impacts: an injury risk function for concussion. Ann Biomed Eng. 2012;40(1):1-13.
17. Rowson S, McNeely DE, Brolinson PG, Duma SM. Biomechanical analysis of football neck collars. Clin J Sport Med. 2008;18(4):316-321.
18. Safran MR. Nerve Injury about the Shoulder in Athletes, Part 2. Am J Sports Med. 2017;32(4):1063-1076.
19. Standaert CJ, Herring SA. Expert opinion and controversies in musculoskeletal and sports medicine: stingers. Arch Phys Med Rehabil. 2009;90(3):402-406.
20. Viano DC, Melvin JW, McCleary JD, Madeira RG. Measurement of head dynamics and facial contact forces in the Hybrid III dummy. SAE Transactions. 1986;95(5):798-818.