Athletic Training and Sports Health Care

Original Research 

Motion Created in an Unstable Cervical Spine During the Removal of a Football Helmet: Comparison of Techniques

Dewayne N. DuBose, PhD, LAT, ATC, NCPT; Sean Connolly, BS; Brian Hatzel, PhD, AT, ATC; Laura Ann Zdziarski, BS, LAT, ATC; Gianluca Del Rossi, PhD, LAT, ATC; Ira Hill, PhD; Mark Prasarn, MD; Glenn Rechtine, MD; MaryBeth Horodyski, EdD, LAT, ATC, FNATA

Abstract

Helmet removal is necessary to maintain airway access in a suspected cervical spine injury. The aim of this investigation was to determine which of two football helmet removal techniques minimized angular and translational displacement in a suspected cervical injury. This repeated measures study used five fresh cadaveric specimens. An electromagnetic device measured angular (degrees) and translational (millimeters) displacements at an unstable C5–C6 segment. The removal techniques were facemask removal and then helmet removal (FMH) and direct helmet removal (Helmet). The authors found that the FMH technique resulted in significantly less flexion-extension (P = .023) and axial rotation (P = .023) than the Helmet technique. FMH caused significantly less anterior-posterior (P = .035), medial-lateral (P = .013), and axial (P = .028) translations than the Helmet technique. The FMH technique created significantly less motion than the Helmet technique in this helmet model. Future research on different helmet models may confirm that the FMH technique minimizes the potential for secondary injury. [Athletic Training & Sports Health Care. 2015;7(6):242–247.]

Abstract

Helmet removal is necessary to maintain airway access in a suspected cervical spine injury. The aim of this investigation was to determine which of two football helmet removal techniques minimized angular and translational displacement in a suspected cervical injury. This repeated measures study used five fresh cadaveric specimens. An electromagnetic device measured angular (degrees) and translational (millimeters) displacements at an unstable C5–C6 segment. The removal techniques were facemask removal and then helmet removal (FMH) and direct helmet removal (Helmet). The authors found that the FMH technique resulted in significantly less flexion-extension (P = .023) and axial rotation (P = .023) than the Helmet technique. FMH caused significantly less anterior-posterior (P = .035), medial-lateral (P = .013), and axial (P = .028) translations than the Helmet technique. The FMH technique created significantly less motion than the Helmet technique in this helmet model. Future research on different helmet models may confirm that the FMH technique minimizes the potential for secondary injury. [Athletic Training & Sports Health Care. 2015;7(6):242–247.]

Banerjee et al.1 defined spinal column injury as “a structural distortion of the cervical spinal column associated with actual or potential damage to the spinal cord.” Participation in sports is the second leading cause of catastrophic cervical spine injury in people younger than 30 years.2 Injuries to the cervical spine occur more often in sports that include equipment-laden athletes. During tackling and blocking, head impact commonly occurs with the neck slightly flexed.3–5 This position decreases the natural lordosis of the neck and aligns the cervical vertebrae into a rigid column.6 From the point of impact, axial load forces are transmitted down the rigid spine while in the flexed position, resulting in distribution of the forces among the soft and hard tissues. Panjabi et al.7 have shown that the cervical spine can withstand a critical axial load of 10.5 N before the vertebrae begin to buckle.7 Loads in excess of this value may cause vertebral buckling and intervertebral angulations may occur as soft and hard tissues are disrupted.8 In the segmented vertebral column, the structural change that occurs is a deflection of the individual vertebrae.9 This deflection enables the offloading of excessive compressive forces onto surrounding soft tissue. These deflections and disruptions are the primary cause of injury to the spinal cord.9,10

When a helmeted athlete has a suspected cervical spine injury, first responders must manage the athlete carefully, minimizing the amount of motion while maintaining airway access. Helmets and shoulder pads worn by the athlete may interfere with and increase the complexity of emergency management of these patients, specifically pertaining to maintaining the airway and access to the chest.5,8,11–14 Cantu and Cantu8 found that newer helmets can change the protection around the mandible, making it harder for medical personnel to do the head-tilt chin-lift. Delaney et al.11 published that the chinstrap can interfere with the placement of the bag valve mask. A study by Del Rossi et al.12 established that the protective equipment slows down cardiopulmonary resuscitation (CPR). The shoulder pads can prevent the full recoil of the chest after a compression during CPR.12 The National Athletic Trainers' Association prescribes that when a spinal injury is suspected, rescuers should immediately attempt to expose the airway, removing any existing barriers.15 Studies have shown that removing only the helmet results in approximately 14° of hyperextension of the cervical spine.16,17 Such hyperextension has been shown to reduce the diameter of the vertebral canal and may compress the patient's spinal cord.18,19 This is because the shoulder pads elevate the torso off the ground while the helmetless head extends to the ground. Decoster et al.20 and Del Rossi et al.21 concluded that in circumstances requiring immediate helmet removal, hyperextension of the cervical spine caused by the shoulder pads is prevented if appropriate padding is placed under the occiput.

Appropriate care must be taken to remove the helmet while minimizing the chance of secondary injury to the patient. This study examines two helmet removal techniques: facemask removal followed by helmet removal (FMH) or complete helmet removal (Helmet). Currently, no studies have performed a comparison of differences in post-injury motion between these techniques in a biological model. The purpose of this study was to compare angular and translational displacements during football helmet removal in a cadaveric model with cervical spine instability. We hypothesized that the FMH removal technique would cause significantly less angular displacement than the Helmet technique. We also hypothesized that the FMH technique would cause significantly less translational displacement than the Helmet technique. Data collected in this study will help improve the airway management of helmeted athletes with suspected cervical spine injuries.

Methods

Experimental Design

This study was a prospective comparison study conducted in a repeated measures format. The dependent variables included: angular displacement (flexion-extension, lateral bending, and axial rotation) recorded in degrees and translational displacement (anterior-posterior, medial-lateral, and axial) recorded in millimeters. The independent variable was the football helmet removal technique: FMH or Helmet. The two techniques were tested three times on all five cadavers (n = 15 trials for each technique). The order of the helmet removal trials was determined using a computerized random number generator. Data were collected over a 5-day period with testing occurring on one cadaver per day.

Subjects

The removal techniques were performed on five fresh cadavers (3 males and 2 females) with no history of cervical spine injury. The mean age and mass of the cadavers were 63.8 ± 14.32 years and 137 ± 15.28 kg, respectively. The removal techniques were performed by two male athletic trainers (mean age: 34 ± 1.5 years; mean mass: 112.25 ± 14.75 kg). Each athletic trainer had more than 10 years of experience and completed all helmet removal procedures. The investigators performing helmet removal techniques were not blinded to the purpose of this study.

Equipment

Cadavers were fitted with an Adams Helmet (Cookville, TN) shell and open cage facemask secured by bilateral high and low button hookups. The cadavers were also fitted with Riddell Power SPX shoulder pads (Riddell, Elyria, OH).

Instrumentation

LIBERTY equipment (Polhemus Inc., Colchester, VT) was used to quantify the amount of segmental motion during removal trials. This three-dimensional motion capture equipment is a six degree-of-freedom electromagnetic tracking system that determined the position and orientation of its receivers in three-dimensional space.22,23 A custom LabVIEW (National Instruments, Austin, TX) program developed by the biomedical engineer on our research team was used to collect angular and translation data for each trial (Figure 1). A power drill was used to anchor the receivers to the posterior aspect of the lamina of C5 and C6 vertebrae with dry wall screws.22,23 Each receiver recorded three-dimensional position and orientation data from its respective location at a rate of 120 Hz.24 The position and orientation was transmitted to a global positioning cube placed in the cadaver's thoracic cavity.25 The maximum capture volume for the electromagnetic tracking system was a hemisphere with a radius of approximately 79 cm.25 This data collection technique has been used successfully by our research team in previous studies.22–24,26

Polhemus motion tracker placement at C5–C6.

Figure 1.

Polhemus motion tracker placement at C5–C6.

Experimental Procedures

Before the helmet removal trials, the range of motion for the cervical spine was collected for each cadaver before the instability was created. Range of motion trials were performed by attaching Gardner Wells tongs to the head and a scale was hooked to the tongs to ensure the same amount of force was used for the test trials. The scale was used to pull the head into desired cervical spine motions (flexion, lateral bending, and axial rotation). The same researcher moved the cadaver's head into extension using a motion similar to the head-tilt chin-lift procedure. This gave a baseline to compare to the cervical spine once the instability was created at the C5–C6 segment.

To test a worst-case spinal injury, an orthopedic spine surgeon created a complete segmental injury at C5–C6 using two incisions. The first was a midline cervical incision on the posterior surface of the neck that allowed excision of the supraspinous, interspinous, and facet ligaments, as well as the posterior longitudinal ligament, the ligamentum flavum, and the posterior annulus. A second incision followed on the anterior surface of the neck to disrupt the anterior longitudinal ligament, the anterior annulus, and the disc space. The technique used to create the instability has been used previously in other studies by our research team.24,26–28 The same range of motion trials were repeated to ensure that an instability had been created.

The athletic trainers performing the helmet removal techniques attended a training session of approximately 45 minutes. During the session they reviewed and practiced the execution of the removal techniques. The athletic trainers were assigned roles and performed those roles throughout the study.

Both techniques began with the helmet fully in place. The chin-strap was cut and then cheek pads removed as the initial step of both techniques. For the FMH removal technique, the facemask was removed using a handheld cordless screwdriver (Black & Decker Model 3.6-Volt 3/8-in Cordless Screwdriver; New Britain, CT). The screws for the helmet were removed in the following order: right ear side, left ear side, right frontal, and then left frontal.27 Then, the remaining helmet shell was removed per the National Athletic Trainers' Association Position Statement.15 For the Helmet removal technique, the helmet was removed using the two rescuer-two hands approach.28,29 The athletic trainer maintaining initial spinal alignment transferred control to a second athletic trainer, who stabilized the cadaver from the front. The first athletic trainer then spread the helmet shell at the location of the removed cheek pads and gently slid the helmet off the cadaver.15 After the helmet was removed, the head was placed onto padding to maintain spinal alignment (Figure 2). The trial began when the first athletic trainer initiated in-line stabilization and the trial was finished when the second athletic trainer gave the first rescue breath using a bag valve mask.

Occiput supported with towel to prevent hyperextension of the neck after helmet removal.

Figure 2.

Occiput supported with towel to prevent hyperextension of the neck after helmet removal.

Statistical Analysis

Six 2 × 3 (removal technique x trial) repeated measures analysis of variance (ANOVA) tests were used to analyze the six variables of interest (flexion-extension, lateral bending, axial rotation, anterior-posterior translation, axial translation, and medial lateral translation). Analyses were completed using SPSS software (version 21.0; SPSS, Inc., Chicago, IL) to evaluate the amount of angular and translational motion during the helmet removal trials. Degrees were the unit of measure for angular displacement and millimeters were the unit of measure for translation. Data were expressed in means ± standard deviation. These data were the mean total amount of motion that occurred during angular and translational displacement. When appropriate, post hoc analyses were completed using least significant difference. The level of statistical significance was set a priori at .05.

Results

The results of this study (Table 1) indicated that there were significant differences in motion between the FMH and Helmet techniques. FMH technique caused significantly less flexion-extension (F (2,1) = 13.417, P = .023) and axial rotation (F (2,1) = 15.046, P = .023) than the Helmet technique. Lateral bending did not show a significant difference between the two techniques (F (2,1) = 12.438, P = .063). There were significant differences in translational displacement between the removal techniques. The FMH technique caused significantly less anterior-posterior (F (2,1) = 9.190, P = .035), medial-lateral (F (2,1) 17.322, P = .013), and axial (F (2,1) = 11.657, P = .028) translations than the Helmet technique.

Average Motion During Helmet Removal

Table 1:

Average Motion During Helmet Removal

Discussion

Our investigation has addressed the question of which technique minimizes motion of the cervical spine during helmet removal. We created a global instability at C5–C6 because a catastrophic injury at this level is the most functionally impairing, nonlethal spinal cord injury that could be encountered by athletic trainers.30–32 We hypothesized that the FMH technique would cause significantly less angular displacement than the Helmet technique. We also hypothesized that the FMH technique would cause significantly less translational displacement than the Helmet technique. Our data indicated that the FMH technique for helmet removal resulted in less motion than the Helmet technique. This finding is in support of our hypothesis that the facemask preserves the integrity of the helmet, thereby reducing the ability to widen the helmet at the ear holes. We suspect that removal of the facemask allowed a little more flexibility of the helmet, decreasing the forces necessary to remove the helmet.

Equipment removal in the event of injury is not unique to tackle football. Bradney and Bowman5 recently made recommendations for removal techniques of lacrosse helmet facemasks in the event of catastrophic spinal injury. Radiographic analyses of collegiate lacrosse athletes have shown that helmet removal increases cervical flexion,33 which is opposite the findings for American football and ice hockey.34–36 Hyperflexion also occurs in the helmeted motorcyclist.27 Whereas shoulder pads offset the elevation of the helmet's padding in the football player, a motorcyclist with a suspected cervical spine injury lacks similar torso elevation. Removal of the motorcycle helmet brings the spine into neutral alignment.37 It is important to remember the purpose of equipment removal in these circumstances. Achieving secure, neutral alignment on a spine board is a precondition for emergency transportation. Neutral alignment minimizes cervical extension, which decreases the risk of secondary injury.17,38 Appropriately trained personnel should ensure the protective equipment is removed to attain neutral alignment while ensuring airway access in the event of cardiorespiratory emergency.

Equipment varies greatly across level of play, team, and individual preference. A single helmet shell may even be fitted with variable forms of cage masks, each with a unique fastening design. This heterogeneity in protective head equipment poses a challenge to generalization of this study's results. Athletic trainers and paramedics must be prepared to address differences in equipment to manage the injured athlete expeditiously. Our results are most applicable to athletes wearing the Adams model.

Limitations

The use of cadavers has limitations. Foremost, the complete C5–C6 instability created in our investigation simulated a worst-case scenario. Cervical spine injuries encountered on the playing field are unlikely to be global instabilities. Cadavers rarely emulate the muscle and ligamentous structures of a football athlete. The need to access the vertebral structures for motion tracker placement also partially compromised the soft tissue integrity of the neck. This soft tissue damage may permit greater movements than would occur in an on-the-field injury. The football equipment used in our laboratory setting does not resemble the on-the-field setting. In many cases, it is unrealistic to expect new screws and clean facets to be the norm during the course of the football season. Additionally, manual screwdrivers or pruning shears may be used for the helmet removal process.4 These nonelectric methods may be the dominant techniques employed in some situations when electronic devices are not available. Finally, only one model of helmet was tested in this study. The Adams helmet may not be the only helmet worn on the field during practice or a game.

Advantages

One advantage of using the cadaver model is that the investigators were able to create a complete instability at a standardized anatomical location. Another advantage is the motion-tracking hardware can be placed directly on the vertebrae in a cadaver, eliminating measurement artifact that would occur if the sensors had been placed on skin. The elimination of artifact allows for a more accurate measurement on the changes in angulation and translation.

Implications for Clinical Practice

In the management of an athlete sustaining a potential cervical spine injury in football, recommendations for accessing the airway have suggested that the face-mask and in many instances the helmet be removed. The FMH removal technique allows rescuers to remove the helmet with less angular and translational motion than the Helmet removal technique. Thus, when the athlete is not in immediate respiratory distress the FMH technique should be used to remove the helmet.

Conclusion

Our results indicated that removal of the facemask followed by removal of the helmet shell resulted in significantly less angular and translational displacement than complete helmet removal in a global instability model. Future research including various brands and styles of helmets might confirm that the FMH technique offers clinicians a way to minimize the potential for secondary injury. Future research should compare a helmet with four screws to a helmet with a quick release system in a cadaveric model with a global instability.

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Average Motion During Helmet Removal

MOTIONFACEMASKHELMETP
Flexion-extension (degrees).023a
  Mean1.5907.076
  Number1515
  SD0.7083.670
Axial rotation (degrees).023a
  Mean1.3593.035
  Number1515
  SD0.4851.542
Lateral bending (degrees).063
  Mean1.1222.663
  Number1515
  SD0.6762.012
Medial-lateral translation (mm).013a
  Mean0.7862.913
  Number1515
  SD0.4771.386
Axial translation (mm).028a
  Mean1.3976.506
  Number1515
  SD0.9233.695
Anterior-posterior translation (mm).035a
  Mean1.2994.716
  Number1515
  SD0.7412.901
Authors

From the University Athletic Association (DND), College of Medicine (SC), College of Engineering (IH), and Department of Orthopaedics and Rehabilitation (LAZ, MH), University of Florida, Gainesville, Florida; Grand Valley State University, Allendale, Michigan (BH); the Department of Orthopaedics and Sports Medicine, University of South Florida, Tampa, Florida (GD, GR); and the Department of Orthopaedics, University of Houston, Houston, Texas (MP).

Supported in part by the Southwestern Medical Foundation.

The authors have no financial or proprietary interest in the materials presented herein.

Correspondence: Dewayne N. DuBose, PhD, LAT, ATC, NCPT, 1115 NW 40th Drive, Gainesville, FL 32605. E-mail: dubosdn@ortho.ufl.edu

Received: May 17, 2015
Accepted: August 17, 2015

10.3928/19425864-20151029-05

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