Analysis of remaining motion using one innovative upper airway opening cervical collar and two traditional cervical collars

The aim of this study was to compare the remaining motion of an immobilized cervical spine using an innovative cervical collar as well as two traditional cervical collars. The study was performed on eight fresh human cadavers. The cervical spine was immobilized with one innovative (Lubo Airway Collar) and two traditional cervical collars (Stifneck and Perfit ACE). The flexion and lateral bending of the cervical spine were measured using a wireless motion tracker (Xsens). With the Weinman Lubo Airway Collar attached, the mean remaining flexion was 20.0 ± 9.0°. The mean remaining flexion was lowest with the Laerdal Stifneck (13.1 ± 6.6°) or Ambu Perfit ACE (10.8 ± 5.8°) applied. Compared to that of the innovative Weinmann Lubo Airway Collar, the remaining cervical spine flexion was significantly decreased with the Ambu Perfit ACE. There was no significant difference in lateral bending between the three examined collars. The most effective immobilization of the cervical spine was achieved when traditional cervical collars were implemented. However, all tested cervical collars showed remaining motion of the cervical spine. Thus, alternative immobilization techniques should be considered.

Although evidence of the effectiveness of cervical collars is rare 1-3 , the use of rigid cervical collars in preclinical trauma care is known to be a common immobilization technique. The importance of immobilization of the cervical spine is recognized in national and international recommendations for initial trauma care. The application of the cervical collar to avoid secondary injuries of the cervical spine 4,5 is recommended as one of the first emergency measures 6,7 .
Nevertheless, immobilization of the cervical spine by rigid collars is controversially discussed in the literature [8][9][10][11][12] . Cervical spine immobilization with collars can be accompanied by disadvantages, such as pain, discomfort 13,14 or pressure ulceration 13,15,16 . Furthermore, the application of a cervical collar can also lead to considerably serious and even life-threatening complications. In particular, restricted respiratory function 17 and difficult airway management 18 have been described, which can quickly lead to severe complications or even death, especially in trauma patients 7 . To ease airway management, an innovative cervical collar has been developed that should combine cervical spine immobilization and airway protection. This innovative cervical collar is equipped with a flexible belt for the mandible 19 . While this innovative collar seems to succeed in airway protection, the quality of cervical spine immobilization has not been proven, so far. However, the effectiveness of a cervical collar depends on its perfect fit [20][21][22] .
The aim of this study was to compare the remaining motion of the cervical spine using an innovative cervical collar as well as two traditional cervical collars on fresh human cadavers.

Materials and methods
Study design. The study was performed on fresh human cadavers. The body donors were given detailed information before death and had to give their written informed consent to the body donation. After death, the body was made available for scientific research purposes. Fresh human cadavers were briefly frozen after death. For the experiments, the bodies were thawed to room temperature. This method enabled the simulation of the www.nature.com/scientificreports/ In the experimental setup, fresh human cadavers were placed on a spineboard (Laerdal BaXstrap, Stavanger, Norway) in supine position and fixed by a harness fixation system (MIH-Medical Spiderstrap, Georgsmarienhütte, Germany). One motion tracker was attached to the forehead, and one motion tracker was attached to the thorax of the fresh human cadaver (Fig. 2). The 3D data were synchronized every 20 microseconds by the Xsens recording tool. However, with the help of the motion trackers, rotation and extension were recorded in the respective measured direction of motion (Fig. 3A).
The head of the fresh human cadaver was passively moved ventrally for flexion (Fig. 3A) and to the right for lateral bending. The traction force was 100 N. This force is in the range and in the direction as it may be applied during intubation or patient transport and may therefore initiate or aggravate an assumed spinal injury 3,29,30 . The force was measured with an electronic spring balance (LENI, Fa. Korona, Sundern, Germany).
In the standardized motion protocol, flexion and lateral bending were first analyzed for each fresh human cadaver without the cervical collar (control group). Subsequently, the motion analysis was performed with the three cervical collars in place.

Statistical data analysis.
In the present study, statistical calculations were performed to determine possible differences between the three tested cervical collars. With the D' Agostino and Pearson test, the three groups were tested for normal distribution. The statistical comparison between the four groups was performed using analysis of variance (ANOVA). A p-value of < 0.05 was considered statistically significant.

Results
Study collective. Eight fresh human cadavers were included in the present study. The mean age of the cadavers at death was 79.0 ± 12.8 years (range: 56-94 years). The study included five female and three male fresh human cadavers.
The mean flexion of the cervical spine with the Weinmann Lubo Airway Collar on was almost twice as high as that with the Ambu Perfit ACE applied. Compared to the Weinmann Lubo Airway Collar, the remaining cervical spine flexion was significantly (p = 0.0474) decreased with the Ambu Perfit ACE (Fig. 3B). The differences in remaining cervical spine flexion between the Laerdal Stifneck and the Weinmann Lubo Airway Collar (p = 0.1655) and between the Laerdal Stifneck and the Ambu Perfit ACE (p = 0.7923) were not significant. There was no significant difference in cervical flexion with Weinmann Lubo Airway Collar applied or no collar applied (p = 0.3611). Between the control examination and the Laerdal Stiffneck (p = 0.0049) and the Ambu Perfit ACE (p = 0.0008) there was a significant reduction in remaining cervical spine flexion.

Discussion
The aim of this study was to measure and to evaluate quantitatively the remaining motion of the cervical spine during immobilization using one innovative upper airway opening cervical collar and two traditional cervical collars. The present study showed that the attached innovative and traditional cervical collars resulted in significantly different remaining flexion of the immobilized cervical spine. The design of the cervical collars seems to have an influence on their fit and thus on the effectiveness of the immobilization.
The data of the present study showed that compared to traditional cervical collars, the innovative cervical collar allows for twofold increased flexion of the cervical spine. There was no significant difference in the cervical spine flexion whether the innovative cervical collar was applied or not. The novel upper airway opening design is probably decisive for the poor result. The innovative cervical collar has a one-belt system; whereby the mandible is addressed with an extra flexible belt (Fig. 1A). In contrast, both traditional cervical collars address the mandible as well as the occiput, sternum, clavicle, shoulders and upper back with their rigid form (Fig. 1B,C) 19,21,31 . The novel fixation system therefore seems to perform worse than the classic cervical collars in the important flexion motion. The Weinmann Lubo Airway Collar can support airway clearance, but a classic cervical collar should be used in unconscious and intubated patients with suspected cervical spine injury.
According to a study by Lubovsky et al., the innovative Weinmann Lubo Airway Collar, which combines an external airway protector in combination with a cervical collar, appears to be safe and effective in opening and maintaining open airways in anesthetized supine patients 19 . In addition, the authors recommend that further clinical trials are indicated to evaluate the safety and utility of this device under preclinical conditions 19 . To our knowledge, the efficacy of the collar toward cervical spine immobilization has not been tested so far. According to the data of the current study, efficiency of the innovative cervical collar by the means of cervical spine immobilization is worse compared to traditional cervical collars.
The study by Karason et al. also compared widely used cervical collars 32 . The endpoints of the remaining motion were analyzed using a gonimeter. In addition, the intracranial pressure was extrapolated, and the wearing Table 1. Results of the remaining motion examination of the three cervical collars and the control group. www.nature.com/scientificreports/ comfort was evaluated subjectively. As in the present study, the classic rigid cervical collars were shown to achieve safe immobilization. Karason et al. were able to determine a remaining motion of immobilization of the cervical spine of 18.0° ± 7.0°. The present study showed significantly better immobilization values. The extent to which this depends on the measurement method used or is even due to the test subjects should be analyzed in further studies.
The motion values that have been measured for the traditional cervical collars were in the same range as in other studies. Hostler et al. found a mean flexion of 9.2° ± 5.0° with the Ambu Perfit ACE applied 33 . Thus, complete immobilization of the cervical spine could not be achieved by a cervical collar alone. These findings are supported by various other studies 3,34 . In addition, many cervical collars are not applied correctly 35 ; therefore, their effectiveness is further reduced.
Since a secondary injury or a worsening of an existing injury cannot be completely excluded in cases of remaining cervical spine motion 4,36 , alternative immobilization techniques should be considered. Cervical spine immobilization by a collar could be substantially improved by additionally fixing the patient to a spine board 34 . However, in this case, the main immobilization will derive from fixation on the spineboard, and the cervical collar is dispensable 37,38 . The full body immobilization technique is especially recommended during patient transport 25 . Limitations. The present study is limited to some extent. Only human cadavers with an intact cervical spine were analyzed. For patients with an already injured cervical spine, different results can certainly be expected. Furthermore, the cervical spine force was applied in a standardized manner only for flexion and lateral bending. Combined movements were not performed. There is no literature that provides any indication of the magnitude and direction of the force required to cause or even to aggravate a cervical spine injury. Previous studies have shown that after an initial trauma, no further injury or aggravation can occur through further manipulation 39 . However, recent biomechanical studies have shown a direct correlation between manipulation of the severely injured cervical spine and the width of the dural sac 29,30,40 . Furthermore, the application of a cervical collar itself may aggravate a spinal injury 29 . Thus, in future studies, not only the remaining cervical spine motion but also the manipulation that is caused by the collar's application should be analyzed. Here, significant differences have been previously shown 41 . In addition, it should always be remembered that the cervical support immobilizes best when other immobilization tools are applied 26 . Three cervical collars were examined in the current study; and, according to the literature, many additional cervical collars are available 33 . This efficiency of these other collars should be addressed in further studies.

Conclusions
The results of the present study indicate that the best immobilization of the cervical spine could be achieved if the cervical collar has a nonmobile, rigid design that is closely attached to the mandible, occiput, sternum, clavicle, shoulders and upper back. However, all tested cervical collars showed remaining motion of the cervical spine. Thus, alternative immobilization techniques should be considered.