A Postural Support Belt Can Be Used as a Substitute for a Lap Belt

Ann Adv Automot Med. 2011 Oct; 55: 3–fourteen.

Kid Posture and Shoulder Belt Fit During Extended Dark-Time Traveling: An In-Transit Observational Study.

Abstract

Agreement pediatric occupant postures can help researchers indentify injury risk factors, and provide information for prospective injury prediction. This study sought to observe lateral head positions and shoulder belt fit amongst older child automobile occupants during a scenario likely to result in sleeping - extended travel during the night. An observational, volunteer, in-transit study was performed with 30 pediatric rear-seat passengers, ages 7 to 14. Each was restrained by a three-betoken seatbelt and was driven for seventy-5 minutes at night. 10 subjects used a high-back booster seat, ten used a low-dorsum booster seat, and ten used none (based on the subject height and weight). The subjects were recorded with a depression-light video photographic camera, and one frame was analyzed per each minute of video. The loftier-back booster group exhibited a statistically significant (p<0.05) decrease in the mean frequency of poor shoulder belt fit compared to the no-booster and low-back booster groups. The high-back booster group also exhibited statistically significant decreases in the xc^th percentile of the absolute value of the relative lateral motion of the head. The low-back booster grouping did not issue in statistically significant decreases in poor shoulder belt fit or lateral head motion compared to the no-booster group. These results are consistent with the presence of large lateral supports of the high-back booster which provided support to the head while sleeping, reducing voluntary lateral occupant motion and improving shoulder belt fit. Future work includes examining lap belt fit in-transit, and examining the effects of these observations on predicted injury risk.

INTRODUCTION

The postures of child machine occupants are highly variable, afflicted by private behaviors, anthropometries, external stimuli, and the restraints used (Andersson et al. 2010, Charlton et al. 2010). Posture has the potential to touch on factors contributing to injury run a risk during a collision, including the interaction of the child with restraints, the kinematics of the kid, and the potential for interaction with other structures in the interior of the vehicle (van Rooij et al. 2005).

Understanding realistic pediatric occupant postures can help researchers place potential injury chance factors, facilitating the development of protective countermeasures. For case, in the last two decades research into mail service-toddler postures in adult seats highlighted concerns such as poor lap belt and shoulder belt fit (Arbogast et al. 2007, Bidez and Syson 2001, Jermakian et al. 2007, Nance et al. 2004, Reed et al. 2005a, Klinich et al. 1994, Nance et al. 2004, Reed et al. 2005a). Such observations prompted recommendations, and increases in use, of belt-positioning booster seats (Jermakian et al. 2007, Klinich et al. 1994, Sherwood et al. 2006, Winston et al. 2003, Winston et al. 2004).

In addition to the identification of hazard factors, understanding the range of possible child postures can provide input for biomechanical studies seeking to predict injury take a chance in fake collisions. Typical biomechanical evaluations (sled tests, total-calibration crash tests, crash simulations) employ surrogate occupants (dummies or computer models) seated in a position either divers past an industry standard, or by the boilerplate position observed in a laboratory posture study (e.g., Reed et al. 2005b, Reed et al. 2006). Express studies, however, take sought to investigate the sensitivity of predicted child occupant responses (including injury adventure) to changes in surrogate occupant posture (Arbogast et al. 2007, van Rooij et al. 2005). While in some cases out-of-position biomechanics studies should target artificially defined "worst instance scenarios", some studies may seek to target typically-occurring positions. This requires quantified information on the range and distribution of postures observed in the field.

Previous investigations into child occupant posture and belt fit fall into 3 categories: laboratory studies, inspection studies, and observational studies. Laboratory studies detect and measure out postures of children volunteers seated in a vehicle seat either mounted in a laboratory, or located in a stationary examination vehicle (Huang and Reed 2006, Klinich et al. 1994, Reed et al. 2005, Reed et al. 2006, Reed et al. 2009). Those studies typically intend to quantify anthropometric characteristics in a single seating position, not necessarily investigating aberrant positions or time-varying postural changes or behaviors.

Inspection studies use on-site vehicle inspections and interviews to find restraint use in the field (Decina and Knoebel 1997, Decina and Lococo 2005, Koppel and Charlton 2009, Morris et al. 2000, O'Neil et al. 2009, Paine and Vertsonis 2001, Staunton et al. 2005). These typically involve recording observations of motorists recruited at sites such every bit gas stations, parking lots, or police roadblocks. In those studies the recruitment and interview process interrupts normal transit, misreckoning the study of behavioral aspects of belt fit and posture. Instead, inspection studies typically seek to study basic restraint use and the quality of installation of kid restraints.

In contrast to laboratory or inspection studies, observational studies (too termed "naturalistic" studies) seek to observe existent-world behaviors, restraint fit, and postures of occupants in-transit. This typically involves recording occupants traveling in a exam vehicle outfitted with video cameras mounted to the vehicle interior. Meissner et al. (1994) summarized an observational study of child occupant postures recorded using hidden cameras during extended trips, providing a qualitative clarification of types of postures observed. Charlton et al. (2010) described an observational report using an instrumented vehicle lent to 12 volunteer families. That report qualitatively described the overall postures of children ranging from 1–8 years during trips ranging from 2 minutes to 3.half-dozen hours (hateful 19 minutes). Andersson et al. (2010) described an observational study investigating the event of two dissimilar booster seat designs on posture. That report performed organized trials with vi children ages 3–6, with trips of forty–50 minute length. That study establish that the children tended to sit with their head forward from the head rest for a greater percentage of time when seated in a booster with large lateral head supports. They attributed this beliefs to the children wanting to encounter around the head supports, out the window or across the interior of the vehicle, and postulated that this may remove any protective benefit of the lateral caput supports in a side touch collision. Although information technology was not the aim of that report to investigate belt fit specifically, the authors did notation observing some cases of gross misfit such as the routing of the belt under the arm. All of the trials of Andersson et al. (2010), and about (89%) of the trips recorded past Charlton et al. (2010) occurred during daylight.

While the previous studies have provided valuable information on children'south behaviors during daytime driving, none accept yet targeted postures attained while sleeping. Sleeping children have the potential to showroom postures non commonly observed while awake, given the relaxation of the body and the necessity of resting the caput against a supporting object. This may be exacerbated for older, larger children, who practice not benefit from the whole-body support provided past child safety seats. This study sought to examine the lateral caput position and shoulder belt fit among older children (with booster seat use based on the size of the subjects) in an observational study with atmospheric condition conducive to sleep – extended trips during the night. This paper asked the questions: In an in-transit scenario probable to produce sleeping of kid automobile occupants, is there any effect of booster seat presence or type on A) the xc^thursday percentile lateral motion of the head and B) the position of the shoulder chugalug on the shoulder?

METHODS

An in-transit, observational study was performed with child volunteers. Lateral head positions and shoulder belt fit were observed during organized trips (trials) of 75 minute length, performed at night. The children were seated in the rear seat, and were observed with a low-light video photographic camera mounted to the rear of the passenger seat. The report and analysis methods are described in detail below.

Volunteers

Xxx pediatric volunteers participated in the written report. Inclusion criteria were that the children were of ages vii–xiv years, with a maximum height of 165 cm. Subjects were selected to result in three equal groups (x subjects in each) based on the booster seat acme and weight criteria described below. Exclusion criteria included children with an acute illness, previous show of motion sickness, difficulty sleeping inside of a vehicle, morbid obesity, or any musculoskeletal disorder described as a disease. The study subjects were accompanied at all times by a parent or caregiver.

These trials were performed every bit a office of a concurrent study to investigate a positioning device to amend kid passenger comfort and sleeping in-transit. The trials reported hither represent the baseline (the tests performed in a default configuration without the device tested in the larger written report). Informed consent information forms covering all aspects of the study procedures were presented to, reviewed, and approved by a parent prior to the initiation of each trial. The subject/parent pairs were provided with 70€ every bit compensation for their time. All recruitment and written report procedures were reviewed and approved by the University of Navarra Ethics Review Board.

Trip Method

Trials consisted of organized trips in a written report vehicle. To promote sleeping, each trip began at either 21:thirty or 23:00 hours (depending on the randomized order of trials inside the concurrent report mentioned above). The parents were asked to avoid having their children nap during the day of the trial, to feed them dinner as normal prior to the trial, and to wearing apparel them in light comfortable clothing.

During the trips, the study bailiwick was seated in the correct rear seat (of a left-driving vehicle), and a parent or caregiver was seated in the correct front passenger seat. Prior to the initiation of the trip, the child was outfitted with a headband and taped-on shirt markers to facilitate observation of the position of various anatomical landmarks (Effigy 1). The headband also included an integrated centre-shade to farther promote sleeping. The kid was then seated and the seatbelt was installed, and the child was asked to sit upward-right with their head back to record an initial position.

Typical video view with the center head and sternal-notch markings highlighted (also shown: video-view reference marks that were added during post-processing).

A high back booster seat (2010 Rodi model, Maxi-Cosi) was used with all subjects under 32 kg in weight. A low-back booster (2010 Indy Squad model, Jane) was used with subjects greater than or equal to 32 kg, just less than 147 cm in height. No booster seat was used for subjects greater than 147 cm.

The trips consisted of a combination of city and highway driving (approximately equal mix) on a predetermined circuit in the vicinity of Pamplona, Espana. All trials were performed in a 2005 mid-sized, luxury, sports utility vehicle. The vehicle was piloted by a dedicated study driver.

Throughout the trip, the kid's posture in the coronal plane was recorded with a camera (Sony Handycam model DCR-SR35) with low-light, infrared recording capability. The photographic camera was mounted underneath the headrest of the front passenger seat. A second camera was used to record an orthogonal side-view of the subjects. This view was obscured, even so, by the lateral caput supports in the high-back booster cases. Because this represented a systematic, biased data loss, the side-view camera was non used in the analysis presented here.

The trips were recorded for a duration of 75 minutes. Temperature in the vehicle interior was controlled to between 22 and 23 C. The children were asked to relax comfortably, close their eyes, and to sleep if they wished. Trips were interrupted if a marker on the test bailiwick became mispositioned, in which instance the driver would stop the vehicle, reposition the marking, and and then go on the trip.

Video Assay and Variables

A sample of 75 video frames (the first frame per each minute of video) was analyzed for each trial. Output variables were called to quantify the change in lateral position of the caput in the coronal plane, and to qualitatively describe the fit of the shoulder belt on the shoulder.

The shoulder belt fit was examined for each selected frame. The fit was qualified as "off of the shoulder" if the entirety of the belt crossed the upper arm lateral to the acromion (Figure 2a). The fit was qualified as "into the neck" if the belt was visibly pressed into the lateral surface of the cervix, or if the belt was supporting the neck (Figure 2b). The fit was qualified as "above the sternum" if whatever portion of the belt crossed the occupant midline superior to the sternal notch marker (Figure 2c). Each of these were considered "poor" belt positions.

Illustrations of the diverse belt fit definitions. A) Off of the shoulder – the belt crosses the upper arm lateral to the acromion. B) Into the neck – the belt is visibly pressing into or supporting the neck. C) Above the sternum – any portion of the chugalug crosses the occupant midline superior to the sternal notch mark. D) No "poor" belt position notes.

The position of several points on the head and thorax were digitized for each video frame. These included the position of three markers on the brow, the tip of the olfactory organ, the inferior-almost points of the ears, and a marker on the sternal notch. These points were digitized in each frame using Phantom Loftier Speed Camera Control software (Version 9.0.649.0, Vision Research Inc.). Because the purpose of the electric current report was to examine lateral head motion, only the position of the center brow marker is presented here (Effigy 1). Whenever the marker moved exterior of the field of view, the frame number and direction of the excursion was noted. When the marking was obscured or mispositioned, the position entry for that frame was left blank.

Assay

Belt position

The qualitative belt position notes were used to report the percentage of trip time in which the diverse types of "poor" belt positions were observed. The percentage of frames exhibiting each belt-position blazon was determined for each subject. The resulting values were continuous variables (between 0 and one) representing sample-derived percentages of trip time spent with each belt position blazon, for each subject. These variables are termed P_any (percentage of frames with any poor belt position), P_neck (belt pressing into the cervix), P_sternum (belt above the sternal notch), and P_shoulder (belt laterally off of the shoulder) for the residuum of this manuscript.

Head position

The lateral movement of the center forehead marking was determined for each analyzed frame. The initial (time goose egg) position was subtracted from the position in each frame to decide the relative lateral displacement of the marker. Whenever the marking moved laterally out of the frame, the displacement value was truncated to the maximum value observable inside the frame for that subject (note: because the relative displacement was reported, the truncation values varied between subjects due to differences in the initial position of the head).

Because truncated values were present in some observations, not-parametric descriptors were used to summarize the caput deportation data. Maximum and minimum values, and 10th, 50^thursday, and 90^th percentile values were determined for each discipline. The 90^th percentile of the absolute value of the lateral displacement was likewise calculated for each field of study. This variable is termed Y_xc for the residual of this manuscript.

Comparison Between Groups

The P_any , P_neck , P_sternum , P_shoulder , and Y_xc values were compared betwixt the three report groups in ii different means. First, an analysis of variance (ANOVA) was performed. A two-manner ANOVA was performed with the independent variables defined as the presence of a depression-back booster ("depression-back" = 0 or 1) and the presence of a high-back booster ("high-back" = 0 or 1). In that assay the no-booster grouping was used as a baseline for comparison. That analysis produced comparisons of the means of the low-back group and the high-back booster group relative to the no-booster grouping. An additional two-style ANOVA was performed with the presence of no booster ("no-booster" = 0 or ane) and the presence of a high-back booster as independent variables, with the depression-back booster group equally a baseline. That produced a comparison betwixt the no-booster and low-back booster groups (redundant with the ANOVA in a higher place), and a comparison between the high-back and low-back booster groups. Differences were considered to be statistically significant if the p-values were less than 0.05.

Although ANOVA is useful in identifying statistically meaning differences between groups of data, information technology does not provide insight into the magnitude of those differences. Linear regression models were adult to examine the magnitude of whatever potential differences between the means of the no-booster group (the baseline) and the low-back and high-back booster groups. The linear regression models took the course shown in Equation 1, where C_LB is the model coefficient associated with the use of a low-back booster, C_HB is the model coefficient associated with the utilize of a loftier-back booster, C_None is the coefficient (constant) associated with the baseline status of the group with no booster seat. The variable LB is equal to one if a low-back booster is used; the variable HB is equal to ane if a high-back booster is used. The output variable Ten represents the dependent variable of interest (P_any , P_neck , P_sternum , P_shoulder , or Y₉₀ ).

X =C _None +C _LB  ×LB +C _HB  ×HB

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RESULTS

All thirty trials were performed successfully. The characteristics of the study subjects are shown in Table 1.

Table 1:

Subject field Information

Subject	Historic period	Gender	Height (cm)	Weight (kg)	Booster*
ane	9	F	142	37	LB
2	8	F	139	31	HB
iii	8	F	123	31	HB
4	eight	M	132	25	HB
5	10	F	144	xl	LB
six	viii	F	131	28	HB
7	10	F	134	32	LB
8	8	M	126	24	HB
9	8	F	127	31	HB
x	8	M	132	32	LB
11	12	F	163	41	N
12	8	M	129	26	HB
xiii	nine	M	136	34	LB
fourteen	xiii	Thousand	158	48	N
15	13	F	156	44	N
16	11	F	152	43	N
17	11	M	150	44	N
18	10	F	138	39	LB
xix	9	F	140	42	LB
20	12	F	155	56	N
21	12	Thousand	153	44	N
22	9	F	147	42	LB
23	13	F	163	48	Northward
24	7	F	131	xxx	HB
25	10	F	144	42	LB
26	12	M	153	37	N
27	9	F	139	37	LB
28	8	Thou	122	21	HB
29	xiv	F	164	49	N
30	10	F	127	27	HB

Chugalug Position

The percentages of frames exhibiting poor belt positions are shown in Table 2 and Figure three. The no-booster group exhibited poor belt positions during an average of 78% of the frames examined, with a range from 16% to 99%. The most commonly observed poor belt position in that group consisted of the belt impinging on or supporting the neck ("into the neck"). In the depression-dorsum booster grouping, 61% of the frames exhibited a poor belt position. In the loftier-back booster group, 17% of the frames exhibited a poor chugalug position.

Mean values for the percent of frames exhibiting poor chugalug positions, by booster seat use and past belt position category. The mistake bars betoken + i standard difference. The asterisks indicate statistically-significant (p<0.05) differences between group pairs (via two-way ANOVA).

Table ii:

Percent of frames (N=75 per field of study) exhibiting the various "poor" belt position classifications, by subject number and booster seat type (standard deviations for means shown in parentheses).

		Chugalug Position
	Subject	Any Bad, Pany †	Into Cervix, Pcervix	Above Sternum, Psternum	Off Shoulder, Pshoulder
No Booster Seat	11	forty.0	26.7	13.3	0.0
	14	85.iii	85.three	0.0	0.0
	fifteen	94.7	0.0	94.7	0.0
	16	16.0	4.0	0.0	12.0
	17	98.seven	98.7	0.0	0.0
	xx	98.7	90.vii	8.0	0.0
	21	xc.vii	37.3	53.3	0.0
	23	96.0	0.0	96.0	0.0
	26	98.7	66.seven	32.0	0.0
	29	57.three	48.0	ix.3	0.0
	Mean	77.6 (29.5)	45.7 (38.3)	30.seven (38.0)	1.2 (3.eight)
Low Back Booster Seat	one	88.0	20.0	0.0	68.0
	five	74.7	74.7	0.0	0.0
	seven	62.seven	58.seven	iv.0	0.0
	10	ninety.7	13.3	54.vii	22.vii
	13	57.three	40.0	ix.3	8.0
	18	46.7	fourteen.7	14.7	17.3
	19	90.7	38.seven	26.7	25.iii
	22	1.3	0.0	0.0	1.3
	25	96.0	26.7	69.3	0.0
	27	1.3	0.0	0.0	1.iii
	Hateful	60.nine (35.3)	28.7 (24.5)	17.9 (25.0)	xiv.4 (21.3)
High Dorsum Booster Seat	2	0.0	0.0	0.0	0.0
	3	62.7	62.7	0.0	0.0
	4	0.0	0.0	0.0	0.0
	6	sixty.0	lx.0	0.0	0.0
	eight	fourteen.7	0.0	0.0	14.7
	9	0.0	0.0	0.0	0.0
	12	0.0	0.0	0.0	0.0
	24	i.3	1.iii	0.0	0.0
	28	32.0	1.3	thirty.seven	0.0
	30	0.0	0.0	0.0	0.0
	Mean	17. (25.5)	12.5 (25.vii)	three.one (9.7)	ane.5 (4.vi)

Relative Lateral Caput Position

Observations of the lateral caput position (including truncated instances of the marker outside of the frame) were recorded for 81% of the frames (1825 frames out of a possible 2250). In the remainder, the caput marker was inside the video frame, but was obscured past an object, a torso part, by video glitches, or by rotation of the head. Of the observations made, four% (3% of the total frames) were notes of the marker positioned outside of the field of view.

The maximum, minimum, and percentile values for the relative lateral head deportation for each subject are shown in Figure 4. The 90^th percentiles of the accented values of the relative lateral head deportation (Y₉₀ ) are shown in Table three. The minimum relative head deportation values ranged from −35 cm (a truncated value; negative indicates move towards the subject'south correct, towards the window/door) to −4 cm. The maximum relative displacement ranged from 0 cm to xxx cm. The 50^th percentile (median) relative displacements ranged from −35 cm (a truncated value) to 8 cm. The 90^th percentile, absolute value lateral head displacements ranged from 3 cm to 35 cm (a truncated value).

Box plots of the lateral head displacement (from the initial position) showing the 10^thursday, 50^th, and xc^th percentile values, and the maximum and minimum values. Negative values signal movement towards the subject's right, towards the window/door. The asterisks indicate values that were truncated due to the mark traveling outside of the video frame.

Tabular array 3:

90^th percentiles of the absolute value of the relative lateral head movement for each subject (Y₉₀ ), by booster seat type (standard deviations for means shown in parentheses)

No Booster		Low-Back Booster		High-Back Booster
Field of study	Yxc (cm)	Subject field	Y90 (cm)	Subject	Y90 (cm)
xi	nineteen.3	1	35.4†	2	viii.5
xiv	35.4	5	25.vi	3	6.3
15	22.vii	7	16.0	4	five.4
xvi	21.2	10	25.4†	6	ix.i
17	25.4	xiii	22.2	8	12.1
twenty	22.6	eighteen	26.9	9	10.0
21	23.3	19	14.two	12	vii.8
23	12.0	22	three.0	24	3.ii
26	26.vii	25	31.ane	28	7.0
29	25.0	27	11.one	30	7.6
Mean	23.4 (5.9)	Mean	21.i (nine.9)	Mean	seven.7* (2.v)

Group Comparison

The results of the ANOVA comparisons are shown in Effigy 3 and Tabular array iii. For the high-dorsum booster, the mean values of P_any (percentage of frames with whatever poor belt position), P_cervix (chugalug pressing into the neck), P_sternum (chugalug passing higher up the sternal notch), and Y_ninety (90^th percentile, absolute value lateral caput motion) were significantly different than the no-booster grouping (p<0.05). For the low-dorsum booster grouping, only the mean value of P_shoulder (chugalug passing lateral to the acromion) was significantly dissimilar than the no-booster group. The mean values of P_any , P_shoulder , and Y_xc were significantly different between the high-dorsum and low-back booster groups.

The coefficients for the linear regression models are shown in Table four. The C_None coefficients for all of the models were significantly greater than nix (p<0.001). This indicates that the no-booster group resulted in hateful values for each of the output variables (P_any , P_neck , P_sternum , P_shoulder , or Y_ninety ) that were significantly greater than cypher. The C_LB and C_HB coefficients indicate if, and by what magnitude, the presence of a low-back or loftier-back booster alters the mean values of the output variables relative to the baseline no-booster condition. For example, in the P_whatsoever model the C_None coefficient indicates that the subjects of the baseline no-booster group exhibited any poor belt position in an average of 78% of the video frames examined. The model coefficient associated with depression-back booster utilise (C_LB ) was not significantly different than zero (p=0.231), indicating that the mean P_any value for the depression-dorsum booster group was not significantly different from the no-booster group. In contrast, the coefficient associated with high-back booster use (C_HB ) was significantly different from zero (p<0.001), indicating that the mean P_any was significantly different from the no-booster group. The betoken approximate for that coefficient (−0.607) indicates that the high-back booster group exhibited a decrease in the mean P_any value of 61 pct points relative to the no booster group. The 95% confidence interval for that coefficient indicates that decrease may range from 89% to 33%.

Table 4:

Linear regression model coefficients for the belt position, and the ninety^thursday percentile, absolute value, relative lateral head position (N=30 subjects, up to 75 frames each).

			Coefficient	p†	95% C.I.
Chugalug Position, Percentage*	Any Bad, Pwhatsoever	No Booster, CNone **	0.777	<0.001	0.579, 0.975
		Low Back Booster, CLB	−0.167	0.231	−0.447, 0.113
		High Dorsum Booster, CHB	−0.607	<0.001	−0.887, −0.327
	Into Neck, Pcervix	No Booster, CNone **	0.458	<0.001	0.262, 0.654
		Depression Back Booster, CLB	−0.171	0.217	−0.449, 0.107
		High Back Booster, CHB	−0.33	0.021	−0.611, −0.055
	In a higher place Sternu thousand, Psternum	No Booster, CNone **	0.306	0.001	0.132, 0.480
		Low Back Booster, CLB	−0.127	0.300	−0.374, 0.120
		High Dorsum Booster, CHB	−0.275	0.030	−0.522, −0.028
	Off Shoulder, Pshoulder	No Booster, CNone **	0.012	0.768	−0.071, 0.095
		Low Dorsum Booster, CLB	0.131	0.030	0.014, 0.248
		High Back Booster, CHB	0.002	0.972	−0.115, 0.119
Lat. Head Position, Abs. Value, 90th %, Y90 (cm)		No Booster, CNone **	23.6	<0.001	19.2, 28.one
		Low Back Booster, CLB	−2.26	0.466	−8.51, 4.00
		High Dorsum Booster, CHB	−14.4	<0.001	−twenty.7, −8.eighteen

Consistent with the ANOVA results, the high-back booster group exhibited statistically-pregnant (p<0.05) negative (decreasing) model coefficients for the hateful P_any , P_neck , P_sternum , and Y_xc values, relative to the no-booster condition. In addition to the P_any results described above, the model coefficients indicate a decrease of 33 percentage points for the mean P_cervix value, 28% for P_sternum , and xiv cm for Y₉₀ . The low-back booster group did non upshot in any statistically-significant model coefficients, except for a small (thirteen%), only statistically significant (p=0.03) positive (increasing) coefficient for the P_shoulder variable.

Word

Shoulder Belt Fit

40-half-dozen percent of the frames examined exhibited a poor belt position of a medial nature, with the belt impinging on the cervix or located superior to the sternal notch. Placing the belt in this manner has the potential to load the cervical spine, carotid arteries, trachea, and other vulnerable structures of the neck during a standoff. Although belt-related spine and neck injuries to children are rare (Garcia-España and Durbin 2008), they tin accept devastating consequences in the circumstances in which they occur (Deutsch and Badawy 2008, Jeffery and Melt 1991, Lynch et al. 1996, Skold and Voigt 1977). The loftier-frequency of medial-related poor belt positions should also be considered when designing deployable devices integrated into the shoulder belts of rear seat restraints, such as pretensioners (Forman et al. 2008) or belt-integrated airbags (Forman et al. 2010).

In 6 percent of the frames the belt was located laterally off of the shoulder. Shoulder belts are designed to load the relatively strong structures of the clavicle, shoulder, and upper chest. Placing the shoulder belt laterally to the acromion limits the benefit gained from the force of those structures. Instead, such a position would likely issue in loading of the arm and mid-to-lower breast during a collision. This reduction in restraint of the upper trunk may also let greater movement of the chest and head in a collision (Sherwood et al. 2005), resulting greater risk of hit interior surfaces or other occupants.

Lateral Head Position

A considerable range of lateral head positions was observed (Effigy 4), especially inside the no-booster and depression-back booster groups. Most of this motility occurred to the occupants' right, with 73% of the median values occurring in the negative (outboard) management. This is consequent with a propensity to rest the head towards (or confronting) the window when attempting to sleep in-transit. This is also consistent with the relatively high frequency of medial-related "poor" shoulder belt positions, with the belt impinging on or supporting the neck, or with the belt passing superior to the sternal notch.

The lateral head position was truncated by moving exterior of the visible range for 3% of the video frames. It is unlikely that this limited truncation affected the results of this study. Statistically significant differences were observed between the loftier-back booster group and the low-back and the no-booster groups. Since the data truncation only afflicted the 90^th percentile, absolute value lateral caput positions of select low-dorsum booster cases (Table 3), removing this truncation would tend to increase the observed differences between that group and the high-back booster group. Removing the truncation would non affect the observed differences betwixt the 90^thursday percentile values of the high-back and no-booster groups. Thus, even if the express truncation present was avoided, the conclusions of this study would remain unchanged.

Consequence of Booster

The subjects with a high-dorsum booster seat exhibited statistically significant decreases in the percentage of frames with poor chugalug fit, and in the xc^th percentile of the accented value of the relative lateral motion of the head, compared to the group with no booster seat. This is consistent with previous laboratory studies that take observed improved shoulder chugalug fit in static conditions with loftier-back boosters (Reed et al. 2009). This is the first report (to the authors' knowledge) to ostend those laboratory observations via an in-transit observational study targeting sleeping children positioned at their ain will.

The low-back booster group tended to showroom decreases in most of the poor belt position variables compared to the no booster seat group, still well-nigh of those decreasing trends were not statistically significant. The most notable exception is the incidence of the "off-shoulder" poor chugalug position. Although the low-back booster tended to exhibit a bottom incidence of whatever poor belt position relative to the no-booster grouping, the depression-back booster group exhibited a statistically-pregnant greater incidence of the "off-shoulder" poor belt position relative to the no-booster group. This suggests that amongst the subjects and frames that exhibited poor belt positions, a greater proportion of the low-back booster cases tended to lean inboard, causing the chugalug to slip laterally off of the shoulder. In contrast, a greater proportion of the no-booster, poor belt position cases tended to lean outboard, causing the chugalug to press into the neck or pass above the sternal notch. Equally discussed below, the injury adventure implications of these two types of poor belt fit are currently unknown. Futurity work should include studying the implications of these positions to identify priorities for comeback.

The high-back booster group exhibited statistically pregnant decreases in the per centum of frames with poor belt fit, and in the 90^th percentile lateral head motion, relative to the low-back booster group. This is somewhat in contrast to the daytime observational written report of Andersson et al. (2010). That study observed that the presence of large lateral caput supports on a high-back booster resulted in children moving their heads exterior of the volume of the booster seat to gain a better view out the window or across the interior of the vehicle. In the current report, the large lateral caput supports provided support for the caput while sleeping, resulting in less lateral motion of the head and improved shoulder belt fit. Such contrasting results are non just academic, but could potentially accept existent implications in booster seat design. In the absence of other data, the results of the Andersson et al. study could potentially be interpreted to criticize loftier-back boosters with large lateral caput supports. The electric current study, however, demonstrates a benefit of booster seats with big lateral head supports under weather not considered by previous studies. It is unknown, yet, if a low-profile loftier-back booster (like the alternative studied by Andersson et al.) would provide similar lateral head back up to a sleeping child.

The observations of the current study are consistent with the field injury trends observed by Arbogast et al. (2005). That report plant that high-dorsum booster seats reduced the risk of AIS 2+ injuries (Abbreviated Injury Scale 1990 Revision) to pediatric rear seat occupants in side collisions compared to children without a booster seat, generally through a reduction of caput injuries. Depression-dorsum booster seats did non consequence in a statistically significant reduction of injury risk. The electric current study suggests several mechanisms that may result in the reduction of chance with a loftier-back booster, including improved shoulder belt fit, maintaining a greater initial distance between the head and the door, and the presence of the lateral caput support wings which may potentially absorber a laterally-directed accident.

It is important to note that the subjects in this study were not randomized by size - booster seats were assigned based on the tiptop and weight of the subjects. Those criteria were designed specifically to amend chugalug fit for smaller children whose top would result in a poor belt fit and posture with an developed restraint and seat. The results advise that both the high-dorsum and low-dorsum booster were successful in this regard, in that the shoulder belt appeared to fit well with both groups when the children were seated upright with their backs against the seats. Likewise, the children in the no-booster group were tall enough (by design) so that the belt fit well when they were saturday upright. Therefore, the variation in belt fit amid the examination groups was not necessarily a part of the discipline anthropometry (in relation to the geometry of the seats and restraints), but instead was a function of the voluntary motion of the children during travel. Considering of the lateral back up provided, the children moved less with the high-back booster, resulting in a more consistently appropriate fit of the shoulder chugalug.

Head Rotation

This written report used a mark located at the eye of the forehead to quantify caput movement. The location of this marking may be affected by the rotation of the head, potentially causing artifactual motion observations of a magnitude up to the radius of the head (approximately half-dozen cm). This potential error is pocket-sized, notwithstanding, compared to the difference in xc^th percentile lateral caput motions observed between the groups (approximately 16 cm difference between the ways of the loftier-back and the no-booster groups). As a bank check against the worst-case scenario – even if the maximum possible error of 6 cm were subtracted from absolute value head motions of the no-booster grouping, the hateful xc^th percentile values of that grouping would still be significantly greater than the original values of the high-dorsum booster group (p<0.01, ANOVA). That represents an extreme example, attributing a 100% written report group bias to any artifacts resulting from head rotation. In reality, head rotation artifacts were relatively unbiased (i.e., similar across the study population). The magnitude of head rotation can be qualitatively assessed by examining the number of frames in which the lateral-most markers on the forehead were obscured by rotation of the head to the left or right. The percentage of frames with a rotation-induced obscuring of those markers was not significantly dissimilar betwixt any of the groups (p>0.i for all study grouping comparing combinations, based on ANOVA). As a consequence, it is unlikely that adjusting for head rotation artifacts would impact the conclusions of this written report regarding the effect of booster seats on lateral head motion.

Video View

This manuscript only presents the motion of the occupants in the coronal plane, recorded by an anterior video view. A lateral-view video photographic camera was present during this report, but it provided limited data due to visual obstruction by the lateral head supports of the high-back booster. Previous observational studies recorded rear seat occupant behaviors using oblique video views (Andersson et al. 2010, Charlton et al. 2010). While that type of video view renders it hard to determine quantitative measures of move in any of the chief planes, it does facilitate the qualitative observation of motion in several different axes. Time to come observational studies may consider using a combination of video cameras located orthogonal to the principal planes for quantitative motion analyses, in addition to obliquely-mounted cameras to obtain qualitative overall descriptions.

Future Work

The goals of this report were to examine shoulder belt fit and lateral head motion in older children sleeping in-transit. The shoulder belt represents simply one point of concern for chugalug fit amid pediatric occupants – the other beingness the fit of the lap belt. Improper lap chugalug fit may lead to an increased hazard of loading of the abdomen or lumbar spine during a collision (Arbogast et al. 2007). Like with the shoulder belt, it is possible that the lap belt may migrate into a suboptimal location as the kid moves during transit. Future work could include examining real-world lap belt fit with sleeping children in-transiit.

Finally, this study intentionally used conservative definitions of "poor" chugalug fit, relating to chugalug position categories that were distinctly definable. The nature and magnitude of the effects of these chugalug positions on injury run a risk remain to be investigated. Information technology is also likely that there be chugalug and body positions other than those classified hither as "poor" that may negatively impact injury gamble (van Rooij et al. 2005). Future efforts should include exploring the effects of body and belt position on predicted injury risk. This may be best accomplished through reckoner simulations, with the positions observed here serving as a realistic range to target for study.

CONCLUSION

This study observed the lateral head position and upper shoulder belt fit of thirty pediatric volunteers, while riding in the rear seat of a vehicle for an extended period during the night. The written report group using a high-dorsum booster exhibited a statistically significant (p<0.05) decrease in the mean frequency of poor shoulder belt fit, compared to the no-booster group and the depression-back booster grouping. The loftier-back booster grouping also exhibited statistically significant decreases in the 90^th percentile of the accented value of the relative lateral movement of the caput. The low-back booster grouping tended to exhibit decreases in the frequency of poor shoulder belt fit (compared to the no-booster group), but those decreases were not statistically significant (p=0.231 for any bad belt position). The low-back booster group did not result in decreases in the 90^th percentile, absolute value, relative lateral motion of the caput relative to the no-booster group. These results are consistent with the presence of big lateral head supports with the high-back booster, which reduced voluntary occupant motion by providing support to the head while sleeping. Future work could include expanding this study to examine lap belt fit in-transit, and examining the effects of these observations on predicted injury risk (potentially through figurer modeling).

Acknowledgments

This study was supported in part by Siesta System, Inc. This study was besides supported in part by a Whitaker International Scholars Grant, and by general funds from the European Heart for Injury Prevention. The opinions expressed here are solely those of the authors, and exercise not necessarily express the consensus opinions of the funding organizations.

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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256839/

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