Development of a Modular Design,
Custom-Fitted Protective Helmet
Steve Ryan, PEng
Greg Belbin, CO(c)
Mendal Slack, BS, CO(c)
Stephen Naumann, PhD, PEng
Rod Moran, DDS
Introduction
Many children and young adults with neuromuscular and seizure disorders suffer falls,
which can result in severe head and facial
injuries unless appropriate protective headwear is worn. While effective protection for
the head and face is a priority for these individuals, headwear should also provide unobstructed vision and adequate ventilation and
be lightweight, cosmetically acceptable and
reasonably priced.
This article details the design, development and clinical assessment of a modular,
custom-fitted helmet that strives to incorporate these features.
Background
Providing effective headwear is a problem
for many orthotists charged with the care of
individuals who have a high risk of head or
facial injury following a fall. Parents, caregivers and clinicians often have no choice but
to use commercial sports helmets or other
types of adjustable off-the-shelf headwear to
provide the protection necessary.
Although commercial helmets are adaptable and relatively inexpensive, a number of
features make them generally unsuitable for
the disabled population:
- Commercial helmets protect the cranium but leave the facial area, particularly the
chin and oral structure, vulnerable. Commercial face shields could provide the extra
protection, but they may impede vision and
add to a "caged in" feeling. In addition, because of a face shield's remote placement, it
could contribute to neck injury if caught on a
stationary object during a fall.
- Usually commercial helmets are designed with ventilation slots and liner cooling
paths, which are conduits for forced air
movement through the helmet. Cooling occurs as the wearer moves. This form of ventilation is inefficient for the disabled population since, for the most part, they move at or
below normal walking speed.
- Suspension in commercial headwear is
provided primarily by a chin cup attached to
the helmet by straps, which are tightened to
prevent helmet movement. Constant pressure applied to the chin could lead to orthodontic problems, particularly in the growing child.
Recognizing the deficiencies in commercial devices, several professionals have developed customized protective headwear for
the physically challenged. One such development, the "Muckamore Abbey Cosmetic
Helmet," consisted of a one-piece polypropylene outer shell and a medium-density
polyethylene foam liner, which were both
custom-made to suit a specific client (1). An
Irish tweed cap was added to the outer shell
to conceal the headwear for cosmetic purposes. While the resulting product was lightweight, the process was labor-intensive, and
the helmet provided no facial protection.
Investigations into the biomechanical
properties of concealable liner materials and
material combinations for seizure-prone individuals were conducted in an effort to enhance the cosmetic appearance of protective
headgear (2). A customized polyethyleneviscoelastic foam laminate performed comparably to commercial helmets, but target
users rejected it because it was bulky. Also,
it did not guard against facial injury.
Other researchers reported on the development of maxillofacial protective headwear
in a case study (3). A commercial felt-lined
leather helmet was reinforced with Orthoplast and given a remote frontal face bar for
protection (4). The patient suffered no injuries while using the modified device. However, the helmet was custom-tailored with limited regard for its cosmetic appearance, and
it was untested in the degree of protection
afforded to the cranial vault. A modified version of this same concept was tried by others,
with similar results (5).
In another case study, a helmet was created from a commercial hockey helmet shell
and a two-part viscoelastic foam liner (6).
The inner shape of the liner was developed
from a positive mold of the patient's head,
using modified orthotic techniques. The
headwear proved effective for that particular
patient, but ventilation was limited. Its
weight and appearance were not reported.
At the Hugh MacMillan Rehabilitation
Centre in Toronto, Canada, a vacuum formed custom-fabricated helmet was developed to address this need (7). The helmet
was a one-piece construction consisting of a
hard polyethylene shell and a foam liner,
which was vacuum-formed over a plaster
replication of the user's cranial area. Areas
covering the chin and forehead were built up
to protect the facial features from falls on fiat
surfaces. Cut-out areas at the top of the helmet provided ventilation, reduced weight
and provided a flexible hinge for connecting
the anterior and posterior shell sections.
This approach is still being used at the
Centre and has proven to be clinically effective in providing appropriate protection for
the head and face. To date, more than 300
custom-fabricated helmets have been produced for physically challenged children and
young adults.
While this technique has successfully provided the essential features required of protective headwear, it was proposed that a
modular custom-fitted helmet design could
afford the same degree of protection to many
individuals, faster and at a significantly reduced cost (8). Appearance and ventilation
were also addressed in the modular helmet's
development.
Design
The production helmet consists of three industrially fabricated parts: an anterior section, posterior section and chin protector.
Each part is comprised of a rotational molded, polyethylene outer shell and a low-density polyethylene foam liner set.
The liners in the anterior and posterior
shells are die-cut with uniform conduction
channels to promote heat flow from the inside to the top of the helmet. This cooling
action is augmented by providing an opening
at the crown of the helmet. While the protective nature of the device is limited at this
location, this portion of the head is at minimal risk based on the falling pattern of the
target population.
The chin liner is compression-molded with
a deep depression and has three narrow
grooves at its base to eliminate pooling of
drool, which was identified as a problem during the preproduction prototype investigations.
The helmet's anterior and posterior sections are interconnected at fitting. The anterior projections of the posterior section are
trimmed at fitting to customize the helmet's
length. The anterior section overlaps the
posterior section, and they are attached by a
low-profile screw/nut combination and a
locking fastener set on the helmet's lateral
aspects. The screw sets serve as the pivot
points for the connection between the two
shell halves. The locking fasteners are commercial snap fasteners designed to provide
auditory feedback when secured. Using this
type of fastener can also discourage unwanted removal of the helmet by an uncooperative wearer while the push-button release is
easy for a caregiver to actuate.
Each side of the chin protector overlaps
the temporal-mandibular aspect of the anterior shell and is secured by a pair of screw/
nut sets at fitting.
The assembled helmet's anterior aspect
extends out to provide protective clearance
for the face following a fall forward. The
posterior section is contoured to tuck under
the occiput without extending too far downward, thereby minimizing the risk of neck
injury. In combination with the posterior
section, the chin protector cups under the
chin to offer a secure, functional fit.
Both small-medium (S-M) and medium-large (M-L) sizes were developed. The anatomical criteria for determining the appropriate size for individuals were related to
head circumference, length and breadth
measurements (see Table 1
).
S-M helmets weigh 320 g; M-L helmets
weigh 450 g. Variations in weight occur depending on the degree of customization required during a fitting.
The helmet was developed as a kit to facilitate its use by orthotic clinics. To simulate
this use during fittings, project orthotists
were given all the components, fasteners and
fitting jigs envisaged as part of the helmet
kit. The assembled helmet and kit are shown
in Figure 1
and Figure 2
, respectively.
Clinical AssessmentProcedure
Initially, 10 children and young adults-
eight males and two females-participated
in the clinical evaluation of the S-M production headwear. Four young adults were also
fitted with the M-L helmet toward the end of
the project, but formal clinical evaluations
were not conducted for these subjects.
Subjects for the S-M helmet were six to 20
years of age. They presented diagnoses of
cerebral palsy, hydrocephalus, seizure disorders and other neurological impairments.
Eight subjects were ambulatory; two were
ambulatory to varying degrees, only occasionally leaving their wheelchairs. All subjects had prior experience with custom-fabricated headwear; however, one subject had
only limited experience.
Clinical trial periods lasted six to 10
weeks, after which time the children and
their parents returned to the Centre for a
follow-up visit. They then judged specific
features of the helmet and rated its performance. Questions were posed in an interview type format. The project orthotists who performed the initial fittings inspected and evaluated the devices' durability at this point.
Clinical ResultsDiscussion of Fittings
and Post-Trial Evaluations
Of the 10 helmets fitted, only one was not
dispensed. (One helmet was not a proper fit
for the person, and there was concern it
could compromise protection.)
The research helmet was found to be an
orthotic device that could be readily dispensed in a clinical setting in one appointment. On average, it required two hours to
measure, evaluate and fit a subject. The project orthotists felt that, with experience, the
helmet could be fitted in less than two hours
except in cases where special modifications
were required. The orthotists remarked on
the ease with which they could dispense the
helmet using the specially designed jigs and
fixtures provided.
No major technical problems or mechanical failures were identified during the helmets' post-trial evaluation.
Discussion of Caregiver Evaluations
Caregivers most appreciated the protection
offered by the helmets. They also liked the
speed with which the helmet was fitted and
its appearance. Six caregivers reported that
their children accepted wearing the helmet,
suggesting that it was comfortable to wear.
Although the helmet was not worn extensively during the hot summer months, all
caregivers thought the helmet ventilation
was acceptable. All but one said the helmets'
weights were very good.
The production helmets' value was further
recognized when caregivers were asked if
they would like their child to continue using
it. All caregivers responded positively. The
extent to which the helmets met caregivers'
expectations, and their ratings of overall performance are shown in Figure 3
and Figure 4
.
Conclusion
Evaluation results indicated the helmet was
well-received by both caregivers and clinicians. The production helmet seemed to afford the protection required for the subjects
tested, as evidenced by the injury-free service provided. It appears to be durable although longer term monitoring will be necessary to determine the device's service life.
The preliminary analysis indicated the helmets should offer at least the same degree of
protection as custom-fabricated versions yet
be dispensed by headwear clinics in under
three hours for less than 40 percent of the
cost.
Despite development of this new design,
custom-fabricated headwear is still necessary
in some cases. Children and young adults
who exhibit self-abusive behavior (Lesch-Nyham Syndrome), those who have a tendency to ingest non-edibles (Pica Syndrome)
or who have irregular head shapes or sizes
should not wear the modular design, custom-fitted protective helmet.
An estimated 75 percent of people with
disabilities who require protective headwear
could benefit from this helmet. Helmet use
should be prescribed by an appropriate medical specialist and be fitted, dispensed and
adjusted by a certified orthotist only. The
modular helmet is now commercially available in two sizes through Variety Ability Systems Inc. (VASI) located in Scarborough,
Ontario, Canada.
Acknowledgments
This project was supported by the National
Health Research and Development Programme
of Health and Welfare Canada, grant number
6606-3451-59 and by VASI.
Steve Ryan, PEng, is a mechanical engineer in the rehabilitation engineering department at the Hugh MacMillan Rehabilitation Centre, 350 Rumsey Road, Toronto, Canada, M4G 1R8.
Greg Belbin, CO(c), is manager of the orthotic services deparmetn at the Hugh MacMillan Rehabilitation Centre in Toronto, Canada.
Mendal Slack, BS, CO(c), is coordinator of orthotic research in the orthotic services department at the Hugh MamMillan Rehabilitation Centre.
Stephen Naumann, PhD, PEng, is the associate director of the rehabilitation engineering department at the Hugh ManMillan Rehabilitation Centre.
Rod Moran, DDS, is the director of the dental department and the Protective Headwear Clinic at teh Hugh MacMillan Rehabilitation Center.
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