Rigid Orthoses for the Insensitive Foot:
The "Rigid-Relief" Orthosis
Andrew Novick, MA, PT
James A. Birke, MS, PT
Alicia S. Hoard, OTR
Denise M. Brasseaux, PT
John B. Broussard, PT
Elizabeth S. Hawkins, DPM, MPH
Introduction
The management of neuropathic plantar ulcers can be broadly categorized into two
phases: 1) healing of the wound and 2) maintenance of the former lesion in its healed
state. Clinical experience has shown that in
many cases the latter is the more difficult
challenge.
It is well documented that neuropathic
plantar ulcers are primarily the result of repetitive mechanical stress to vulnerable areas of the insensitive foot (1-6). Studies have
shown that these lesions most often occur at
sites of maximum load, usually associated
with a bony prominence. Ctercteko et al.
found increased vertical force under the 1st
metatarsal head (MTH) in diabetic patients,
both with and without metatarsal head ulcers, when compared to normals (6). In
those patients with ulcers, the lesions occurred at sites of maximum force, and peak
forces were significantly greater than those
recorded in controls. Similar results showing
increased vertical force or pressure under
the MTHs in diabetic patients were obtained
by several investigators (7-11). Pollard and
LeQuesne also recorded maximum horizontal shear forces at the site of neurotrophic
ulceration (10). Decreased loading of the
toes was also measured, resulting in increased loading of the metatarsal heads due
to the reduced surface area onto which
forces are distributed (6-9).
Several types of specialized devices have
been used to successfully heal plantar ulcers,
including total contact casts (TCC), plaster
posterior walking splints, molded double-rocker plaster shoes (MDRPS) and patellartendon-bearing (PTB) orthoses (10,12-22).
Quantitative studies have examined the effect of these devices on reducing plantar
force/pressure. Birke, Sims and Buford, and
Pollard, LeQuesne and Tappin showed significant decreases in force/pressure under
the metatarsal heads with the TCC (23,25).
Novick et al. found similar reductions with a
TCC at the MTHs using either a rubber
walking heel or cast boot when compared to
a standard leather oxford shoe (24). A significant reduction was similarly measured under the heel. The study also examined the
posterior walking splint, which was found to
be essentially as effective as the TCC in reducing plantar forces under the heel and
forefoot. Correspondingly, there was an increase in force at the midfoot, which partially explains the decreased loading at the heel
and forefoot. PTB orthoses have also been
shown effective in reducing plantar pressure
(22,26). Birke and Nawoczenski reported no
difference in pressure reduction under the
heel and forefoot between the PTB orthosis
and a short-leg orthosis (26).
The effectiveness of these healing footwear devices can be explained by several factors. First, the weightbearing forces are
evenly distributed throughout the entire
plantar surface of the foot due to the total
contact fit of the device's footbed. Increasing
the surface area that accepts weightbearing
forces results in a reduced force being applied to any one specific area of the foot.
Secondly, reliefs are built into the footbed by
either placing foam padding over the lesion
prior to applying plaster for the TCC and
walking splint, or by grinding-out the
footbed material beneath the lesion before
attaching the PTB orthosis. Lastly, all devices, except the MDRPS, transfer weightbearing forces to the lower leg through their
proximal extensions. Stress-relieving concepts have also been applied to clinically
proven devices such as foam aperture pads
(felted-foam), molded Plastazote? sandals,
Plastazote? boots, Scotchcast? boots and
Unna/fiberglas boots (27-30).
Once the ulcer has healed, the patient can
progress to more conventional, permanent
footwear. However, for the lesion to remain
healed, the same force-/pressure-reducing
principles common to the previously described devices must be used in the definitive
footwear. Nawoczenski, Birke and Coleman, and Schaff and Cavanagh found significant pressure reduction in the forefoot with
the use of a rigid rocker-sole on a leather
oxford shoe (31,32). Holmes and Timmerman effectively reduced peak pressures under MTHs by affixing a metatarsal pad directly on the foot's plantar surface just proximal to the site of maximum pressure (33).
Perhaps the most important defense in
preventing recurrent ulcers is orthotic intervention. The orthosis is typically one of two
types: 1) a flat insole made from a single
layer of soft, low-durometer material, such
as PPT (The Langer Group, Deer Park,
N.Y. 11729) or Spenco (Spenco Medical
Corp., Waco, Texas 76710), or 2) a custom-molded orthosis made from a soft or semi-rigid material, such as Plastazote #1 or #2
(Bakelite Sylonite Ltd., Hertfordshire, England), Pelite (Cascade Orthopedics, York,
Pa. 17402) or Aliplast (Alimed Inc., Dedham, Mass. 02026). These materials provide
total contact and can accommodate biomechanical faults through posting (3,34-36).
Reliefs may also be made on their undersurface, corresponding to observed or marked
areas of high pressure to further decrease
pressure at these sites. The molded orthosis
may be covered with a layer of soft insole
material for greater shock absorbency.
Despite the use of insoles and custom-molded orthoses, often in conjunction with
rigid rocker-soled shoes or other shoe modifications, many patients are prone to reulceration. For this reason, an alternative type of
orthosis was sought. It was reasoned that an
orthosis combining the shock-absorbing features of soft insole material with the TCC's
rigid, custom-molded, pressure-relieving design might yield a more favorable outcome.
The use of rigid material has also been supported by Rubin, Cohen and Rzonca, and
Reigler (35,37). In addition, the shape of the
foot appears to change between the non-weightbearing (NWB) and full-weightbearing (FWB) positions (38). Historically, the
foot is casted NWB in the subtalar neutral
position, and the molded orthosis formed
over this positive model. However, when the
weightbearing foot is placed on this NWB
orthosis, the lowering of the medial longitudinal arch, and change in both length and
width of the foot, creates an imperfect fit.
This mismatch could be critical in the success
or failure of an orthosis made from a rigid
material. To accommodate this, it was decided the foot should be casted in FWB to obtain the foot's exact contour in its functional
position when the greatest forces are applied
and the resultant osseous and soft tissue reactions have occurred. Reigler also advocated casting the foot in the weightbearing position to obtain its more physiologic position
(37).
This article describes a method of fabricating a rigid device vacuum-formed over a full-weightbearing plaster model. Neoprene
crepe (Southern Leather Co., New Orleans,
La. 70113) is added to the plaster model at
the healed lesion sites prior to molding to
create the relief between the orthosis and the
healed lesion site. This rigid-relief orthosis is
then covered with a soft, shock-absorbing
material and placed in a shoe having adequate height in the toe box, such as an extra-depth shoe or leather tennis shoe.
Fabrication MethodsCasting Procedures
The healed lesion site is marked on the patient's foot with a felt-tipped pen for later
identification on the positive plaster model.
The patient is placed in FWB stance position
with weight evenly distributed between both
feet. Two sets of six-inch-wide plaster of paris splints, each three layers thick, are overlapped in the center and cut long enough to
cover the front of the toes and the posterior
heel. The plaster is moistened then placed on
a piece of one-inch-thick foam rubber that is
covered with a thin sheet of plastic for protection from moisture. After smoothing, it is
placed under the patient's foot. The plaster
is molded and allowed to dry while the foot is
maintained in its optimal position for maximum function (see Figure 1
). This may be
subtalar neutral position or the position
deemed most suitable based upon existing
deformities or limitations of mobility.
Positive Model Preparation
After drying, the site of the healed lesion is
identified in the shell and remarked with the
felt-tipped pen (see Figure 2a
and Figure 2b
). Plaster is poured into the shell and the hardened
positive model is removed and smoothed.
The sulcus between the forefoot and toes is
eliminated with additional plaster, built-up
even with the plane of the heel and MTHs
(see Figure 3
). This effectively lowers the
distal end of the orthosis and prevents edge
pressure against the anterior forefoot.
The healed lesion site is identified on the
positive model. A piece of 1/4-inch-thick neoprene crepe is cut so it extends beyond the
edges of the site by approximately 1/4-inch on
all borders (see Figure 4a
and Figure 4b
). This allows a slope to be ground into the crepe,
removing its sharp edge while maintaining
full thickness under the healed lesion site. It
also reduces the risk of edge pressure from
side-to-side movement of the site over the
orthosis while supporting the bone just proximal to the healed lesion site, much like a
metatarsal pad. When the site is under an
MTH, the crepe is extended at least one inch
so the orthosis will allow for distal migration
of the MTH. The crepe relief pad is briefly
heated in the oven then affixed onto the
model with contact cement.
An additional piece of 1/4-inch crepe is
buffed then similarly added on top of the
first to obtain proper depth of the relief (see
Figure 5
). Usually some minor buffing is required to achieve the final shape of the crepe
relief so the final thickness measures between 3/8- and 1/2-inch (see Figure 6
). Two 1/4inch rather than one 1/2-inch crepe were used
since it was easier to mold the thinner material. Other materials, including plaster, can
be used to create the relief.
Orthotic Fabrication
A piece of Subortholen (three- or four-mm
thick) [JMS Berkshire Resource Inc., Garfield, N.J. 07026] is heated and molded over
the positive model in a vacuum chamber.
When cooled, the material is cut from the
model with a cast saw. Rough edges are
smoothed, and the device is placed under the
FWB patient to identify final trimlines. The
length of the finished rigid-relief orthosis extends to the junction of the toes with the
forefoot (approximately one inch beyond
the MTHs) to prevent edge pressure (see
Figure 7
). This reduces MT joint extension,
but the rocker design of the shoe can substitute for this motion. The inner edges of the
orthosis are beveled from the inside out to
reduce edge pressure (see Figures 8a, b, c and
d
). A piece of firm orthotic material is secured under the Subortholen shell and
ground level to the bottom of the relief (see
Figure 9
). When the relief is under the 1st
MTH, it can be used as a medial post, if
necessary. The orthosis is lined with Spenco
or PPT to provide a soft, shock-absorbent
interface (see Figure 10
).
Case Studies
Two case studies describing the application
of the rigid-relief orthosis in the management of patients with chronic reulceration
follow. In both cases the lesions were healed
with either a TCC or walking splint, but reulcerated while wearing shoes with a semi-rigid orthosis or molded sandals.
Case 1
Patient GE is a 60-year-old female who has
had diabetes for 24 years and Type I diabetes
for the last 17 years (see Figure 11
,and Figures 12a and
b
). Examination showed no sensation on the
dorsal or plantar aspects of either foot. An
ischemic index of greater than .85 was measured on the left, while the right vessels were
unable to be occluded. Her initial foot problem was an ulcer under the right 4th toe in
1983 that subsequently developed an infection and was amputated. She had repeated
episodes of stress fractures in her right foot
during 1984-85 and surgery to the tendons of
her right lesser toes in 1986. In November
1987, a large blistered area developed into
an ulcer under the right 4th MTH following a
full day of walking in bedroom slippers. This
lesion was successfully healed with casting
and a molded sandal relieved under the lesion.
In September 1988, she was progressed to
a semi-rigid, molded orthosis covered with
PPT and relieved under the right 4th MTH.
The orthosis was placed in a rigid rockersoled shoe. She required maintenance callus
trimming and minor orthotic modifications,
noting at times discoloration due to subcutaneous hematoma, but no lesions to the 4th
MTH. Reulceration of the right 4th MTH
occurred in May 1989 after walking all day in
molded sandals at a shopping mall. A plaster
walking splint was made, and the wound
healed in three months.
An examination on July 20, 1990, revealed
the initial lesion at the right 1st MTH, for
which a walking splint was made. The patient returned for four follow-up visits
-which included wound care and callus
trimming-until the ulcer healed in seven
weeks. At this time she was instructed to
wear the splint for one more week then alternate the splint with the molded sandals. She
also was allowed to begin gradual wearing of
extra-depth shoes and semi-rigid orthoses,
beginning at one hour/day and adding one
hour each day. The 1st MTH was found to
have reulcerated Oct. 1, 1990, prompting a
return to the splint. The lesion healed in two
weeks, but again reulcerated by Nov. 5,
1990, after wearing the shoes/semi-rigid
orthosis for periods of up to four hours/day
instead of the prescribed one hour/day. This
lesion healed with a cast, but she experienced three more episodes of 1st MTH reulceration over the next five months.
When the last lesion healed by April 12,
1991, the rigid-relief orthosis was issued. She
was instructed in a gradual break-in period
for the shoes/rigid-relief orthosis to be worn
for only one hour during both a morning and
afternoon session for a three-day time period, followed by an additional hour each session for each three-day period. At all other
times she was to wear the splint. This allowed complete knowledge of the effects of
the shoe/rigid-relief orthosis since the splint
was known to permit healing at the 1st
MTH.
When she returned April 26, 1991, she had
been wearing the shoe/rigid-relief orthosis
for five hours in both the morning and afternoon sessions and developed only a small
callus. The callus was trimmed, and she was
instructed to continue increasing her time
with the rigid-relief orthosis until she was
wearing it full time. She returned May 10,
1991, with a small hematoma under the 1st
MTH that she stated was not present until
she wore her molded sandal for two hours.
Wearing of the rigid-relief orthosis had increased to seven hours for each time period
the previous week ending May 4, 1991, and
she reported wearing the rigid-relief orthosis
for 16 hours May 4, 1991, and 10 hours May
5, 1991, each time without any problems.
The patient then went on vacation for over
three weeks, wearing the rigid-relief orthosis
part-time for up to 6 hours/day and remained
ulcer-free at both the 1st and 4th MTHs for a
total of more than two months.
Case 2
Patient MG is a 63-year-old male with Hansen's disease (see Figure 13a
, Figure 13b
, and Figure 14
) with
lack of sensation on the plantar aspects of
both feet and a resultant long history of bilateral plantar foot lesions. More recent involvement to the left foot included an ulcer
at the 1st MTH in January 1988 that measured 15 mm in diameter and 15 mm in depth.
The lesion was healed with the use of a plaster walking splint. The next recorded ulcer
on Sept. 2, 1988, was of two weeks' duration
under the left 1st and 3rd MTHs. These were
treated with a Plastazote boot with reliefs cut
out under the lesions. Three weeks later, a
small spicule of necrotic bone was noted and
removed. A splint was applied Oct. 12, 1988,
promoting closure of the 3rd MTH ulcer by
Jan. 5, 1989, and the 1st MTH lesion approximately two months later. Custom shoes with
a rigid rocker-sole and semi-rigid orthoses
were issued in June 1989. Reulceration of
the 3rd MTH, 1 cm in depth, was noted one
month later. Additional PPT was placed on
the left orthosis and the rocker repositioned
more posteriorly. The lesion was healed by
Aug. 25, 1989, but reopened by Oct. 2, 1989.
Notes indicate the 1st MTH ulcer recurred
twice more, measuring 3 mm in depth and 2
mm in diameter on July 31, 1990. The Plastazote boot, followed by a short course with
the splint, promoted healing by Sept. 17,
1990.
The patient returned to his custom shoes
with semi-rigid orthosis, alternating with the
molded sandal, and remained healed until
the 1st MTH lesion recurred Oct. 30, 1990.
Having made multiple modifications to the
shoes and semi-rigid orthosis, he was casted
for a rigid-relief orthosis. It was delivered
Nov. 28, 1990, and the patient was closely
monitored while wearing only the shoe/rigid-relief orthosis until his departure for a three-week vacation Dec. 18, 1990. At that time
the lesion had improved but remained open.
He returned Jan. 9, 1991, and was examined
one week later. The 1st MTH ulcer had
healed while wearing the rigid-relief orthosis
in a standard low-top tennis shoe with a rigid
rocker-sole and occasionally a molded sandal. The lesion has remained healed for
more than eight months while the patient
continues to wear the rigid-relief orthosis in
the tennis shoe, with only occasional use of
the molded sandal.
Summary
The rigid-relief orthosis has been clinically
shown to be an effective, adjuvant modality
in preventing recurrent plantar ulcers. lts
benefits can be summarized as follows:
- the rigid relief reduces or totally eliminates pressure on the vulnerable, healed lesion site;
- weightbearing casting results in more
even distribution of weightbearing forces
throughout the remaining plantar foot;
- the rigid material resists deformation,
thereby providing original protection for the
life of the device; and
- the rigid material does not bottom-out,
which extends longevity and requires fewer
replacements.
The following precautions must be heeded
to minimize complications:
- the orthosis must be carefully broken in, following the schedule described in the
first case study, and
- properly fitting shoes are necessary to
prevent sliding of the foot over the contoured, rigid orthosis.
Minor modifications can easily be made to
the orthosis, if necessary, through grinding
or spot heating and remolding. Rigid-relief
orthoses should ideally be used in conjunction with a rigid rocker-soled shoe. They can
also be incorporated into an AFO by extending the material proximally behind the posterior shank for those patients requiring rearfoot stability or dorsiflexion assist. The rigid-
relief orthosis is only part of a total program
that must include comprehensive patient education, with emphasis on careful inspection
to detect problems early.
Acknowledgments
Sincere thanks are extended to Carol Langlois,
Jerry Simmons and Val Coor at the Paul W.
Brand Biomechanics Lab, Rehabilitation Research Department, Gillis W. Long Hansen's Disease Center, for providing artwork, photography
and technical assistance.
Andrew Novick, MA, PT, is a research physical
therapist at the Gillis W. Long Hansen's Disease
Center, Carville, La. 70721.
James A. Birke, MS, PT, is director of physical
therapy at the Gillis W. Long Hansen's Disease
Center, Carville, La. 70721.
Alicia S. Hoard, OTR, is deputy director of
physical therapy at the Gillis W. Long Hansen's
Disease Center, Carville, La. 70721.
Denise M. Brasseaux, PT, is a staff physical
therapist at the Gillis W. Long Hansen's Disease
Center, Carville, La. 70721.
John B. Broussard, PT, is a staff physical therapist at the Gillis W. Long Hansen's Disease Center, Carville, La. 70721.
Elizabeth S. Hawkins, DPM, MPH, is a research podiatrist at the Gillis W. Long Hansen's
Disease Center, Carville, La. 70721.
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