The Buckled Insert: Fabrication and Fitting Instructions

Child Prosthetic and Orthotic Studies, New York University Post-Graduate Medical School, New York, New York


This article describes the fabrication and fitting of the Buckled Insert (BI). The design of the BI (Figure 1-A. ) derives from the UC-BL Shoe Insert1; but the shoe insert cannot control some deformities: "Undercorrection of . . . valgus . . . results in an unstable position of the foot. The insert cannot support abnormal forces of the magnitudes developed under these circumstances and therefore should not be used in such cases in which undercorrection is a necessary phase of treatment."2

The BI is designed to hold the foot in correct alignment, if that alignment can be achieved passively, or in the best alignment achievable by manipulation. To achieve this result the HI differs from the UC-BL Shoe Insert in two respects: it has a medial portion which extends proximal to the medial malleolus, and it has a strap which encircles both the proximal portion of the medial extension and the lateral upright of a conventional orthosis.

Originated in polyester laminate, the BI may also be made of orthopedic-grade polypropylene (polypropylene alloyed with small amounts of butyrate and polyethylene) or Subortholen. As compared with the thermoplastic version, the laminated orthosis is thinner and permits graduation of flexibility in the plantar surface; but polyester laminate is more difficult to fabricate and is less durable than polypropylene or Subortholen.

The BI is presently designed for children. For subjects wearing orthoses with double uprights or a lateral upright, the purpose of the BI is to reduce flexible pes valgus more effectively than conventional valgus-correction (T or Y) straps, pads, or the UC-BL Shoe Insert.

Conventional leather valgus-correction straps tend to stretch and lose their corrective value quite rapidly. Although they are adjustable, this adjustability often is not utilized by parents because the adjustability has not been explained to the family, or because they may be afraid to compress tissue over the bony malleolus, especially if the skin is anesthetic there. Furthermore, the strap often is not effective because its shape has been altered through stretching. The BI overcomes these problems because its medial extension cannot change shape, and the strap is reinforced so that it does not stretch.

Pads often press against only a small portion of the malleolus and, therefore, cause intolerably high pressures. The BI, however, applies its corrective forces over a large area, thus reducing the malleolar pressure.

The theoretical basis of the BI involves the application of sufficient forces to the foot-ankle complex to hold the bones in the best achievable alignment. The orthosis applies total contact, so forces are distributed over a sufficient area to keep skin pressures tolerable. Further, since the materials are not alterable in shape in the supported areas when the orthosis is worn, the application of the corrective pressures remains constant over the entire area supported.

Total contact about the foot and ankle permits application of forces to control deformity with pressures more evenly distributed than those applied with orthoses of conventional design.

The primary three-point force system consists of medially directed forces on the calf at the calf-band level and at the lateral side of the foot, and a laterally directed force at, around, and above the medial malleolus, extending as much as 2 cm (3/4 in.) above the top of the shoe. Secondarily, body weight is transmitted to the bottom of the insert, stabilizing it in the shoe. The rigidity of the insert holds the medial extension relatively vertical. Thus, the medial extension can maintain laterally directed forces against the malleolar and perimalleolar areas. Laterally directed forces are counteracted by medially directed forces applied by the BI against the lateral side of the foot. These secondary forces are applied independently of the rest of the orthosis and only in weight-bearing.

Materials and Equipment

The casting equipment and materials required, with one exception, are identical for both the laminated and thermoplastic Hi's.

1. Elastic or Regular Plaster Bandage

Plaster-of-Paris bandage, 8 cm (3 in.) wide, is used. Depending on the size of the foot, one or two rolls are needed. Elastic bandage makes it somewhat easier to achieve close molding.

2. Tubing

Latex tubing or other suitable flexible material, about 30cm (12 in.) long and 1 cm (3/g in.) in diameter, is used to form a tunnel under the plaster wrap for the introduction of bandage scissors to remove the wrap.

3. Balloon or Tubular Gauze

A large rubber balloon, 20 x 92 cm (8 x 36 in.), is inflated and then invaginated over the foot to provide a smooth surface on the inside of the plaster wrap. In addition, the balloon exerts relatively uniform compression on the soft tissues of the foot, providing snug fit in the completed insert.

A length of Tubegauz tubular gauze or stockinette, equal to twice the distance from the toe to the knee as measured along the posterior aspect of the limb, will separate the plaster from the skin. There may be a slight difference in contour between a cast taken with fabric and a cast done with a balloon.

4. Contoured Standing Surface

Since the BI must fit the shoe as well as the foot, a standing surface which has a suitable configuration must be used. A prefabricated, plastic standing surface, with the heel and forefoot portions planar, is satisfactory. The contralateral foot must be supported on a surface that allows symmetrical stance.

A typical standing surface is shown in Figure 1-B. , and the actual contour is shown in Figure 2. .

5. Casting Stand (optional)

A casting stand (Figure 3. ) is employed to minimize the need for moving the foot once the patient is brought to the standing position. It consists of a revolving platform to which a pipe support has been added, and the assembly is mounted on a suitable base. The stand enables the patient to remain upright and to be rotated 180 degrees so that the orthotist can observe the calcaneus and maintain the foot in a corrected weight-bearing position as the plaster hardens.

6. Plastics

a. Polyester Laminate

Polyester laminate is used for the major portion of the BI. The most suitable resin is two parts rigid (Laminac No. 4110) to one part flexible (Laminac No. 4134). The layup is made with a tightly knitted synthetic stockinette such as Perlon, 6 cm (2 and 1/2 in.) wide and equal in length to five times the posterior distance from the toes to the midshank, and fine-weave fiberglass cloth, 2--4cm (3/4 to 1 and 1/2 in.) wide and equal in length to twice the medial distance from the sole to the midshank.

b. Thermoplastic

The thermoplastic version of the BI requires rigid plastic, such as orthopedic-grade polypropylene, 0.3--0.5 cm (1/8 to 3/16 in.) thick, depending on the strength needed. A sheet approximately 50 x 20 cm (20 x 8 in.) will be required. Nylon parachute cord, Teflon rods, or lead rods, are also required.

7. Closed-Cell Foam

PE LITE or similar closed-cell foam sheeting 0.3 cm (1/8 in.) thick is used for the malleolar pad. A circle approximately 2--4 cm (3/4 to l and 1/2 in.) in diameter will be needed.

8. Reinforced Strap

A strip of cowhide leather, 2 cm (3/4 in.) wide and approximately 38 cm (15 in.) long, is sewn to a strip of dacron webbing. Horsehide leather lines the strap. A buckle is riveted to one end of the strap.

9. Basic Supplies

A tape measure, indelible pencil, scissors, cast-cutter or knife, skiving blade, mandrel pipe, coarse file, sand screen, hammer, sanding cone, vacuum system, router, felt cone, and leather punch are required. Items such as petrolatum or silicone spray, nylon hose, pressure tape, tacks, contact cement, eyelets, and rivets also will be needed.

 

Fabrication Procedures

 

The laminated and thermoplastic versions of the BI are formed over the same modified cast, and steps 1--9 of the fabrication sequence are identical for both. For the thermoplastic BI, steps 10A--11B replace steps 10 and 11 of the lamination procedure. Fitting and wear instructions (steps 12--15) are identical for both BI's.

1. Examination of Limb

Note the amount of positional correction which can be obtained manually without loss of mediolateral alignment. Maximum control may be sacrificed to avoid excessive skin pressure. After a period of wearing the orthosis, a second BI with additional control can be made. Note also the changes which occur in the foot when the subject goes from nonweight-bearing to weight-bearing. Measure the calf circumference and the widths of the forefoot and heel. Record the results of the examination and the specifics of the insert to be fabricated on the Orthotist's Information Form (Figure 4. ).

With indelible pencil mark the skin over the following areas: medial malleolus, lateral malleolus, navicular tuberosity, first metatarsal head, fifth metatarsal head, and any calluses and other pressure-sensitive areas.

2. Establishment of Shoe Line on Subject

The subject should sit comfortably on an examining table or its equivalent, with his bare foot in his shoe. If the shoe has a high quarter, draw a line with indelible pencil on the foot along the medial border of the shoe upper. If the shoe has a low quarter, draw the line 2 cm (3/4 in.) above the medial malleolus. The subject then removes his shoe.

3. Determination of Midpoint of Ankle Excursion

For the medial extension of the insert to be oriented correctly, the plaster wrap must be made with the ankle positioned in the proper degree of dorsiflexion. The orthotist may cast the limb in the neutral position, wherein the lateral midline of the shank is perpendicular to the plantar surface of the shoe sole.

If, however, the subject walks with marked dorsiflexion, the neutral position may not be optimal. The position of the medial extension can be established in the following manner. Note the excursion of the ankle as the subject walks in his conventional orthosis. The approximate midpoint of this excursion should coincide with the midline of the medial extension. For example, if the subject generally moves from 5 degrees plantarflexion to 15 degrees dorsiflexion as he walks, the total ankle excursion is 20 degrees, and the 10-degree midpoint occurs when the ankle is dorsiflexed 5 degrees. Thus, the plaster wrap should be made with the ankle dorsiflexed 5 degrees.

4. Application of Balloon or Gauze

The subject, still seated, extends his foot and leg toward the orthotist. Place a fully inflated balloon with the closed end against the toes of the extended foot of the subject (Figure 5. ). (In the case of a small child or of a subject with a flail leg, this procedure may require two persons, one to hold the child or to steady the leg, and the other to apply the balloon.) Carefully push the balloon onto the foot, gradually releasing air so that the balloon will slide freely upon itself. The following technique is a simple way of controlling the release of air and maintaining control over the balloon. The orthotist holds the open end of the balloon against his abdomen while using both hands to guide the balloon onto the foot. The orthotist's trunk movement controls the rate of air release. If the balloon is applied over the toes without restricting the release of air until it is well upon the heel, the toes will be much more comfortable because they will be under less pressure. Pressure of the balloon against the toes may cause them to bend, but unless there is acute discomfort, the bending is not a problem, since the toes will not be included in the completed insert. When completely deflated, the balloon should extend above the malleoli as shown in Figure 6. Stretch and cut the projecting mouth of the balloon, as shown in Figure 7. Place the fingers of both hands under the cut edge; then stretch and pull the balloon onto the leg, as shown in Figure 8. The balloon must extend at least 2 cm (3/4 in.) higher than the anticipated proximomedial trim line.

If tubular gauze or stockinette's used, apply one or two layers between the knee and a point 3 cm (1 and 1/8 in.) distal to the toes, eliminating wrinkles.

5. Establishment of Trim Lines

With an indelible pencil, draw trim lines on the balloon or fabric. These lines will transfer to the cast and, ultimately, to the plaster model.

The plantar trim line is at the metatarsophalangeal crease. The distomedial and distolateral trim lines begin at the medial and lateral ends of the metatarsophalangeal crease and continue dorsally two-thirds of the way toward the dorsa of the first and fifth metatarsals.

The anteromedial and anterolateral trim lines run proximally from the upper ends of the distomedial and distolateral trim lines, respectively, and parallel to the respective metatarsals. The posterior trim line and the posterior half of the lateral trim line should be 0.6 cm (1/4 in.) below the level of the distal tip of the lateral malleolus.

Figure 9. illustrates the location of the trim lines on the patient's bare foot, without balloon or fabric, for purposes of clarity.

The medial extension should be slightly wider than the anteroposterior dimension of the malleolar pad, with the extension being parallel to the midline of the leg.

Blend the trim lines with each other, maintaining a 2--5 cm (3/4 to 2 in.) radius between the trim line on the posterior edge of the medial extension and the horizontal trim line around the Achilles tendon (Figure 10-A. ). An even gentler curve should exist between the trim line on the anterior edge of the medial extension and the anteromedial trim line.

If a high-quarter shoe is to be worn (it is recommended that a high-quarter shoe cover no more than 25 per cent of the tibial length), the medial extension of the BI should reach proximally beyond the top of the shoe by a distance of 0.6 cm (1/4 in.), plus the width of the strap to be used, 2 cm (3/4 in.). If a low-quarter shoe is to be worn, the medial extension of the BI should terminate approximately 2 cm (3/4 in.) above the malleolus.

6. Plaster-Wrap Procedure

Prior to making the plaster wrap, place a sheet of paper on the standing surface on which the wrapped foot will rest, to aid in removal of the cast. If the casting stand is not used, an assistant or a walkerette should be available to assist the subject in standing and in maintaining his balance.

Also, before the wrap is made, place a strip of flexible tubing, coated with petrolatum or a silicone spray, on the balloon over the dorsum of the foot and anterior leg. Secure the tubing with several pieces of tape, as shown in Figure 10-B. If fabric is used, insert the strip between the skin and the material. If an oscillating-blade cast-cutter is used, it is unnecessary to lubricate the strip.

The subject is seated with the leg and foot hanging freely.

Wrap the foot in plaster bandage as follows.

Hold the foot perpendicular to the leg during the wrapping stage. The wrapping procedure begins just above the heel. Hold the bandage roll with the roll toward the foot (the subsequent circumferential spiral wrap requires more control of bandage tension, and with the bandage started in the reverse manner as indicated, it will be possible to do the circular wrap in the orthodox manner). Figure 11. summarizes the wrapping sequence.

a. From the starting position the bandage is brought distally along the sole of the foot, then over the toes.

b. It is continued proximally along the medial border of the foot and then around the heel to secure the starting end of the bandage.

c. The wrap is continued distally along the lateral border of the foot.

d. Carry the bandage across the toes, proximally along the medial border of the foot, and continue over the heel onto the Achilles tendon.

e. At this point fold the bandage over the fingers and bring it distally along the sole, around the toes, and then proximally along the medial border and around the heel to secure the area at the fold.

f. Carry the bandage along the lateral border approximately to the instep, at which point the circular wrapping of the foot begins.

g. Wrap the foot in the spiral manner from heel to toe. Continue the wrap proximally from the foot onto the ankle and then onto the leg to a level slightly higher than the most proximal trim line.

Exert only enough tension on the bandage to reproduce the limb's contours. Too much tension will produce grooves in the plaster, especially over fleshy areas, and will bridge the bandage over bony areas, producing hollows in the east and in the orthosis.

7. Alignment and Corrections During Weight-Bearing

While the plaster is still pliable, assist the subject to the standing position on the casting stand or other suitably elevated platform, with his back to the orthotist. The subject maintains his balance with the aid of the railing on the casting stand, a walkerette, or an assistant. The orthotist is then seated on a stool of appropriate height to bring his eyes to the level of the patient's midcalf. The orthotist carefully positions the wrapped foot on the shaped surface (Figure 12. ), locating the entire heel on the upper horizontal surface of the standing block. The orthotist manipulates the forefoot with one hand and the hindfoot and leg with the other hand to achieve the desired correction.

If weight-bearing is not possible because the subject cannot stand without an orthosis or because an assistant is unavailable, the subject can remain seated. After wrapping the limb, press a casting board against the sole to give proper contour to the bottom of the cast. Manually hold as much correction as possible. This technique is not as accurate, and the cast will require more modifications.

Dorsiflex the ankle by rotating the leg forward to the degree determined by observations made in accordance with instructions in the section: "Determination of Midpoint of Ankle Excursion," (generally such that the leg is perpendicular to the floor). The foot may have to be plantarflexed slightly to avoid pes valgus or skin breakdown. Plantarflexion requires the addition of a heel lift inside and, at times, also outside the shoe.

To raise the arch, the orthotist externally rotates the leg with one hand and maintains the metatarsal heads flat on the standing surface with the other (Figure 13. ). If necessary, use the thumb or fingers of the near hand to press the medial malleolar area to attain full correction. Observe the effect of these corrections on the Achilles tendon, a useful indicator of the relation of the heel to the leg. The Achilles tendon is straight when the foot is well aligned.

The subject should bear less weight on the foot until the correction is made. He can then gradually apply equal weight to both feet. It is relatively easy to hold the foot in an already corrected position in full weight-bearing.

After the plaster sets, slide the wrapped foot sideways to break any seal between the plaster and the standing surface. The subject is instructed to ease his weight carefully off the wrapped foot before sitting. CAUTION: Do not lift, or allow the subject to lift, the foot from the standing surface until the seal has been broken by the aforementioned sideways movement. Otherwise, the plantar surface of the east may be deformed.

Before cutting the wrap, draw several horizontal reference lines over the tubing to aid in reassembling the cast after removal. Then remove and close the cast in the usual manner.

8. Wrap Modification

Reduce residual valgus and incorporate any plantar or dorsiflexion that could not be achieved when the wrap was taken, modifying the cast to the extent that judgment dictates will result in an effective orthosis which the skin can tolerate. This is done by removing wedges of the plaster wrap and bending the cast to the desired position. One should be extremely careful to remove wedges at the level of, or slightly distal to, a line between the sagittal midlines of the malleoli at the level of the distal border of the medial malleolus, parallel to the ankle axis. Wedges should be removed both anteriorly and posteriorly, so that the pivot point is

midline. Removing wedges elsewhere will distort the relationship of the BI to the bony prominence. Wedges should equal the amount of correction desired and should be measured in degrees. Once these modifications have been made, fix these positions and seal the openings with plaster splints.

9. Modification of Plaster Model

The model is poured in the standard manner. When the wrap is removed, small surface imperfections caused by air entrapment can he removed by light sanding. Rasp smooth any discrepancies where the bandage may have restricted soft tissue. Remove 50 per cent of the convexities from the area surrounding the constrictions, then fill the remaining portion of the constricted concavities.

Modify the model by applying 0.3 cm (1/8-in.) plaster buildups to the pressure-sensitive areas. Drive a tack into the apex of the medial malleolus, leaving a 0.3 cm (1/8-in.) protrusion. Cover the tack for the buildup. Smooth the buildup to feather its edges. Add plaster to create flares along the anterior, proximal, and posterior trim lines of the medial extension. The flares should extend 0.3--0.6 cm (1/8 to 1/4 in.), and should have a radius of about 1 cm (3/8 in.). They are designed to relieve edge pressure on the skin.

The plantar surface of the orthosis should fit the patient's foot and his shoe, accommodating the heel height of thc shoe that is to be worn without distorting the relative position of plantar or dorsiflexion which exists in the heel. The forefoot and heel should appear slightly flattened on the plantar surface of the model and should be in parallel planes, with the difference between forefoot and heel heights determined by the shoe.

Adjust the width of the heel and forefoot to correspond to the recorded measurements.

Smooth the model with sand screen.

Plastic-Laminate Buckled Insert

10. Application of Malleolar Pad

Fabricate a malleolar pad from foam, O.3 cm (1/8 in.) thick, and 2--4 cm (3/4 to 1 and 1/2 in.) in diameter, slightly larger than the malleolar prominence, and skive the circumference. Center the pad and cement it temporarily over the prominence of the medial malleolus on the model, with the skived surface facing away from the model.

11. Lamination

Vacuum laminate in the conventional manner. The layup consists of five layers of Perlon stockinette. Two strips of fine-weave fiber-glass cloth 2--4 cm (3/4 to 1 and 1/2 in.) wide, extending from the top of the medial extension to immediately proximal to the plantar surface of the insert, are also used. One strip should be placed between the first and second layers of Perlon, and the other strip should be inserted between the fourth and fifth layers. So that the anterior portion of the insert will be flexible and fit easily into the shoe, arrange the five layers of Perlon in the following manner. The inner and outer layers cover the entire cast. Stagger the anterior ends of the three layers that are sandwiched between the inner and outer layers. Terminate the distal edge of one layer approximately 1 cm (3/8 in.) proximal to the metatarsophalangeal crease. Terminate the distal edge of another layer approximately 2 cm (3/4 in.) proximal to the crease. Terminate the distal edge of the remaining layer approximately 4cm (1 and 1/2 in.) proximal to the crease. The order of the three layers is to individual preference. The resin is two parts rigid (Laminac No. 4110) to one part flexible (Laminac No. 4134).

The completed lamination is removed from the plaster model and trimmed to the desired contour, as indicated on the plaster model by the indelible pencil marks which transferred from the balloon (or skin) to the wrap to the model. The malleolar pad is removed from the plaster model and glued in place in the insert.

Thermoplastic Buckled Insert

 

10a. Model Completion

Place the mandrel of the model into the suction pipe which is attached to the vacuum system. Pull nylon hose over the model (nylon prevents suction from being omitted from any portion of the model, because the fabric pores allow air withdrawal from the space between the model and the plastic). Fasten the nylon with pressure tape around the suction pipe; cut off excess fabric.

10b. Application of Malleolar Pad and Reinforcements

Fabricate a malleolar pad from foam 0.3 cm (l/8 in.) thick and 2--4 cm (3/4 to l and 1/2 in.) in diameter, slightly larger than the malleolar prominence, and skive the circumference. Center the pad and cement it temporarily over the prominence of the medial malleolus on the nylon-covered model, with the skived surface facing away from the model. Glue two reinforcing strips made of nylon parachute cord, Teflon rods, or lead rods, over the malleolar pad. If the pad is 4 cm (1 and 1/2 in.) wide, center the strips 1--2cm (3/8 to 3/4 in.) apart, over the pad. Extend the rods from the distal edge to the proximal edge of the insert, following the direction of the medial extension. The strips will corrugate the plastic, thereby reinforcing it.

11a. Thermoplastic Preparation

The most suitable plastic is orthopedic-grade polypropylene, 0.3--0.5 cm (1/8 to 3/16 in.) thick, depending on the strength needed. Total polypropylene is satisfactory, but more rigid. Polyethylene alone is too flexible. Subortholen is satisfactory, but is more difficult to vacuum form and is more expensive.

Cut the plastic the length of the foot and medial extension, from the distal to the proximal end of the model, and as wide as the greatest circumference of the model plus 2 cm (3/4 in.).

11b. Thermoplastic Molding

If orthopedic-grade polypropylene is used, heat it in an oven preheated to 205 degrees C (400 degrees F) approximately six minutes until transparent. Follow manufacturer's instructions for other, similar, thermoplastics. Remove the plastic from the oven and drape it over the model. With the fingers (protected by heavy gloves), seal the edges together, as well as the junction around the pipe beyond the tape. Apply suction until the plastic hardens and becomes translucent, about 1--2 minutes on a wet model and 2--3 minutes on a dry model. Premature removal of suction from a wet model may cause steam to pucker the plastic surface, creating a rough interior on the BI. Early cessation of suction from a dry model will prevent the plastic from conforming intimately to the model. Let the plastic cool completely to room

temperature, approximately 15--30 minutes. Cut the plastic with an oscillating-blade cast-cutter. If the plastic is cut while warm, it may warp. Follow the trim lines previously established. The reinforcing strips and malleolar pad will leave the model with the plastic. Remove and save the malleolar pad; remove and discard the strips. Glue the pad in place with contact cement.

Smooth the edges of the BI with a router, first with a sanding cone and then with a felt cone.

Fitting Procedures

12. Preliminary Fitting

The insert is checked on the subject for fit and comfort, and further trimmed or modified as necessary, particular attention being paid to the trim lines and areas of high pressure.

13. Application of Strap

A strap with a buckle is fabricated and applied to hold the insert to the lateral upright. The strap should be about 2 cm (3/4 in.) wide. Its outermost layer should be of leather (or equivalent) and the innermost of horsehide; the center layer should be of Dacron webbing to prevent stretching. The strap should be mounted with a single rivet at the top of the medial side of the medial extension of the insert, immediately below the proximal flare

14. Fitting

Check the insert on the subject. Tighten the strap around the lateral upright until the desired alignment of the root is achieved. Punch a single hole in the strap to maintain this position when the strap is buckled. The hole may be reinforced with an eyelet.

After a few minutes of wear, check again for comfort and areas of high compression. Modify the insert if necessary.

15. Wear

Instruct the subject to wear the insert for an hour or two, and to remove it to check for excessive pressure marks. This monitoring should continue, at longer intervals, for the first several days.

The subject may experience some internal discomfort for the first week to 10 days. This discomfort is attributed to the changes in position of skeletal structures and to the stretching of tight soft tissues.

References:

 

    1. Henderson, W. H., and J. W. Campbell, UC-BL shoe insert casting and fabrication. Bull Prosthet Res, 10-11:215-235, Spring 1969.

 

  1. Ibid., p. 234.