The Basics

The Basics

Key Terms

Activation time

Conformability/drapability

Low-temperature thermoplastic material (LTTM)

Memory

Resistance to stretch

Rigidity

Surface impressionability

Thermoplastic

Velcro hook

Velcro loop

Working time

Learning Outcomes

Upon completion of this chapter, you will be able to:

List and describe different characteristics of thermoplastic materials used for orthotic fabrication.
Describe methods for testing each of the thermoplastic material characteristics.
Outline the equipment needed to design and fabricate an orthosis.
Describe three safety precautions to consider when fabricating an orthosis.
Describe three ergonomic considerations for the orthotic fabrication process.
Outline the steps involved when designing an orthosis.
Outline the steps of pattern making.
List the steps involved in evaluating a completed orthosis.

Introduction

Today, practitioners take advantage of the multitude of products and materials available on the market for orthotic fabrication. Low-temperature thermoplastic material (LTTM) is the most commonly used material for orthotic fabrication by occupational therapists, occupational therapy assistants, and physical therapists. By definition, thermoplastic means materials that are activated by heat. They become softened and can be molded and formed around body parts. As they cool, they harden in whatever shape they have been formed. Temperatures for heating LTTM range between 140° to 160°F (60° to 65°C) and are tolerated well on the skin. LTTM is available in a wide variety of thicknesses, colors, and styles. Orthoses can also be formed from neoprene and other fabric-like materials or from a combination of thermoplastic and fabric-like materials. Practitioners should continually educate themselves on what new materials are available. Newer products typically offer some advantage over older materials. For example, new products might have longer working times (the material stays soft longer to allow the practitioner more time to mold the orthosis), quicker activation times (the time it takes for the thermoplastic material to soften), more color choices, and even lighter-weight versions than older materials. Moreover, practitioners should become familiar with the different characteristics of materials, the advantages and disadvantages of each characteristic, and the clinical utility and applicability of each. Sales representatives and product specialists from each company that sell orthotic materials and supplies are good sources of information about the products they carry.

Characteristics of Low-Temperature Thermoplastic Material

LTTM typically comes in 18 x 24-inch sheets. It is available for purchase in single sheets, double sheets, or cases of four sheets. Extra-large sheets are also available in 24 x 36-inch sizes. Samples can also be ordered in 6 x 9-inch or 9 x 12-inch sizes when a single orthosis is to be fabricated or for testing an unfamiliar product.

It is critical to be familiar with the various characteristics of the different materials. Each type of material offers the practitioner different benefits for making an orthosis that is appropriate for a particular client and his or her specific condition. Learning how to work with different materials takes time and is as important as understanding the specifics of a client’s condition and the most appropriate treatment protocol that applies to a particular client. Selecting the proper LTTM for a specific orthosis will make the fabrication process easier. The client will also likely be more comfortable wearing the orthosis and more inclined to adhere to the prescribed wearing schedule. Refer to Table 3-1 for a summary of LTTM.

The following terms are the key characteristics of LTTM:

Memory: Memory refers to the ability of the material to return to its original size and shape once it has been stretched out and then reactivated/reheated (Figure 3-1). Orthoses that require frequent remolding should be made from materials with high memory because the material will revert back to the original pattern size. This is a good feature for the new practitioner as well because the orthosis can be remolded if necessary without needing to use additional material.
Rigidity: This refers to how strong and supportive the material is on its own (Figure 3-2). Materials with high rigidity are best suited for larger orthoses, larger clients, and those clients who present with strong deforming forces such as high muscle tone. Less rigid materials are better suited for smaller clients and smaller body parts.
Resistance to stretch: This refers to how easy or difficult it is to stretch the material around the body part (Figure 3-3). Material with high resistance to stretch will require a firm handling of the material in order to work with it, whereas material with low resistance to stretch requires a gentle handling approach because the material is likely to stretch beyond the needed size. Low-resistance materials tend to have more drapability and conform well to intricate anatomical features. Care is required with handling not to overstretch these materials during orthotic fabrication because they rarely have memory and cannot be remolded easily.
Conformability/drapability: These two terms refer to the ability of the material to conform or drape and mold around contours of the individual’s anatomy (see Figure 3-3). Material with high conformability will mold easily around joints and bony prominences without much effort, letting gravity assist. Material with limited conformability and drape should not be selected for intimate fitting orthoses. These low-conforming materials may be better suited for larger orthoses where a high degree of conformability is not required.
Surface impressionability: This refers to the surface of the material and whether it easily marks up with fingerprints and etching or has a dense and strong surface that is not easily marked (Figure 3-4). Softer materials may easily be left with indentations and marks from the practitioner’s fingerprints as the material is handled. This can create pressure on the inside of the orthosis and adversely affect the appearance of the completed orthosis. Materials with a matte or glossy finish are collectively easier to handle but tend to be more rigid and less conformable.

Other important variations in LTTM are reflected in the thickness, the presence or absence of a nonstick coating, and the presence or absence of perforations:

Thickness: LTTM is typically available in several thicknesses: 1/8 inch, 3/32 inch, 1/12 inch, and 1/16 inch (Figure 3-5). The thickness of the material will have a direct effect on the rigidity of the finished orthosis. In general terms, the practitioner should select a thicker material to support a larger body part or make a large multiple joint orthosis and a thin material to support a smaller client or a smaller body part. Forearm- and hand-based orthoses may be fabricated from medium-weight materials, but thick and thin materials may also be used. Use thinner materials for small pediatric orthoses, finger orthoses, circumferential orthoses, and for clients who need light support as appropriate.
Solid or perforated: LTTM comes in a large assortment of solid or perforated patterns and designs. Perforated materials allow ventilation of the skin and may be more comfortable for clients in warmer climates or for those who perspire a great deal, have open wounds, or have very sensitive skin. Each manufacturing company calls the perforation patterns by different terminology and names. Materials may also vary in the amount of perforations present (Figure 3-6). Make sure to check the supplier’s catalog or website to verify the desired perforation style. Solid materials have no perforations, offer more rigidity, and may be more suited for orthoses where the material requires significant stretching to conform to the body part. Stretching perforated materials may cause a localized area of weakness in the material (Figure 3-7).
Nonstick coating: Most materials today are coated to allow greater ease in handling. The coating can be removed when desired by scraping, sanding, filing, or with using a special solvent. Removing the coating before bonding straps, adhering two pieces of LTTM together, or attaching outriggers is important. Material that is not coated may be very sticky and tacky on the skin, but it bonds more easily to outriggers and attachments. Newer coatings claim to be antibacterial and may be more resistant to smells and dirt.
Working and activation time: Each material has a specific activation time prior to molding and an optimum working time after activation in hot water (150° to 160°F [60° to 65°C]). Typically, this allows the practitioner ample time to mold the material into the proper position before the material begins to harden. The practitioner should check the information provided by the manufacturer for specific information for each product.
- Thicker material (3.2 mm or 1/8 inch) will take longer to activate and remain soft and malleable for longer than thinner material (1.6 mm or 1/16 inch).
- Thicker material should be slightly warmed or softened prior to cutting out patterns, then reheated fully prior to molding.

Table 3-1

TYPES OF LOW-TEMPERATURE THERMOPLASTIC MATERIAL AND THEIR APPLICATIONS

Figure 3-1. Example of LTTM with memory.

Figure 3-2. (A) Rigid LTTM provides needed support to counteract large opposing forces (such as a heavy, large hand or clients who have spasticity). (B) Less rigid materials are more suited for smaller orthoses or those that require an intimate fit.

Figure 3-3. (A) This hand and wrist immobilization orthosis is made from LTTM that is resistant to stretch. The material does not conform as well around bony prominences and other anatomical landmarks but provides the necessary support for immobilizing large hands or multiple joints. (B) This hand-based fourth- and fifth-digit immobilization orthosis (also known as an ulnar gutter) is made from LTTM that is less rigid and conforms well over the metacarpophalangeal joints and the arches of the hand.

Figure 3-4. Note that fingerprints can be transferred to the thermoplastic material. Always handle the material using broad, smooth strokes to avoid this.

Figure 3-5. LTTM come in a variety of thicknesses. The most common are 1/8 inch, 3/32 inch, 1/12 inch, and 1/16 inch.

Figure 3-6. The degree of perforation varies based on the LTTM manufacturer. Note the descriptors used: microperforated and mini perforated.

Figure 3-7. A localized area of weakness may be created when perforated material is stretched. A solid material may be more suitable.

Figure 3-8. Velcro strapping come in a variety of colors, sizes, and material choices.

TESTING OF LOW-TEMPERATURE THERMOPLASTIC MATERIAL

If a practitioner is unsure of the characteristics of any LTTM, it is relatively easy to perform several quick tests to learn its specific properties. Refer to the Appendix at the end of the chapter for step-by-step instructions on how to test the different properties of LTTM.

MATERIAL MANUFACTURERS AND DISTRIBUTORS

LTTM is manufactured and distributed by a variety of different companies. Each company’s website is a valuable source of information. The reader is encouraged to check these for new product information, techniques for working with materials, and instructions. In addition to LTTM, these companies carry most of the additional materials and products necessary for orthotic fabrication.

Strapping Materials

Strapping materials should hold the orthosis securely onto the relevant body part so that the orthosis does not move on the client’s extremity. Strapping must be sized according to the size of the body part. Strapping generally comes in 1- and 2-inch widths but can be cut to lesser widths as needed. Strapping is typically cut from Velcro loop (Velcro BVBA), and adhesive Velcro hook is placed on the orthosis to anchor the Velcro loop straps. There is a wide choice of colors, sizes, and materials that can be used as strapping (Figure 3-8).

Figure 3-9. Orthoses for children may need to be designed to discourage them from removing the orthosis, such as using Coban wrap (3M) or an Ace bandage (3M) or covering the orthosis with stockinette.

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