Lower Extremity Orthotic Device Prescriptions: Basics of Evaluation and Management

Abstract

This paper provides a basic overview for the role of some lower extremity orthotic devices in the rehabilitation and support of the maximization of function for individuals with neuromusculoskeletal conditions. It provides a comprehensive overview of orthotic principles, designs, indications, and limitations, emphasizing the importance of thorough patient assessment in device prescription. Key terminology, including definitions of orthoses and the role of certified orthotists, is clarified. The paper discusses various types of orthotic devices, comparing custom-made to off-the-shelf options, and examines the materials used, such as leather, metal alloys, and thermoplastics, each with distinct characteristics. Additionally, this article highlights functional considerations, fitting protocols, and the need for ongoing follow-up care to prevent complications like pressure injuries. The conclusion underscores the necessity of individualized orthotic prescriptions, addressing specific patient needs to optimize rehabilitation outcomes and enhance mobility while acknowledging the trade-offs in energy expenditure and gait velocity associated with orthotic use.

Introduction

Orthotic devices serve as artificial supports or braces for the limbs or spine, playing a crucial role in rehabilitation and support for individuals with neuromusculoskeletal conditions. Understanding the principles, designs, indications, and limitations of orthotic devices is essential for effective patient care.

What is an Orthotic Device?

Orthotic devices are artificial supports or braces designed to assist, align, or protect weakened or injured limbs or the spine. These devices are fabricated and fitted by board-certified orthotists (CO) or certified prosthetist orthotists (CPO) with a master’s degree in orthotics and/or prosthetics.^1,2

Orthotic Terminology

Key terminology includes orthosis (singular), orthoses (plural), orthotic (adjective), and orthotist (trained professional). An orthotist is a person who is trained to properly fit and fabricate orthoses. The orthotist is usually credentialed by the American Board for Certification (ABC) and common certifications include Certified Prosthetist/Orthotist (CPO) and Certified Orthotist (CO).

Standard nomenclature for an orthotic device is based on the joint of which the device crosses, such as foot (F), ankle (A), knee (K), and hip (H). For example, a device that supports the distal lower extremity is referred to as an AFO because it crosses the ankle and foot.^1,2,3

Principles and Factors in Orthotic Design

An orthotic prescription is based on comprehensive patient assessment; this includes history, physical examination with considerations such as skin issues & texture, reliability of the patient to utilize the orthotic device, cognitive issues, ability to use the hands to don or doff the device, edema, contracture, or anatomical abnormalities. Orthotic devices can provide support, protection, and immobilization while correcting deformities or off-loading troublesome anatomy. However, they may have disadvantages such as discomfort, limited effectiveness in certain cases, nerve injury from pressure and muscle weakness after prolonged usage.^4,5

Other factors influencing the design of an orthotic device include the weight of the device, the material strength, flexibility and durability of the device, the forces or loads that are going to be translated by the device, cosmetic appearance, cost, availability, ease of care, and adjustability of the device.^2,4

Functionally, orthotics can be dynamic, static, or neurophysiological. A dynamic brace facilitates body motion to allow for optimal function and has moving parts. A static brace is rigid and does not have moving parts and is utilized to support weakened or paralyzed body parts and maintain a particular position. Neurophysiological orthotics are utilized to control neurologic tone. In an ideal world, an orthotic would be totally functional, fit well, be lightweight, be easy to don and doff, be easy to maintain, inexpensive, and locally manufactured. There are several comparable orthotic devices that achieve improved function for most patients, each with its own risks and benefits. It is best to collaborate with the certified orthotist to select the most appropriate device for the individual and problem.^4,5

Types of Orthotic Devices and Functional Considerations

The choice between off-the-shelf and custom-made orthotic devices depends on patient needs, such as the amount of ankle control, obesity, or if specific needs are required. Functional considerations include factors like the weight and material of the orthotic, as well as patient-specific characteristics such as muscle strength, sensation and fluctuation in limb size. In general, customized orthoses will more effectively limit or control motion better than a prefabricated/off-the-shelf orthosis.^2,4

For example, if the patient needs an ankle-foot orthosis (AFO) only because they have weakness in ankle dorsiflexion, it is likely that an off-the-shelf AFO would provide enough support for the patient. Conversely, if the patient lacks inversion/eversion ankle control, obese, or if needs custom plantarflexion or dorsiflexion stops, then it is likely that they would need a custom-made device.

Materials Used in Orthotic Devices

Orthotic devices can be made from various materials, each with their own characteristics and suitability for specific applications. Materials include leather, metal alloys (steel/aluminum), thermosets (carbon fiber composites), and thermoplastics. Each of which offers different levels of stiffness, durability, and adjustability.

Leather is an easily formed and manipulable material but is not durable over the long term or as hygienic as other types of materials. Metal alloys, like steel and aluminum, are also easily formed by hand and are often used for heavy duty applications, though not necessarily. Metal AFOs can accommodate for much larger limb volume fluctuations and can be used in hotter climates since they have less total skin contact. These advantages come at the cost of the heavier total device weight (Figure 1).

Figure 1.

Example of a metal double upright AFO with a leather calf band.

Thermosets, also known as carbon fiber composites, are light, thin, and stiff. Their main drawback is that they are not as adjustable and cannot withstand very heavy loads. These AFOs are often pre-fabricated, off-the-shelf devices (Figure 2).

Figure 2.

Example of a thermoset/carbon fiber AFO.

Thermoplastic built orthoses have variable stiffness and require vacuum forming for fit but can be modified by the use of heat. Thermoplastics are hygienic, easily cleaned, corrosion proof, are customizable in appearance, and are often lighter than leather or metal alloy braces (Figure 3).^4,5

Figure 3.

Examples of thermoplastic AFOs include a hinged thermoplastic AFO with a pre-flexed articulated joint (left) and a solid ankle thermoplastic AFO (right).

Lower extremity orthotic devices come in many different styles, shapes, and can be made up of a mixture of materials that best fit the needs of the patient (Figure 4).

Figure 4.

Examples of other different orthoses: off-the-shelf composite KO (left) and custom thermoplastic KAFO (right).

Orthotic Fitting, Follow-up

Proper fitting and follow-up care are crucial in orthotic management to ensure effectiveness, patient comfort, and safety. A patient should have a set wearing schedule for each device that they have. Given the relationship between pressure magnitude and time with regards to pressure injury formation, the patient should slowly advance wearing time for a brace full-time to reduce risk of pressure injuries.

A sample wearing schedule is detailed in Table 1.⁴

Table 1.

An example wearing schedule of an orthotic device.

Time Period	Weightbearing Status	Brace Wearing Schedule
Days 1–2	Nonweightbearing	15–30-minute intervals
Days 3–7	Intermittently bearing weight	15–30-minute intervals
Second Week	Weightbearing as tolerated	Gradual increase in brace-wearing time
After 2 Weeks	Full weightbearing	Brace worn full-time

Indications and Prescription of Orthotic Devices

Orthotic prescription is guided by functional considerations and aims to address specific patient needs. Custom orthoses offer better control and fit, while off-the-shelf options may be suitable for certain conditions and may be adjusted by the orthotist. Considerations include weight, material, cosmesis, patient comfort, and the functional role of the orthotic device.^5,6,7,8

Additional considerations include:

• Will it hold up to the forces required to control the body part?

• Will it break abruptly?

• Will it fatigue easily?

• Does the patient need accommodation for swelling?

• Does this control the motion of the joint adequately?

• Will this device last 3–5 years (insurance requirements)?

• Is this device the most minimal weight and material as what is appropriate for the patient?

• Is the patient going to be a functional utilizer of the device?

A prescription for lower extremity orthosis should include the following information:

• Patient’s name, age, gender, current date

• Patient’s diagnosis

• Patient’s functional goals

• Description of the orthotic:

  • Area covered, flexible or rigid, custom or off-the-shelf, any needed extra components, biomechanical control desired, and any plane of motion restrictions

• Precautions

• Physician Information

Limitations and Concerns in Orthotic Use

Orthotic use may be associated with concerns such as pressure duration, skin issues, and loss of function. Strategies for mitigating limitations include setting wearing schedules to prevent pressure injuries and ensuring proper fitting and follow-up care.

Some other specific considerations to keep in mind when prescribing orthotic devices for ambulation include the significant changes to the energy cost for ambulation and ambulation velocity. Typically, the rate of oxygen consumption with normal ambulation is around 12 mL/kg/min. Figure 5 details how the rate of oxygen consumption, and therefore energy consumption, increase with different orthotic devices.^9,10,11

Figure 5.

Rate of oxygen consumption in normal ambulation versus ambulation with various assistive devices including manual wheelchairs (MWC), ankle foot orthosis (AFO) and knee ankle foot orthosis (KAFO).¹¹

Another important factor to consider when prescribing orthotic device is ambulation velocity. When adding an orthotic device (s) for patient to use, patients need to expect that their velocity of gait may decrease, and they may not walk within normal velocity or cadence that they are used to. Normally, a human will ambulate with a velocity of around 80 m/min. Figure 6 details how the velocity of ambulation changes with different orthotic devices.^6,9,10,12

Figure 6.

Average velocity of normal ambulation versus ambulation with various assistive devices including manual wheelchairs (MWC), ankle foot orthosis (AFO) and knee ankle foot orthosis (KAFO).¹¹

It is also important to consider patient’s baseline strength with manual muscle testing to determine if they would benefit from utilizing an orthotic. For example, when looking at ambulation in the spinal cord injury population, the patient needs to have at least 3/5 strength (antigravity strength per the Medical Research Council scale) in one hip flexor and knee extensor with the maximum of one KAFO and AFO to be a community ambulator. This given that they have adequate truncal support to stand on their own lowering their risk of fall. It has been shown that impaired static postural control will reduce single support stance phase, inducing asymmetry of gait and thus increasing energy expenditure.^6,9,12

Conclusion

Understanding the principles, designs, indications, and limitations of orthotic devices is essential for providing effective patient care. Orthotic devices play a vital role in rehabilitation and support for individuals with musculoskeletal conditions, and optimizing their use requires comprehensive assessment, individualized prescription, and ongoing follow-up care.