The orthosis is considered a class 1 medical device which often originates from a nonstructured development process. As these devices are mainly developed by small- and medium-sized enterprises, with no standard research method, the result can be an unadapted device which may not respond to the user’s needs and which in the short term may be abandoned. One way to solve this problem is to define and apply standard rules and procedures throughout the development/design process. Although methodologies may solve the “empiricism” in orthosis design problems, these design strategies are not applied during orthosis development due to the particularities of this field and the difficulties in linking the required knowledge and the actors that may be present during the orthosis development. The objective of this work is to develop a methodology to structure the orthosis design process that takes into account both the device life cycle and the different stakeholders involved in the design process. A case study was used to validate the proposed methodology. It was applied to the development of an orthosis to treat a specific postural disorder called camptocormia, also known as bent spine syndrome. This disorder is characterized by the anteroflexion of the trunk and especially affects elderly people. Contrary to scoliosis, the characteristics of camptocormia are not permanent, which means that the patient is able to straighten his posture. A postural brace is used to treat this disorder which enables the patient to redress and maintain the correct upright posture of the trunk.
The design of orthopaedic devices, or orthoses, may include particular requirements and design specifications, mainly related to the patients’ varying characteristics, such as morphological changes or treatment evolution. The reason is that the orthosis is in permanent direct contact with the patient’s body and consequently should be adaptable and comfortable.
Since orthoses are considered as a class 1 medical device, there are no strict rules and stages that should be respected during the development process [
One of the current challenges in the field of orthoses is to develop a device to treat camptocormia [
The purpose of this study was to develop a design methodology devoted specifically to the orthosis and its application during the development of a brace to treat camptocormia.
Using the breakdown of the design process proposed by Pahl and Beitz [
The first stage of the proposed methodology corresponds to task clarification, which may include the
Orthosis development should include several stakeholders from different domains, according to the complexity and requirements of the device. Based on this, the development of medical devices such as orthoses may consider stakeholders from three domains: Medical domain: there are two main actors with respect to the medical domain, the doctor and the orthoprosthesist. The doctor is responsible for the diagnosis and the medical design specifications of the orthosis. The orthoprosthesist, working with the other members of the design team, is responsible for the geometrical materialization of the support in the orthosis and adapting it to the patient’s body. Industrial domain: there are two main actors with respect to the industrial domain, the mechanical designer and the technical department. The mechanical designer checks the specifications of the medical domain, and then, with the technical department, he develops the concept and the functional prototypes in the early design stages. Later, both the actors produce the orthosis. User domain: since an orthosis is in strict contact with the patient’s body, patient feedback is key throughout the design process in order to include comfort and ergonomic criteria.
Orthosis development stakeholders.
Orthoses can be divided into different families according to the criteria and functions considered. By taking into account whether or not there is a mechanism to connect the several supports of the orthosis and which consequently displaces one with respect to the other, orthoses can be divided into two groups: orthoses with no mechanism (ONM) and orthoses with mechanism (OWM).
These groups can be subdivided still further. The ONM can be divided into rigid (e.g., plaster) and deformable (e.g., elastic knee brace), while the OWM can be divided into positioning (e.g., foot orthosis) and accompaniment (e.g., leg orthosis) (Figure
Orthosis families ((a) knee orthosis; (b) arm orthosis; (c) toe feet orthosis; (d) leg orthosis).
Each type of OWM can be divided into two main components: supports and mechanism. Additionally, the supports can be divided into initial support (IS) and final support (FS). The body segment in contact with the supports is called the reference. The designation of initial reference (IR) and final reference (FR) is used according to the support that it is connected with [
The notion of life situation involves breaking down the different moments during the use of a device [
Orthosis usage life situations.
The definition of the life situation of the orthosis marks the end of the task clarification stage and the beginning of the orthosis development.
The proposed methodology is composed of six stages:
These stages can be arranged according to the definition given by Pahl and Beitz (Figure
Orthosis design methodology.
The methodology will be explained in the next sections of this paper and the final overview presented at the end of the Materials and Methods section.
The aim of the first stage (Figure
The first stage is divided into four phases where the designer defines the following: The number of solids included in the kinematics chain The kinematics between the supports The dependency between translations and rotations (when the rotation generates small translations) The usefulness of considering additional degrees of freedom in the kinematics chain to what is necessary in order to establish a nonessential DoF for the limb The advantage of having superabundant degrees of freedom
The second stage (Figure displacement constraints, taking into account the medical prescription dimensional constraints, taking into account the patient’s morphology general design constraints
The third stage (Figure
During this stage, the mechanical designer analyzes the hyperstatism problems related to the type of orthosis. In the case of an orthosis, hyperstatism can cause local discomfort due to parasite efforts at the links between elements.
Both types of orthosis need to be analyzed independently, and for this reason, the proposed methodology considers a bifurcation at this stage (Figure
Orthosis methodology synoptic.
Accompaniment orthosis Odra (
The mechanical designer may choose to treat the degree of hyperstatism by changing the interface between the references and the supports or by modifying the functional gap and tolerances. If the mechanical designer chooses to change the interface between the references and the supports, he has two options: first, he can increase the number of links in order to unblock relevant DoF and second, he can introduce deformable links.
By modifying the functional gap, the mechanical designer is able to change locally the small displacements allowed by the links, which increases the mobility of the link and reduces the hyperstatism of the chain.
The mechanical chains obtained.
In this case, the mechanical designer may treat the hyperstatism problems by introducing solids and links or introducing deformable links between the references and the supports.
The fourth (Figure
Based on this, at this stage, the designer defines the number of links that should be blocked how to block these links
In the fifth stage (Figure
The last stage (Figure
An extended synopsis is presented in Figure
This methodology was validated through a specific case study, proposed by Lagarrigue. The objective was to develop a postural brace to treat a postural disorder called camptocormia or bent spine syndrome, which affects elderly populations.
The methodology was then applied to the development of a brace to treat a postural pathology named camptocormia. Also known as bent spine syndrome, it is characterized by the progressive anteroflexion of the trunk during walking and in the standing position (Figure
Camptocormia patient’s typical posture.
Even if presently the etiologies of camptocormia are not completely understood by the medical community, and still exists several questions without answers, the treatment combining physiotherapy sessions with a brace has presented satisfying results [
From the stakeholders’ definition, the design team in accordance with the medical domain establishes the orthosis specification (Table
Camptocormia brace specifications.
No. | Functions | Criteria | Level | |
---|---|---|---|---|
Mechanism | 1 | Admit a vertical adjustment |
|
|
2 | Be easily removable | Tasks | Tasks |
|
3 | Reduce the number of solids | Solids | Solids |
|
4 | Resist to the collapse of the trunk | Euler’s force | Euler’s force |
|
5 | Be lightweight | Mass | m |
|
|
||||
Supports | 6 | Easy positioning | Steps | Steps |
Reproducible positioning | Mass | m |
||
7 | Admit a morphological fit | Visual marks | Visual marks |
|
8 | Easy opening | Squashing |
|
|
9 | Easy positioning | Steps | Steps |
From the specifications, it was observed that the orthosis should permit movement between the orthosis supports in order to promote the redress of the trunk.
According to the classification described above (Figure
The methodology was applied while considering the specifications established in Table
In order to propose the optimal solution, an exhaustive mechanism database was used, as developed in Duarte’s PhD thesis [
Orthosis mechanism chain (three joints) dimensioning.
At the third stage,
As the brace covers one of the body parts that frequently changes its morphology and the retained solution from the first stage represents an isostatic chain, in this specific case, the mechanical designer decided to introduce a deformable interface.
Thus, during the
Camptocormia brace components.
The following stage,
The next stage,
The last stage,
The development of medical devices is a demanding task, especially with respect to orthoses because of the way in which they are classified. In some cases, this results in deficient products that do not meet the patient’s needs.
The primary aim of the present work was to develop an orthosis design methodology based on dividing up life situations and integrating the design constraints in different knowledge domains. This methodology was then applied to the development of a new orthosis, a brace to treat camptocormia.
Although several concepts emerged, in this study, only a representative group of specifications were considered, and for this reason, only one concept has been presented. The selected concept meets the main device specifications in terms of straightening the patient’s posture.
This straightening was possible through the link chain proposed during the conceptual design stages and allows a vertical displacement of the chest. Concerning comfort, two aspects were considered. The first was the use of a neoprene layer between the rigid part of the supports and the body, and the second was the fact that with the proposed concept it is possible to tighten the supports to the body and consequently adjust the orthosis to the patient’s morphology.
The blocking system of the proposed concept was specially taken into account in terms of ergonomics. Since the developed orthosis will be manipulated by elderly people and in some cases by patients with Parkinson’s disease, the fact that their fine motor skills are often reduced must be considered.
As it is a design method, there are no medical data attached. We decided to use a case study related with camptocormia but in fact this methodology may be applied in any other orthosis mechanical designs. This means that the patient data analysis is not available.
The authors declare that they have no conflicts of interest.
The authors gratefully acknowledge funding from ANRT and Lagarrigue, Pessac, France.