Design of an Articulated Flexo-Extension and Rotation System for the Adaptation of Canadian Crutches for a User With Sequelae of Polyomelitis

The word poliomyelitis was first used in 1879 by the German doctor Adolf Kussma (1822 - 1902) and derives from Greek poliós - grey; myelós - medulla and the suffix itis - inflammation, so the term poliomyelitis or polio can be defined, as a highly contagious infectious disease caused by poliovirus.

In the vast majority of infections with this virus there were no symptoms, however, 5 to 10 of every 100 infected people showed signs similar to flu. Whereas in 1 to 200 cases the virus destroyed parts of the nervous system, causing permanent paralysis in the upper or lower extremities. And, although it was very rare, the virus could even attack the parts of the brain that help breathing, leading to death.

According to data from the Pan American Health Organization (PAHO) 30 years ago, polio paralyzed almost 1,000 children every day in 125 countries around the world. According to statistics, the last polio case in Mexico dates from 1990.

It is known that before 1946 in our country, poliomyelitis was little known by doctors, because many of its manifestations were confused with other neurological conditions such as meningitis, encephalitis, myelitis or cerebral palsy. However, it was from 1949 when the foundations were laid to better understand the disease, proving that it was a viral disease, transmissible, from which the microorganism causing it was in the digestive tract and its sequelae had to be treated by surgical techniques specifically designed for these patients, as well as by the invention of orthopedic appliances to enable their mobility.

If someone had polio as a child, teenager, or young adult, but maintained or regained partial or full mobility of weakened upper or lower limbs, they are at risk of becoming weaker as their age progresses. This condition is known as Post Polio Syndrome (PPS), which can affect poliovirus survivors between 15 and 40 years after recovering from the initial infection, presenting symptoms such as muscle weakness, fatigue and joint pain.

Design Considerations

Prescription

The indication of the prescription of crutches responds to the needs of the patient, which crutches can help counteract, such as moderate balance disorders and the need for significant discharges of joint weight, its prescription usually applies to the use of one or to crutches.

• Forearm arm cuff: It should encircle the proximal part of the forearm and be positioned 5 cm from the elbow.
• Handgrip: It should be at the level of the greater trochanter of the femur, located approximately 5 to 10 cm below the iliac crest. This allows the upper limb grasping the crutch to generate an elbow flexion of approximately 30°, in order to avoid a direct impact on the joint of this, and in turn, favor a muscular work of the limb.
• Foot: It should be positioned slightly in front of the body, 10 cm from the homolateral femoral limb.

Materials

According to the diagram presented in Figure 1, a list of the materials corresponding to the components that make up the Canadian crutch acquired for its subsequent adaptation was made (Table 1).

User's anthropometric measurements and user's requirements

According to the user’s requirements, the measures of the crutches should have: 

a) a length of 10 cm in the vertical segment of the forearm under the curvature

b) 13 cm in length of the segment of the forearm before reaching the curvature

c) clamp with a diameter of 9 cm and a width of 5.4 cm

d) handle of 10 cm in length

e) cane of 69 cm in length

f) cane tip of 7 cm in depth with and external length of 4.5 cm

The percentiles shown in Figure 2 were taken into account

Where:

7: Elbow height

8: Flexed elbow height

12: Knee height

55: Hip height

Requirements assessment

By means of a first approach with the user, a survey of the client's requirements was carried out, focused on what is expected from the product. After identifying these needs, the technical requirements with the engineering solutions suggested to meet the request were made, all of which are shown in Table 2.

Special thanks...

We want to thank the rest of the team that was collaborating in the realization of this project, especially Eng. Rita Suarez Toscano for her full support during the development of this project, without her none of this would not be possible.

We would also like to thanks Andrés Badillo Lavenant for always being willing to help in the development of this work, as well as for always showing the greatest enthusiasm in collaborating.

And finally to Alexia García Sánchez, Sebastian Eugenio Reyes and Diego Cano Rodríguez for their contribution to this project.

Based on the design considerations shown above, the following conceptual design was proposed for the articulated system that was adapted to the crutches.

Description of Canadian crutches purchased

The crutches to acquire are fixed without any type of articulation (Fig. 3), made of a resistant material which is aluminum, can be shortened up to 94 cm or extended up to 116 cm, has ergonomic cuffs, bracelet and plastic handle.

From the previously acquired crutches, cut up to 10 cm before the clamp as shown in Figure 4.

*Repeat this step on both crutches.

Insert a 15 cm long PVC tube that matches the diameter tube of the previously cut crutches (Fig. 5), and then perform 3 through bores with a diameter of 5mm, in order to attach the tube to the crutches.

The CAD drawings of each of the parts that make up the joint of the Canadian crutches were made for their readaptation, these were made in the SolidWorks 2022-2023 software. The joint of the crutches is made up of the following parts:

1. Connector: Connection between the tube of existing canadian crutches and the articulated system (Fig. 6).

2. Head: Connection between the connector and the clamp that will allow the crutches to flex max 180° (Fig. 7).

3. Clamp: Component that will allow the head to rotate at 5° (Fig. 8).

*The CAD and STL files of the pieces are attached below.

Considerations for printing the parts:

• Pattern: Crystal (1)
• Filling density: 80 - 100

Insert the PVC tube into the printed connector, and attach it with an M5 screw and nut to prevent it from rotating and moving from its place, as shown in Figure 9.

Once segment 1 is assembled, the head is placed at the back, so that its medial walls have contact with the sides of the connector, it is also important to align the lateral borer that they have, so that they coincide to fix them with a screw M5 and a nut and thus prevent these from moving and at the same time, providing a axis of movement for the flexo-extension of the articulated system, as shown in Figure 10.

Finally, to achieve the final assembly, the clamp must be placed on the top of the head, so that the flat faces come into contact and their respective barrels coincide, Subsequently, an M5 screw and a nut must be placed to fix the latter axis to achieve the rotation of the joint, as shown in Figure 11.