Design of a Height-adjustable System for Transtibial Pediatric Prosthesis

An amputation is a surgical procedure in which a part or all a limb is removed from the human body, leaving a resulting limb called a stump. Amputations are classified by lower and upper segment; within the lower segment we find transtibial amputations, which occur below the knee.

In the United States, approximately 1.8 million people have an amputation, while in Mexico there are approximately 935,000 people who present them, in both cases lower limb amputations are the most recurrent.

On the other hand, according to the World Health Organization (WHO) prostheses are externally applied devices that are used to replace a missing limb fully or partially. Therefore, these devices allow people who have a physical disability or functional limitation to have a healthy, productive, and independent life for their free participation in the educational, work environment and within their social life.

The prostheses in the pediatric stage need to be replaced continuously, due to the growth rate of children who increase in height approximately 7.6 cm/year between 12 months and 10 years. Therefore, transtibial prostheses have been developed systems that accompany the growth of the patient thanks to the modulation of the height of the prosthesis.

Requirements.

• This modular system was designed based on the following requirements:
• Adjustable adjustment every 5 mm
• Support 15 kg.
• Safety factor twice the weight.
• That the complete system measures 120 mm.

• PLA filament
• 8 threaded inserts for 3D printed parts
• 2 Button Socket Head Screw Stainless Steel M4 x 10 mm
• 3D printer

The heigh-adjusting device consist of two 3D printed parts:

·      Part A – It is designed to be placed directly on the patient’s socket without the need for a connector, this part has holes that are used to adjust the height of the device.

·      Part B – The smaller cylinder with the inserts is designed to be placed inside an aluminum tube connecting the device to the prothesis foot while the upper part is made to go over the cylinder of part A.

*We made the holes for the screws with a diameter of 5.6 mm to fit threaded heat set inserts inside of them, if you chose to not use them change the diameter of the holes to 4 mm to fit the screws tightly

*A prothesis must be custom made to fit the needs of your patient, so there might be a need to make some adjustments to different parts of design of this device to make it fit on different prothesis, we’ve included the STL and CAD files below.

Use a 3D slicer software compatible with your printer to prepare both STL files, we strongly recommend printing with the following parameters in mind:

·      Pattern – Either Crystal (1) or Cubic

·      Filling density – 50% or more

·      Exterior wall thickness – 1.6 mm

Apply the M4X10 3D printing inserts into each of the holes in part A of the height modulator system as shown in Figure 4 using a soldering iron to apply heat to the insert, pressing it into the hole and allowing it to cool afterwards.

Subsequently, for the second segment, introduce the M4X10 inserts in the two holes of part B as shown in figure 5. 

Finally, once the first and second segments are assembled, join both by fitting the notches on the sides of each of the parts and insert the M4X20 screws into the two holes of the assembly as shown in figure 6.

Insert part A’s cylinder inside the hole on the top of part B. Adjust the height of the device by changing what hole in part A’s cylinder is used to affix both parts together.