Lower limb prosthetics by 3D prototyping from North Africa people

1

Keywords:

• Lower limb prosthetics
• 3D prototyping
• reverse engineering
• custom implants

1. Introduction

The amputation of the lower limbs has been increasing in recent years in the North African region for various reasons such as dysvascularity, infections, trauma (Windrich et al. 2016) and several other reasons (road accidents, anti-people mines, …).

The cost of making prostheses for the lower limbs remains a challenge for the different health departments (Rathore et al. 2016).

Using reverse engineering techniques, such as 3D scanning, it is possible to capture stump’s size and shape and have a digital 3D model to work with in order to manufacture prosthetics socket. Additive manufacturing provides an economic and fast way to directly manufacture sockets and socket moulds depending on the material to be used in prosthetic socket manufacture and 3D prototyping(Rocha et al 2012; Jaimes et al. 2018).

The aim of our work is to develop a new technique based on computer aided design and the fast prototyping techniques to provide assistance to the prosthetic fitter for amputations of the lower limbs. The goal is to reduce the time of delivery and cost of these products. This approach is based on the concept of cooperation between engineers, fitters and orthopedic surgeons to facilitate tasks. The development of a biomechanical product is designed around real 3D models from reverse engineering techniques. Our approach replaces the work environment through a CAD environment to implement the various desired operations and build and optimize the product. The results provide a new vision for the development of orthopedic products around the concept ‘customized product for each patient’.

2. Methods

2.1. Patient populations

In our study, the anatomy of North Africa people was used to improve the treatments by designing custom lower limb prosthetics. In this order the activities of populations influence the life.

2.2. 3D CAD models of the lower limb

The reverse engineering approach can be considered as a methodology to reduce risk and satisfy the constraints in systems engineering. Different techniques in engineering design are used at each stage in the reverse engineering. Reverse engineering calls for the acquisition of dimensions on parts with various shapes (mechanical parts, medical devices …). As shown in Figure 1 the medical field is among the areas that solicits this activity. We start from an existing physical patient and collect data from various scanners. The digitization system is very important and each application or part requires the use of specific system (coordinate measuring machine, 3D scanner, MRI scanner …). In the design process of the lower limb prosthesis, the most difficult point is how to find a good position of our patient in order to obtain a good contact surface between prosthetics and lower limb.

Figure 1. Process to reconstruction of the lower limb amputated and design a custom prosthetics implants.

2.3. MEF analysis of custom lower limb prosthetics-sockets

To validate the model of the socket obtained we will carry out a study of pressure (static study) with the finite element method. We made different meshes for the geometry studied to determine the type of mesh that will bring us to better results.

We notice that the results start to stabilize when the number of nodes is in the order of 200,000.This justifies our choice to use a tetrahedral mesh with an algorithm which conforms to parametric surfaces and an average refinement.

We notice that:

• The distribution of stresses, displacements and deformations is the same for the different loads applied.

• The maximum values of the stresses and deformations are in the zones of the supports and counter-supports.

• The maximum displacement values are found in the upper ends of the socket (the wings).

• The increase in the applied load implies an increase in the values of the stresses, displacements and deformations.

• The variation of stresses, displacement and deformation according to the load is linear.

The results obtained show that:

• PLA gives better results for stress, displacement and deformation by comparing with other materials (after plexiglass and ABS) as shown in Table 1.

  Table 1. Extract from different scenarios.

  Test N	Thickness (mm)	Material	Load (Mpa)	Displacement(mm)	Constraints(Mpa)	Deformation(10^-3)	Mass(g)
  1	6	ABS	0.4	0.92921	20.509	7.8918	256.565
  2			0.6	1.3938	30.764	11.838
  3			1.0	2.323	51.274	19.729
  4		Plexiglass	0.4	0.83308	20.509	7.0754	431.604
  5			0.6	1.2496	30.764	10.613
  6			1.0	2.0827	51.274	17.688
  7		PLA	0.4	0.69027	20.509	5.8624	299.725
  8			0.6	1.0354	30.764	8.7937
  9			1.0	1.7257	51.274	14.656
  10	8	ABS	0.4	0.47973	12.038	5.4214	355.4433
  11			0.6	0.7196	18.058	8.1322
  12			1.0	1.1993	30.096	13.554
  13		Plexiglass	0.4	0.43011	12.038	4.8606	597.942
  14			0.6	0.64516	18.058	7.2909
  15			1.0	1.0753	30.096	12.151

• In terms of mass, the socket made of ABS is the lightest.

3. Results and discussion

In order to study the influence of North Africa people activities on lower limb amputated, it is necessary to design the different elements of the lower limb and the socket, with regard the recommendations of surgeons and in cooperation with engineers. Therefore, this study develops the CAD environment and data collecting in the upstream design stage applying reverse engineering techniques help the development of this knowledge and the results significantly contribute to a custom sockets for lower limb by 3D printing.

Results obtained by Reverse engineering techniques are cloud of points. Exploiting this point cloud is an increasing trend in the design process structure and Computer Aided Design practice.

The finite element analysis of the complete socket is of great significance because it gives almost a complete knowledge of its mechanical behavior.

The different stages for the realization of the socket prototype are: Conversion of the final model into STL format; Importing into Maker-Ware; Adjusting the different parameters; Simulation of printing; Exporting the print file; Start printing.

The product obtained and his influence in amelioration the activities of patients is the interest contribution of the custom sockets by 3D printing.

4. Conclusions

The results of our study indicate different parameters obtained from the 3D models reconstruction in order to design the custom sockets from lower limbs. By 3D printing techniques we can save time for manufacturing, material and cost for the North African peoples.