The Fourth IEEE RAS/EMBS International Conferenceon Biomedical Robotics and BiomechatronicsRoma, Italy. June 24-27, 2012

978-1-4577-1198-5/12/$26.00 ©2012 IEEE 878

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D. Reconstruction of the hip (femur + half-pelvis)

Now we will explain the different results obtained from the 3D reconstruction of the bon elements of the hip joint. From a standpoint of symmetry, it is best to study only one side of the hip. In this case we chose the left side of the patient. To this end, we present the results of 3D CAD phase modeling of the members studied (pelvis and femur) for a single patient anonymous suffering from osteoarthritis. To ensure good reproducibility morphological and morphometric models reconstructed step analysis of the deviations is made to address the differences arising during the modeling process.

E. 3D Modeling

Figure 4, illustrates the reconstruction of the femur on the left side of our patient:

a. Cloud

points.

b. Mesh

smoothing

c. Filling

the holes

d. Refined

mesh

e. Parametric

curves

f. CAD

model.

g. Deviation

curve-mesh.

i. Deviations

surface-mesh

Figure 4. Reconstruction the CAD model of the left femur.

Figure 5, illustrates the reconstruction of the pelvis on the left half of our patient:

a. Cloud

points.

b. Mesh

smoothing

c. Filling the

holes

d. Refined

mesh

e. Parametric

curves

f. CAD

model.

g. Deviations

curve-mesh.

h. Deviations

surface-mesh

Figure 5. Reconstruction the CAD model of the half-pelvis.

Deviations "curve-mesh" and "surface-mesh" are evaluated automatically using the "Analysis of deviations" functionality present in the "Scan To 3D" for SolidWorks. These deviations describe the maximum deviation, minimum and average on the one hand between the parametric curves and the mesh, the other between the outer surface of the reconstructed model and the mesh. This function evaluates

the quality of our reconstruction. Table 1, summarizes the values of deviation of the 3D femur model and a half left pelvis (deviation mesh-parametric curves and surfaces, mesh deviation).

TABLE I. The deviation values of the 3D femur model and half left pelvis.

Curves-mesh Surface-mesh

Femur Pelvis Femur Pelvis

Deviation maxi (mm) 0.5845 4.5067 6.4640 4.2871

Deviation mini (mm) 0.0000 0.0000 -1.2173 -1.5406

Deviation average (mm) 0.0509 0.0625 -0.0871 0.0138

We observe in Table 1, that the mean deviations of the femur and pelvis reconstruction are the order of one hundredth of a millimeter which justifies the good reproducibility. Deviations max and min of the mesh with the outer surface of the femur are reconstructed by smoothing is 6.4640mm and -1.2173mm respectively. Thus the deviations max and min with the outer surface of the pelvis reconstructed by smoothing is 4.2871mm and -1.5406mm respectively. This deviation is due to the smoothing of parametric curves, since the number of points of parametric curves are different, thus smoothing the path does not optimal [16].

III. INNOVATIVE DESIGN OF A STANDARD SIZE

PROSTHESIS

A. Presentation of the innovative prosthesis

The innovative prosthesis standard size is still very useful especially when it comes to custom prosthesis, the size of existing prostheses on the market is fixed and their location in the body of the patient sometimes requires the approximation of the patient femur size to prosthesis size nearest existing stock in the hospital, especially in urgent cases where it cannot wait for the arrival of a prosthetic right size for our patient. Order to find the perfect size for the patient may be exceeded if we can design a Multi-prosthesis size (standard size).

Figure 6. Generation of inner curves of the femur according

to the axial plane of the human body.

Using the smoothing function existing in SolidWorks, through the curves (Fig. 6) we have built a body so that it replaces the bone marrow of the femoral stem. It will be shrunk to make way for 4mm cement [17]. The shrinkage will be done by removing material from the surface offset contribution to the outer surface of the stem, then using the "thickening" by removal of material existing in SolidWorks. The shape of the stem is shown in Figure 7.

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Figure 7. Shape of the

femoral stem.

Figure 8. Concept of

modular femoral stem with

channel.

The angle and length of the neck of the prosthesis and the position of the center and diameter of the femoral head can be determined using the function wizard surface. This function can approximate the mesh faces to geometrical surfaces such as a conventional cylinder, cone, sphere. Cervical length is between the axis of the femoral stem and the center of the head. On the other hand the evaluation of the angle between these two axes is very easy using the function "measure". For the design of our stem, these approximations allow us to point the axis and direction of the pass. We used a Morse cone axis to allow the incarceration of the ball with the stem which acts as the joint ball and socket joint. Figure 8 illustrates the concept of modular femoral stem with channel.

The ball is a spherical implant that replaces the femoral head. Its outer surface is reduced to 56% of the surface of the acetabular iliac bone of the patient [18]. This reduction of the surface is optimal for the proper functioning according to two phenomena: friction and life, in other words, the friction of the link between the ball and the socket is minimal while their lifetimes are maximum. On the other hand, the ball having a hole in the shape of a cone Morse adaptable than the stem assembly to authenticate each other. The assembly of the prosthesis in the previously reconstructed model is shown in Figure 9.

Figure 9. Assembly the prosthesis on the 3D model.

B. Application of the TRIZ method to create an innovative

total hip prosthesis

The core of TRIZ is the theory of technical system evolution. Such theory points out that technical system is always in the process of evolution, solving conflict acts as the driving force for its evolution, evolution speed decreases with the resolution of general conflicts in technical system, the only method that leads to its mutation is to solve underlying conflicts that impede its evolution [19].

Under the multiple sizes of existing prostheses, it was suggested to design a prosthesis that is standard size so it can implement a wide range of size and have a longer life. In this context, we find the work that has already been made on the influence of the size of the prosthesis with a range of implant angle ranging from 115-155 ° and the length of 10-20mm to the hardness of the THP [6], we chose to design a prosthesis that has an angle between 115-151 ° and a length of 10-20mm while remaining within industry standards.

(a)Femoral stem made of

one part

(b)Positioning

parameters to vary.

Figure 10. Illustration of the femoral stem and the parameters

to vary

1) Problem: Designing prosthesis with length and angle

variables.

Data problems: femoral stem made of one part fixed in its

workspace (Figure 10);

Specific problems: variable Angle, variable length;

Modeling (Specific Problem to generic Problem);

Generic problems: a static object length 1(angle), static

object length 2 (length) as the variation of specific

parameters affect the strength of the prosthesis, so its

sustainability, it is directly related to the configuration of the

prosthesis selected.

2) Conflict with the other parameters

It has a single conflict between the length of a static object

and sustainability of a static object, thus the TRIZ

contradiction matrix is reduced to a matrix (1×1) (table II).

TABLE II. Contradiction matrix

TRIZ matrix of the problem

Improvement in

conflict with

Parameter to maintain: the sustainability of a

static object

Parameter to

improve: the length of

a static object

1. Segmentation 10. preliminary action

35. parameter changes -

According to the contradiction matrix, there are three generic solutions to solve the trade-off between improving the length of a static object and sustainability of a static object and segmentation, the preliminary action and change parameter are the three principles of resolution that will give us a solution to our generic problem.

881

882

2) Phase to improve the quality of design

In this design phase focusing on the quality of design, because after the design that provides the required function of the prosthesis is now seeking to improve the quality of the prosthesis with respect to: The visual appearance; the weight; the strength. To reduce the weight of the prosthesis we make a cavity in prosthesis, and then it smooth out sharp angles to enhance the visual appearance of the prosthesis and the strength of the prosthesis to static loading. Two possibilities of the prosthesis cavity are illustrated in Figure 16.

Figure 15. Final design of

the angle variable.

Figure 16. Possibilities for

cavities in the prosthesis for

weight reduction

It brings together all parts of the configuration desired. That gives us prosthesis of Figure 17, it is adapted for our patient (115° and 10 mm).

Figure 17. Assembling the standard THP according to the

configuration of patient (115° et 10mm), prototypes of

custom prosthesis and the innovative prosthesis.

IV. CONCLUSION

The method used in the reconstruction of 3D model is very useful from a set of points containing parasites due to defects of materials or loss of data, or false use of the MRI scanner. This step summarizes the reconstruction of the 3D model of the pelvis from a cloud points obtained by the segmentation of MRI images. 3D modeling will allow us later to simulate the forces applied by the other organs of the body on the hip. The reconstruction gives us an opportunity to study all the parameters needed before the completion of the prosthesis. The reconstruction of the hip under SolidWorks is very beneficial to design a tailored total hip prosthesis PTH. The sizes of the implants to be inserted must correspond to the pelvis and femur, keep the exact angle and length of the femoral neck, the center of rotation in the femoral head with acetabular surface and height and the location of femur. The implantation of the prosthesis tailored in the reconstructed model under SolidWorks allows us to simulate the forces applied by the hip during the gait cycle. Concerning the standard prosthesis, the use of TRIZ innovation methodology has facilitated the work to find a model of this prosthesis. The only difficulty was how to

make specific solution feasible economically and technologically.

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