FR2729481A1 - Generation of instructions for formation of hip replacement joint - Google Patents

Abstract

The instructions are generated from measurements of femurs taken from a statistically significant population to define precisely the form of the femur in the region where hip replacements are fitted. The data is processed in a computer to develop algorithms defining a profile for the hip replacement. A frontal and side view of the femur of a patient is taken, and measurements from these views provided to the algorithms. The computation applies the algorithms to generate a hip replacement profile appropriate to the data taken from the measurements. The results are delivered as data to control the manufacture of the hip replacement.

Description

 The present invention relates to the production of prostheses and relates more particularly to the production of hip prostheses.

 The hip prosthesis generally has a femoral implant engaged in the upper part of the medullary canal of the femoral shaft.

 This implant is formed of a femoral stem intended to be engaged and fixed in the medullary canal of the femur after resection of its upper end and having at its end intended to remain outside the femoral shaft, a protrusion forming a prosthetic neck of the femur. a replacement head of the femoral head.

 Among prostheses known to date, there may be mentioned prostheses with single or double curvature do not reproduce the normal diaphyso-metaphyseal anatomy of the femoral shaft due to lack of metaphyseal adaptation of the femoral stem, which leads to poor filling of the canal medulla by the stem of the prosthesis, and consequently gives rise to areas of excessive pressure and areas of insufficient pressure and thus to a non-uniform distribution of pressure on the stem, even with the use of cement.

 Aseptic loosening of the femoral magpies remains one of the major complications of hip replacements.

 The study of the evolution of femoral implants during the last twenty five years shows a general tendency towards the use of massive prostheses and the limitation or even the suppression of the employment of the customer as well as the search for a optimal filling of the medullary cavity of the femoral shaft.

 The aim of the invention is to create a hip prosthesis femoral implant whose shapes are particularly well adapted to the femur to be prosthesis while improving the anchoring of the implant and reducing the risks of mobility generating drive movements, varisation and rotation of the prosthesis relative to the femur that receives it.

It therefore relates to a method for generating digital instructions for controlling the production of a femoral implant with optimized primary stability, characterized in that it consists of
a) to take from a statistically significant population of femur cases to treat characteristic data to accurately define the shape of the femur in the region of placement of a hip prosthesis,
b) to process these data taken from a computer to develop algorithms defining a typical prosthesis profile,
c) to take an image at least in the frontal plane and in the sagittal plane of a femur on which a prosthesis is to be placed,
d) to record on said images, the data corresponding to those used in the elaboration of the algorithms,
e) introducing said data into the computer for processing using the standard prosthesis algorithms and generating the digital instructions for producing said prosthesis.

 The subject of the invention is also a femoral implant comprising a femoral stem intended to be engaged and fixed in the medullary canal of a femur and a projection forming a prosthetic neck for supporting a replacement head of the femur head, characterized in that what it is achieved by the method defined above.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:
- Fig.1 is a schematic sectional view of a hip provided with a prosthesis according to the invention;
FIG. 2 is a diagrammatic view in the plane of the prosthesis of FIG. 1 showing certain parameters to be taken into account in order to define the shape of the prosthesis according to the invention;
FIG. 3 is a schematic view in the sagittal plane of certain geometric parameters contributing to defining the shape of the prosthesis according to the invention;
- Fig.4 is a view in the frontal plane of the prosthesis according to the invention;
- Fig.5 is a view in the sagittal plane of the prosthesis of Figure 4; and
FIG. 6 is a flowchart illustrating the process of generating data relating to the prosthesis to be produced.

 In FIG. 1, there is shown schematically an implant 1 comprising a rod 2 engaged in the medullary canal 3 of a femur 4.

 The end 5 of the implant 1 which protrudes out of the femur 4 forms neck and carries a sphere 6 engaged in a cavity 7 of a cup 8 fixed in the acetabular cavity 9 of the patient.

 During loading, the femoral implant is subjected to forces, the resultant of which passes through the center of the spherical connection which constitutes the articulation of the prosthetic parts used in the orthoplasty of the hip.

By its direction and intensity, this resultant can cause the mobility of the implant according to three main movements
- the depression E
- the varisation V
the rotation R denoted by the corresponding arrows in FIG.

 The success of hip arthroplasty requires the achievement of primary stability that leads to the realization of an implant optimally adapting to the prosthesis femur.

 The great diversity of femur forms highlighted in statistical studies and clinical observations, imposes a direct relationship between the shape of the femur and the shape of the implant.

 This relationship is established by the definition of geometric elements and dimensions that reflect the practitioner's technical choices as well as the characteristics of the forms of the femur.

These parameters, which will be described below with reference to FIGS. 2 and 3, constitute a database derived from
- a statistical study of 515 preoperative files,
- clinical observation of 800 cases,
- an experiment on a test bench.

 The database thus constituted allows the definition of the shapes of the implant and its production.

 The schematic view along the front plane shown in Figure 2 shows a number of para in very important for the constitution of the database.

 Point C is the articulation center of arthroplasty.

 The axis 1F is the projection of the axis of the prosthetic neck 5 (Fig.l) in the frontal plane.

 The segment AB is a segment that positions the implant in the frontal plane and defines its width in the cutting plane of the femur.

 The BD arc defines the area of internal cortical support.

 The DE segment defines the conical termination area of the implant.

 The AF arc defines the external connection area.

 The segment FG defines the zone of external cortical support.

 In Fig.2, there is also shown the axis 1H which is the projection of the axis of the prosthetic neck 5 (Fig.l) in the horizontal plane.

 Reference will now be made to FIG. 3, on which other parameters useful for the constitution of the database appear.

 The axis 1S is the projection of the axis of the prosthetic neck 5 (Fig.l) in the sagittal plane.

 The axis 2 defines the axis of the upper third of the femoral canal 2 in the sagittal plane.

 Larl is the thickness of the implant in the cutting plane of the prosthetic femur.

 Lar2 is the thickness of the implant in the middle part.

 Axis 3 defines the axis of the medial portion of the femoral canal in the sagittal plane.

 Axis 4 defines the axis of the lower third of the femoral canal in the sagittal plane.

 The above-mentioned parameters from a large number of cases are converted into digital form and processed in a computer to develop data defining a typical femoral prosthesis profile.

 In order to proceed to the generation of the forms of an implant intended to be placed in the femur of a particular patient, the prosthesis is performed on the femur for imaging, radiography, computed tomography or other, according to the frontal plane and the sagittal plane and if necessary according to horizontal planes.

 Then, we take from the images obtained the parameters corresponding to those described above which were used to build the database contained in the computer.

 Parameters relating to the femur to be treated are introduced into the computer, and using algorithms constructed from the database contained therein, the forms of the prosthesis to be obtained are defined by generating instructions. corresponding numbers.

In the Cartesian coordinate system whose vertical axis is defined by the intersection of the frontal and sagittal planes, and whose center is the center C of the articulation, the previously defined geometric elements make it possible to construct, according to the flow chart of FIG. .6
1) a continuous left guideline L whose radius of curvature and torsion radius vary continuously, and such that
the projection in the frontal plane at each of its points shown in FIG. 4 is equidistant from the internal edges BD, DE and external AF, FG previously determined,
the projection in the sagittal plane represented in FIG. 5 is tangent to the axes Ax2, Ax3 and
Axis 4 shown in FIG.

2) a planar generating profile P, of ovoid shape, whose plane is constantly orthogonal to the guideline (Fig.4) and whose pole 0 is the intersection of the guideline with the plane of this profile, this profile being such as
the major axis of its projection in the frontal plane, is constantly relying on the internal edges BD, DE and external AF, FG,
- The length of the major axis of its projection in the sagittal plane varies continuously to reach, at the coordinates where they were found, the values Lar2 and Larl (Fig.3). The diaphyseal portion of the prosthesis stem is defined to ensure the bone-implant contact in the areas selected by the surgeon, as well as to facilitate the placement of the implant.

 The volume is generated by displacement of the generator profile P along the guideline L. The continuous variation of the curvilinear abscissa of the point 0 on it, causes the continuous variation of the parameters of the profile P. This displacement comprises an overall rotation of the profile P around its normal vector passing through 0. The upper part of the volume of the prosthesis stem, is limited by the resection plane, defined by the segment AB and the normal vector, orthogonal to AB and passing through the center of articulation C.

The prosthetic neck is a volume of revolution whose axis is defined by its projections AxelF, AxelS and
Axis 1H. it is connected to the tail of the implant at the level of the resection plane, with a flange 10 bearing on the calcar.

 The prosthesis may also be devoid of such a collar according to the surgeon's choice.

 Finally, opposite the flange 10, is provided a chamfer 12 for facilitating the mounting of the prosthesis.

 As shown in the outgoing sections of FIG. 4, where the traces of the frontal plane P are observed, the material of the upper part of the prosthesis stem is distributed asymmetrically with respect to the large ase of the P profile. This distribution is the main feature of the implant. It is possible to control the shape, placing the implant in a frame centered on the point C and for the main axis, the axis of the neck 5, axis 1F (Fig.2).

 The repository thus defined can be used to manufacture the prosthesis using a numerically controlled machine tool.

 By means of the algorithms contained in the computer, one proceeds in a manner that will now be described with reference to FIG.

After entering data on the prosthesis femur, during phase 20, we proceed to phases 21,22, and 23 to the calculation of the frontal projection of the guideline L, the sagittal projection of the guideline L and generator profile parameters
P.

 Then during phase 24, we define the guideline L and during phase 25, we define the generator profile P.

 Finally, during phase 26, the instructions for generating the volume, that is to say the femoral prosthesis to be obtained, are produced.

 By way of illustrative example, but in no way limiting, hereinafter orders the elements of the prograse by means of which the process according to the invention is implemented.

 This original process of generation of a complex volute, makes it possible to realize the objective of adaptation of the prosthesis to the metaphyseal cavity of the femur, essential to obtain the primary stability of the implant, while positioning the center of the articulation under optimal biomechanical conditions. In addition, this method also offers great ease of production, since from a small number of geometrical parameters, the shape to be produced can be defined continuously, thus digitized with a precision adapted to the production process, either for realize a personalized prosthesis, to realize a range of prostheses likely to answer the greatest number of cases.

PROGRAM ELEMENTS FOR IMPLEMENTING THE PROCESS OF
THE INVENTION.

FNLimoz DEF (REAL X, REAL Txa (*))
IF X <= Txz (1,1) THEN
RETURN Txz (1,3) @ (X-Txz (1,1)) + Txz (1,2)
ELSE
IF X <= Txz (1.4) THEN
RETURN ((Txz (Z, 1) + X + Txz (3,2)) * X + Txz (3,3)) + X + Txz (3,4)
ELSE
IF X <= Tx = (2.1) THEN
RETURN ((Tez (4,1) * X + Txz (4,2)) * X + Txz (4,3)) * X + Txz (4,4)
ELSE
RETURN Txz (2,3) * (X-Txz (2, 1)) + Txz (2,2)
END IF - END
END IF
FNEND
FNSecy DEF (REAL R, REAL Ray, REAL Rq)
RETURN Ray * COS (R) * Rq
FNEND
DEF FNSecz (REAL R, REAL Lar, REAL Rqu, REAL Depext)
RETURN Lar * SIN (R) * (1 + Depext * (1-SIN (1.5 * R))) * Rqu
FNEND
DEF FNLa (REAL T, REAL Q, REAL Width (*), REAL Z) 'PROFILE WIDTH
IF T <Width (4) THEN
RETURN (Width (1) * T + Width (2)) * T + Width (@)
ELSE
RETURN Width (5)
END IF
FNEND
DEF FNPlan (REAL M (*), REAL U (*), REAL V (*)) @ @ RETURN (M (1) -U (1)) * V (1) + (M (2) -U (2) )) * V (2) + (M (3) -U (3)) * V (3)
FNEND
DEF FNRight (REAL Y, REAL Z, REAL Hundred (*), REAL Mm (*), INTEGER P2)
RETURN (Y-Cent (1)) * (Mm (P2,2) -Cent (2)) - (Z-Cent (2)) * (Mm (P2.1) -Cent (1))
FNEND
DEF FNTh (REAL T)
RETURN (EXP (2 * T) -1) / (EXP (2 * T) +1)
FNEND
DEF FNRr (REAL X, REAL Bx, REAL Dx, REAL Rb, REAL Dac, REAL Rac)
IF X <Bx THEN
RETURN Rb + (X-Bx) * TAN (Dac)
END IF
IF X <Dx THEN
RETURN Rb
ENt 'IF
RETURN Rb + Rac-SQR (Rac ^ 2- (Dx-x) ^ 2) FNEND
FNLimcy DEF (REAL X, INTEGER I, REAL Fpst (*))
IF X <Fpst (I, 1) THEN
J = 9
ELSE
IF x <Fpst (1,3) THEN
J = 12
ELSE
IF @ <Fcst (I, 5) THEN
J = 15
ELSE
J = 18
END JF
END IF
END IF
PETURN (Fost: I. 0) @ 2 + F @ st (I, 0 + 1)) @@ + Fpst (I.J + 2) DcF FNT abl @REAL @, REAL @ (*))
INTEGER Y
Y = PROUND (X, O)
IF Y <T (1) THEN
RETURN T (3) @ (XT (1)) + T (4)
ELSE
IF Y <= T (2) THEN
RETURN T (Y)
ELSE
RETURN T (5) * (XT (2)) + T (6)
END IF
END IF
FNEND
DEF FNTablp (REAL X, REAL T (*))
INTEGER Y
Y = PROUND (X, O)
IF Y <T (1) +5 THEN
RETURN T (3)
ELSE
IF Y <= T (2) -5 THEN
RETURN (T (Y + 5) -T (Y-5)) / (10 * T (7))
ELSE
RETURN T (5)
END IF
END IF
FNEND
DEF FNLimoyp (REAL X, INTEGER I, REAL Fpst (*))
IF X <Fpst (I, 1) THEN
J = 9
ELSE
IF X <Fpst (I, @) THEN
J = 12
ELSE
IF X <Fpst (I, 5) THEN
J = 15
ELSE
J = 18
END IF
END IF
END IF
RETURN 2 * Fpst (I, J) * X + Fpst (I, J + 1)
FNEND
DEF FNDepext (REAL T, REAL O)
RETURN. 3 * (1-FNTh (.01 * (TQ))) -NENO
DEF FNAntev (REAL T, REAL Q)
RETURN (1-FNTh (.05 * (TQ))) / 2
FNEND

Claims (12)

 1. A method for generating digital instructions for controlling the production of a femoral implant with optimized primary stability, characterized in that it consists of  a) to collect from a statistically significant population of femur cases to treat characteristic data to accurately define the shape of the femur in the region of placement of a hip prosthesis,  b) to process these data taken from a computer to develop algorithms defining a typical prosthesis profile,  c) to take an image at the oins in the frontal plane and in the sagittal plane of a femur on which a prosthesis is to be placed,  d) to record on said images, the data corresponding to those used in the elaboration of the algorithms,  e) introducing said data into the computer for processing with standard prosthetic algorithms and generating the generic instructions for making said prosthesis.  2. Method according to claim 1, characterized in that one proceeds also to images taken by tomodensitometry.  3. Method according to one of claims 1 and 2, characterized in that the profile of the prosthesis is defined from a left (L) directional curve whose projection in the frontal plane is equidistant projections (BD, DE , AF, FG) in the frontal plane of the contour of the prosthesis stem and whose projection in the sagittal plane is tangent to the axis (Axis2) of the upper third of the femoral canal (2) of the prosthesis femur, in the plane sagittal, at the axis (Axis3) of the medial part of the femoral canal (2) in the sagittal plane and at the axis (Axis4) of the lower third of the femoral canal in the sagittal plane and by a planar generating profile (P) of ovoid shape moved along the guideline (L) and the plane of said profile being constantly orthogonal to the guideline (L) and its pole (O) being the intersection of the guideline (L) with the plane of the profile (P).  4. Method according to claim 3, characterized in that the major axis of the projection of the profile (P) in the frontal plane is constantly supported on the inner (BD, DE) and outer (AF, FG) edges of the projection. the contour of the prosthesis stem in the frontal plane.  5. A method according to claim 4, characterized in that the length of the major axis of the projection of the profile (P) in the sagittal plane varies continuously to reach the coordinates where they have been recorded the values (Lar2 and Larl) of the thickness of the implant respectively in its median part and in the resection plane (AB) of the prosthesis femur.  6. Method according to one of claims 3 to 5, characterized in that the continuous variation of the coordinates of the pole (O) of the profile (P) due to the displacement of this point along the left guideline (L) causes the continuous variation of the parameters of the generator profile (P).  7. A method according to claim 6, characterized in that the displacement of the generator profile (P) along the left guideline (L) comprises an overall rotation of said generator profile around its normal vector passing through its pole (O).  8. Method according to one of claims 5 to 7, characterized in that the volume of the prosthetic neck (5) is a volume of revolution whose axis is defined by its projections (AxelF, AxelS, AxelH) in the frontal planes , sagittal and horizontal and connects to the prosthesis stem at the level of the resection plane (AB).  9. Femoral implant comprising a femoral stem (2) intended to be engaged and fixed in the medullary canal (3) of a femur (4) and a projection forming a prosthetic neck (5) for supporting a head (6). ) of the head of the femur, characterized in that the femoral stem (2) is constituted by a volume generated by displacement of an ovoid-shaped generating profile (P) along a left guideline (L ) whose projection in the frontal plane is equidistant from projections (BD, DE, AF, FG) in the frontal plane of the contour of the prosthesis stem and whose projection in the sagittal plane is tangent to the axis (Axis2) of the upper third of the femoral canal (2) of the prosthesis femur, in the sagittal plane at the axis (Axis3) of the medial part of the femoral canal (2) in the sagittal plane and at the axis (Axis4) of the lower third of the femoral canal in the sagittal plane, the plane of said generating profile (P) being constantly orthogonal to the guideline (L) and its pole (O) being the intersection of the guideline (L) with the plane of said generating profile (P).  Femoral implant according to Claim 9, characterized in that the prosthetic neck (5) is a volume of revolution whose axis is defined by its projections (AxelF, AxelS, AxelH) in the frontal, sagittal and horizontal planes and connects to the prosthesis stem (2) at the resection planes (AB).  11. femoral implant according to one of claims 9 and 10, characterized in that the material of the upper part of the prosthesis rod (2) is distributed asymmetrically with respect to the major axis of the generator profile (P).  12. Femoral implant according to one of claims 9 to 11, characterized in that it is carried out by the method according to any one of claims 1 to 8.