ITPI20130090A1 - APPARATUS FOR CORRECTION OF PECTUS EXCAVATUM PATHOLOGY. - Google Patents

Description

DESCRIPTION OF THE INVENTION

APPARATUS FOR THE CORRECTION OF THE PATHOLOGY OF THE PECTUS EXCAVATUM TECHNICAL SECTOR

The present invention relates to an elongated bar with an optimized structure of the type included in an apparatus for repairing the pathology of pectus excavatum.

The invention also concerns a method for removing the aforementioned bar from a patient's chest.

STATE OF THE ART

The pathology of pectus excavatum is one of the most common deformities of the anterior part of the chest and consists of a more or less accentuated retroversion of the sternum that causes a depression of the front central part of the chest.

The most commonly used and effective technique for the treatment of the aforementioned pathology is described in US 6,024,759 A. This document discloses an apparatus consisting of an elongated bar with a preferably rectangular section and falling within a certain range of dimensions in length, height and thickness. , and having suitable mechanical characteristics of resistance to deformation, stiffness or yield strength, which is suitable for assuming such a conformation as to keep the chest in the desired shape. The aforementioned bar is bent to make it assume a convex shape, is passed under the sternum with the convexity facing posteriorly, is then rotated by 180 ° so that the convexity faces anteriorly and so that the sternum is lifted from the bar in the desired position, and finally the bar is constrained in this latter position by sutures that stop the ends of the bar to the muscles of the lateral thoracic wall, directly or through the interposition of suitable stabilizing elements. The material of the bar is preferably 316LVM stainless steel, which is particularly used in medical applications and has physical properties such as to ensure the aforementioned mechanical characteristics with the necessary maximum dimensions in height and thickness of the bar provided for this specific application. The document also provides for the possibility of making the bar in different materials and precisely other bio-compatible metal materials such as titanium or chromium-cobalt.

An inherent limitation in the use of the aforementioned metal materials is the need to provide in any case, at the end of the treatment period, an intervention to remove the metal bar from the patient's body. This intervention, although less complex than the intervention summarily described above necessary for the application of the bar, is in any case an invasive and complex intervention both because of the size of the bar itself and because of the possible adhesions formed over time between the bar and the surrounding tissues.

Still in the document US 6,024,759 A, the possibility is also provided of making the bar in a bio-resorbable material which can for example be chosen from polymers and co-polymers of PLLA, PGA, PDLA, or it can be another reabsorbable material.

The use of a resorbable material could make the removal of the bar superfluous. However, in the document cited itself, the use of a bar made entirely of a resorbable material is proposed only in theory as currently the physical properties of the resorbable materials are not able to ensure the necessary mechanical characteristics while at the same time falling within the dimensions. bar maximums foreseen for this type of application. Furthermore, since the physical properties of resorbable materials also depend on time, it is even more difficult to study or identify a resorbable material which has the functional duration suitable for this type of application in which the bar is left in place for an average period. about three years.

In many medical applications, a resorbable material is used exclusively as a surface coating of a non-resorbable component, metal or other material, capable of ensuring the prescribed mechanical and structural characteristics. Similarly, a resorbable material coating could be applied to an elongated metal bar, however this could solve the problem of the formation of adhesions between the bar and the surrounding tissues, but it would not eliminate the need for invasive removal of the same. .

Again in US 6,024,759 A, it is described that the elongated bar could be a single bar or even a plurality of bars aligned and arranged adjacent to each other, constrained or not to each other by removable means or by welding, in any case to obtain the prescribed minimum mechanical characteristics as a whole. As shown in Figures 1A, 1B and 1C of the same document, the bar can be made up of several cylindrical or rectangular section bars arranged adjacent to each other, side by side or overlapping. The use of several distinct bars can be advantageous in the intervention of removal of the bar since, if they are physically separated from each other, they can be removed one at a time separately with a less invasive intervention as it is sufficient to prepare a The smaller the size of the single element of the bar, the smaller the size of the extraction channel. However, this solution entails further complications in the already complex application of the apparatus since it is necessary to provide suitable means for keeping the individual elements of the bar mutually constrained during its application and further means capable of stabilizing the position of each single element throughout the treatment period, until removal.

SUMMARY OF THE INVENTION

The aim of the present invention is therefore to propose an apparatus for correcting the pathology of pectus excavatum capable of overcoming the above-mentioned limits of the known art.

A further purpose of the present invention is to propose an apparatus for the correction of the pathology of pectus excavatum which does not give problems of compatibility with the body tissues and which allows to appropriately regulate, by means of chemical functionalization, the inflammatory and fibrotic response of the organism to plant.

Another object of the present invention is to propose an apparatus for the correction of pectus excavatum which is easily removable at the end of the treatment period.

Another object of the present invention is to propose a method for the removal from the chest of a patient of an apparatus for the correction of the pathology of pectus excavatum which is minimally invasive and simple to implement.

According to an aspect of the present invention, the aforementioned and other purposes are achieved by means of a device according to what is expressed and characterized in independent claim 1.

The claims dependent on claim 1 disclose other features of the present invention or variants of the main solution idea.

Conventionally, an apparatus for correcting the pathology of pectus excavatum comprises at least an elongated bar provided with a first and a second end, and suturing means suitable for binding said elongated bar in proximity of the relative first and second ends, to body tissues, directly or by means of suitable stabilizing elements. The aforesaid elongated bar has a height dimension such as to be able to be inserted in an intercostal space, and has a yield strength and rigidity such that said bar is suitable to be bent in a convex conformation and suitable, in said convex conformation, to be inserted beyond under the patient's sternum to keep the patient in the desired shape.

According to the present invention, the aforementioned elongated bar consists of a matrix in resorbable material within which there is a plurality of elongated elements in metal material. The elongated elements are arranged aligned with each other according to the direction of the length of the bar and are spaced between them with the absorbable material interposed. Furthermore, each of the elongated elements has a length substantially equal to the length of the elongated bar.

The matrix in resorbable material guarantees the perfect bio-compatibility of the prosthetic implant and keeps in position the metal elements which have a structural function and however, given the very small section dimensions, can be removed in an extremely easy way, simply by "pulling them out" from the polymer matrix.

Advantageously, the resorbable material is selected from poly (ortho esters), poly-L-lactic acid, homopolymers and copolymers of poly hydroxy butyrate, poly-�-caprolactone, poly (SA-HDA anhydride), poly (BPA iminocarbonate), while the material of the elongated elements is chosen from stainless steel, titanium alloy, tungsten alloy.

Still advantageously, each of the elongated elements has a substantially constant section for the entire length with an area not exceeding 20 mm <2>, while the ratio between the overall area of the plurality of elongated elements and the overall area of the section of said elongated bar is not greater than 0.85.

Preferably the elongated elements have the shape of lamellae, while alternatively they are filiform or have a still different section.

According to another aspect of the present invention, the objects listed above are achieved by means of a method according to what is expressed and characterized in independent claim 8.

According to the present invention, a method for removing from a patient's chest an apparatus for correcting the pathology of pectus excavatum, in which the apparatus comprises at least one elongated convex-shaped bar positioned transversely under the patient's chest with the convexity facing anteriorly so as to keep the sternum raised in a desired position, and in which the elongated bar is made up of a matrix in resorbable material inside which there is a plurality of fibers in metallic material, said fibers being arranged aligned between according to the direction of the length of said bar, said fibers being spaced apart with said resorbable material interposed, each of said fibers having a length substantially equal to the length of said elongated bar, comprises the execution of an incision of a length not exceeding 1.5 cm into the patient's lateral chest wall at a d in the two end surfaces of said elongated bar, the extraction by pulling off said elongated elements one at a time in succession until all said elongated elements of said elongated bar are extracted, and the suture of said incision.

The removal method outlined above is minimally invasive as the extraction of the metal parts of the elongated bar takes place by removing the latter from a single small incision made at one of its two ends.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will be more easily understood from the following description of preferred embodiments thereof, provided as non-limiting examples, with reference to the attached figures in which:

Figure 1 shows a perspective view of a prosthetic implant according to the present invention, in particular an implant for correcting the pathology of pectus excavatum;

- Figure 2 schematically shows in a front view the implant of Fig. 1 implanted in the chest of a patient;

- figure 3 shows a perspective view of an end of an elongated bar according to the present invention: in fig. 3a shows a first embodiment, in fig.3b a second embodiment is shown;

- figure 4 shows a summary table of the stresses to which an elongated bar is subjected (with metal elements having lamellar geometry, as in figure 3a) for different combinations of materials; - figure 5 shows a summary table of the percentage elastic deformation values to which the elongated bar is subjected for the same combinations of materials and again considering a lamellar geometry of the metal elements;

- figure 6 shows a summary table of the stresses to which an elongated bar is subjected (with metal elements having filiform geometry, as in figure 3b) for different combinations of materials;

- figure 7 shows a summary table of the percentage elastic deformation values to which the elongated bar is subjected for the same combinations of materials and again considering a filiform geometry of the metal elements;

- figure 8 shows a graph of the trend of the maximum deformation as a function of the percentage of metal alloy with respect to the polymeric material, for a given combination of materials and considering both geometries (lamellar in figure 3a and filiform in figure 3b) for the elements metallic.

DESCRIPTION OF THE PREFERRED MANUFACTURING FORMS

Figures 1 and 2 show an apparatus, 1, for correcting the pathology of pectus excavatum consisting of an elongated bar, 2, provided with a first end, 21, and with a second end, 22, in correspondence with which there are restraining means which may comprise end stabilizers, 3.

As occurs according to the known technique, the bar 2, suitably curved, is passed under the sternum with the convexity facing posteriorly by inserting it through an incision made on one side of the chest. Once the bar has passed through the thoracic cavity it is rotated so that the convexity faces anteriorly in order to keep the raised sternum in the desired position. The bar is fixed in position thanks to the constraint means present at the first and second ends 21 and 22 comprising the stabilizers 3 provided with holes, 31, which by means of sutures are fixed to the pectoral muscles. To perform the operation of insertion of the apparatus it is therefore necessary to make at least two incisions, in substantially symmetrical positions, at the points where the first and second ends 21 and 22 of the elongated bar 2 will be located.

As shown in Fig. 3, the elongated bar 2 is made of a composite material consisting of a bio-resorbable polymer matrix, 23, and a plurality of elongated metal elements, 24, 24 ', internal to the matrix. The elongated elements 24, 24 'are arranged aligned according to the direction of the length of the elongated bar 2, equally spaced between them with the matrix of bioabsorbable material interposed between them. Furthermore, each of the elongated elements 24, 24 'extends substantially for the entire length of the elongated bar 2.

In the example of construction of fig. 3a the elongated elements 24 have the shape of lamellae and their section has the dimension of the width which substantially has the extension of the width of the elongated bar 2, while their thickness is very low so that the thickness of the elongated bar 2 is made up of three elements elongated 24 overlapping suitably spaced apart by interposing the bioabsorbable polymeric material 23.

In the example of construction of fig. 3b the elongated elements 24 'are metal wires of circular section arranged neatly in the section of the elongated bar 2 to form two rows and seven columns suitably spaced by the interposition of the bioabsorbable polymeric material.

The elongated metal elements 24, 24 ', which have the main function of ensuring the load resistance of the elongated bar 2, can obviously also have a different section and be organized within the bioabsorbable polymer matrix 23 according to other geometries.

The metal material of which the elongated metal elements 24, 24 'are made is preferably chosen from AISI 316 L stainless steel, the titanium alloy Ti-6Al-4V, or tungsten. The breaking load of these materials varies from about 400 MPa to about 1800 MPa; the yield strength varies from about 150 MPa to about 1200 MPa; the elongation at break ranges from about 10% to about 50%, the elastic modulus varies between about 100 GPa and about 500 GPa, while the Poisson's modulus is between 0.25 and 0.35.

As for the polymeric matrices, these can be made up of a variety of polymers whose degradability profile is compatible with the expected implantation times for the elongated bar 2. Among the polymeric materials preferable for this application are: poly (ortho- esters) such as poly (ortho ester) t-CDM: 1.6-HD = 35:65 and poly (ortho ester) t-CDM: 1.6-HD = 90:10; poly-L-lactic acid, homopolymer and copolymers of poly hydroxy butyrate such as the copolymer 22% HV, poly-�-caprolactone, poly (SA-HDA anhydride), poly (BPA iminocarbonate).

The tensile strength of these materials varies from about 4 MPa to about 50 MPa, while the elastic modulus is between about 40 MPa and about 3000 MPa (Engelberg and Kohn 1991).

Appropriate finite element simulations have highlighted the mechanical behavior of an elongated composite bar, made up of the materials listed above.

For example, simulations were performed considering a bar of length 300 mm, width 12.7 mm and thickness 3.5 mm constrained at its ends, and considering the composite structure with three metal lamellas of 0.9 mm thickness (volume of each lamella 3321 mm <3> and ratio between the total volume of the metal lamellae and the total volume of the elongated bar equal to approximately 0.75) that run through the entire matrix, for its length (embodiment of Fig.3a) and considering a force of 250 N applied to the center of the bar (a value greater than the maximum pressure found in the literature for the correction of pectus excavatum, according to Weber et al. 2006), and the values of maximum stress, and maximum percentage deformation of the bar were obtained, which are reported in the tables of figure 4 and figure 5, respectively.

As shown by the values shown in the tables, all combinations of materials cause a stress on the bar which is less than the breaking load of all three metals or metal alloys considered. The yield strength of the AISI 316 L steel alloy is exceeded for all combinations of materials, except in the association with poly-L-lactic acid which remains slightly below. All combinations of polymeric materials with titanium alloys Ti-6Al-4V and Tungsten, on the other hand, provide maximum stress values that are much lower than the yield strength of these two metals.

The combination of materials that allows to have the lowest percentage deformation (and, consequently, the lowest total deformation of the bar) is that constituted by poly-L-lactic acid and Tungsten.

All the materials and combinations of materials listed above are therefore substantially suitable for making an elongated bar for the correction of pectus excavatum according to the present invention.

Further simulations were performed considering still a bar of length 300 mm, width 12.7 mm and thickness 3.5 mm constrained at its ends, and considering the composite structure with fourteen metal rods with a diameter of 1.45 mm (volume of each rod 1980 mm <3> and ratio between the total volume of the metal rods and the total volume of the elongated bar equal to approximately 0.52) that run through the entire matrix, due to its length (embodiment of Fig.3b) and still considering a force of 250 N applied to the center of the bar. Also in this case the values of maximum stress and maximum percentage deformation of the bar have been obtained, which are reported in the tables of figure 6 and figure 7, respectively.

As shown by the values shown in the tables, the breaking load of the AISI 316 L steel alloy is exceeded in all combinations with the different polymers. The yield strength of the titanium alloy Ti-6Al-4V, on the other hand, is only exceeded if poly (SA-HDA anhydride) is used. When using titanium, the yield point of the metal is never reached. However, in the case of using poly (SA-HDA anhydride) in combination with this metal, the maximum percentage deformation of the bar reaches values higher than 19%, which are beyond the elongation limit of the tungsten itself (i.e. about 10%) . The combination of materials that allows to have the lowest percentage deformation (and, consequently, the lowest total deformation of the bar) is still the one constituted by poly-L-lactic acid and Tungsten, which can therefore be considered, at the current state of the art , the combination of materials preferred from the structural point of view, but not limiting as it can be replaced with other combinations of materials following, for example, evaluations of an economic nature.

With regard to the geometry and dimensions of the elongated metal elements, these are defined by identifying a compromise between a desired flexibility of the metal elements 24, 24 'themselves, which favors their removal, and their ability to withstand high pressure loads. For example, in the case of the slat geometry 24, a decrease in the thickness of the slats themselves may be desirable, to increase their flexibility and thus facilitate their removal (simply "sliding them" from the matrix), once the corrective action of the bar has been exhausted. elongated 2. Figure 8 shows, for the combination of poly-L-lactic acid Tungsten materials, the trend of the maximum stress acting on the elongated bar 2 as the volumetric percentage of metal inside the bar varies (directly proportional to the thickness metal plates 24 or metal rods). The graph shows the yield strength and the structural limit of Tungsten with dashed lines. The points identified by rhombuses, 71, in the case of the lamellae and by triangles, 72, in the case of rods refer to the maximum stress values acting on the bar in correspondence with different dimensions of the metal elements themselves (and therefore of different percentages of metal in the structure). It is clear that the minimum thickness for the metal lamellas is 0.4 mm and the minimum diameter of the rods is 0.75 mm: below these values the yield strength (and also the breaking one) characteristic of Tungsten is exceeded.

Obviously, the results of the aforementioned simulations demonstrate the possibility of making an elongated bar according to the present invention with numerous combinations of materials, but the above list of the latter must be considered as an example only and not exhaustive. Furthermore, also with regard to the geometry of the elongated metal elements 24, 24 'and of the composite material as a whole, numerous variations may be possible, without thereby departing from the concept of the present invention.

The use of an elongated bar 2 according to the present invention, made of composite material, makes it possible to implement a particular method of removing it at the end of the treatment period.

In fact, according to the method of the present invention, to remove the apparatus 1 for the correction of pectus excavatum it is sufficient to make an incision with a maximum length of about 1.5 cm, then remove all the elements in succession, one at a time. elongated metal 24, 24 ', and finally close the incision with sutures. The high flexibility of each single elongated metal element 24, 24 'allows for a particularly easy removal and the fact that they are incorporated into the polymer matrix prevents them from damaging body tissues.

The removal procedure is extremely simple and non-invasive as the need to remove the elongated bar 2 is limited to the need to remove the elongated metal elements 24, 24 '. In fact, the bioabsorbable polymer matrix remains in situ and is gradually reabsorbed by the body. Similarly, also the stabilizers 3, when present, are made of bioabsorbable polymeric material and therefore do not need to be removed. Alternatively, if a greater structural strength of the stabilizers is required, they are made of metallic material and coated with bio-resorbable polymeric material and in this case the removal method will include steps dedicated to the removal of the stabilizers. A further alternative is to use composite stabilizers which, similarly to the bar, consist of a bioabsorbable matrix within which metal structural elements are positioned. The latter solution would also allow minimally invasive removal of the metal elements of the stabilizers, in addition to those of the bar. The metal structural elements may have, similarly to what happens in the bar, lamellar or filament geometry and are sufficient in number and section to provide the stabilizer element with the required mechanical characteristics.

Obviously, in addition to the steps provided for by the method of removal of the invention, the removal procedure could include further steps and surgical procedures deemed necessary or appropriate.

The advantages of an apparatus for the correction of pectus excavatum and of a method for its removal according to the present invention remain unchanged even in the presence of further variants or modifications, made while always remaining within the scope of protection defined by the claims following.

Claims (9)

CLAIMS 1. Apparatus (1) for correcting the pathology of pectus excavatum comprising at least one elongated bar (2) provided with a first and a second end (21, 22), and suturing means suitable for constraining said elongated bar in proximity to the relative first and second extremities, to body tissues, directly or by means of suitable stabilizing elements (3), and in which said elongated bar (2) has such a dimension in height as to be able to be inserted in an intercostal space, and has a yield load and stiffness such that said bar (2) is suitable to be bent in a convex conformation and suitable, in said convex conformation, to be inserted under the patient's sternum to keep the latter in the desired shape; characterized by the fact that said elongated bar (2) is constituted by a matrix in resorbable material (23) inside which there is a plurality of elongated elements (24) in metallic material, said elongated elements (24) being arranged aligned according to the direction of the length of said bar (2), said elongated elements (24) being spaced apart with said resorbable material (23) interposed, each of said elongated elements (24) having a length substantially equal to the length of said elongated bar (2 ). 2. Apparatus according to claim 1 characterized in that said resorbable material (23) is selected from poly (ortho esters), poly-L-lactic acid, homopolymers and copolymers of poly hydroxy butyrate, poly-�-caprolactone, poly (SA -HDA anhydride), poly (BPA iminocarbonate). 3. Apparatus according to one of the preceding claims characterized in that said elongated elements (24) are made of a material selected from stainless steel, titanium alloy, tungsten. 4. Apparatus according to one of the preceding claims characterized in that each of said elongated elements (24) has a substantially constant section for the entire length with an area not exceeding 20 mm <2>, the ratio between the total volume of said plurality of elements elongated bars (24) and the overall volume of said elongated bar (2) being no greater than 0.85. 5. Apparatus according to one of the preceding claims characterized by the fact that said elongated elements (24) are uniformly distributed within said matrix in resorbable material (23). 6. Apparatus according to the preceding claim characterized in that said elongated elements (24) have the shape of lamellae. 7. Apparatus according to claim 5 characterized in that said elongated elements (24) are filiform. 8. Apparatus according to one of the preceding claims characterized in that it comprises stabilizing elements (3) made of composite material consisting of a matrix of resorbable material in which metallic structural elements are contained. 9. Method for removing from a patient's chest an apparatus (1) for correcting the pathology of pectus excavatum, in which said apparatus comprises at least one elongated bar (2) of a convex shape positioned transversely under the patient's chest with the convexity facing forward so as to keep the sternum raised in a desired position, characterized by the fact that said elongated bar (2) consists of a matrix in resorbable material (23) inside which there is a plurality of elongated elements (24) made of metal material, said elongated elements (24) being arranged aligned with each other according to the direction of the length of said bar (2), said elongated elements (24) being spaced apart with said resorbable material (23) interposed, each of said elongated elements (24) having a length substantially equal to the length of said elongated bar (2), and in which said removal method comprises: execution of an incision no longer than 15 mm in the patient's lateral chest wall at one of said first and second ends (21, 22) of said elongated bar (2); the extraction by extraction of said elongated elements (24) one at a time in succession until the extraction of all said elongated elements (24) of said elongated bar (2); and the suture of said incision.