WO2019076420A1

WO2019076420A1 - A patient specific spacer

Info

Publication number: WO2019076420A1
Application number: PCT/EG2018/000021
Authority: WO
Inventors: Mahmoud Alm EL Din HAFEZ
Original assignee: Hafez Mahmoud Alm El Din
Priority date: 2017-10-22
Filing date: 2018-10-22
Publication date: 2019-04-25

Abstract

This invention relates to a patient specific spacer maintaining the joint position fits into the joints which face the removal of the prosthesis for treatment of infection. The spacer was designed in a specific shape to fit the bone shape and anatomy and based on the images captured from the CT-scan and/or MRI and X-ray. The design of the spacer depends on the femoral canal size in case of hip replacement, and tibial canal in case of knee replacement. The spacer was manufactured in two methods, the first method by 3D printing with accredited biomaterials to be implanted into the patient. In this method, the spacer is cannulated to allowing the surgeon to add metallic supports inside it for forcing the spacer. The second method using a mold with a cavity identical to the designed spacer, the surgeon fills the mold cavity by the cement intraoperatively and produces the required spacer.

Description

A patient-specific spacer

This application claims the benefit of Egyptian Provisional application No. 27/2017 filed on October 22, 2017 and Egyptian Patent Application No. 654/2018 on April 19, 2018

Technical Field:

The present invention is related to a patient-specific temporary prosthetic joint (also known as patient-specific spacer) for usage in surgeries for replacing an original femur prosthetic joint with a temporary one. The spacer may be used in cases of infections in the original prosthetic femur joint or fractures in the femur joint.

Problem or Deficiencies in Prior Art:

Implantation of spacer is a common procedure taken in cases of critical injuries or infections to the original prosthetic joint. However, there is always the challenge of determining a proper size for the femur that matches the anatomic profile of the femur joint. This limits the lifetime of the spacer inside the patient's body. A perfect duration for a permanent prosthetic joint inside the body is six months following the surgery. Also, any infection in the original prosthetic joint forces the surgeon to replace it with a larger size spacer, since the cavity of the acetabulum connected to the head of the femur becomes larger than the normal size as a result of a first surgery, a past fracture, or the patient's medical history.

Total dependence on 2D X-ray for planning for the surgery limits the possibilities of total success, such as the correct alignment and placement of the spacer in the cavity of the femur. It does not also provide the surgeon with the ability to predetermine the exact size of the spacer before performing the surgery. Some postoperative health problems may also occur in cases where the size of the joint does not match the anatomic profile of the femur joint, especially the acetabulum. This may be manifested in the patient's weight adding load to the joint and also when practicing daily activities. Many papers and studies demonstrate the effect of mismatch of the size and alignment of the spacer inside the femur on the well- functioning of the joint when practicing the day-to-day activities.

In addition, only three sizes are available in the market for spacers. Definitely, the only available sizes may not be suitable to all patients, thereby restricting usage to certain sizes, which may not suit patients' medical cases.

Conventional spacers are expensive. Their cost is even comparable to the cost of permanent prosthetic ones. This definitely imposes financial burden on patients and governments financing these surgeries under their medical insurance systems, thereby increasing the numbers of patients placed on waitlists.

Disclosure of the Invention;

The present invention is related to a patient-specific spacer for usage in surgeries for replacing an original femur prosthetic joint with a temporary one. Spacers may be used in cases of infections in the original prosthetic femur joint or fractures in the femur joint. The design of the spacer, according to the present invention, is based on the CT scan made to the patient's femur joint and is produced with the help of 3D printers.

Detailed Description of the Invention:

The present invention is related to a patient-specific spacer for usage in cases of infections in the original prosthetic femur joint or fractures in the femur joint. The design of the spacer, according to the present invention, is based on a CT scan made to the patient, which is then converted into a 3D model for the joint. The size and dimensions of the spacer may be determined to match the anatomic profile of the joint, the patient's medical case, and the cavity of the femur, thereby insuring the best fit of the spacer inside the patient's body. The spacer is produced by means of 3D printing, depending on an electronic file containing the 3D design of the spacer, and by the use of printed medical materials implantable inside the patient's body.

The spacer, according to the present invention, is disposable. The design and placement of this patient-specific spacer is based on the preoperative CT scan of the femur bone made to the patient before undergoing a hip replacement surgery. A CT scan of one patient cannot be similar to that of any other individual. The CT scan made to the patient is converted into a 3D model for the joint with the help of specialized software. This demonstrates the novelty of the invention, since the surgeon will no more need to compare between the existing sizes of prosthetic joints or be obliged to use a joint size unsuitable to the medical case and the anatomic profile of the femur joint.

The spacer, according to the present invention, comprises paths therein, wherein surgical wires may be placed to strengthen the spacer, ensure its ability to withstand the patient's daily activities, and lengthen its lifetime inside the body, according to the patient's medical case and the surgeon's or physician's diagnosis.

One of the said two paths comprised into the spacer is a longitudinal path. The said longitudinal path aligns the femur, thus helping the spacer to withstand the shear and vertical loads resulting from the body weight and the patient's movements when practicing the day-to-day activities, such as walking, standing up, sitting down, and some other simple motor skills. The other path is transversal, passing across the head of the spacer in an inclined way on the stem thereof to increase its ability to withstand vertical loads and ensure that no fractures or inflections occur inside the spacer.

The design of the spacer, according to the present invention, is based on software- assisted preoperative planning. The 2D CT scan is first inputted into a computer program then converted into a 3D model for the joint. The said 3D model shows all the details and anatomic features of the surface of the femur joint, such as the dimensions and thickness of the femur, the size of the internal cavity, the mass of the marrow, the profile of the acetabulum and the amount of bone therein, the quality of the bone in the position where the spacer shall be implanted, and the degree of withstanding the density and thickness of the bone as required to implant the spacer. All this data may be obtained after converting the 2D CT scan of the femur joint into a 3D model with the help of specialized software.

After obtaining a 3D model for the pelvic joint, a spacer with proper dimensions matching the anatomic profile of the patient's femur joint is designed. The designed spacer comprises a stem matching the internal cavity of the femur, according to the thickness of the bones therein, and a head matching the internal cavity of the acetabulum. Accordingly, this spacer is patient-specific since the design thereof is based on the patient's CT scan and can never be used with more than one patient.

In this way, the dimensions and external features of the spacer may be the same as those of the patient's femur joint. The quantity of antibiotics loaded inside the spacer may be adjusted through the paths comprised therein, as determined by the surgical and medical procedures followed by the surgeon or physician to ensure the well-functioning of the joint during its lifetime inside the body. In addition, the external surface of the spacer may be coated with a layer of medical cement to ensure fixation thereof in its proper position and prevent the dislocation of the stem from the femur or the head from the acetabulum. This is considered one of the advantages of the spacer, according to the present invention, over prior art conventional ones, wherein the latter have instability and loosening possibilities as a result of the patients' daily activities, especially non-compliant patients and those maintaining a very active lifestyle.

After designing the 3D model of the spacer, an electronic file thereof is produced in a printed form by means of 3D printers. In other words, the electronic file is sent to a 3D printer, which converts it into real model that may be used in surgical operations. Other manufacturing techniques may be used, thereby providing the surgeon with different options to choose from according to the desired quality and final price.

The spacer, according to the present invention, may be made of nylon. Nylon has excellent mechanical and physical properties compared to many other materials, especially with regard to withstanding heavy loads, whether fixed or movable loads. Also nylon is an implantable material that can last for a period up to six months inside the body. This six-month period is sufficient for the spacer to be replaced with a permanent prosthetic one. Nylon is an FDA-approved material for implantation inside living tissues without any medical complications. As outlined above, 3D printing technology is used for producing the spacer, according to the present invention. The following two methods may be used:

• Fused deposition modeling (FDM): A method for printing objects by using plastic wires made of the material to be printed. In case of out spacer, the material used is nylon.

• Selective laser sintering (SLS): A method for printing objects by using laser for sintering nylon powder to produce the required profile of the patient- specific spacer.

Both 3D printing methods are FDA approved and the materials used, that is, plastic wires or nylon powder, may be implanted in living tissues for a period up to six months.

The production cost of the spacer, according to the present invention, as compared to conventional prior art ones, is 1 : 12, according to current market prices. Hence, the spacer, according to the present invention, represents an ideal solution for both the surgeon and the patient since it may significantly lower the costs incurred. As described above, conventional spacers are expensive, thereby imposing financial burden on patients and governments financing these surgeries under their medical insurance systems, and increasing the numbers of patients placed on waitlists accordingly. The present invention, however, provides the design and production of a patient-specific femur spacer with the use of a low-cost technology, as compared to other techniques. It, thus, provides an inventive solution that may help surgeons to guarantee the success of complication-free surgical operations by the use of low-cost joints, thereby reducing the numbers of patients on waitlists. Description of the Figures:

Figure (1) is a two-dimensional front elevation for the patient-specific femur spacer, illustrating parts thereof: head (1), stem (2), and nerve (3).

Figure (2) is a two-dimensional elevation for the patient-specific femur spacer, illustrating parts thereof: head (1), stem (2), nerve (3), and the opening (4) of the longitudinal internal path across inside the stem.

Figure (3) is a two-dimensional side elevation for the patient-specific femur spacer, illustrating parts thereof: head (1), stem (2), nerve (3), and the opening (4) of the longitudinal internal path passing across the stem.

Figure (4) is a three-dimensional view for the patient-specific femur spacer, illustrating parts thereof: head (1), stem (2), and nerve (3).

Figure (5) is a two-dimensional internal sector for the patient-specific femur spacer, illustrating the internal paths thereof: the longitudinal path (5) and the transversal path (6).

Figure (6) is a three-dimensional view for the acetabulum (7), illustrating the cavity thereof (8).

Figure (7) is a two-dimensional side elevation for the femur spacer and the acetabulum (7), showing the spacer best fitted into the correct position (9) inside the cavity of the acetabulum. Figure (8) is a two-dimensional front elevation for the femur spacer and the acetabulum (7), showing the spacer best fitted into the correct position (9) inside the cavity of the acetabulum.

Figure (9) is a three-dimensional view for the femur spacer and the acetabulum (7), showing the spacer best fitted into the correct position (9) inside the cavity of the acetabulum.

Figure (10) is a two-dimensional internal sector for the femur (10) illustrating the internal cavity (1 1) thereof.

Figure (11) is a two-dimensional front elevation for the femur spacer and the femur

(10) , showing the spacer best fitted into the correct position (12) inside the cavity of the femur.

Figure (12) is a two-dimensional elevation for the femur spacer and the femur (10), showing the stem (2) best fitted into the correct position inside the internal cavity

(11) of the femur.

Figure (13) is a two-dimensional front elevation for the acetabulum (7) and the femur (10), showing the femur spacer placed there between (13).

Figure (14) is a two-dimensional side elevation for the acetabulum (7) and the femur (10), showing the femur spacer placed there between (13).

Figure (15) is a three-dimensional view for the acetabulum (7) and the femur (10), showing the femur spacer placed there between (13).

Claims

1. A patient-specific spacer for usage in cases of infections in the original prosthetic femur joint or fractures in the femur joint, wherein the said spacer is designed by the use of the patient's CT scan, which is converted into a 3D model, thereby determining the sizes and dimensions of the spacer according to the anatomic profile of the patient's joint, the cavities of the femur and acetabulum, the latter representing the two bones forming the femur joint, and wherein the spacer is produced by means of 3D printing using implantable medical materials.

2. A patient-specific spacer according to claim (1), wherein the said spacer comprises three parts; a stem, a head, and a nerve connecting the said stem and the said head.

3. The stem, according to claim (2), wherein the said stem in the spacer has a conical shape with a larger diameter in the upper part and a smaller diameter in the lower part to facilitate its insertion and fixation inside the cavity of the femur.

4. The head, according to claim (2), wherein the said head in the spacer has a spherical shape with the lower third thereof being cut to ensure the free movement of the head inside the cavity of the acetabulum and to facilitate its connection with the nerve connecting the stem.

5. The nerve, according to claim (2), wherein the said nerve connecting the stem and head of the spacer has a square shape to move between the conical shape of the stem and the spherical shape of the head, and wherein the said square shape supports the body of the spacer and helps in balancing its mass and withstanding the loads resulting from the patient's weight and the daily fixed and motor activities.

6. A patient-specific spacer according to claim (1), wherein the said spacer comprises internal paths with one-sided open ends to install surgical metal wires therein in order to maintain the stability and rigidness of the spacer and help it to withstand loads resulting from the patient's weight and daily activities.

7. The internal paths, according to claim (6), wherein the said internal paths in the spacer extend longitudinally across the stem and transversely across the head.

8. The internal paths, according to claim (6), wherein the said longitudinal path passing across the stem has an open end and a closed end to maintain the stability of the surgical metal wire and prevent possible inflections or fractures in the stem that may occur due to shear and vertical loads resulting from the patient's weight and daily fixed and motor activities.

9. The internal paths, according to claim (6), wherein the said transversal path passing across the head has an open end and a closed end to maintain the stability of the surgical metal wire and prevent possible fractures in the head that may occur due to vertical and horizontal loads resulting from the patient's weight and daily fixed and motor activities.

10. The internal paths, according to claim (6), wherein the said internal paths in the spacer extending longitudinally across the stem and transversally across the head may be filled with the necessary antibiotics to ensure no postoperative complications.

1 1. A patient-specific spacer according to claim (1), wherein the said spacer has dimensions matching the dimensions and anatomic profile of the cavities and hollow parts of the femur and acetabulum, wherein the femur and acetabulum are the two bones forming the femur joint.

12. A patient-specific spacer according to claim (1), wherein the said spacer is designed according to the patient's CT scan, thereby it matches the anatomic profile of the patient's femur joint.

13. A patient-specific spacer according to claim (1), wherein the external surface of the said spacer is rough enough to enable the surgeon to coat it with medical cement to ensure its fixation in the proper position inside the cavity of the femur and the cavity of the acetabulum.

14. A patient-specific spacer according to claim (1), wherein the said spacer is made of nylon, which has physical and mechanical properties that enable it to withstand shear, vertical and horizontal loads resulting from the patient's fixed and motor activities, and wherein the said nylon is a FDA-approved material that may be implanted inside living tissues without any medical complications.