CUSTOM MADE HIP IMPLANT

Abstract

The present disclosure relates to a customized medical implant for attachment to and at least partly covering the natural femoral head of a hip joint of a subject. The medical implant includes a dome shaped shell having a height h, an inner equatorial shell radius r.sub.s, an orifice radius r.sub.o, a thickness t.sub.s at the equatorial line, and a thickness t.sub.t at the top of the dome. The implant is constructed such that one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are customized to the hip joint of the subject based on at least one 3D computed tomography image showing substantially the entirety of the natural femoral head and the acetabulum of said hip joint.

Claims

1. A customized medical implant for attachment to and at least partly covering the natural femoral head of a hip joint of a subject, said medical implant comprising a dome shaped shell having a height h, an inner equatorial shell radius r.sub.s, an orifice radius r.sub.o, a thickness t.sub.s at the equatorial line, and a thickness t.sub.t at the top of the dome, wherein one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are customized to the hip joint of the subject based on at least one 3D computed tomography image showing substantially the entirety of the natural femoral head and the acetabulum of said hip joint and wherein the thickness at the top of the dome is larger than the thickness at the equatorial line t.sub.t>t.sub.s.

2. The medical implant according to claim 1, wherein the dimensions of the medical implant are customized to the hip joint of the subject such that one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are selected by fitting a sphere to the femoral head and/or the acetabulum in said 3D computed tomography image.

3. The medical implant according to claim 1, wherein customization of the thickness t.sub.t at the top of the dome is based on a radiographic measurement of the leg length discrepancy such that leg length discrepancy can be corrected or reduced.

4. The medical implant according to claim 1, wherein customization of the orifice radius r.sub.o is selected such that r.sub.o corresponds to the maximum diameter of said femoral head, said maximum diameter optionally obtained from the 3D computed tomography image(s).

5. The medical implant according to claim 1, wherein customization of the outer equatorial shell radius is selected to correspond to the diameter of said acetabulum, said acetabulum diameter optionally determined from the radius of a circle or sphere that fits in the acetabulum in the 3D computed tomography image(s).

6. The medical implant according to claim 1, wherein customization of the height is determined from the orifice radius, the outer equatorial shell radius and the thickness of the shell.

7. A decision support system for assessing eligibility of a subject for an implant and/or for selecting one or more parameters for the implant, said implant comprising: a customized medical implant for attachment to and at least partly covering the natural femoral head of a hip joint of a subject, said medical implant comprising a dome shaped shell characterized by parameters describing a height h, an inner equatorial shell radius r.sub.s, an orifice radius r.sub.o, a thickness t.sub.s at the equatorial line, and a thickness t.sub.t at the top of the dome, wherein said decision support system is based on at least one 3D computed tomography image showing substantially the entirety of the natural femoral head and the acetabulum of said hip joint, and wherein the system comprises: a processing unit configured for extracting the shapes of the femoral head and acetabulum from said at least one 3D computed tomography image, wherein the processing unit is further configured for evaluating the shapes of the femoral head and acetabulum extracted from said at least one 3D computed tomography image to determine subject eligibility.

8. (canceled)

9. The system according to claim 7, wherein the extraction of the shapes of the femoral head and acetabulum are based on at least one intensity threshold for distinguishing at least the cortical bone from the rest of the tissue.

10. The system according to claim 7, wherein the extraction of the shapes of the femoral head and acetabulum is based on a reference scan or a reference model such that the segmentation of the reference scan can be deformed or transformed to the scan of the patient, thereby acting as a reference for segmentation of a scan.

11. The system according to claim 7, wherein the system is configured for evaluating the shape of the femoral head based on the roundness of the femoral head in at least one cross-sectional scan and/or for evaluating the shape of the acetabulum based on the roundness of the acetabulum in at least one cross-sectional scan.

12. The system according to claim 7, wherein the system is configured for selecting a patient as eligible based on a tolerance zone of the roundness of at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm.

13. The system according to claim 7, wherein the evaluation of the shape of the femoral head is based on the sphericity of the femoral head and/or wherein the evaluation of the shape of the acetabulum is based on the sphericity of the acetabulum.

14. The system according to claim 7, wherein the system is configured for selecting a patient as eligible based on a tolerance zone of the sphericity of at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm.

15. The system according to claim 7, wherein the system is configured for selecting a patient as eligible when the radius of the femoral neck below the femoral head is at least 1 mm, or at least 1.5 mm or at least 2 mm, or at least 2.5 mm lower than the radius of the femoral head.

Description

DESCRIPTION OF DRAWINGS

[0022] FIG. 1 shows a cross-sectional side view of one embodiment of the customized medical implant for attachment to the femoral head.

[0023] FIG. 2 is an example of a 3D computed tomography image of the pelvic area of a patient used for the presently disclosed invention.

[0024] FIG. 3 shows an example of a 3D computed tomography image where the femoral bone part has been isolated.

[0025] FIG. 4 shows an example of a 2D X-ray image anterior-posterior projection of both hip joints. The X-ray image is based on a computerized tomography scanning. The femoral heads are encircled by digital means.

[0026] FIG. 5 shows an example of a 2D X-ray horizontal plane of the right hip joint. The X-ray image is based on a computerized tomography scanning. The femoral head is encircled by digital means.

[0027] FIG. 6 is an example of a CT scan of both hip joints in anterior-posterior plane. Both the femoral head and the acetabulum are encircled by digital means. The diameters of the circles are also shown, which may be used as an indicator for the thickness of the potential implant.

[0028] FIGS. 7A-D are screenshots from ITK-SNAP used in one embodiment for segmentation of the scan and identification of bones and surfaces. Here, only the program with its built-in functions was used for segmentation.

[0029] FIGS. 8A-D are screenshots from ITK-SNAP used in another embodiment for segmentation of the scan and identification of bones and surfaces. Some points have been created and/or adjusted manually to create a better model of the joint.

[0030] FIG. 9 shows a surface representation of the pelvic bone from a scan. The raw scan shown on the right contains many edges and steps. A marching cubes algorithm together with a surface reconstruction algorithm is used to produce the smooth surface shown on the left.

[0031] FIG. 10 is an illustration of the scanned femoral bone (left), points on the surface of the bone used for determining implant dimensions (middle) and the bone surface with a sphere fitted to the femoral head (right).

[0032] FIG. 11 shows a visualization of the scanned bones of a hip joint and an implant calculated and customized to fit the specific joint.

DETAILED DESCRIPTION OF THE INVENTION

[0033] As mentioned earlier the implant needs to be customized in order to perfectly fit the diseased hip of the patient. Therefore, the shell is preferably constructed such that one or more of the thickness at the equatorial line t.sub.s, the thickness at the top t.sub.h the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are selected by fitting a sphere to the femoral head in said 3D computed tomography image. The shell may furthermore be constructed such that one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are selected by fitting a sphere to the acetabulum in said 3D computed tomography image. The implant should be constructed such that the implant fits between the femoral head and acetabulum in the best way possible such that pain and discomfort is relieved as much as possible. The parameters may also be determined from slices of a 3D computed tomography image, from x-ray images of the hip or alternatively by using trial and error fitting of the implant in a computer model of the hip. Furthermore, the parameters may be determined by fitting circles to 2D images of the hip joint.

[0034] Preferably the implant is constructed such that the equatorial shell radius is larger than the orifice radius r.sub.s>r.sub.o, and the height is larger than the equatorial shell radius h>r.sub.s. The orifice radius should fit the radius of the femoral head such that the implant can be pushed onto the femoral head. Selecting the orifice diameter to match the largest diameter of the femoral head means that the implant can be attached without risking damaging the femoral head. Cartilage and other soft tissue extending to and below the equatorial region of the femoral head may deform when the implant is attached and may reduce the risk of the implant becoming detached from the femoral head. In one embodiment the orifice is circular and defined by a circumferential rounded edge. This will make it easier to force the implant onto the femoral head and reduce the risk of damaging the bone in the process. Although the implant may be forced onto the femoral head it may still be customized such that it can move relative to the femoral head. Therefore, in another embodiment the medical implant is configured for at least initial unconstrained attachment to the genuine diseased femoral head.

[0035] In order for the implant to move efficiently relative to the acetabulum and with as little friction as possible, the outer surface of the shell is preferably spherical at least above the equatorial plane. More preferably the entire outer surface of the shell is spherical. The shell is preferably unconstrained at least initially after implanted in the hip. Therefore, in a further embodiment the inner surface of the shell is spherical at least above the equatorial plane. More preferably the entire inner surface of the shell is spherical. Having spherical inner and outer surfaces allows the implant to freely rotate and tilt relative to both the femoral head and the acetabulum and reduces the risk of implant impingement at the acetabular rim. Alternatively, the outer and/or inner surfaces may have other shapes such as paraboloidal or ellipsoidal. As a further means for reducing the friction, the implant is in one embodiment constructed such that the inner surface and/or the outer surface of the shell are smooth and preferably polished to obtain a surface roughness less than 0.1 mm.

[0036] In one embodiment of the invention the thickness of the shell is selected to be constant such that t.sub.s=t.sub.t. In another embodiment the thickness at the top of the dome is larger than the thickness at the equatorial line t.sub.t>t.sub.s. In yet another embodiment the inner and outer surfaces of the shell are spherical, but where the radius of curvature of the inner surface of the shell is less than the radius of curvature of the outer surface of the shell such that the thickness of the shell at the top of the dome is larger than the thickness of the shell at the equatorial line t.sub.t>t.sub.s. Having an even thickness of the shell is preferred. However, selecting a larger thickness of the shell at the top than at the equator of the shell may be used to compensate leg length discrepancy. Therefore, in yet another embodiment the thickness t.sub.t at the top of the dome is selected based on a radiographic measurement of the leg length discrepancy such that leg length discrepancy can be corrected or reduced. This method is preferred when the customization of the implant allows for increased thickness at the top of the shell and when the patient's leg having a diseased hip is shorter than the other leg.

[0037] The thickness of the shell should be selected to be as large as possible based on the 3D computed tomography image of the joint. This will increase the strength of the implant such that the risk of damage or deformation is reduced and will make the implant more durable. In one embodiment of the invention the minimum thickness of the shell is selected to be at least 0.6 mm, or at least 0.75 mm, or at least 1.0 mm, or at least 1.2 mm, or at least 1.5 mm, or at least 1.8 mm, or at least 2.0 mm, or at least 2.5 mm. The minimum thickness of the shell may also depend on the size of the joint it is inserted into. In some embodiments the thickness of the shell is at least 1.0 mm for humans and at least 0.75 mm for dogs. In another embodiment the edge at the orifice of the shell is rounded such that the radius of curvature is half of the thickness of the shell at the orifice. This means that there are no sharp edges on the implant that could potentially damage the bone during attachment of the implant to the femoral head or after surgery.

[0038] As mentioned earlier, the implant may be constructed such that the thickness of the shell varies in order to reduce or correct for leg length discrepancy. In one embodiment this is achieved by displacing the inner surface of the implant compared to the outer surface, such that they do not share a common center. For example, the inner surface could be displaced downward (towards the orifice) by some amount, thereby increasing the thickness at the top of the implant.

[0039] In order for the medical implant to be attachable to the femoral head, the orifice should be large enough for the implant to be forced onto the femoral head. Therefore, in one embodiment the orifice radius r.sub.o is selected such that r.sub.o corresponds to or is larger than the maximum diameter of the bone material of the genuine femoral head in said 3D computed tomography image. The implant is preferably constructed such that the height of the shell is greater than the equatorial shell radius such that the rounded or spherical shape of the shell extends below the equatorial plane of the shell, thereby allowing better movement of the joint. In another embodiment the ratio between the height and equatorial shell radius h/r.sub.s is therefore selected to be at least 1.24, or at least 1.27, or at least 1.30, or at least 1.32, or at least 1.35, or at least 1.38.

[0040] Alternatively the ratio between the height and equatorial shell radius h/r.sub.s is selected to be less than 1.40, or less than 1.35, or less than 1.32, or less than 1.30, or less than 1.27, or less than 1.24. Because the orifice is equal to or larger than the femoral head and the height of the shell is larger than the equatorial shell radius, the femoral head will be slightly smaller than the equatorial shell radius. This should not cause complications as it allows the implant to be initially unconstrained and move relative to the femoral head. Furthermore, cartilage and other soft tissue extending to and below the equatorial area of the femoral head may reversibly deform when the implant is forced over the femoral head and then at least partly return to the original shape. This will help ensuring that the implant is firmly attached and reduces the risk of the implant detaching from the joint. Over time the implant may become attached to either the femoral head or the acetabulum which will occur by natural tissue forming around the implant.

[0041] In a preferred embodiment, the outer equatorial shell radius is determined from the radius of a circle or sphere that fits in the acetabulum in said at least one 3D computed tomography image. Matching the equatorial shell radius with the radius of a circle or sphere that fits in the acetabulum ensures a good fit between the implant and the acetabulum. Thereby, pain and discomfort from the implant are reduced.

[0042] The selected orifice radius, outer equatorial radius and shell thickness based on the at least one 3D computed tomography image are preferably used for determining the parameters needed in order to construct the implant. In one embodiment the height may also be determined from the orifice radius, the outer equatorial shell radius and the thickness of the shell. Additionally, a possible measured difference in leg length may be used for determining if and how much the thickness of the shell should vary.

[0043] In some cases the femoral head may not be close to spherical and may e.g. have a large diameter in one direction and a smaller diameter in another direction. It may then be advantageous to deform the implant in a reversible manner prior to attachment to the femoral head such that the implant becomes at least partly elliptical. The implant can then be forced onto the femoral head in its deformed state and then return at least partly to its original shape.

[0044] The material used for fabricating the shell may be a metal or an alloy. In a preferred embodiment the material for the shell is a cobalt chromium molybdenum alloy such as the Co28Cr6Mo alloy such as the Wrought (UNS R31537, UNS R31538 or UNS R31539) alloys. In another embodiment the material for the shell is a steel alloy such as 316LVM, or a titanium alloy such as Ti6Al4V.

[0045] The present invention is furthermore related to a method for determining the most suitable hip joint treatment for a subject. This method includes the step of obtaining at least one 3D computed tomography image of the diseased hip. In some cases the two parts of the joint may appear too close together in the 3D computed tomography image. This may be caused by damaged or missing cartilage in the joint. In such cases it is difficult to separate the femoral head and the acetabulum for customization of the implant. Therefore, in one embodiment of the invention the at least one 3D computed tomography image of the hip is performed with traction applied to the leg. Joint traction may improve the 3D computed tomography such that the femoral and acetabular bones become discernable in cases where it is otherwise problematic. The traction force applied to the leg may in some embodiment be at least 10 kg or about 100 N. Traction may be applied using a traction brace that applies force between the pelvis and the leg e.g. the thigh, the calf or preferably the foot. The traction brace should preferably be constructed from non-metallic materials in order to not interfere with the 3D computed tomography scan. In another embodiment an x-ray fluoroscopy image of the hip of the subject is used to determine if traction to the leg is necessary during 3D computed tomography imaging of the hip.

[0046] The femoral head and the acetabulum should preferably be sufficiently preserved for the implant to alleviate the pain as much as possible. The shapes of the femoral head and acetabulum obtained from the at least one 3D computed tomography are evaluated in order to assess patient eligibility. Therefore, in one embodiment of the method the evaluation of the shape of the femoral head is based on the roundness of the femoral head in at least one cross-sectional scan. In another embodiment the evaluation of the shape of the acetabulum is based on the roundness of the acetabulum in at least one cross-sectional scan. In yet another embodiment the roundness should have a tolerance zone of at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm for the patient to be eligible for the medical implant. The tolerance zone means that e.g. the femoral head in a cross-sectional scan should fit within two circles having a difference in radii equal to the tolerance. In yet another embodiment the roundness should be at least 0.70, or at least 0.80, or at least 0.85, or at least 0.90, or at least 0.93, or at least 0.96 for the patient to be eligible for the medical implant.

[0047] The roundness is preferably determined from a 2D cross-sectional scan of the femoral head or acetabulum. However, the evaluation may also be based on the sphericity, which is preferably assessed from the shapes extracted from the at least one 3D computed tomography image. In one embodiment of the method the evaluation of the shape of the femoral head is based on the sphericity of the femoral head. In another embodiment the evaluation of the shape of the acetabulum is based on the sphericity of the acetabulum. In yet another embodiment the sphericity should have a tolerance zone of at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm for the patient to be eligible for the medical implant. Similar to the roundness, this means that the shape of e.g. the femoral head should fit between two spheres having a difference in radii equal to the tolerance. In another embodiment the sphericity should be at least 0.80 or at least 0.85, or at least 0.9, or at least 0.93, or at least 0.95, or at least 0.98 for the patient to be eligible for the medical implant.

[0048] Instead of or in addition to determining roundness or sphericity of the femoral head and/or acetabulum, the scan of the joint may in another embodiment also be used to fit a circle or sphere to the femoral head and/or acetabulum. Such a fit may be performed by selecting points belonging to the femoral head or acetabulum and use for example the method of least squared to fit a circle or sphere to the selected points. Selecting the points belonging to the femoral head or acetabulum is preferably automatic. In another embodiment the points may be selected manually. In yet another embodiment, automatically selected points may be adjusted manually by including and/or excluding and/or moving points. Customizing the implant may also be performed by fitting the smallest sphere that can include the entire femoral head or the largest sphere fitting inside the acetabulum.

[0049] When the implant is attached to the subject, the bone should preferably be shaped such that the implant cannot easily detach from the femoral head. Therefore, in one embodiment the radius of the femoral neck below the femoral head should be at least 1 mm, or at least 1.5 mm or at least 2 mm, or at least 2.5 mm lower than the radius of the femoral head for the patient to be eligible for the medical implant. This will keep the implant attached to the femoral head. However, it is still preferred that the implant is at least initially unconstrained after attachment to the femoral head. Soft tissue may then develop at the implant which may lead to the implant becoming attached to the femoral head or the acetabulum. In a further embodiment of the invention, the thickness at the top of the shell t.sub.t and the thickness at the equatorial line t.sub.s are selected based on measurements of the length of both legs of the subject. This is used to determine leg length discrepancy of the subject such that this measure may be used when customizing the implant. The thickness of the implant may then be used for reducing or correcting leg length discrepancy when possible.

[0050] The present disclosure is furthermore related to a decision support system for assessing eligibility of a subject for the customized medical implant and/or for selecting the parameters for the implant. This system is based on at least one 3D computed tomography image of the diseased joint. The system further comprises a processing unit configured for extracting the shapes of the femoral head and acetabulum from said at least one 3D computed tomography image and for evaluating the shapes of the femoral head and acetabulum to assess subject eligibility. In one embodiment the processing unit is further configured for determining the roundness of the femoral head and/or acetabulum in at least one cross-sectional scan of a hip joint of said subject. In another embodiment the processing unit is further configured for determining the sphericity of the femoral head and/or acetabulum in the at least one 3D computed tomography image of a hip joint of said subject. In yet another embodiment the processing unit is further configured for determining the degree of narrowing at the femoral neck compared with the femoral head.

[0051] The decision support system may further comprise a non-transitive, computer-readable storage device for storing instructions that, when executed by a processor, performs a method for assessing eligibility of a subject for the customized medical implant and/or for selecting the parameters for the implant as herein described. The system may comprise a mobile device comprising a processor and a memory and being adapted to perform the method but it can also be a stationary system or a system operating from a centralized location, and/or a remote system, involving e.g. cloud computing. The invention further relates to a computer program having instructions which when executed by a computing device or system cause the computing device or system to identify an unauthorized access of an account of an online service according to the described method. Computer program in this context shall be construed broadly and include e.g. programs to be run on a PC or software designed to run on smartphones, tablet computers or other mobile devices.

[0052] In order to more carefully screen and select patients eligible for the customized medical implant, the decision support system is in one embodiment configured to include certain criteria for the patient. Criteria for a patient to be eligible for the implant may include patients with clinical complaints with unilateral or bilateral hip osteoarthritis with a preserved roundness of the femoral head, where conservative treatment has become unsuccessful and insufficient. Criteria excluding a patient from eligibility may be selected from the group of: secondary osteoarthritis following congenital hip dislocation, Calve-Legg-Perthes disease, infectious hip joint disease with deformed femoral head, moderate to severe hip dysplasia, hip fracture surgery with pinning or dynamic hip screw or intramedullary nails with hip screw, slipped femoral capital epiphysiolysis, acetabular fractures, aseptic femoral head necrosis and dysbaric osteonecrosis.

[0053] The decision support system is preferably configured for segmentation of the different bones in the scan such that the surfaces of the bones may be analyzed in order to customize the implant. The segmentation of the bone may be carried out manually or automatically by a computer or a combination where a computer provides a suggestion for the segmentation which is subsequently adjusted manually. In one embodiment the extraction of the shapes of the femoral head and acetabulum are based on at least one intensity threshold for distinguishing at least the cortical bone from the rest of the tissue. The threshold of the scan may be adjusted such that it identifies the rapid change in values of the scan at the edge of the cortical bone. This threshold value may be set manually or automatically. The segmentation process is preferably automatic. However, it may happen that software for automatic segmentation of the scan will not yield good results. In such cases it may be necessary to adjust the segmentation manually. Such cases may be when the cortical bone is thin or when the cortical bone surface of two bones are only separated by a small distance.

[0054] A model for automatic segmentation can be constructed in various ways. One method is to use a reference model for segmentation of subsequent scans. Therefore, in another embodiment the extraction of the shapes of the femoral head and acetabulum is based on a reference scan or a reference model such that the segmentation of the reference scan can be deformed or transformed to the scan of the patient, thereby acting as a reference for segmentation of a scan.

[0055] In another embodiment a model for automatic segmentation may be based on a large dataset. This can be achieved by having a number of scans that have been manually adjusted to obtain good segmentation of the bones. This dataset of segmented scans may then be used for the model to learn anatomic variations between subjects and use this to better identify and segment bones in new scans. This may provide better automatic segmentation than other models.

[0056] The at least one 3D computed tomography image will consist of a number of voxels giving the image a given resolution. Because of the finite, and in some cases limited, number of voxels, the image may appear rough containing many steps and edges. In one embodiment the image is smoothened by a surface reconstruction algorithm. In one embodiment the marching cubes algorithm is applied to provide a polygonal mesh giving the model a smoother surface. In another embodiment a surface reconstruction algorithm, such as the Markov ransom field surface reconstruction algorithm, is applied to provide an even smoother surface than the polygonal mesh.

DETAILED DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 shows a cross-sectional view of one embodiment of the customized medical implant 1 for relieving pain in a diseased hip joint. The dome-shaped shell 1 is in this embodiment spherically shaped. The implant has an orifice 5 at the bottom of the shell such that the shell can be mounted on the femoral head of a patient. The implant is furthermore characterized by an outer shell radius 2 and an inner shell radius 3. The edge 4 at the orifice is preferably rounded.

[0058] FIG. 2 is an example of a 3D computed tomography image of a patient showing both hip joints. The top part of the femoral bone 7 is seen at the bottom of the image along with the femoral neck 8 and femoral head 9. The entire pelvis 6 is visible in the image including the outer edge of the acetabulum 10 where the femoral head 9 connects to the pelvis 6.

[0059] FIG. 3 is an example of the femoral bone part isolated from a 3D computed tomography image of a hip joint. The femoral bone 7 together with the femoral neck 8 and the femoral head 9 are shown in the image. Separating the femoral bone part from the pelvic bone part, i.e. the acetabulum, is useful when determining the optimum parameters for the customized medical implant.

[0060] FIG. 4 shows an example of a 2D X-ray image anterior-posterior projection of both hip joints. The image is based on a computerized tomography scanning. The image shows the femoral bone 7, femoral neck 8, femoral head 9, acetabulum 10 and part of the pelvic bone 6. In the image both femoral heads are encircled 11 by digital means. This is used to determine the diameter of the customized implant.

[0061] FIG. 5 shows an example of a 2D X-ray horizontal plane of the right hip joint of a patient. Again, the femoral bone 7, femoral neck 8, femoral head 9, acetabulum 10 and part of the pelvic bone 6 are shown in the image. Such images may be used to determine parameters for the customized implant and for determining eligibility for the surgery. In this case the femoral head 9 is well preserved and has a high degree of roundness. Again, the femoral head 9 is encircled 11 by digital means. The image furthermore shows clear separation between the femoral head 9 and acetabulum 10 of the hip joint. In cases with less separation, traction to the leg may be necessary for sufficient separation between the femoral head 9 and the acetabulum 10.

[0062] FIG. 6 is an example of a CT scan of a patient showing both hip joints in anterior-posterior plane. Both hips show radiological signs of osteoarthritis with subchondral bone sclerosis and rim osteophytes. The femoral head and acetabulum are clearly separated for both hips. The femoral head of each hip is encircled 11 by digital means. The diameter 13 of this circle is also shown. Similarly, the acetabulum of each hip is encircled 12 by digital means and again the diameter 14 is shown. The diameters of the femoral head and acetabulum may be used as an indicator for the thickness of the potential implant.

[0063] FIGS. 7A-D show screenshots from ITK-Snap used in one embodiment of the invention. The program is used for segmentation of the scan and identification of bones and surfaces. For this embodiment only the program with its built-in functions was used for segmentation. In FIG. 7A the highlighted areas show the segmented bones with the femoral head 9 and the pelvic bone 6 clearly separated. FIG. 7B shows a different angle with less clear separation between the femoral head 9 and acetabulum 10. FIGS. 7C and 7D each show other angles of the segmented bones for this embodiment.

[0064] FIGS. 8A-D are screenshots from ITK-Snap used in another embodiment for segmentation of the scan and identification of bones and surfaces. In this embodiment some points have been created and/or adjusted manually to create a better model and better segmentation of the joint. It may sometimes be necessary to adjust and/or create and/or delete and/or move some points of the segmented bones manually to obtain a better and/or smoother and/or more correct model of the joint. FIG. 8A shows the same scan as FIG. 7A, but now with better segmentation due to manual adjustment such that each bone is identified and highlighted in different grayscales. FIGS. 8B-D show similar views of the joint as FIGS. 7B-D of the manually adjusted segmentation with different bones highlighted in different grayscales.

[0065] FIG. 9 shows a surface representation of the pelvic bone from a scan. The raw scan shown on the right may contain edges and steps because of the resolution of the scan. The rough surface may be smoothened using various techniques. One method shown in the embodiment to the left is to use a marching cubes algorithm together with a surface reconstruction algorithm to yield a higher quality surface of the bone for customizing the implant.

[0066] FIG. 10 shows is an illustration of the scanned and smoothened femoral bone. Points on the surface are shown in the middle part of the figure. In this embodiment the points belonging to the femoral head have been manually selected. This process could also be automatic, or an automatic selection of points could be suggested and then manually corrected if needed. The points belonging to the femoral head are used to fit a sphere to the femoral head (right). This is used to determine the radius of said sphere which is used to determine the inner equatorial shell radius of the implant. The sphere may be fitted using the method of least squares. The sphere may also be fitted to determine the smallest sphere fitting on the outside of the femoral head.

[0067] FIG. 11 shows the scanned bones of a hip joint and an implant according to one embodiment of the invention. The left part shows the segmented bones as obtained from the scan with subsequently smoothened surfaces. An implant calculated and customized to fit the specific joint is shown inserted into the joint in the middle part of the figure. The right part shows of the figure shows a smoothened and slightly transparent version of the implant inserted in the joint.

FURTHER DETAILS OF THE PRESENT DISCLOSURE

[0068] The present disclosure may be described by the following items: [0069] 1. A customized medical implant for attachment to and at least partly covering the natural femoral head of a hip joint of a subject, said medical implant comprising a dome shaped shell having a height h, an inner equatorial shell radius r.sub.s, an orifice radius r.sub.o, a thickness t.sub.s at the equatorial line, and a thickness t.sub.t at the top of the dome, wherein one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are customized to the hip joint of the subject based on at least one 3D computed tomography image showing substantially the entirety of the natural femoral head and the acetabulum of said hip joint. [0070] 2. The medical implant according to item 1, wherein one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are selected by fitting a sphere to the femoral head in said 3D computed tomography image. [0071] 3. The medical implant according to any of the preceding items, wherein one or more of the thickness t.sub.s, the thickness t.sub.t, the equatorial shell radius r.sub.s, the orifice radius r.sub.o and the shell height h are selected by fitting a sphere to the acetabulum in said 3D computed tomography image. [0072] 4. The medical implant according to any of the preceding items, wherein the equatorial shell radius is larger than the orifice radius r.sub.s>r.sub.o, and the height is larger than the equatorial shell radius h>r.sub.s. [0073] 5. The medical implant according to any of the preceding items, wherein the orifice is circular and defined by a circumferential rounded edge. [0074] 6. The medical implant according to any of the preceding items, wherein the implant is configured for at least initial unconstrained attachment to the natural diseased femoral head. [0075] 7. The medical implant according to any of the preceding items, wherein the outer surface of the shell is spherical at least above the equatorial plane. [0076] 8. The medical implant according to any of the preceding items, wherein the entire outer surface of the shell is spherical. [0077] 9. The medical implant according to any of the preceding items, wherein the inner surface of the shell is spherical at least above the equatorial plane. [0078] 10. The medical implant according to any of the preceding items, wherein the entire inner surface of the shell is spherical. [0079] 11. The medical implant according to any of the preceding items, wherein the inner surface and/or the outer surface of the shell are smooth and preferably polished to obtain a surface roughness less than 0.1 mm. [0080] 12. The medical implant according to any of the preceding items, wherein the thickness of the shell is selected to be constant such that t.sub.s=t.sub.t. [0081] 13. The medical implant according to any of items 1 to 11, wherein the thickness at the top of the dome is larger than the thickness at the equatorial line t.sub.t>t.sub.s. [0082] 14. The medical implant according to any of the preceding items, wherein the inner and outer surfaces of the shell are spherical, but where the radius of curvature of the inner surface of the shell is less than the radius of curvature of the outer surface of the shell such that the thickness of the shell at the top of the dome is larger than the thickness of the shell at the equatorial line t.sub.t>t.sub.s. [0083] 15. The medical implant according to item 14, wherein the thickness t.sub.t at the top of the dome is selected based on a radiographic measurement of the leg length discrepancy such that leg length discrepancy can be corrected or reduced. [0084] 16. The medical implant according to any of the preceding items, wherein the minimum thickness of the shell is selected to be at least 0.6 mm, or at least 0.75 mm, or at least 1.0 mm, or at least 1.2 mm, or at least 1.5 mm, or at least 1.8 mm, or at least 2.0 mm, or at least 2.5 mm. [0085] 17. The medical implant according to any of the preceding items, wherein the edge at the orifice of the shell is rounded such that the radius of curvature is half of the thickness of the shell at the orifice. [0086] 18. The medical implant according to any of the preceding items, wherein the orifice radius r.sub.o is selected such that r.sub.o corresponds to or is larger than the maximum diameter of the genuine femoral head in said 3D computed tomography image. [0087] 19. The medical implant according to any of the preceding items, wherein the outer equatorial shell radius is determined from the radius of a circle or sphere that fits in the acetabulum in said at least one 3D computed tomography image. [0088] 20. The medical implant according to any of the preceding items, wherein the height is determined from the orifice radius, the outer equatorial shell radius and the thickness of the shell. [0089] 21. The medical implant according to any of the preceding items, wherein the ratio between the height and equatorial shell radius h/r.sub.s is selected to be at least 1.24, or at least 1.27, or at least 1.30, or at least 1.32, or at least 1.35, or at least 1.38. [0090] 22. The medical implant according to any of the preceding items, wherein the ratio between the height and equatorial shell radius h/r.sub.s is selected to be less than 1.40, or less than 1.35, or less than 1.32, or less than 1.30, or less than 1.27, or less than 1.24. [0091] 23. The medical implant according to any of the preceding items, wherein the material for the shell is a metal or an alloy. [0092] 24. The medical implant according to any of the preceding items, wherein the material for the shell is a cobalt chromium molybdenum alloy such as the Co28Cr6Mo alloy such as the Wrought (UNS R31537, UNS R31538 or UNS R31539) alloys. [0093] 25. The medical implant according to any of the preceding items, wherein the material for the shell is a steel alloy such as 316LVM, or a titanium alloy such as Ti6Al4V. [0094] 26. A method for determining the most suitable hip joint treatment for a subject, comprising: [0095] obtaining at least one 3D computed tomography image showing substantially the entirety of the femoral head and the acetabulum of a hip joint of said subject, [0096] extracting the shape of the femoral head and/or the acetabulum from said at least one 3D computed tomography image, and [0097] evaluating the shapes of the femoral head and/or the acetabulum to determine the most suitable treatment. [0098] 27. The method according to item 26, wherein the at least one 3D computed tomography image of the hip is performed with traction applied to the leg. [0099] 28. The method according to item 27, wherein the traction force applied to the leg is at least 10 kg or at least 100 N. [0100] 29. The method according to any of items 26 to 28, wherein an x-ray fluoroscopy image of the hip of the subject is used to determine if traction to the leg is necessary during 3D computed tomography imaging of the hip. [0101] 30. The method according to any of items 26 to 29, wherein the evaluation of the shape of the femoral head is based on the roundness of the femoral head in at least one cross-sectional scan. [0102] 31. The method according to any of items 26 to 30, wherein the evaluation of the shape of the acetabulum is based on the roundness of the acetabulum in at least one cross-sectional scan. [0103] 32. The method according to any of items 30 to 31, wherein the roundness should have a tolerance zone of at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm for the patient to be eligible for the medical implant according to any of items 1 to 25. [0104] 33. The method according to any of items 30 to 32, wherein the roundness should be at least 0.70, or at least 0.80, or at least 0.85, or at least 0.90, or at least 0.93, or at least 0.96 for the patient to be eligible for the medical implant according to any of items 1 to 25. [0105] 34. The method according to any of items 26 to 33, wherein the evaluation of the shape of the femoral head is based on the sphericity of the femoral head. [0106] 35. The method according to any of items 26 to 34, wherein the evaluation of the shape of the acetabulum is based on the sphericity of the acetabulum. [0107] 36. The method according to any of items 34 to 35, wherein the sphericity should have a tolerance zone of at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm for the patient to be eligible for the medical implant according to any of items 1 to 25. [0108] 37. The method according to any of items 34 to 36, wherein the sphericity should be at least 0.80 or at least 0.85, or at least 0.9, or at least 0.93, or at least 0.95, or at least 0.98 for the patient to be eligible for the medical implant according to any of items 1 to 25. [0109] 38. The method according to any of items 26 to 37, wherein the radius of the femoral neck below the femoral head should be at least 1 mm, or at least 1.5 mm or at least 2 mm, or at least 2.5 mm lower than the radius of the femoral head for the patient to be eligible for the medical implant according to any of items 1 to 25. [0110] 39. The method according to any of items 26 to 38, wherein the thickness t.sub.t and the thickness t.sub.s are selected based on measurements of the length of both legs of the subject. [0111] 40. A decision support system for assessing eligibility of a subject for the customized medical implant according to any of items 1 to 25 and/or for selecting the parameters for the customized medical implant, given at least one 3D computed tomography image showing substantially the entirety of the femoral head and the acetabulum of a hip joint of said subject, the system comprising: [0112] a processing unit configured for extracting the shapes of the femoral head and acetabulum from said at least one 3D computed tomography image, [0113] wherein the processing unit is further configured for evaluating the shapes of the femoral head and acetabulum extracted from said at least one 3D computed tomography image to determine subject eligibility. [0114] 41. The system according to item 40, wherein the processing unit is further configured for determining the roundness of the femoral head and/or acetabulum in at least one cross-sectional scan of a hip joint of said subject. [0115] 42. The system according to any of items 40 to 41, wherein the processing unit is further configured for determining the sphericity of the femoral head and/or acetabulum in the at least one 3D computed tomography image of a hip joint of said subject. [0116] 43. The system according to any of items 40 to 42, wherein the processing unit is further configured for determining the degree of narrowing at the femoral neck compared with the femoral head.