Patent Publication Number: US-2021177605-A1

Title: Hip joint device and method

Description:
TECHNICAL FIELD 
     The present invention relates generally to medical devices for implantation in a hip joint. 
     BACKGROUND ART 
     The hip joint is a synovial joint, joining the pelvis to the proximal portion of the femoral bone. Synovial joints are the most common types of joints in mammals, and are typical of nearly all limb joints. The contacting surfaces of said the pelvic, the acetabulum, and the contacting surface of the femoral bone, the caput femur, are smooth and rounded, and covered by articular cartilage. A synovial membrane, encapsulates the joint, forming a hip joint cavity, which contains synovial fluid. Outside the synovial membrane is a fibrous capsule and ligaments, forming an articular capsule. 
     There are both natural and pathological processes leading to deteriorated joint function. With age and wear, the articular cartilage becomes less effective as a shock absorber and a lubricated surface. Different degenerative joint diseases, such as arthritis, osteoartrithis, or osteoarthrosis, accelerate the deterioration. 
     Hip joint Osteoarthritis is a syndrome in which low-grade inflammation results in pain in the hip joints, caused by abnormal wearing of the Cartilage that acts as a cushion inside if the hip joint. This abnormal wearing of the cartilage also results in a decrease of the joints lubricating fluid called Synovial fluid. Hip joint Osteoarthritis is estimated ID affect 80% of all people over 65 years of age, in more or less serious forms. 
     The present treatment for hip osteoarthritis comprises NSAID drugs, local injections of Hyaluronic acid or Glucocorticoid ID help lubricating the hip joint, and replacing parts of the hip joint with a prosthesis through hip joint surgery. 
     The replacing of parts of the hip joint is one of the most common surgeries to date performed at hundreds of thousands of patients in the world every year. The most common method comprises placing a metal prosthesis in lemur and a plastic bowl in Acetabulum. This operation is done through an incision in the hip and upper thigh and through Fascia Iata and the lateral muscles of the thigh. To get access to the joint, the supporting Capsule attached to lemur and Ilium needs ID be penetrated, making it difficult to get a fully functional joint after the surgery. Femur is then cut at the neck with a bone saw and the prosthesis is placed in femur either with bone cement or without Acetabulum is slightly enlarged using an Acetabular reamer, and the plastic bowl is positioned using screws or bone cement. 
     The complications after hip joint surgery includes dislocation of the hip joint and loosening of the prosthesis from its fixation in the femoral bone. The loosening and/or dislocation of the prosthesis could be induced by an abnormal strain being placed on the hip joint from e.g. the patient falling or nuking a rapid movement of the hip, or by a bodily macrophage reaction. 
     SUMMARY 
     A medical device for implantation in a hip joint of a patient is provided. The medical device is adapted to be fixated to the femoral bone of the patient. The medical device comprises an inner and an outer surface, wherein a contacting portion of said inner surface is spherical and adapted to face the center of the hip joint when said medical device is implanted, and wherein said medical device is adapted to receive a prosthetic replacement for the caput femur fixated to the pelvic bone having a spherical portion. The medical device comprises at least one extending portion, extending said contacting portion of said inner surface such that said at least one extending portion clasps said spherical portion of said prosthetic replacement for the caput femur, such that said spherical portion is restrained in said medical device. 
     According to one embodiment, the medical device is adapted ID receive a prosthetic replacement for the caput femur having a spherical portion, wherein said prosthetic replacement for the caput femur is adapted to be fixated ID the pelvic bone by a connection via an elongated portion fixated to said spherical portion of said prosthetic caput femur. The inner surface comprises an equator line, being the largest circular circumference of said inner contacting surface, being a surface adapted to be in contact with said caput femur, or prosthetic replacement therefor, and the at least one extending portion passes beyond said equator line, such that the end portion of said contacting portion of said inner surface forms a circular extension line having a smaller circumference than said equator line. The at least one extending portion circumferentially extends discontinuously along said equator line, such that a portion of said elongated member can be placed between said extension line and said equator line. 
     A medical device for implantation in a hip joint is further provided. The medical device is adapted to be fixated to the femoral bone and receive a prosthetic replacement for the caput femur having a spherical portion, wherein said prosthetic replacement for the caput femur is adapted to be fixated to the pelvic bone by a connection via an elongated portion fixated to said spherical portion of said prosthetic caput femur. An inner surface comprises an equator line, being the largest circular circumference of said inner surface, at least one extending portion passes beyond said equator line, such that the end portion of said contacting portion of said inner surface forms a circular extension line having a smaller circumference than said equator line, and said at least one extending portion circumferentially extends discontinuously along said equator line, such that a portion of said elongated member can be placed between said extension line and said equator line. 
     According to one embodiment, said extension line is placed dorsal to the equator line, when the medical device is implanted. 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, dorsal to the right-left axis of pelvis when being in the defined base position (further disclosed with reference to  FIG. 1 b   ). 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, dorsal to the coronal pelvis plane PXY and proximal to the horizontal pelvis PXZ plane when being in the base position. 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, dorsal to the coronal pelvis plane PXY and distal to the horizontal pelvis PXZ plane when being in the base position. 
     According to one embodiment, one extending portion extends circumferentially along said equator line dorsal to the coronal pelvis plane PXY and proximal to the horizontal pelvis PXZ plane, and one extending portion extends dorsal to the coronal pelvis plane PXY and distal to the horizontal pelvis PXZ plane when being in the base position. 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, in the proximal quadrant of the equator line when being in the base position. 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, in the distal quadrant of the equator line when being in the base position. 
     According to one embodiment, two extending portions extends circumferentially along said equator line, in the distal and proximal quadrant thereof when being in the base position. 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, in the proximal and dorsal quadrant thereof when being in the base position. 
     According to one embodiment, said at least one extending portion extends circumferentially along said equator line, in the distal and dorsal quadrant thereof when being in the base position. 
     According to one embodiment, at least one extending portion extends circumferentially along said equator line, in the distal, dorsal and proximal quadrant thereof when being in the base position. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said second portion circumferentially extends along at least ¼ of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said second portion circumferentially extends along at least ⅓ of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said second portion circumferentially extends along at least ½ of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said first portion circumferentially extends along at least ¼ of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said first portion circumferentially extends along at least ⅓ of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said first portion circumferentially extends along at least ½ of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said first portion circumferentially extends along at least 1/10 of said circular equator line. 
     According to one embodiment, at least a first portion of said medical device is an extending portion, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said first portion circumferentially extends along at least 1/10 of said circular equator line, and said second portion circumferentially extends along at least ¼ of said circular equator line. 
     According to one embodiment, at least two first portions of said medical device are extending portions, extending beyond said circular equator line, and at least a second portion is a portion not extending beyond said circular equator line, wherein said first portions each circumferentially extends along at least 1/10 of said circular equator line, and said second portion circumferentially extends along at least ¼ of said circular equator line. 
     According to one embodiment, at least two first portions of said medical device are extending portions, extending beyond said circular equator line, and wherein one of said extending portions extends further than the other extending portion. 
     According to one embodiment, said medical device further comprises two second portions not extending beyond said circular equator line, and wherein said two first extending portion circumferentially extends along said equator line between said two second portions. 
     According to one embodiment, said medical device further comprises at least one hole, and wherein said at least one hole is adapted to receive a fixating member, for fixating said medical device to the femoral bone. 
     According to one embodiment, said hole is adapted to receive a screw for fixating said medical device to the femoral bone. 
     According to one embodiment, said medical device comprises at least one extending portion adapted to clasp the caput femur, or a prosthetic caput femur, for restraining said caput femur, or prosthetic caput femur in said medical device, and wherein said medical device is adapted to release the caput femur or prosthetic caput femur from said medical device when a predetermined strain is placed on said medical device. 
     According to one embodiment, said extending portion, when implanted, is adapted to be placed such as to restrict the motion range of the hip joint, and wherein said extending portion is adapted to be placed such that adduction is restricted more degrees than flexion. 
     According to one embodiment, said extending portion, when implanted, is adapted to be placed such as to restrict the motion range of the hip joint, and wherein said extending portion is adapted to be placed such that abduction is restricted more degrees than flexion. 
     According to one embodiment, said extending portion, when implanted, is adapted to be placed such as to restrict the motion range of the hip joint, and wherein said extending portion is adapted to be placed such that adduction is restricted more degrees than extension. 
     According to one embodiment, said extending portion, when implanted, is adapted to be placed such as to restrict the motion range of the hip joint, and wherein said extending portion is adapted to be placed such that abduction is restricted more degrees than extension. 
     The medical device could further comprise a prosthetic replacement for the caput femur, adapted to be received in the bowl shaped inner surface, wherein said prosthetic replacement for the caput femur replacement comprises a spherical portion and an elongated member, adapted to be fixated to the pelvic bone by the elongated member being fixated to said spherical portion of said prosthetic replacement for the caput femur, wherein
         a) said inner surface comprises an equator line, being the largest circular circumference of said inner contacting surface, being a surface adapted to be in contact with said caput femur, or prosthetic replacement therefore, and   b) said at least one extending portion passes beyond said equator line, such that the end portion of said contacting portion of said inner surface forms a circular extension line having a smaller circumference than said equator line, and   c) said at least one extending portion circumferentially extends discontinuously along said equator line, such that a portion of said elongated member can be placed between said extension line and said equator line, when said medical device being implanted.       

     The medical device could comprises a prosthetic replacement for the caput femur having a spherical portion, comprising a spherical portion and an elongated member, adapted to be fixated to the pelvic bone by a connection via the elongated member fixated to said spherical portion of said prosthetic caput femur, wherein:
         a) an inner surface comprises an equator line, being the largest circular circumference of said inner surface,   b) at least one extending portion passes beyond said equator line, such that the end portion of said contacting portion of said inner surface forms a circular extension line having a smaller circumference than said equator line, and   c) said at least one extending portion circumferentially extends discontinuously along said equator line, such that a portion of said elongated member can be placed between said extension line and said equator line, when said medical device being implanted.       

     The medical device could have at least one of extending portion, when implanted, is adapted to be placed such as to restrict the motion range of the hip joint, and wherein said extending portion is adapted to be placed or shaped such that at least one of adduction, abduction, flexion, extension, a combination of flexion and adduction or abduction, a combination of extension and adduction or abduction, rotation in, rotation out, and any combination of rotation in or out and the other described movements, is restricted more degrees from maximal movement than any of the other. 
     The at least one extending portion could allow different movement restrictions in different movement directions, wherein said extending portion is constructed according to at least one of the following alternatives; a) circumferentially extending s discontinuously along said equator line having with enough circumferential distance lacking any extending portion and b) extendings with different distal extension in different extending portions or part of such portions of said circumferential extension, in either a orb allowing for different movement restrictions in different movement directions. 
     The medical device could, comprising a locking member for in situ locking the medical device, wherein: said locking member is adapted to lock said a prosthetic replacement for the caput femur fixated to the pelvic bone, such that the caput femur or prosthetic caput femur remains clasped and restrained in said inner surface, and said locking member is adapted to lock said at least one extension portion, when implanted, having at least the end portion of the extension portion radially fixed within said circular extension line. 
     The locking member is adapted to lock in at least a first and second locking position. 
     The locking member is adapted to lock in at least a first and a second locking position, and wherein said locking member is adapted to; in said first locking position, lock a first size caput and/or collum femur, and in said second locking position, lock a second smaller size caput femur and/or collum femur. 
     A method using a medical device according to any of the preceding medical device claims is further provided, for implantation in a hip joint of a patient, comprising the steps of;
         fixating said medical device to the femoral bone of the patient, and wherein said medical device comprises an inner and an outer surface, wherein a contacting portion of said inner surface is bowl shaped and spherical and adapted to face the center of the hip joint,   placing the inner bowl shaped surface facing proximally towards the center of the hip joint, and   fixating a prosthetic replacement for the caput femur fixated to the pelvic bone having a ball shaped spherical portion   receiving said prosthetic replacement for the caput femur inside said inner bowl shaped surface, wherein said medical device comprises at least one extending portion, extending said contacting portion of said inner surface such that said at least one extending portion clasps said spherical portion,   clasping said prosthetic replacement for the caput femur, such that said spherical portion is restrained in said bowl shaped inner surface of said medical device.       

     The inner surface comprises an equator line, being the largest circular circumference of said inner contacting surface, being a surface adapted to be in contact with said caput femur replacement, and
         said at least one extending portion passes beyond said equator line, such that the end portion of said contacting portion of said inner surface forms a circular extension line having a smaller circumference than said equator line, and   said at least one extending portion circumferentially extends discontinuously along said equator line, such that a portion of said elongated member can be placed between said extension line and said equator line, when said medical device being implanted together with the prosthetic replacement for the caput femur, wherein the method comprising the steps of;
           wherein the step of placing the inner surface involves the step of placing an inner surface comprising at least one extending portion   moving said femoral bone to place said elongated member between said extension line and said equator line.   
               

     The method could further comprises the steps of cutting the skin in the hip region dissecting the hip joint implanting the medical device in a hip joint of a patient, fixating a ball shaped replacement of caput femur on the opposite side therefore to the pelvic bone of the patient, fixating a bowl shaped acetabulum replacement on the opposite side and therefore to the femoral bone of the patient, wherein said acetabulum replacement comprises an inner and an outer surface, having a contacting portion of said inner surface being spherical and bowl shaped facing the inner surface to the center of the hip joint having at least one extending portion, extending a contacting portion for contacting the caput femur replacement, placing a caput femur replacement, such that said extending contacting portion of said inner surface is clasping said spherical portion of said caput femur replacement, such that said caput femur replacement is restrained in said bowl shaped inner surface. 
     The inner surface comprising an equator line being the largest circular circumference of said inner contacting surface, wherein said at least one extending portion is
         passing beyond said equator line, such that the end portion of said contacting portion of said inner surface forms a circular extension line having a parallel smaller circumference than said equator line, the end portion being the most distal portion of the inner surface being in contact with said caput femur or artificial replacement therefore,   placing said caput femur or artificial replacement therefore symmetrically in said inner surface, and wherein said at least one extending portion is   extending circumferentially discontinuously along said equator line, wherein said caput femur replacement is extending into an elongated member, the method involves,   placing a portion of said elongated member between said extension line and said equator line when moving said caput femur or artificial replacement therefore in relation to said inner surface.       

     The at least one extending portion is mounted according to at least one of the following alternatives:
         a) extending circumferentially discontinuously along said equator line having enough circumferential distance lacking any extending portion and b) extending with different distal extension in different extending portions or part of such portion of said circumferential extension.       

     The method could comprise the following steps:
         a) cutting the skin in the hip region   b) dissecting the hip joint   c) implanting the medical device M a hip joint of a patient,   d) fixating the artificial replacement of an acetabulum to the femoral bone of the patient, comprising an inner and an outer surface, having a contacting portion of said inner surface being spherical and bowl shaped   e) facing the inner surface to the center of the hip joint having at least one extending portion, extending a contacting portion for contacting the caput femur or a prosthetic replacement therefore,   f) placing a caput femur or an artificial replacement therefore to the pelvic bone having a spherical portion, such that said extending contacting portion of said inner surface is   g) clasping said spherical portion of said caput femur, or an artificial replacement therefore,   h) placing said locking member such that said caput femur, or artificial replacement therefore is restrained in said bowl shaped inner surface, and   i) locking said caput femur or artificial caput femur in said clasped and restrained position in said inner surface, by   j) fixating radially at least the end portion of the at least one extension portion within said circular extension line.       

     Please note that any embodiment or part of embodiment, feature, method, associated system, part of system described herein or in the associated figures may be combined in any way. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1 a    shows pelvis in a frontal view, 
         FIG. 1 b    shows pelvis in a frontal view, 
         FIG. 1 c    shows the hip joint in section, 
         FIG. 2 a    shows pelvis in a lateral view, 
         FIG. 2 b    shows pelvis in a lateral view, 
         FIG. 2 c    shows pelvis in a perspective view from below, 
         FIG. 2 d    shows pelvis in a perspective view from below, 
         FIG. 2 e    shows the acetabulum, schematically, 
         FIG. 2 f    shows the acetabulum, schematically, 
         FIG. 2 g    shows pelvis in a perspective view from below, 
         FIG. 3  shows pelvis in a lateral view, 
         FIG. 4  shows a prosthetic replacement for the acetabulum, according to one embodiment, 
         FIG. 5  shows the hip joint in section, when a prosthetic replacement for the acetabulum, and a medical device has been implanted, 
         FIG. 6 a    shows the pelvic region in a frontal view, 
         FIG. 6 b    shows the pelvic region in a frontal view, 
         FIG. 7  shows the pelvic region in a frontal view, 
         FIG. 8  shows a medical device placed in the femoral bone, 
         FIG. 9  shows the femoral bone in a lateral view, 
         FIG. 10  shows the femoral bone in a lateral view, 
         FIG. 11  shows the femoral bone in a lateral view, 
         FIG. 12  shows the femoral bone in a lateral view, 
         FIG. 13  shows the femoral bone in a lateral view, 
         FIG. 14  shows a medical device placed in the femoral bone, 
         FIG. 15 a -15 f    shows embodiments of prosthetic replacements for the acetabulum, 
         FIG. 16 a    shows an embodiment of the locking/releasing member, 
         FIG. 16 b    shows the hip joint in section in an embodiment when the locking/releasing member locks an artificial caput femur in artificial acetabulum. 
         FIG. 16 c    shows the hip joint in section in an embodiment when the locking/releasing member releases the artificial caput femur from the artificial acetabulum. 
         FIG. 16 d    shows another embodiment of the locking/releasing member, 
         FIG. 16 e    shows the hip joint in section in an embodiment when the locking/releasing member according to the embodiment of  FIG. 36 d    locks the artificial caput femur to the artificial acetabulum. 
         FIG. 16 f    shows the hip joint in section in an embodiment when the locking/releasing member according to the embodiment of  FIG. 36 d    releases the artificial caput femur from the artificial acetabulum. 
         FIG. 16 g    shows another embodiment of the locking/releasing member, 
         FIG. 16 h    shows another embodiment of the locking/releasing member, 
         FIG. 16 i    shows the hip joint in section when an artificial hip joint is being assembled, 
         FIG. 16 j    shows the hip joint in section when an artificial hip joint is being assembled, 
         FIGS. 16 k  and 16 l    shows the hip joint in section when an artificial hip joint is assembled, 
         FIGS. 16 m  and 16 n    shows the hip joint in section according to the embodiment of  FIG. 16 k   , when released. 
     
    
    
     DETAILED DESCRIPTION 
     The hip joint is a synovial ball and socket joint which permits a large motion range for allowing a plurality of different movements of the lower limb. Hem a neutral position the following movements of the hip joint are normally possible: Lateral or external rotation, 30° with the hip extended, 50° with the hip flexed, medial or internal rotation 40°, extension or retroversion 20°, flexion or anteversion 140°, abduction 50° with hip extended, 80° with hip flexed, adduction 30° with hip extended, 20° with hip flexed. 
     When replacing the natural hip joint with a prosthetic hip joint, the depth of the prosthetic acetabulum will affect the motion range, the deeper the acetabulum bowl is made the more restrictive it is to the motion range. A deeper bowl has the advantage of reducing the risk of hip joint luxation, the risk of which is a major drawback with prosthetic hips of today. 
     The anatomy of the hip joint and its surroundings is further disclosed in Marieb et al., Human Anatomy, 2003, Benjamin Cummings, San Francisco, pages 195-202 and in Moore et al., Clinically oriented anatomy, 1999, Lippincott, Williams &amp; Wilkins, Baltimore, pages 501-653, both hereby incorporated by reference. 
     Centrally in the body should herein be understood as a point of reference located at the intersection of the Median plane and the Coronal plane and in the center part of the heart along a longitudinal axis (Caudal Cranial). Proximal and distal are direction or location terms used in relation to said point centrally in the body and hence a distal point is a point farther away from the central point in relation a proximal point of the same structure. Any plane disclosed herein is to be understood as having infinite extension. Other anatomical terms used herein are further described in Moore et al., Clinically oriented anatomy, 1999, Lippincott Williams &amp; Wilkins, Baltimore, pages 2-10, which is hereby incorporated by reference. 
     Functional hip movements are to be understood as movements of the hip that at least partly correspond ID the natural movements of the hip. On some occasions the natural movements of the hip joint might be somewhat limited or altered after hip joint surgery, which makes the functional hip movements of a hip joint with prosthetic surfaces somewhat different than the functional hip movements of a natural hip joint. 
     Everyday activities is to be understood as activities which are not connected to any extreme movements, such that some physical sports require. For example, everyday activities comprise: walking, sitting, cycling etc. 
     The functional position of an implantable medical device or prosthesis is the position in which the hip joint can perform functional hip movements. The final position is to be understood as a functional position in which the medical device needs no further position change to function. 
     Arthroscopy is to be understood as key hole surgery performed in a joint, since the arthroscopic procedure could be performed in the abdomen of the patient some of the steps of this arthroscopic procedure is more laparoscopic, however for the purpose of this invention the two terms arthroscopy and laparoscopy is used synonymously and for the purpose of this invention the main purpose of these methods are is that they are minimally invasive. 
     Elastic deformation is when a material deforms under stress (e.g. external forces), but returns to its original shape when the stress is removed. A more elastic material is to be understood as a material having a lower modulus of elasticity. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region. The elastic modulus is calculated as stress/strain, where stress is the force causing the deformation, divided by the area ID which the force is applied; and strain is the ratio of the change caused by the stress. 
     Elasticity is to be understood as a materials ability to deform in an elastic way. 
     Stiffness is to be understood as the resistance of an elastic body to deformation by an applied force. 
     Biocompatible material is to be understood as being a material with low level of immune response. Biocompatible materials are sometimes also referred. In as biomaterials. Analogous is bio compatible metals a bio compatible metal with low immune response such as titanium or tantalum. The biocompatible metal could also be a biocompatible alloy comprising at least one biocompatible metal. 
     Formfitting is to be understood as an element having a part or section which is adapted to enable a mechanical connection of said element to at least one other element using said part or section. Form fitted structure is a structure of an element which enables form fitting. 
     In the following a detailed description of embodiments of the present invention will be given. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and are not in any way restricting the scope of the invention Thus, any references to direction, such as “up” or “down”, are only referring to the directions shown in the figures. Also, any dimensions etc. shown in the figures are for illustration purposes. 
       FIG. 1 a    shows the pelvis in a frontal view. Pelvis comprises the right and left hip bone making up the pelvic bone, in turn comprising the Sacrum  1803 , Ilium  1802 , Pubis  1804  and Ischium  1801 . The hip joint houses the right and left acetabulum  8   a,b  placed laterally and distally in the pelvis. The acetabulum  8   a,b  being a spherically shaped cavity in the hip bones making up one of the parts of the hip joint, the acetabulum  8   a,b  being adapted to house the caput femur  5 , being the proximal portion of the femoral bone  7  having a spherical contacting surface adapted to be placed in the acetabulum  8   a,b  and thus creating the operable hip joint. The pelvis has a right-left axis X extending substantially from the bottom of the left acetabulum  8   a  to the bottom of the right acetabulum  8   b , the pelvis further having a caudal-cranial axis Y extending perpendicular to said right-left axis, centrally and substantially along the length of the patient, passing the dorsal portions of the pubic symphysis  1805  and substantially following the spinal cord  1806 , intersecting the left-right axis X. 
       FIG. 1 b    shows the pelvis in a frontal view disclosing a second, displaced coordinate system. The second displaced coordinate system has its origin O′ in the bottom of the acetabulum bowl  8   a . The axis X and Y have, in a frontal view, been rotated the angle β, creating the axis X′ and Y′. In the defined base position, the acetabulum center axis X′ is aligned with the caput and collum femur center axis CX the caput and collum femur center axis CX is an axis in the extension of the collum and caput femur axis, in the center thereof. The hip joint substantially being in its base position when the patient is standing up or lying down. In said base position, the acetabulum center axis X′ goes through a point O′ being the origin O′ in the bottom of the acetabulum bowl  8   a , and a center point CP, being a point in the center of a circle defined by the edges of the acetabulum bowl  8   a , and further trough the top of the caput femur  5  and following inside of the collum femur  6 , aligned with the collum femur  6 . The axis Y′ is perpendicular to the axis X and goes through the origin O′ in the bottom of the acetabulum bowl  8   a , parallel to a plane defined by the circle defined by the edges of the acetabulum bowl  8   a.    
       FIG. 1 c    shows the right pelvic bone  9  in section disclosing the second, displaced coordinate system. The origin O′ is in the bottom of the acetabulum bowl  8 . The axis X′ is aligned with the caput  5  and collum  6  femur center axis CX, when the hip joint is in its base position when the patient is standing up or lying down with extended leg. In said base position the axis X is goes through a point O′ being the bottom of the acetabulum bowl  8 , and a center point CP, being a point in the center of a circle defined by the edges of the acetabulum bowl  8 , and further trough the top of the caput femur  5 ′ and following inside of the collum femur  6 , aligned with the collum femur  6 . The axis Y is perpendicular to the axis X, goes through the origin O′ in the bottom of the acetabulum bowl  8 , parallel to the plane FC defined by the circle defined by the edges of the acetabulum bowl  8 . 
       FIG. 2 a    shows the pelvis in a labral view, thus displaying the posterior side of Ilium  1802 , the anterior side of Ichum  1801 , the anterior side of Pubis  1804 , and Sacrum  1803  in a lateral view. The pelvis has furthermore a dorsoventral axis Z being perpendicular to the caudal-cranial axis Y and the right-left axis X shown in  FIG. 1 , and intersecting them both creating a common origin O for the three axis X,Y,Z. The dorsoventral axis Z and the caudal-cranial axis Y thus being oriented such that a horizontal pelvis plane PXZ extends from the dorsoventral axis Z, and a coronal plane PXY extends from the caudal-cranial axis Y. 
       FIG. 2 b    shows the pelvis in a plane view from the side and slightly from below, in the direction of the axis X (further disclosed with reference to  FIGS. 1 b  and 1 c   ). The view of  FIG. 2 b    displaying the axis Y and Z′ with origin O′ in the bottom of the acetabulum bowl  8  making up the acetabulum coordinate system. The axis Y, Z′, in this plane view, dividing the acetabulum bowl  8  into four quadrants: the proximal-frontal quadrant  1807 , the distal-frontal quadrant  1808 , the distal-dorsal quadrant  1809  and the proximal-dorsal quadrant  1810 . 
       FIG. 2 c    shows the pelvis in a perspective view from below and slightly from the front, displaying the right-left axis X passing through the center of the right and left acetabulum  8 . The right-left axis X is perpendicular to the dorsoventral axis Z which also is perpendicular in the caudal-cranial axis Y. The coronal plane PXY extends from the dorsoventral axis Y, and the horizontal pelvis plane PXZ extends from the dorsoventral axis Z, thus being perpendicular to the coronal plane PXY. 
       FIG. 2 d    shows the coordinate system X,Y,Z and planes PXY, PXZ of  FIG. 2 c   , and the second, displaced, coordinate system X′, Y′, Z′ being the coordinate system of the acetabulum  8 , also shown in  FIG. 2 b   . The axis of the coordinate system of the acetabulum X′, Y′, Z′ having their origin O′ in the bottom of the acetabulum bowl  8 , the axis X′ being aligned with the caput and collum center axis.  FIG. 2 d    further discloses the vertical acetabulum plane PX′Y′ and the horizontal acetabulum plane PX′Z′, PX′Y′ being defined by the axis X′,Y′ and the vertical acetabulum plane PX′Z′ being defined by the axis X′,Z′. The planes PX′Y′ and PX′Z′ dividing the acetabulum bowl  8  into four quadrants, the proximal-frontal quadrant  1807 , the distal-frontal quadrant  1808 , the distal-dorsal quadrant  1809  and the proximal-dorsal quadrant  1810 , in accordance with what is previously disclosed, with reference to  FIG. 2 b   .  FIG. 2 d    further shows the location of foramen obturatum  1871 . 
       FIG. 2 e    shows, schematically how the acetabulum coordinate system X′,Y′,Z′ relates to the hemisphere defined by the acetabulum bowl  8 . 
       FIG. 2 f    shows, schematically, how the vertical acetabulum plane PX′Y′, and the horizontal acetabulum plane PX′Z′ divides the acetabulum  8  into four quadrants; the proximal-frontal quadrant  1807 , the distal-frontal quadrant  1808 , the distal-dorsal quadrant  1809  and the proximal-dorsal quadrant  1810 , in accordance with the previously disclosed, with reference to  FIGS. 2 b    and  2   d.    
       FIG. 2 g    shows the view of  FIG. 2 d   , and in addition it shows the horizontal and vertical acetabulum planes PX′Y′ and PX′Z′ also being the caput and collum femur horizontal and vertical planes PX′Y′ and PX′Z′, analogically dividing the caput and collum femur into four quadrants. 
       FIG. 3  shows pelvis in the same view as  FIG. 2 b   . Here the vertical and horizontal acetabulum planes PX′Y′ and PX′Z′ (further disclosed with reference to  FIG. 2 d   ) are shown in a strict plane view. Two further planes PX″Y″ is introduced in  FIG. 3 , which planes are rotated an angle α of 45° clockwise. The planes PX″Y″ and PX″Z″, analogous to the planes PX′Y′ and PX′Z′, divides the acetabulum bowl into four different quadrants, being a proximal quadrant  1811 , a frontal quadrant  1812 , a distal quadrant  1813  and a dorsal quadrant  1814 . 
       FIG. 4  shows a medical device for implantation in a hip joint of a patient. The medical device is adapted to be fixated to the femoral bone of the patient in an opposite embodiment, for example by means of an adhesive, such as bone cement, or mechanical fixating members, such as orthopedic screws. The medical device comprises an inner  1827  and an outer  1828  surface. A contacting portion of the inner surface  1827  is spherical and faces the center of the hip joint, when the medical device is implanted. The inside of the medical device is adapted to receive a prosthetic replacement fora caput femur adapted to be fixated to the pelvic bone having a spherical portion, and the spherical contacting portion of the inner surface  1827  is adapted to be in contact with a spherical portion of the outer surface of the prosthetic replacement of the caput femur. The medical device, comprises two extending portions  1823   a,b , extending the contacting portion of the inner surface  1827 ′ such that the extending portions  1823   a,b  clasps the spherical portion of a prosthetic replacement of a caput femur, for restraining the spherical portion in the medical device. The medical device is adapted to receive the prosthetic spherical portion, fixated to the pelvic bone, connected via a prosthetic elongated portion. The inner surface  1827  comprises an equator line  1821 , being the largest circular circumference of the inner surface. The two extending portions passes beyond the equator line  1821 , such that an end portion  1829  of the contacting portion, here being of the extending portion  1823   b  of the inner surface  1827 , forms a circular extension line  1822  placed proximal to the equator line  1821 , when the medical device is implanted, and having a smaller circumference than the equator line  1821 ; thus a distance  1826  between a center axis P of the medical device and the extension line  1822  is shorter than a distance  1825  between the center axis P and the equator line  1821 . 
       FIG. 5  shows the medical device described with reference to  FIG. 4  when implanted. According to this embodiment the medical device is adapted to be fixated using orthopedic screws  1830 , mechanically fixating the medical device to the femoral bone  5 , by the medical device comprising holes through which the screws  1830  are placed. In  FIG. 5  the contacting portion of the inner surface  1827  has been placed in contact with the prosthetic spherical portion being connected to a the prosthetic elongated portion  2201 , the prosthetic spherical  45  and elongated portions  2201  replacing the proximal portion of the femoral bone. The two extending portions  1823   a  and  1823   b  extending the contacting portion of the inner surface and clasping the spherical portion  45 , for restraining the spherical portion in the medical device. The inner surface comprising the equator line  1821 , and the extending portions  1823   a,b  passing beyond the equator line  1821  and comprising the more proximal extension line  1822  having a smaller circumference than the equator line  1821 . The more proximal extension line  1822  being placed at a distance D 1  from the equator line  1821 . According to this embodiment the extension line  1822  is parallel to the equator line  1821 , however this is not necessarily so in other embodiments. The extension portion  1823   a  according to the embodiment shown in  FIG. 5  extends circumferentially along the equator line, a distance D 2 . Along another portion of the equator line, a distance D 3 , there are no extending portion, which enables the elongated portion  2201  to enter the space between the first and second extending portions  1823   a,b  which creates a larger movement range of the hip joint, for further increase of the movement range, the recess  2203  in the elongated portion  2201  is adapted for some section of the extending portion to enter the recess  2203 . 
     The extending portion, according to any of the embodiments, adapted ID clasp the prosthetic spherical portion, for restraining it the prosthetic acetabulum  65 , could further be adapted ID release the prosthetic spherical portion  45  when a large enough strain is placed on the joint. This feature enables the prosthetic spherical portion to be fixedly attached in the prosthetic acetabulum  65  in normal use, and be released from the prosthetic acetabulum, e.g. in case of an accident, thus reducing the risk of damaging the bodily structures, such as the femoral bone, or the fixations between bodily structures and prosthetic parts. 
     According to one embodiment, the extending elements are placed such that the extending elements restricts the motion range minimally, or in ways which am not limiting the motion range used in everyday life. This is enabled through the placing of the extending portions, or the interaction between the extending portion and adaptations of the prosthetic elongated portion. The hip joint is a synovial ball and socket joint which permits a large motion range for allowing a plurality of different movement of the lower limb. From a neutral position, the following movements of the hip joint are normally possible: lateral or external rotation, 30° with the hip extended, 50° with the hip flexed, medial or internal rotation 40°, extension or retroversion 20°, flexion or anteversion 140°, abduction 50° with hip extended, 80° with hip flexed, adduction 30° with hip extended, 20° with hip flexed. In the movement ranges of abduction and adduction the depth of the acetabulum bowl and thus the extending portions does not restrict the motion range in a critical way since the motion range of the normal hip is restricted in these movements, in normally agile persons, by the muscles, tenors and ligaments surrounding the hip joint. 
       FIG. 6 a    shows a frontal view of pubis and the proximal portions of the femoral bones  7  when two embodiments prosthetic replacement for the acetabulum  65  has been implanted in the hip joint. The prosthetic replacements for the acetabulum shown comprises one extending portion  1823 , here placed dorsal to the vertical acetabulum plane PX′Y′ in the base position, thus only partially limiting abduction in far excess of 50°. According to the embodiment shown, the extending portion  1823  extends circumferentially along the equator line  1821  about 1/10 of the length of the equator line  1821 , however in other embodiments the extending portion  1823  extends along as much as half of the length of the equator line  1821 , and in other embodiments the extending portion  1823  extends as little as about 1/30 of the length of the equator line  1821 . The prosthetic replacement for the acetabulum placed in the left femoral bone comprises two extending portions  1823   a,b , both being placed dorsal the corresponding vertical acetabulum plane PX′Y′ of the left acetabulum (not shown) in the base position, thus limiting the motion range of the hip joint in a non restrictive way, in relation to everyday activities. In both the right and left embodiment the extending portions  1823  extends discontinuously along the equator line  1821  thus enabling the elongated portion  2201  to partially be placed between the equator line and the extension line, and in the left embodiment, be placed between the extending portions  1823   a,b  thus entering the cavity between the extending portions  1823   a,b . The recess  2203  of the prosthetic elongated portion  2201  implanted in the right hip joint is radially placed, in relation to the caput and collum center axis, such that the a section of the prosthetic elongated portion  2201 , can enter the recess for further increasing the movement range of the prosthetic acetabulum surface  65  in relation to the elongated  2201  and spherical  45   a  portion. The curving of the prosthetic elongated portion  2201  implanted in the left hip joint is radially placed, in relation to the caput and collum center axis, for further increasing the movement range of the prosthetic acetabulum surface  65  in relation to the elongated  2201  and spherical  45   b  portion. 
       FIG. 6 b    shows a frontal view of pubis and the proximal portions of the femoral bones  7 , when two further embodiments of the prosthetic replacements have been implanted. The embodiment shown placed on the right side is an embodiment in which the prosthetic elongated portion  2201   a  comprises a first  2203   a  and second  2203   b  recess placed at the restricting portion of the elongated portion  2201   a . The prosthetic elongated portion  2201  is connected to a prosthetic spherical portion  45   a  which is restrained in a prosthetic replacement for the acetabulum  65   a  fixated to the femoral bone. The prosthetic replacement for the acetabulum  65   a  comprises extending portions  1823  clasping the prosthetic spherical portion  45   a  and thus restraining the spherical portion in the prosthetic replacement for the acetabulum  65   a . The extending portions  1823  is placed in the proximal quadrant in the base position, thus limiting the motion range of the hip joint in a non restrictive way, in relation to everyday activities. According to the embodiment shown, the extending portion  1823  extends circumferentially along the equator line  1821  about 1/10 of the length of the equator line  1821 , however in other embodiments the extending portion  1823  extends along as much as half of the length of the equator line  1821 , and in other embodiments the extending portion  1823  extends as little as about 1/30 of the length of the equator line  1821 . The prosthetic elongated portion  2201   b  shown placed in the left hip joint comprises a narrow portion connected to the prosthetic spherical portion  45   b . The narrow portion enables a relatively large motion range in relation to the elongated portion even though the prosthetic replacement for the acetabulum comprises extending portions  1823   a,b  extending beyond the equator line of the prosthetic spherical portion  45   b , thus clasping the spherical portion and restraining it in a fixated position. 
       FIG. 7  shows the pelvis and the proximal portions of the femoral bones  7  including the embodiment of  FIG. 25 a   , with the difference that the natural caput femur has been replaced by a prosthetic replacement for the acetabulum. The prosthetic elongated portion  2201  is here coordinated with the extending portions  1823  of the prosthetic replacement for the acetabulum  65   a,b  for further improving the motion range of the hip joint, or not limiting the natural motion range of the hip joint. 
       FIG. 8  shows the medical device according to an embodiment in which the medical device comprises two extending portions  1823   a,b . The medical device is placed on a prosthetic elongated portion  2201 , to which a prosthetic spherical portion  45  is attached. The prosthetic elongated member  2201  is here adapted to further improve the motion range of the hip joint, or not limiting the natural motion range of the hip joint, by the prosthetic elongated portion  2201  comprising a recess  2203  in which the extending portions  1823  can enter. 
       FIG. 9  shows the pelvis in a lateral view, the prosthetic replacement for the acetabulum  65  in the femoral bone comprises two extending portions  1823   a,b , both extending circumferentially along the equator line (as disclosed in for example  FIG. 5 ) dorsal to the caudal-cranial axis Y when being in the base position and being adapted to clasp the caput femur or a prosthetic replacement therefor. The extending portions  1823   a,b  extending dorsal ID the caudal-cranial axis Y when being in the base position and thus reducing the limiting effect that the extending portions  1823   a,b , have on the motion range of the hip joint According to the embodiment shown in  FIG. 9  the extending portion  1823   a , placed proximally in the acetabulum, extends circumferentially a distance of about ¼ of the length of the equator line, and the extending portion  1823   b , placed distally in the acetabulum when being in the base position, extends circumferentially a distance of about 1/10 of the length of the equator line, however it is equally conceivable that this relationship is the other way around, or that any of the extending portions circumferentially extends a distance of as much as half of the length of the equator line, thus extending the entire distance of the equator line being dorsal to the vertical acetabulum plane PX′Y′, or that any of the extending portions  1823   a,b  extends a distance being as little as 1/30 of the distance of the equator line. According to the embodiment shown in  FIG. 9 , the first extending portion  1823   a  extends in distal-lateral direction from the acetabulum, and the second extending portion  1823   b  extends medially towards foramen obturatum when being in the base position. 
       FIG. 10  shows the pelvis in a lateral view, the prosthetic replacement for the acetabulum  65  in the femoral bone comprises two extending portions  1823   a,b , the two extending portions  1823   a,b  extends in the proximal quadrant  1811  and the distal quadrant  1813  when being in the base position, respectively. 
     There are multiple ways in which the extending portions  1823  can be adapted to reduce the effects that the extensions have on the motion range of the hip joint. 
       FIG. 11  shows the pelvis in a lateral view, the prosthetic replacement for the acetabulum  65  in the femoral bone shown comprises one extending portion  1823  extending and being adapted to clasp the caput femur, or a prosthetic replacement therefor. The extending portion  1823  extends circumferentially along the equator line within the proximal quadrant  1811  when being in the base position, which is further disclosed with reference to  FIG. 3 . According to the embodiment shown in  FIG. 4 , the extending portion  1823  extends in distal-lateral direction from the acetabulum when being in the base position. 
       FIG. 12  shows the pelvis in a lateral view, the prosthetic replacement for the acetabulum  65  in the femoral bone shown comprises a continuously extending portion  1823  with two extending portions  1823   a  and  1823   b  extending further in relation to the average extension of the extending portion. The entire extending portion is placed in the proximal, distal and dorsal quadrant and the extending portions  1823   a,b  extending further than the average extension of the extending portion  1823  extends in the proximal and distal quadrant when being in the base position. 
       FIG. 13  shows the pelvis in a lateral view, the prosthetic replacement for the acetabulum  65  in the femoral bone shown comprises four extending portions  1823   a,b,c,d , wherein the first  1823   a  and second  1823   b  extending portions extends in the proximal and distal quadrant, respectively, thus the first extending portion  1823   a  extending in distal-lateral direction from the acetabulum, and the second extending portion  1823   b  extending medially towards foramen obturatum when being in the base position. The third extending portion  1823   c  when being in the base position extending in the frontal quadrant  1812 , out from the acetabulum in dorsal direction, extends less than the first and second extending portion, since extending portions  1823   c  in the frontal quadrant is more limiting in the normal motion range of the hip joint. The fourth extending portion  1823   d  extends in the dorsal quadrant in accordance with the third extending portion  1823   c  do not extend as far as the first and second extending portions when being in the base position. 
       FIG. 14  shows an alternative embodiment of the prosthetic replacement for the acetabulum  65 . In the alternative embodiment, the prosthetic replacement for the acetabulum  65  comprises a first part  1841  adapted to be fixated to the femoral bone of the patient. The first part comprises an inner contacting surface adapted to be in movable connection with an outer contacting surface of a second part  1842 . The second part  1842  is rotatably fixated to the first part  1841  by a rotatable connecting member  1843 . An outer contacting surface of a prosthetic spherical portion  45  is adapted to be placed in contact with the inner surface of the second part  1842  and be movable in multiple directions, thus replicating the natural ball and socket joint of the hip. The second part  1842  comprises two extending portions  1823   a,b  extending beyond the equator line  1845  of the second part  1842 . The extending portions  1823   a,b  extends longitudinally discontinuously along the equator line, thus creating an area between the extending portions, in which area a portion of the prosthetic elongated portion can be placed, thus being placed partially between the equator line  1845  and the extension line  1846 . The construction shown in  FIG. 26  enables the second part  1842  to rotate if the prosthetic elongated portion  2201  engages the extending portions  1823   a,b , which are sloped for this purpose. This way the second part  1842  are always placed such that the prosthetic elongated portion  2201  can be placed partially between equator line  1845  and the extension line  1846 , which creates an optimal range of movement whilst the second part clasps the prosthetic spherical portion  45 , and thus restricting the spherical portion  45  in the second part  1842  of the prosthetic replacement for the acetabulum  65 . 
       FIG. 15 a    shows the prosthetic replacement for the acetabulum  65  according ID one embodiment. In this embodiment the prosthetic replacement for the acetabulum  65  comprises two extending portions  1823   a, b . The prosthetic replacement for the acetabulum  65  is according to this embodiment adapted ID be fixated to the femoral bone by means of an adhesive which is adapted to be placed in connection with the adhesive recesses  1870  of the outer surface of the prosthetic replacement for the acetabulum  65 . 
       FIG. 15 b    shows a prosthetic replacement for the acetabulum  65  similar to the prosthetic replacement for the acetabulum  65  disclosed with reference to  FIG. 15 a   , but with the difference that it comprises three equally extending portions  1823   a,b,c.    
       FIG. 15 c    shows a prosthetic replacement for the acetabulum  65 , similar to the prosthetic replacement for the acetabulum  65  disclosed with reference to  FIG. 15 a   , but with the difference that it comprises two equally extending portions  1823   a,b  and one less extending portion  1823   c.    
       FIG. 15 d    shows a prosthetic replacement for the acetabulum  65  similar to the prosthetic replacement for the acetabulum  65  disclosed with reference to  FIG. 15 a   , but with the difference that it comprises four equally extending portions  1823   a,b,c,d.    
       FIG. 15 e    shows a prosthetic replacement for the acetabulum  65  similar ID the prosthetic replacement for the acetabulum  65  disclosed with reference to  FIG. 15 a   , but with the difference that the two extending portions are placed further from each other, and thus being adapted to be placed in the proximal and distal quadrant, when implanted and being in the base position. 
       FIG. 15 f    shows a prosthetic replacement for the acetabulum  65  similar ID the prosthetic replacement for the acetabulum  65  disclosed with reference to  FIG. 15 a   , but further comprising a less extending portion  1823   c  placed between the first and second extending portions  1823   a,b.    
     The extending portions of the prosthetic replacement for the acetabulum  65  which have been described could be made from an elastic material, enabling the extending portions to pass onto the a prosthetic spherical portion, according to any of the embodiments herein. 
       FIG. 16 a    shows an embodiment of a locking/releasing member  116 , wherein the locking/releasing member  116  comprises a surface  1353  adapted to be in contact with the artificial convex hip joint surface (replacement for the caput femur) ( 112  in  FIG. 16 b   ), being a first piece, and slide against the hip joint surface, the locking member  116  is adapted to, in a first state, lock the artificial caput femur  112  to the artificial acetabulum surface ( 1340  in  FIG. 16 b   ), and in a second state, release said artificial caput femur  112  from said artificial acetabulum  1340 . The locking/releasing member  116  is adapted to change from the first to the second state when a predetermined amount of strain is placed on the locking/releasing member  116 . The locking/releasing member  116  comprises four holding members, here being elastic portions  1351 , and the locking/releasing member  116  is adapted to change from the first to the second state using the elasticity of the elastic portions  1351 . The locking member  116  is adapted to be fixated to the femoral bone  7  using screws adapted to be placed in holes  1352  adapted therefor. According to another embodiment (not shown) the holding members  1351  comprises at least one holding member adapted to roll against the first piece, being the artificial convex hip joint surface  112 . 
       FIG. 16 b    shows the hip joint in section when the two state locking/releasing member  116  locks the artificial caput femur  112  in the artificial acetabulum  1340 . The two state locking/releasing member  116  is fixated to the femoral bone  7  using screws  121 , and is here shown in its first stale in which the locking/releasing member  116  locks the artificial caput femur  112  to the artificial acetabulum  1340 . 
       FIG. 16 c    shows the hip joint in section according to the embodiment of  FIG. 16 b   , but when the two state locking/releasing member  116  is in its second state, in which the locking/releasing member  116  releases the artificial caput femur  112  from the artificial acetabulum surface  1340 . The construction with the locking/releasing member  116  reduces the risk of strain placed on the artificial joint injuring the fixation points, i.e. the contact with bone; it further enables the artificial joint to be non-invasively relocated in case of luxation. 
       FIG. 16 d    shows an alternative embodiment of the two-state locking/releasing member  116 , in which the two-state locking/releasing member  116  further comprises an elastic band  1361  adapted to encircle the artificial caput femur  112 , when implanted. The elastic band  1361  could be an elastic polymer band, such as a polyurethane or silicone band. 
       FIG. 16 e    shows a hip joint in section when the two-state locking/releasing member  116  has been implanted, and being in its first state. The two-state locking/releasing member  116  is fixated to the femoral bone  7  using screws  121 . 
       FIG. 16 f    shows the implantable device comprising the two-state locking/releasing member  116  when in its second state, i.e. in the state in which the locking/releasing member  116  is adapted. In release the artificial caput femur  112  through the elastic band  1361  encircling the artificial caput femur  112  is stretched so that the artificial caput femur  112  can exit from the artificial acetabulum  1340 . The construction with the locking/releasing member  116  reduces the risk of strain placed on the artificial joint injuring the fixation points, i.e. the contact with bone; it further enables the artificial joint to be non-invasively relocated in case of luxation. 
     The locking/releasing member  116  described with reference to  FIGS. 16 a -16 f    are depicted in embodiments with a large hole in the pelvic bone  9  occupied by a prosthetic part  118 , however, it is equally conceivable that the two state locking/releasing member  116  is used in embodiments with a small hole in the pelvic bone  9 , for a less invasive procedure, it is furthermore conceivable that the all of the embodiments disclosed of the medical device could be installed during conventional open hip joint surgical procedure, penetrating the hip joint capsule. In this case the two state locking/releasing member  116  could be a part of a full prosthesis. 
       FIG. 16 g    shows an embodiment of a locking/releasing member  116 , wherein the locking/releasing member  116  comprises a spring  1371  creating the elasticity needed to change from a first state to a second state for releasing the artificial caput femur  112  from the artificial acetabulum  1340 . The locking/releasing member  116  is adapted to change from the first to the second state when a predetermined amount of strain is placed on the locking/releasing member  116 . According to the embodiment shown in  FIG. 16 g    the medical device further comprises a calibration screw  1372  placed in connection with the spring  1371  for calibrating the elasticity and thereby the amount of strain required for the locking/releasing member ID change from the first to the second state. 
       FIG. 16 h    shows an embodiment of the locking/releasing member in which the locking/releasing member comprises four rupture pins  1373  adapted to fail at a pre-determined strain, for allowing the locking/releasing  116  members to change from the first to the second state. The pins are, according to this embodiment, made from a brittle material which could be adapted for the particular patient. In other embodiments (not shown) the rupture pins  1373  could be replaced by a rupture band, similar to the elastic band, but adapted to fail at a pre-determined strain, or a rupture band placed centrally. 
       FIG. 16 i    shows the hip joint in section when an artificial caput femur  1375   a,b  comprising two parts  1375   a  and  1375   b  is adapted ID be interconnected to form an interconnected artificial caput femur. Each of the two artificial parts  1375   a ,  1375   b , furthermore comprises a fixating portion  1374   a ,  1374   b  adapted ID be fixated. In the inside of the acetabulum  8 . The artificial caput femur is, after the interconnection, adapted to be placed in an artificial concave acetabulum  1340  placed in the proximal portion of the femoral bone  7 , for creating a functional hip joint in an opposite embodiment. 
       FIG. 16 j    shows the hip joint in section when the interconnected artificial caput femur  1375  has been placed in the acetabulum  8 , and been fixated using the fixating portion  1374 . The locking/releasing member  116  has been placed onto the artificial caput femur  1375  using the spring  1371  creating the elasticity required ID enable the artificial caput femur  1375  to be placed such that the locking/releasing members clasps the artificial caput femur  1375 . 
       FIG. 16 k    shows the hip joint in section when the two stab locking/releasing member  116  locks the interconnected artificial caput femur  1375  in the artificial acetabulum  1340 . The two state locking/releasing member  116  is fixated to the femoral bone  7  using screws  121 , and is here shown in its first state in which the locking/releasing member  116  locks the artificial caput femur  112  to the artificial acetabulum  1340 . 
       FIGS. 16 m  and 16 n    shows the hip joint in section according to the embodiment of  FIG. 16 k   , but when the two state locking/releasing member  116  is in its second state, in which the locking/releasing member  116  releases the artificial caput femur  112  from the artificial acetabulum surface  1340 , by means of the spring  1371  creating the required elasticity. The construction with the locking/releasing member  116  reduces the risk of strain placed on the artificial joint injuring the fixation points, i.e. the contact with bone; it further enables the artificial joint in be non-invasively relocated in case of luxation. 
     Please note that any embodiment or part of embodiment as well as any method or part of method could be combined M any way. All examples herein should be seen as part of the general description and therefore possible to combine in any way in general terms. 
     The medical device according ID any of the embodiments could comprise at least one material selected from a group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxy (WA) and fluorinated ethylene propylene (FEP). This furthermore conceivable that the material comprises a metal alloy, such as cobalt-chromium-molybdenum or titanium or stainless steel, or polyethylene, such as cross-linked polyethylene or gas sterilized polyethylene. The use of ceramic material is also conceivable, in the contacting surfaces or the entire medical device such as zirconium or zirconium dioxide ceramics or alumina ceramics. The part of the medical device in contact with human bone for fixation of the medical device to human bone could comprise a poorhouse structure which could be a porous micro or nano-structure adapted to promote the growth-in of human bone in the medical device for fixating the medical device. The porous structure could be achieved by applying a hydroxy-apatite (HA) coating, or a rough open-pored titanium coating, which could be produced by air plasma spraying, a combination comprising a rough open-pored titanium coating and a HA top layer is also conceivable. The contacting parts could be made of a self lubricated material such as a waxy polymer, such as PTFE, PFA, FEP, PE and UHMWPE, or a powder metallurgy material which could be infused with a lubricant, which preferably is a biocompatible lubricant such as a Hyaluronic acid derivate. This also conceivable that the material of contacting parts or surfaces of the medical device herein is adapted to be constantly or intermittently lubricated. According to some embodiments the parts or portions of the medical device could comprise a combination of metal materials and/or carbon fibers and/or boron, a combination of metal and plastic materials, a combination of metal and carbon based material, a combination of carbon and plastic based material, a combination of flexible and stiff materials, a combination of elastic and less elastic materials, Corian or acrylic polymers. 
     Please note that any embodiment or part of embodiment as well as any method or part of method could be combined in any way. All examples herein should be seen as part of the general description and therefore possible to combine in any way in general terms.