Abstract:
A support apparatus for supporting an end of a distraction marrow nail includes a base plate attachable to the pelvis, and a mounting device on the base plate for mounting of the support end of the distraction marrow nail. The mounting device includes a ball seat having a cavity forming a ball seat surface for mounting a ball on the support end of the distraction marrow nail, wherein the inside radius of the ball seat surface corresponds to the outside radius of the ball, and wherein the ball seat is arranged so that the ball of the distraction marrow nail can be movably mounted such that the distraction marrow nail can perform a movement sufficient for an extensively normal movement pattern of a femur and cannot luxate out of the ball seat when implanted in the femur.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a support apparatus that can be mounted on the pelvic bone as well as to an apparatus having the support apparatus, for stretching soft tissue parts in the hip region. 
       SUMMARY OF THE INVENTION 
       [0002]    Endoprosthetic hip joint replacement is a widespread operative method if the human hip joint is worn out and severe pain results from this. In this regard, a socket is implanted at the same location where the natural hip joint is placed, in which socket an artificial, round joint head that is anchored in the femur with a shaft can articulate. 
         [0003]    If the hip joint has been displaced toward the head (in the cranial direction) due to an incorrectly placed (dysplastic) socket or after an accident event or after a tumor resection, leg shortening regularly takes place, on the one hand, and, on the other hand, a clear restriction of movement generally occurs, with what is called a neo-joint generally forming around the pelvic head, which joint guarantees support that is able to withstand stress. 
         [0004]    In the case of such a starting situation, in which the hip joint has migrated toward the head, it has only been possible to implant an artificial hip joint with very unsatisfactory results up to the present, because on the one hand, implantation of an artificial joint in the region of the iliac wing yields very poor long-term results, and, on the other hand, placement of the artificial joint in an anatomically correct position is only possible if the femur is pulled in the foot direction and thereby the soft tissue parts are stretched or if shortening of the femur is undertaken. Acute stretching by more than about 2 cm normally leads to damage to the sciatic nerve and thereby to functional failures. In the case of shortening of the femur, a significant leg length difference generally remains, along with dysfunction, because major muscle insertions have to be sacrificed. 
         [0005]    Continuous lengthening procedures, which reduce the risk of nerve damage, were possible in the past only with external fixators, which were attached to the pelvis, for one thing, and to the femur, for another. However, these fixators are extremely stressful for the patient, and there is a significant risk of infection or at least of contamination, something that is particularly problematical in view of the subsequent hip endoprosthesis. 
         [0006]    It is known to carry out leg lengthening procedures with fully implantable, motorized distraction marrow nails, as they are described, for example, in EP 1 371 346 A1. Now a further area of use of these distraction marrow nails is not only to lengthen a bone, but also to stretch the soft tissue parts, for example in order to displace the femur in the foot direction, as in the situation described above, in order to subsequently be able to implant a hip joint endoprosthesis in a regular position. 
         [0007]    The first clinical uses in this regard, as described in “J Bone Joint Surg Vol. 87-B, No. 4, April 2005,” already occurred more than ten years ago. The support apparatus used in this application comprises a mounting device that has a slot, into which the support end of the telescoping part of the distraction marrow nail was introduced, with the movement of the support end being greatly restricted and taking place in uncontrolled manner with regard to the lever effects. 
         [0008]    The problem therefore lies in supporting the support end of the distraction marrow nail on the proximal side facing the pelvis, because here, on the one hand, sufficient axial forces have to be absorbed, but on the other hand, the scope of movement should be restricted as little as possible, because otherwise, the attachment of the apparatus would break out due to the lever forces of the leg. 
       SUMMARY OF THE INVENTION 
       [0009]    The task underlying the invention now lies in implementing a support apparatus that is adapted to the anatomical conditions on the outside of the pelvic bone, and is attached in the lower region, where enough bone mass is present at the acetabular bone, in such a manner that the tensile forces and shear forces that occur here are absorbed, while the resulting pressure forces in the upper region are transferred over the full area. Furthermore, it holds true, on the one hand, that the greatest possible freedom of movement of the leg should be made possible, so that the lever forces resulting from the length of the leg (approximately 1 m) do not pull the fixation screws of the apparatus out of the pelvic bone and thereby lead to loosening, and on the other hand, no luxation (the joint partners moving away from one another) takes place. 
         [0010]    The task underlying the invention is accomplished by means of a support apparatus having the characteristics of claim  1 . Advantageous embodiments of the support apparatus according to the invention are the object of claims  2  to  11 . 
         [0011]    An apparatus provided with the support apparatus, for stretching of soft tissue parts in the hip region, comprises the characteristics of claim  12 . A further apparatus for stretching soft tissue parts in the hip region comprises the characteristics of claim  13 . 
         [0012]    In the support apparatus according to the invention, which can be mounted on the pelvic bone, the mounting device comprises a ball seat having a cavity that forms a ball seat surface, for accommodating a ball provided at the support end of the telescoping part or of the anchoring part. The inside radius of the ball seat surface corresponds to the outside radius of the ball. The ball seat is configured and disposed in such a manner that the telescoping part or the anchoring part is able to perform a sufficient movement for an extensively normal movement pattern of the femur, and cannot luxate out of the ball seat when the telescoping part or the anchoring part is implanted in the femur. 
         [0013]    Sufficient movement is guaranteed, for example, if the longitudinal axis of the telescoping part or of the anchoring part can move within a region of an imaginary cone having a cone angle of approximately 25-45°, preferably approximately 35°, when the anchoring part or the telescoping part is implanted in the femur and the support apparatus is mounted in the pelvic bone. 
         [0014]    Preferably, at least two passage openings disposed at a distance from one another, distally with regard to the mounting device, are provided in the base plate. At these passage openings, the support apparatus is attached to the pelvic bone by means of spongiosa screws. This attachment is sufficient for being able to absorb tensile forces and for transferring pressure forces to the pelvic bone. Attachment openings proximal to the mounting device are therefore not necessary, but they can be provided for further stabilization. The proximal edge of the base plate can be pushed under the muscles that lie against the pelvic bone, without additional attachment being required here, because pressure forces primarily occur in this region. 
         [0015]    In a preferred embodiment, the ball seat comprises a base, preferably formed by a support block, having a sub-cavity with a first partial ball seat surface, which is configured and disposed in such a manner that the ball can be freely laid into the sub-cavity. A covering with a second, small partial ball seat surface can be attached in such a manner that the first partial ball seat surface makes a transition into the second partial ball seat surface to form a total ball seat surface, with the total ball seat surface being larger than the external hemispherical surface of the ball. The covering thereby forms an undercut that prevents luxation of the ball out of the cavity of the ball seat. 
         [0016]    In this case, sufficient security is guaranteed if the total ball seat surface is larger by 2% to 5% than the external hemispherical surface. 
         [0017]    The inside circumference of the total ball seat surface must at least be larger at this location than half the circumference of the ball. 
         [0018]    If the base plate is flattened at its proximal edge, the proximal edge of the base plate can be pushed under the muscles on the pelvic bone without risk of injury. 
         [0019]    To reduce sliding friction, a plastic shell is preferably inserted into the cavity or a friction-reducing coating is applied to the ball or the cavity is coated with friction-reducing material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Exemplary embodiments of the invention will be explained in greater detail below, using drawings. These show: 
           [0021]      FIG. 1 , a perspective view of a support apparatus according to the invention; 
           [0022]      FIG. 2 , a top view of the support apparatus of  FIG. 1 ; 
           [0023]      FIG. 3 , a median cross-section of the support apparatus of  FIG. 1 ; 
           [0024]      FIG. 4 , an apparatus having the support apparatus, for stretching soft tissue parts in the implanted state, at the beginning of a treatment; 
           [0025]      FIG. 5 , the apparatus of  FIG. 4  after stretching of the soft tissue parts toward the end of a treatment; 
           [0026]      FIG. 6 , a further apparatus having the support apparatus, for stretching soft tissue parts in the implanted state at the beginning of a treatment; 
           [0027]      FIG. 7 , the apparatus of  FIG. 6  after stretching of the soft tissue parts toward the end of a treatment; and 
           [0028]      FIG. 8 , a partial section of a distraction marrow nail between an intermediate piece for movable mounting in the support apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    First,  FIGS. 4 and 5  will be described. In  FIGS. 4 and 5 , the skeletal structure of a patient in the hip region is shown schematically, with the left thigh of the patient being displaced toward the head (in the cranial direction) in  FIG. 4 . This displacement can result from an incorrectly placed socket or after an accident event or after a tumor resection. 
         [0030]    The pelvis  2  is disposed in the lower region of the torso  1 . In  FIG. 4 , the joint head  9  is correctly disposed in the hip socket  7  at the upper end of the femur  6  of the right thigh  5 . In the case of the left thigh  3  of the patient, the femur  4  has been displaced upward toward the head with reference to the hip socket  8 . 
         [0031]    In order to allow displacement of the femur  4  toward the foot and to stretch the corresponding soft tissue parts, a distraction marrow nail  12  is implanted in the femur  4 , which nail comprises an anchoring part  14  that is implanted in the femur  4 , in the longitudinal direction of the latter, which part is attached to the femur  4  by means of at least one attachment screw  22  disposed transversely. A telescoping part  16  is guided in the anchoring part  14  so as to be displaceable in the longitudinal direction of the anchoring part  14 . A ball  20  is attached at the proximal end, i.e. the end facing the torso  1 , of the telescoping part  16 , for example by means of a conical press fit, which ball is mounted in a mounting device  18  of a support apparatus  10  in articulated manner. The support apparatus  10  is mounted on the iliac bone of the pelvis  2 . The telescoping part  16  can be displaced in the proximal direction by means of a motor disposed in the anchoring part  14 . To control the motor, the motor is connected with an antenna  24  disposed underneath the skin of the thigh, by way of a cable  26 . A corresponding design of a marrow nail is known, for example, from EP 1 371 346 A1. 
         [0032]    The telescoping part  16  is displaced in the proximal direction, step by step, over an extended period of time, by means of the motor. The telescoping part  16  is supported on the support device  10 , during this process, by way of the ball  20  disposed at the proximal support end of the telescoping part  16 , which ball is mounted in the mounting device  18  in articulated manner; the support device in turn is mounted on the iliac bone of the pelvis  2 . In this way, the femur  4  is displaced in the distal direction, i.e. away from the torso  1 , and at the same time, the soft tissue parts are stretched. Such a method for stretching the soft tissue parts is described in the document “J Bone Joint Surg Vol. 87-B, No. 4, April 2005,” so that the method will not be described in any further detail below. 
         [0033]    A further apparatus for stretching soft tissue parts will be described in connection with  FIGS. 6 and 7 . It shall be noted that the skeletal structure having a left thigh that has been displaced upward, as is illustrated in  FIGS. 6 and 7 , corresponds to the skeletal structure illustrated in  FIGS. 4 and 5  and is denoted by the same reference numerals. To avoid repetitions, reference shall be made to the description of  FIGS. 4 and 5  provided above. 
         [0034]    The apparatus for stretching soft tissue parts includes a distraction marrow nail  12   a  implantable in the femur  4  and a support apparatus  10  for proximally supporting the distraction marrow nail  12   a . The support apparatus  10  is identical to the support apparatus shown in  FIGS. 4 and 5  and will be described in more detail hereafter in connection with  FIGS. 1 and 3 . 
         [0035]    The distraction marrow nail  12   a , in turn, comprises an anchoring part  14 , a telescoping part  16  mounted displaceably in the anchoring part  14 , and a drive disposed in the anchoring part  14  for linearly displacing the telescoping part  16  relative to the anchoring part  14 . The drive comprises a motor and a gear unit. These are not shown in  FIGS. 6 and 7 . By actuating the drive, the telescoping part  16  can be extended and retracted in the longitudinal direction of the anchoring part  14 . The control of the motor, in turn, takes place by way of a cable  26  and an antenna  24  disposed underneath the skin of the thigh. 
         [0036]    The distraction marrow nail  12   a  thus comprises the same components as the distraction marrow nail  12  in  FIGS. 4 and 5  and differs from the same in that the ball  20  for mounting on the support apparatus  10  is disposed at the end of the anchoring part  14  located opposite the telescoping part  16 . Correspondingly, the apparatus for stretching soft tissue parts shown in  FIGS. 6 and 7  differs from the apparatus shown in  FIGS. 4 and 5  in that the distraction marrow nail  12   a  is movably mounted on the support apparatus  10  by way of the anchoring part  14  thereof, and the telescoping part  16  can be attached to the femur  4  by way of a transversely disposed fastening screw  22 . Compared to the arrangement in  FIGS. 4 and 5 , the distraction marrow nail  12   a  in  FIGS. 6 and 7  is thus disposed rotated by 180°.  FIG. 6  shows the apparatus for stretching soft tissue parts in the implanted state at the beginning of a treatment. The telescoping part is in a retracted position. Only the distal end of the telescoping part  16  protrudes from the distal end of the anchoring part  14  and is attached to the femur by way of a nail  22 . So as to allow a displacement of the femur  4  toward the foot and stretch the corresponding soft tissue parts, the telescoping part  16  can be incrementally displaced in the distal direction (that is away from the torso  1 ) by way of the motor. As a result of the incremental extension of the telescoping part  16 , the femur  4  is displaced in the distal direction. The apparatus shown in  FIGS. 6 and 7  thus achieves the same result as the apparatus in  FIGS. 4 and 5 . The only difference is the orientation and mounting of the distraction marrow nail  12   a , which in the embodiment shown in  FIGS. 6 and 7  is attached with the telescoping part  16  thereof to the femur  4  and movably mounted in the mounting device  10  with a ball  12  affixed to the proximal end of the anchoring part  14 . 
         [0037]    According to one implementation, the distraction marrow nail  12   a  described in connection with  FIGS. 6 and 7  can furthermore comprise an intermediate piece  100  disposed between the ball  20  and the proximal end of the distraction marrow nail  12   a . The position of the intermediate piece  100  is indicated in  FIG. 6 .  FIG. 8  schematically shows the proximal end of the distraction marrow nail  12   a  together with the intermediate piece  100  and the ball  20 . 
         [0038]    The intermediate piece  100  is attached with its distal end  120  to the anchoring part  14  of the distraction marrow nail  120   a . For this purpose, the intermediate piece  100  can be connected to the proximal end of the anchoring part  14  in a form-locked or integral manner. At the proximal end  110  of the intermediate piece  100 , furthermore the ball  20  is attached for movable mounting in the support apparatus  10 . The intermediate piece  100 , together with the ball  20 , thus forms the support end of the distraction marrow nail  12   a . By using the intermediate piece  100 , a conventional distraction marrow nail can thus be used to implement the apparatus for stretching soft tissue parts described in connection with  FIGS. 6 and 7 . The conventional distraction marrow nail only has to be provided with the intermediate piece  100  with the ball  20  described herein. 
         [0039]    According to the embodiment shown in  FIG. 8 , the ball  20  is attached to the rod-shaped proximal end of the intermediate piece  100  and rigidly connected thereto. Alternatively, it is also conceivable that the ball  20  is designed as a one-piece support element together with the intermediate piece  100 . Independently of the one-piece or two-piece design described herein, according to one advantageous embodiment the intermediate piece  100  can furthermore have a constriction  130  extending in the circumferential direction of the intermediate piece  100  (see  FIG. 8 ), which is disposed (directly) behind the ball  20  on the intermediate piece  100 , considered from the proximal end. As a result of this constriction  130  at the intermediate piece  130 , the scope of movement of the distraction marrow nail relative to the support apparatus  10  is further increased. 
         [0040]    The structure of the support apparatus  10  and mounting of the ball  20  of the telescoping part  16  or of the anchoring part  14  in the mounting device  18  is shown in detail in  FIGS. 1 to 3 . 
         [0041]    The support apparatus  10  is configured symmetrically with reference to a center plane ME that runs perpendicular to the plate plane. In the following, the terms “proximal” and “distal” will be used with regard to the placement of individual elements, with proximal meaning facing the torso  1  and distal meaning facing away from the torso  1 . 
         [0042]    The support apparatus  10  comprises a base plate  28  that has two side edges  30 ,  32 , which run parallel to one another and parallel to the center plane ME in the distal section, and subsequently run curved toward the center plane ME in the proximal direction, so that they form a rounded-off front tip  42  at the intersection point with the center plane ME. In the distal side edge  34 , which runs perpendicular to the center plane ME, in total, an indentation  36  is formed in the center. On both sides of the center line ME, two passage openings  38 ,  40  pass through the base plate  28  adjacent to the distal side edge  34 . A further passage opening  39  is configured in the center between the passage openings  38  and  40 . 
         [0043]    Proximal to the passage openings  38 ,  39 ,  40 , a mounting device  18  is provided on the base plate  28 , which device comprises a ball seat  48 , in which a cavity  58  is configured, in which the ball  20  is mounted on the support end of the telescoping part  16  or at the support end of the anchoring part  14 . 
         [0044]    The ball seat  48  consists of two elements, which each form a partial ball seat surface. A support block  56  extends upward from the top of the base plate  28 . A sub-cavity  84  is configured in the support block  56 , which cavity defines a first partial ball seat surface. The sub-cavity  84  is open in the distal direction, and is delimited by a face edge  60  that runs perpendicular to the center plane ME. 
         [0045]    As can be seen in  FIG. 3 , the ball sector of the spherical section of the sub-cavity  84  is slightly smaller than the hemisphere sector of the ball  20  of the telescoping part  16  or of the ball of the anchoring part  14 . The surface of a slanted step  62  extends from the lower end of the spherical part of the sub-cavity  84 , essentially tangentially in the distal direction, at an upward slant. 
         [0046]    The sub-cavity  84  of the support block  56  is therefore configured in such a manner that the ball  20  of the telescoping part  16  or of the anchoring part  14  can be laid into the sub-cavity  84  if no covering  72  is affixed, without the ball  20  having to be acutely displaced in the distal direction. 
         [0047]    The covering  72  is affixed to the face side of the support block  56 . The covering  72  is essentially configured in U shape and lies on the slanted step  62  with the free ends of its shanks. A passage opening  74  and  76  is configured at the ends of the two free shanks, in each instance, through which openings the attachment screws can pass, which screws attach the covering  72  to the support block  56 . The inside of the covering  72  forms a second partial ball seat surface  86  in the upper, arc-shaped region, which surface follows flush with the partial ball seat surface of the cavity  58 , thereby increasing the total ball seat surface in such a manner that it is larger than the hemispherical surface of the ball  20 . In other words, an undercut is formed by the covering  72 , which undercut prevents the ball  20  from being able to luxate out of the ball seat  48  when the covering  72  is affixed to the support block  56 . 
         [0048]    For firm anchoring of the covering  72  on the support block  56 , a groove  64  is configured in the top section of the support block  56 , adjacent to the face edge  60 , thereby defining an edge projection  66  at the edge  60 . At the same time, an engagement shank  70  having an engagement groove  68  is configured in the covering  72 , which groove engages into the groove  64  by way of the edge projection  66 . By means of the formation of the engagement groove  68 , an engagement shank  70  is thereby formed at the proximal edge of the covering  72 , which shank engages into the groove  64 . In this way, a shape-fit connection of the covering  72  with the support block  56  is created when the covering  72  is attached to the support block  56  by means attachment screws that pass through the passage openings  74 ,  76 . 
         [0049]    In order to reduce the slide friction between the ball  20  in the cavity  58  of the ball seat  48 , a plastic shell  50  is disposed in the cavity  58 , which shell lies against the seat surface. A projection  52  is configured on the plastic shell  50 , in the proximal region, which projection engages into a recess  54  in the cavity  58 , thereby preventing spherical displacement of the plastic shell and guaranteeing secure hold of the plastic shell  50  in the cavity  58 . The plastic shell  50  thereby forms the actual cavity, the inside diameter of which corresponds to the outside diameter of the ball  20 . 
         [0050]    The ball seat  48  in total is configured in such a manner that the longitudinal axis LT of the telescoping part  16  or of the anchoring part  14  can move within a range of an imaginary cone having a cone angle of 25-45°, preferably 35°, when the anchoring part  14  or the telescoping part  16  is implanted in the femur  4  and the support apparatus  10  is mounted on the pelvic bone  2 . 
         [0051]    Proximal to the mounting apparatus  18 , the base plate  28  is flattened toward the tip  42 , thereby making it possible to push the tip  42  under the muscles that lie against the pelvic bone without any risk of injury. 
         [0052]    In particular, the base plate  28  is designed as a flat plate, which has a flat plate side (that is flat plate back side) located opposite the mounting device  18 . The support apparatus  10  can thus be placed with the flat back side of the base plate against the pelvic bone and attached thereto. At the same time, the mounting device  18  disposed on the base plate front side allows the ball  20  to be movably mounted so as to ensure good movability of the distraction marrow nail  12 ,  12   a  in the frontal and sagital planes. 
         [0053]    The base plate  28 , together with the mounting device  18  except for the covering  72 , preferably forms one part, with all the borders and edges being rounded off in order to minimize the risk of injury. 
         [0054]    The base plate  28 , with the mounting device  18  and the covering  72 , is preferably formed from steel or titanium. The plastic shell  50  is preferably formed from PTFE or PEEK. 
       REFERENCE SYMBOL LIST 
       [0000]    
       
           1 —torso 
           2 —pelvic bone 
           3 —left thigh 
           4 —left femur 
           5 —right thigh 
           6 —right femur 
           7 —right hip socket 
           8 —left hip socket 
           9 —joint head 
           10 —support apparatus 
           12 ,  12   a —distraction marrow nail 
           14 —anchoring part 
           16 —telescoping part 
           18 —mounting device 
           20 —ball 
           22 —screw 
           24 —antenna 
           26 —cable 
           28 —base plate 
           30 —right side edge 
           32 —left side edge 
           34 —distal side edge 
           36 —indentation 
           38 —passage opening 
           39 —passage opening 
           40 —passage opening 
           42 —tip 
           48 —ball seat 
           50 —plastic shell 
           52 —projection 
           54 —recess 
           56 —support block 
           58 —cavity 
           60 —face edge 
           62 —slanted step 
           64 —groove 
           66 —edge projection 
           68 —engagement groove 
           70 —engagement shank 
           72 —covering 
           74 —passage opening 
           76 —passage opening 
           82 —flattened part 
           84 —sub-cavity 
           86 —partial ball seat surface 
           100 —intermediate piece 
           110 —intermediate piece, proximal end 
           120 —intermediate piece, distal end 
           130 —constriction