Abstract:
The invention relates to a surgical retractor, particularly for the retraction of a separated sternum, with a holding device and two spreader arms, wherein the spreader arms are mounted with one end on the holding device, at a distance from each other that is adjustable in a spreading plane, and at least two retaining elements for retention of bone material, for example of the separated sternum, are arranged on each of the spreader arms. To develop this retractor for sternotomy in such a way as to permit gentler opening of the separated sternum, it is proposed that at least one of the retaining elements is mounted such that its position can be modified in the retraction direction with respect to that end of the spreader arm mounted on the holding device.

Description:
[0001]    This application is a continuation of International application No. PCT/EP2012/074802 filed on Dec. 7, 2012 and claims the benefit of German application no. 10 2012 100 284.3 filed on Jan. 13, 2012, which are incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a surgical retractor, particularly for the spreading of a parted sternum, with a holding device and two spreader arms, said spreader arms being held with one end on the holding device at a spacing from one another that is adjustable in a spreading plane. One or more retaining elements are arranged on each of the spreader arms for the retention of bone material, for example the parted sternum. 
         [0003]    Surgical retractors of the aforementioned type are used, in particular, for operations on the heart in order to gain suitable access. The sternum is parted centrally in the longitudinal direction thereof and the sternum halves are forced back to either side, i.e. retracted, together with the adjacent ribs, by means of the retractor. 
         [0004]    As a result of the shape and arrangement of the ribs, the observed stiffness at the cranial end of the sternum halves is significantly greater than at the caudal end. 
         [0005]    As a result of the varying stiffness, with conventional retractors in particular, in which the achieved opening widths of the sternum are the same in the cranial and caudal directions, in the absence of any additional setting or adjusting capability, unfavourable forces arise along the vertical axis of the sternum. 
         [0006]    Particularly in the case of the cranially positioned ribs, due to the substantially greater stiffness there, larger forces occur than at the caudally positioned ribs. This, in turn, results in increased stresses in these ribs, as a result of which greater postoperative pain can occur. 
         [0007]    The pain results, above all, if a cranially positioned rib damages the brachial plexus (Plexus brachialis) which is positioned in the region of the shoulder, due to the deformation of said rib or even splintering of pieces off the rib in this region. 
         [0008]    In an extreme case, the breakage of a cranially positioned rib can even occur. Since these ribs are positioned under the clavicle, rib breakages are not detected in a normal X-ray image. However, recent studies show that they occur more often than previously suspected. 
         [0009]    From US 2007/0161865 A1, there is known a surgical retractor in which this problem is partially taken into account in that the holding device is configured slightly bow-shaped so that the retaining elements arranged at the free ends of the spreader arms perform a slightly bow-shaped movement during retraction. A further adaptation is enabled by a spreader arm which is held on the holding device pivotable in the spreading plane. However, the latter requires additional intervention and adjustment, making the process more complex and more time-consuming. 
         [0010]    It is an object of the present invention further to develop the retractor mentioned in the introduction for sternotomy such that a gentler opening of the parted sternum is made possible. 
       SUMMARY OF THE INVENTION 
       [0011]    The object of the present invention is achieved with a surgical retractor having the features set forth in the claims and discussed in detail below. 
         [0012]    Due to the mounting of at least one of the retaining elements being positionally changeable in the retraction direction relative to a spreader arm, it is possible, when the sternum is opened by the retractor, to change and adapt within a certain range the forces which act on the cranially and caudally positioned rib arches. This is achieved in many of the embodiments of the invention without the surgeon having to intervene or make adjustments for this purpose. 
         [0013]    In this way, the ribs adjacent to the sternum are more evenly loaded so that the danger of stress peaks in individual ribs which, in the worst case, can lead to fractures, can be significantly reduced. 
         [0014]    If a pair of retaining elements mounted to be positionally adjustable is provided, they can be held on a common spreader arm or preferably in opposing positions, each on one of the spreader arms, for example, each adjacent to the end of the spreader arms held on the holding device. 
         [0015]    It is most preferable if all the retaining elements are held so as to be positionally adjustable on the spreader arms. 
         [0016]    For the positionally adjustable mounting, there are several preferred possibilities, which will be discussed subsequently. If a plurality of the retaining elements of a rectractor according to the invention are mounted to be positionally adjustable, they can be held in different ways on the spreader arms according to the different possibilities, as discussed below. 
         [0017]    According to a first preferred embodiment of the invention, the at least one retaining element is mounted in its position in the retraction direction resiliently relative to the spreader arm. By means of the resilient mounting, the adaptation of the forces acting on the parted sternum is achieved with a noticeable effect even when using single-piece, rigid spreader arms. 
         [0018]    More preferably, a pair of the retaining elements is resiliently mounted on the spreader arm(s) and most preferably, all the retaining elements are mounted resiliently in the retraction direction on the spreader arms. 
         [0019]    In a second preferred embodiment according to the invention, at least one of the spreader arms of the surgical retractor is divided into two sections wherein a first section of the spreader arm is held substantially rigidly on the holding device and a second section of said spreader arm is held on the first section rotatable about an axis perpendicular to the spreading plane. The positional change is achieved here by means of pivoting of the second part of the spreader arm during the retraction process, again without any manual intervention by the surgeon. 
         [0020]    Preferably, in this embodiment, the second section is resiliently held in a starting position substantially colinear or coaxial with the first section. As force acts parallel to the spreading plane during the retraction, the second section is pivoted against the first section, against the resilience. 
         [0021]    More preferably, the pivoting movement is limited to a predetermined angle by means of a stop. 
         [0022]    Preferably, in this embodiment of the retractor according to the invention, both spreader arms are subdivided into two sections wherein a first section of each spreader arm is held substantially rigidly on the holding device and the second section of the spreader arms is held on the first section rotatable about a pivot axis perpendicular to the spreading plane. 
         [0023]    Preferably, in this embodiment, a first retaining element is held on the first section of the spreader arm which is rigidly connected to the holding device and a second retaining element is held on the second, pivotable section of the spreader arm. 
         [0024]    In a variant of this embodiment, it can be provided that the second section can be locked, if needed, in a position pivoted relative to the first section. 
         [0025]    In a further variant of this embodiment, it is provided that the second section is pivotable relative to the first section by means of a drive, wherein the drive is preferably configured to be self-locking. 
         [0026]    Preferably, in the second embodiment of the retractor according to the invention, the first section of the spreader arm(s) has a length which is greater than half the overall longitudinal extent of the spreader arm. 
         [0027]    In a third embodiment of the retractor according to the invention, two retaining elements are arranged on the second section, wherein the pivot axis which connects the first section to the second section is arranged between the retaining elements. Preferably, approximately half of the second section overlaps, in the longitudinal extent thereof, with the longitudinal extent of the first section of the spreader arm. There is then preferably no retaining element arranged on the first section of the spreader arm. 
         [0028]    In the second and third embodiment, according to one variant, the first section of the spreader arm is formed substantially straight. In a further variant, the free end of the first section, on which the second section is pivotably mounted, is formed angled, the angled region projecting in the spreading plane toward the respective other spreader arm. The second section is then mounted on the free end of the angled part, pivotable in the spreading plane. 
         [0029]    Here also there are several variants for the mounting of the second section on the first section of the spreader arm. 
         [0030]    According to a first variant, the second section of the spreader arm is resiliently held in a starting position with a preferably parallel orientation relative to the first section. 
         [0031]    According to a second variant, the second section is lockable on the first section in a pre-defined pivot position. 
         [0032]    According to a third variant, the pivotability of the second section relative to the first section is limited by a stop. 
         [0033]    According to a fourth variant, the second section is mounted pivotable relative to the first section by means of a drive, wherein the drive is preferably configured to be self-locking. 
         [0034]    In general, it is preferred in the second and third embodiments if the retaining elements are arranged at a substantially equal spacing from the pivot axis of the second section of the spreader arm. The pivot axis is preferably arranged substantially centrally to the longitudinal direction of the second section. 
         [0035]    Furthermore, the pivot axis of the second section can be fixable at a plurality of positions along the longitudinal direction of the second section. Preferably, the second section has a plurality of mounting bushings for this purpose. 
         [0036]    In another alternative, it is provided that the pivot axis is formed by a bearing element which is displaceably held on the first section. 
         [0037]    According to a fourth embodiment of the invention, the second section is held at a flexibly elastic region of the first section. 
         [0038]    If the first section of a spreader arm is configured to be angled at the free end thereof, in one variant, the angled region can be divided to be fork shaped in the spreading plane. Then the second section is preferably subdivided into two separate longitudinal elements of which each is connected to one of the fork prongs. 
         [0039]    The second spreader arm itself also can be configured flexibly elastic in the spreading plane and can thus further lead to or contribute to the positionally changeable holding of the retaining elements. 
         [0040]    The invention also relates to a surgical retractor of the type mentioned in the introduction, wherein the two spreader arms are subdivided into two segments seen in the longitudinal direction, wherein a first segment is held with one end on the holding device in a substantially unchangeable orientation relative to the spreading plane and wherein a second segment is held at the free end of the first segment, so as to be pivotable about a pivot axis in a plane perpendicular to the spreading plane. Typically, the pivot axis extends transversely to the longitudinal direction of the spreader arms. 
         [0041]    Preferably, the pivotal angle of the second segment is restricted by means of a stop so that preferably a pivot movement of the second segment is possible only in a direction out of the spreading plane. 
         [0042]    According to a further preferred aspect, the length of the first segment is smaller than that of the second segment and is preferably approximately 30% or less of the overall length of the spreader arm. 
         [0043]    More preferably, the retaining elements are directly or indirectly held exclusively on the second segment of the spreader arms. 
         [0044]    The subdivision of the spreader arms into two segments wherein the second segment is pivotably held on the first segment has the advantage that the geometry of the surgical retractor can adapt to the shape of the torso of the patient, so that the space required by the device and thus at the same time any possible hindering of the surgeon can be lessened. 
         [0045]    Insofar as the spreader arms are subdivided into a first and a second section, the joint connection between the first and the second segment is preferably arranged in the first section. 
         [0046]    It should be noted at this point that the subdivision of the spreader arms, firstly, into a first and a second section and, secondly, into a first and a second segment do not represent competing concepts, but rather two concepts which can be simultaneously realised in one embodiment of a surgical retractor according to the invention. 
         [0047]    In all the previously described embodiments and all the variants thereof, in additional to the positional adjustability possibly provided there, the retaining elements can be resiliently held on the spreader arms or the first and/or second sections thereof. The resilient mounting can be used herein for further improvement of the adaptation of the forces acting on the parted sternum. 
         [0048]    For all the above described embodiments, it is the case that the retaining elements are preferably adjustable in the spacing thereof along the spreader arm. This enables a further optimisation of the retractor according to the invention with regard to the introduction of the forces onto the bone material lying against the retaining elements. 
         [0049]    In order to achieve the most favourable possible geometry for introducing the retractor into the gap of the parted sternum, the retaining elements of the two spreader arms are arranged offset relative to one another in the longitudinal direction thereof. Thus the spreader arms can initially be brought into maximum proximity to one another. 
         [0050]    Further preferred retaining elements which can be used in the retractors according to the invention are formed in two parts. 
         [0051]    Preferably in this regard, a first part of the retaining element is held as a bearing part on the spreader arm and the second part, which is formed as a retaining surface, is mounted on the first part to be movable, in particular pivotable about an axis oriented perpendicular and/or parallel to the spreading plane. 
         [0052]    Preferred retaining elements have a retaining surface with a maximum extent parallel to the longitudinal direction of the spreader arm in a region with which the bone material typically comes into contact, whilst the extent thereof adjacent, on the one hand, to the spreader arm and/or, on the other hand, at the free end of the retaining surface is selected to be smaller. This provides the surgeon with a better view, for example, during preparation of an Arteria mammaria. 
         [0053]    Particularly advantageous is a web-like narrowly constructed free end of the retaining surface which can also be configured bent over so that the bone material of the sternum is securely gripped. 
         [0054]    Preferred retaining elements have a bearing part in which a locking device is integrated, with which a releasable locking connection to the spreader arm can be made. For this purpose, the spreader arm preferably has pre-determined locking positions so that defined placement of the retaining elements along the spreader arms is possible. Thus retaining elements can be placed, in particular opposing one another on different spreader arms, precisely aligned to one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0055]    This and other advantages of the invention will now be described in greater detail based on the drawings, in which: 
           [0056]      FIG. 1  shows an embodiment of a retractor according to the invention; 
           [0057]      FIG. 2  shows another embodiment of a retractor according to the invention; 
           [0058]      FIG. 3  shows another embodiment of a retractor according to the invention; 
           [0059]      FIGS. 4A and 4B  show a variant of the embodiment of the retractor of  FIG. 3 ; 
           [0060]      FIG. 5  shows a further variant of the embodiment of the retractor of  FIG. 3 ; 
           [0061]      FIG. 6  shows another embodiment of a retractor according to the invention; 
           [0062]      FIG. 7  shows another embodiment of a retractor according to the invention; 
           [0063]      FIG. 8  shows another embodiment of a retractor according to the invention; and 
           [0064]      FIGS. 9A and 9B  show a preferred retaining element for a retractor according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0065]      FIG. 1  shows an embodiment of a retractor  10  according to the invention, having a holding device  12  and two spreader arms  14  and  16  arranged on the holding device  12  and positionable at a variable spacing from one another. The two spreader arms  14  and  16  are arranged substantially perpendicularly to the longitudinal direction of the holding device  12  and parallel to one another and define the spreading plane of the retractor  10 . 
         [0066]    The holding device  12  comprises a substantially straight rail  18  on one end  20  of which one end of the second spreader arm  16  is formed integrally. The spreader arm  14  is arranged to be displaceable in the longitudinal direction of the rail  18 . For this purpose, the spreader arm  14  has a bearing element  22  which engages round the rail  18  of the holding device  12 . 
         [0067]    The rail  18  has a substantially rectangular cross-section in which a row of teeth  24  is provided at a narrow side thereof. The bearing element  22  has a drive mechanism  26  with a rotary body (not shown in detail), for example, a pinion or a gearwheel, which meshes with the row of teeth  24 . This rotary body is held rotationally fixed on a bearing shaft  28  which extends perpendicularly to the longitudinal axis of the rail  18  and to the spreading plane and is rotatably held in the bearing element  22 . At the free end, oriented upwardly in the Figure, the bearing shaft  28  has a grip element  30  with which the rotary body can be rotated and, consequently, the spacing of the two spreader arms  14  and  16  from one another along the rail  18  can be changed. 
         [0068]    The spreader arms  14 ,  16  each have straight first sections  34 ,  36  which are arranged adjacent to the holding device  12 , and straight second sections  38 ,  40  which are pivotably held at the free end of the first sections  34 ,  36  of the spreader arms  14  and  16 . The length of the first sections  34 ,  36  is somewhat greater than the length of the second sections  38 ,  40 . 
         [0069]    For the mounting of the second sections  38 ,  40 , the first sections  34 ,  36  of the spreader arms  14  and  16  comprise forked bearing elements  42 ,  44  in each of which a holding device-side end of the second sections  38 ,  40  is held so as to be pivotable in the spreading plane by means of a pivot bearing  46  or  48 . 
         [0070]    Two retaining elements  50 ,  51  and  52 ,  53  are held on each of the spreader arms  14 ,  16 . Each of the retaining elements  50  and  52  is arranged on a first section  34  and  36  and each of the retaining elements  51  and  53  is arranged on a second section  38  and  40  of the spreader arms  14  and  16 . The retaining elements  50 ,  51 ,  52 ,  53  are each formed in two parts with a bearing part  54 ,  55 ,  56 ,  57  and retaining surfaces  58 ,  59 ,  60 ,  61  held thereon rotatable about an axis perpendicular to the spreading plane. The bearing parts  54 ,  55 ,  56 ,  57  are preferably configured such that they are held displaceably on their respective associated sections of the spreader arms  14  and  16  and can be fixed in different positions. Due to the somewhat greater length of the first sections  34 ,  36  in relation to the length of the second sections  38 ,  40 , it is ensured that the retaining elements can be positioned symmetrically to the pivot bearings  46 ,  48  making use of the overall length of the second sections  38 ,  40 . 
         [0071]    Due to the division of each of the spreader arms  14  and  16  into two sections  34 ,  38  and  36 ,  40  and the pivotable mounting of the second sections on the first sections, mounting of the retaining elements  58 ,  59 ,  60 ,  61  with changeable positions in the spreading plane is achieved. During retraction of the longitudinally parted sternum of a patient, the substantial forces to be applied can be introduced differently regulated over the length of the parted sternum so that a gentler opening of the parted sternum is possible. 
         [0072]    The pivotable mounting of the second sections  38 ,  40  on the first sections  34 ,  36  of the spreader arms  14 ,  16  can be realised in various ways. 
         [0073]    Firstly, the second sections  38 ,  40  can be held resiliently on the first sections  34 ,  36  in a straight orientation, as shown in  FIG. 1 . This can be achieved, for example, by means of extension springs, compression springs or torsion springs, wherein the spring moduli for the individual second sections can be different and, in particular, adjustable. Only when the retraction forces occur due to the actuation of the drive mechanism  26  of the bearing element  22  do the second sections  38 ,  40  pivot in the spreading plane against the spring force of the mounting. The angles through which the second sections can be deflected from the straight line configuration are preferably limited by a stop. Preferably the stops limit the deflection to approximately 30°. 
         [0074]    Furthermore, the pivot bearings  46 ,  48  can be replaced by pivot drives with which a deflection drive can be pre-determined. 
         [0075]    A device for locking the second sections in a pivot position, once reached, can also be provided. 
         [0076]    The length of the first sections  34 ,  36  is greater than half the overall longitudinal extent of the spreader arms  14  and  16 , so that the pivot bearings  46 ,  48  are arranged approximately in the centre of the longitudinal extent of the spreader arms  14 ,  16 . 
         [0077]    A further embodiment of the retractor according to the invention  80  is shown in  FIG. 2 . The retractor  80  comprises a holding device  82  and two straight, rigid spreader arms  84 ,  86  arranged parallel, of which the first spreader arm  84  is held at one side and is longitudinally displaceable on the holding device  82  or the rail  88  thereof, whilst the second spreader arm  86  is formed integrally and at right angles onto one end  90  of the holding device  82 . The two spreader arms  84  and  86  define the spreading plane of the retractor  80 . 
         [0078]    The rail  88  is provided over the major part of its longitudinal extent and on a narrow side of its rectangular cross-section with a row of teeth  94 . 
         [0079]    The spreader arm  84  is arranged to be displaceable on the rail  88  with a bearing element  92 . The bearing element  92  includes a drive mechanism  96  which comprises a rotary body (not shown in detail) which comprises, for example, a gearwheel which engages in the row of teeth  84 . The drive mechanism  96  comprises a shaft  98  held in the bearing element  92 , said shaft being rotatable by means of a grip element  100  so that a linear displacement of the spreader arm  84  along the longitudinal direction of the holding device  82  or along the rail  88  thereof results therefrom and therefore a change in the spacing between the two spreader arms  84  and  86 . 
         [0080]    Retaining elements  102 ,  103  and  104 ,  105  are arranged in pairs on the two rigid spreader arms  84 ,  86 . The retaining elements  102 ,  103 ,  104 ,  105  are mounted on the spreader arms  84  and  86  preferably so as to be displaceable along the longitudinal direction of said spreader arms and are also preferably fixable at respective pre-defined positions. 
         [0081]    Further preferably, the number of retaining elements provided corresponds to the number of ribs held on the sternum. 
         [0082]    The retaining elements  102 ,  103 ,  104 ,  105  are also formed in a plurality of parts and comprise a holder part  110 ,  111 ,  112 ,  113  on which retaining surfaces  106 ,  107 ,  108 ,  109  are pivotably held, preferably about an axis perpendicular to the spreading plane. The holder parts  110 ,  111 ,  112 ,  113  comprise a bearing part (not shown in detail) which engages round the substantially rectangular cross-section of the spreader arms  84  or  86 , and a resiliently biased holder  120 ,  121 ,  122 ,  123  thereon. The resilient biasing of the holders  120 ,  121 ,  122 ,  123  is preferably selected for the individual retaining elements  106 ,  107 ,  108 ,  109  depending on the position thereof, so that force can be applied to each region of the sternum during retraction according to the anatomical conditions. 
         [0083]    Based on the resilient holding of the retaining elements  106 ,  107 ,  108 ,  109 , the possibility exists of positionally adjustable mounting of the retaining elements or of the retaining surfaces which come into contact with the bone materials, so that the substantial forces that must be applied during retraction of a sternum can again be exerted in a regulated manner and adapted to the different elasticity of the sternum and the rib arches adjacent thereto. 
         [0084]      FIG. 3  shows a further embodiment of a retaining device  140  according to the invention with a holding device  142  and two spreader arms  144 ,  146  held on one side on the holding device  142 . The holding device  142  comprises a rail  148  which is configured substantially straight and has a substantially rectangular cross-section. The rail  148  has a row of teeth  150  on one of its narrow sides. 
         [0085]    The spreader arm  144  is displaceable along the longitudinal direction of the rail  148  so that the spreader arm  144  can be moved closer to the spreader arm  146  or the spacing of the two spreader arms from one another can be increased. For this purpose, the spreader arm  144  is displaceably held by means of a bearing element  152  on the holding device  142  or on the rail  148  thereof. The bearing element  152  comprises a drive mechanism  154  which comprises a rotary body (not shown in detail), for example, in the form of a pinion or a gearwheel which is mounted rotationally fixed on a drive shaft  156  which protrudes upwardly from the bearing element  152  and is equipped there with a grip element  158 . 
         [0086]    Through rotation of the shaft  156  with the aid of the grip element  158 , by means of the rotation movement of the rotary body, a displacement of the spreader arm  144  along the rail  148  can take place. Preferably, the rotary body of the drive device  154  can be configured such that a self-blocking connection is formed between the rotary body and the row of teeth  150  of the rail  148 . 
         [0087]    The second spreader arm  146  is integrally formed onto one end  160  of the holding device  142 . The two spreader arms  144 ,  146  lie in one plane, the spreading plane. 
         [0088]    The two spreader arms  144 ,  146  are formed in two parts wherein a straight first section  162 ,  164  is held on the holding device  142  at a right angle. At their free end opposed to the holding device  142 , the two first sections  162 ,  164  have bearing locations  166 ,  168  on each of which a straight second section  170 ,  172  of the spreader arms  144 ,  146  is pivotably held. Preferably, the second sections can be locked in an orientation parallel to the first sections, so that application of the retractor is simplified. 
         [0089]    In a modified embodiment, only one spreader arm is formed in two parts, wherein a larger pivot angle of the second section of the divided spreader arm is to be permitted. During the retraction process, the position of the holding device is then changed. This embodiment has the advantage that the number of parts needed is reduced. 
         [0090]    In contrast to the embodiment of  FIG. 1 , the second sections  170 ,  172  are not attached at one of the ends thereof to the first section  162 ,  164 , but are centrally rotatable about an axis perpendicular to the spreading plane at the free end of the first sections  162 ,  164  of the spreader arms  144 ,  146 . As a consequence, the second section  170 ,  172  overlaps with approximately half of the length thereof with the free end of the first sections  162 ,  164  of the spreader arms  144 ,  146 . 
         [0091]    The retractor  140  also has four retaining elements  180 ,  181 ,  182 ,  183  which, however, are held in pairs on the second sections  170 ,  172 . Preferably, the retaining elements  180 ,  181 ,  182 ,  183  are held longitudinally displaceable on the second sections  170  and  172  and fixable in the respective pre-determined positions thereof. 
         [0092]    The retaining elements  180 ,  181 ,  182 ,  183  are also formed, similarly to the retaining elements of the embodiment of  FIG. 1 , in two parts wherein a first part constitutes a holder part  184 ,  185 ,  186 ,  187  on which retaining surfaces  188 ,  189 ,  190 ,  191  are held pivotable about an axis perpendicular to the spreading plane. 
         [0093]    When the retraction forces are applied to the longitudinally parted sternum, the second sections  170 ,  172  with their retaining elements  180 ,  181 ,  182 ,  183  automatically become oriented according to the resistance forces exerted by the bone material of the sternum and the rib arches adjacent thereto so that a positionally changeable mounting of the retaining elements is produced and a regulated introduction of forces according to the different elasticities of the individual sections of the parted sternum with the rib arches adjacent thereto is possible. This embodiment of the invention enables the matching of the forces without spring elements, resulting in advantages in relation to the non-linear spring moduli of the ribs in the sternotomy. In particular, this retractor according to the invention also reacts automatically and individually to different thoracic cages of the patients according to the leverage/force ratio. 
         [0094]      FIGS. 4A and 4B  show a variant of the retractor  140  according to the invention of  FIG. 3  in the form of a retractor  200 . The retractor  200  comprises a holding device  202  and two spreader arms  204 ,  206  held thereon on one side and in one plane, the spreading plane. 
         [0095]    The spreader arms  204 ,  206  are again formed in two parts and with a straight first section  208 ,  210 , each held on the holding device  202  on one side. At their free end  212 ,  214  opposed to the holding device  202 , they carry a straight second section  216 ,  218  which is pivotable about an axis perpendicular to the spreading plane. The second sections  216 ,  218  again overlap in large parts with the associated first section  208 ,  210  of the spreader arms  204 ,  206 , so that both pairs are held on retaining elements  222 ,  223 ,  224 ,  225  on the respective second sections  216 ,  218  of the spreader arms  204 ,  206 . 
         [0096]    However, although in the embodiment of  FIG. 3 , the second sections are unchangeably pivotably centrally fixed on the associated first section, in the embodiment of  FIGS. 4A and 4B , it is provided that the position of the mounting on the second section  216 ,  218  can be changed and preferably, for this purpose, a plurality of mounting locations  220   a ,  220   b ,  220   c ,  220   d  are provided on the second section  216 ,  218 . 
         [0097]    Thus the leverage of the sections L1 and L2 of the second sections  216 ,  218  of the spreader arms  204 ,  206  can be changed and therefore adapted according to the conditions for a patient, as shown schematically in  FIG. 4 . 
         [0098]      FIG. 5  shows a further embodiment of the retaining device  240  according to the invention with a holding device  242  and two spreader arms  244 ,  246  held on one side of the holding device  242 . The holding device  242  comprises a rail  248  which is formed substantially straight and has a substantially rectangular cross-section. The rail  248  has a row of teeth  250  on one of the narrow sides thereof. 
         [0099]    The spreader arm  244  is displaceable along the longitudinal direction of the rail  248  so that the spreader arm  244  can be moved closer to the spreader arm  246  or the spacing of the two spreader arms from one another can be increased. For this purpose, the spreader arm  244  is displaceably held by means of a mounting element  252  on the holding device  242  or the rail  248  thereof. The bearing element  252  comprises a drive mechanism  254  which comprises a rotary body (not shown in detail), for example, in the form of a pinion or a gearwheel, which is mounted rotationally fixed on a drive shaft  256  which protrudes upwardly from the bearing element  252  and is equipped there with a grip part  258 . 
         [0100]    Through rotation of the grip part  258  and thereby of the drive shaft  256 , by means of the rotation movement of the rotary body, a displacement of the spreader arm  244  along the rail  248  can take place. Preferably, the rotary body of the drive mechanism  254  can be configured such that a self-blocking connection is formed between the rotary body and the row of teeth  250  of the rail  248 . 
         [0101]    The second spreader arm  146  is integrally formed onto one end  260  of the holding device  242 . The two spreader arms  244 ,  246  lie in one plane, the spreading plane. 
         [0102]    The two spreader arms  244 ,  246  are formed in two parts wherein a first section  262  or  264  is held on the holding device  142  at a right angle. At their free end opposed to the holding device  242 , the two first sections  262 ,  264  have angled regions  266 ,  268  projecting opposite one another, on which bearing locations  270 ,  272  are provided, on each of which a straight second section  274 ,  276  is pivotably held. 
         [0103]    The retractor  240  has four retaining elements  280 ,  281 ,  282 ,  283  which are held, preferably displaceably, in pairs at the second sections  274 ,  276 . 
         [0104]    The retaining elements  280 ,  281 ,  282 ,  283  are configured similarly to the retaining elements  50 ,  51 ,  52 ,  53  of  FIG. 1 , so that reference can be made to the description of the retaining elements relating thereto. 
         [0105]    When the retraction forces are applied to the longitudinally parted sternum, the two second sections  274 ,  276  become oriented according to the resistance forces exerted by the bone material of the sternum and the rib arches adjacent thereto so that, in this embodiment also, a positionally changeable mounting of the retaining elements is produced and a reglated introduction of forces takes place according to the different elasticities of the individual sections of the parted sternum with the rib arches adjacent thereto. 
         [0106]    A further embodiment of a retractor of the present invention will now be described making reference to the retractor  300  illustrated in  FIG. 6 . 
         [0107]    The retractor  300  comprises a holding device  302  and two spreader arms  304 ,  306  held at right angles on the holding device  302 . The holding device  302  comprises a rail  308  which is formed substantially straight with a substantially rectangular cross-section and has a row of teeth  310  on one of the narrow sides thereof. 
         [0108]    The spreader arm  304  is displaceable along the longitudinal direction of the rail  308  so that the spreader arm  304  can be moved closer to the spreader arm  306  or the spacing of the two spreader arms from one another can be increased. For this purpose, the spreader arm  304  is displaceably held on the rail  308  by means of a mounting element  312 . The bearing element  312  comprises a drive mechanism  314  which comprises a rotary body (not shown in detail), for example, in the form of a pinion or a gearwheel which is mounted rotationally fixed on a drive shaft  316  which protrudes upwardly from the bearing element  312  and is equipped there with a grip element  318 . 
         [0109]    If the shaft  316  is rotated with the aid of the grip element  318 , by means of the rotation movement of the rotary body which is mounted rotationally fixed on the drive shaft  316 , a displacement of the spreader arm  304  along the rail  308  can take place. Preferably, the rotary body of the drive device  314  is configured such that a self-blocking connection is formed between the rotary body and the row of teeth  310  of the rail  308 . 
         [0110]    The second spreader arm  306  is formed integrally onto one end  320  of the holding device  302 . The two spreader arms  304 ,  306  lie in one plane and thus define the spreading plane. 
         [0111]    The two spreader arms  304 ,  306  are formed in a plurality of parts, wherein a first section  322 ,  324  is held on the holding device  302  at a right angle to the rail  308 . At their ends remote from the holding device  302 , the spreader arms  304 ,  306  have mutually opposed angled regions  326 ,  328  lying in the spreading plane and which are divided in forked manner in the spreading plane. 
         [0112]    Preferably, the angled regions  326 ,  328  consist substantially of the fork prongs  330 ,  331  and  332 ,  333  which are arranged parallel. 
         [0113]    Formed approximately at right angles onto the free ends of the parallel fork prongs  330 ,  331 ,  332 ,  333  are straight rail elements  334 ,  335 ,  336 ,  337  which, in pairs, assume the function of a second section of the spreader arms  304 ,  306 . 
         [0114]    The cross-section of the fork prongs  330 ,  331 ,  332 ,  333  and/or of the rail elements  334 ,  335 ,  336 ,  337  is selected so that sufficient elastic positional variability is obtained for the free ends of the rail elements  334 ,  335 ,  336 ,  337 , which ensures that the retaining elements  338 ,  339 ,  340 ,  341  arranged thereon can exert forces which are adapted to the prevailing resistance forces during retraction of the parted sternum with the adjacent ribs. In each of these variants, the rail elements are held pivotably independently of one another in the spreading plane. The rail elements  334 ,  335 ,  336 ,  337  can also have different lengths. 
         [0115]    It can also be advantageous if the flexural strength of the rail elements changes along the longitudinal direction in order thereby to realise, at each spacing of the fork prongs  330 ,  331 ,  332 ,  333 , an elastic stiffness which is adapted to the ribs. 
         [0116]    Furthermore, it can be provided in one variant that a stop delimits the maximum deflection of a rail element in the spreading plane. 
         [0117]    Preferably, the retaining elements  338 ,  339 ,  340 ,  341  are arranged to be displaceable in the longitudinal direction of the rail elements  334 ,  335 ,  336 ,  337 . By this means, the retractor according to the invention can also be adapted to the conditions of an current operation situation. 
         [0118]    The retaining elements  338 ,  339 ,  340 ,  341  are substantially configured similarly to the retaining elements  50 ,  51 ,  52 ,  53  described above in relation to  FIG. 1 , so that reference can be made to the detailed description given there. 
         [0119]      FIG. 7  shows a further embodiment of the retractor  360  according to the invention with a holding device  362  on one side of which two spreader arms  364 ,  366  are held. The holding device  362  comprises a rail  368  which is formed substantially straight with a substantially rectangular cross-section, on one of the narrow sides of which a row of teeth  370  is formed. 
         [0120]    The spreader arm  364  is displaceable along the longitudinal direction of the rail  368  so that the spreader arm  364  can be moved closer to the other spreader arm  366  or away from the other spreader arm  366 . The two spreader arms  364 ,  366  are oriented parallel to one another and define the spreading plane of the retractor  360  according to the invention. 
         [0121]    The spreader arm  364  is displaceably held with a holding device  372  on the rail  368  by means of a bearing element  372 , wherein the bearing element  372  comprises a drive mechanism  374  which comprises a rotary body (not shown in detail), for example, in the form of a pinion or a gearwheel which is mounted rotationally fixed on a drive shaft  376 . The drive shaft  376  protrudes upwardly out of the bearing element  372  and is equipped at the free end thereof with a grip part  378 . 
         [0122]    With the aid of the grip element  378 , the drive shaft  376 , and therewith the rotary body, can be rotated so that, resulting therefrom, the bearing element  372  and the spreader arm  364  held thereon can be moved in the longitudinal direction of the rail  368 . Preferably, the rotary body of the drive device  374  can be configured such that a self-blocking connection is formed between the rotary body and the row of teeth  370  of the rail  368 . The spreader arm  366  is formed with one end thereof onto one end  380  of the holding device  362 . 
         [0123]    The two spreader arms  364 ,  366  are formed in two parts, wherein a first section  382 ,  384  is held on the holding device  362  at a right angle. At their free end opposed to the holding device  362 , the two first sections  382 ,  384  have angled regions  386 ,  388 , which are also arranged in the spreading plane of the retractor  360 . Bearing locations  390 ,  392  are provided at the free ends of the angled regions  386 ,  388 . 
         [0124]    The second sections  394 ,  396  of the spreader arms  364 ,  366  are configured as paired rail elements  400 ,  402  and  404 ,  406 , which are respectively held with one end thereof pivotable at the bearing locations  390 ,  392 . The mounting of the rail elements is achieved preferably in resilient manner, in particular by means of extension springs, compression springs or torsion springs (not shown), wherein the spring constants of the individual rail elements can be differently selected. Due to the sprung mounting, the rail elements  400 ,  402 ,  404 ,  406  are held in a substantially parallel orientation to the first spreader arm section  382 ,  384  before the retraction movement starts. 
         [0125]    The rail elements  400 ,  402 ,  404 ,  406  can also have different lengths. 
         [0126]    The rail elements  400 ,  402 ,  404 ,  406  carry, at the free ends thereof, retaining elements  408 ,  409 ,  410 ,  411 , which are configured similarly to the retaining elements  50 ,  51 ,  52 ,  53  described above in relation to  FIG. 1 , so that reference can be made to the detailed description of the retaining elements given there. 
         [0127]    Preferably, the retaining elements  408 ,  409 ,  410 ,  411  are arranged along the longitudinal direction of the straight rail elements  400 ,  402 ,  404 ,  406  and thus permit positioning adapted to the respective application case. 
         [0128]    Due to the elastically pivotable mounting of the rail elements  400 ,  402 ,  404 ,  406 , during retraction of the spreader arms  364 ,  366 , the retraction force is exerted adequately on the respective sections of the parted sternum and on the rib arches adjacent thereto. 
         [0129]      FIG. 8  shows a surgical retractor  450  in which the principles of the present invention are also applied. 
         [0130]    Two spreader arms  454 ,  456  are held on a holding device  452 , wherein the spreader arm  456  is formed integrally onto the holding device  452 , whereas the spreader arm  454  is held on the holding device  452  displaceable by means of a drive mechanism  458 . 
         [0131]    The spreader arms  454  and  456  are each divided into two segments  460 ,  461  and  462 ,  463 , of which the respective first segment  460  or  462  is held on the holding device  452  in a fixed, substantially unchangeable orientation to the spreading plane of the retractor  450 . 
         [0132]    The two segments  460 ,  461  and  462 ,  463  are pivotably connected to one another by means of a joint  464 ,  466  in each case, wherein the pivot angle of the second segments  461 ,  463  to the respective associated first segment  460 ,  462  is limited by means of a stop  468 ,  470  so that, for example, in the embodiment shown in  FIG. 8 , the second segments  461 ,  463  are pivotable only downwardly out of the orientation shown so that the holding device  452  which typically comes to lie laterally along the torso of the patient can be pivoted downwardly so that the space required by the retractor  450  seen in the spreading plane is minimised. 
         [0133]    In the retractor of  FIG. 8 , another concept of the present invention is also realised, specifically the subdivision of the spreader arms  454 ,  456  into a first and a second section, of which the respective first section  472 ,  476  is held directly on the holding device  452  and on the respective free end  480  or  482  thereof holds the second section  474  or  478  pivotable in the spreading plane. The free ends  480 ,  482  of the first sections are each configured angled opposing one another in the spreading plane relative to the longitudinal direction of the spreader arms  454  or  456 . 
         [0134]    With regard to the subdivision into first and second sections of the spreader arms  454  and  456 , the concept substantially corresponds to the concept shown in, and described in relation to,  FIG. 5 , so that for further details, reference can be made to the description of  FIG. 5 . 
         [0135]    Furthermore, in the context of the embodiments of  FIG. 8 , it is provided that the retaining elements can be mounted at different defined positions along the second sections  474 ,  478  of the spreader arms. For this purpose, the second sections  474 ,  478  have recesses  488  as locking positions on the respective rear side  484 ,  486  thereof, into which retaining elements can be fixed in locking manner, as described below in relation to  FIGS. 9A and 9B  in detail. 
         [0136]    Due to the configuration of the locking positions  488  on the second sections  474  and  478  of the two spreader arms  454 ,  456 , it is possible by simple means to place retaining elements positioned opposing and oriented toward one another on the second sections  474 ,  478  of the two spreader arms. 
         [0137]    During a retraction with the surgical retractor  454 , adaptation of the forces exerted on the parted sternum again takes place automatically in that the second sections  474 ,  478  can be pivoted in the spreading plane according to the forces occurring and thus exert the retraction forces in an adapted manner on the parted sternum. 
         [0138]      FIGS. 9A and 9B  show a specific embodiment of a retaining element  500  which is configured in two parts and comprises a bearing element  502  and a retaining surface  504 . 
         [0139]    The retaining surface  504  is mounted on the bearing element  502 , rotatable about an axis  506  perpendicular to the spreading plane. 
         [0140]    The bearing element  502  has a substantially rectangular cross-section on which on one side, the retaining surface  504  is arranged with the rotation axis  506 . 
         [0141]    Provided in the rectangular cross-section of the bearing element  502  is a rectangular recess  510  which substantially corresponds, in the cross-section thereof, to the cross-section of the second section  474  or  478  of the retractor  450 . 
         [0142]    The recess  510  accommodates the cross-section of the second sections  474 ,  478  of the spreader arms  454  or  456  in sliding manner and can be placed, due to a spring-loaded ball thrust member  512  arranged on the narrow side of the bearing part  502  opposed to the bearing  506 , at the pre-defined locking positions  488  of the second sections  474  or  478 .