as shown in fig1 , an embodiment of a surgical retractor 1 comprises a rail 2 , a first arm 3 and a second arm 4 . the first arm 3 may be integral with the rail 2 or connected to the rail 2 in a rigid manner . the second arm 4 is connected to the rail 2 by a block 5 housing a drive mechanism 6 . the drive mechanism engages with a toothed edge 7 of the rail 2 and can be operated by turning a drive shaft 8 . the drive shaft 8 may exhibit a hand wheel or a detachable manipulation handle ( not shown ) for easier turning . the drive mechanism 6 permits adjustment of the distance between the first and second arms 3 , 4 . in particular , the retractor 1 can be spread or contracted by turning the drive shaft 8 in one or the other direction . preferably , the drive mechanism 6 is configured in a self - blocking manner , i . e ., the second arm 4 can be moved only by turning the drive shaft 8 , but not by an external force acting upon the second arm 4 itself . alternatively , fixation means might be provided for fixing the second arm 4 at a desired position on the rail 2 . the first arm 3 and the second arm 4 both protrude approximately at right angles from the rail , both arms being substantially parallel to each other . the first and second arms 3 , 4 comprise rods 10 ′, 10 ″, respectively . the second arm 4 may be detachable from the rail 2 . after detaching the second arm 4 from the rail , the drive mechanism 6 may be disassembled for easy cleaning . as is further shown in fig1 , two holding elements 20 ′, 20 ″ are mounted on the first arm 3 , and two further holding element 20 ′″, 20 ″″ are mounted on the second arm 4 . each of the holding elements 20 ′, 20 ″, 20 ′″, 20 ″″ holds a respective retractor blade 30 ′, 30 ″, 30 ′″, 30 ″″. in a surgical operation , the retractor blades 30 ′″, 30 ″″ engage with the tissue edge 9 and the retractor blades 30 ′″, 30 ″″ engage with the tissue edge 9 ′, the tissue edges 9 , 9 ′ being symbolically indicated in fig1 by the broken lines . in order to hold the tissue edges 9 , 9 ′ apart from each other , the blades 30 ′, 30 ″, 30 ′″, 30 ″″ are oriented such that their respective tissue gripping surfaces are directed away from the space to be held open between the tissue edges 9 , 9 ′. correspondingly , the holding elements 20 ′, 20 ″ mounted on the first arm 3 are directed substantially opposite to the holding elements 20 ′, 20 ″″ mounted on the second arm 4 . the holding elements 20 ′, 20 ″, 20 ′″, 20 ″″ are positioned on the respective arms 3 , 4 such that a net torque arising from the counter - force exerted by the retracted tissues on the respective blades 30 , 30 ′, 30 ″, 30 ′″, 30 ″″ is largely avoided . in particular , the holding elements 20 ′, 20 ′″ and 20 ″, 20 ″″ may each form a pair of two holding elements opposing each other . further functional elements such as an illumination device 40 may be mounted on the first and / or second arms 3 , 4 . the first arm 3 with rod 10 ′, holding elements 20 ′, 20 ″, blades 30 ′, 30 ″ and illumination device 40 is shown in a perspective view in fig2 . each holding element 20 ′, 20 ″ comprises a holding element body 21 ′, 21 ″ and a blade holder 22 ′, 22 ″. each blade 30 ′, 30 ″ comprises a blade head 31 ′, 31 ″ and a blade shaft 32 ′, 32 ″. the lower parts of the blades 30 ′, 30 ″ are not shown in fig2 . the illumination device 40 comprises a light guide holder 41 , a light guide 42 , and a light connector 43 . light guide 42 and light connector 43 form a substantially rigid unit which can be fixed on the light guide holder by a snap - in mechanism 44 . the light guide holder 41 comprises a recess into which the rod 10 ′ is inserted to mount the light guide holder 41 on the arm 3 . a light cable transmitting light from an external light source ( not shown ) can be connected to the light connector 43 . the light connector 43 may comprise optical elements for an efficient coupling of light into the light guide 42 , and for adapting the numerical aperture of the illumination light to the desired illumination characteristics . the distal end section 45 of the light guide 42 may be provided with an illumination optics and is oriented to illuminate the surgical site . fig3 shows a side view of the surgical retractor 1 from the direction indicated by the arrow “ a ” in fig1 . as can be seen in fig3 and will be explained in detail further below , each holding element 20 ′, 20 ′″ comprises a body 21 ′, 21 ′″ and a blade holder 22 ′, 22 ′″ connected to the body 21 ′, 21 ′″ by a ball - and - socket joint . the body 21 ′, 21 ′″ forms an open frame with a recess 23 ′, 23 ′″ into which the rod of the respective arm can be inserted ( not shown ). the fixation screw 24 ′, 24 ′″ and the ball 25 ′, 25 ′″ of the ball - and - socket joint protrude into the recess 23 ′, 23 ′″ for fixing the body 21 ′, 21 ′″ on the rod and for locking the ball - and - socket joint against the rod . the blades 31 ′, 31 ′″ are held by the blade holders 22 ′, 22 ′″ with their respective blade gripping surfaces 33 ′, 33 ′″ directed away from each other . the blade gripping surfaces 33 ′, 33 ′″ exhibit grooves 34 ′, 34 ′″ and protrusions 35 ′, 35 ′″ for holding tissue firmly . an illumination device 40 is mounted adjacent to the holding element 20 ′, as described above . fig4 shows a side view of the surgical retractor 1 from the direction indicated by the arrow “ b ” in fig1 . the holding elements 20 ′, 20 ″ are mounted on the rod 10 ′ of the first arm 3 . as can be seen in fig4 , the fixation screws 24 ′, 24 ″ exhibit a hexagonal recess for insertion of a screwdriver . the blades 30 ′, 30 ″ are shown in fig4 with their respective tissue gripping surfaces 33 ′, 33 ″ which are structured with grooves 34 ′, 34 ″ and protrusions 35 ′, 35 ″. the protrusions may be ridges transverse to a longitudinal axis of blades 30 ′, 30 ″, respectively , or may be pyramid - shaped elevations , as indicated in fig4 . the illumination device 40 is mounted between the holding elements 20 ′, 20 ″ on the rod 10 ′ by means of a light guide holder 41 . the light guide holder 41 can be fixed on the rod 10 ′ by tightening a fixation screw 46 which is accessible by a corresponding tool when the light guide 42 and the light connector 43 are detached from the light guide holder 41 . by tightening the fixation screw 46 , the light guide holder 41 can be clamped on the rod 10 ′. in particular , the screw 46 acts from a first side of a recess to press the rod 10 ′ against a second side of the recess , the latter exhibiting a cylindrical ridge fitting into a cylindrical groove of the rod 10 ′, the latter being described below . fig5 shows details of a holding element 20 in a partial sectional view . the holding element 20 comprises a holding element body 21 and a blade holder 22 , the blade holder being 22 connected to the body 21 via a ball - and - socket joint 26 . the ball 25 is held unreleasably within the body 21 , the socket being formed by a bottom shell 26 ′ and side members 26 ″ being integral with the body 21 , and a top shell 26 ′″. an upper cylindrical section of the top shell 26 ′″ fits into a corresponding bore in the body for inserting the ball 25 in the manufacturing process ; the top shell 26 ′″ is soldered or welded into the body 21 to form an integral part of it . a stud 27 of the ball is fixed to the blade holder 22 , e . g . by screwing a threaded bolt of the stud 27 in the blade holder 22 ( as shown in fig5 ), and / or soldering or welding . the body 21 comprises a recess 23 into which a rod 10 can be inserted . the rod 10 , which is shown in cross - section in fig5 , is partly rectangular in its cross - section , having first and second surfaces 11 , 12 , and substantially flat top and bottom surfaces 13 , 14 . the top surface 13 may be parallel to the bottom surface 14 . the first surface 11 has a first surface section 11 ′ which is substantially flat , but may be inclined at an angle other than 90 ° to the top and bottom surfaces 11 , 12 . the second surface 12 has a second surface section 12 ′ which is concave , and may , in particular , have the shape of a longitudinal section of a cylinder surface , the cylinder having a radius corresponding approximately to the radius of the ball 25 . in order to facilitate introduction of the rod 10 into the recess 23 , the upper edge 15 , where the second surface 12 meets the top surface 13 , recedes with respect to the lower edge 16 , where the second surface 12 meets the bottom surface 14 . a fixation screw 24 is housed within the body 21 , which abuts the first surface of the rod 10 when the rod is present in the recess 23 . the fixation screw 24 has an axis 28 forming an angle to the planes defined by the top and bottom surfaces 13 , 14 of the rod 10 , i . e . to a plane defined by the recess 23 of the body 21 . these planes may be parallel to the plane of the retractor 1 as defined by the rail 2 and the first and second arms 3 , 4 ( see fig1 ). thus , when the fixation screw 24 is operated by means of a screwdriver which is held along the screw axis 28 , the screwdriver protrudes out of the plane of the surgical retractor 1 . when the holding element 20 is to be mounted on the rod 10 , the fixation screw 24 is loosened to recede substantially out of the recess 23 . the ball 25 still protrudes into the recess 23 by an extent depending on the play permitted by the bottom and top shells 26 ′, 26 ′″ and the side members 26 ″ forming the socket of the joint . the top surface 13 has a width to permit introduction of the rod 10 from below into the recess 23 . when the holding element 20 has been put on the rod 10 , the fixation screw 24 is turned to protrude into the recess 23 , thus inhibiting removal of the rod 10 from the recess 23 , but still enabling shifting of the holding element along a longitudinal direction of the rod 10 , which is perpendicular to the plane of the drawing in fig5 . in this position of the fixation screw 24 , the ball 15 of the ball - and - socket joint 26 is still free to rotate , so that the blade 30 introduced into the blade holder 22 can be rotated to assume any desired orientation . when a the holding element 20 has a suitable position and the blade 30 has a suitable orientation , the fixation screw 24 is tightened , its tip 28 ′ contacting the inclined first surface section 11 ′ and thus pressing the rod 10 with its second surface section 12 ′ against the ball 25 . the ball 25 is pressed against the side members 26 ″, forming at least one contact point with each side member 26 ″. thus , the ball 25 is fixed between the second surface section 12 ′ of the rod 10 and its socket , and the rod is fixed between the ball 25 and the fixation screw 24 . fixation is improved by extended contact lines or contact areas between ball 25 and second surface section 12 ′ and / or first surface section 11 ′ and the tip 28 ′ of the fixation screw 24 . as for a rigid clamping a considerable force has to be exerted by the fixation screw 24 upon the rod 10 and by the rod 10 upon the ball 25 , the holding element may be reinforced by a frame 29 . the frame 29 may be made of a hardened material . in total , due to the axis 28 of the screw being inclined , the holding element has an arcuate shape . the lower part of the blade 30 is not shown in fig5 . as depicted in fig6 a - c , the holding element 20 permits the blade 30 to be rotated in three rotational degrees of freedom . in particular , the blade 30 can be pivoted or swiveled about a horizontal axis parallel to a longitudinal axis of the rod 10 when inserted into the recess 23 of the body 21 of the holding element , as is indicated by the arrow in fig6 a . the blade 30 can also be pivoted with respect to a horizontal axis perpendicular to the longitudinal axis of the rod 10 , as indicated by the arrow in fig6 b . moreover , the blade can be pivoted about a vertical axis , as shown by the curved arrow in fig6 c . finally , the holding element can be shifted along the rod 10 as indicated by the straight arrow in fig6 c , thus shifting the blade 30 in a self - parallel manner . as indicated in fig7 , the surgical retractor 1 may further comprise a third arm 50 extending parallel to the rail 2 and being mounted on one of the arms 3 , 4 . the third arm comprises a third arm holding element 51 and a rod 52 . the third arm holding element 51 is mountable on the rod 10 ′, 10 ″ of the first or second arms 3 , 4 in a similar way as the illumination device 40 . in the configuration shown in fig7 , the rod 52 of the third arm 50 crosses over the second arm 4 in order to make the retractor 1 form a closed frame , but permitting free adjustment of the distance between the first and second arms 3 , 4 by operating the drive mechanism 6 of the second arm 4 . for enhanced stiffness , the third arm 4 may be connectable to the second arm 4 ( not shown ). the rod 52 is arranged parallel to the rail 2 but slightly elevated , a bottom surface of the rod 52 coinciding with the plane formed by the top surfaces of the rods 10 ′, 10 ″ of the first and second arms 3 , 4 . the third arm holding element 51 provides for the corresponding elevation of the rod 52 . further holding elements or further functional elements can be mounted on the rod 52 of the third arm 50 . as indicated in fig7 , the free end of the rod 52 may be equipped with a resilient ratchet mechanism , e . g . a spring - born ball 53 . in this way , unintentional loss of a holding or further functional element can be avoided when the fixation screw of the element is in a position to permit translation along the rod , but not removal from the rod . the free ends of the rods 10 ′, 10 ″ of the first and second arms 3 , 4 may exhibit similar mechanisms . reference numerals not explicitly mentioned in the description of one of the figures have the same meaning as in the other figures .
a surgical retractor has a rail , a first arm protruding from the rail at an angle , a second arm being movably mounted on the rail and extending substantially parallel to the first arm , and a multiplicity of holding elements mounted on the first and second arms . a holding element has a multi - axis joint for pivotably holding a blade for engaging tissue to be retracted . in this way , a most flexible surgical retractor is provided .