Patent Publication Number: US-11389359-B2

Title: Surgical tables

Description:
FIELD OF THE INVENTION 
     The present invention relates to surgical tables. 
     BACKGROUND 
     Surgical tables, or operating tables, comprising a base for standing on a floor, a column extending from the base, and a tabletop providing a patient support surface are well known. There is a general need in the art for surgical tables to have variable height to enable the tabletop to be located at a selected height which is most suitable for the required surgical, therapeutic or diagnostic treatment of a patient positioned on the surgical table. The column is extendable, typically by a telescoping arrangement, to allow the column to be moved between contracted and extended positions in order to lower and/or raise the tabletop to a desired height. 
     SUMMARY OF THE INVENTION 
     There is a particular need in the art for the column to have a wide range of lengths to enable the tabletop to be located at any position within a wide range of heights. The column has a most contracted configuration and a most extended configuration, and the distance separating those configurations constitutes the operating range of the column. The column is adapted to be movable to any position within that operating range. 
     It is particularly desired for the column to be structured so that when the column is in the most contracted configuration, at which the tabletop is at the lowest position of the height range, the height of the tabletop above the floor on which the surgical table is standing is as low as possible. A low operating height for the surgical table can provide easier loading and unloading of the patient onto and from the surgical table. Also, a low operating height for the surgical table can more easily permit laproscopic surgery and improves the ergonomics of the table for the surgeon. 
     However, it is also particularly desired for the column to be structured so that when the column is in the most extended configuration, at which the tabletop is at the highest position of the height range, the height of the tabletop above the floor on which the surgical table is standing is as high as possible. A high operating height for the surgical table may be required for some operating procedures, for example orthopaedic surgery. 
     Therefore there is a need for a wide operating range for the tabletop height and also the ability to provide as low a height as possible for the lowest position of the tabletop within that operating range. 
     Still further, the tabletop of the surgical table is generally required to be movable relative to the column so as to be tiltable about two orthogonal horizontal axes, namely a tilt axis extending longitudinally along the length of the tabletop and a trend axis extending transversely across the length of the tabletop. 
     The structure of the tabletop and the column, and of the actuator mechanisms to move the tabletop relative to the column about the tilt axis and/or the trend axis, must enable free movement about the tilt axis and/or the trend axis over a wide range of tilt/trend angles, and over a wide range of table operating heights. 
     Therefore there is a need for a wide operating range for the tabletop height and also the ability to provide as low a height as possible for the lowest position of the tabletop within that operating range while still permitting wide tilt/trend functionality. 
     In addition, there is a generally need for the column and the associated actuator mechanisms which raise and lower the tabletop to have a small cross-sectional area, with small length (in the table length direction) and width (in the table width direction), so that the “footprint” of the column in minimised. This in turn can permit the dimensions of the base to be minimised, which assists access to the patient by medical personnel. 
     Finally, the weight of patients is generally increasing as a result of increasing obesity in some countries. The column must be capable of bearing a vertical load of, for example, more than 500 kg and must be capable of bearing a correspondingly high offset load, when the tabletop is tilted about the trend or tilt axis. 
     Current commercial surgical operating tables have a typical minimum operating height of 580 to 600 mm or higher. In this specification the “minimum operating height” of an operating table means the minimum height of all parts of the entire tabletop surface, including the part of the tabletop that is located directly above the column, relative to the floor when the operating table is free-standing on the floor. The measurement is made without any mattresses which are conventionally removably placed onto the tabletop. The operating table may have a base which is movable, for example incorporating castors, or fixed, for example having fixed feet. 
     The requirement that the height must be measured for all parts of the entire tabletop surface means, for example, that the minimum height cannot be measured simply by measuring the height of a head portion of the tabletop when the head portion is lowered into a trend configuration, and so the head portion is a lowermost part of the tabletop and the centre and leg parts of the tabletop are significantly higher, with the leg portion being higher than the part of the tabletop that is located directly above the column. 
     There is a need in the art to provide a surgical table which has a lower minimum operating height, but which can also have a wide range of height adjustment, high trend and reverse trend angles and a small column footprint. 
     There is a need for a surgical table with a more compact mechanism for disposing a tabletop in a wide range of different configurations. 
     The present invention provides a surgical table 
     Optional and/or preferred features are defined in the various embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic side view of a surgical table in accordance with an embodiment of the present invention; 
         FIGS. 2 a  and 2 b    are each is a schematic perspective side view from above of the column and a mechanism for controlling the trend angle and height of a trend frame of the surgical table of  FIG. 1 , respectively showing the column at minimum height and the trend frame at minimum height and the column at minimum height and the trend frame at maximum height; 
         FIG. 3  is a schematic side view of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the column at minimum height and the trend frame at minimum height; 
         FIG. 4  is a schematic side view of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the column at minimum height and the trend frame at maximum height: 
         FIG. 5  is a schematic side view of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the column at minimum height and the trend frame at an intermediate height, and with the trend frame at a reverse trend angle of 45°; 
         FIG. 6  is a schematic side view of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the column at  FIGS. 7 a , 7 b  and 7 c    are schematic side views of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the trend axis at an intermediate height and the trend frame respectively in a horizontal configuration, in a reverse trend configuration and in a trend configuration; 
         FIGS. 8 a , 8 b  and 8 c    are schematic side views of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the trend axis at a minimum height and the trend frame respectively in a horizontal configuration, in a reverse trend configuration and in a trend configuration; 
         FIG. 9  is a schematic side view of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 , showing the column at an intermediate height and the trend frame in a reverse trend configuration; 
         FIG. 10  is a schematic perspective side view of an embodiment of a stabiliser for the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 ; 
         FIG. 11  is a schematic cross-section through the stabiliser of  FIG. 10 ; 
         FIG. 12  is a schematic plan view of the column and the mechanism for controlling the trend angle and height of the trend frame of the surgical table of  FIG. 1 ; 
         FIG. 13  is a schematic bottom view from below of the column of the surgical table of  FIG. 1 ; 
         FIGS. 14 a  and 14 b    are each a schematic perspective view of a locking and/or braking mechanism of the surgical table of  FIG. 1  at respective different heights of the movable framework relative to the column; 
         FIG. 15  illustrates a cable management system for the column of the surgical table of  FIG. 1 , with the column in a contracted configuration; 
         FIG. 16  illustrates the cable management system of  FIG. 15 , with the column in an extended configuration; 
         FIGS. 17 a  and 17 b    schematically illustrate the cable configuration in the cable management system of  FIG. 15  when the column is in the contracted or extended configuration respectively; 
         FIG. 18  is a schematic perspective side view from above of a column and a mechanism for controlling the trend angle and height of a trend frame of a surgical table in accordance with a further embodiment of the present invention; 
         FIG. 19  is a schematic perspective view of a tilt mechanism of a surgical table in accordance with an embodiment of the present invention; 
         FIGS. 20 a  and 20 b    illustrate a tilt frame of the tilt mechanism of  FIG. 19  rotated about the tilt axis at two opposite end positions relative to a central level position; 
         FIG. 21  is a schematic perspective view of a tilt mechanism of a surgical table in accordance with a further embodiment of the present invention; 
         FIG. 22  is a schematic perspective view of a tilt mechanism of a surgical table in accordance with a further embodiment of the present invention; 
         FIG. 23  is a schematic perspective view from one end view of a tilt mechanism of a surgical table in accordance with a further embodiment of the present invention with the tilt frame in a level configuration; 
         FIG. 24  is a schematic perspective view from the opposite end of the a tilt mechanism of  FIG. 23  with the tilt frame in a level configuration; and 
         FIG. 25  is a schematic side view of the tilt mechanism of  FIG. 23  with the tilt frame in an inclined configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 to 17   b , a surgical table, designated generally as  2 , comprises a base  4  or standing on a floor. The base  4  typically includes wheels for moving the table  2  along the floor. Alternatively, the base  4  may be fixed, for example having fixed feet. A column  6  of adjustable height is mounted on and extends from the base  4 . A tabletop  8 , which provides a patient support surface  10 , is supported above the column  6 . 
     As described hereinafter, the surgical table  2  includes a mechanism for inclining the tabletop  8  relative to the column  6  by inclining the tabletop  8  about transverse and longitudinal horizontal axes of the tabletop  8 . Inclination about the transverse horizontal axis of the tabletop  8  is referred to in the art as “trending”, while inclination about the longitudinal horizontal axis of the tabletop  8  is referred to as “tilting”. Compound movements also are possible, in which the tabletop  8  is inclined about both the transverse and longitudinal axes of the tabletop  8  at the same time. 
     As used herein, the longitudinal axis of the tabletop  8  is the major axis of the tabletop  8  and the transverse axis of the tabletop  8  is the orthogonal minor axis of the tabletop  8 . The longitudinal direction of the tabletop  8  is parallel to the major axis and the transverse direction of the tabletop  8  is parallel to the minor axis. That is, the transverse direction of the tabletop  8  is perpendicular to, or orthogonal to, the longitudinal direction of tabletop  8 . 
     As depicted in  FIG. 1 , the tabletop  8  is typically divided into five sections, namely a head section  12 , an upper torso section  14 , a lower torso section  16  and a pair of laterally adjacent leg sections  18 , of which only one is shown in  FIG. 1 . The lower torso section  16  is coupled to the column  8 . Each of the sections of the tabletop  8  provides a portion of the patient support surface  10 , and each of the sections has a respective separate mattress (not illustrated) removably fitted to the respective section. As is well known in the art, the tabletop sections can be individually moved relative to an adjacent section and some sections can be detached from the tabletop  8 . 
     Referring in particular to  FIGS. 6, 12 and 13 , the column  6  comprises a plurality of column elements  30 ,  32 ,  34  which form a telescoping assembly  36 . The telescoping assembly  36  surrounds an actuator  37 , which is shown schematically and in phantom in  FIG. 13 , for raising and lowering the column  6 . The actuator  37  comprises a column drive mechanism located within the inner column element  34  of the plurality of column elements  30 ,  32 ,  34 . The plurality of column elements comprises an outer column element  30  and an inner column element  34 . The outer column element  30  externally surrounds the inner column element  34  and defines an external surface  38  of the column  6  when the column elements  30 ,  32 ,  34  are telescoped into a contracted configuration. The plurality of column elements further comprises at least one intermediate column element  32  between the outer column element  30  and the inner column element  34 . In the illustrated embodiment there is only one intermediate column element  32 , although a telescoping series of plural intermediate column elements  32  may be provided. 
     The actuator  37  typically comprises an electric actuator  37 . The actuator  37  is coupled between the outer column element  30  and the base  4  and drives the outer column element  30  upwardly and downwardly relative to the base  4 , with the plurality of column elements  30 ,  32 ,  34  being coupled together so as to be raised or lowered in synchronism. The actuator  37  has an upper end  39  coupled to a drive surface  41  affixed to the outer column element  30  of the plurality of column elements, and the drive surface  41  is a provided by a plate  43  located inwardly of, and affixed to, the outer column element  30 . 
     The actuator  37  may comprise a two-stage synchronised telescopic leadscrew, or ballscrew/leadscrew combination. The lifting load is directed entirely through the leadscrew ballscrew/leadscrew combination and there are no axial bearings required to support the lifting load. Alternatively, the actuator  37  may comprise two ballscrews, or a leadscrew/ballscrew combination. In this specification a ballscrew comprises a type of leadscrew and so when a reference is made herein to a leadscrew that term may also be construed to encompass a ballscrew. 
     Position sensors and high/low limit switches may be provided on the column  6 . End stops may be provided to limit the high/low positions of the plurality of column elements. 
     The column  6  comprises a plurality of linear motion guide units  40  between each pair of adjacent column elements  30 ,  32 ,  34 . The linear motion guide units  40  are recirculating ball-type linear guides. The linear motion guide units  40  extend in a telescoping direction D and are mutually spaced. There is a pair of linear motion guide units  40  between each pair of adjacent column elements  30 ,  32 ,  34 . The linear motion guide units  40  of each pair are located on opposite sides of the trend axis T-T and on opposite sides of a tilt axis X-X orthogonal to the trend axis T-T. 
     The column  6  has a substantially rectangular cross-section, which in the illustrated embodiment is a square cross-section, for example having dimensions of 180 mm×180 mm. Each pair of linear motion guide units  40  are located at opposite corners  42  of the rectangular cross-section. 
     The column elements  30 ,  32 ,  34  are thin-walled tubular sections. The linear motion guide units  40  located at opposite corners  42   a ,  42   b ,  42   c ,  42   d  of the rectangular cross-section maximise the torsional rigidity of the column structure and equalise the offset load capability in both the cranial and caudal directions. The maximum footprint of the column  6  is typically 180 mm×180 mm. 
     As shown in the illustrated embodiment, the column  6  has one intermediate column element  32  between the outer column element  30  and the inner column element  34 . A first pair of linear motion guide units  40   a ,  40   b  between the outer column element  30  and the intermediate column element  32  are located at first opposite corners  42   a ,  42   b  of the rectangular cross-section and a second pair of linear motion guide units  40   c ,  40   d  between the inner column element  34  and the intermediate column element  32  are located at second opposite corners  42   c ,  42   d  of the rectangular cross-section. 
     Each linear motion guide unit  40  comprises an elongate channel  44  fixed to one column element of the pair of adjacent column elements and an elongate bar  46  fixed to the other column element of the pair of adjacent column elements, the elongate bar  46  being slidable in the elongate channel  44 . Bearings, not shown, are provided between the elongate bar  46  and the elongate channel  44  to provide a low friction slider arrangement. Preferably, the elongate channel  44  is fixed to an outer column element of the pair of adjacent column elements and the elongate bar  46  is fixed to the inner column element of the pair of adjacent column elements. 
     As shown particularly in  FIGS. 2 a    to  13 , the surgical table  2  incorporates a mechanism for controlling the trend angle and height of a trend frame  50 , which is beneath the tabletop  8 . The trend frame  50  can be rotated about a trend axis, and the angle of inclination of the trend frame  50  sets the trend angle of the tabletop  8 . 
     Referring in particular to  FIGS. 2 a  to 8 c   , a movable framework  50 , constituting a trend frame  50 , is mounted between the tabletop  8  and the column  6 . The movable framework  50  enables at least a part of the tabletop  8 , for example the lower torso section  16 , to be rotatable about the trend axis T-T. The trend axis T-T extends through the movable framework  50  in a transverse direction across the tabletop  8 . The tilt axis X-X extends through the movable framework  50  and is orthogonal to the trend axis T-T. The tilt axis X-X is parallel to a central longitudinal axis C-C of the tabletop  8 . 
     The trend frame  50 , provided by the movable framework  50 , is adapted to move about the trend axis T-T, and a tilt frame (not shown) is mounted above the movable framework  50  at the pivot points  500  shown in  FIG. 2 a    to enable the tilt frame to move independently by a separate drive system (not shown) about the tilt axis X-X. Various drive systems for such a tilt frame are known to those skilled in the art. The lower surface of the tabletop  8  is directly fitted to the tilt frame. The tilt frame is located above the trend axis T-T. 
     Accordingly, movement of the movable framework  50  about the trend axis T-T, or when the trend axis T-T is translated upwardly or downwardly, causes corresponding movement of the tabletop  8  which is fitted to the tilt frame carried by the trend frame  50 , provided by the movable framework  50 , and the tilt frame can further impart additional tilting motion and positioning to the tabletop  8 . 
     A first actuator mechanism  52  is coupled to the movable framework  50  and arranged to raise and lower the movable framework  50  relative to the column  6  and to rotate the movable framework  50  about the trend axis T-T. The first actuator mechanism  52  is external of the column  6 . 
     The first actuator mechanism  52  comprises first and second actuators  54 ,  56 . The first actuator  54  is connected to a first portion  58 , preferably located at one end, of the movable framework  50  and the second actuator  56  is connected to a second portion  60 , preferably located at an opposite end, of the movable framework  50 . The first and second portions  58 ,  60  are mutually spaced and located on opposite sides of the trend axis T-T and on opposite sides of the tilt axis X-X. The movable framework  50  is substantially rectangular and the first and second portions  58 ,  60  are located at diagonally opposite corners  62 ,  64  of the movable framework  50 . The movable framework  50  has a rigid frame having opposite first and second end portions  58 ,  60  mutually spaced a fixed distance. 
     In the embodiment, the first and second actuators  54 ,  56  are the only actuators coupled between the column  6  and the movable framework  50  for causing movement of the movable framework  50  relative to the column  6 . 
     The first actuator  54  has an upper first end  66  connected to the first portion  58  of the movable framework  50 . The first actuator  54  has a lower second end  68  coupled to the column  6 . The second actuator  56  has an upper first end  70  connected to the second portion  60  of the movable framework  50  and a lower second end  72  coupled to the column  6 . The second end  68 ,  72  of each of the first and second actuators  54 ,  56  is coupled to an external surface  74  of the column  6 . 
     The first and second actuators  54 ,  56  each comprise an electric motor  76 , which comprises an elongate element  78  having an upper end  80  connected by a pivot joint  82  to the movable framework  50  and a drive assembly  84  for extending, or retracting, the elongate element  78  so as respectively to raise, or lower, the respective first and second portions  58 ,  60  of the movable framework  50 . 
     In the illustrated embodiment, the elongate element  78  comprises a leadscrew  86  and the drive assembly  84  is adapted to rotate the leadscrew  86  to extend, or retract, the leadscrew  86  so as respectively to raise, or lower, the respective first and second portions  58 ,  60  of the movable framework  50 . 
     In an alternative embodiment, the elongate element  78  may comprise a hydraulically operated piston. Any other type of actuator may be used that is suitable to raise, or lower, the respective first and second portions  58 ,  60  of the movable framework  50 . The present invention is not limited to any particular drive mechanism for the first and second actuators  54 ,  56 . 
     First and second stabilisers  88 ,  90  are also provided. Each first and second stabiliser  88 ,  90  is associated with a respective one of the first and second actuators  54 ,  56 . However, in a modified embodiment only one of the actuators is provided with a stabiliser. 
     The stabiliser  88 ,  90  comprises an extendable assembly which is fitted between the movable framework  50  and a lower mount pivotally coupled to the column  6 , typically the lower mount being pivotally coupled to the drive assembly  84 . An upper end of the extendable assembly is fitted to an upper end of the elongate element  78  of the respective actuator  54 ,  56 . In the illustrated embodiment, the extendable assembly and the elongate element  78  of the respective actuator  54 ,  56  are in parallel, but in alternative embodiments a non-parallel arrangement may be provided. 
     In the illustrated embodiment, each stabiliser  88 ,  90  comprises a rigid elongate guide rod  92 , which is parallel to the elongate element  78  of the respective first or second actuator  54 ,  56 . The guide rod  92  is fitted at its upper end  83  to the respective pivot joint  82 . 
     A hollow guide  94  slidably receives the lower portion  81  of the guide rod  92  and is pivotally coupled to the column  6 . The guide rod  92  is slidable within the hollow guide  94  when the respective elongate element  78  is extended or retracted. The guide rod  92  and hollow guide  94  form the extendable assembly. The fitting between the upper end  83  of the guide rod  92  and the respective pivot joint  82  is translationally fixed, and so the guide rod  92  and its associated elongate element  78  commonly move translationally when the elongate element  78  is extended or retracted by operation of the respective electric motor  76 . 
     The first and second stabilisers  88 ,  90  function to minimise the lateral loading acting on the first and second actuators  54 ,  56 , in particular the elongate elements  78 . The first and second stabilisers  88 ,  90  each ensure that the actuator loading is essentially in-line with the axis of the respective elongate element  78 . Accordingly, buckling loads on the elongate element  78  are minimised, particularly when the elongate element  78  is in a highly extended position which is required for certain configurations of the movable framework  50 , i.e. the trend frame  50 , as discussed below. 
     The first and second stabilisers  88 , 90  also function to provide a hard end stop for the respective elongate elements  78  when the elongate element  78  is in the most extended or most retracted configuration. As shown in the structure of the stabilisers  88 ,  90 , which is shown in  FIGS. 10 and 11 , this is provided by stop members  91 ,  93  that are fitted to the guide rod  92  and are respectively urged against a respective movement limiter  95 ,  97  of the hollow guide  94  to define a maximum upward or downward position for the guide rod  92  relative to the hollow guide  94  and thereby limit the maximum upward extension or downward retraction of the elongate element  78 . Stop member  91  and movement limiter  95  define a minimum-dimension contracted position for the first and second stabilisers  88 ,  90  and stop member  93  and movement limiter  97  define a maximum-dimension extended position for the first and second stabilisers  88 ,  90 . 
     One or more position sensors are located on each of the first and second stabilisers  88 ,  90  to enable the translational position of the guide rod  92 , and thereby the associated elongate element  78 , to be detected. In the illustrated embodiment, a contracted position sensor  99   a  comprises a magnet  201   a  on an upper end of the elongate element  78  and a magnetic sensor  203   a  on the hollow guide  94  and an extended position sensor  99   b  comprises a magnet  201   b  (shown in phantom) on a lower end of the elongate element  78  and a magnetic sensor  203   b  on the hollow guide  94 . The position sensors  99   a ,  99   b  can permit the position of the elongate element  78  relative to an upper or lower limit to be detected. 
     The provision of a hard end stop and position sensors  99   a ,  99   b  on the first and second stabilisers  88 ,  90  rather than directly on the associated elongate element  78 , i.e. helical screw, of the first and second actuators  54 ,  56  provides the advantages as compared to known designs where such functions are provided directly on the helical screw. Locating a hard end stop or position sensor on a helical screw is difficult to implement because the screw runs through the gearbox of the drive assembly  84  and ends stops on a helical screw may interfere with the maximum stroke or maximum or minimum height achievable by the elongate element  78 . 
     By locating the hard end stop and position sensors  99   a ,  99   b  on the first and second stabilisers  88 , rather than on the elongate element  78 , the required functions to detect and limit the position of the elongate element  78  are achieved indirectly by detecting and controlling the associated guide rod  92  without compromising the stroke range and freedom of motion of the elongate element  78 . 
     The drive assembly  84  of each first and second actuator  54 ,  56  is pivotally connected to the movable framework  50  by a pivot mount  51 . Therefore each of the first and second actuators  54 ,  56 , including a respective electric motor  76 , elongate element  78 , and drive assembly  84 , and a respective one of the first and second stabilisers  88 ,  90 , is rotatable about the respective pivot mount  51 . 
     The first and second actuators  54 ,  56  can be operated independently so as to be driven in the same or opposite directions. Therefore the rotational orientation of the first and second actuators  54 ,  56  about the respective pivot mount  51  can be different. 
     The first and second actuators  54 ,  56 , and correspondingly the respectively associated first and second stabiliser  88 ,  90 , are not oriented in a geometrically vertical orientation, i.e. aligned with the direction of orientation of the column  6 , but instead are inclined to the vertical, i.e. aligned to the direction of orientation of the column  6 . 
     The elongate element  78  is linear and is inclined at an acute angle from a plane including a longitudinal axis of the column  6  and the trend axis T-T so that the upper end  80  is oriented further from the plane than a lower portion  85  of the elongate element  78 . The elongate elements  78  of the first and second actuators  54 ,  56  are oriented in opposite directions from the plane. The acute angle of inclination of each elongate element  78  from the plane decreases as the extension of the elongate element  78  increases. 
     The angles of the first and second actuators  54 ,  56  to the vertical when extended or retracted depends on various parameters, including the length of the actuator when extended or retracted, the horizontal distance separating the lower pivots of the first and second actuator  54 ,  56  (which is typically from 60 to 100 mm) and the length of the movable framework  50  between the upper pivots of the first and second actuator  54 ,  56 . In one embodiment, when the first or second actuator  54 ,  56  is configured so that the respective leadscrew  86  is fully retracted, so as to lower the respective first or second portion  58 ,  60  of the movable framework  50 , the first or second actuator  54 ,  56  is in a first pivot position in which the leadscrew  86  is oriented at a relatively large acute angle (for example 10 to 25°) relative to the vertical, i.e. the direction of orientation of the column  6 , the angle also being dependent upon the height of the other actuator. 
     Correspondingly, in that embodiment, when the first or second actuator  54 ,  56  is configured so that the respective leadscrew  86  is fully extended, so as to raise the respective first or second portion  58 ,  60  of the movable framework  50 , the first or second actuator  54 ,  56  is in a second pivot position in which the leadscrew  86  is extended and at a relatively small acute angle (for example 6 to 16°) relative to the vertical, i.e. the direction of orientation of the column  6 , the angle also being dependent upon the height of the other actuator. 
     When the first and second actuators  54 ,  56  are both fully retracted in that embodiment, each leadscrew  86  is oriented at an acute angle of from 18 to 25° relative to the vertical. When the first and second actuators  54 ,  56  are both fully extended in that embodiment, each leadscrew  86  is oriented at an acute angle of from 12 to 17° relative to the vertical. When one of the first and second actuators  54 ,  56  is fully extended and the other of the first and second actuators  54 ,  56  is fully retracted, the extended leadscrew  86  is oriented at an acute angle of from 5 to 8° relative to the vertical and the retracted leadscrew  86  is oriented at an acute angle of from 9 to 13° relative to the vertical. 
     The movable framework  50  defines an internal opening  98  which is larger than an upper end  100  of the column  6 . The first actuator mechanism  52  is capable of lowering the movable framework  50  relative to the column  6  to a lowermost position in which the movable framework  50  is below the upper end  100  of the column  6  and annularly surrounds the column  6 . In the lowermost position the trend axis T-T is below the upper end  100  of the column  6 , and extends through an upper part of the outer column element  30  which surrounds the inner column element  34  when the column elements  30 ,  32 ,  34  are telescoped into the contracted configuration, and typically the movable framework  50  is entirely below the upper end  100  of the column  6 . 
     The first actuator mechanism  52  is capable of raising the movable framework  50  relative to the column  6  to an uppermost position in which the movable framework  50  is above the upper end  100  of the column  6 . In the uppermost position the trend axis T-T is above the upper end  100  of the column  6 , and is spaced by a spacing height from an uppermost part of the column  6 , and typically the movable framework  50  is above, preferably entirely above, the upper end  100  of the column  6 . The first actuator mechanism  52  is fitted to the outer column element  30  and when the column elements  30 ,  32 ,  34  are telescoped into an extended configuration the first actuator mechanism  52 , the movable framework  50  and the tabletop  8  are raised relative to the base  4 . 
     In the illustrated embodiment two linear guide mechanisms  102  are provided on opposite sides of the column  6 . Each linear guide mechanism  102  extends along at least a part of the column  6 . Each linear guide mechanism  102  comprises a first part  104  coupled to the column  6  and a second part  106  coupled to the movable framework  50 . Each linear guide mechanism  102  comprises a respective pair of first and second parts  104 ,  106 . 
     The first and second parts  104 ,  106  are relatively movable along a linear axis L-L, shown in  FIG. 5 , of the linear guide mechanism  102  to enable the movable framework  50  to be translated along the linear axis L-L by relative movement of the first and second parts  104 ,  106 . The first part  104  is a fixed linear guide member  110 , fixed to the column  6 , and the second part  106  is a movable linear guide member  112 , coupled to the movable framework  50  at a trend pivot  118 . The first part  104  is an elongate channel  114  and the second part  106  is an elongate slider  116  within the channel  114 , although the opposite configuration may be employed. 
     In the illustrated embodiment, the two linear guide mechanisms  102  are raised or lowered synchronously with the raising or lowering of the trend pivots  118 . The two linear guide mechanisms  102  ensure that the trend pivots  118  can only move vertically. 
     Optionally, the linear guide mechanisms  102  may be provided with a locking mechanism to lock the linear guide mechanism  102  at a selected height, and thereby lock the trend pivots  118 , and the trend axis T-T, at a selected height. 
     Additionally or alternatively, the linear guide mechanisms  102  may be provided with a braking mechanism which can be activated to brake the movement of the linear guide mechanisms  102 . Both the locking mechanism and the braking mechanism act to take at least a proportion of the applied tabletop load from the first and second actuators  54 ,  56 . 
     The locking and/or braking mechanism may be an electric actuator, a hydraulic cylinder or a locking gas spring, all of which constructions are known to those skilled in the art. 
     Referring additionally to  FIG. 4 , a brace mechanism  108  is coupled to, and mounted between, the pair of linear guide mechanisms  102 . The brace mechanism prevents twisting of the trend pivot  118  and the associated linear guide mechanisms  102 . The brace mechanism  108  comprises a brace element  120  having a central plate member  122  and two opposite end plate members  124 ,  126  that are orthogonal to the central plate member  122  and oriented in a common direction. A free end  128  of each end plate member  124 ,  126  is rigidly affixed, for example by bolts or screws, to a respective movable linear guide member  112 , and thereby coupled to the movable framework  50 . 
     The brace mechanism  108  functions to connect together the pair of linear guide mechanisms  102  for the trend pivot so that the movable framework  50  does not twist when under a high applied mechanical load, for example particularly when a heavy patient is on the tabletop  8 . The brace mechanism  108  ensures that the two opposite linear guide mechanisms  102  are located at the identical height. 
     A twisting force applied to the movable framework  50 , i.e. the trend frame  50 , at least partly about an axis extending orthogonal to the trend axis T-T, acting for example to urge one lateral side of the movable framework  50  downwardly relative to the opposite lateral side of the movable framework  50 , is resisted by the brace mechanism  108 . The plate members  122 ,  124 ,  126  are typically composed of heavy gauge steel so as to exhibit high rigidity and resistance to shear forces in the plane of the respective plates. 
     In a preferred modification to increase the rigidity of the brace mechanism  108 , as shown in  FIG. 12  the central plate member  122  is movably fitted to the column  6  by one or more linear brace guides  121  which extend along the column  6 . Each linear brace guide  121  has a fixed linear brace guide member  123 , fixed to the column  6 , and a movable linear brace guide member  125 , coupled to the movable framework  50 . The movable linear brace guide member  125  is an elongate channel  130  and the fixed linear brace guide member  123  is an elongate slider  132  within the channel  130 , although the opposite configuration may be employed. 
     The first actuator mechanism  52  is fitted to an external surface  136  of the outer column element  30 . The linear guide mechanisms  102 , and when present the one or more linear brace guides  124 , are also fitted to the outer column element  30 , in particular to the external surface  136  of the outer column element  30 . When the column elements  30 ,  32 ,  34  are telescoped into an extended configuration, the linear guide mechanisms  102  and the brace mechanism  108  are raised relative to the base  4 . 
     The movable framework  50 , and consequently the tabletop  8  thereon, is supported on the column  6  ( i ) by the first and second actuators  54 ,  56  and the respective associated stabilisers  88 ,  90  and (ii) by the linear guide mechanisms  102  and the associated brace mechanism  108 . In order to provide enhanced resistance of the surgical table  2  to twisting forces which may be encountered in use, rather than over-strengthening the actuators  54 ,  56 , stabilisers  88 ,  90 , linear guide mechanisms  102  and/or brace mechanism  108 , which would enlarge the weight and dimensions of the column and would reduce the ability of the column to be contracted to a low height, and increase component costs, the surgical table  2  is preferably provided with a further twist-resisting mechanism. The twist-resisting mechanism may comprise a connection between at least one of the actuator/stabiliser assemblies and the column  6  at a location between the upper and lower ends of the actuator/stabiliser assembly so that twisting of the actuator/stabiliser assembly relative to the column  6  is prevented or at least minimised. One embodiment of a twist-resisting mechanism is shown in  FIGS. 1 to 6 and 9 . 
     Referring to  FIG. 9 , to provide a twist-resisting mechanism  900  at least one of the hollow guides  94 , forming a stabiliser body, is slidably and rotatably connected to the column  6  via pin bearing member  901  on the hollow guide  94 . The pin bearing member  901  is slidably received in an arc-like slot  902  in a bracket  903  that is fitted to the column  6 . This provides a slot and bearing arrangement  904  to allow the stabiliser body and the associated actuator to rotate about a horizontal axis at pivot mount  51  but prevents torsional rotation of the stabiliser body and the associated actuator and rotation of the stabiliser body and the associated actuator about any other axis. 
     The slot and bearing arrangement  904  provides a reinforcement against twisting within the tabletop  8  that may be created by an operator-applied load acting on the side of the table  2 . The slot and bearing arrangement  904  also minimises any buckling load acting on the stabilisers  88 ,  90  and elongate elements  78  of the first and second actuators  54 ,  56 . 
     As shown in  FIGS. 14 a  and 14 b   , the locking and/or braking mechanism  101  comprises an assembly of two oppositely oriented vertically oriented gas springs  801   a ,  801   b . A first, lower, gas spring  801  a has a free end  803   a  of a piston element  804   a  pivotally fitted to the brace mechanism  108  by a rigid plate  805  fixed to, and extending downwardly from, the brace mechanism  108 . A second, upper, gas spring  801   b  has a free end  803   b  of a piston element  804   b  pivotally fitted to the column  6 . Each gas spring  801   a ,  801   b  has a respective cylinder element  802   a ,  802   b . The two cylinder elements  802   a ,  802   b  are connected to each other so as to be fixed together in a vertical direction. The two cylinder elements  802   a ,  802   b  may optionally additionally be (i) slidably fitted to the brace mechanism  108  or the column  6  by a sliding joint (not shown) and/or (ii) guided by a guide device (not shown), in each case to ensure vertical motion of the gas springs  801   a ,  801   b  and prevent lateral deflection of the assembly of two oppositely oriented vertically oriented gas springs  801   a ,  801   b  when under load. 
     In the illustrated embodiment the locking and/or braking mechanism  101  is fitted directly to the brace mechanism  108  and thereby indirectly to the linear guide mechanisms  102  to which the brace mechanism  108  is coupled. In an alternative embodiment, the locking and/or braking mechanism  101  is fitted directly to one or both of the linear guide mechanisms  102 . In each embodiment, the locking and/or braking mechanism  101  can provide a locking and/or braking function between the movable framework  50 , and thereby the tabletop  8 , and the column  6 . 
       FIG. 14 a    illustrates the position and configuration of the gas springs  801   a ,  801   b  when the movable framework  50  is at maximum height relative to the column  6 . The brace mechanism  108  is in a high position and the gas springs  801   a ,  801   b  are both fully contracted.  FIG. 14 b    illustrates the position and configuration of the gas springs  801   a ,  801   b  when the movable framework  50  is at minimum height relative to the column  6 . The brace mechanism  108  is in a low position and the gas springs  801   a ,  80   l  b are both fully extended. 
     The gas springs  801   a ,  801   b  may be controlled in known manner, for example by a solenoid control, to provide: a braking function for downward or upward movement of the movable framework  50  relative to the column  6 ; a lift function for raising the movable framework  50  relative to the column  6 ; and/or a locking function for locking the position of the movable framework  50  relative to the column  6 . The double gas spring arrangement can provide a low contracted height and a high stroke, corresponding with the movement range of the movable framework  50  and the column  6 . 
     Other locking and/or braking mechanisms will be apparent to those skilled in the art. For example, a single gas spring and solenoid actuator assembly may be provided between the movable framework and the column, and/or a rail clamp may be provided on the brace mechanism for selectively clamping, using an actuator, to one or more rails fitted to the column. 
     When the locking and/or braking mechanism  101  is configured to provide a lift function, the locking and/or braking mechanism  101  may comprise a second actuator mechanism coupled to the linear guide mechanism  102  and arranged to cause relative movement of the first and second parts  104 ,  106  thereby to raise and lower the trend axis T-T relative to the column  6 . 
     In the surgical table  2  of the illustrated embodiment, a lifting and orienting mechanism for the trend frame  50 , which is movable framework  50 , is fitted around the outside of the column. The lifting and orienting mechanism comprises the first actuator mechanism  52 , which in turn comprises the first and second actuators  54 ,  56 . The first and second actuators  54 ,  56  can have a ballscrew or leadscrew construction. 
     Each respective electric motor  76  drives the respective elongate element  78  through a gearbox in the electric motor  76 . The first and second actuators  54 ,  56  are positioned so that the trend frame  50  is supported on opposite sides of the column  6 , each side extending transverse to the trend axis T-T and constituting a “front” or “rear” side of the column  6  as would be understood by those skilled in the art, at diagonally opposite corners of the trend frame  50 . 
     The linear guide mechanisms  102  on opposite sides of the column  6  allow the central trend pivot axis T-T to be raised and lowered and act as trend pivot guides. The opposite trend pivots  118  are mounted to the linear guide mechanisms  102  and can move vertically along the direction of the column  6 , guided by the linear guide mechanisms  102 . 
     The brace mechanism  108  connects together the trend pivot guides. The brace mechanism  108  may have sufficient stiffness and resistance to twisting to brace the opposite trend pivots  118  so that the opposite trend pivots  118  are maintained at exactly the same height, although the stiffness may be enhanced by at least one linear brace guide  124  between the brace mechanism  108  and the column  6 . The trend frame  50  pivots about the opposite trend pivots  118  and is located between the first and second actuators  54 ,  56  and the tilt frame. The trend frame  50  has a high degree of freedom of motion, as described in further detail below. 
     The operation of the surgical table  2  will now be described. 
     As described above, the surgical table  2  incorporates a mechanism for controlling the trend angle and height of a trend frame  50 , which is beneath the tabletop  8 . The trend frame  50  can be rotated about a trend axis, and the angle of inclination of the trend frame  50  sets the trend angle of the tabletop  8 . The height of the column  6  can be controlled independently from the height of the trend frame  50 . 
       FIGS. 2 b    and  4  show the column  6  at minimum height and the movable framework  50 , constituting the trend frame  50 , at maximum height. In this configuration, the elongate elements  78  of the first and second actuators  54 ,  56  and the first and second stabilisers  88 ,  90  are extended (and these elements are fully extended at 45 degree trend/reverse trend angles). In this configuration, the linear guide mechanisms  102  are fully extended, to provide the brace mechanism  108  in a fully raised position. The first and second stabilisers  88 ,  90  and the brace mechanism  108  prevent twisting of the movable framework  50  under the action of any applied load on the table  2 . 
     The trend axis T-T is raised relative to the column  6 . The movable framework  50  is raised relative to the column  6  to an uppermost position in which the movable framework  50  is above the upper end  100  of the column  6 , the trend axis T-T is above the upper end  100  of the column  6 , and the movable framework  50  is entirely above the upper end  100  of the column  6 . The column elements  30 ,  32 ,  34  are telescoped into a contracted configuration. The movable framework  50  and the tabletop  8  are raised relative to the base  4  by the first and second actuators  54 ,  56 . 
     In this configuration, the trend axis T-T is typically 410 mm above the bottom of the column  6  which is mounted on the base  4 . This configuration could be used as a rest position for the surgical table  2 . 
     When it is desired to lower the tabletop  8  even further, for example to transfer a patient onto or from the tabletop  8 , the movable framework  50  can be lowered even further, which lowers the tabletop  8  supported thereby. 
     Accordingly,  FIGS. 2 a    and  3  shows the column  6  at minimum height and the movable framework  50 , constituting the trend frame  50 , at minimum height. In this configuration, the elongate elements  78  of the first and second actuators  54 ,  56  are fully retracted. 
     The trend axis T-T is lowered relative to the column  6 . The movable framework  50  is lowered relative to the column  6  to a lowermost position in which the movable framework  50  is below the upper end  100  of the column  6  and annularly surrounds the column  6 . In the lowermost position the trend axis T-T is below the upper end  100  of the column  6  and extends through an upper part of the outer column element  30  and the movable framework  50  is entirely below the upper end  100  of the column  6 . 
     In this configuration, the trend axis T-T is typically 290 mm above the bottom of the column  6  which is mounted on the base  4  and the column height is typically less than 380 mm above the base  4 . 
     When it is desired to incline the tabletop at a trend angle, as shown in  FIG. 5  the column  6  can be set at its minimum height, as described above, and the trend frame  50  can be set at an intermediate height, and with the trend frame  50  at a forward or reverse trend angle of up to 45°. The trend angle may be controlled by providing that one of the elongate elements  78  of the first and second actuators  54 ,  56  is retracted (in  FIG. 5 , second actuator  56 ) and the other of the elongate elements  78  of the first and second actuators  54 ,  56  (in  FIG. 5 , first actuator  54 ) is extended. 
     At the maximum trend angle of +45° or −45° (or even greater trend angle values) one of the elongate elements  78  of the first and second actuators  54 ,  56  is fully retracted and the other of the elongate elements  78  of the first and second actuators  54 ,  56  is fully extended. This provides a large range of trend angles, over an angular range of 90°, from endpoints of +45° to −45° even when the column  6  is fully retracted, and so the tabletop  8  is at a relatively low height, with the trend axis typically being no more than 410 mm above the base  4 . 
       FIG. 6  shows the fully extended column  6  at maximum height and the movable framework  50  of the trend frame  50  also at maximum height relative to the column  6 . In this configuration, the elongate elements  78  of the first and second actuators  54 ,  56  are extended (and these elements are fully extended at 45 degree trend/reverse trend angles). In this configuration, the linear guide mechanisms  102  are fully extended, to provide the brace mechanism  108  in a fully raised position. The trend axis T-T is raised relative to the column  6  to the uppermost position as described above. 
     In this configuration, the trend axis T-T is typically 945 mm above the bottom of the column  6  which is mounted on the base  4 . 
     The above-described lifting and orienting mechanism for the trend frame  50  permits a number of different motions which can be selected by the user by controlling the first and second actuators  54 ,  56 . The particular structural relationship between the first and second actuators  54 ,  56  and the trend frame  50  achieves a remarkable variety and range of motions of the trend frame  50 . 
     The trend frame  50 , and therefore the tabletop  8 , can be rotated into either reverse trend or trend by driving either each of the first and second actuators  54 ,  56  individually or both of the first and second actuators  54 ,  56  at the same time in opposite directions, depending upon the initial position of the trend axis T-T relative to the column  6 . Operating two trend actuators together has the benefit of increasing the speed of trend movement as a result of a reduction in the distance that each trend actuator, namely the first and second actuators  54 ,  56 , has to drive for any given change in trend or reverse trend angle. 
     In particular, the trend frame  50  can be raised or lowered, with the trend frame at any given orientation, for example level, i.e. horizontally oriented. This function is achieved by driving both of the first and second actuators  54 ,  56  simultaneously in the same direction, i.e. extending to raise elongate element  78  or retracting to lower elongate element  78 , and at the same translational rate. The position of the trend axis T-T is correspondingly raised or lowered, which raises or lowers the brace mechanism  108  coupled to the pair of linear guide mechanisms  102  fitted to the outer column element  30  of the extendable column  6 . 
     The trend frame  50  can therefore be raised or lowered relative to the outer column element  30  of the column  6 , and, independently therefrom, the outer column element  30  can be raised or lowered relative to the base  4  of the surgical table  2  since the column  6  is extendable. The cumulative effect is that the vertical motion of the trend frame  50  relative to the base  4  of the surgical table  2  can combine the vertical motion of the trend frame  50  relative to the column  6  in an additive sense with vertical motion of the extendable column  6 . 
     The total range of vertical motion of the trend frame  50  relative to the base  4  of the surgical table  2  is very high, and higher than known surgical tables. Consequently, the lowermost position of the tabletop  8  is very low, and the highest position is very high, as compared to known surgical tables. 
     In addition, the trend frame  50  can be raised or lowered so as to orient the trend frame at any given orientation relative to the horizontal, i.e. to a reverse trend orientation (with the lower torso section  16  coupled to the trend frame  50  inclined so that the head section  12  of the tabletop  8  is above the leg sections  18  of the tabletop  8 ) or to a trend orientation (with the lower torso section  16  coupled to the trend frame  50  inclined so that the head section  12  of the tabletop  8  is below the leg sections  18  of the tabletop  8 ). This function is achieved, depending upon the start position of the tabletop  8  and the trend frame  50 , by driving one or both of the first and second actuators  54 ,  56 . 
     For example, if the tabletop  8  and the trend frame  50  are initially level relative to the horizontal, as shown in  FIG. 7 a   , the first and second actuators  54 ,  56  can be driven simultaneously in opposite directions, i.e. extending to raise one elongate element  78  and retracting to lower the other elongate element  78 , and at the same translational rate, which may be termed a symmetric mode to achieve a reverse trend position as shown in  FIG. 7 b    or a trend position as shown in  FIG. 7   c.    
     When the first and second actuators  54 ,  56  are driven simultaneously in opposite directions, the vertical position of the trend axis T-T is stationary, and the trend frame  50  rotates about the trend axis T-T. Driving the first and second actuators  54 ,  56  simultaneously in opposite directions, provides the advantage that very fast trend, or reverse trend, movement can be achieved. The enhanced speed is achieved since both sides of the trend frame  50  are raised or lowered relative to the trend axis T-T, and so the translational distance that each of the first and second actuators  54 ,  56  need to extend or retract is minimised for a given change in trend angle. The reduced actuator driving distance for a given change in trend angle permits faster trend movement. 
     It is very desirable for the surgical table to reduce the time period to achieve a trend position, for example from a horizontal position, since in many surgical procedures it may be necessary in an emergency to put the surgical table into a trend position to maximise blood flow to the patient&#39;s head as quickly as possible. 
     Alternatively, the trend frame  50  can be raised or lowered so as to orient the trend frame at any given orientation relative to the horizontal, i.e. to a reverse trend orientation or to a trend orientation by driving only one of the first and second actuators  54 ,  56 , or by driving both of the first and second actuators  54 ,  56  in an asymmetric mode, i.e. the first and second actuators  54 ,  56  are driven in other than an opposite and simultaneous manner. 
     For example if the tabletop  8  and the trend frame  50  are initially level relative to the horizontal, and the tabletop  8  is at a minimum height, as shown in  FIG. 8 a   , the second actuator  56  can be undriven so that its elongate element  78  is stationary, and remains retracted, and the first actuator  54  can be driven in an upward direction, i.e. extending to raise its elongate element  78 , as shown in  FIG. 8 b   . The pivot joint  82  of the second actuator  56  thereby defines the effective trend axis T 1 -T 1  for the trend frame  50 . The central trend axis T-T is correspondingly raised relative to the effective trend axis T 1 -T 1  and the rotational motion of the trend frame  50  is about the effective trend axis T 1 -T 1  rather than the central trend axis T-T. 
     Conversely, as shown in  FIG. 8 c    if the first actuator  54  is undriven, and remains retracted, and the second actuator  56  is driven to extend the elongate element  78 , the pivot joint  82  of the first actuator  54  thereby defines a second effective trend axis T 2 -T 2  for the trend frame  50 . Furthermore, the trend or reverse trend position can be achieved by lowering one of the first and second actuators  54 ,  56  and keeping stationary the other of the first and second actuators  54 ,  56 . 
     It may be seen that by providing a mounting for the central trend axis T-T which can move vertically, by vertical motion of the opposite trend pivots  118  which are mounted to the linear guide mechanisms  102 , and by providing that the first and second actuators  54 ,  56  can be driven entirely independently, the effective trend axis, i.e. the axis that the trend frame  50  actually pivots about during a trend or reverse trend motion, can be selectively located at one of three positions, namely the trend pivots  118  (defining trend axis T-T), the pivot joint  82  of the second actuator  56  (defining trend axis T 1 -T 1 ) or the pivot joint  82  of the first actuator  54  (defining trend axis T 2 -T 2 ). 
     Yet further, as shown in  FIG. 9 , if both of the first and second actuators  54 ,  56  are driven simultaneously but other than both (i) in opposite directions and (ii) simultaneously, then the effective trend axis  200 , i.e. the axis that the trend frame  50  actually pivots about during a trend or reverse trend motion, can be virtually located at any position between the pivot joint  82  of the first actuator  54  (T 2 -T 2 ) and the pivot joint  82  of the second actuator  56  (T 1 -T 1 ). For example if the first actuator  54  is raised at a velocity of X m/s and the second actuator  56  is lowered at a velocity of −2X m/s, the effective trend axis  200  is virtually located at a position between the trend pivots  118  and the pivot joint  82  of the second actuator  56  (T 1 -T 1 ). 
     It may therefore be seen that by varying the relative velocity and direction of motion of the first and second actuators  54 ,  56 , the location of the effective trend axis, which may be at a physical pivot or at a virtual pivot, can be at any position from, and including, the physical pivot joint  82  of the first actuator  54  (defining trend axis T 2 -T 2 ) to, and including, the physical pivot joint  82  of the second actuator  56  (defining trend axis T 1 -T 1 ), and may be at the physical trend pivots  118  (defining trend axis T-T), or any position therebetween as a virtual pivot. 
     A control mechanism  150 , illustrated schematically in  FIG. 1  as a wireless control, may be provided to cause the height of the effective trend axis to be variable within a first dimensional range and to cause the location of the effective trend axis in a direction orthogonal to the transverse axis to be variable within a first dimensional range. 
     By providing an ability to select the location of the effective trend axis across the length of the trend frame  50 , i.e. in a direction along the central axis C-C, the relationship between the trend/reverse trend orientations and height of the tabletop  8  has a very high freedom of movement. 
     For example, if the tabletop  8  is initially in a medium height horizontal position, the tabletop  8  can be driven to a trend position very quickly by simultaneously driving the first and second actuators  54 ,  56  in opposite directions, which lowers the head and raises the feet of the patient, and the effective trend axis would be at the physical trend pivots  118  (defining trend axis T-T). 
     However, if the tabletop  8  is initially in a low height horizontal position, it may not be possible further to lower the head to a trend position simply by rotating the trend frame  50  about the central trend axis T-T defined by the trend pivots  118 , because the head section  12  may already be at its minimum height. 
     Therefore, the tabletop  8  can be driven to a trend position quickly by only driving the first actuator  54  and by keeping the second actuator  56  stationary. This inclines the entire tabletop  8 , and raises the feet of the patient, but keeps the head of the patient at substantially the same height relative to the floor. The effective trend axis would be at the physical pivot joint  82  of the second actuator  56  (defining trend axis T 1 -T 1 ). 
     This provides the advantage that the tabletop  8  can quickly attain a trend position from a low initial height merely by tilting the tabletop about a selected non-central trend axis and without requiring the entire tabletop to be raised in height; in contrast, in known surgical tables it would be necessary to raise the entire tabletop relative to the floor to achieve a trend position from an initial low tabletop starting position, which would delay and slow down the trend operation. 
     Conversely, if the tabletop  8  is initially in a high height horizontal position, and it is possible further to lower the head towards the floor into a trend position, the trend frame  50  may be rotated about an effective trend axis at the physical pivot joint  82  of the first actuator  54  (defining trend axis T 2 -T 2 ), because the leg sections  18  may already be at their maximum height. Therefore, the tabletop  8  can be driven to a trend position quickly by only driving the second actuator  56  and by keeping the first actuator  54  stationary. 
     It should be clear that any non-symmetric simultaneous motion of the first and second actuators  54 ,  56  can locate the effective trend axis at any physical or virtual pivot in the distance extending from the physical pivot joint  82  of the first actuator  54  to the physical pivot joint  82  of the second actuator  56 , which further enhances the versatility, with regard to height and speed, of achieving the trend/reverse trend orientations of the tabletop  8 . 
     Of course, this versatility is further enhanced by providing the lifting and orienting mechanism for the trend frame  50  on the extendable column  6  which can be independently driven from the first and second actuators  54 ,  56  which drive the trend frame  50 . 
     Consequently, the versatility, with regard to height and speed, of achieving the trend/reverse trend orientations of the tabletop  8  are significantly higher than as compared to known surgical tables. 
       FIGS. 12 and 13  show that the footprint  700  of the column  6 , and the mechanism for controlling the trend angle and height of the trend frame  50 , is small when the column and the mechanism are fully retracted. The footprint of the combination of both the column  6  and the first and second actuators  54 ,  56  typically has a length (along the longitudinal axis of the tabletop  8 ) of 330 mm or less and a width (along the transverse axis of the tabletop  8 ) of 305 mm. 
       FIGS. 15, 16 and 17   a  and  17   b  illustrate a cable management system for the column  6 .  FIG. 15  illustrates the column in a contracted configuration and  FIG. 16  illustrates the column in an extended configuration, and the cable management system  300  is configured to be retractable and extendable corresponding to the column  6  without causing a kinking and damage to cables within the cable management system  300 .  FIGS. 17 a  and 17 b    schematically illustrate the cable configuration when the column  6  is in the contracted or extended configuration respectively. 
     In the surgical table  2 , power and control cables  302  need to be connected between the base  4  and the tabletop  8 . The cables  302  extend up the column  6  from the base  4  to be connected as required within the tabletop  8 . 
     A pair of flexible chain cable guides  304 ,  306  are provided. A first cable guide  304  has a first end portion  308  fitted, directly or indirectly, to the base  4  and a second end portion  310  fitted, directly or indirectly, to the intermediate column element  32  (or one intermediate column element  32  if there are plural telescoped intermediate column elements). A second cable guide  306  has a first end portion  312  fitted, directly or indirectly, to the intermediate column element  32  and a second end portion  314  fitted, directly or indirectly, to the outer column element  30 . 
     The first end portion  308  of the first cable guide  304  is connected to a lower elongate bracket  316 , which includes one or more fitting holes  317  for fitting the lower elongate bracket  316  to the base  4  by screws. The lower elongate bracket  316  defines an elongate guide slot  318  which is upwardly oriented and within which first end portion  308 , and the adjacent portion of the first cable guide  304 , are received. The lower elongate bracket  316  is fitted, directly or indirectly, to the base  4 . 
     The second end portion  310  of the first cable guide  304  is connected to a centre bracket  320  from which extends an elongate wall  322  which is upwardly oriented. The centre bracket  320  is fitted, directly or indirectly, to a lower part  324  of the intermediate column element  32 . The second end portion  310 , and the adjacent portion of the first cable guide  304 , can be aligned against one face  326  of the elongate wall  322 . 
     The first end portion  312  of the second cable guide  306  is connected to the centre bracket  320  on an opposite side from the second end portion  310  of the first cable guide  304 . The first end portion  312 , and the adjacent portion of the second cable guide  306 , can be aligned against the opposite face  328  of the elongate wall  322 . 
     The second end portion  314  of the second cable guide  306  is connected to a higher bracket  330  which is fitted, directly or indirectly, to a lower part  332  of the outer column element  30 . The higher bracket  330  defines a guide slot  334  which is upwardly oriented and within which second end portion  314  is received. The guide slot  334  of the higher bracket  330  is shorter than the elongate guide slot  318  of the lower elongate bracket  316 . 
     The first and second cable guides  304 ,  306  each comprise a flexible chain  336  which is formed of a plurality of linked elements  338 . The elements  338  each have a central channel portion  340  so that the resultant flexible chain  336  has a central elongate channel  342  along its length. One or more cables  302  is received in the elongate channel  342 . 
     The cables  302  from the base  4  enter the first end portion  308  of the first cable guide  304 , exit the second end portion  310  of the first cable guide  304  in the vicinity of the centre bracket  320 , then enter the first end portion  312  of the second cable guide  306  and exit the second end portion  314  of the second cable guide  306  to be connected to the tabletop  8 . 
     As shown in  FIG. 15 , In the vicinity of the centre bracket  320 , the cables  302  hang down as a downwardly depending loop  344  from the centre bracket  320 . The downwardly depending loop  344  is located at a substantially central position across a lateral width of the cable management system  300 . The pair of flexible chain cable guides  304 ,  306  therefore provide that the cables  302  are secured in a fixed loop  344  at the central position  321 , provided by the centre bracket  320 , of the cable management system  330  where the cables connect together the two flexible chain cable guides  304 ,  306 . 
     A generous bend radius can be provided at this central position  321  which can be equivalent to the bend radii provided at the top of each upwardly extending loop  345 ,  347  of the respective flexible chain cable guides  304 ,  306 . A typical width of the cable management system  330  is about 180 mm. 
     As shown in  FIG. 17 a   , in the contracted configuration of the column  6 , the cables  302  have three large radius bends at loops  344 ,  345  and  347  and the cables  302  are fixed at three points corresponding to the lower elongate bracket  316 , the centre bracket  320  and the higher bracket  330 . The cables  302  generally form an m-shape. The central part of the cables  302  is guided by the centre bracket  320 . 
     As shown in  FIG. 17 b   , in the extended configuration of the column  6 , the cables  302  still have three large radius bends at loops  344 ,  345  and  347 . The cables  302  generally form a stepped m-shape. The central part of the cables  302  remains guided by the centre bracket  320 . 
     As compared to a typical conventional S-shape arrangement for the cables extending up a column of a surgical table, in which the cables are not directly supported at the centre of the S-shape, the central bracket prevents the cables and associated cable guides from sagging at the central position. This minimises stress at the central position, as the central position is driven by the column and therefore the cables are fully supported at the centre. This also reduces cable stress at the top loop  347 . 
     In the illustrated embodiment, first and second cable guides  304 ,  306  are provided and these may be provided by two individual cable guides that intersect at the centre bracket  320 , or alternatively a single cable guide member is provided which is bent at the centre bracket  320  to form the first and second cable guides  304 ,  306 . 
     The first and second cable guides  304 ,  306  are composed of a polymer, for example polypropylene. These cable guides are known in the art, and a suitable cable guide is sold on commerce under the trade mark “Energy chain®” by Igus (UK) Limited of Northampton, UK. 
     In the contracted configuration the first and second cable guides  304 ,  306  are laterally adjacent, and form a shape of an inverted W, and the cable management system  300  has a minimum total height, and in the extended configuration the second cable guide  306  is substantially above the first cable guide  304  and the cable management system  300  has a maximum total height. 
     As shown in  FIG. 15 , when the column  6  is in the contracted configuration, each of the first and second cable guides  304 ,  306  is in a contracted configuration and has a minimum total height. Also, since the first and second cable guides  304 ,  306  are in a side-by-side configuration because the lower part  324  of the intermediate column element  32  and the lower part  332  of the outer column element  30  are aligned and adjacent to the base  4 , the total height of the entire cable management system  300  is minimised. 
     As shown in  FIG. 17 a   , the first and second cable guides  304 ,  306  are each configured to be, in the contracted configuration, in the form of an inverted U, and thereby have substantially parallel pairs of upright opposed legs  346 ,  348  and  350 ,  352  of substantially the same length. Each pair of legs  346 ,  348  and  350 ,  352  is interconnected at the respective upper ends  354 ,  356  by a transverse interconnection  358 ,  360 . In the illustrated embodiment, in which the column  6  has a contracted height of typically less than 380 mm, the first and second cable guides  304 ,  306  each have a contracted height of typically 250 mm. 
     In the contracted configuration, the elongate guide slot  318  of the lower elongate bracket  316 , the elongate wall  322  of the centre bracket  320 , and the guide slot  334  of the higher bracket  330  all assist the first and second cable guides  304 ,  306  assuming the desired contracted configuration of minimum total height and with the first and second cable guides  304 ,  306  being each configured in the form of an inverted U. This avoids damage and kinking of the cables in the contracted configuration. 
     As shown in  FIGS. 16 and 17   b , in contrast, when the column  6  is in the extended configuration, each of the first and second cable guides  304 ,  306  is in an extended configuration and has a maximum total height. The first and second cable guides  304 ,  306  are each configured in the form of an inverted J. The opposed legs  346 ,  348  and  350 ,  352  of each pair have different length. In the first cable guide  304 , the leg  346  connected to the base  4  is longer than the leg  348  connected to the intermediate column element  32 . In the second cable guide  306 , the leg  350  connected to the intermediate column element  32  is longer than the leg  352  connected to the outer column element  30 . 
     In the illustrated embodiment, in which the column  6  has a contracted height of typically less than 380 mm, the total extended height from the cable entrance  362  of the first cable guide  304  at first end portion  308  to the cable exit  366  from the second cable guide  306  at second end portion  314  is typically 525 mm. 
     In the extended configuration, the elongate guide slot  318  of the lower elongate bracket  316 , the elongate wall  322  of the centre bracket  320 , and the guide slot  334  of the higher bracket  330  again all assist the first and second cable guides  304 ,  306  assuming the desired extended configuration of maximum total height and with the first and second cable guides  304 ,  306  being each configured in the form of an inverted J with substantially parallel legs. Again, this avoids damage and kinking of the cables in the extended configuration, and when transitioning between the extended configuration and the contracted configuration. 
     The lower elongate bracket  316 , the centre bracket  320 , and the higher bracket  330  are typically composed of sheet metal. These brackets prevent excess cable pressure, otherwise generated by the spring tension in the cables, particularly when the cables are bent around a tight radius. Such excess cable pressure would cause unwanted lateral movement and sagging of the first and second cable guides  304 ,  306 . 
     The cable management system  330  enables a low contracted height to be achieved in combination with a high stroke. The cables can be connected from the base  4  to the top section of the column  6  without requiring the cables to extend upwardly along the full contracted height of the column. 
     In the extended position, the cables connect securely to the top element  30  of the column  6  but the uppermost part of the cable management system  300  remains located a distance significantly below the upper end  100  of the column  6 . 
     This assists minimising the footprint of the column  6  and assists permitting clearance for other table components, particularly the trend frame  50 , in extreme trend positions. 
     In an alternative embodiment of the present invention, as illustrated in  FIG. 18 , instead of the brace mechanism there is provided a second actuator mechanism  408  which is coupled to the linear guide mechanism  102 . The brace mechanism is passive and unpowered, and in that embodiment the power for lifting and tilting the trend frame  50  is provided by the first and second actuators. 
     In the embodiment comprising the second actuator mechanism  408 , the second actuator mechanism  408  is active and powered, and in this embodiment additional power, additional to that provided by the first and second actuators, for lifting and tilting the trend frame  50  is provided by the second actuator mechanism  408 . 
     Although only one linear guide mechanism  102  may optionally be provided, in the illustrated embodiment the second actuator mechanism  408  is arranged to cause relative movement of the first and second parts  104 ,  106  thereby to raise and lower the trend axis T-T relative to the column  6 . Like the first actuator mechanism  52 , the linear guide mechanism  102  and second actuator mechanism  408  are external of the column  6 . The second actuator mechanism  408  comprises a pivotable arm  418  having a first end  420  pivotally attached to the second part  106  and a second end  422  pivotally coupled to a third linear actuator  424 . The arm  418  is pivoted about a pivot  426  located between the first and second ends  420 ,  422  and fixed to the column  6 . A pin  428  is mounted on the second part  106  and the first end  420  has a slot  430  in which the pin  428  is received. The pin  428  is slidable along the slot  430  when the arm  418  is pivoted about the pivot  426 . 
     In the illustrated embodiment two linear guide mechanisms  102  are provided on opposite sides of the column  6 , and correspondingly the second actuator mechanism  408  comprises two pivotable arms  418 , each pivotable arm  418  being attached to a respective second part  106  and coupled to the third linear actuator  424 . The second end  422  of each pivotable arm  418  is pivotally coupled to the third linear actuator  424  by a drive rod  432  which is pivotally fitted between the second ends  422 . The drive rod  432  is pivotally fitted to a movable end  434  of an elongate linear drive member  436  of the third linear actuator  424 . 
     The arrangement is such that linear movement of the third linear actuator  424  causes rotation of the arm  418  about the pivot  426  and movement of the second part  106  thereby to raise and lower the trend axis T-T relative to the column  6 . Typically, the second actuator mechanism  408  incorporates a locking mechanism for locking the trend axis T-T at a selected height position relative to the column  6 , the locking mechanism being incorporated within the third linear actuator  424 . 
     When it is desired to raise the trend axis T-T relative to the column  6 , the elongate linear drive member  436  of the third linear actuator  424  is retracted so that the pivotable arms  418  are rotated (in a clockwise direction in the Figure) to push up the movable linear guide member  112 , coupled to the movable framework  50  at the trend pivot. 
     When it is desired to lower the trend axis T-T relative to the column  6 , the elongate linear drive member  436  of the third linear actuator  424  is extended so that the pivotable arms  418  are rotated (in an anti-clockwise direction in the Figure) to push down the movable linear guide member  112 , coupled to the movable framework  50  at the trend pivot. 
     Referring to  FIG. 19 , there is shown a schematic perspective view of a tilt mechanism  450  of the surgical table  2  in accordance with a further embodiment of the present invention.  FIGS. 20 a  and 20 b    illustrate a tilt frame  452  of the tilt mechanism  450  rotated about the tilt axis X-X at two opposite end positions relative to a central level position. 
     As described above, the surgical table  2  has a trend mechanism for enabling at least a part of the tabletop  8  to be independently rotated about the trend axis T-T which extends in a transverse direction across the tabletop  8 . The trend mechanism enables at least a part of the tabletop  8  to be rotated about the trend axis T-T. The tilt mechanism  450  is located between the tabletop  8  and the trend mechanism for enabling at least a part of the tabletop  8  to be independently rotated about the tilt axis X-X which extends in a longitudinal direction along the tabletop  8 . The tilt frame  452  is located above the trend axis T-T. 
     The tilt axis X-X extends through the tilt frame  452  comprising a second movable framework. As described above, the trend and tilt mechanism comprises the trend frame  50 , which comprises a first movable framework mounted to at least one of the base  4  and the column  6 . A first drive system, comprising the first and second actuators  54 ,  56 , is fitted between the trend frame  50  and at least one of the base  4  and the column  6  for rotating the trend frame  50  about the trend axis T-T. 
     The tilt frame  452 , which comprises a second movable framework, is mounted between the trend frame  50  and the tabletop  8 . The tilt axis X-X extends through the trend frame  50  and the tilt frame  452 . A pivotable connection  453  is oriented along the tilt axis X-X and interconnects the trend frame  50  and the tilt frame  452 . Typically, the trend frame  50  is located within the tilt frame  452 . 
     The tilt axis X-X is above the trend axis T-T. The tilt frame  452  is above the trend frame  50 . The tilt frame  452  surrounds the trend frame  50 . The trend frame  50  and the tilt frame  452  are annular and the tilt frame  452  annularly surrounds the trend frame  50 . 
     A second drive system  454  is fitted between the trend frame  50  and the tilt frame  452  for rotating the tilt frame  452  about the tilt axis X-X. The second drive system  454  is adapted to rotate the tilt frame  452  about the tilt axis X-X over a tilt angle range of at least 50°, for example by a tilt angle of at least +/−25° from a central level position. Typically, the second drive system  454  is fitted within the tilt frame  452  above the trend axis T-T. 
     Accordingly, the second drive system  454  is a drive arrangement to allow table top tilt movement. The tilt frame movement is independent to and isolated from trend movement unlike some systems used on conventional operating tables where the tilt and trend drive actuators are both connected back to the column. With the latter conventional arrangement, trend movement can instigate small amounts of tilt movement without the tilt drive being operated, which is not desirable. 
     With the structural arrangement of the preferred embodiments of the present invention, the tilt frame  452  is intentionally fitted outside of the trend frame  50  and rotates about the trend frame  50  and not the column  6 . This structural arrangement prevents skewing of the tabletop  8 , i.e. the tabletop being moved out of line with the longitudinal axis of the base  4 ) when both trend and tilt are applied, that would otherwise occur if the tilt frame was fitted inside the trend frame to rotate about the column and with the trend frame rotating about the tilt frame. 
     In the embodiment illustrated in  FIG. 19 , and  FIGS. 20 a  and 20 b   , the second drive system  454  comprises a rack and pinion drive system  454 . The rack and pinion drive system  454  comprises a curved rack  456  fitted to the trend frame  50 , a rotatable pinion  458  fitted to the tilt frame  452  and a drive motor  460  connected to the pinion  458  for rotating the pinion  458 . In this embodiment, the pinion  458  is located above the rack  456 . The drive motor  460 , with gearbox  461 , is fitted to the tilt frame  452 . 
     The curved rack  456  typically has a diameter of at least 100 mm, optionally from 100 to 110 mm. Typically, an uppermost portion  462  of the curved rack  456  is no more than 105 mm above the tilt axis X-X, optionally from 95 to 105 mm above the tilt axis X-X. 
     The second drive system  454  preferably further comprises helical or split gears between the drive motor  460  and the pinion  458 . In addition, the rack  456  and pinion  458  preferably have respective helical teeth which mutually engage between the rack  456  and pinion  458 . 
     These features are preferably provided to minimise backlash in the tilt mechanism  450 , which therefore minimises movement or free play in the tabletop  8 . The position of the pinion  458  relative to the rack  456  may be adjustable so that a close mesh between the rack  456  and pinion  458  can be reliably achieved. 
     Preferably, the tilt mechanism  450  also comprises a force applicator  414  which can be switched between an operative mode in which a force is applied to the rack and pinion drive system tilt mechanism  450  to enhance engagement between the rack  456  and pinion  458  and an inoperative mode in which the force is not applied or is reduced as compared to the operative mode. 
     In an alternative embodiment illustrated in  FIG. 21 , a rack and pinion drive system  504  comprises a curved rack  506  which is located above the pinion  508 . The curved rack  506  fitted to the trend frame  50 , the rotatable pinion  508  is fitted to the tilt frame  502  and a drive motor  510 , fitted to the tilt frame  502 , is connected to the pinion  508  for rotating the pinion  508 . 
     Again, the curved rack  506  typically has a diameter of at least 100 mm, optionally from 105 to 115 mm. Typically, an uppermost portion of the curved rack  506  is less than 105 mm above the tilt axis X-X, optionally from 80 to 90 mm above the tilt axis X-X. 
     In the embodiments of  FIGS. 19 to 21 , as shown in  FIG. 19 , at least one damper element  412  (schematically illustrated) may be fitted between the trend frame  50  and the tilt frame  402  for damping the motion of the tilt frame  402  about the tilt axis X-X. The damper element  412  typically comprises a gas spring or a rotary damper. In addition, a braking system  414  (schematically illustrated) may be fitted to the tilt frame  402  for braking the motion of the tilt frame  402  about the tilt axis X-X. Typically, the braking system  414  comprises an electrical brake. 
     The embodiments of  FIGS. 19 to 21  provide a drive arrangement to allow table top tilt movement. The tilt frame  402 ,  502  movement is independent to, and isolated from, the trend frame  50  movement. In contrast, some systems used on conventional surgical operating tables provide that the tilt and trend drive actuators are both connected back to the column; with such an arrangement, trend movement can instigate small amounts of tilt movement without the tilt drive being operated, which introduces clearly undesirable tilt movement. 
     The embodiments of  FIGS. 19 to 21  also provide that the tilt frame  402 ,  502  is fitted outside of the trend frame  50  and rotates about the trend frame  50  and not the column  6 . This prevents the tabletop skewing (i.e. the tabletop being moved out of line with the longitudinal axis of the base) when both trend and tilt are applied, that would otherwise occur if the tilt frame is fitted inside the trend frame and rotates about the column with the trend frame rotating about the tilt frame. 
     The tilt drive mechanism includes a motor and gearbox drive unit with a curved rack and pinion arrangement to allow tilt movement of the tabletop over a tilt angle range. The tilt angle range is a minimum of 25° in either direction from a level position, providing a minimum total tilt angle movement of at least 50°. The large rack diameter enables high torque transmission loads to be achieved in combination with a low overall height for the combination of the trend and tilt mechanism and the column, for example having a vertical distance of less than 105 mm from the top of the curved rack to the tilt pivot axis T-T. This small vertical height of the tilt drive mechanism helps to achieve a low minimum overall tabletop height, typically less than 510 mm from the floor to top of table top, in conjunction with the trend mechanism and column as described with reference to  FIGS. 1 to 14 . 
     In a further embodiment, as illustrated in  FIG. 22 , the tilt drive system  600  comprises a belt drive system  604 . As shown in  FIG. 22 , the belt drive system  604  comprises an endless belt  606  fitted to the tilt frame  602  via a rotatable driven element  612  such as a pulley wheel. A rotatable drive element  608 , such as a pulley wheel, is fitted to the trend frame  50  and engages the belt  606 . A drive motor  610  is connected to the rotatable drive element  608  for rotating the drive element  608 . As the drive motor  610  rotates the drive element  608  in one of two opposite rotational directions, the endless belt  606  correspondingly rotates the rotatable driven element  612  and rotates the tilt frame  602  about a desired tilt angle in a desired tilt direction. Alternatively, the endless belt may be fitted to the trend frame  50  and the rotatable drive element is fitted to the tilt frame  602 . 
     A further embodiment of the present invention is illustrated in  FIGS. 23, 24 and 25 . According to this embodiment, as for the first embodiment, a surgical table comprises a base for standing on a floor; a column mounted on and extending from the base; and a tabletop providing a patient support surface. As shown in  FIGS. 23, 24 and 25 , a movable framework  700  is provided to which at least a part of the tabletop (not shown) is directly or indirectly fitted. A rack and pinion mechanism  702  is fitted to the movable framework  700  between the tabletop and the column for enabling the movable framework  700 , and the part of the tabletop fitted thereto, to be rotated about a pivot axis  704 . 
     In the illustrated embodiment, the pivot axis  704  is a tilt axis extending in a longitudinal direction along the tabletop, and the movable framework  700  is a tilt frame  700  pivotally fitted around a trend frame  50  as described above for the embodiment of  FIGS. 2 to 17   b.    
     The rack and pinion mechanism  702  comprises a pair of opposed first and second curved racks  706 ,  708  mounted on opposite sides of the pivot axis  704 . The racks  706 ,  708  face inwardly towards the pivot axis  704  and are oriented upwardly. A pair of first and second rotatable pinions  710 ,  712  is provided, and each first and second pinion  710 ,  712  arranged to engage a respective first and second curved rack  706 ,  708 . Each curved rack  706 ,  708  typically has a radius of at least 200 mm, optionally from 200 to 230 mm. Each pinion  710 ,  712  typically has a radius of at least 30 mm, optionally from 30 to 45 mm, for example about 38 mm. 
     In this embodiment, the movable framework  700  is a first movable framework, in particular a tilt frame pivotable about the tilt axis, and the curved racks  706 ,  708  are fitted to a second movable framework, in particular a trend frame pivotable about the trend axis, located beneath the first movable framework  700 . 
     A drive system  714 , including a drive motor  716  and gearbox  717 , is connected to the pinions  710 ,  712  for rotating the first and second pinions  710 ,  712  in a common rotational direction. In other words, as shown in the side views of  FIGS. 23 and 24 , when the first pinion  710  is rotated in a clockwise direction, the second pinion  712  is rotated in a clockwise direction, and vice versa. The drive system  714  is configured so that the first and second pinions  710 ,  712  move in opposite respective upward or downward directions along the respective first and second curved racks  706 ,  708  to rotate the movable framework  700  about the pivot axis  702 . 
     The drive system  714  is fitted to the movable framework  700 . The first and second pinions  710 ,  712  are fitted to the movable framework  700 . The curved racks  706 ,  708  are fitted to the trend frame. The drive system  714  comprises a primary drive wheel  722  which is coupled, directly as illustrated or by additional gear wheels (not shown), to the first and second pinions  710 ,  712 . The drive motor  716  is adapted to be driveable in opposite rotational directions to rotate the primary drive wheel  722  in opposite rotational directions and thereby pivot the movable framework  700  in opposite rotational directions. 
     The movable framework  70 ) is configured to be pivotable about the pivot axis  704  in opposite rotational directions about a central position of the movable framework,  700 . In the central position, the first and second pinions  710 ,  712  each engage the respective first and second curved racks  706 ,  708 , as shown in  FIGS. 23 and 24 . 
     Furthermore, the first and second pinions each engage the respective first and second curved racks  706 ,  708  over a preset angular range of the movable framework  700  about the central position. Typically, the preset angular range extends to at least +/−5° about the central position, for example at least +/−7° about the central position. 
     Outside the preset angular range, as shown in  FIG. 25  an upper pinion of the first and second pinions  710 ,  712  is above, and out of contact with, the respective first and second curved rack  706 ,  708  and the lower pinion of the first and second pinions  710 ,  712  remains engaged with the respective first and second curved rack  706 ,  708 . 
     Each curved rack  706 ,  708  has an upper free end  718 ,  720  and the respective first and second pinion  710 ,  712  is configured to be located above the respective first and second curved rack  706 ,  708  outside the preset angular range. 
     In an alternative embodiment, the movable framework  700  is configured to be pivotable about the trend axis extending in a transverse direction across the tabletop. The pivot axis  702  is the trend axis. The curved racks  706 ,  708  are fitted to the column and are in a fixed position relative to the column. 
     The twin rack and pinion inclination mechanism of  FIGS. 23, 24 and 25 , whether used to incline a tilt frame about a tilt axis, with the tilt frame mounted on a trend frame, or whether used to incline a trend frame about a trend axis, with the trend frame mounted on a column or a tilt frame, provides a number of advantages. In particular, by providing a twin rack and pinion inclination mechanism, at low inclination angles both pinions are engaged with a respective curved rack, so the load on each rack/pinion is low, but the total load and torque applied by the pair of racks and pinions can be very high. Furthermore, the diameter of each curved rack can be high, and the diameter of the pinions can also be high, and so the number of teeth engaged between each rack and associated pinion can also be high, thereby enhancing the contact area between the rack and pinions to allow high torque transmission. These high torques can be achieved at low angles of inclination of the movable framework, while keeping the height of the torque transmission system low. 
     When used for inclining a trend frame, the twin rack and pinion inclination mechanism of  FIGS. 23, 24 and 25  can be fitted around a column, for example when the trend pivot is fitted to the column, and below the top of the column. This provides the advantage of a low overall tabletop height. 
     The preferred embodiments of the present invention can provide that the ancillary actuator for controlling the height of the trend axis relative to the column can be locked, either directly by a locking mechanism therein or by using a separate braking mechanism. This minimises undesirable lateral movement or free play in the tabletop. 
     It may therefore be seen that the preferred embodiments of the present invention can provide a highly versatile column and trend mechanism which can provide a wide range of trend angles and a wide range of tabletop heights in a compact unit having a small footprint. The column has a small footprint yet high loading capacity and high torsional rigidity. The column has a small height yet a high stroke. 
     In the preferred embodiments of the present invention, leadscrew actuators are used in which the lifting load is entirely through the leadscrews. Accordingly, no rotary bearings are required to support the load on the tabletop. 
     In the preferred embodiments of the present invention, the trend frame actuators can be driven synchronously with column height adjustment. 
     In the preferred embodiments of the present invention, position sensors can be integrated into the column sections. 
     The preferred embodiments of the present invention can provide a minimum tabletop height (excluding mattress thickness) of no greater than 510 mm from the floor surface. 
     The preferred embodiments of the present invention can provide a minimum column height of less than 380 mm from the base of the surgical table. The trend pivot is below the top of the column and is less than 290 mm from the base of the surgical table. A low minimum tabletop height is achieved because component or assemblies above the column can be lowered directly onto the column without the need for clearance above the column. In contrast, in a conventional surgical table design with fixed trend pivot positions, clearance above the column is required to allow for trend and tilt movement. By providing an adjustment of the position of the trend pivot relative to the column height, the height adjustment of the tabletop can be increased compared to the height adjustment of only the column, while still facilitating a low minimum tabletop height. 
     The contracted height to stroke ratio is maximised by using through-spindle electric actuators, in which the screw can be driven through the gearbox, in the preferred embodiments of the invention. This in turn provides that a low table height and large trend angles can be achieved. The use of such actuators provides that the gearbox does not add to the height of the actuator compared to conventional actuators that have the screw connected directly above the gearbox. 
     The preferred embodiments of the present invention can also provide a tabletop height adjustment range of up to 645 mm. 
     The preferred embodiments of the present invention can provide that the ratio of the overall column and trend frame height extension to the minimum height of the column and trend frame is far higher than is currently achieved by any commercially available surgical table. For example, the surgical table of the present invention can provide that the ratio between the extended maximum height of the tabletop from the floor and the retracted minimum height of the tabletop from the floor is at least 2.1, and typically greater than 2.25. These dimensions can provide a trend pivot centre height, from the base of the surgical table, with a maximum/minimum ratio of at least 3.22 (calculated as [(290+645)/290]). Correspondingly, these dimensions can provide a trend pivot centre height, from the floor, with a maximum/minimum ratio of at least 2.26 (calculated as [(510+645)/510]). 
     The preferred embodiments of the present invention can also provide a column height adjustment range of at least 525 mm. 
     The preferred embodiments of the present invention can also provide a vertical lifting capacity of 550 kg and an offset loading moment capacity of at least 1600 Nm. 
     The preferred embodiments of the present invention can provide large, steep trend angles of at least 45 degrees, typically up to 90° from endpoints of +45° to −45°, at low column heights while still providing sufficient clearance for table coverings and ancillary components around the column. The trend axis, and trend frame, can be raised above the column to provide a high level of clearance from the column to permit large trend angles even at low tabletop heights. 
     The preferred embodiments of the present invention can provide two actuators which support offset loads on the trend frame, which improves the dynamic lifting performance and offset loading capacity at a given trend angle. Furthermore, more compact and less powerful actuators can be employed to achieve a high dynamic performance. 
     The preferred embodiments of the present invention can provide a stabiliser system which minimises lateral loading on the actuators for raising the trend frame and varying the trend angle, providing that the actuator loading is primarily in line with the axis of the elongate element of the actuator. This reduces bucking loads on the actuators, particularly at high extension dimensions, for example up to 210 mm, for the elongate element of the actuator. The stabiliser system can enable the use of smaller diameter elongate elements of the actuators, with correspondingly smaller drive systems and gearboxes, permits a smaller footprint, large tilt and trend angles and maximum patient imaging on opposite sides of the column. The stabiliser system can also minimise free play or movement in the tabletop by minimising lateral movement in the actuator system. Hard end stops may be integrated into the stabiliser system to securely limit the effective range of movement of the actuators. Position sensors can be integrated into the stabiliser system, remote from the actuators and the associated drive systems. 
     Various modifications can be made to the above-described embodiments without departing from the scope of the present invention, which is defined by the claims.