Abstract:
A dynamic trunk positioning device comprises a frame adapted to be removably mounted to an operating table. A number of pads are provided for engaging the trunk of a patient. Each pad is independently adjustably mounted to the frame for movements along three independent directions in order to permit 3-D manipulation thereof by a surgeon either before the surgery while a patient is being positioned or during the surgery when additional corrective forces on the patient&#39;s thorax are needed, thereby providing not only for stable positioning of the patient on the operating table but also providing for active application of individual corrective forces at different locations on the patient&#39;s trunk.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a positioning device for maintaining a patient in an optimal prone position during a back surgery and, more particularly, to a dynamic positioning device which allows the surgeon to apply and adjust individual corrective forces to the patient&#39;s trunk at any time during the surgery. 
   2. Description of the Prior Art 
   Positioning of the patient is an important consideration in back surgery. Initially patients were simply placed faced down with their stomachs pressed on the operating table. It has been found that when a patient lies on his or her stomach in a prone position, added pressure is induced on the inferior vena cava, resulting in increased bleeding. It was later found that blood loss could be reduced by supporting the patient in a prone position with the abdomen pendulous and free. 
   Current devices used in operating rooms for supporting patients in a prone position with the abdomen pendulous and free are passive devices designed only to provide support to the patient&#39;s trunk on the operating table during the surgery in order to avoid pressure sores of the skin over bony prominences and/or hemorrhage during prolonged surgeries. The most frequently used device is the Relton-Hall frame which is a four poster passive support under the iliac crests and the upper thorax below the clavicles. Tables similar to the Relton-Hall frame are sometimes referred to as four posts, chest roll, and the Jackson table. It has been demonstrated that such passive frames can provide some changes in spinal configuration by virtue of the gravity effect. Studies have also shown that the position of the patient during scoliosis surgery is a critical step that may significantly affect the post-operation results. 
   During surgical correction of a spinal deformity, the surgeon has to perform manipulation on the spine with various surgical instruments in order to obtain the best possible correction; it would be desirable to have a positioning device that could actively help the surgeon to perform these corrective maneuvers, by applying corrective forces on the thorax of the patient. To the applicant&#39;s knowledge, there are currently no such positioning devices for operating tables that can provide active correction of a spinal deformity during surgery for a spinal deformity. 
   Existing positioning devices also present some limitations at the level of the initial positioning of the patient in that the patient positioning pads can only be roughly adjusted to the morphology of the patient. 
   SUMMARY OF THE INVENTION 
   It is therefore an aim of the present invention to improve patient positioning on an operating table during surgery. 
   It is also an aim of the present invention to provide a new device for supporting a patient in a prone position during surgery, the device allowing the surgeon to apply and adjust individual corrective forces at various locations on the trunk of the patient prior as well as during the surgery in order to maintain the patient in an optimal position. 
   It is also a further aim of the present invention to provide a prone surgical positioning device which is adapted to be retrofitted to commonly available operating tables: 
   Therefore, in accordance with the present invention, there is provided a dynamic positioning device for supporting a patient in a prone position for surgery. The device comprises a frame adapted to be mounted to an operating table, and a number of patient positioning modules mounted to the frame. Each of a plurality of the patient positioning modules comprises a first carriage mounted for longitudinal translational movement relative to the frame, a second carriage riding on the first carriage for lateral translational movement relative to the frame, and a patient positioning pad mounted to the second carriage, the patient positioning pad being vertically movable relative to the frame; thereby providing for preoperative and per-operative independent adjustments of the plurality of patient supporting modules along three orthogonal directions. 
   According to a further general aspect of the present invention, there is provided a positioning device that allows not only the stable positioning of a subject on an operating table but also can accomplish active correction of the spinal deformity by virtue of a number of corrective pads that can be manipulated and displaced in 3-D by the surgeon either before the surgery when the patient is positioned, or during the surgery when additional corrective forces on the patient&#39;s thorax are needed. The corrective pads can be added or removed as needed on the operating table. They function by applying forces on the trunk at various areas, forces which are transmitted by the soft tissues (skin, muscles, etc.) and the rib cage to the spine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which: 
       FIG. 1  is a perspective view of a dynamic frame adapted to be removably mounted to a standard operating table for positioning a patient in a prone position for surgery; 
       FIG. 2  is a perspective view of a patient lying face down on an operating table, the trunk of the patient being supported at the sides thereof by the dynamic frame so that the abdomen of the patient hangs freely over the table; 
       FIG. 3  is a perspective view of a patient positioning unit forming part of the dynamic frame shown in  FIG. 1 ; 
       FIG. 4   a  is a frontal view of one side of the dynamic frame shown in  FIG. 1  illustrating the radio-transparent and radio-opaque zones of the frame; and 
       FIG. 4   b  is a side view of a mobile pad support unit forming part of the frame shown in FIG.  1  and illustrating the radio-transparent and radio-opaque zones of the frame. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  illustrate a trunk positioning system  10  adapted to be removably mounted to a standard operating table  12  for positioning and maintaining a patient P in an optimal prone position during surgery. The system  10  is particularly suited for use by spinal surgeons (orthopedic surgeons or neurosurgeons) for any surgery on patients with thoracic lumbar or lumbo-sacral spinal deformities, such as scoliosis, kyphosis or lordotic anomalies. As will be seen hereinafter, the positioning system  10  advantageously permits at any time, in the course of the surgical intervention, to change and re-adjust the location as well as the magnitude of the forces applied to the trunk of the patient. The system  10  allows not only a stable positioning of the patients on the operating table, but also provides for active correction of spinal deformities by a system of movable corrective pads and cushions manipulated by the surgeon before and during surgery, in order to provide optimal correction of a trunk deformity. 
   As best shown in  FIG. 1 , the trunk positioning system  10  generally comprises a rectangular frame  14  having a universal mounting structure  16  for allowing the system  10  to be installed on a variety of operating tables. The frame  14  includes a pair of longitudinally extending rails  18  maintained in space and parallel relation by a pair of transversally extending end members  20 . The side and end members  18  and  20  are preferably bolted together and made of a structural material, such as aluminum. As shown in  FIG. 1 , spaced-apart positioning holes or pegs  22   b  are defined in the end members  20  for allowing the rails  18  to be secured at various positions thereon. In this way the frame  14  can be adjusted in different configuration for accommodating patients of different sizes and facilitating the placement of the patient on the operating table. 
   An abdomen plate  23  is mounted to the end members  20  between the rails  18  in order to protect the space for the X-ray cassette, if the patient were obese. The plate  23  does not need to be used in every case so it is easy to remove and just rests on top of the end members  20 . The plate  23  is made of lexan or some other radio-transparent material. Holes  22  are defined in the end members  20  for receiving fasteners in order to removably attach the plate  23  to the frame  14 . The universal mounting structure  16  includes a pair of adjustable fixation legs  24  depending from opposed ends of each transversal end member  20 . Each fixation leg  24  includes a bracket  26  mounted for sliding movement in a vertically extending slot  28 . Each bracket  26  is provided with a set screw  30 , such as a thumb screw, for releasably securing the frame  14  to the longitudinally extending rails  32  ( FIG. 2 ) normally provided at the sides of standard operating tables. By adjusting the position of the brackets  26  in the slots  28 , the frame  14  can be readily installed at various heights on the operating table  12 . 
   As shown in  FIG. 4   a , the frame  14  provides enough clearance to permit the insertion and removal of a radiographic cassette C on the table  12  beneath the trunk of the patient P. 
   As shown in  FIG. 1 , the trunk positioning system  10  further includes a plurality of patient positioning modules  34  (two pairs in the illustrated example). More particularly, as shown in  FIGS. 1 and 2 , the positioning modules  34  may include one pair of pelvis pads  34   a  and one pair of upper chest pads  34   b  adjustably and removably mounted to the frame  14 . These pads  34   a  and  34   b  insure proper initial positioning of the patient. Alone these pads  34   a  and  34   b  will provide some initial correction of the patient&#39;s deformity. As shown in  FIG. 2 , the positioning modules  34  may further include a number of adjustable corrective pads  34   c  (two in the illustrated example) that can be used intra-operatively for applying corrective forces to the thoracic and lumbar regions of the patient P while correction rods (not shown) are being implanted on each side of the spinal column of the patient P by the surgeon. As opposed to the pelvis and upper chest pads  34   a  and  34   b , the corrective pads  34   c  are preferably removably mounted through sterile sheets to the rails  32  extending at the sides of the operating table  12 . The corrective pads  34   c  are mounted to the rails  32  only when needed, i.e. just before the implantation of the correction rods. After the rods have been implanted, the corrective pads  34   c  are typically removed from the operating table  12 . 
   As shown in  FIG. 3 , each patient positioning module  34  comprises a first slider  36  slidably mounted to one of the rails  18 , a second slider  38  slidably mounted on a transversally extending rail  40  secured to the top of the first slider  36 , a pad support structure  42  slidably and rotatably mounted to a cylindrical post  44  extending vertically from a top surface of the second slider  38 , a resilient pad  46  mounted to the pad support structure  42  and preferably made of hyper-elastic and visco-elastic foams (for instance a cushion of polyurethane foam or silicon covered with PVC), and a locking mechanism  48  for releasably securing the pad support structure  42  at a desired elevation and in a desired angular position on the cylindrical post  44 . 
   The first slider  36  is provided in the form of a C-shaped aluminum sleeve  50  sliding along one of the aluminum rails  18 . Alternatively, it could consist of a dovetail sleeve, tubbing, acme screw or any mechanism used for linear translation. A set screw (not shown) or other locking means are provided for releasably securing the sleeve  50  in position on the rail  18 . The transversal rail  40  is provided in the form of a delrin slide or other types of radio-transparent rail suitable for supporting the second slider  38 . 
   The second slider  38  includes a radio-transparent a C-shaped sleeve  54  slidably mounted to slide  40 . The slider  38  is preferably made of Delrin. A set screw (also made of radio-transparent material) or the like is provided for releasably securing the sleeve  54  in position on the slide  40 . A support plate  56  is mounted on top of the sleeve  54 . The vertical post  44  extends from the support plate  56 . The vertical post  58  has a tubular bottom section  60  and a main section  62  secured to the bottom tubular section  60 , as by a screw. The tubular bottom section  60  is preferably made of aluminum whereas the main section  62  is made out of a radio-transparent material, such as nylon or PVC. 
   The pad support structure  42  includes a rectangular box-like section  64  preferably made of aluminum and housing the locking mechanism  48  used for releasably securing the support structure  42  in position on the post  44 . The pad support structure  42  further includes a cushion or pad receiving section  66  mounted to the box-like section  64  for receiving one resilient pad. 
   The locking mechanism  48  is preferably provided in the form of a “Manfrotto grip” and comprises a vertical tube  68  fitted about the post  44  and a plug  70  mounted for sliding movement in a rectangular housing  72  received in the box-like section  64 . The plug  70  is normally biased in the vertical tube  68  against the vertical post  44  by a spring  73 . A handle or lever  74  is connected to the plug  70  through a pivot axis extending transversally through the housing  72  for moving the plug  70  against the biasing force of the spring  73  to permit movement of the pad support structure  42  along and about the post  44 . In this way, the surgeon has solely to manually pivot the lever  74  towards the tube  68  to unlock the support structure  42  and, thus, the patient cushion from the post  44 . When the surgeon releases the lever  74 , the plug automatically presses against the post  44  to hold the pad support structure  42  in place. 
   The vertical tube  68  includes a base section  76  which is integral to the housing  72  and an upper end section  78  press fitted into the base section  76  by means of a locking ring  80 . The housing  72 , the base section  76  and the lever  74  are made of cast aluminum, whereas the upper end section  78  and the pad receiving section  68  are made of a radio-transparent material, such as nylon. 
   One of the constraints imposed by the scoliosis surgery is the radiographic verification of the position of the instrument along the spinal column. Radio-opaque objects must thus be eliminated from the radiographic field of the vertebrae so that clear intra-operative x-rays of the spine, thorax and pelvis (posto-anterior (PA) and lateral views) can be acquired. As shown in  FIGS. 4   a  and  4   b , the materials used for the patient cushions  46 , the slide  40 , the pad receiving section  66  and the C-shaped sleeve  54  provide for a radio-transparent field of sufficient area to permit x-rays visualization of all the spinal column from posto-anterior or lateral views. 
   The height of the radio-opacity of the structural components of the patient positioning units  34  has been limited to the iliac ridge of the patient&#39;s pelvis ( FIG. 4   b ). In this way, it can be generally said that the inferior parts of the locking mechanism  48 , the second slider  38  and the slide  52  are made out of radio-opaque structural materials, such as aluminum, whereas the upper parts thereof (which are less mechanically solicited) are made out of radio-transparent materials, such as polyurethane, Nylon and PVC. 
   As shown in  FIGS. 1 and 3   a , the cushions or pads  46  are shaped to follow the general curvature of the patient&#39;s trunk. As opposed to conventional patient position cushion, which are concave, the cushions  46  present a convexity in order to increase the area of support and, thus, ensure appropriate dispersion of the pressure forces applied to the patient&#39;s trunk. The cushion itself is made of different layers of gel and foam on a plastic base and back. 
   Up to now, the rib or lumbar humps (lumbar or thoracic deformations due to the rotation of the vertebrae and the deformation of the ribs) have been corrected intra-operatively by applying manual forces on the hump during the derotation maneuvers performed by the surgeon on the patient. The corrective forces must be maintained for a certain period of time and the manual application of such forces has the disadvantage of being not uniform over time. The corrective pads  34   c  overcome these drawbacks by providing a mechanical means for applying constant and uniform mechanical corrective forces on the patient&#39;s torso. 
   As shown in  FIG. 2 , each corrective pad  34   c  is articulately clamped to the rails of the operating table  12  by means of a C-shaped slider  84  and a set screw  86 . A system of articulated rods  88 ,  90  and  92  is carried by the slider  84  for allowing 3-D adjustment of the position of the corrective pads  34   c . The corrective pad  34   c  is mounted to the distal end of the last rod  92 . A sleeve and clamping screw arrangement  94  is provided between each rod  88 ,  90  and  92 . After loosening the clamping screws  96 , the rods can be longitudinally slid and pivoted about their longitudinal axis to provide for a complete adjustment of the position of the pads  34   c . Once the pads  34   c  have been appropriately positioned to correct the gibosities by exerting a pushing force in a direction opposite thereto, the rods  88 ,  90  and  92  are locked back in position by tightening the clamping screws  96 . It is noted that various types of joint could be used to adjustably connect the rods  88 ,  90  and  92  together. In any event, the system of rods must provide at least three degree of freedom to permit proper adjustment of the position of the corrective cushions  34   c . Unlike cushions  34   a  and  34   b , the corrective cushions  34   c  have a concave curvature, thereby allowing applying the corrective forces at a more specific target point on the patient&#39;s back. 
   In use, the system is placed on an operating table and fixedly secured to the side rails thereof by means of the fixation legs. The patient is then placed on the cushions  34   a  and  34   b  in a similar manner as the existing Relton-Hall cushions. Shoulder cushions will then be adjusted to account for and correct patient asymmetries. The surgery will commence and continue as usual until just prior to rod insertion. Then, the external rib and lumbar hump cushions  34   c  will be positioned to further correct the patient&#39;s deformity. Placement of the cushions is at the discretion of the surgeon but, based on the results of a preliminary study, they will be positioned simultaneously on the lumbar and rib hump regions. The first and second rods will be tightened (the rod inserted into hooks or screws secured to the vertebrae in order to correct the deformity). Pressure from the rib and lumbar hump cushions  34   c  will be released and the patient will be closed. The corrective cushions  34   c  will only be implanted during a section of the surgery to reduce the amount of time that pressure is exerted on the patient. 
   It is understood that the system could be made completely radio-transparent. The entire frame could be made of carbon fiber, strong plastics like Delrin or any other structurally sound ratio-transparent materials.