Abstract:
The present inventive subject matter describes a device and system for positioning, adjusting, and stretching a patient&#39;s extremity for surgical procedures where alignment is critical and minute adjustments may be required repeatedly. The device helps in maintaining the patient&#39;s extremity stationary, once the physician has selected the precise position for the elected procedure. The device uses using a combination of an articulating and a rotating frame, support plates and support rings that are attached to the extremity surgical positioning system. The system acts as a limb splint that is firmly attached to the surgical table. The support plates are attached to the patient via a series of adjustable straps preventing the extremity from moving independently of the support plate. A locking rack and gear configuration has adjustable locking pivot points that are positioned along and within the outer/inner proximal tube and outer/inner distal tube that lengthens or rotates various portions of the extremity.

Description:
PRIOR APPLICATIONS 
       [0001]    This continuation-in-part application claims priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 13/397,783, Filed Feb. 16, 2012, that claims priority to U.S. Provisional Applications No. 61/443,318 filed on Feb. 16, 2011, which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present inventive subject matter relates to an extremity surgical positioning device. In particular, a device or fixture that holds the limb of a patient stationary, so that medical procedures can be performed. 
         [0003]    Traditionally surgery on the limb of a patient is accomplished by two individuals: the surgeon who is responsible for the actual operation on the limb and the assistant, who is responsible for holding the limb in the proper position while surgery occurs. To improve the job of the assistant, a number of devices are employed to help hold the limb in position. These devices vary, but typically consist of pads, straps, and various fixtures. For example, the Bryton Corporation (Indianapolis, Ind.) markets a number of products that aid in surgery. Also, Allen Medical Systems (Acton, Mass.), markets a variety of surgical positioning aids. 
         [0004]    U.S. Pat. No. 5,290,222 (Mar. 1, 1994) issued to Feng discloses a non-invasive distraction system for ankle arthroscopy that utilizes a sling wrapped around the patient&#39;s ankle with an adjustable tension device that provides distraction of the leg and joints because the knee is cradled in a conventional urology leg holder and held relatively stationary. The device can be mounted on a standard operating table and utilizes the bent knee and the patient&#39;s weight to aid in the distraction. 
         [0005]    U.S. Pat. No. 6,953,443 (Oct. 11, 2005) issued to Hay discloses a tibial distraction device that is essentially a triangular ramp that functions similarly to Guhl, but is not mounted directly to the operating table. 
         [0006]    U.S. Pat. No. 6,491,273 (Dec. 10, 2002) issued to King et al. discloses a fluid filled “multi-joint arm-like” support with releasable and lockable limb sections for “holding, tools, instruments and the like.” 
         [0007]    Although these methods and devices have their uses, they have their pitfalls because they are not very precise, are prone to slippage, and can be difficult to adjust. 
         [0008]    In general there is a need for an extremity surgical positioning device that provides: 
         [0009]    Better access to surgical sites of the upper and lower extremities 
         [0010]    Distraction of fractures and/or joints 
         [0011]    Compression of fractures post re-alignment 
         [0012]    Ability to rotate the distal aspect of the limb during distraction or compression. 
         [0013]    Reduce the need for external fixation traction 
         [0014]    Better access of intra-operative radiography 
         [0015]    Un-obstructed x-ray view of bones through radio-lucent material. 
         [0016]    It is therefore an object of the present inventive subject matter to provide an extremity surgical positioning device that is easily adjusted, capable of distraction, precise, easily mounted and dismounted to the operating table and slip resistant. 
       SUMMARY 
       [0017]    The present inventive subject matter overcomes problems in the prior art by providing a device or fixture for positioning a patient&#39;s limb, whether that may be an upper or lower extremity. 
         [0018]    In various operations and medical procedures it is required that the extremity is held stationary and located and adjusted precisely. An example of this would be surgery to pin or reconstruct a shattered bone. Alignment is critical and minute adjustments may be required. Furthermore, the device must not allow the patients extremity to move once the surgeon has selected the precise position for the elected procedure. 
         [0019]    The present invention achieves these desired results through a combination of an articulating and rotating frame with thigh/upper arm supporting plate, lower leg/forearm supporting plate, and a foot/hand supporting plate that attach to support arms and act as a limb splint that is firmly anchored or attached to the surgical table. The supporting plates are securely attached to the patient via a series of adjustable straps around the patient&#39;s thigh/upper arm, shin/forearm, ankle/wrist, and foot/hand which not only prevents the extremity from moving independently of the supporting means, but do so in a non-invasive manner to the patient&#39;s tissue and skin. 
         [0020]    Once the patient&#39;s extremity is securely attached to the supporting plates via the straps the surgeon can manipulate the extremity in a number of ways due to a rack and gear configuration and a myriad of adjustable pivot points positioned along and within the support arms to either lengthen or rotate various portions of the extremity against each other to align the extremity such as in repositioning of the limb or in setting a broken limb for example. 
         [0021]    Each of these adjustable pivot points and rack and gear components have a means of locking them in a stationary position either by a friction means or by a spring and pawl mechanism. This aids in the precise adjustment of the extremity. 
         [0022]    The inventive subject matter also describes an extremity surgical positioning device having a mount configurable to connect to a table, chair, or other equipment used for supporting and/or positioning a patient during surgery. The mount is rotatable in two degrees of freedom along the plane of the operating table; a proximal segment and distal segment having two opposing ends, and wherein each segment is telescopically retractable and extendable, and wherein one end Of the proximal segment is connected to the table clamp; a proximal segment has an attachment point and a rotatable support point. 
         [0023]    These and other embodiments are described in more detail in the following detailed descriptions and the figures. The foregoing is not intended to be an exhaustive list of embodiments and features of the present inventive subject matter. Persons skilled in the art are capable of appreciating other embodiments and features from the following detailed description in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is an oblique view of the Extremity Surgical Positioning Device with patient&#39;s lower extremity positioned in it; 
           [0025]      FIG. 2  is an oblique view of the Extremity Surgical Positioning Device with identification markers for referenced characters; 
           [0026]      FIG. 3  is a schematic perspective view of a lift apparatus, system and method according to the invention; 
           [0027]      FIG. 4  is a side cross-sectional view, taken along lines A-A of  FIG. 3 , of the lift apparatus in the lower position; 
           [0028]      FIG. 5  is a side cross-sectional view, taken along lines A-A of  FIG. 3 , of the 1 lift apparatus in the upper position; 
           [0029]      FIG. 6  is a side view of the lift apparatus; 
           [0030]      FIG. 7  is a top view of the lift apparatus; 
           [0031]      FIG. 8  is a bottom view of the lift apparatus; 
           [0032]      FIG. 9  is a front view of the lift apparatus; and 
           [0033]      FIG. 10  is a rear view of the lift apparatus. 
       
    
    
     LIST OF REFERENCE CHARACTERS 
       [0000]    
       
         
           
               001 : Patient 
               002 : O.R. Table (Generic) 
               100 : Extremity Surgical Positioning System 
               105 : Table Clamp Cam-Lock 
               110 : Table Clamp 
               115 : Base 
               120 : Rotary Joint Cam-Lock (Locks Adduction/Abduction) 
               125 : Rotary Joint (Adduction/Abduction) 
               130 : Proximal Hinge (Proximal Joint Flexion/Extension) 
               135 : Proximal Hinge Cam-Lock (Locks Proximal Joint Flexion/Extension) 
               140 : Outer Proximal Tube 
               145 : Outer Proximal Tube Cam-Lock (Locks Int/Ext Rotation of Proximal Joint and Distraction/Compression) 
               150 : Proximal Support Cam-Lock 
               155 : Proximal Support Arm 
               160 : Proximal Support Plate 
               165 : Inner Proximal Tube 
               170 : Proximal Distraction/Compression Ring 
               175 : Proximal Distraction/Compression Engagement Lever 
               180 : Intermediate Hinge (Distal Limb Flexion/Extension) 
               185 : Intermediate Hinge Cam-Lock (Locks Distal Limb Flexion/Extension) 
               190 : Distal Limb Support Cam-Lock 
               195 : Distal Limb Support Arms 
               200 : Distal Limb Support Plate 
               205 : Distal Limb Support Plate Lock Knob 
               210 : Outer Distal Limb Tube 
               215 : Distal Tube Clocking Ring 
               220 : Inner Distal Limb Tube 
               225 : Distal Limb Distraction/Compression Ring 
               230 : Distal Limb Distraction/Compression Engagement Lever 
               235 : Foot/Hand Support Clocking Lever 
               240 : Foot/Hand Plate Ball Joint Cam-Lock 
               245 : Foot/Hand Support Arm 
               250 : Foot/Hand Plate Ball Joint 
               255 : Foot/Hand Plate 
               260 : Ring Support 
               265 : Ring Support Cam-Lock 
               270 : Ring Support Rings (Vary in Size) 
               275 : Ring Support Ring Retention Pin 
           
         
       
     
       DETAILED DESCRIPTION 
       [0072]    Representative embodiments according to the inventive subject matter are shown in  FIGS. 1-2 , wherein similar features share common reference numerals. 
       Description of the Inventive Subject Matter 
       [0073]    The inventive subject matter of a multi-purpose positioning device has the following method of operation. 
         [0074]      FIG. 1  shows an oblique view of a patient  001 , an operating room table  002 , an extremity surgical positioning system (hereinafter “positioning system”). 
         [0075]      FIG. 2  shows an oblique view of the positioning system  100 , which shows a table clamp  110 , table clamp cam-lock  105 , a positioning system base  115 , rotary joint cam-lock  120 , and a rotary joint  125  connected to proximal hinge  130 , with a proximal hinge cam-lock  135 , an outer proximal tube  140 , outer proximal tube cam-lock  145 , proximal limb support cam-lock  150 , proximal limb support arm  155 , proximal limb support plate  160 , inner proximal tube  165 , proximal limb distraction/compression ring  170 , proximal limb distraction/compression engagement lever  175 . 
         [0076]    The inner proximal tube  165  is connected to an intermediate hinge  180 , an intermediate hinge cam-lock  185 , distal limb support cam-lock  190 , distal limb support arms  195 , distal limb support plate  200 , distal limb support plate lock knob  205 , outer distal limb tube  210 , outer distal tube clocking ring  215 , inner distal limb tube  220 , distal limb distraction/compression ring  225 , distal limb distraction/compression engagement lever  230 . 
         [0077]    The inner distal tube  220  is connected to a foot/hand support clocking lever  235 , foot/hand plate ball joint cam-lock  240 , foot/hand support arm  245  connects to a foot/hand plate ball joint  250  and a foot/hand plate  255 . 
         [0078]    A modular ring support  260  can be attached and locked to the outer proximal tube or outer distal tube with the ring support cam-lock. The ring support ring  270  is held in the ring support  260  by a ring support ring retention pin  275 . 
         [0079]    The configuration of the aforementioned inventive subject matter should not be limited to any single embodiment described, instead all possible configurations that can be implemented and derived by one skilled in the arts are understood to be embodied herein. Method and Operation of the Inventive Subject Matter 
         [0080]    The inventive subject matter of a multi-purpose positioning device has the following method of operation. 
         [0081]    The patient is placed into position on the operating table.  FIG. 1  shows a patient  001 , with an extremity surgical positioning system  100 , this is mounted to an operating room table  002 , via a table clamp  110 , and lockable into position with the table clamp cam-lock  105 . The lower extremity is placed in the extremity surgical positioning system  100 , the proximal lower extremity is placed on the proximal limb support plate  160 , the patient&#39;s distal lower extremity is placed on the distal limb support plate  200 , and the foot is placed against the foot/hand plate  255 . The limb is further secured to the support plate via commonly used sterile strapping and wraps. 
         [0082]    The length of the outer proximal limb tube  140 , and inner proximal limb tube  165 , are adjustable to provide for specific patient limb length. This is also used for distraction/compression and is actuated through the proximal limb distraction/compression engagement lever  175 , and fine movements are controlled through the proximal distraction/compression ring  170 . The length of the outer distal limb tube  210 , and inner distal limb tube  220 , are adjustable to provide for specific patient limb length. This is also used for distraction/compression and is actuated through the distal limb distraction/compression engagement lever  230 , and fine movements are controlled through the distal distraction/compression ring  225 . The foot/hand support arm  245 , is adjustable for internal/external rotation and/or valgus/varus alignment of the lower limb and is lockable in to position from the foot/hand support clocking lever  235 . 
         [0083]    The foot/hand plate ball joint  250 , can be adjusted for height, flexion, extension, pronation, supination and rotational movements and is lockable into position from the foot/hand plate ball joint cam-lock  240 . 
         [0084]    This extremity surgical positioning system  100 , allows for the use of variety of ring support rings  270 , that are placed in a ring support  260 , maintained in place by a ring support retention pin  275 , and secured to the outer proximal limb tube  140  and/or distal limb tube  210 , and lockable into position from the ring support cam-lock  265 . 
         [0085]    An extremity can be flexed/extended at the proximal joint through the proximal hinge  130 , and lockable into position from the proximal hinge cam-lock  135 . Abduction/adduction is controlled via the rotary joint  125 , and lockable into position via the rotary joint cam-lock  120 . Internal/external rotation is controlled through pivoting of the outer proximal limb tube  140 , and inner proximal limb tube  165 , and lockable from the outer proximal limb tube cam-lock  145 . 
         [0086]    An extremity can be flexed/extended at the intermediate joint through the intermediate hinge  180 , and lockable into position from the intermediate hinge cam-lock  185 . Abduction/adduction is controlled via the rotary joint  125 , and lockable into position via the rotary joint cam-lock  120 . 
         [0087]    The materials as depicted in  FIG. 2 , can be fabricated from materials generally used in operating room environments. These materials may be also constructed from metal, fiberglass, carbon fiber or plastic. The use of wood laminates and/or wood can be utilized. In operating environments where X-Rays will need to be taken while the limb is positioned into the extremity surgical positioning system  100 , the material should be fabricated from radio-lucent material. 
       Certain Advantages of the Inventive Subject Matter Over the Prior Art 
       [0088]    The inventive subject matter is a multi-purpose positioning device that can be used for certain surgical procedures, including, but not limited to, ankle arthroscopy, tibia fractures, fibula fractures, bimaleollar/trimaleollar fractures as well as pylon fractures. The inventive subject matter provides for: 
         [0089]    multiplanar motion for fracture reduction 
         [0090]    quick lockdown of a reduction through positioning with distraction and compression 
         [0091]    control of the varus/valgus drift after reduction 
         [0092]    provide a consistent, easy to manipulate, control, and measure sterile non-invasive distraction was well as a compression device. 
         [0093]    eliminates need for external fixation pins and unnecessary additional surgical wounds. 
         [0094]    less trays/equipment to have available on the surgical field. 
         [0095]    quick limb position changes for easier surgical approach 
         [0096]    bilateral wound closure access for surgeon and the assistant 
         [0097]    raised limb elevation during surgery minimizing need for tourniquet use 
         [0098]    eliminate need for sand bag/bump under buttock to control ankle/foot neutral position 
         [0099]    eliminates concerns of lumbar spine clearance 
         [0100]    eliminates concerns of low back pain complications in patients with past history of low back pain/injury/surgeries 
         [0101]    devise design provides better surgical site access 
         [0102]    There is an overall reduction on operation time due to better surgical site access, quicker fracture reduction, faster x-ray time, and faster wound-closure through better positioning. 
         [0103]    Referring to  FIGS. 3 through 10 , a lift apparatus, system and method  300  may be used to lift, position, and set an extremity (e.g. limb) of the patient  1  between a lower position  304  to an upper position  305 , or positions there-between. The lift apparatus  300  is configured to be positioned on a bar  302  of an extremity surgical positioning system  100  such as, for example, the outer distal tube  210 . The lift apparatus  300  is configured to use mechanical advantage to lift a human limb positioned on the support assembly  360  by manual force alone, e.g. from its use for such applications as lifting and pushing. The lift apparatus  300  may be used in the extremity surgical positioning system  100  to position and lift a support plate  155 ,  165  and/or support assembly  360  between a lower position  304  to an upper position  305 , or positions there-between as desired. For example, for attaching the proximal limb support plate  160  to the proximal limb support arm  155  and/or for attaching the distal support plate  200  to the distal limb tube  210 , each described herein and shown in  FIGS. 1 and 2 . While the lift apparatus, system and method  300  is described to lift, position, and set an extremity of a limb of the patient  1  as shown in  FIG. 1 , one skilled in the field will recognize that the lift apparatus  300  may be useful for other surgical applications to lift, position, and set other body parts and/or extremities such as, for example, a shoulder or torso. 
         [0104]    Referring to  FIGS. 3-6 , the lift apparatus  300  comprises clamp body  310  operably connected to a support assembly  360  by the interconnections between a lift assembly  330 , a runner block assembly  350 , a ratchet bar assembly  390 , and a pawl assembly  400 . A ratchet assembly  370  with a force bar  376  and a handle assembly  380  pivoting around a fixed hinge (pivot)  340  is configured to advance a pawl  403  along a series of equally spaced teeth  395  formed in a ratchet bar  390  so as to raise the support assembly  360  or be lowered by a spring-loaded finger action of the pawl  403  that disengages and/or engages the teeth  395 . The bar  302  comprises a solid or hollow tubular construction that may be formed having a substantially triangular, circular, oval, and/or rectangular cross-section as is shown in  FIGS. 3-5 . 
         [0105]    Referring to  FIGS. 3 through 6 , the lift apparatus  300  comprises an arm clamp body  310  configured to be positioned on the bar  302 . The arm clamp body  310  may be formed from materials having suitable strength and durability such as, stainless steel, surgical stainless steels, aluminum, and other metals and metal alloys. The arm clamp body  310  may be formed from solid metal extrusions comprising a body portion  311  extensions formed as an upper section having a lip portion  313  at an end thereof, and a lower section  314 . The upper section  312  and lower section  314  form an inner cavity  315  adapted to receive the bar  302  therein and for fastening the clamp assembly  323  thereto. 
         [0106]    The body portion  311  further comprises a ratchet arm opening  316  at an upper edge thereof configured for receiving a ratchet arm as is discussed in herein. The clamp body portion  311  comprises one or more openings  317 ,  318 , and  319  (shown in FIGS.) suitable to receive and/or accept one or more pins  320 ,  321 , and/or rods  322  so as to operably connect the lift assembly thereto. The lift apparatus  300  further comprises a clamp assembly  323  for operably connecting to the bar  302 . According to an embodiment of the invention, clamp assembly  323  consisting of a threaded shaft  324  with a foot portion  325  of the threaded shaft  324  for operably connecting to the bar  302  using a knob  326  for tightening or loosening of the clamp assembly  323  to the outer distal tube  210 . 
         [0107]    Referring to  FIGS. 3 and 4 , the lift apparatus  300  comprises a lift assembly  330  configured with an upper arm  331  and a lower arm  332 . Each of the upper arm  331  and the lower arm  332  may be formed having sufficient longitudinal length to span between the arm clamp body  310  and the support assembly  360 . Each of the upper arm  331  and the lower arm  332  may be formed from a solid, flat or hollowed tubular construction of sufficient strength and durability to position and hold the limb on the support assembly  360 . Each of the longitudinal arms  331 ,  332  comprises openings formed at each end. For example, an opening  333  for positioning adjacent the body portion  311  and for receiving pin  336  therein may be formed on an end of the upper and lower arms  331 ,  332 . Similarly, an opening  334  for positioning adjacent the support base  361  and for receiving pin  337  therein may be formed on an end of the upper and lower arms  331 ,  332 . Each of the pins  336  secured through the opening  330  of the upper arm  331  in the opening  318  in the body portion  311  forms a hinge (pivot)  338  with the body portion  311 . Each of the pins  336  secured through the opening  330  of the lower arm  332  in the opening  317  in the body portion  311  forms a hinge (pivot)  338  with the body portion  311 . Similarly, each the pins  337  secured through the opening  334  of the upper arm  331  in an opening  365  in the support base  361  forms a hinge (pivot)  339  with the support base  361 . Each of the pins  337  secured through the opening  334  of the lower arm  332  in the opening  366  in the support base  361  forms a hinge (pivot)  339  with the support base  361 . A mid-point opening may be formed in one of the longitudinal arms  331 ,  332 , preferably the upper arm  331  for fastening a fastener or rod  345  to the runner block assembly  350  and forming a fixed hinge (pivot)  340 . 
         [0108]    Referring to  FIGS. 4-10 , a runner block assembly  350  comprises a body portion  351  with a ratchet opening  352  extending between a top surface  353  and a bottom surface  354 , a rod opening  355  extending between a front surface  356  and a rear surface  357  and a plurality of side surface openings  358  formed on each side surface  359  of the body portion  351 . The ratchet opening  352  is configured to receive a pawl assembly  400 . The rod opening  355  is configured to receive a climbing bar assembly  410 . The body portion  351  may be formed with a pushpin assembly opening The plurality of side surface openings  358  may be configured to be positioned adjacent the mid-portion opening  335  one of the longitudinal arms  331 ,  332  for receiving a fastener  338  therein and securing the fastener  338  to and adjacent one of each of the plurality of side surface openings  358  formed in the runner block assembly  350 . Each of the fasteners  345  secured through the mid-portion opening  335  of the lower arm  332  on each side, however, a mid-portion opening  335   a  may be located on the upper arm  331 , and the lower arm  332  in the opening  366  in the runner block assembly  350  forms a fixed (pivot) with the runner block assembly  350   
         [0109]    Referring to  FIGS. 3 and 4 , the support assembly  360  comprises a support base  361 , a limb platform  362 , one or more openings  363 ,  364  formed in the support base  361  adapted to receive one or more pins  365 ,  366  therein. The support base  361  may further comprise an adjustment slot  369  configured to slidably operably connect with a ball portion  368  disposed on a base, wherein the ball is configured to be received in a socket  367  of the limb platform. The support base  361  when raised to the upper position  306  and/or lowered to the the lowe position  304  allows the integral ball stand  368  with the limb of the patient  1  thereon to slide in the adjustment slot  369  when operating the lift apparatus  300 . 
         [0110]    Referring to  FIGS. 3 and 4 , a ratchet assembly  370  comprises one or more handle arms  371  and  372 , each arm configured with an opening  373  positioned at an end to be disposed adjacent the runner block assembly  350 , and another opening  374  configured to be form a handle end  380 . The ratchet assembly  370  may further comprise a mid-point opening  375  formed in each of the one or more handle arms  371  and  372  configured for positioning adjacent the support base  361  and the lower arm  332  and for receiving therein pin  337  to operably connect the one or more handle arms  371 ,  372  and the lower arm  332  in the opening  318  in the body portion  311  to form a hinge (pivot)  338  with the body portion  311 . On each end  373  of the ratchet arms  371 , an opening  378  is configured to receive a force bar  376  and to secure the force bar  376  with fastener  345  between the ratchet arms  371 . The force bar  376  may be formed with a flat portion  377  configured on a side adjacent to the runner block assembly  350 . The force bar  376  is configured to push and/or operably connect with the longitudinal arms  331 ,  332  and the runner block assembly  350  so as to slide the bar member  391  and raise the support assembly  360  to locate to the upper position  305  from the lower position  304 , or in any intermediary positions. Similarly, on each end  375  of the ratchet arms  371 , an opening  379  is configured to receive a handle assembly  380  comprising a cross-member or handle bar  381  and a sleeve  382  that may be formed in a grip  383 . The handle bar  381  may be with fastener  345  between the ratchet arms  371 . The handle assembly  380  is adapted to apply force to the force bar  376  to push and/or operably connect with the longitudinal arms  331 ,  332  and the runner block assembly  350  around the hinge (pivot)  338  on the body portion  311 . 
         [0111]    The ratchet bar  390  comprises a bar member  391  made from metal and/or metal alloy materials of sufficient strength and durability such as, for example, stainless steel, surgical stainless steel, steel-alloys, and other metals and metal-alloys. The bar member  391  comprises a elongated bar body  392  that generally may be formed smooth with at least one smooth portion  393  and a linear rack  394  with series of equally spaced notches or teeth  395 . 
         [0112]    The smooth portion  393  and a linear rack  394  of the ratchet bar  390  interacts with the push pin pawl assembly  400  located in the runner block assembly  350 . A body block end  397  of the bar member  391  may be formed with an opening  398  so as to receive the pin  322  thereby securing to ratchet arm opening  316  in the body portion  311  of the arm clamp body  310 , whereby once the runner block end  396  of the bar member  391  has been pulled and/or pushed through the runner block assembly  370  and past the pawl  403 , and with the body block end  397  fixed to the body portion  311  by the pin  322 , a ratchet action of the linear rack  394  prevents the bar member  391  from being pulled back and, in operation, any resulting advances of the pawl  403  along the linear rack  394  raises the support assembly  360 . Using the push button pawl assembly  400 , a disengaging action can be achieved by the user pushing on the button body  401  that releases the pawl  403  from the linear rack  394 , whereby the bar member  391  may slide so as to locate the support assembly  360  to the lower position  304  from the upper position  306 , or in any intermediary positions, 
         [0113]    Referring to FIGS., a pawl assembly  400  comprises a button body  401  may be inserted into the ratchet opening  352  in the body portion  351  of the runner block assembly  350  with the bar member opening  402  aligned with the opening  355 . A bias member or spring  404  next may be inserted in the ratchet opening  352  and enclosed using an end cap  405 , whereby the end cap  405  provides a force and a compression of the spring  404  between the button body  401  and the end cap  405 . The button body  401  may be configured with a bar member opening  402  and a pawl  403  formed in the button body  401  configured to align and receive slidably the bar member  391  there-through. The button body  401  may further have a button cap  405  configured to be received through a button opening  352   a  to provide spring-loaded finger action of the pawl  403  that disengages and/or engages the teeth  395 . The button opening  352   a  is dimension smaller than ratchet opening  352  so as to provide a stop wall  352   b  for the button body  401  having the cap  405  extending there-through. The button body  401  may be formed from metal and/or metal alloy materials of sufficient strength and durability such as, for example, stainless steel, surgical stainless steel, steel-alloys, and other metals and metal-alloys. The opening  352  may be formed by milling manufacturing techniques whereby the ratchet opening  352  is milled to a predetermined depth to form the stop wall  352   b  and a dimension of the button body  401  with the button opening  352   a  in a dimension of for the button head  406  subsequently milled therein. 
         [0114]    Persons skilled in the art will recognize that many modifications and variations are possible in the details, materials, and arrangements of the parts and actions which have been described and illustrated in order to explain the nature of this inventive concept and that such modifications and variations do not depart from the spirit and scope of the teachings and claims contained therein. 
         [0115]    All patent and non-patent literature cited herein is hereby incorporated by references in its entirety for all purposes.