Abstract:
A method and system for distracting a patient&#39;s hip joint are disclosed. The method allows for free movement and re-positioning of the hip joint during hip arthroscopy or other surgical procedures while the hip joint remains distracted and located at a fix point of rotation. The system comprises a frame, leg support, a first pivot assembly, a second pivot assembly, and a rotation assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of provisional application No. 61/454,583 (Attorney Docket No. 42628-703.101), filed on Mar. 21, 2011, the full disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to medical methods and systems. More particularly, the present invention relates to a system and method of its use for distracting and pre-positioning a leg and distracting a hip joint to allow access for hip arthroscopy, open surgery, and other surgical and non-surgical procedures, as well as for examination. 
         [0004]    To gain access to a hip joint to perform hip arthroscopy, the femoral head must be pulled away (distracted) from the socket in the pelvis. A variety of devices and protocols are known to provide such distraction. Typically, the patient is placed in a supine (lying on the back) or lateral (lying on the side) position, and the hip is anchored by attachment to a surgical table, use of a peroneal post (a post positioned between the patient&#39;s legs), or often a combination of both. Tension is then applied to the ankle or other region of the leg, with the leg straight or slightly bent to position the femoral head relative to the socket while the joint remains distracted. 
         [0005]    While functional, these methods and systems suffer from certain shortcoming. During distraction, the nerves in and around the hip joint are stretched, and the duration of the procedure must be limited in order to prevent injury to these nerves. The pressure against the peroneal post during distraction can reduce or entirely block blood flow to the lower leg, increasing the risk of deep vein thrombosis. Additionally, most or all present distraction systems limit movement of the leg while the hip joint is distracted, thus necessitating repeated cycles of distraction and release from distraction should repositioning of the femoral head be desired. Third, to the extent existing distraction mechanisms allow the leg to pivot and rotate, the point of rotation of those system lies several inches away from the true center of the femoral head. Such displacement will disproportionately change the degree of distraction and greatly limit the physician from repositioning the leg without the need to release the joint from distraction, as discussed above. 
         [0006]    These limitations, when taken together, not only increase the risk to the patients, they also lengthen the procedure time and make the procedure more complex for the treating physician. To overcome these difficulties, some physicians will distract the hip joint more than might otherwise be necessary. Distracting hip joint more than the procedure requires can also risk unnecessary injury to the patient. 
         [0007]    For all these reasons, it would be desirable to provide improved methods and systems for distracting the hip during hip arthroplasty and other surgical interventions. It would be particularly desirable if the methods and systems permitted the physician to conveniently distract the hip joint at the beginning of the procedure, allow the physician to freely reposition the leg and the hip joint during the procedure while maintaining the initial distraction with minimum disturbance, and allow the physician to freely access the hip joint to perform a desired surgical procedure regardless of the degree of distraction and position of the leg and hip joint. At least some of these objectives will be met by the inventions described below. 
         [0008]    2. Description of the Background Art 
         [0009]    Relevant patents and published applications include: U.S. Pat. No. 7,947,006; U.S. Pat. No. 7,832,401; U.S. Pat. No. 7,677,249; U.S. Pat. No. 5,802,641; (Reissue Pat. No. 41,412); U.S. Pat. No. 5,608,934; U.S. Pat. No. 5,162,039; U.S. Pat. No. 5,025,802; US2011/0190676; US2009/0182340; US2009/0105710; and US2006/0100562. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides methods and systems for distracting a hip joint during hip arthroscopy and other surgical and examination procedures. The methods and systems of the present invention are particularly advantageous since they allow a very simple protocol for the initial distraction of the hip joint, provide the physician with the freedom to reposition the hip joint during the surgical procedure while maintaining the initial distraction, allowing the physician to periodically relieve distraction during the procedure, and providing the physician with complete access to the hip joint with minimal or no interference from the system used for the hip distraction. 
         [0011]    In a first aspect of the present invention, methods for distracting a patient&#39;s hip joint comprise supporting a leg on a repositionable leg support with the knee bent and the hip distracted. The leg support may be freely repositioned in a first plane, typically to allow the hip joint to move in a first plane in the medial and lateral directions (referred to as adduction and abduction) while the hip joint remains distracted and located at a fixed point of rotation. The method further comprises repositioning the leg support in a second plane perpendicular to the first plane, to allow flexion and extension of the hip joint while the hip joint remains distracted and located at the fixed point of rotation. The methods still further comprise rotating the leg support about an axis generally aligned with the femur and intersecting the fixed point of rotation, typically to provide internal and external rotation of the hip joint, while the hip joint remains distracted and located at the fixed point of rotation. 
         [0012]    The ability of the present invention to manipulate the leg support in such a way that the hip joint is caused to rotate about a fixed point of rotation which coincides with the physiological point of rotation of the hip joint itself, opens new possibilities to physicians and provides better access to certain areas of the hip joint. The present invention allows the leg to be distracted in an anatomically easier position and the leg to then be moved to a surgically or otherwise convenient position. Such movement will lower the maximum pressure applied in the groin area during the distraction, thus minimizing the risk of injuries. The present invention further allows for rapid and precise distraction and release of distraction, which in return can reduce the total time distraction is applied during the procedure and reduce trauma to nerves and soft tissue in the hip joint area. In preferred aspects, the present invention further allows for “indexing” of the system so that, after temporary release of distraction, the system can be returned to a previous configuration to return the leg to the same position and level of distraction as before the release. 
         [0013]    The methods may further comprise bending the knee while the leg support engages the lower leg at a point below the knee so that the lower leg acts as a lever and applies tension to the upper leg and femur to distract the hip joint. This aspect of the invention allows the physician to conveniently establish the initial hip joint distraction and further allows the initial distraction to be maintained (or re-established as noted above) by simply holding or locking the knee in the initial bent position throughout the remainder of the procedure. 
         [0014]    In other specific aspects of this method, the leg support may be selectively locked or otherwise be prevented from movement in any one or more of the first or second planes or rotational aspects. Typically, the leg support will be selectively locked to prevent movement in the first and second planes as well as to prevent rotation while the arthroscopy or other surgical procedure is being performed. Additionally, the leg support will typically be locked in at least two of the available repositioning and rotating movements while it is being repositioned and the other of the movements. This allows the leg support and hip joint to be effectively repositioned in only one of the three degrees of freedom (while the remaining two remain locked). Alternatively, in other embodiments of the present invention, the leg support and hip joint may be repositionable and rotatable in all three movements simultaneously, allowing the hip to be freely repositioned and subsequently locked when the desired position is reached. 
         [0015]    In a second aspect of the present invention, a method for distracting a patient&#39;s hip joint comprises immobilizing the patient&#39;s hip joint on a table with the hip joint at a point of rotation. Tension is applied to the patient&#39;s femur to distract the hip joint, and the lower leg and femur may then be pivoted on a first plane while the hip joint remains distracted and at the point of rotation, typically to allow adduction and abduction of the joint. The lower leg and femur may further be pivoted in a second plane perpendicular to the first plane while the hip joint remains distracted and at the point of rotation, typically to allow flexion and extension of the hip joint. Finally, the lower leg may be located about an axis of rotation aligned with the femur and intersecting the point of rotation while the hip joint remains distracted and at the point of rotation, typically to allow internal and external rotation of the hip joint. 
         [0016]    The methods of the present invention may be performed with the patient lying in a supine or lateral position, and the patient will typically be positioned over a peroneal post or other structure immobilizing the patient&#39;s groin. 
         [0017]    Tension may be applied to the femur in at least three ways. As illustrated in the drawings hereinafter, tension may be applied by flexing the knee with a location on the lower leg held against a fulcrum structure so that the knee is drawn away from the torso to apply tension to the femur (thigh or upper leg) to distract the hip joint. Usually, the fulcrum structure comprises the upper end of a leg support which holds the lower leg. Alternatively, the fulcrum structure may be moved away from the hip to push the lower leg and apply tension on the knee support to distract the hip joint. In a third embodiment, the structure may combine both methods by applying tension on the knee support while flexing the knee. 
         [0018]    Pivoting the lower leg and the femur in the first plane typically comprises engaging the lower leg or the upper leg and moving the leg through an arc in the first plane, typically in a lateral plane when the patient is in the supine position. The leg is typically secured in a leg support which is mechanically constrained to allow movement of the leg in the first plane without moving the location of the hip joint. The leg may be engaged either by manually repositioning the leg and the leg support or by actuating a mechanism to move the leg support which in turn repositions the leg. This mechanism may be controlled by a level mechanism or other mechanical actuator extending outside of a draped area over the patient. The draped area usually extends from the patient&#39;s abdomen and over the thigh. The lever may pass through portal(s) in the drape which allow access to the hip for performing the operation. 
         [0019]    Pivoting the lower leg and femur in the second plane typically comprises engaging the lower leg or upper leg and moving the leg to an arc in the second plane. The second plane is typically a vertical plane while the patient is in the supine position. Engaging the leg usually comprises securing the leg in a leg support which is mechanically constrained to allow movement of the leg in the second plane without moving the location of the hip joint. Engaging the leg may comprise manually repositioning the leg and the leg support or may further comprise actuating a mechanism to move the leg support which in turn moves the leg. The mechanism may be controlled by a lever or other mechanical actuator that extends out of the draped area. 
         [0020]    Rotating the lower leg about the axis of rotation typically comprises engaging the lower leg and applying torque to the lower leg to move the lower leg in a plane normal to the axis of rotation (when the leg is bent). Engaging typically comprises securing the leg and the leg support which is mechanically constrained to allow rotation of the lower leg without moving the location of the hip joint. Engaging may further comprise manually repositioning the lower and/or the leg support, or may further comprise actuating a mechanism to move the leg support which in turn rotates the lower leg. The rotation mechanism may be controlled by a lever or other mechanical actuator that extends out of the draped area. 
         [0021]    In the further aspect of the present invention, a system for distracting and repositioning a hip joint comprises a frame, a leg support, a first pivot assembly, a second pivot assembly, and a rotation assembly. The pivotal and rotational assemblies are arranged to define a virtual point of rotation (which is located at a point in space away from all components of the system). The frame usually has markers to help position the patient so that the virtual point of rotation is coincident with the patient&#39;s hip joint. By “coincident, is meant that the virtual point of rotation is aligned closely or identically with the physiological center of rotation of the hip joint. It will be appreciated, of course, that some variance in the locations of the virtual and physiological centers will typically be present. 
         [0022]    The leg support comprises a lower leg attachment member and a bracket. The lower leg attachment member is pivotally secured to the bracket, thus allowing bending of the knee and distraction of the hip joint as will be described in more detail hereinafter. 
         [0023]    The first pivot assembly mechanically couples the bracket of the leg support to the frame and constrains the leg support to travel in an arc-like path in the first plane relative to the virtual point of rotation. The first pivot assembly will typically be directly attached to the frame, but in other embodiments could be attached indirectly to the frame. 
         [0024]    The second pivot assembly mechanically couples the bracket of the leg support to the frame and constrains the leg support to travel in an arcuate path in a second plane which is perpendicular to the first plane. The second pivot assembly will typically be attached between the first pivot assembly and the rotation assembly, although any one of positions of these three assemblies may be interchanged. 
         [0025]    The rotation assembly mechanically couples the bracket to the frame and constrains the bracket to be rotated about an axis extending radially from the virtual point of rotation, typically being aligned with the patient&#39;s femur. The rotation assembly is typically attached between the second pivot assembly and the leg support, but as noted above the positions of these assemblies may be interchanged. 
         [0026]    In order to allow the leg and hip joint to be both repositioned and to be locked during the procedure, each of the first pivot assembly, the second pivot assembly, and the rotation assembly will include a locking mechanism so that the pivotal and rotational movement of the leg support can be selectively allowed and prevented. The locks may be active locking assemblies or alternatively may be frictional drivers which prevent movement of the assembly when they are not actively being actuated. 
         [0027]    Additional locks or indexing mechanisms may be provided to allow the system to be returned to a previous configuration, typically after distraction has been temporarily released and/or the leg has been temporarily repositioned. Indexing systems may be as simple as providing indicia on the components so that an initial position can be recorded and subsequently re-established based on the indices. Often, the indexing system will comprise collars, pins, locks, or other components which may be set at any system configuration and allow any one or more of the pivotal and rotational assemblies to be returned to that set configuration. For motorized systems, the indexed configuration can be recorded by the system controller and be automatically re-established at any time. Thus, a variety of manual, automatic, and programmable indexing mechanisms can be utilized alone or in combination. 
         [0028]    A particular advantage of this system is that the virtual point of rotation may be sufficiently offset from all mechanical components of the system to allow the hip joint to remain surgically accessible during the procedure regardless of the position of the leg support. In that way, the physician may freely reposition the leg and hip joint by manipulating the leg support without limiting his or her ability to perform the desire hip arthroscopy or other surgical procedure. 
         [0029]    The frame may be constructed as a stand-alone surgical table, but will more typically be adapted to be removably secured to existing and conventional surgical tables. 
         [0030]    As with the repositioning and rotation assemblies, the leg support will typically comprise a lock for selectively immobilizing the leg attachment member relative to the bracket. This allows the knee to be bent at a selective angle in order to provide a desired degree of hip joint distraction and to then be locked at that position during the remainder of the procedure and/or repositioned during the procedure if a different level of distraction is desired. The leg support may also comprise an indexing mechanism as described above. 
         [0031]    The lower leg member will be adapted so that the lower leg may be secured at different positions or locations on the lower leg member so that the knee can be raised and lowered relative to the bracket. By raising and lowering the leg relative to the bracket, a different mechanical leverage can be obtained on the knee joint and femur to allow the physician to adjust the degree of hip distraction provided when the knee joint is bent, as described in the methods above. 
         [0032]    In a specific embodiment of the system, the first pivot assembly comprises a support arm and a linkage assembly. The linkage assembly is attached to the frame, and the support arm is coupled to the second pivot assembly. The linkage assembly allows the support arm to reposition the leg support around the virtual point of rotation in the first plane. Such movement of the leg, of course, allows the hip joint to be adducted or abducted as described above in connection with the methods. 
         [0033]    The second pivot assembly typically comprises a linkage assembly which is attached between the first pivot assembly and the rotation assembly. The second pivot assembly allows the leg support to be repositioned in the second plane about the virtual point of rotation. Such repositioning, of course, allows the hip joint to be flex or extended as described above in connection with the methods of the present invention. The linkage assembly of the second pivot assembly may comprise a parallelogram support structure, and the second pivot assembly may further comprise a driver adapted to manipulate the parallelogram structure to effect movement of the leg support. 
         [0034]    The rotation assembly typically comprises a rocker assembly attached between the second pivot assembly and the bracket of the leg support. A rocker assembly allows the leg support to be rotated about the axis. The rocker assembly is useful since it allows the point of attachment of the rotation assembly to be offset from the axis of the leg supported on the leg support while still having the axis of rotation be aligned with the femur of the leg. 
         [0035]    While the system and method as described above are particularly suitable for distracting a hip and repositioning the leg while the hip remains distracted, the systems are also used for hip distraction alone and for leg repositioning alone. In particular, the system can be used without distraction to collect data, track rehabilitation, map the anatomy, examine the patient, and for other activities before, during, and after surgical intervention. 
         [0036]    The systems of the present invention will comprise at least the first and second pivotal assemblies and the rotation assembly. These assemblies will be mechanically coupled to the main frame either directly or indirectly, i.e., in tandem. Each of the assemblies may be actuated manually, via pre-loaded springs, using motors, or in any other way that such mechanical systems may be driven. The illustrated embodiments are suitable for manual actuation but could readily be adapted for motorized and/or automatic control. 
         [0037]    The systems of the present invention could also be adapted to be driven to apply continuous or discontinuous motion to the leg for purposes of diagnosing and/or therapy for the hip and/or the knee. 
         [0038]    In further embodiments, the motion of any of the movable assemblies can be free or be balanced by a spring, and the ranges of motion can be limited to allow leg and joint movements over certain ranges of motion but prevent them over other ranges of movement. All systems described herein could be used for rehabilitation purposes, after certain injuries or in relation with any medical intervention in the area of the joints. 
         [0039]    The first and second pivotal assemblies, the rotation assembly, and the distraction assembly are all movable assemblies that can be actuated in a variety of ways, including manually, utilizing preloaded springs or using motors. In one embodiment of the present invention, the movement of each one of the movable assemblies can be controlled manually by the operator. 
         [0040]    In further embodiments of the present invention, motors can be used to move any one or all of the moveable assemblies. The range of motion for each assembly can be pre-programmed, and the systems can be used to apply continuous motion to both hip and knee joints. The motion of any of the movable assemblies can be set to be free or to be balanced by a spring, and the range of motion can be limited to allow leg movements and movement of the joints in one area but prevent movement in other areas. The embodiments as described above individually or in combination, could be used for rehabilitation purposes, after certain injuries or in relation with any medical intervention in the area of the joints. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]      FIG. 1  illustrates the relevant anatomy of the hip. 
           [0042]      FIG. 2  illustrates the Positioning and Distraction Apparatus (PDA) of the present invention attached to a surgical table. 
           [0043]      FIG. 3  shows the PDA attached to a frame of a non-surgical table. 
           [0044]      FIG. 4  is an exploded view of the three major functional components of PDA. 
           [0045]      FIG. 5  is an exploded view of the Positioning and Distraction Mechanism (PDM) which provides for repositioning of the leg in the first and second orthogonal planes and for rotating the leg about a femoral axis. 
           [0046]      FIG. 6  shows an abduction/adduction mechanism of the PDM of  FIG. 5  in a position of complete adduction. 
           [0047]      FIG. 7  shows the abduction/adduction mechanism of the PDM of  FIG. 5  in a position of complete abduction. 
           [0048]      FIG. 8  shows the abduction/adduction mechanism of the PDM of  FIG. 5  in a position of transition between complete adduction ( FIG. 6 ) and complete abduction ( FIG. 7 ). 
           [0049]      FIGS. 9-11  shows an abduction carriage which is part of the abduction/adduction mechanism of the PDM. 
           [0050]      FIGS. 12-14  show a parallelogram mechanism which is part of the PDM of  FIG. 5 . 
           [0051]      FIGS. 15-16  show a leg rotation mechanism which is part of the PDM of  FIG. 5 . 
           [0052]      FIGS. 17-19  show three positions of the rotation mechanism and the distraction mechanism which are part of the PDM of  FIG. 5 . 
           [0053]      FIGS. 20-21  show a distraction mechanism which is part of the PDM of  FIG. 5 . 
           [0054]      FIG. 22  shows the peroneal post assembly which is part of the PDM of  FIG. 5 . 
           [0055]      FIG. 23  shows a passive leg support, including a subframe, attached to the main frame. 
           [0056]      FIGS. 24-28  show a patient positioned on an operating table with a right hip being distracted and a right leg being repositioned in accordance with the methods of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0057]    Referring to  FIG. 1 , a hip joint comprises a “ball-and-socket” joint for a patient&#39;s femur has a femur head FH which is received in the acetabulum A (socket) of the hip H. This ball-and-socket joint allows the hip joint to move in three distinct motions referred to as flexion/extension when the leg moves in an anterior/posterior direction relative to the body. The second motion is referred to as adduction/abduction where the patient&#39;s postrious leg moves laterally in and out relative to the patient&#39;s body. Finally, the third motion of the hip joint comprises internal/external rotation where the leg rotates generally about an axis running through or parallel to the femur. 
         [0058]      FIG. 2  provides a complete view of Positioning and Distraction Apparatus PDA  290  as it is attached to a surgical operating room table  300 . 
         [0059]      FIG. 3  shows PDA  290  attached to a frame of a non-surgical table  295  for the purpose of examination. 
         [0060]      FIG. 4  shows the three major functional components of PDA  290 , including a Positioning and Distraction Mechanism (PDM)  280  which provides for repositioning of the leg in the first and second orthogonal planes and for rotating the leg about a femoral axis, a Peroneal Post Assembly (PPA)  285  for stabilizing the patient&#39;s hip and groin during the distraction, and a Passive Leg Support Assembly (PLSA)  270  for supporting the leg while allowing flexion of the knee. 
         [0061]    As shown in  FIG. 5 , PDM comprises a main frame  250  which attaches to OR table  300  via attachment pins  255 . An abduction/adduction mechanism  240  is controlled by abduction control bar  260 . A parallelogram mechanism  230  is responsible for flexion /extension motion and connects to a leg rotation mechanism  220  via rotation support plate  210  which is integrated with an upper leg length adjustment bracket  211 . A distraction assembly  200  is pivotally attached to a rotation mechanism. Assembly paths are shown. 
         [0062]    As shown in  FIG. 6 , the abduction/adduction mechanism  240  ( FIG. 5 ) is in a position of complete adduction. Subframe  252  is pivotally attached to the main frame  250  via a main pivot  251 . Subframe  252  supports abduction carriage  245  via secondary pivot  241 . An abduction control bar  260  is supported by table support  261  and directly connected to the abduction carriage  245  which is guided by a main guide  243  via a linear guide  244 . The main guide  243  is supported by the main frame  250  via linear support  242  and is pivotally attached to the subframe  252 . Collars  262  and  263  are placed on control bar  260  and can be positioned by locking on the bar to selectively limit movement of the control bar in one or both directions. The collars then act as “stops” that can be used to retain and/or return the mechanism to a particular configuration. 
         [0063]    As shown in  FIG. 7 , the abduction mechanism  240  ( FIG. 4 ) is in a position of complete abduction. Abduction mechanism  240  supports abduction carriage  245  in a way that the later travels between the end positions on a trajectory close to an arc. 
         [0064]      FIG. 8  is a composite drawing showing one central and two end positions of the abduction/adduction mechanism  240 . Relative positions of the individual components are indicated by a “b,’ “c,” or “d” following the associated reference numeral. Position “b” represents full abduction. Position “d” represents full adduction, and position “c” represents a central position between full abduction and full adduction. Subframe  252  and the linear guide  244  are shown in each of the three positions. Main guide  243  is pivoted to the subframe  252  via pivot  247 . The trajectory of pivoted connector  246  between abduction control bar  260  and abduction carriage  245  is shown as  246   t.  As the abduction carriage moves, its edge follows trajectory  245   t.  Both trajectories  245   t  and  246   t  closely follow an arc with center at VA- 1  which is the position of the Virtual Axis  1  which is aligned with the patient&#39;s hip joint as shown in  FIG. 1 . All components attached to the abduction carriage  245  rotate around the vertical virtual axis VA- 1 . The abduction control bar  260  preferably extends outside the draped area (defined above) so that its handle remains accessible beyond the drape throughout the entire range of motion of the bar. 
         [0065]    The abduction carriage  245  shown in  FIG. 9  is in a close to complete abduction position when linear guide  244  is close to pivot  247  and remote from linear guide  242  while traveling on main guide  243 . Abduction carriage  245  moves along a path that closely follows rotation around vertical virtual axis VA- 1 . 
         [0066]    The abduction carriage  245  as shown in  FIG. 10  is in a close to complete adduction position when linear guide  244  is close to linear guide  242  and remote from pivot  247  while traveling on main guide  243 . Abduction carriage  245  moves in a way that closely resembles rotation around vertical Virtual Axis VA- 1 . 
         [0067]      FIG. 11  is an exploded view showing the major assembly components of abduction mechanism  240  and the way they are assembled and attached to the main frame  250 . Subframe  252  is pivotally attached to the main frame  250  via a main pivot  251 . Subframe  252  supports abduction carriage  245  via a secondary pivot  241 . Abduction control bar  260  is connected to the abduction carriage  245  which is guided by the main guide  243  via linear guide  244 . Main guide  243  is supported by the main frame  250  via linear support  242  and is pivoted to the subframe  252  via pivot  247 . Main frame mounting pins  255  are shown. 
         [0068]    A parallelogram mechanism  230  is shown in  FIGS. 12 and 13 . The mechanism is attached to the abduction carriage  245  via pivots  131  and  133 . Line  137  crossing these two pivots is the primary parallelogram line. A thrust bearing  237  allows lead screw  238  to rotate and supports its load to the bearing housing  236  which is pivotally attached to the abduction carriage via pivot  132 . Hand crank  139  and screw nut  239  together control the position of the parallelogram mechanism  230 . The parallelogram mechanism  230  comprises members  231 ,  232 ,  233 ,  234  and  235 . Member  235  is supported via pivots  135  and  136 . A secondary parallelogram  138  line crosses the centers of pivots  135  and  136 . Primary and secondary parallelogram lines  137  and  138  intersect along a virtual axis VA  2 . As the parallelogram mechanism moves, member  235  rotates around VA  2 . Rotation support plate  210  is firmly attached to member  235  and serves as a housing for the pivots of leg rotation mechanism  220 . The position of member  235  shown is close to the lowest position of the parallelogram mechanism which corresponds to leg extension. 
         [0069]    The parallelogram mechanism  230  is shown in a position corresponding to leg extension in  FIG. 12  and leg flexion in  FIG. 13 . Member  235  rotates around VA  2  as the parallelogram mechanism is raised by rotating hand crank and lead screw  238 . 
         [0070]      FIG. 14  is a composite drawing depicting two position of the parallelogram mechanism  230 . The movement is controlled by rotating hand crank  139  which moves up as the mechanism is raised. Member  235  rotates around VA  2 . Parallelogram mechanism  230  allows member  235  to be raised further up than shown on  FIG. 14 . 
         [0071]    Rotation support plate  210  houses two pivots  221  connecting the arms  222  of the leg rotation mechanism  220  to the upper leg length adjustment bracket  211  used to control and compensate for differences in the length of the upper leg, as shown in  FIG. 15 . Adjustment screw  212  supports and moves bracket  211  along the length of the pivots  221  as shown by arrow  111 . Leg rotating arms  222  rotate around pivots  221  and support distraction frame  224  through secondary pivots  223 , causing the distraction pivoting frame  224  to rotate around virtual Axis VA  3 . VA  3  is generally going through the area occupied by the knee and through the hip joint. 
         [0072]    The leg rotation mechanism  220  is shown in two positions relative to rotation support plate  210  of distraction frame  224  and the upper leg length adjustment bracket  211  in  FIG. 16 . Position  128  is shown in solid line and position  129  in dashed line. Arms  222  are pivotally attached to the rotation support plate  210  via pivots  221 . The distraction frame  224  is pivotally attached to the arms  222  via pivots  223 . Distraction frame  224  rotates around VA- 3  which dynamically moves with the movement of frame  224  but generally remains in a small area. Two positions of VA- 3  are shown on  FIG. 15 . The distraction frame  224  supports the distraction assembly  200  via two pivots  225 . Pivots  225  form an axis of rotation, and distraction assembly  200  rotates together with distraction frame  224  around VA- 3 . 
         [0073]    Distraction assembly  200  along with distraction frame  224  are shown in positions which are to the left of the central position when viewed from atop rotational plate  210  in  FIG. 17 . Distraction assembly  200  comprises a main calf support  201 , rear side rails  202 , a rail connector  203 ,a lower leg support  204 , front side rails  205 , and an ankle bar  207 . Multiple adjustments holes  206  on front side rails  205  allow ankle bar  207  to be assembled in various positions to the front side rails  205 . Distraction frame  224  is connected to rotational support plate  210  via pivots  221  and arms  222 . Adjustment bracket  211  defines the longitudinal position of pivots  221 . 
         [0074]    Distraction assembly  200  along with distraction frame  224  are shown in positions which are to the right of the central position when viewed from atop rotational plate  210  in  FIG. 18 . The movement of distraction frame  224  relative to rotational support plate  210  is supported by arms  222  and can be locked in any position by tightening lock  227  to positioning bar  226 . Collars  291  and  292  are selectively positionable along the bar  226  to allow for both locking and repositioning of the mechanism. To reposition, one of the collars is left in place so that the bar can later be returned to precisely the same position. Distraction assembly  200  can be rotated around the axis defined by pivots  225  and can be locked in any position by tightening lock  209  to a long positioning bar  229 . Lock  209  is attached to lock support plate  208 . Collars  293  and  294  are selectively positionable along the bar  229  to allow locking and repositioning of the distraction assembly in a manner similar to that described with respect to collars  291  and  292 . Lock  227  and long positioning bar  229  are attached to locking bracket  228 . Adjustment bracket  211  defines the longitudinal position of pivots  221 . 
         [0075]    As shown in  FIG. 19 , distraction assembly  200  comprises components to the left of the dashed line except for pivots  225 . A calf support  201  is mounted to the rear rails  202 . A lower leg support  204  is mounted to the front side rails  205 . Front side rails  205  are connected to the rear side rails  202  via rail connectors  203  and lock support plate  208 . Multiple adjustments holes  206  on front side rails  205  allow ankle bar  207  to be assembled in various positions to the front side rails  205 . The distraction assembly  200  along with distraction frame  224  rotates relative to rotational support plate  210  around VA- 3 . This rotation can be locked in any position by tightening lock  227  (mounted to locking bracket  228 ) to positioning bar  226 . Distraction assembly  200  rotates relative to distraction frame  224  around the axis defined by pivots  225 . This rotation can be locked by tightening lock  209  which is mounted on lock plate  208 . 
         [0076]    Distraction assembly  200  rotates around pivots  225  relative to distraction frame  224  and is shown in a relatively horizontal position in  FIG. 20 , which is usually the initial position prior to distraction. Rotation of distraction assembly  200  is locked by tightening lock  209  to long positioning bar  229  which is attached to locking bracket  228 . 
         [0077]    Distraction assembly  200  rotates around pivots  225  relative to distraction frame  224  and is shown in a relatively vertical position, which may be the final distraction position in  FIG. 21 . Rotation of distraction assembly  200  is locked by tightening lock  209  to long positioning bar  229  which is attached to locking bracket  228 . 
         [0078]    The peroneal post  285  comprises components  282 ,  283 ,  287 ,  288  and  289  as shown in  FIG. 22 . A peroneal mounting bracket  286  is attached to main frame  250  and can move along in a direction shown by arrow  186 . The peroneal mounting bracket  286  is locked to main frame  250  prior to installing peroneal post  285 . The peroneal post frame  287  slides atop bracket  286  in direction shown by arrow  185  and can be moved by tightening the tensioner  283 . After positioning in a desired location it is locked in position by tightening the peroneal post lock  282 . An inner body  288  is attached to the peroneal post frame  287  and outer body  289  is secured around the inner body  288 . Components  241  and  252  are shown for clarity. Usually, the peroneal post  285  will initially be movable and be locked to the bracket  286  only after it has been properly positioned relative to the patient. The patient will first lie on the table and will be positioned so that the hip joint is aligned with the virtual point of rotation defined by the pivotal and rotational assemblies as described above. Conveniently, the vertical alignment axis can be marked on the main frame  250 . The peroneal post is then positioned against the patient&#39;s groin with a slight pressure. 
         [0079]    A passive leg support subframe  265  attached to the main frame  250  is shown in  FIG. 23 . Subframe  265  slides over main frame  250 , and multiple holes in subframe  265  ensure mounting flexibility both with main frame  250  and with shaft  264 . Passive leg support  270  rotates around the longitudinal axis of shaft  264 , and the distance between frame  267  and subframe  265  is maintained and adjusted by multiple hex nuts  266 . Frame  267  has two pivots  272  allowing passive leg support  270  to rotate around the axis formed be pivots  272 . This rotation is controlled and maintained by tightening lock  276  to long positioning bar.  269  at any position along the bar  269 . Long positioning bar  269  is attached through a ball joint to the shaft  264 . Passive leg support consist of calf support  271 , lower leg support  275 , rear rails  273 , rail brackets  274 , front rails  277  and ankle bar  278 . Multiple holes in both rear rails  273  and front rails  277  ensure multiple assembly choices. 
         [0080]    A patient placed on the PDA with a right leg to be distracted and a left passive leg is shown in  FIG. 24 . 
         [0081]    As shown in  FIG. 25 , Leg distraction is performed by rotating distraction assembly  200  around the axis A- 4 . Axis A- 4  is relatively horizontal and is parallel to the natural axis of bending the knee. 
         [0082]    As shown in  FIG. 26 , the distracted leg may be rotated around axis VA- 1  to perform abduction (when compared to position on  FIG. 25 ). VA- 1  is relatively vertical and goes through or close to the center of rotation of the femoral head, as shown in  FIG. 1 . 
         [0083]    As shown in  FIG. 27 , the distracted leg is raised up in flexion and rotated around VA- 2  (when compared to the position on  FIG. 25 ). VA- 2  is relatively horizontal and goes through or close to the center of rotation of the femoral head. 
         [0084]    As shown in  FIG. 28 , the lower leg is moved inward and the distracted leg is rotated around VA- 3  in lateral rotation (when compared to  FIG. 25 ). VA- 3  goes through or close to the femoral head and the knee.