A pelvic positioning device for stabilizing a patient while lying on their side in a lateral decubitus position. The device includes an anterior pelvic support mechanism including anterior support pads for contacting both pubic tubercles and the ASIS on one or both sides of the patient's body. In a preferred embodiment, the anterior pelvic support mechanism includes two ASIS pads. To provide additional stabilization an upper torso pad may be included proximate the sternum of the patient's rib cage. In addition, the device includes a posterior pelvic support mechanism including a telescopic vertical member and a crescent shaped posterior support pad. The posterior support pad is mounted by a collar to a free end of the telescopic vertical member so as to be freely rotatable in a horizontal plane parallel with the operating table. As the anterior and posterior pelvic support mechanisms are moved towards the patient's body, the posterior support pad freely rotates about the vertical member and automatically properly positions itself along the central line of the sacrum and terminating proximate the distal end of the coccyx.

FIELD OF THE INVENTION
 The present invention relates generally to a positioning device for
 stabilizing a patient while lying on their side on a surgical table and,
 more particularly, to a midline pelvic positioner for stabilizing a
 patient during total hip replacement surgery.
 DESCRIPTION OF THE PRIOR ART
 During some types of surgical procedures, such as total hip replacement
 (THR) surgery, the patient is positioned lying on one side, referred to as
 the lateral decubitus position. While in the lateral decubitus position
 the patient's body is unstable and must be supported. Conventional pelvic
 positioners used to limit the motion of the patient's body during surgery
 while lying in the lateral decubitus position generally include vertical
 anterior and posterior pads that apply pressure to the pelvis. The
 anterior and posterior pads of these conventional devices contact the body
 in areas of varying soft tissue thickness, such as the abdomen and the
 buttocks, and stabilize motion of the pelvis by applying pressure to the
 overlying soft tissue. Although the body is constrained between the two
 pads, the pelvis is still subject to an undesirable degree of motion as a
 result of the resiliency of the soft tissue. Movement of the patient's
 body during THR surgery significantly increases the difficulty of
 accurately positioning of the acetabular components relative to the
 standing pelvic orientation.
 SUMMARY OF THE INVENTION
 An object of the invention is to provide an improved pelvic positioning
 device for precisely and repeatably orienting the position of the
 patient's body relative to the operating table.
 Another object of the invention is to provide an improved pelvic position
 device that imparts greater pelvic stability during surgery so that the
 surgeon may exactly orient the acetabular components relative to the
 patient's pelvis by referencing the axes of the operating table.
 The pelvic positioning device in accordance with the present invention is
 directed to a positioning device for supporting a patient's body in a
 lateral position on a table. In a preferred embodiment, the pelvic
 positioning device includes an anterior pelvic support mechanism including
 a first anterior support pad positioned so as to support both pubic
 tubercles of the patient's body; and a second anterior support pad
 positioned so as to support an anterior superior iliac spine on one side
 of the patient's body. The first and second anterior support pads are
 displaceable independently of one another and in three directions with
 each direction being substantially perpendicular to the others.
 Furthermore, the first anterior support pad is adapted so as to be
 separated by a distance from a pubic symphysis of the patient's body.
 The positioning device also includes a crescent-shaped posterior support
 pad having a cephalad end and a caudad end. The posterior support pad is
 arranged so as that it extends along the sacrum of the patient's body with
 the caudad end terminating proximate a coccyx of the patient's body.
 In addition, the invention is directed to a method for using the
 positioning device described above. Initially, a first anterior support
 pad is positioned so as to be proximate both pubic tubercles of the
 patient's body and a second anterior support pad is positioned
 independently of the first anterior support pad so as to be proximate an
 anterior superior iliac spine on one side of the patient's body.
 To provide additional stability, a crescent-shaped posterior support pad
 having a cephalad end and a caudad end is positioned so that it extends
 along the patient's sacrum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 For ease of explanation, terms such as anterior, posterior, horizontal,
 vertical, upper, lower, etc. are used with reference to the drawings.
 These terms are not intended to apply to the actual orientation of the
 party during use.
 FIGS. 1a and 2 are different embodiments of the anterior support mechanism
 100 of the pelvic positioning device in accordance with the present
 invention supporting a patient in the lateral decubitus position on an
 operating table 105. An operative side of the patient's body is a side of
 the patient's body to be operated on and farthest away from the operating
 table. In FIG. 1a, the patient is supported anteriorly by two pads 110,
 120 that contact the body in a region of the pubic tubercles and anterior
 superior iliac spine (ASIS), respectively. In an alternative embodiment
 shown in FIG. 2, the anterior support mechanism 100 may include an
 additional pad 140 substantially aligned in a vertical direction relative
 to pad 120 that contacts the body in a region of the ASIS on the lower
 (non-operative) side of the patient's body relative to the operating table
 105. Pad 140 provides additional support to the anterior of the pelvis
 thereby improving the overall stability of the patient. Conventional
 supporting pads, such as an upper torso pad 160 placed proximate the
 sternum of the patient's body, may also be used in conjunction with the
 anterior pelvic support mechanism in accordance with the present
 invention. In a preferred embodiment, each anterior pad 110, 120, 140 has
 a concave inner surface, as shown in the cross-sectional view in FIG. 5,
 in contact with one of the ASIS or both pubic tubercles, thereby further
 restricting movement of the patient's body. The concave inner surface is
 also advantageous in that it ensures that the support pad does not engage
 the pubic symphysis.
 Anterior pelvic support mechanism 100 provides three-dimensional movement.
 Specifically, movement in the x-direction is realized via a C-shaped track
 130a that is mounted to the operating table 105. A vertical member 130b
 has a T-shaped fixed end that is received in and displaceable along the
 track 130a in the x-direction. It should be noted that any complementary
 shaped displaceable tracking system may be used.
 Pubic tubercle pad 110 is releasably secured directly to the vertical
 member 130b using a thumb screw 145. The two ASIS pads, 120, 140, however,
 are indirectly mounted to the vertical member 130b by way of horizontal
 members 130c, 130d, respectively. Each horizontal member 130c, 103d has a
 free end to which the pad is attached and an opposite end with an
 elongated slot 150 through which a thumb screw 145 is received to
 releasably secure the horizontal member to the vertical member 130b. By
 adjusting the thumb screws 145 the horizontal members 130c, 130d may be
 displaced independently of one another along the y-axis to properly
 position the pads in a region of one of the ASIS, preferably centered over
 the ASIS. The vertical height of the pads may be varied so that they
 contact the body in proper location, that is, on one of the ASIS or both
 pubic tubercles, by releasing the thumb screws and raising/lowering the
 pad 110 and/or horizontal arms 130c, 130d. Accordingly, the relative
 position of the anterior pelvic support pads may be adjusted in the
 multiple directions to allow for varying pelvic morphology in all
 patients.
 As shown in FIG. 3, the posterior support mechanism 200 includes a
 posterior support pad 205 rotatably mounted to a free end of two or more
 telescopic tubes that form a vertical member 210b. Posterior pad 205 is
 preferably crescent-shaped with a cephalad end 205b and a caudad end 205a.
 As shown in FIG. 3, the cephalad end 205b is preferably wider than the
 caudad end 205a. The posterior pad is arranged along the central line of
 the sacrum with the caudad end 205a terminating proximate the distal end
 of the coccyx. In a preferred embodiment, posterior support pad 205 is
 mounted to the vertical member 210b, for example, using a collar 215, so
 as to freely rotate at substantially the same vertical elevation relative
 to the operating table as the pubic tubercle pad 110. Other means for
 rotatably mounting these two components are contemplated and within the
 intended scope of the invention. A fixed end of the vertical member 210b
 is T-shaped and received in a C-shaped track 210a, whereby the vertical
 member is displaceable in an x-direction. A vertical measuring scale (not
 shown) may be identified on the vertical members 130b, 210b of the
 anterior and posterior support mechanisms, respectively, as a guide for
 adjusting the height of the vertical member 210b so that the collar 215
 and pubic tubercle pad 110 are at substantially the same elevation
 relative to the operating table 105.
 After being properly positioned in the x-direction vertical members 130b,
 210b of the anterior and posterior support mechanisms, respectively, are
 fixed in position by releasable locking means, preferably disposed beneath
 the operating table 105. In a first embodiment shown in FIG. 4a vertical
 members 130b, 210b are independently displaceable along the x-axis and
 fixed in position by a thumb screw 155 inserted into an elongated slot 150
 defined in the closed side of the track 130a and the operating table. The
 free end of the thumb screw is received in a threaded aperture defined in
 the fixed end of vertical members 130b, 210b.
 A second embodiment of the releasable locking means is shown in FIG. 4b. In
 this embodiment, the vertical members 130b, 210b of the anterior and
 posterior support mechanisms 100, 200, respectively, are displaceable
 simultaneously along the x-axis (as shown by the arrow) using a single
 threaded rod assembly 250. Threaded rod assembly 250 is preferably
 installed beneath the operating table 105 and includes a threaded rod 240
 extending through an aperture in base members 220, 230. The base members
 220, 230, in turn, are connected to vertical members 130b, 210b,
 respectively. As the threaded rod 240 is turned in a first direction, for
 example, in a clockwise direction, the vertical members are displaced
 towards one another within tracks 130a, 210a causing the anterior and
 posterior pads to contact the patient. On the other hand, when the
 threaded rod 240 is turned in an opposite direction, such as a
 counter-clockwise direction, the vertical members are moved away from one
 another. The simultaneous displacement of the vertical members in this
 manner is advantageous in that a single technician may properly position
 the patient without assistance.
 In a third embodiment shown in FIG. 4c, vertical members 130b', 210b' of
 the anterior and posterior support assemblies 100, 200 may be displaced
 along the x-axis (as shown by the arrows) independently of one another.
 The embodiment shown in FIG. 4c is similar to that shown in FIG. 4b,
 except that two threaded rod mechanisms 250a' and 250b' are used to
 independently control movement of each vertical member. Alternative means
 for releasably locking the vertical member are contemplated and within the
 intended scope of the invention, such as a ratchet mechanism.
 Although the tracks in the Figures are shown mounted to the upper surface
 of the operating table, it is also within the intended scope of the
 invention for the tracks to be recessed and/or mounted to the lower
 surface of the operating table. Likewise, the releasable locking means for
 fixing in place the vertical member of the anterior and posterior pelvic
 support mechanisms may be arranged either on the upper or lower surface of
 the operating table. Furthermore, other known means for displacably
 mounting the vertical members to the table may be used instead of tracks.
 The anterior and posterior support assemblies will constrain the three
 planes of the pelvis relative to the operating table. The three planes of
 the pelvis, namely the sagittal plane, the transverse plane, and the
 anterior pelvic plane are shown in FIGS. 6a-c, respectively, as defined
 when the patient is in a standing position. FIG. 6a is a view of the
 pelvis as viewed from the head of the body while in a standing position.
 The solid line in FIG. 6a denotes the sagittal plane. The posterior pad
 205 of the positioner device in accordance with the present invention
 ensures that the patient's sagittal plane remains substantially parallel
 to the operating table 105. FIG. 6c is a side view of the pelvis, in which
 the solid line represents the anterior pelvic plane as defined by the two
 ASIS and both pubic tubercles. The position and orientation of the
 anterior pelvic plane is guided by the anterior pads positioned proximate
 the two ASIS and the two pubic tubercles. FIG. 6b is a front view of the
 pelvis, wherein the solid line denotes the transverse plane defined by the
 iliac crest. Positioning the anterior and posterior pelvic support
 assemblies in accordance with the present invention, ensures that the
 transverse plane, and thus the patient's body, are substantially
 perpendicular to the operating table.
 In operation, while the patient is positioned lying on the operating table
 105 in a lateral decubitus position, the anterior pelvic support mechanism
 100 is moved along the x-axis towards the patient's body. Then, pads 120,
 140, 110 are positioned both horizontally and vertically so as to be
 proximate and in contact with the two ASIS and both pubic tubercles. The
 upper torso pad, if provided, is then horizontally and vertically
 positioned so as to be in contact with the sternum of the rib cage.
 Next, the posterior pelvic support mechanism 200 is drawn toward the
 patient and the telescopic vertical member 210b is adjusted so that the
 posterior support pad 205 is approximately the same vertical height as the
 pubic tubercle pad 110. This may be easily accomplished using a vertical
 measuring scale identified on the vertical members 130b, 210b of the
 anterior and posterior pelvic support mechanisms, respectively, or other
 known means for substantially aligning the two components in a vertical
 direction. Thereafter, the two vertical members 130b, 210h are
 simultaneously or independently drawn closer towards one another thereby
 securing the patient's body therebetween. Posterior pad 205 rotates freely
 about vertical member 210b and thus, properly positions itself
 automatically when the posterior pelvic support mechanism is brought into
 contact with the patient's body. In an alternative embodiment, positioning
 of the posterior pelvic support mechanism may occur before the anterior
 pelvic support mechanism.
 Thus, while there have been shown, described, and pointed out fundamental
 novel features of the invention as applied to a preferred embodiment
 thereof, it will be understood that various omissions, substitutions, and
 changes in the form and details of the devices illustrated, and in their
 operation, may be made by those skilled in the art without departing from
 the spirit and scope of the invention. For example, it is expressly
 intended that all combinations of those elements and/or steps which
 perform substantially the same function, in substantially the same way, to
 achieve the same results are within the scope of the invention.
 Substitutions of elements from one described embodiment to another are
 also fully intended and contemplated. It is also to be understood that the
 drawings are not necessarily drawn to scale, but that they are merely
 conceptual in nature. It is the intention, therefore, to be limited only
 as indicated by the scope of the claims appended hereto.