Acetabulum spacing device

A spacing device for supporting a joint adjacent to diseased bone or missing bone tissue, including a support piece and a semi-resilient pad. The pad is shaped to cradle and support the healthy bone joint. The reverse side of the pad is fixedly connected to one end of the support piece. The other end of the support piece is shaped to straddle healthy tissue adjacent the damaged area, such as the ilium when supporting a hip joint and is to be fixedly connected to the adjacent healthy tissue, using a suitable mechanism, such as biocompatible Steinman pins. Diseased, damaged, or necrotic tissue can be removed without requiring removal of the natural bone joint. Because the undamaged bone joint is not replaced, the problems commonly experienced during and following bone joint replacement are avoided. In particular, blood loss during surgery, surgical cost, surgical time, and rehabilitation of the patient after surgery is reduced. The method of implanting the spacer for supporting a bone joint includes the steps of exposing the joint; cutting damaged tissue from the bone; selecting an appropriately sized spacer for the joint; inserting the spacer into position adjacent healthy bone tissue and the joint; seating the spacer in an appropriate position; and fixedly securing the spacer in the position.

TECHNICAL FIELD
 The present invention is directed generally to devices that can be inserted
 into the body in place of damaged bone tissue to provide underlying
 support for bone joints, without requiring complete or even partial
 replacement of the bone joint.
 BACKGROUND OF THE INVENTION
 Endoprostheses have been commonly used to replace the damaged ball of the
 femur and/or the acetabular socket of the hip bone when these parts are
 damaged or deteriorate and do not properly function. In cancer-damaged hip
 bones, a portion of the pelvis (ilium) is attacked by cancer and is thus
 incapable of supporting the acetabulum in the usual manner. While a hip
 replacement is not necessitated due to failure of the femoral ball or the
 acetabulum, it is commonly performed in such a situation because there has
 been no way to preserve the acetabulum cup while removing the damaged
 tissue from the pelvis beneath, and supporting the natural acetabulum to
 withstand the forces to which it is commonly subject. The acetabulum cup
 has routinely been removed prior to tissue removal and completely replaced
 with an artificial prosthesis after removal of the damaged pelvic tissue
 below.
 Heretofore, total hip prosthesis surgery has been performed wherein a cup
 is fitted in the acetabulum, and a femoral prosthesis member, which
 comprises a stem or shank portion and an artificial head, is fixed to the
 femur to provide a prosthetic hip joint. Subtotal hip replacement formerly
 necessitated by the above-described pelvic damage has involved removal and
 replacement of the acetabulum with a metal acetabular cup, wherein the
 metal cup provides a metal-surfaced socket for receiving the head of the
 femur.
 Total and subtotal hip replacement is undesirable in cases of pelvic damage
 where the natural ball and socket of the hip joint is undamaged. A
 significant number of total or subtotal hip joint implants have failed by
 the acetabular prosthesis coming loose from its mount. A loose acetabulum
 prosthesis can erode bone in the direction of the applied forces during
 use, i.e., in the superior and posterior directions. This is particularly
 true where the loosened prosthesis had been implanted using bone cement,
 polymethylmethacrylate (PMMA), and/or screws and pins. This accelerated
 erosion shortens the life of the implant.
 While the prior art has addressed improvements in the field of bone joint
 replacement, it has not addressed the problem of unnecessarily removing
 healthy bone joints only because the support structure under the bone
 joint was diseased or damaged. For example, U.S. Pat. No. 5,326,367 to
 Robioneck discloses an endoprostheses for a cancer-damaged pelvis. The
 endoprostheses comprises distal and proximal parts that can be screwed
 together, and include mounting extensions to be screwed to the hip bone,
 or alternatively, to a vertebra. However, while Robioneck discloses a
 potentially viable device and method to implant a prosthesis in a damaged
 pelvis, it does not address the issue of how to support the bone joint
 without replacing it with an artificial prosthesis.
 Consequently, there is a need for joint preservation rather than routine
 joint removal and replacement when only a portion of the pelvic bone is
 destroyed. Thus, a need exists for a device that can be inserted into the
 body in place of damaged bone tissue that provide underlying support for
 bone joints, preempting the requirement for complete or partial
 replacement of the bone joint, and methods for inserting such devices.
 Furthermore, the following device and method is likewise suitable for
 other joints within the human body.
 SUMMARY OF THE INVENTION
 It is a primary object of the present invention, therefore, to overcome the
 disadvantages of the prior art and provide a durable, reliable spacing
 device that can support a joint in a damaged bone so that replacement of
 the joint is not required.
 It is a further object of the present invention to provide a method to
 implant such a spacing device.
 A further object of the present invention is to reduce surgical time for
 the removal of damaged bone tissue adjacent to a joint previously
 requiring complete reconstruction of the socket portion of the joint.
 A still further object of the present invention is to reduce blood loss by
 up to 80% over prior procedures by incorporating the above-noted surgical
 procedure in place of previously partial or full bone joint
 reconstruction. Additionally, surgical time and surgical complexity are
 significantly reduced.
 Yet another object of the present invention is to decrease a patient's
 rehabilitation time by eliminating the necessity of partial or full bone
 joint reconstruction when removing diseased bone tissue adjacent to a
 joint.
 The aforesaid objects are achieved by providing a spacing device for
 supporting a bone joint adjacent diseased or missing bone tissue,
 comprising a rigid support having a contoured surface and a semi-resilient
 pad. The pad is shaped to cradle and support the healthy bone joint and
 may promote bone integration. The reverse side of the pad is fixedly
 connected to one end of the contoured support piece. The other end of the
 contoured support piece is shaped to straddle healthy bone tissue adjacent
 the damaged area, such as the ilium in the case of a hip joint and is to
 be fixedly connected to the adjacent healthy tissue, using suitable means,
 such as biocompatible Steinman pins and polymethylmethacrylate (PMMA, bone
 cement). Other configurations of the support piece can be utilized
 depending on the joint needing support.
 The result is that the diseased, damaged, or necrotic tissue can be removed
 without requiring removal of the natural bone joint. Because the undamaged
 bone joint is not replaced, the problems commonly experienced during an
 following bone joint replacement are avoided. In particular, blood loss
 during surgery, surgical cost, surgical time, and rehabilitation of the
 patient after surgery is reduced.
 Other objects and advantages of the present invention will become apparent
 from the following detailed description when read in the light of the
 several figures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
 In order for a bone joint, such as a hip, to function properly, it must be
 adequately supported from behind. Cancer and disease can cause necrosis or
 seriously damage the pelvis, rendering the natural support for the hip
 joint inadequate. Ideally, and in accordance with the present invention,
 the dead or diseased portion of the pelvis is removed without removing
 either all or part of the hip joint, and a support is placed behind the
 hip to lend adequate support to the joint. However, following removal of
 the dead or diseased portion of the pelvic bone, the typical procedure
 heretofore has been to remove at least the acetabulum, as well as a
 portion of the pelvis, and implant an artificial prosthesis. The present
 invention provides a time-saving and blood loss-reducing procedure for
 supporting the bone joint without requiring replacement of the joint, thus
 significantly reducing the patient's rehabilitation time.
 While the following description is primarily directed to the hip joint
 region of the human body, it should be appreciated that other joints
 within the body may benefit in a similar manner from the procedure and
 device set forth hereinbelow.
 Referring to the drawings, FIG. 1 is a view of a typical cancerous pelvic
 region, including an intact acetabulum. The ilium (pelvis) 5 is the large
 bone, having a large cancer in contact with the cartilage (cartilage is
 rarely attacked or destroyed by cancer), which in turn supports the
 acetabulum 15. In this view, the cancer has spread to the ilium 5, but has
 not spread within the acetabulum 15 (hip joint space).
 FIG. 2 illustrates the incision area required for insertion of an
 acetabular spacing device into the hip in accordance with the present
 invention. The exposure of the hip joint area is via an incision 20
 through a posterior lateral approach. This view shows the relative
 location of the ilium 5, the cartilage, and the femur 25. Once the
 location of the incision is determined, the incision 20 is carried out to
 expose the cancerous bone tissue 10, the abductor muscle 30, and the
 acetabulum 15, as shown in FIG. 3. The abductor muscle 30 is retracted
 anteriorly to expose the ilium 5 and the cancerous bone tissue 10 above
 the acetabulum 15. The cancerous bone tissue or tumor 10 is best
 visualized as a bulging of the cortex. Once the diseased area is
 determined, the tissue can be removed.
 FIG. 4 illustrates the cutting of the cancerous bone tissue 10 from the
 ilium 5. This step is accomplished with curettes 35 and power drills.
 Removing the cancerous material 10 creates a void 40 with the inner wall
 being the iliacus muscle and lower wall being the subchondular bone and
 articular cartilage of the hip joint. It is important to note that in
 accordance with the present invention, the hip joint is never actually
 entered. Once the diseased tissue is curetted from the area, the area is
 inspected to ensure complete removal of the diseased tissue. FIG. 5
 illustrates the void 40 of the formerly cancerous pelvic area, cleaned and
 prepared for the insertion of an acetabular spacing device 45 in
 accordance with the present invention. As can be appreciated from FIG. 5,
 the acetabulum 15 is left fully intact and is not invaded in any way.
 Moreover, the ball portion of the hip joint remains in place received
 within the acetabulum 15.
 FIG. 6 is a perspective view of the two-piece spacing device 45 in
 accordance with the present invention. The two pieces include a base 52,
 having prongs 55, 57 attached thereto and extending therefrom, and a pad
 50. Base 52 and prongs 55 and 57 are formed of a single piece, and
 preferably are formed of a polymer material such as polyethylene. This
 material is lightweight yet strong enough to support the acetabulum when
 positioned in place of the removed bone tissue. Further, the polymer
 material exhibits an indefinite life within the human body. The pad 50 can
 be formed of numerous materials such as a polymer material, metal alloy or
 other composite material which is compatible with the human body. As with
 the base 52 and prongs 55, 57, the pad 50 is of a material which exhibits
 an indefinite life within the human body. The pad 50 is preferably snap
 fit within the base 52 so as to allow for the interchangebility of the
 support structure of the spacer device 45 and the pad 50. However, the pad
 50 may alternatively be adhesively secured to the base 52 by use of a
 suitable adhesive such as polymethylmethacrolate (PMMA).
 Generally, the spacer device 45 can be supplied in numerous size
 combinations. These combinations can range in sizes of extra small to
 extra large with as many as ten or more combinations being available. The
 proper support structure and pad size for a particular patient and
 particular joint is determined by trial and error once the diseased bone
 tissue has been removed. This trial and error process is carried out by
 use of trial implants which the surgeon positions in place one at a time
 until the most compatible size is determined. once the proper size is
 determined, the actual implant to remain in the body is put into place.
 Again, the above described spacing device can be used in connection with
 the supporting or numerous joints within the human body with various sizes
 being provided for all possible joints. Furthermore, while the pelvic bone
 is a flat bone and a spacing device having prongs to straddle the healthy
 bone tissue is utilized, when supporting the healthy tissue of a joint
 such as a knee joint, the supporting structure would take on the
 configuration of a stem for insertion into a round bone such as a femur
 and secured using bone cement while the base and pad would take on the
 contoured configuration of the articular surface to be supported (joint).
 This is to include joints adjacent long bones such as humerus, femur (knee
 joint), tibia and radius.
 FIG. 7 is a cross sectional view of the assembled spacing device 45 in
 accordance with the present invention. As can be appreciated, the base
 portion 52 and prongs 55 and 57 are preferably formed of a single
 structure while the pad 50 is secured thereto in the manner discussed
 hereinabove.
 Insertion and fixation of the acetabular spacing device 45 is carried out
 as illustrated in FIGS. 8-10. A properly sized acetabular spacing device
 45 is selected for the particular joint of the particular patient, and the
 appropriately sized acetabular spacing device 45 is then placed into the
 void 40. One prong 55 of the acetabular spacing device 45 is placed on the
 inner table of the iliac crest 5, while the other prong 57 (not
 illustrated in FIG. 8) of the acetabular spacing device 45 is placed on
 the outer table of the iliac crest 5.
 Once the acetabular spacing device 45 is in place, the device 45 is secured
 in place. FIG. 9 illustrates the securing of the acetabular spacing device
 45 in place to support the acetabulum 15 in accordance with the present
 invention. After the acetabular spacing device 45 is properly seated,
 biocompatible screws or pins, such as Steinman pins 60, are retrograded
 (the heads are installed below the surface) through the ilium 5, and then
 into the acetabular spacing device 45 for stable fixation. After the pins
 60 are in place, the void 40 is reconstructed by filling it with cement,
 polymethylmethacrylate (PMMA) 65 (commonly known as bone cement). The PMMA
 65 fills the void 40 and more fully secures the acetabular spacing device
 45 in place by preventing any possible transverse or rotational movement
 thereof. Finally, the abductor muscle 30 is reattached and a routine
 standard posterior closure procedure is used to close the incision.
 FIG. 10 illustrates a properly installed acetabular spacing device 45
 within the ilium 5. Steinman pins 60 hold the prongs 55, 57 of the
 acetabular spacing device firmly to the ilium 5. As noted hereinabove,
 bone cement 65 fills the void left after the cutting process to hold the
 acetabulum spacing device 45 in place and prevent transverse or rotational
 movement relative to the adjacent bone. The acetabular spacing device pad
 50 in accordance with the present invention replaces the previously
 existing bone tissue and firmly supports the acetabulum 15, which has not
 been replaced.
 As noted hereinabove, in addition to the acetabulum, the device and method
 of the present invention is adaptable for other ball and socket type
 joints, such as the shoulder. The device and method are further suitable
 for use in any situation where diseased, damaged, or necrotic tissue is
 required to be removed adjacent to a bone joint that is supported by the
 tissue such that the joint cartilage may remain intact and undisturbed
 during the surgical procedure.
 The acetabular spacing device described herein can be inserted into the
 body in place of damaged bone tissue to provide underlying support for
 bone joints, without requiring complete or even partial replacement of the
 bone joint. Use of the present invention in accordance with the detailed
 description herein can reduce surgical time for the removal of damaged
 bone tissue adjacent to a joint previously requiring complete
 reconstruction of the socket portion of the joint. The present invention
 can reduce blood loss by up to 80% over the prior art by incorporating the
 above-noted surgical procedure in place of previously partial or full bone
 joint reconstruction, and it can decrease a patient's rehabilitation time
 by eliminating the necessity of partial or full bone joint reconstruction
 when removing diseased bone tissue adjacent to a joint. Further, this
 device and process significantly decreases operating time and overall
 surgical morbidity.
 While the present invention has been described with reference to a
 preferred embodiment, it will be appreciated by those skilled in the art
 that the invention may be practiced otherwise than as specifically
 described herein without departing from the spirit and scope of the
 invention. It is, therefore, to be understood that the spirit and scope of
 the invention be limited only by the appended claims.