Abstract:
A halo crown has depending posterior legs adjustable in multiple dimensions for conveniently adjusting the halo crown to a patient&#39;s skull. Each leg slides along a single axis yet provides adjustments in three dimensions due to a portion thereof extending downwardly, inwardly and rearwardly and the orientation of the axis.

Description:
FIELD OF THE INVENTION 
     This invention relates to a halo crown having positionally adjustably elements capable of being fitted into a plurality of positions in multiple dimensions. 
     BACKGROUND 
     Halo crowns are used to stabilize the cervical region of the spine and comprise an arch which encircles at least a portion of the skull and pins for attaching the arch to the skull. Typically, halo crowns are provided in a variety of sizes to accommodate varying skull sizes. 
     SUMMARY OF THE INVENTION 
     A medical halo according to the present invention provides enhanced adjustability over prior halos. It comprises an elongated first arch shaped to generally extend about a portion of the periphery of an individual&#39;s head and to lie in laterally spaced relation thereto. At least one leg extends posteriorly from the first arch and over a posterior portion of the individual&#39;s head. The leg is moveable along a first axis having a posterior-anterior component. At least one contact member is provided on the leg. Preferably, the contact member is a pin clamp. 
     The leg preferably comprises a first portion extending posteriorly from and slidably attached to the first arch and a second portion depending inferiorly from the first portion. Preferably, the second portion also extends medially and also extends inferiorly with the first axis also having a posterior-inferior component. Preferably, the first axis also has a medial-lateral component. 
     Preferably, movement of the first portion along the first axis in one direction moves the second portion inferiorly, posteriorly and laterally, and movement of the first portion along the first axis in an opposite direction moves the second portion superiorly, anteriorly and medially. 
     A positioning pad can be provided on the first arch and preferably is elastomeric and shaped to elastically fit onto the first arch. 
     A second arch can be provided which is connected to the first arch and out of planar relationship with the first arch to provide rigidity to the first arch. 
     Preferably, the first arch is injection molded. 
     Preferably, the first arch comprises at least one channel formed therein with at least a portion of the leg slideably disposed within the channel. 
     Preferably, the halo has two legs. 
     Preferably, the halo has at least one slideable member slideably affixed to the first arch and bearing a contact member, such as a pin clamp. The first arch and the slideable member preferably have complimentary interlocking shapes such that the slideable member is slideable along the first arch yet can not rotate around the first arch. 
     Preferably, the slideable member can be affixed to the first arch after the medical halo has been installed on the individual&#39;s head. One way in which this can be accomplished is to provide the slideable member in a first section and a second section which are separable from one another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a halo crown according to the invention; 
     FIG. 2 is a front elevational view of the halo crown of FIG. 1; 
     FIG. 3 is a top plane view of the halo crown of FIG. 1; 
     FIG. 4 is a cross-sectional view taken along lines  4 — 4  of FIG. 1; 
     FIG. 5 is a detailed front elevation view of a slideable member of the halo crown of FIG. 1; 
     FIG. 6 is a side elevation view of the slideable member of FIG. 5; 
     FIG. 7 is a cross-sectional view taken along line  7 — 7  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1-3 illustrate a halo crown  10  according to the present invention. It comprises generally an anterior arch  12  which encircles an anterior portion of a patient&#39;s skull (not shown) and a capital arch  14  which encircles a superior portion of the skull and connects to the anterior arch  12 . A pair of adjustable legs  16  depend from first and second terminal ends,  18  and  20  respectively, of the anterior arch  12 . Pins  22  (such as are commonly known in the art or a pin with a cutting tip as described by Voor in WO 98/30167) extend through the legs  16  and thru slideable members  24  along the anterior arch  12  to contact the patient&#39;s skull and affix the halo crown  10  in place. 
     The anterior arch  12  and capital arch  14  are preferably injection molded of a glass composite nylon  66  resin as an integral part. Such material is nonconductive and transparent to x-rays and MRI in a typical medical procedure. The anterior arch  12  has a v-shaped cross section (see also FIG. 4) having an upper v-portion  26  and lower v-portion  28 . The slidable members  24  (see also FIGS. 5 and 6) have a complimentary internal triangular shape to receive and slide along the anterior arch  12 . The slideable members  24  are preferably formed of aluminum but other materials may be substituted therefore. 
     Each slideable member  24  comprises a first half  30  and second half  32  with the first half  30  having an interior surface  34  conforming in shape to the lower v-portion  28  of the anterior arch  12  and the second half  32  having an interior portion  36  conforming in shape to the upper v-portion  26  of the anterior arch  12 . Each of the interior surfaces  34  and  36  terminate in a hook  38  and  40  respectively to encircle terminal edges  42  and  44  of the lower v-portion  28  and upper v-portion  26  of the anterior arch  12 , thereby affixing the slidable member  24  to the anterior arch  12  so that it can not be removed. A screw  46  extends through an aperture  48  through the first half  30  into a threaded aperture  50  in the second half  32 . Tightening a screw  46  compresses the first and second halves  30  and  32  together and locks the slidable member  24  into a lateral position along the anterior arch  12 . A threaded aperture  52  extends through the first half  30  to receive the pin  22 . 
     The two-piece construction of the slideable member  24  allows it to be placed onto the halo crown  10  even after the halo crown  10  has been installed on a patient. 
     Returning primarily to FIGS. 1-3, the capital arch  14  extends between the anterior arch  12  first and  18  and second end  20 . Its cross-section is shown in FIG.  7 . It provides rigidity to the halo crown  10 . Threaded traction tong attachment holes  54  are provided on the capital arch  14  adjacent where it meets the anterior arch first end  18  and second end  20  and allow a pair of traction tongs to be affixed to the halo crown  10 . 
     The legs  16  attach to receivers  56  integrally molded into and adjacent with the junction of the anterior arch  12  and capital arch  14 . An open ended channel  58  is formed on an interior side  60  of each receiver  56 . Each leg  16  comprises a first sliding portion  62  sized to be received within the channel  58  and a second depending portion  64  connected to the sliding portion  62 . A slot  66  in the sliding portion  62  receives a bolt  68  which extends through the receiver  56  and locks the relative position of the sliding portion  62  to the receiver  56 . 
     The leg depending portion  64  depends downwardly (inferiorly), inwardly (medially), and rearwardly (posteriorly) from the sliding portion  62 . An axis  70  of the channel  58  extends slightly downwardly (inferiorly) and inwardly (medially). Thus, sliding the sliding portion  62  outwardly of the channel (posteriorly) causes the leg depending portion  64  to move rearwardly (posteriorly), outwardly (laterally) and downwardly (inferiorly). With one simple movement, the legs  16  can adjust to accommodate a large variety of skull sizes and shapes. Although shown as two straight sections the legs  16  can of course be curved or otherwise shaped to achieve the desired position. The shape of the legs  16  and orientation of the axis  70  simply and elegantly provide adjustment of the legs in three dimensions. Additional degrees of freedom can be provided beyond movement along the axis  70 , such as rotational connections or sliding along additional axes to ,allow independent adjustment in three dimensions. 
     A positioning pad  72  threads through each leg depending portion  64  and one or more pin receiving apertures  74  extend therethrough as well. A c-shaped silicone pad  76  clips onto the anterior arch  12  between the slidable members  24 . 
     The halo crown  10  is primarily meant to attach to a vest and rod assembly (not shown) as is known in art. Attachment apertures  78  are provided for this purpose. A ridged circular surface  80  surrounds the apertures  78  to allow rotational adjustment of the halo crown  10  with respect to the rod assembly. 
     To position the halo crown  10 , the slidable members  24  are loosely attached to the anterior arch  12  such that they can slide along the inferior arch  12  but will not come off. The bolt  68  on the legs  16  is let loose so that the legs can also be moved. The halo crown  10  is positioned on the patient&#39;s skull with the pad  76  positioned at the forehead. The legs  16  are adjusted to provide good conformance between the legs and the patient&#39;s skull and the bolt  68  is tightened. 
     The positioning pads  72  are tightened against the skull thereby providing three points of contact to provisionally attach the halo crown  10  to the skull. The slideable members  24  are moved to an appropriate location along the anterior arch  12  and the screws  46  are tightened to lock the position of the slidable members  24  on the anterior arch  12 . Four pins  22  are then driven into the patient&#39;s skull, one each through the pin apertures  52  in the slidable members  24  and one each through a pin aperture  74  on each leg  16 . Of course more than four pins can be used. The positioning pads  72  and the c-shaped pad  76  can then be removed. 
     The present invention has been described above. Many modifications and variations thereof may be made without departing substantially from the spirit and scope of the present invention. Accordingly, it should be clearly understood that the form of the invention described and illustrated herein is exemplary only, and is not intended as a limitation on the scope.