Abstract:
A patient head support system comprises a base unit, a head support, and an intervening member for connecting the base unit and the head support. The base unit includes a handle assembly with an elongated body, a bore at one end thereof, and a lever that moves relative to the body between closed and open positions to contract and to expand the bore, respectively. A sleeve retained within the bore is sized to receive and hold a shaft of the intervening member, so as to hold the intervening member in a fixed position when the lever is closed. The sleeve remains retained in the bore when the transition member is disconnected, to resist contracting of the bore caused by inadvertent closing of the lever when the intervening member is unattached, and to protect against the unwanted intrusion of material into the bore.

Description:
RELATED APPLICATION 
     The present application claims priority to U.S. Ser. No. 61/475,795 filed Apr. 15, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a patient head support system suitable for use during neurosurgery, and more particularly, to an improvement related to connecting the base unit handle to another component. 
     BACKGROUND OF THE INVENTION 
     Patient head support systems for securing the head of a patient during surgical or radiological procedures are known in the art. Such head support systems typically include a base unit that connects to a patient table, a skull clamp or headrest that holds a patient&#39;s head, and intervening structure for interconnecting the base unit to the skull clamp or headrest. These components, namely, the base unit, the intervening structure, and the skull clamp or headrest, adjust so the head of the patient may be secured in any one of a number of different positions, either for a particular radiological view or to facilitate access to a patient&#39;s head during a surgical procedure. 
     Typically, the base unit has two legs that connect to a table, a crossbar that extends between the two legs, and a base unit handle. The base unit handle has an elongated body that connects to the crossbar at a first end of the elongated body. The other end of the elongated body connects to an intervening member, such as a transition member or an adaptor, which in turn supports a skull clamp or headrest that holds the patient&#39;s head. These components, i.e. the skull clamp or headrest and the one or more intervening members, along with the base unit handle, enable operating room attendants to adjust the height, distance, and orientation of the skull clamp or headrest with respect to the end of the table, to hold the patient&#39;s head in a desired position. 
     For such head holding systems the intervening member, typically a transition member or an adaptor, has a cylindrically shaped post, or shaft, that is sized to be received within a complementary shaped bore at the second end of the elongated body of the base unit handle. The base unit handle has a lever that moves to and from the elongated body to contract and to expand, respectively, the diameter of the bore. With the lever moved to a closed position, adjacent the elongated body, the contracted diameter of the bore of the base unit handle rigidly holds the post and hence the intervening member. More specifically, once the intervening member, for example, a  6 ″ transition member, is installed, closing the lever of the base unit handle will, via cam action, exert a force to squeeze the bore tightly against the cylindrical post of the transition member. This creates frictional force to immobilize the base unit handle and the transition member. This frictional force must be sufficient to hold the system in a rigid fixed position, to stably support the patient. This closing of the lever of the base unit handle also closes or clamps the first end of the elongated body to the crossbar. 
     To function properly, i.e. to supply sufficient rigidity, the bore of the base unit handle and the post of the intervening member depend on very close tolerances. As a result, the surfaces typically used to achieve this lockable bore-on-post connection require a consistent surface finish, to provide smooth movement in the free state and to provide security when locked. 
     Also, the base unit handle can be damaged by the inadvertent moving of the locking lever into the closed position when the bore is empty. This can cause permanent distortion of the bore due to the compound leverage achieved via the closed lever. This vulnerability can perhaps be better understood with respect to the structure of the elongated body of the base unit handle. More specifically, a slot formed in the elongated body and in communication with the bore allows the elongated body to flex very slightly, so that the bore can constrict when the lever closes, as taught in U.S. Pat. No. 5,564,663. More specifically, the cam linkage of the lever is capable of exerting such a force on this bore structure that it can permanently bend the casting that defines the bore. Once the bore has been bent out of shape, it is highly possible that the post will no longer fit in the bore, at least not with the proper frictional fit. 
     For these reasons, with this type of head support system, the intervening member should always be connected to the base unit handle with the lever in the open position, such that the post of the intervening member is placed inside the bore and then the lever closed thereafter. Also, a caution warning is usually given to the users of such head support systems, to discourage them from closing the lever of the base unit handle when the bore is empty. 
     Also, when the lever moves from the locked to the unlocked position, it can accelerate rapidly if it is not being actively controlled by the user. If not controlled the lever will travel to its limit and stop abruptly. There are minor differences from one casting to another. Depending on the casting the lever stops when the linkage cannot move any further, or it stops when the corresponding cam rod strikes the casting. If the linkage stops because the cam rod is striking the casting, the repeated impact of the cam rod actually can push material into the bore. 
     When this occurs, a bulge of material may intrude into the bore, which can make it difficult or impossible to remove the intervening member. For this reason, in addition to the above described warning to close the lever only when the intervening member is inside the bore, it is also helpful to warn or to encourage such users to actively control the lever during opening, to avoid this striking of the casting by the cam rod. Unfortunately, such warnings are not a failsafe solution to these problems. 
     In addition to these issues, the outer surface of the cylindrical post of the transition member, when separated from the base unit handle, is susceptible to being marred by careless handling. If such marring occurs to the post, the locking function of the base unit handle can be rendered inoperable. In other words, the bore of the base unit handle and the post of the transitional member are in some respects very susceptible to mishandling by surgical attendants, and such mishandling can result in inoperability of the head support system. 
     To some extent these issues are complicated by the consideration that clinicians will want to be able to connect the intervening member to the base unit on either the right side or on the left side, depending on the circumstances, so that the intervening member can be removed from the base handle unit and switched around to face the other direction, when the opposite orientation is required. Clinicians are accustomed to this degree of flexibility in the surgical theatre, and any reduction in this capability would not be acceptable. 
     It is an object of the present invention, with respect to patient head support systems, to eliminate the potential for inadvertently damaging the portion of the base unit handle that forms or defines the bore. 
     It is another object of the present invention to assure consistency and repeatability in achieving an immobilizing force between the bore of a base unit handle and an intervening member of a patient head support system. 
     It is still another object of the present invention to assure a long-lasting, consistent and robust connection of the components of a head support system, without diminishing the degree of flexibility currently achieved by existing components. 
     It is still another object of the invention to preserve and to protect the structure and operability of a base handle unit, in a manner that relies less on operator instructions and warnings, and more on the structure itself. 
     SUMMARY OF THE INVENTION 
     The present invention achieves these objects by retaining a sleeve, or bushing, within the bore of a base unit handle, the sleeve having an external surface that cooperates with the interior surface of the bore, and an internal surface that cooperates with a post, or shaft, of an intervening member. The sleeve supplies resistance to the closing force of the lever of the base unit handle. Because the sleeve remains in the bore, this structure eliminates problems related to the inadvertent closing of the lever when the bore is empty. More specifically, this structure eliminates the damage that would otherwise be caused to the bore of the base unit handle upon inadvertent closing of the lever. It also enables a relaxing of the tolerances of the structures used to hold the intervening member to the base unit handle. 
     Essentially, the sleeve serves as a connector between the base unit and the intervening member, such as an adaptor or a transition member, which in turn supports the skull clamp or headrest. When retained in place as part of a base unit handle, the sleeve protects the delicate surfaces of the bore from distortion and abrasion that could result from careless treatment. 
     According to one aspect of this invention, the sleeve and intervening member provide the connection security of a positive clutch, combined with the infinite positioning of a lockable sliding joint. More specifically, the sleeve or bushing carries a pair of clutch mechanisms, such as ratchet teeth or starburst connectors, at each of its opposite ends. These ratchet teeth are operable to selectively engage a complementary starburst on a protrusion of the intervening member, typically a transition member. These connectors enable the sleeve to be independently secured to the transition member. This can occur, for instance, by threadably securing the post of the transition member into the sleeve, via external threads on the post that complement internal threads of the sleeve. This combination of a threaded connector and the opposed starburst connection allows the transition member and sleeve to be independently connected, so as to be rotatable relative to the bore when the lever is open. But when the lever moves from an unlocked to the locked position, the sleeve and the transition member become fixed in position relative to the bore. 
     The sleeve&#39;s circumferential external surface mimics the outer cylindrical surface of a conventional transition member, so that it will rotate freely in the bore when the lever is open, or unlocked, and be gripped tightly when the lever is closed, or locked. This structure allows non-incremental rotation of the sleeve and the transition member within the bore. The sleeve is sized and/or shaped so as to provide some resistance to contraction of the bore during closing of the lever. The sleeve can be made of any resilient metal, for example, stainless steel, aluminum or titanium, or any other suitable material, including a radiolucent material, if radiolucency is desired. The starburst connectors add to the versatility of this structure. That is, this structure combines non-incremental rotation relative to the base unit handle with the rigidity of a clutch-type connection between the base unit handle and the intervening member, via the starburst connectors. The cooperating ratchets prevent rotation between the transitional member and the sleeve so that they move (or are immobilized) as a single unit when they are fastened together. 
     Also, the sleeve includes a central circumferential groove in its outer surface. This helps to prevent the sleeve from binding rotationally if the cam rod deforms the casting. 
     In summary, the present invention eliminates the potential for damaging the portion of the base unit handle that defines the bore. This invention achieves consistency and repeatability in achieving an immobilizing force between a base unit handle and an intervening member. Moreover, this invention achieves a robust connection of head supporting components without sacrificing any flexibility. Also, the centrally located groove of the sleeve can, to some extent, accommodate any central bulging of material into the bore that might be caused by the cam rod, if the operator does not actively control movement of the lever. 
     These and other features and advantages of the present invention will be more readily understood from the following detailed description of the invention, when considered in conjunction with the accompanying drawings, which are briefly described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a patient head support system, including a base unit, a transition member, and a skull clamp, wherein the base unit includes a base unit handle equipped with a sleeve, according to a first preferred embodiment of the invention. 
         FIG. 2  is a perspective view of the base unit handle shown in  FIG. 1 , with the sleeve unassembled and with an accompanying retaining ring uninstalled, and with the lever in an unlocked position. 
         FIG. 3  is a perspective view, similar to  FIG. 2 , but with the sleeve now located in the bore, with the accompanying retaining ring still uninstalled, and with the lever still in an unlocked position. 
         FIG. 4  is an assembled perspective view, similar to  FIGS. 2 and 3 , with the sleeve located in the bore of the base unit handle, with the retaining ring in place, and with the lever still in an unlocked position. 
         FIG. 5  is a longitudinal cross sectional view, taken along lines  5 - 5  of  FIG. 4 , showing the sleeve located in the bore of the base unit handle. 
         FIG. 6  is a perspective view of the base unit handle shown in  FIGS. 2-4 , with the sleeve located in the bore, and with the lever in the opened and unlocked position. 
         FIG. 7  is a perspective view, similar to  FIGS. 2-4 , and  6 , with the sleeve located in the bore of the base unit handle, with the lever closed, and the sleeve interconnecting the intervening member to the base unit handle. 
         FIG. 8  is a longitudinal cross sectional view, taken along lines  8 - 8  of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a head support system  10  for supporting a patient (head shown in phantom) via a skull clamp  12  at the end of a surgical table  14 . According to the arrangement of components shown in  FIG. 1 , in addition to the skull clamp  12 , the head support system  10  includes a base unit  16 , which includes a crossbar  17  that spans between a pair of spaced connector legs  15 , and a base unit handle  18 . The legs  15  connect to the table  14  and support the crossbar  17 . The base unit handle  18  has a first end  19  that connects to the crossbar  17  and a second end  20  that connects to a transition member  22 . The transition member  22  operatively connects the skull clamp  12  to the base unit  16 . In this example, the transition member  22  serves as an intervening member. Those skilled in the art will readily appreciate that one or more adaptors or transition members could be used as the intervening member, or members, for interconnecting the base unit  16  and the skull clamp  12 . 
     The focus of this detailed description is on the connection between the transition member  22  and the base unit handle  18 , particularly when a post, or shaft  24  of the transition member  22  is received within a bore  27  of the base unit handle  18 , and a lever  23  of the base unit handle  18  is closed to a locked position. One conventional structure for a base unit handle is shown in U.S. Pat. No. 5,564,663, entitled “Transitional Pivot Joint For Head Support Base Unit,” which is expressly incorporated herein by reference in its entirety. The present invention incorporates a sleeve  25 , or bushing, into the cylindrical bore  27  of the base handle unit  18 . Thus, it is the sleeve  25  that interconnects the base unit handle  18  to the intervening member  22 . Because the sleeve  25  is retained in the bore  27  (see  FIG. 2 ), the sleeve  25  eliminates damage that could otherwise occur due to the inadvertent closing of the lever  23 . As described previously, closing the lever  23  causes the bore  27  to circumferentially contract. With the present invention this closing of lever  23  causes the bore  27  to clamp the outer surface of the sleeve  25 , which in turn cooperatively holds the post  24  of the intervening member  22  in place, relative to the base unit handle  18 . 
       FIG. 2  shows that the sleeve  25  includes an annular groove or depression  38  circumferentially surrounding its outer surface. The groove  38  helps to prevent the sleeve  25  from binding rotationally, if the cam rod deforms the casting. 
       FIGS. 2-4  show the relative size and shape of the sleeve  25 , compared to the bore  27 . These Figures show that the sleeve  25  is preferably retained in the bore  27  of the base unit handle  18  by a flange  30  located at one end thereof and a retaining ring  31  removably secured at the other end thereof. Stated another way, the flange  30  and the retaining ring  31  prevent inadvertent removal of the sleeve  25  from within the bore  27 . Those skilled in the art will recognize that there are other acceptable ways to retain the sleeve  25  within the bore  27 , for instance via alternative structure such as a set screw, an oblique cross pin, or any other analogous holding mechanism, preferably so that the sleeve  25  is retained so as to not bend or bind within the bore  27 . With the sleeve  25  retained within the bore  27 , the base unit handle  18  is much less vulnerable to damage resulting from careless operation by attendants. 
       FIG. 5  shows a longitudinal cross sectional view of the sleeve  25  within the bore  27 . This view shows the relatively close tolerances between the sleeve  25  and the bore  27 .  FIG. 5  also shows that sleeve  25  has an internal thread  39  extending therethrough. This internal thread  39  is sized and shaped to accept a complementarily shaped external thread  41  formed on the post  24  of the transition member  22 , as shown in  FIG. 6 . 
       FIGS. 6 ,  7  and  8  also show that the transition member  22  preferably includes multiple pieces, namely a transition member body  42  and the post  24  that is threadably extendable into the bore  27 . The post  24  is threadably extended into the bore  27  by turning a knob  43  located on the opposite side of the transition member body  42 , with the knob  43  being connected to, or even an integral part of the post  24 . To connect the intervening member  22  on an opposite side of the base unit handle  18 , the intervening member  22  is simply positioned so that the post  24  is inserted into the opposite end of the sleeve  25 , and the knob  43  turned so as to cause the threads  41  to engage the internal threads  39  from the opposite side. 
     When the lever  23  is moved to the closed position, the sleeve  25  and the intervening member  22  are held in a secure position relative to the base unit handle  18 . Because the intervening member  22  can connect to either side of the sleeve  25 , as shown in  FIG. 6 , this assembly maintains the positioning freedom that is available with conventional patient head support assemblies. 
     The two opposite ends of the sleeve  25  preferably include a pair of clutch mechanisms  35  and  37 , for instance a pair of starburst connectors, to facilitate connection to the intervening member  22  on either side. That is, either of the clutch mechanisms  35  and  37  of the sleeve  25  can provide a secure connection with the complementary teeth of a connector  45  formed on the transition member body  42 , to independently secure the sleeve  25  to the intervening member  22  via rotation of the knob  43 . Thus, turning the knob  43  causes the threads  41  to engage the threads  39  of the bore  27 , and also causes the starburst  45  to connect to either connector  35  or connector  37 , depending on which side the transition member  22  is located. This connection prevents relative rotation between the transition member  22  and the sleeve  25 . Also, the transition member  22  and the sleeve  25 , when secured together, may rotate together within the bore  27  of the base handle unit  18  when the lever  23  is not locked. Thus, this structure serves as a positive clutch, which uses interlocking teeth or lugs to accomplish engagement, rather than a frictional clutch. It is to be understood that a positive clutch in a form other than that which is illustrated herein could also be used in the present invention, In addition, a frictional clutch could be used in the present invention as well. 
     These Figures illustrate an exemplary embodiment that uses a sleeve  25  with a positive clutch construction, for example, in the form of starburst ratchets  35  and  37 , on both ends thereof. The interior of the sleeve  25  has threads  39  to accept the corresponding external threads  41  of the post  24 . The exterior surface of the sleeve  25  is fabricated with a specific finish and/or size to allow it to fit closely in the bore  27 . The shaft  25  will rotate freely when the lever  23  is unlocked, but will resist rotation when the lever  23  is locked. The sleeve  25  may retain these characteristics even though it is permanently “captured” in the bore  27 . 
     Where appropriate, the sleeve  25  of the present invention could be used for the connection of other components of a patient head support system  10 , or even any other medical apparatus or non-medical apparatus. In such instances, a permanently or removably installed sleeve  25  could provide a secure connection of appropriate support components, while reducing the risk of deforming those components. For instance, the incorporation of such a sleeve  25  could be used to provide increased positioning freedom at the connection of a skull clamp or headrest, by allowing non-incremental rotation, whereas a typical swivel adaptor with a starburst connector does not provide non-incremental rotation. 
     The structure of this invention is more robust and it is easier to manufacture than conventional connection mechanisms for head support systems. The threaded connection of the intervening member  22  to the base unit handle  18  is more forgiving of slight differences in tolerance, due to the material of the sleeve  25 . In addition, the structural arrangement of the present invention maintains the flexibility that is currently available with conventional mechanisms, while at the same time being more tolerant of operator mishandling. To some extent, this increased ability to withstand mishandling is due to the fact that the sleeve  25  can remain in the bore  27 . 
     Those skilled in the art will appreciate that these Figures and this detailed description represent one preferred embodiment of the present invention, and that the structures shown and described are susceptible to various modifications and permutations. Accordingly, the appended claims are to be interpreted in light of and understood with respect to the embodiment shown and described. However, the claims are not to be construed as necessarily limited to the specific structure shown and described. Moreover, the recitation in this specification of “objects” of the invention is intended to help explain the story behind this invention. Their inclusion in this specification should not be interpreted to limit the claims, or to mean that any one single claim must be interpreted or construed so as to achieve each and every one of the stated objects.