Abstract:
An ancillary tool and method for manipulating and implanting a prosthetic acetabulum including a tool provided, adjacent a distal part, with a head for interacting with an endpiece that is used for gripping the acetabulum and, in its proximal part, with a surface for application of a force along the handle. The endpiece is preferably removably connected to the distal end of the handle. The endpiece includes an elastically deformable ring having an outer face for expanding radially outwardly to initially grip the acetabulum and an opposite face for interaction with the head of the handle, such that upon a force being applied to drive the head into a cavity of the endpiece, the ring is radially expanded to expand the acetabulum in place after which the ring elastically returns to its original shape as the head is removed from the cavity.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an ancillary tool for positioning an acetabular prosthesis in an anatomical or prosthetic cavity of a patient&#39;s hip that includes a handle for supporting an endpiece having an elastically expandable ring portion that is used to grip the acetabulum. The endpiece is cooperative radially expanded to seat the acetabulum by force applied to a head carried by the handle when a force is applied along the handle to urge the head into the endpiece. 
     BRIEF DESCRIPTION OF THE RELATED ART 
     This type of ancillary tool, commonly called “gripper/impactor tool”, is used during surgical operations for implanting a rigid acetabulum, generally made of metal, in the patient&#39;s hip. Once the acetabulum has been implanted in the bone, a polymer cup is housed in the acetabulum, this cup being itself intended to receive the hemispherical head of a femoral implant or of the anatomical femur. The polymer cup is either connected directly to the acetabulum, by wedging of corresponding truncated surfaces borne by the cup and the acetabulum, or connected to a metallic shell which is received in articulated manner, substantially in the manner of a ball-and-socket joint, in the acetabulum fixed to the bone. A cotyloidal assembly with double mobility is spoken of in the latter case. 
     A first example of this type of ancillary tool consists in a rigid handle at the distal end of which is permanently connected a head made of supple plastics material, such as ertafluor (Registered Trademark). This head, whose outer dimensions are slightly greater than the inner dimensions of the acetabulum to be implanted, is introduced and wedged in this acetabulum, allowing gripping then positioning thereof up to the location of impaction of the hip. However, the use of such a one-piece head presents numerous drawbacks, as the supple material used does not allow an efficient grip if the inner dimensions of the acetabulum are not adapted to those of the head, this often obliging the surgeon to seize the acetabulum to be implanted in one hand, in order to wedge the head efficiently. The conditions of sterility are therefore not always respected. Moreover, the supple material of the head is often difficult to sterilize. Furthermore, once the impaction of the acetabulum is effected, it is generally difficult to disengage the head wedged in the acetabulum. 
     U.S. Pat. No. 5,169,399 discloses another example of such a tool in which a gripper/impactor handle is adapted for positioning a prosthetic assembly constituted by a metallic acetabulum and a polymeric insert, the acetabulum and the insert being positioned and impacted simultaneously by the handle. The latter presents at its distal end a split head whose two jaws are spaced apart from each other by a compression spring. When the surgeon brings the two jaws towards each other by compressing the spring, the head may be introduced inside the polymeric insert, then, by releasing one of the jaws, the prosthetic assembly formed by the insert and the acetabulum retained on the insert undergoes a gripping effort by the head. This tool is complex to make and to manipulate, the effort of grip depending directly on the force of the compression spring interposed between the jaws of the head. Moreover, insofar as the zone of contact between the head of the tool and the prosthetic assembly is formed by the end part of the polymeric insert of greatest diameter, the effort of impaction applied by the handle on the prosthetic assembly cannot attain high values without risk of damage to the insert and the guiding of the acetabulum by the head during impaction is unreliable. Under these conditions, there is no guarantee that the surgeon will not use one of his hands to hold the prosthetic assembly during grip thereof by the tool. Furthermore, this tool is not applicable to the positioning of a cotyloidal assembly with double mobility set forth hereinabove, the grip of the insert not ensuring hold of the acetabulum to be implanted. 
     Document WO 95/11641 discloses another tool of the afore-mentioned type, which further comprises a metallic endpiece removably added to the distal end of the handle for manipulating the acetabulum to be implanted. A deformable member of the endpiece is constituted by four quadrants, namely two diametrically opposite rigid quadrants fixedly connected to a proximal part of the endpiece by bridges of matter, and two diametrically opposite mobile quadrants, each connected to one of the rigid quadrants by an elastically deformable hinge. Pivoting of the two mobile quadrants is controlled by screwing the handle in the proximal part of the endpiece. However, the use of these two mobile quadrants ensures an efficient wedging of the acetabulum only in two diametrically opposite zones of its inner face, in other words only with a limited gripping force. 
     It is an object of the present invention to provide a tool which is adapted to manipulate and implant acetabula of different dimensions and configurations and which ensures both an efficient grip of an acetabulum and a good application of the force of impaction, without hindering the withdrawal of the tool once positioning and expansion of the acetabulum has been effected. 
     SUMMARY OF THE INVENTION 
     To that end, the invention relates to an ancillary tool for positioning an acetabular prosthesis in an anatomical or prosthetic cavity of a patient&#39;s hip comprising a handle for manipulating the acetabulum provided, in its distal part, with a head for gripping the acetabulum and, in its proximal part, with a surface for application of a force of impaction, and at least one added endpiece adapted to be removably connected to the distal end of the handle and defining both a face for wedging the acetabulum and an opposite face for interaction of the endpiece with the head of the handle, wherein the endpiece comprises a supple ring radially deformable with respect to the longitudinal axis of the endpiece, on which are formed the wedging and interaction faces. 
     The use of the radially deformable ring makes it possible both to guarantee an efficient grip, the surgeon being able to control hold of the endpiece by the head of the handle, and to efficiently transmit at least a part of the effort of impaction up to the acetabulum. By having available a series of endpieces of different sizes, the surgeon is able to use the same manipulation handle for positioning acetabula of different dimensions and/or nature. 
     According to other characteristics of this ancillary tool, taken separately or in all technically possible combinations, the ring is elastically radially deformable over substantially the whole of its periphery and the face of the endpiece intended for wedging the acetabulum is constituted by substantially the whole outer face of the ring. Further, the endpiece includes both a supple part including the deformable ring and a rigid part secured to the supple part and provided with means for removable connection to the distal end of the handle. The rigid part of the endpiece is constituted by a metallic insert fixed to the supple part and the deformable ring is elastically connected to a base of the supple part. The deformable ring includes a plurality of petals, the wedging and interaction faces being respectively constituted by the outer and inner surfaces of each of these petals. The rigid part of the endpiece defines a stop surface, in the longitudinal direction of the handle, for the head of the handle and the supple part of the endpiece has at least one surface for transmission of the force of impaction between the handle and the acetabulum. The head of the handle defines a ramp surface adapted to cooperate with an interaction face of the endpiece. The handle includes a rigid rod on which the head is movably mounted, as well as means for driving the head with respect to the rod in a movement of translation in the longitudinal direction of the rod. The handle may also include a sleeve disposed coaxially to the rod and at the distal end of which the head is rigidly fixed and the means for driving the head with respect to the rod may include a grip screwed on the rod and connected in translation with the sleeve, this sleeve being immobilized in rotation with respect to the rod. Also, the ring is axially interposed between the sleeve and the screwed grip. 
     The invention also relates to a method for positioning an acetabular prosthesis in an anatomical or prosthetic cavity of a patient&#39;s hip, comprising the steps of:
         using, on the one hand, a handle for manipulating the acetabulum, provided, in its distal part, with a head for gripping the acetabulum and, at its proximal end, with a surface for application of a force of impaction, and, on the other hand, a series plurality of endpieces of different dimensions and/or geometry, each having a supple ring that is elastically radially deformable with respect to a longitudinal axis of the endpiece, on which are formed both a face for wedging with the acetabulum and an opposite face for interaction of the endpiece with a head of the handle;   selecting, from the plurality of endpieces, an endpiece of which the wedging face is substantially complementary of an inner wall of the acetabulum to be positioned;   connecting the selected endpiece to the distal end of the handle;   placing the endpiece in the acetabulum;   placing the endpiece in engagement with the head of the handle so as to provoke radial deformation of the ring and consequently grip of the acetabulum by the endpiece;   positioning the acetabulum in the cavity of the patient&#39;s hip;   applying a force of impaction on the corresponding surface of the handle;   disengaging the head from the endpiece and such that the ring returns to its non-deformed configuration; and   withdrawing the endpiece from the positioned acetabulum.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood on reading the following description, given solely by way of example, and with reference to the accompanying drawings that are described below. 
         FIG. 1  is an exploded view in perspective of an ancillary tool according to the invention, and of an acetabular prosthesis. 
         FIG. 2  is a longitudinal section through the tool of  FIG. 1 . 
         FIG. 3  is a view of detail III in  FIG. 2 . 
         FIG. 4  is a longitudinal section of a variant endpiece of the tool of  FIG. 1 . 
         FIG. 5  is a longitudinal section of a part of the tool provided with the endpiece of  FIG. 4 . 
         FIG. 6  is a longitudinal section through a variant of a tool according to the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the drawings, and firstly to  FIGS. 1 to 3 , an ancillary tool  1  for positioning a metallic acetabular prosthesis  2  is shown. This tool essentially comprises a handle  4  extending about an axis X-X and an added endpiece  6  adapted to be removably connected to the distal end of the handle. The acetabulum  2  comprises a substantially hemispherical inner wall  2   a  and is intended to form, with an internal shell (not shown), a cotyloidal assembly with double mobility as set forth hereinbefore. 
     The handle  4  comprises a rigid rod  10  at the proximal end of which is rigidly fixed a knob  12 . This knob presents a slightly convex proximal surface  14 , forming a surface for application of a force of impaction. 
     Passing from the proximal end of the rod  10  towards its distal end, the rod comprises a first cylindrical section  15  on which is fixedly added a knob  16  for manipulation, connected to the rod by, for example, a tapered pin  18 . The rod then comprises a threaded section  20  of diameter larger than the section  15 , then a smooth section  22  of smaller diameter and on the outer surface of which is formed a longitudinal groove  24 . The distal end of the rod is formed by a projecting catch  28  coaxial to the axis X-X and threaded. 
     The handle  4  also includes a tubular sleeve  32  that is movable with respect to the rod  10  and arranged coaxially to sections  20  and  22 . The sleeve is provided at its distal end with a head  34  whose outer shape is truncated and convergent towards the distal end of the handle. Consequently the head defines a truncated ramp surface  36  as well as a substantially planar distal surface  38 . 
     The proximal end of the sleeve  32  forms a substantially cylindrical foot  40  from which a projecting end flange  42  extends radially. 
     The foot  40  is provided with a cylindrical pin  44  which extends inside a substantially complementary recess formed in a direction radial with respect to axis X-X. The length of this pin is greater than the thickness of the foot, with the result that a part of the pin extends inside the sleeve  32  and is engaged in the longitudinal groove  24  of the rod  10 . The sleeve  32  is thus immobilized in rotation with respect to the rod, but free to move in a movement of translation in the direction X-X. 
     The ancillary tool  1  comprises means for driving the sleeve  32  in translation with respect to the rod  10 , these means being in the form of a tubular body  46  of generally cylindrical shape and essentially disposed coaxially with respect to the threaded section  20 . Internally, the body  46  defines a tapping  48  complementary of the section  20  of the rod  10 . At its distal end, the body  46  is provided with two diametrically opposite re-entrant flanges  50  spaced apart from each other by a distance greater than the outer diameter of the end flange  42  of the sleeve  32 . Consequently, these flanges  50  form for the sleeve  32  hooks for drive in direction X-X. Externally, the body  46  presents flat portions  52  ensuring correct grip of the body with a view to urging it in a movement of rotation about its axis. 
     A ring  54 , made of synthetic material, for example polyacetal, is axially interposed between the sleeve  32  and the tubular body  46 . More precisely, this ring comprises a cylindrical body  56  presenting an outer thread complementary of the thread of the tapping  48 , and an annular skirt  58  of outer diameter greater than the diameter of the recess  48 . The skirt  58  forms a protective layer for the sleeve  32  when the rod  10 , and therefore the body  46  screwed on this rod, is under stress, by application of a force of impaction on the knob  12 . 
     As for the endpiece  6 , it extends about an axis Y-Y, coaxial to axis X-X in  FIG. 2 . It is formed by a supple body  60 , constituted for example by polyacetal, and by a metallic insert  62  connected to the body  60  by, for example, a pin  88 . 
     More precisely, the body  60  comprises a hemispherical base  64  whose outer shape is substantially complementary of the inner wall  2   a  of the acetabulum  2 , as well as a ring  66  of petals  68  connected to the base  64  by elastically deformable connecting zones  70 . By simultaneous deformation of these zones  70 , the ring  66  presents a considerable capacity of radial deformation with respect to axis Y-Y. In other words, the ring  66  is radially deformable over substantially the whole of its periphery, the petals  68  being able to move apart radially in homogeneous manner. 
     To that end, the ring  66  defines a face  72  for wedging the acetabulum  2 , constituted by the outer surfaces  74  substantially in the form of spherical frustum of each of the petals  68 , and a face  76  for interaction of the endpiece  6  with the head  34  of the sleeve  32 , constituted by the inner surfaces  78  of the petals  68  which form counter-ramp surfaces for the ramp surface  36  of the head  34 . Each inner surface  78  comprises a cylindrical part extended rearwardly by a flared part convergent towards the base  64 . 
     The metallic insert  62  is formed by a cylinder  80  from which a flange  82  extends radially at one of its ends. The cylinder  80  is screwed in the base  64  of the body  60  and forms a tapping  84  complementary to the projecting catch  28  secured to the rod  10 . The flange  82  forms a stop surface  86  for the planar surface  38  of the head  34 . 
     The ancillary tool  1  is used as follows. 
     Considering the handle  4  in the mounted state as shown in  FIG. 2 , the surgeon introduces the distal end of the rod  10  in the endpiece  6 , rendering axes X-X and Y-Y coaxial. The endpiece  6  is connected to the handle  4  by screwing the catch  28  in the tapping  84  of the insert  62 . The surgeon then grips the tool in one hand at the level of the manipulation knob  16  and in the other hand at the level of the body  46  forming grip, and rotates the grip  46  with respect to the rod  10  in clockwise direction, observing the body from its proximal end. In the manner of a screw-nut system, the grip  46  pushes the sleeve  32  in a movement of translation along axis X-X, taking the head  34  inside the ring  66  of the endpiece. By continuing this drive movement, the ramp surface  36  cooperates with the counter-ramp surfaces  78  borne internally by the petals  68  so as to radially expand the ring  66  and thus apply the outer surfaces  74  of the petals against the inner wall of the acetabulum  2 . In other words, the ring  66  passes from a configuration of rest to an outwardly expanded configuration, of which the substantially circular outer contour presents a diameter greater than that of the contour of the ring in its configuration of rest. It will be understood that the whole outer face  74  of the ring  66  then participates in the wedging of the acetabulum  2 . In this respect it will be noted that, for the tool  1  shown, the petals  68  of this ring are identical, which does not limit the invention in that the radial deformation of the ring by the head of the tool must be provided in particular to bring about the virtually simultaneous abutment of the essential of the outer surface of the ring on the inner concave face of the acetabulum to be manipulated. 
     The surgeon continues this movement until he considers that the endpiece is sufficiently retained by the head to guarantee a correct grip of the acetabulum by the endpiece by wedging. The stop surface  86  borne by the endpiece avoids any risk of excessive deformation of the petals, the insert  62  thus imposing a maximum axial position for the head  34 . 
     The surgeon then manipulates the acetabulum freely with the aid of the ancillary tool  1 , positions it on the patient&#39;s hip at the level of an anatomical cavity or a prosthetic one, i.e. formed by a previously implanted bone-reconstructing plate. Then, with the aid of a suitable hammer, he applies a force of impaction on the surface  14 . The effort of impaction is transmitted in the direction X-X of rod  10  to the rigid insert  62  which is screwed on this rod, then from the insert to the base  64  of the supple body  62 , and finally from this base to the acetabulum  2  through the outer surface  64   a  of the base, causing the acetabulum to be force-fitted in the corresponding cavity of the hip. 
     Once the impaction is effected, the surgeon rotates the grip  46  with respect to the rod  10  in anti-clockwise direction so as to disengage the head  34  from the endpiece  6 . By elastic return deformation of the connecting zones  70 , the petals  68  resume their initial position, making it possible to withdraw the endpiece from the implanted acetabulum without effort. 
     The ancillary tool according to the invention thus makes it possible easily to manipulate an acetabular prosthesis to be implanted, and with precision. The surgeon is at no moment obliged to touch the acetabulum with his hands. The effort of impaction is efficiently transmitted to the acetabulum, in the longitudinal direction of the handle  4 , and this through the supple part of the endpiece. The risks of marking, and even damaging the impacted acetabulum are thus limited, unlike the impactor tools disclosed in the prior art, such as those envisaged in U.S. Pat. No. 5,169,399 and WO-95/11641 mentioned hereinbefore, for which hard parts of the tools are applied directly on the edge of the acetabulum, in other words at the level of a fragile zone of restricted area. 
     The ancillary tool according to the invention advantageously comprises a series of endpieces whose dimensions and geometries are different. For example, this series comprises, in addition to endpiece  6 , an endpiece  6 ′ shown in  FIG. 4 , having the same general structure as the endpiece  6 , but of which the outer face of the supple body is formed for an acetabulum whose inner wall is partly truncated. This endpiece is adapted for the grip and impaction of acetabula in which a polymeric insert is directly connected by wedging. 
     More precisely, the endpiece  6 ′ is essentially constituted by the same elements as the endpiece  6 , these latter having the same reference figures to which a prime is added. In this way, endpiece  6 ′ comprises a body  60 ′ of supple material and a rigid insert  62 ′, rigidly fixed to each other by a screw  88 ′. The body  60 ′ includes a ring  66 ′ defining a face  72 ′ for wedging the acetabulum with the head  34 . Apart from the geometry of its outer face, endpiece  6 ′ of an axis Y′-Y′ differs essentially from endpiece  6  by the shape of its petals  68 ′ and the zones  70 ′ for connection with a base  64 ′. Further, an outer face  74 ′ of each petal  68 ′ is truncated, and convergent toward the base  64 ′, and an inner face  78 ′ of each petal  68 ′ is flared over the whole of its length. The connection zones  70 ′ also extend parallel to axis Y′-Y′. 
     As shown in  FIG. 5 , the head  34  of the handle  4  is then equipped with a bush  90  connected to the rest of the sleeve  32  by a retaining clip  92 . This bush increases the outer dimension of the head  34  so as to adapt the latter to the endpiece  6 ′ and thus laterally defines a ramp surface adapted to cooperate with the interaction face  76 ′ of the endpiece. 
     The use of the ancillary tool  1  provided with the endpiece  6 ′ is substantially similar to the use described previously. During the application of the effort of impaction, the force is essentially transmitted to the acetabulum by the truncated surfaces  74 ′ of the petals  68 ′. 
       FIG. 6  shows a variant of the ancillary tool  1  which essentially differs from the tool of  FIGS. 1 to 3  by the following: 
     Contrarily to the manipulation handle  16  of the preceding Figures, which is rigidly connected to the rod  10 , the ancillary tool of  FIG. 6  comprises a manipulation handle  100  which is connected to the grip  46  screwed on the rod  10 . The use of this variant is substantially similar to that of the tool of  FIGS. 1 to 3 , the user having, in order to provoke the displacement of the head  34  in translation with respect to the rod  10 , to apply a movement of rotation on the grip  46 /handle  100  assembly, for example by gripping the handle  100  in one hand and the knob  12  with the other hand. 
     Various arrangements and variants of the ancillary tool according to the invention may also be envisaged:
         materials other than polyacetal may be used for making the supple body of the endpiece  6 , the materials retained having both to combine a good shock resistance by reason of the transmission of the efforts of impaction, and a good resistance to sterilization, and not to damage the inner wall of the acetabulum to be implanted; and/or   the endpiece added to the distal end of the handle of the ancillary tool is formed in one piece, for example of synthetic material, formed by a supple part comprising a ring which is radially deformable in homogeneous manner, similar to ring  66 , and by a more rigid part, for example of reinforced material, in which the handle is removably connectable.