Surgical device for implanting a total hip prosthesis

[0001] This application claims priority from U.S. Provisional Patent Application, Ser. No. 60/543,274 which was filed on Feb. 11, 2004 with the same inventors and title.

[0002] The present invention relates to a surgical device for implanting a total hip prosthesis.

[0003] A total hip prosthesis conventionally comprises, on the one hand, a femoral part constituted by a stem, at one end of which is fixed a femoral head defining a globally spherical convex articular surface and, on the other hand, a cotyloid part to be fixed to the bone of the pelvis, comprising for example a cotyloid metal cup in hemispherical form, inside which is housed an insert made of plastics material or ceramics in which the femoral head is articulated.

[0004] When such a total hip prosthesis is fitted, the surgeon implants, on the one hand, the femoral stem inside a cavity hollowed out longitudinally in the bone of the femur and, on the other hand, the cotyloid part of the prosthesis in a globally hemispherical cavity hollowed out in the bone of the pelvis. The direction of implantation of the femoral stem in the bone of the femur is globally imposed by the elongated shape of the femur bone, while the surgeon has greater liberty to choose the position of implantation of the cotyloid part in the cavity hollowed out in the pelvic bone. The choice of this position has a direct influence on the position of the axis of revolution of the theoretical cone of mobility of the implanted prosthesis, this axis of revolution corresponding in fact to the axis of revolution of the hemispherical cup connected to the pelvic bone.

[0005] It has been noted that the positioning of the acetabulum at the level of the zone of implantation of the pelvis has an effect on the mechanical behaviour of the implanted prosthesis. More precisely, when the prosthesis is articulated in movements of extreme amplitude, particularly in movements combining elementary displacements of the hip in flexion/extension, in abduction/adduction and/or in medial rotation/lateral rotation, it may happen that it is urged outside the cone of mobility of the prosthesis, in that case provoking a bearing contact between the femoral neck of the prosthesis and the edge of the acetabulum. Under these conditions, the prosthesis may be dislocated.

[0006] U.S. Pat. No. 6,205,411 proposes a method for fitting a hip prosthesis which assists the surgeon in implanting the prosthesis with a view to limiting the risks of subsequent dislocations of the prosthesis by adapting it to the anatomy of the patient treated. To that end, it is provided to use, on the one hand, a pre-operative simulator of the biomechanical kinematics of the patient's hip provided in virtual manner with the prosthesis to be subsequently implanted and, on the other hand, a device for per-operative guiding of the surgeon's gestures to fit the prosthesis, this device being controlled from the results issuing from the biomechanical simulation carried out by the simulator. To allow the simulator to determine an adequate positioning of the prosthesis to be implanted, it is necessary to provide it with a complete and detailed mapping of the patient's bone structure, particularly by means of non-invasive tomographic techniques. All these data are processed by computer in order to re-create the patient's osseous anatomy virtually, and then, still pre-operatively, to simulate its behaviour with a virtual prosthesis. This method therefore necessitates very considerable data processing means which are expensive, as well as a large amount of pre-operative data, which prolongs the duration and cost of hospitalization of the patient.

[0007] It is an object of the present invention to propose a surgical device which assists the surgeon more simply, more rapidly and more economically during the procedure of implanting a total hip prosthesis, with a view to limiting the risks of subsequent dislocations of the prosthesis, by being adapted as best possible to the anatomy of each patient treated.

[0008] In that spirit, the invention relates to a surgical device for implanting a total hip prosthesis, characterized in that it comprises means for per-operative measurement and for memorization of a plurality of positions of a given femoral prosthetic direction and means for per-operative comparison of these positions with the cone of mobility of the prosthesis to be implanted, the position of the axis of revolution of this cone being, during the implantation of the prosthesis, adjustable with respect to the zone of the pelvis where the implantation of an acetabulum of the prosthesis is provided.

[0009] By using the device according to the invention, the surgeon may, during the surgery proper, compare the cone of mobility of the prosthesis associated with the prosthesis to be implanted with the different measured positions of the femoral prosthetic direction considered, these positions preferably corresponding to extreme articular configurations of the operated patient's hip, namely articular configurations combining the movements of flexion/extension, of abduction/adduction and/or of medial/lateral rotation, such as for example the cross-legged configuration which combines the movements of flexion, of abduction and of lateral rotation. During the surgical operation of fitting the prosthesis, the surgeon then chooses a preferential direction to implant the acetabulum of the prosthesis, allowing the subsequent manipulation of the prosthesis up to in these extreme articular configurations without risking dislocation thereof. In other words, the surgical device according to the invention allows the surgeon to determine this preferential direction of implantation, or a plurality of these preferential directions, that the surgeon will then respect at the end of the surgical operation to implant the acetabulum of the prosthesis.

[0010] According to other characteristics of this device, taken separately or in any technically possible combinations:

• • [0011] it comprises means for communicating to the surgeon the comparison between the positions of the femoral prosthetic direction and the cone of mobility of the prosthesis,
  • [0012] the communication means comprise a means for displaying symbolic representations of the positions of the femoral prosthetic direction and of the position of the cone of mobility of the prosthesis,
  • [0013] it comprises means for selection by the surgeon or for calculation and memorization of at least one preferential position of the axis of the cone of mobility of the prosthesis,
  • [0014] it further comprises, on the one hand, an impactor for definitively positioning the acetabulum of the prosthesis in the zone of implantation of the pelvis, equipped with means for locating in space and, on the other hand, means for comparing the direction of impaction of this impactor with the preferential position,
  • [0015] the measuring means comprise a phantom femoral component defining the femoral prosthetic direction, positions of this femoral component with respect to the zone of implantation of the pelvis corresponding to the positions of the femoral prosthetic direction to be compared with the cone of mobility of the prosthesis,
  • [0016] it comprises means for determining the centre of an osseous cavity of the pelvis, constituting the zone of implantation of the pelvis and adapted to receive the phantom femoral component when the different positions of this component are measured,
  • [0017] it comprises a support for the phantom femoral component, adapted to be fixedly connected to the femur and to bear means for locating in space, this support being for example constituted by all or part of a femoral rasp, a femoral pin or a prosthetic stem,
  • [0018] the phantom femoral component defines an articular surface adapted to be directly articulated on the zone of implantation of the pelvis and substantially identical to the outer surface of the acetabulum of the prosthesis to be implanted,
  • [0019] it comprises a phantom acetabulum reproducing the axis of the cone of mobility of the prosthesis and equipped with a means for manual manipulation with respect to the zone of implantation of the pelvis, provided with means for locating in space.

[0020] The invention also relates to a surgical method for implantation of a total hip prosthesis, in which, per-operatively and successively:

• • [0021] the bone of the femur and the bone of the pelvis of a patient to be treated are located in space,
  • [0022] a plurality of positions of a given femoral prosthetic direction with respect to a cavity of the pelvis are measured and memorized,
  • [0023] these measured positions are compared with the cone of mobility of the prosthesis to be implanted, the position of the axis of revolution of this cone being adjusted with respect to the cavity in the course of the surgical operation,
  • [0024] at least one preferential position of this axis of revolution is determined, and
  • [0025] a cotyloid part of the prosthesis is impacted in the cavity of the pelvis in said preferential position.

[0035] Referring now to the drawings, the surgical device 1 of FIG. 1 comprises a computer 2 associated with a unit for emitting and receiving infra-red radiations. This unit comprises a sensor 3 connected to the computer and a source of infra-red emission 4 covering the operative field in which is partly shown a hip of a patient to be treated. The hip comprises the upper part of a femur F and a corresponding part of the pelvic bone B.

[0036] In order to allow the computer 2 to locate the bones of the femur F and of the pelvis B in space, the device 1 comprises respective groups of markers 5 and 6 which passively return the infra-red radiation in the direction of the sensor 3. Each group of markers 5 or 6 forms a three-dimensional marking system allowing the computer 2/sensor 3 assembly to follow in space the respective displacements of the femur and pelvis. As the use of such markers is well known in the domain of orthopaedics, they will not be described here in greater detail.

[0037] Each group of markers 5 or 6 is fixed to the bone of the femur or pelvis by means of one or more rigid pins. As will be understood hereinafter, these pins are placed so as to leave the markers visible for the sensor 3 both when the articulation of the hip is reduced (as in FIG. 1) or when it is dislocated.

[0038] The computer 2 of the device 1 is also associated with one or more screens 7 adapted to display information useful for the surgeon, particularly the information relative to the position of the bones F and B and other data described hereinafter, preferably in the form of three-dimensional graphic representations as detailed hereinafter.

[0039] The device 1 also comprises control means 8, for example in the form of a pedal adapted to be actuated by the surgeon's foot.

[0040] The surgical device 1 further comprises other components which will be described in detail hereinafter in the description of a detailed example of use of the device with a view to implanting a total hip prosthesis 10 shown alone in FIG. 2. This prosthesis is constituted by a femoral part 11 to be implanted in the bone of the femur F and by a cotyloid part 12 to be implanted in the bone of the pelvis B. More precisely, the femoral part 11 comprises a stem 13 of longitudinal axis A-A, intended to be housed and retained in a diaphyseal cavity hollowed out in the medullary cavity of the femur F. The upper end of this stem extends, in a direction inclined with respect to axis A-A, in the form of a neck 14 at the free end of which is fixed a truncated spherical head 15, of axis of symmetry B-B and globally corresponding to the longitudinal axis of the neck 14.

[0041] The cotyloid part 12 comprises an acetabulum 16 in the form of a substantially hemispherical metallic cup intended to be connected to the bone of the pelvis B. C-C denotes the axis of revolution of the concave internal surface of the acetabulum 16. Inside this cup is provided to be fixedly housed a likewise hemispherical insert 17, of axis of revolution C-C, constituted by a plastics or ceramic material. The inner surface of the insert 17 is shaped in manner substantially complementary to the outer surface of the femoral head 15, so that the latter articulates in the manner of a ball-and-socket joint with respect to the cotyloid assembly 12.

[0042] The prosthesis 10 described hereinabove is given only by way of example and other prostheses, of different geometries and/or natures, may be implanted by means of the device 1 in accordance with the surgical method of implantation described hereinafter. In particular, the invention is applied to the fitting of prostheses of which the cotyloid part is constituted by one sole cup to be cemented on the bone of the pelvis and in which the prosthetic femoral head is directly articulated or of which the cotyloid part comprises, in addition to a first metal cup to be fixed to the pelvis, a second cup mounted in this first cup in articulated manner (in which case it is called a cotyloid assembly with double mobility). In any case, the cotyloid part of the prosthesis defines an axis of revolution for the concave inner surface of the cup to be fixed to the pelvis, similar to axis C-C.

[0043] In a first step, the surgeon incises the patient and collects a certain amount of data relative to the anatomical geometry of the bones of the femur F and of the pelvis B. To that end, different means for acquiring these data may be envisaged. By way of example, the surgeon uses a feeler 9 located by the computer 2/sensor 3 assembly and previously calibrated. This feeler 9 is passed over the noteworthy places of the bones and, at each of these positionings, the surgeon actuates the control pedal 8 so that the computer 2 records the position of the feeler 9 and consequently deduces the anatomical characteristics of the femur F and of the pelvis B. From these data and the tracking of the markers 5 and 6, the computer 2 is capable of locating in space the bones of the femur and of the pelvis.

[0044] During this data acquisition step, the articulation of the hip is successively dislocated and reduced, the reflecting markers 5 and 6 remaining visible for the sensor 3.

[0045] In a second step, the anatomical head of the femur F is, if necessary, resectioned.

[0046] In a third step, a cavity, intended subsequently to receive the femoral stem 13 of the prosthesis 10, is hollowed out in the diaphysis of the femur F. To that end, the surgeon firstly uses a rigid pin (not shown) which he introduces in the anatomical medullary cavity of the femur and which he marks in space by means of the computer 2/sensor 3 assembly by palpating for example one end of this pin bearing a predetermined relief. The surgeon then positions the pin thus marked so that it extends in a diaphyseal direction X-X intended to constitute the axis of implantation of the femoral part 11 of the prosthesis. This diaphyseal direction X-X is for example arbitrarily chosen by the surgeon as a function of the shape and state of the femur. When this pin is suitably positioned, the surgeon actuates the control pedal 8 and the computer 2 memorizes the position of axis X-X, particularly with respect to the femur F.

[0047] After having withdrawn the pin, the surgeon then uses a femoral rasp 20 shown in dotted lines in FIG. 3. This rasp 20 presents an active surface whose shape is substantially identical to the femoral stem 13. It is equipped with a group of reflecting markers 21, similar to markers 5 or 6, with the result that the computer 2/sensor 3 assembly makes it possible to display the position of the rasp with respect to the femur on the display screen 7. The surgeon thus employs this information to guide the rasp along axis X-X and to hollow out the desired femoral cavity.

[0048] At the end of the rasping step, the axis X-X of implantation of the femoral part 11 is replaced by the axis of rasping effectively made if the latter has moved away from the diaphyseal axis provided by the pin.

[0049] In a fourth step, independent of the second and third steps described hereinbefore and which may therefore be inverted with these latter, a globally hemispherical cavity C is hollowed out in the zone of the pelvis B where the implantation of the acetabulum 16 of the prosthesis 10 is provided, as shown in FIG. 4. To allow the computer 2 to know the geometrical characteristics of the hollowed out cavity C, several solutions may be envisaged. A first solution consists in equipping the mill for hollowing out the cavity, with an assembly of reflecting markers similar to markers 5 or 6, so as to record the advance of this mill in the bone of the pelvis and thus allow the computer 2, which knows in advance the geometrical characteristics of the mill used, to determine in particular the position of the centre O of the milled cavity. Another solution, which may possibly be combined with the first, consists in palpating the cavity once it has been hollowed out. A third solution consists in using a phantom cup equipped with reflecting markers similar to markers 5 or 6 and in positioning this phantom cup at the bottom of the milled cavity.

[0050] In any case, at the end of this step, the computer knows the position in space of the centre O of the cavity C, as well, possibly, as other geometrical characteristics relative to this cavity, particularly its radius.

[0051] In a fifth step, a plurality of configurations of articulation of the reduced hip of the patient are measured and memorized. To that end, a phantom femoral component 22 is used, shown in FIG. 5, presenting a shape globally similar to the upper end part of the femoral part 11 of the prosthesis 10, but with larger dimensions. More precisely, this femoral component 22, hereinafter referred to as “mega-head”, comprises a substantially hemispherical head proper 23 with axis of symmetry Y-Y. The head 23 is fast with an essentially cylindrical neck 24 of axis Y-Y. The free end of the neck 24 is provided with means for connection to the upper free end of the rasp 20, left in place in the diaphysis of the femur F at the end of the rasping step.

[0052] The head 23 of the mega-head 22 defines an articular surface 25 substantially identical to the outer surface of the acetabulum 16 of the prosthesis 10 to be implanted. The head 23 is thus able to be articulated directly in the milled cavity C of the bone of the pelvis B. The position in space of the mega-head 22, particularly of its axis Y-Y, is known by the computer 2 via the sensors 5 since the mega-head is borne by the handle of the rasp 20 whose position with respect to the femur F has been determined and memorized by the computer during the third step of the operation.

[0053] While the mega-head 22 is articulated inside the cavity C, the surgeon manipulates the patient's hip so that it successively occupies a plurality of configurations considered as extreme, i.e. configurations that the local morphology of the patient imposes on him as natural limits. The patient's hip is thus manipulated into one or more configurations combining movements of flexion/extension, abduction/adduction and/or medial/lateral rotations, for example in the cross-legged configuration. Each of these extreme configurations characterizes an articular amplitude inherent in the hip of the patient operated on that the prosthesis 10 to be implanted is subsequently supposed to be able to reproduce without running the risk of being dislocated.

[0054] When the surgeon manipulates the hip joint in one of these extreme configurations, he actuates the control pedal 8 and the computer 2/sensor 3 assembly physically measures and memorizes the position of the axis Y-Y of the mega-head 22 with respect to the bone of the pelvis B. As shown in FIG. 6, the different positions thus really measured, for example six in number, are displayed on the screen 7, particularly in the form of symbolic bars Y₁, Y₂, . . . Y₆, the pelvis B being schematically represented by a parallelepiped B′ and the cavity for implantation C being represented by a corresponding, substantially hemispherical hollow C′, the graphic representations of these elements B′ and C′ being a function of the prior measurements of the pelvis B and of the cavity C.

[0055] Once these measurements are effected, the hip joint is dislocated and the mega-head 22 is withdrawn.

[0056] In a sixth step, the surgeon uses a cotyloid ancillary tool 30 shown by itself in FIG. 7, which comprises a phantom acetabulum 31 fixedly connected to a rigid handle 32 for manipulation equipped with reflecting markers 33 similar to markers 5 or 6. The phantom acetabulum 31 is in the form of a hemisphere defining a convex articular surface 34 substantially identical to the outer surface of the acetabulum 16 of the prosthesis 10 to be implanted. The axis of generation of this phantom acetabulum is denoted Z-Z and is permanently marked in space by the computer 2/sensor 3 assembly, the computer knowing in advance the fixed geometrical relationship between this axis Z-Z and the markers 33.

[0057] By means of the handle 32, the phantom acetabulum 31 is manipulated so as to be housed in the milled cavity C so that its axis Z-Z passes substantially through the centre O of this cavity. As shown in FIG. 6, the computer 2 then displays on its screen 7, in superposition of the bars Y₁ to Y₆, the cone P of mobility of the prosthesis associated with the prosthesis 10 to be implanted, as a function of the position effectively occupied by the phantom acetabulum 31 in the cavity C, i.e. as a function of the position of its axis Z-Z. In effect, the computer 2 knows in advance the structural characteristics of the prosthesis 10, in particular the vertex angle of the cone of mobility of the prosthesis, only the position of the axis of revolution of this cone, simulated by the axis Z-Z of the phantom acetabulum 31, being adjustable by the surgeon.

[0058] The surgeon then visually compares the position of bars Y₁ to Y₆ representative of the maximum articular mobility of the patient's hip with the cone P of mobility of the prosthesis envisaged in the exact position of the phantom acetabulum 31 in the milled cavity C. If, as in FIG. 6, all the bars Y₁ to Y₆ appear, on the display screen 7, within the cone P, the position of the axis Z-Z is considered as acceptable, i.e. the prosthesis 10 thus implanted will allow the patient, from the point of view of prosthetic mobility, to limit as much as possible the risks of dislocations of the prosthesis. On the other hand, if one or more of the bars Y₁ to Y₆ lie outside the prosthetic cone P, the surgeon displaces the phantom acetabulum 31 until a position is found in which the risks of subsequent dislocations of the prosthesis 10 are considerably limited. To that end, complementary information on the respective angles of the bars Y₁ to Y₆ and of axis Z-Z may be furnished to the surgeon to allow him to find this position rapidly and easily. Moreover, other angles of view of the elements of FIG. 6 are advantageously proposed, particularly the angle at which the cone P globally appears in the form of a circle, the graphic representation of axis Z-Z in that case being directed perpendicularly to the plan of view.

[0059] When the surgeon has found a satisfactory position for the phantom acetabulum 31, he records the position of its axis Z-Z by means of the computer 2, this direction, denoted Z_p-Z_p in FIG. 6, in that case being chosen as the preferential direction for subsequently implanting the cotyloid part 12 of the prosthesis 10.

[0060] Optionally, parallel to or after the determination of the preferential direction of axis Z-Z, it is possible to monitor this direction by equipping the rasp 20 with a test femoral head (not shown), with geometrical dimensions substantially identical to the femoral head 15 of the prosthesis 10. This test head is then able to be articulated inside the phantom acetabulum 31 which reproduces the internal geometrical characteristics of the insert 17 of the prosthesis 10. The hip joint thus formed is in that case reduced then manipulated by the surgeon in different extreme articular configurations, in order to verify in particular that the neck of the test head does not come into contact with the osseous matter of the pelvis B, provoking the dislocation of the prosthesis.

[0061] After having withdrawn the phantom acetabulum 31, the surgeon then uses, in a seventh step, an impactor (not shown) to definitively place the acetabulum 16 of the prosthesis 10 in position. To enable this acetabulum to be impacted so that its axis C-C merges with the preferential direction Z_p-Z_p, this ancillary tool is equipped with means for marking in space allowing the computer 2/sensor 3 assembly to display on the screen 7 the position of its direction of impaction I, as shown in FIG. 8 in which the impactor is symbolized by a tube I′. Before applying the effort of impaction on the acetabulum 16, the surgeon positions the impactor so that the direction I, in line with axis C-C of the acetabulum, is substantially aligned with the preferential position Z_p-Z_p of the axis of the cone of mobility of the prosthesis. To that end, the computer 2 displays a virtual guiding tube G, partially hollowed out, inside which the symbolic representation I′ of the impactor must be placed coaxially in order to ensure alignment of the directions I and Z_p-Z_p. A visual signal, such as a change of colour or a flashing, indicates the alignment to the surgeon.

[0062] The insert 17 is then housed in the implanted acetabulum.

[0063] Once the impaction is effected, all the femoral components of the device 1 are withdrawn and the femoral part 11 of the prosthesis 10 is, in an eighth step, implanted so that the axis A-A of its stem 13 substantially merges with the axis of femoral implantation X-X. Insofar as the rasp 20 has made a diaphyseal cavity substantially complementary of this stem, it suffices to impact the stem 13 in the femur F in conventional manner in order to obtain merging of the axes A-A and X-X.

[0064] The device 1 according to the invention thus enables the prosthesis 10 to be positioned in optimum manner in order to reproduce as best possible the kinematic capacities of the anatomical hip of the patient operated on. It will be noted that the eight per-operative steps described hereinabove are carried out during a surgical operation proper, i.e. during which the patient is for example under anaesthetics.

[0065] Moreover, the different data recorded during the fit of the prosthesis 10 may be used for making a post-operative check-up and thus enable the articular capacities of the prosthesis in its state of implantation in the hip bones to be characterized with precision. It is also possible to determine the elongation between the femur F and the pelvis B during the surgical operation. However, it will be noted that the data acquired are clearly less numerous than those necessary for the functioning of a biomechanical simulator of the hip to be operated on and the corresponding data processing means of the device according to the invention are therefore less expensive and less complex to manipulate.

[0066] As indicated hereinabove, the implantation device 1 is, in addition, easily applicable to prostheses of different geometries, only the characteristics of prosthetic mobility having to be furnished to the computer 2 to allow the cone P to be displayed. Corresponding sets of mills and rasps are provided, as well as a set of a plurality of phantom acetabula 31 of different sizes and geometries, adapted to be connected to the same handle 32.

[0067] Various arrangements and variants of the implantation device 1 described hereinabove may in addition be envisaged.

[0068] In particular, the use of the cotyloid ancillary tool 30 is not indispensable since the data relative to the cone P of mobility of the prosthesis are known by the computer 2 in advance, only the position of the axis Z-Z with respect to the cavity C of the pelvis B having to be adjusted during the operation in order to guarantee subsequent functioning without dislocation of the prosthesis 10. It may therefore be envisaged that the surgeon use only virtual representations to adjust the position of this axis Z-Z, by displaying the different cones of mobility of the prosthesis which correspond to different positions of the axis Z-Z, for example by means of an appropriate computer interface allowing it to modify the position of the virtual axis Z-Z and to choose the preferential axis Z_p-Z_p.

[0069] Other variants are set forth hereinbelow:

• • [0070] to support the mega-head 22, the rasp handle 20 may be replaced by a femoral pin or by the femoral stem of the prosthesis to be implanted, in which case the mega-head is possibly integral with its femoral support,
  • [0071] the mega-head 22 described hereinabove may be replaced by a phantom femoral component constituted by a head whose dimensions are substantially identical to those of the prosthetic femoral head and by a hemispherical dome articulated on this head, whose dimensions are substantially identical to those of the prosthetic cotyloid part,
  • [0072] the means for locating the bones of the femur F and of the pelvis B are not limited to markers reflecting the infra-red, it being possible to use, for example, markers sensitive to ultra-sounds or to the electromagnetic fields,
  • [0073] the cavity C may be milled after having determined the preferential direction Z_p-Z_p; in that case, the anatomical cavity of the hip is used as articular housing for the mega-head 22 in order to measure the different extreme articular configurations,
  • [0074] means other than a display screen may be envisaged for communicating to the surgeon a return of information on the comparison between the measurements of the extreme articular configurations and the cone of mobility of the prosthesis; sound or touch indications may thus inform the surgeon as to the state of this comparison and guide him in the determination of the preferential direction Z_p-Z_p, and/or
  • [0075] the determination of the preferential direction Z-Z may be integrally ensured by an appropriate software equipping the computer 2, from the comparison of the cone P and the measurements of the different extreme articular configurations measured per-operatively, and this by calculation and extrapolation.