FR2766355A1 - Prosthesis medullary shank, e.g. femoral shank of hip prosthesis - Google Patents

Abstract

Prosthesis medullary shank (1), made with a tapering medullary section (2), a neck (4) and a head to receive an articulated joint, has a hole (5) through its metaphysis zone (2a) in the frontal plane, inclined at about 45 deg to the lengthwise axis of the shank, and a series of other holes (6, 7, 8) in two perpendicular planes, covering a substantial part of the medullary section. The holes in the medullary section are spaced at intervals of 1.5 cm and lie in frontal and saggital planes and are designed to receive bone screws for fixing the prosthesis shank to the bone.

Description

 The present invention relates to a medullary prosthesis rod, in particular a femoral hip prosthesis rod, a screw for locking this rod to a bone, and an instrument allowing the positioning of this rod.

 A femoral hip prosthesis rod conventionally consists of a tapered medullary part, intended to be engaged in the medullary canal of the femur, a neck, which reconstitutes the anatomical neck of the femur, and a spherical articulation head. attached to the free end of the neck, which reconstructs the head of the femur. This spherical head is intended to be received in a corresponding cavity delimited by an acetabular element fixed to the pelvis.

 A classic technique for attaching a femoral stem is to use a polymerizable synthetic cement.

 Another technique consists in fixing a femoral stem without cement, by bone regrowth through a porous coating which includes the medullary part.

 In addition to the drawbacks specific to each of these techniques (in particular significant bone ablation and necrosis, risk of poor distribution of the cement or air bubbles, with regard to cement fixation; long immobilization time, delicate primary fixation to obtain, in terms of fixation by bone regrowth), the installation of a hip prosthesis, with one or the other of these techniques, involves a deflection of the stresses that the bone normally undergoes, and therefore a disturbance of the physiological stresses of the bone.

 However, it turns out that this physiological stress is essential for maintaining the structure and density of the bone. Otherwise, there is a rarefaction of the bone over the entire upper extremity of the femur, with the consequence of progressive implantation of the implant.

 An intervention is then necessary to replace the implanted rod with another, the fixation of which must be perfect.

 The present invention aims to remedy this essential drawback of the medullary stems of prostheses, which has not yet been satisfactorily resolved.

For this purpose, the rod which it relates comprises
a hole arranged through the metaphyseal zone of the tapered medullary part of the rod, in the frontal plane, so that one of its orifices opens onto the external side of the rod and the other orifice opens onto the internal side thereof, this hole being inclined at approximately 45 "relative to the longitudinal axis of the rod and its orifice located on the external side being closer to the proximal end of the rod than the hole opening out the internal side, and
- Several stepped transverse holes, extending over a large part of the length of said medullary part, at least one of which is arranged in a plane and at least one of which is arranged in a plane substantially perpendicular to this plane, the one or more holes arranged in one plane being alternated with the hole or holes arranged in the other plane, and the spacing between two consecutive holes being of the order of 1.5 centimeters, bone screws being intended to be engaged through these different holes to lock the rod to the bone.

 The rod is thus locked to the bone in a stepped manner and in perpendicular directions. The number and the distribution of these holes make it possible to distribute the stresses exerted on the rod as close as possible to the physiological stresses normally exerted on the femur, which makes it possible to request bone physiology by applying stresses on the femur both at the level of the trochanteric massif and at the level of the diaphysis.

 The diversion of the aforementioned constraints, caused by bone prostheses, whether cemented or non-cemented, is thus eliminated, as well as the drawbacks specific to each of these techniques.

 Thanks to the screw engaged through the aforementioned inclined hole, said physiological distribution of the stresses takes place, in the metaphyseal region, essentially on the trochanteric massif, with a predominance on the lesser trochanter, and on the postero-external face of the greater trochanter.

 In addition, the stepped and perpendicular locking from one hole to the other is advantageous from the dynamic point of view because it makes it possible to block the rod in all directions. I1 therefore cannot exist a secondary movement of valgus-varus, flexum-recurvatum or rotation of the rod around its longitudinal axis.

 The rod according to the invention can be a prosthesis rod called "first line", that is to say intended to be implanted for the first time in a bone, or can be a rod called "recovery", c that is to say, replacing a "first line" rod.

 Preferably, the aforementioned stepped transverse holes are arranged, for some, in the frontal plane and, for the others, in the sagittal plane.

 Advantageously, the rod according to the invention comprises a material or coating capable of promoting osteointegration by bone regrowth, in particular a porous coating of calcium hydroxyapatite. In this case, the locking ensures perfect stability of the rod while the bone regrowth takes place to carry out the additional anchoring.

 The screw for locking the rod to a bone comprises a body with a diameter slightly smaller than that of the holes in the rod; the proximal end of this body is provided with a thread with an external diameter greater than that of the body, this thread being suitable for insertion into the proximal bone cortex.

 The distal end of this body can be provided with a self-tapping thread whose external diameter is less than that of said body, this thread being suitable for insertion into the distal bone cortex.

The instrument allowing the establishment of the rod comprises
a part whose shape corresponds to that of the rod, pierced with holes respectively identical to the holes in the rod, and
- At least one aiming rod connected to this part, which is curved so as to delimit with said part a clearance allowing the introduction of said part into the medullary canal of the bone, this aiming rod comprising respectively oriented portions of perpendicular to the axes of each of the aforementioned holes and being pierced with bores respectively coaxial with these holes.

 In view of its good understanding, the invention is again described below with reference to the appended diagrammatic drawing representing, by way of nonlimiting example, a preferred embodiment of the medullary rod that it relates to.

FIG. 1 is a view of a femoral stem of a hip prosthesis, known as "first line", that is to say intended to be implanted for the first time in the upper end of a femur, of the upper end of a femur, in longitudinal section, and one of the screws allowing the locking of this femoral stem to the bone
FIG. 2 is a side view of an aiming instrument allowing the positioning of this rod, and
Figure 3 is a view of a femoral stem of hip prosthesis, called "recovery", that is to say replacing, if necessary, a rod "first line".

 The femoral stem 1 shown in FIG. 1 conventionally consists of a tapered medullary part 2, intended to be engaged in the medullary canal of the femur 3, of a neck 4, which reconstitutes the anatomical neck of the femur, and of a spherical joint head (not shown), intended to be fixed on the free end of the neck 4 and reconstituting the head of the femur.

 The tapered medullary part 2 comprises a transverse hole 5, arranged through its metaphyseal zone 2a, and three transverse holes 6, 7, 8 stepped, extending over a significant part of the length of the rod 1, that is to say ie at the level of the metaphyseal 2a and diaphyseal 2b zones.

 The hole 5 is arranged in the frontal plane, so that one of its orifices opens onto the external side of the medullary part 2 and the other orifice opens onto the internal side of the latter. This hole 5 is inclined at about 45 relative to the longitudinal axis of the part 2 and its orifice located on the external side is closer to the proximal end 2c of the part 2 than the orifice opening on the internal side.

 The transverse hole 6 consecutive to the hole 5 is arranged in the sagittal plane, at a distance of approximately 1.5 cm from the orifice of the hole 5 opening on the internal side of the part 2. The hole 7 consecutive to the hole 6 is arranged in the frontal plane, that is to say substantially perpendicular to this hole 6, at a distance of approximately 1.5 cm from this hole 6, and the hole 8, similar to the hole 6, is also arranged at a distance of about 1.5 cm from hole 7.

 The instrument 10 shown in Figure 2 comprises a part 11 whose shape corresponds to that of the rod 1, and constituting a template. This template is pierced with holes 15, 16, 17, 18 respectively identical to holes 5, 6, 7 and 8, and is connected to two aiming rods 12, 13, perpendicular to each other. The rod 13 is shown in broken lines, for clarity of the drawing.

 These rods 12, 13 are curved so as to delimit with the template 11 a clearance 20 allowing the introduction of the template 11 into the medullary canal of the femur 3.

 The rod 12 comprises in particular two successive rectilinear portions, namely a portion 21 oriented perpendicularly to the axis of the hole 15 and a portion 22 oriented perpendicularly to the axis of the hole 17. These portions 21 and 22 are pierced with bores 35 and 37, respectively coaxial with holes 15 and 17.

 The rod 13 has a curved portion connected to the rod 12 then a straight portion 23 oriented perpendicular to the axis of the holes 16 and 18. This portion 23 is pierced with coaxial bores in the holes 16 and 18.

 In practice, after adequate preparation of the femur 3, the template 11 is introduced into the medullary canal and is placed in the position that the rod 1 must have after implantation.

 In this position, the rods 12 and 13 are positioned respectively in the frontal plane and in the sagittal plane, as shown in FIG. 2, the portion 21 coming to be placed along the greater trochanter and the portions 22 and 23 along the femoral shaft.

 The different bores that these portions 21 to 23 comprise constitute guns allowing the guiding of a drill for drilling the bone, for the arrangement of proximal holes in this bone, opposite which the proximal orifices of each of the holes 5, 6, 7 and 8 are positioned when the rod 1 is placed in the bone.

 Once this positioning has been carried out, screws 40 of appropriate length are engaged in these holes 5, 6, 7 and 8.

 Each of these screws 40 comprises a body 41 of diameter slightly smaller than that of the holes 5 to 8, comprising a proximal end (on the side of the head 42 of the screw 40) provided with a thread 43 whose external diameter is greater than that of said body 41, and a distal end provided with a self-tapping thread 44 whose external diameter is less than that of said body 41, these threads 43, 44 being suitable for insertion into the corresponding bone cortices.

 The femoral stem shown in FIG. 3 is similar to the stem 1, except that it is of greater length and that it comprises, in addition to the holes 5 to 8 as mentioned above, holes 6a and 7a respectively similar to the holes 6 , or 8, and 7. These different holes are stepped and extend over a significant portion of the length of the medullary part 2 of this rod, the holes 6, 8, 6a arranged in the sagittal plane being alternated with the holes 7 , 7a arranged in the frontal plane, and the distance separating each of these holes also being approximately 1.5 cm.

 This rod is implanted in the same way as the rod 1, replacing a rod already implanted, by means of a sighting instrument similar to the instrument 10, comprising a template and suitable rods.

 It goes without saying that the invention is not limited to the embodiment described above by way of example but that it embraces, on the contrary, all the variant embodiments. Thus, the invention relates not only to a femoral stem of a hip prosthesis but to any type of medullary stem of a prosthesis; said part 11 could be constituted by the medullary rod to be implanted, the aiming rods 12 and 13 being integral with fixing means on this medullary rod the instrument 10 could comprise only a single aiming rod, orientable relative to the part 11 and immobilizable with respect thereto in the appropriate position; the medullary rod could be of the modular neck type, that is to say comprising a medullary part 2 and a series of necks distinct from this part 2, these being able to be adapted on the latter as required.

Claims (7)

 1 - Medullary prosthesis stem, in particular femoral hip prosthesis stem, consisting of a tapered medullary part (2), a neck (4) and a joint head fixed on the free end of the collar, characterized in that it comprises  - a hole (5) arranged through the metaphyseal zone (2a) of the tapered medullary part (2), in the frontal plane, so that one of its orifices opens onto the external side of the rod (1 ) and that the other orifice opens on the internal side of the latter, this hole (5) being inclined at approximately 45C relative to the longitudinal axis of the rod (1) and its orifice located on the external side being more close to the proximal end (2c) of the rod (1) than the hole opening on the internal side, and  - Several stepped transverse holes (6, 7, 8, 6a, 7a,), extending over a significant part of the length of said medullary part (2), at least one of which is arranged in a plane and of which at least one another is arranged in a plane substantially perpendicular to this plane, the hole or holes (6, 8, 6a) arranged in a plane being alternated with the hole or holes (7, 7a) arranged in the other plane, and the spacing between two consecutive holes being of the order of 1.5 centimeters, bone screws (40) being intended to be engaged through these different holes (5, 6, 7, 8, 6a, 7a) to lock the rod ( 1) to the bone (3).  2 - Rod according to claim 1, characterized in that it is a rod called "first line", that is to say intended to be implanted for the first time in a bone.  3 - Rod according to claim 1 or claim 2, characterized in that it is a rod called "recovery", that is to say replacing a rod implanted for the first time in a bone.  4 - Rod according to one of claims 1 to 3, characterized in that the stepped transverse holes (6, 7, 8, 6a, 7a) above are arranged, for some, in the frontal plane and, for others, in the sagittal plane.  5 - Rod according to one of claims 1 to 4, characterized in that it comprises a material capable of promoting osteointegration by bone regrowth, in particular a porous coating of calcium hydroxyapatite.  6 - Bone screw locking to the bone of the rod according to one of claims 1 to 5, characterized in that it comprises a body (41) of diameter slightly smaller than that of the holes (5, 6, 7, 8, 6a, 7a) the proximal end of this body (41) is provided with a thread (43) of external diameter greater than that of the body (41), this thread (43) being suitable for fitting into the cortical bone.  7 - Instrument allowing the establishment of the rod according to one of claims 1 to 5, characterized in that it comprises  a part (11) whose shape corresponds to that of the rod (1), pierced with holes (16 to 18) respectively identical to the holes in the rod (1), and  - at least one aiming rod (12, 13) connected to this part (11), which is curved so as to delimit with said part a clearance (20) allowing the introduction of said part (11) into the medullary canal of the bone, this aiming rod (12, 13) comprising portions (21 to 23) respectively oriented perpendicularly to the axes of each of the aforementioned holes (16 to 18) and being pierced with bores respectively coaxial with these holes.