FR2846545A1 - Intramedullar osteosynthesis implant used, eg, for the fixing of finger or toe interphalangeal joints damaged by osteoarthritis, made of memory material and expanding at body temperature to provide a secure grip - Google Patents

Abstract

An intramedullar osteosynthesis implant, permitting arthrodesis of a joint or diaphysary osteosynthesis of an upper or lower limb comprising two groups of at least two prongs extending either side of a central zone, which are parallel at ambient temperature which are intended to be implanted in the medullary canal of a diaphysis and are made of memory material in such a way that at body temperature they spread out an lock into the canal. At body temperature the prongs spread apart in the same plane. In an alternative version comprising two sets of three prongs, the outer prongs spread apart in the same plane and the central prong in a direction perpendicular to it. At ambient temperature the planes of each group of prongs form an angle of 0-60degrees and preferably about 10degrees. The ends of the prongs may be chamfered. The length of the pairs of prongs may differ, the longer pair being intended for implant into the joint or the proximal diaphysis. The implant is implemented in a titanium-nickel alloy. This comprises 50-60 % titanium and 40-50% nickel. It is preferably 55% titanium and 45% nickel.

Description

IMPLANT OF INTRAMEDULAR OSTEOSYNTHIESE

  Technical field The invention relates to the field of surgical treatment of joint lesions with arthritis and / or deformation of the joints of the upper and lower limbs, with the therapeutic aim of blocking the joint

by bone fusion.

  It relates more particularly to an arthrodesis implant and a method

  surgical treatment of degenerative or post traumatic osteoarthritis and joint deformities using the placement of such an implant.

  The implant is also used as a means of intramedullary osteosynthesis when bone fusion is sought in surgery

trauma or resolved.

  In this application, the aim is to obtain fusion and bone consolidation of a diaphyseal or articular bone by an intramedullary implant. Prior techniques In general, osteoarthritis of the inter-phalangeal joints, whether

  of the foot or hand, is quite frequent, since it is considered to affect around 20% of the population after 55 years, and 40% after 70 years.

  In practice, this osteoarthritis manifests itself by pain, in particular when the patient performs the pincer movement between the thumb and the index or middle finger, which are the most stressed fingers. This arthritis causes different types of deformities, whether the presence of Heberden's nodules, or even angulations or rotations between the phalanges. These deformations generate difficulties in performing a clamp, or cause instabilities in the joint which cause discomfort in performing movements requiring a certain

precision or sufficient force.

  In practice, when the osteoarthritis is relatively weak, whether in

  term of intensity, pain or degree of deformation, applications of anti

  inflammatory, or even local corticosteroid injections may be sufficient to treat early forms. On the other hand, for advanced forms, surgical treatment is the most appropriate. It consists of an arthrodesis of the inter-phalangeal joint, consisting in suppressing the mobility of the joint by causing a bone fusion of the two phalanges concerned.

  Various techniques have already been proposed for carrying out this arthrodesis.

  Thus, bone fusion generally requires a bone cut of the ends of the facing articulars. Many forms of cut have already been proposed, in the shape of tenons or chevrons, or even using

  concave and convex shapes. However, the plane cut is the most used.

  This bone cut is accompanied by the installation of osteosynthesis material which can be of different types.

  Thus, osteosynthesis can be obtained by Kirschner wires with or

  without steel wire strapping, or even by Herbert screws.

  These different osteosynthesis materials generate annoying constraints

  for the patient. Indeed, they generally require immobilization by splint of the joint for several weeks, the time to obtain bone consolidation. It is also necessary to perform a secondary removal of the material after a few weeks, which then leads to a new intervention under anesthesia with additional skin incisions.

  In addition, the pins under the pulp can cause pain, ulceration, or even infection, or even skin perforation. In any event, they cause significant functional discomfort, most often resulting in the fact that the patient no longer uses his finger.

for quite a long time.

  In addition, in about 20% of cases, this arthrodesis causes major complications, among which we can cite osteitis, deep infections, or even poor positions of the two phalanges after bone fusion. Other complications, less significant, are observed in approximately 5 16% of cases, among which we can cite skin necrosis, scar dysesthesia, cold intolerance, superficial infections, or even stiffness of the inter- proximal phalangeal of the same finger. A problem which the invention proposes to solve is to eliminate the drawbacks due to the need to remove all or part of the osteosynthesis material. Another problem which the invention seeks to solve is that of allowing a particularly solid arthrodesis, ensuring fusion of the joint considered. Another objective of the invention is to give the patient the possibility of re-using the operated finger as quickly as possible in the immediate postoperative without being hindered by the osteosynthesis material, and while having a particularly stable osteosynthesis . Another problem which the invention seeks to solve is that of the complications (skin ulceration in the pulp, pulp scar, exclusion of the finger, etc.) which generate osteosynthesis materials.

  existing, at the ends of the fingers.

  DESCRIPTION OF THE INVENTION The invention therefore relates first of all to an intramedullary osteosynthesis implant for arthrodesis and diaphyseal osteosynthesis. By arthrodesis is meant the articular fusion of the joints accessible to intramedullary osteosynthesis of the upper and lower limbs, among which there may be mentioned the proximal and distal inter-phalangeal joints, the inter-phalangeal thumb joint, but also the metacarpophalangeal joints, as well that the carpal and radiocarpal joints The invention also relates to the joints of the lower limb for the

  treatment of osteoarthritis, but also deformities such as claw toes. These include the treatment of interphalangeal joints, metatarsophalangeal joints, as well as tarsal and tibio5 tarsal joints.

  By intramedullary diaphyseal osteosynthesis is meant the application of the implant for the purpose of obtaining a diaphyseal bone fusion in trauma contexts (such as open diaphyseal fractures, joint destruction, replanting of the fingers) or surgery settled (such as

  diaphyseal osteotomy or joint transfer).

  According to the invention, this implant comprises two sets of at least two rods, and in practice two sets of two or three rods, without however excluding a possibly greater number of rods per set. Within a single assembly, these rods are substantially in the same plane and parallel to each other at room temperature. Each set of rods extends on either side of a central zone. Each set of rods is intended to be impacted in the diaphyseal spinal canal. The implant is made from a shape memory material, so that at body temperature, the rods of the same assembly move apart, so that they can be blocked in the medullary canal. In other words, in the version with two pairs of rods, the implant comprises four rods connected two by two in pairs to form a general configuration in H which, when the temperature rises, deforms to conform to a general form in X. When the implant is at room temperature, the rods of the same pair are parallel, thus allowing easy placement in orifices made for this purpose in the articular metaphysis. When the implant is exposed to a higher temperature, including body temperature, the stems

  move away, and anchor the implant in the diaphysis.

  Advantageously in practice, at body temperature, the rods of the same pair deviate in the same plane as that defined when they are parallel to

ambient temperature.

  In an alternative embodiment, the implant comprises two sets of three rods forming a hexapod implant. At room temperature, the three rods of the same assembly are substantially in the same plane and parallel to each other, forming a fork with three branches or parallel trident. Each trident is intended to be impacted in the diaphyseal medullary canal, and at body temperature, the external rods of the same pair deviate and diverge while remaining in the same plane, while the central rod deviates in a plane substantially perpendicular to the plane of the external rods. The three rods are blocked in the medullary canal against the internal wall of the diaphysis of the bone, forming a double diverging tripod which ensures a particularly stable osteosynthesis. 15 Advantageously in practice, at room temperature, the planes defined by

  each set of rods form between them an angle of between 0 and 600, making it possible to adjust the inclination or flexum of the arthrodesis, that is to say the angulation between the bony structures (joints, diaphyses) once they are blocked. 'one over the other.

  Preferably, this angle of inclination or flexum, which therefore corresponds to the angle defined between each pair of rods, varies according to the type of arthrodesis or diaphyseal osteosynthesis to be performed. 25 In practice, to facilitate implant impaction, the ends of each

rod can be bevelled.

  In a particular embodiment, the two pairs of rods can have different lengths, the longest pair of rods being intended to

  be impacted in the proximal joint or shaft.

  In practice, the shape memory material used to obtain the characteristic deformation can be based on an alloy of titanium and nickel, such as for example the alloy known under the name of Nitinole. More specifically, the alloy used comprises between 50 and 60% of titanium, and between 40 and 50% of nickel. 5 The alloy which gave the best results comprises approximately 55% of titanium and approximately 45% of nickel. This alloy is relatively malleable when it is in a martensitic stage, when the implant is in the form of H. It then evolves towards a very resistant austenitic stage when the implant marries an X shape. The deformation of the implant therefore takes place between the temperature of 220C, 10 corresponding to the conditions of installation of the material, and the temperature of 370C, where the

  material finishes its deformation, and ensures the stability of the assembly.

  In practice, the effort measured at the end of the rods of an implant of the order of 10

  millimeters in length varies from 1.5 Newtons at a temperature of 20 ° C, to a value of 13 Newtons at 370C.

  The invention therefore allows the realization of an intramedullary osteosynthesis in order to obtain a bone fusion either articular (arthrodesis) or diaphyseal. The indications are the treatment: * joint deformities which require arthrodesis; * degenerative and post-traumatic arthritis;

  * diaphyseal osteosynthesis in trauma and regulated surgery.

  More specifically, the operating procedure for placing this implant comprises the following 25 steps: * incision of the dorsal surface of the joint; * release of the proximal and distal ends of the joint or of the diaphyses of the joint, in particular by a dislocation of this joint, and therefore the release of the lateral ligaments of the joint; 30 * resection of the ends of the articular bones to obtain surfaces which, when in contact, reproduce the desired angulation after bone consolidation: o for arthrodesis, the angulation carried out during bone cross-cutting depends on the type of joint (as for example, 100 for the distal interphalangeal joint) o for intramedullary diaphyseal osteosyntheses, it is generally not necessary to have angulation, and

  bone cuts parallel to each other.

  * drilling holes (two or three depending on the implant model) in the medullary canal on the proximal bone and then on the distal bone using a

  adapted ancillary or using wicks and an osteosynthesis motor.

  impaction of the implant in the orifices of the proximal bone, then impaction of the distal bone in the distal stems of the implant (two or three rods according to

the implant model).

  A so-called "phantom" implant makes it possible to simulate arthrodesis or definitive diaphyseal osteosynthesis before the implantation of the shape memory implant. This "phantom" makes it possible to correct a possible error in the position of the implant, and in particular the angulation defects in the three frontal, sagittal and horizontal planes.

Summary description of fi2ures

  The manner of carrying out the invention, as well as the advantages which flow therefrom

  will emerge clearly from the description which follows, in support of the figures appended in

which:

  Figure 1 is a top view of an implant according to the invention, comprising two pairs of rods, and shown at room temperature.

  Figure 2 is a side view of the implant of Figure 1.

  Figure 3 is a top view of the implant of Figure 1, shown at

human body temperature.

  Figure 4 is a top view of an implant according to an alternative embodiment of the invention, comprising two sets of three rods, shown in

ambient temperature.

  FIG. 5 is a side view of the implant of FIG. 4.

  Figure 6 is a top view of the implant of Figure 4, shown in

human body temperature.

  FIG. 7 is a side view of the implant of FIG. 4, shown at

human body temperature.

  FIGS. 8 to 16 are views from above and from the side showing the procedure for placing the implant of FIG. 1, as the implementation progresses on the example of a joint

distal interphalangeal.

  Figures 17 and 18 are schematic representations respectively from above and from the side of a finger in which the implant according to the invention has been placed

  in place, and after bone fusion of the phalanges.

  Manner of Carrying Out the Invention The arthrodesis implant (1) illustrated in FIG. 1, comprises two pairs of rods (2, 3, 4, 5) which are substantially parallel, and connected to a central portion (6), so that the implant (1) follows a general H shape. The implant illustrated in FIG. 1 is used mainly for arthrodesis of the distal inter-phalangeal joint of the hands and of the proximal interphalangeal joints of the toes. This implant has a total length of

around 14 millimeters.

  The total width of the implant (1), in the configuration at room temperature illustrated in FIG. 1, is of the order of 4.5 millimeters. Each rod has a width of the order of 1.1 millimeters. The stems of the same pair are

  separated by a space of the order of 4.5 millimeters.

  In the illustrated form, the rods (2, 3), intended to be impacted in the proximal articulation or shaft are slightly longer than the rods (4, 5) intended to be impacted in the distal articulation or shaft. . More specifically, in the example corresponding to the distal interphalangeal joint of the fingers, the longest rods (2, 3) have a length of the order of 8

  millimeters, the shortest stems (4, 5) having a length of 6 millimeters.

  As illustrated in FIG. 2, each pair of rods (2, 3, 4, 5) fits in a plane (P23, P45). In the illustrated form, the planes (P23, P45) form an angle ac of the order of 10 between them. This angle a corresponds substantially to the angle imposed on the phalanges connected by the implant, and therefore defines the flexum of the arthrodesis.

  However, it will be noted that this angle a may vary depending on the type of joint in the hand and on the foot on which it is desired to perform an arthrodesis. In practice, it can vary from 0 to 60, and for diaphyseal osteosyntheses, it is often 00. As illustrated in FIG. 2, we observe that the ends of the rods (2, 3, 4, 5) are slightly bevelled , so as to allow their good penetration into the proximal and distal impaction orifices made in

  articular bone surfaces after cutting adapted to the desired angulation.

  According to an important characteristic of the invention, the implant is made of a shape memory material, as described above, which allows the rods 20 (2, 3, 4, 5) to diverge when the temperature of the implant passes temperature

  room temperature, around 20 C, at human body temperature, 37 C.

  More precisely, this shape transition takes place from 22 C, and up to

about 37 C.

  The shape illustrated in Figure 3 shows the implant at a temperature of 37 C, in which the rods (2, 3) and (4, 5) form an angle 13 of the order of 20 on each other.

  a free implant without bone constraint.

  This angle, when the implant is in the bone, varies as a function of the bone resistance that it encounters in the metaphysis or in the diaphysis. The angle is opened in an osteoporotic bone of low resistance, while it is closed in a resistant bone, because in this case the stresses applied against the bone walls

diaphyseal are more important.

  As already mentioned, the invention also covers implants of more complex shapes. Thus, the diaphyseal arthrodesis or osteosynthesis implant (40) illustrated in FIG. 4, comprises two sets of three rods (41-46) which are substantially parallel, and connected to a central portion (47), such so that

  the implant (40) follows a form of double trident.

  The implant illustrated in FIG. 4 is used especially for arthrodesis of the "large" joints of the upper limb and the lower limb, among which there may be mentioned in particular the proximal interphalangeal joints of the hands and toes, the metacarpophalangeal and metatarsophalangeal joints. . This implant (40) has a total length which can range from 15 to 17 mm for the proximal interphalangeal joints, up to approximately

  33 mm for the metatarsophalangeal joints.

  The total width of the implant (40), in the configuration at ambient temperature illustrated in FIG. 4, is of the order of 5 millimeters. Each rod (41-46) 20 has a width of the order of 1.5 to 2 millimeters. The stems of the same trio are

  separated by a space of the order of 1.5 millimeters.

  In the illustrated form, the rods (41-43), intended to be impacted in the joint or the proximal diaphysis, are slightly longer than the rods (44-46) intended to be impacted in the joint or the diaphysis distal. More precisely, in the example corresponding to the proximal interphalangeal joint of the fingers, the longest rods (41-43) have a length of the order

  10 mm, the shortest rods (44-46) having a length of 7 min.

  As illustrated in Figure 5, each set of rods (41-46) fits into a plane (P41, P44). In the illustrated form, the planes (P41, P44) form between them an angle oa which varies from 0 'to 60 depending on the joint or the diaphysis concerned. This angle ai corresponds substantially to the angle imposed on the phalanges or the mecarpus or metatarsal connected by the implant, and therefore defines the flexum of the arthrodesis. This angle ca varies according to the type of joint in the hand and the foot

  on which one wishes to perform an arthrodesis.

  As already mentioned, the implant is made of a shape memory material, as described above, which allows the outermost stems (41, 42; 44,45) to diverge and deviate in the planes ( P41, P44), when the temperature of the implant changes from ambient temperature, of the order of 20 ° C., to the temperature of the human body, of 370 ° C. At the same time, the central rods (43,46) move apart while moving in a plane substantially perpendicular to the planes of

  displacement (P41, P44) of the outermost stems.

  The shape illustrated in FIG. 6 shows the implant at a temperature of 37 ° C, in which the external rods (41,42) and (44,45.) Form an angle Pl of them

  around 200 on a free implant without bone stress.

  The angle y illustrated in Figure 7, corresponds to the angle of divergence of the rods

  central (43,46) in a vertical plane relative to the planes (P41, P44) of the external rods (41,42; 44,45).

  As already mentioned, the invention also relates to the method of placing this implant at the level of an inter-phalangeal joint. In the example illustrated in FIGS. 8 and 15, the implant is placed on a distal intei-phalangeal joint 25 where the lateral strips of the tendon apparatus

  extensor are sectioned. However, it goes without saying that the operating procedure for placing the implant can be easily transposed to other joints of the upper limb or lower limb while respecting the tendon extensor apparatus and depending on the joint or the diaphysis the surrounding soft anatomical structures (vessels, nerves, tendons, etc.).

  On larger joints than the distal inter-phalangeal joint, hexapod implants are available as illustrated in FIGS. 4 to 7, which provide even greater stability to osteosynthesis, in particular in the case of the inter-phalangeal, metacarpal joints. phalangeal but also the carpal and foot joints. The operating technique varies according to the type of joint, and the example given

  below relates to the arthrodesis of the distal interphalangeal joint of a finger, it being understood that the procedure for the other applications of the invention can be deduced therefrom without difficulty for those skilled in the art.

  Thus, the establishment of the implant first requires making, as illustrated in FIG. 8, an H-shaped incision (10), at the level of the dorsal face (11) of the distal interphalangeal joint. . 15 As illustrated in FIG. 9, the next operation consists in releasing the head (12)

  of the middle phalanx P2 and the base (13) of the distal phalanx P3. This release consists first of all in effecting a dislocation of the joint by releasing the lateral ligaments connecting the phalanges P2 and P3. In the palmar area of the joint, the palmar plate will be fully released at its proximal portion.

  After section of the lateral ligaments and bone cut of the base of the distal phalanx (P3) and the head of the middle phalanx (P2), a space between the two phalanges (P2, P3) greater than 6 mm is obtained after distraction. This space is intended to allow passage of the distal stems of the implant and therefore the impaction of the distal phalanx (P3) on the stems.

  Thereafter, as illustrated in FIG. 10, a resection of the

  osteophytes present on the ends of the two phalanges (P2) and (P3).

  Next, a bone cut is made of the head (12) of the middle phalanx P2 and of the base (13) of the distal phalanx (P3), so as to produce surfaces (14, 15) in very slight palmar inclination for reproduce the angle a of

  of the implant when it is intended for a third finger (middle finger).

  Thereafter, and as illustrated in FIG. 11, one proceeds to the production of orifices (16, 17) in the medullary canal of the middle phalanx (P2). These orifices (16, 17) are produced using an ancillary device (20) comprising a gripping handle (21) extending by two parallel points (22, 23), and having a spacing similar to that of the rods ( 2, 3) of the implant (1). More specifically, the production of the orifices (16, 17) may require, after drilling by the ancillary 10 (20), the use of specific graters making it possible to give the orifices (16, 17) the

  diameter corresponding to that of the rods (2, 3) of the implant (1).

  Thereafter, the same procedures are carried out for the orifices (26,

  27) in the medullary canal of the distal phalanx (P3), as illustrated in Figure 15 12.

  A "phantom" implant will make it possible, before the placement of the final implant, to verify the correct position of the orifices and therefore the absence of angulation (in a horizontal plane) or of rotation (in a frontal plane) at the level of the future arthrodesis. Thus, it is possible to check the correct scaphodian convergence 20 when the fingers are closed and the functional aspect (satisfactory flexum) and

  final esthetics of the finger before the placement of the final implant.

  The final implant is protected in two cylinders, a long proximal and a

  short distal in which the stems are embedded. These cylinders protect the rods 25 to keep them parallel to each other during their conditioning.

  Thereafter, and as illustrated in FIGS. 13 and 14, the long proximal rods (32, 33) are positioned opposite the orifices (16, 17) produced on the middle phalanx P2. One of the conditioning cylinders forming an impactor 30 (30) facilitating the manipulation of the implant, will make it possible to introduce the latter into the orifices (16,17) of the middle phalanx. Subsequently, as illustrated in FIG. 15, the implant (1) is definitively placed, ensuring the impaction of the distal phalanx (P3) on the distal pair of rods (4, 5) of the implant.

  As illustrated in FIG. 16, the flat walls of the two middle phalanxes P2 and distal P3 come into contact with one another. Care must be taken to obtain very good bone contact with no free space at the focal point of the arthrodesis.

  Thereafter, a final verification of the correct orientation of the finger as well as the compressive effect on the focal point of the arthrodesis is carried out by impacting the distal phalanx (P3) on the middle phalanx (P2), before proceeding suturing previously cut skin surfaces. Then we proceed with the release of the tourniquet which causes the temperature rise. The implant then deforms and stresses against the diaphyseal walls of the medullary canal, thus ensuring a

very stable osteosynthesis.

  The procedure in the use of hexapod implants as illustrated

  in Figures 4 to 7 varies depending on the type of joint or shaft treated.

  In the case of more "voluminous" joints of the upper limb or of the lower limb, namely proximal inter-phalangeal, metacarpo-phalangeal, metatarsophalangeal, etc. joints, it is important to carry out an approach which preserves the extensor apparatus by making incisions in the axis of the tendon and without disinsertion to preserve the tendon function especially

  for the more distal joint (s).

  25. Different tests have been carried out on twelve different patients, for eighteen different interventions, concerning the inter-phalangeal joints of the index, middle and little fingers of the hand. More specifically, six interventions are

  intervened on indexes, five on adults, and seven on little fingers.

  Among the patients, ten were female and two male, with an average age of 56 years, distributed between 39 and 75 years. Seven of the twelve patients were of working age, of which three were engaged in manual labor professions, three other patients were in the profession of

  secretary, the last of the assets being a musician.

  In 80% of cases, operations were carried out on the dominant hand.

  Among these twelve patients, the preoperative evaluation revealed

  pain at rest in 58% of cases, and pain in mobilization in 83% of cases. In 83% of cases, these pains were disabling, and in 58% of cases, they were revealed during thermal variations. In 41% of the cases, an analgesic treatment was prescribed.

  In 83% of cases, distortion of the distal interphalangeal joint

  was considered annoying. In 67% of the cases, the mobility of the joint was considered to be severely decreased, and in the remaining 33% considered to be slightly decreased.

  After intervention in accordance with the invention, an evaluation of the

complications was performed.

  Among the complications considered as minor, it was observed in% of the cases of dysesthesia at the level of the scar, and 25% of cold intolerance. On the other hand, no skin necrosis, superficial skin infection, nail dystrophy, or stiffness of the proximal interphalangeal joint was observed. Among the complications considered major, no osteoarthritis of the distal interphalangeal joint was observed, and no case of

  poor position, both in rotation and angulation.

  A case of pseudo arthritis and algodystrophy was identified in the same patient, after six months, this complication having then disappeared after 6

  months at late radiographic control.

  In functional terms, from the immediate post-operative (24 to 48 hours), patients can normally use their hand in flexion-extension of the fingers, but without exerting any stress at the focal point of the arthrodesis. It is from the fourth week, but with a delay of up to 6 months, 5 that bone fusion takes place (radiological bone consolidation). The osteosynthesis material being purely intramedullary without externalization to the skin,

  the use of the hand is possible from the day after the intervention.

  Figures 17 and 18 correspond to illustrations made from 10 x-rays and taken between the second and sixth month, showing a fusion

  significant bone, presenting a character of solidity quite satisfactory.

  It appears from the above that the implant according to the invention, as well as the surgical method of treatment of arthrosis by arthrodesis and of intra-medullary diaphyseal osteosynthesis has multiple advantages, and in particular that of allowing osteosynthesis stable from the immediate post-operative period, without any approach or pulp material, in comparison in particular with the osteosynthesis pins used to date. Thanks to a stable osteosynthesis, the implant placed in accordance with the invention allows early mobilization, and rapid use of the hand without a splint from the postoperative period.

  immediate without waiting for the sometimes considerably long delays in bone fusion confirmed on radiography. This bone fusion, and this whatever the technique, can take months to occur due to the stability of the osteosynthesis.

  The intramedullary osteosynthesis implant according to the invention eliminates the need to wait for this radiological bone fusion.

  In addition, the surgical technique for placing the implant is simple,

  reproducible and fast. In most cases, an ancillary device makes it possible to do without the osteosynthesis motors and therefore to avoid the economic overload of sterilization and the conditioning of an osteosynthesis motor.

Claims (9)

  1 / Intramedullary osteosynthesis implant, in particular allowing arthrodesis (1) of a joint, or diaphyseal osteosynthesis of the upper limb or of the lower limb, comprising two sets of at least two rods (2, 3, 4, 5) each extending on either side of a central zone (6), said rods being substantially parallel at ambient temperature within the same set, each set of rods (2, 3; 4, 5), being intended to be impacted in the medullary canal of a diaphysis, said implant being made from a material 10 with shape memory, so that at body temperature, the rods (2, 3; 4 , 5) of the same assembly move apart so as to be able to block in said medullary canal. 2 / implant according to claim 1, comprising two sets of two 15 rods, characterized in that at body temperature, the rods (2, 3; 4, 5) of a   same whole deviate in the same plane.   3 / Implant according to claim 2, characterized in that at temperature   ambient, the planes (P23, P45) defined by each set of rods (2, 3; 4, 5) 20 form between them an angle (a) between 0 'and 600.   4 / Implant according to claim 3, characterized in that the angle (cc) between   the planes (P23, P45) defined by each pair of rods is close to 10.   5 / Implant (40) according to claim 1, comprising two sets of three rods (41-46), characterized in that at body temperature, the external rods (41,42; 44,45) of the same together deviate in the same plane, the central rod   (43,46) deviating outside said plane.   6 / implant according to claim 1, characterized in that the ends of   each rod (2, 3, 4, 5) are bevelled.   7 / implant according to claim 1, characterized in that the two sets (2, 3; 4, 5) of rods have two different lengths, the set of rods (2, 3) the longest being intended to be impacted in the joint or the proximal shaft.   8 / implant according to claim 1, characterized in that it is produced in a   alloy based on titanium and nickel.   9 / Implant according to claim 8, characterized in that the alloy 10 comprises between 50 and 60% of titanium and between 40 and 50% of nickel.   / Implant according to claim 9, characterized in that the alloy   contains about 55% titanium and about 45% nickel.