Surgical nail

p0001The invention relates to a surgical nail, in particular an intramedullary nail, according to the preamble of patent claim 1.

p0002The locking of martens nails is a part of the prior art. The introduction of the locking screws or locking bolts (hereinafter only the term locking bolt, which also includes the term locking bolt), into the transverse boreholes of the marrow nail is performed either by means of an imaging method (X-ray control) or a more or less complicated aiming device. In both cases, a certain degree of precision is not to be avoided, ie the screw tip can not be aligned exactly coaxially with the center axis of the transverse bore, but deviates by a certain amount. In order for the locking screw to open into the transverse bore despite this target error and to be able to be passed through it, the external diameter of the screw is undersized relative to the diameter of the transverse bore. If the target accuracy remains within the scope of this underdimensioning, the locking screw can be guided without difficulty through the transverse bore despite the target error. However, because of the under-dimensioning, the locking screw now has a certain clearance relative to the transverse bore.

p0003This game defines the amount by which the main bone fragments, which are fixed by means of locking screws in the corresponding locking hole, relative to the nail and therefore due to the rigidity d can it nail relative to other main bone fragments attached to the same nail move. In order to guarantee the applicability of the lock to the surgeon, this game is unavoidable, but it is clinically undesirable in certain indications (eg in the case of metaphyseal fragments).

p0004Even nails with a full cross-section, which can have an internal thread in the locking hole, are not play-free. The internal thread only prevents the nail from moving axially on the locking screw.

p0005From the <patcit id="pcit0001" dnum="WO2004098424A"><text>WO 2004/098424</text></patcit> AESCULAP ​​(basis for the preamble of claim 1), a mark nail with a fixing body for receiving a locking screw is known.

p0006From the <patcit id="pcit0002" dnum="US6296645B"><text>US 6,296,645 HOVER ET AL</text></patcit>. A hollow, intramedullary mark nail made of metal is known which has one or two plastic inserts through which the locking screw can be inserted in the diametrically opposite lateral openings of the transverse bore designated as windows. A disadvantage of this known mark nail is the fact that the window-like plastic inserts can be pressed in under the loads occurring in clinical use, so that the desired function is lost. However, even with a very careful manipulation, the two plastic inserts should be pressed out of their "window" during the passage of the locking screw, which also leads to a loss of the function.

p0007The invention is intended to provide a remedy. The invention is based on the object of providing a surgical nail, in particular an intramedullary nail nail, with which the existing clearance between it and the locking screw is eliminated without risk, and an improved holding force can be achieved between the locking screw and the nail without the user having increased precision In his work.

p0008The invention solves the set problem with a surgical nail which has the features of claim 1.

p0009The following advantages can thus be achieved:<ol><li>(A) the accuracy of the target during the insertion of the locking screw is unaffected;</li><li>B) Nail and insert can be sterile packed separately and the surgeon can choose whether to use the nail without insert or insert. In the latter case, the surgeon can insert the insert himself into the nail and, if necessary, also remove it again. If the surgeon uses the nail without insert, it remains sterile for further use. The physician can thus choose whether or not to use an angularly stable locking of the locking screw, whereby the term "angle-stable" means a restriction of certain degrees of freedom.</li><li>C) Possibility of the angular stability of the bone fragment in certain directions for a certain amount of the load.</li></ol>

p0010A preferred development of the invention consists in the fact that the insert is of rod-shaped design and can be introduced through the longitudinal bore of the nail into the region of the transverse bores. The surgeon can also insert the insert after implantation of the nail (without insert) by advancing the insert from the proximal into the longitudinal bore into the area of ​​the transverse bores.

p0011The material m of the insert preferably has a lower compressive strength f_d &lt;F_d As well as a lower tensile strength f_e.g., &lt;F_e.g., Than the material M.

p0012The modulus of elasticity "e" of the insert is preferably "e" &lt;0.8E and typically "e" &lt;0.7E.

p0013In a particular embodiment, the material m of the insert consists of a biocompatible plastic, preferably a polyethylene or a high molecular weight polyethylene (HMWPE). This has the advantage that no degradation of the plastic with unknown degradation products takes place.

p0014In an alternative, the material of lower hardness introduced into the longitudinal bore of the hollow nail consists of a bioresorbable plastic, which is preferably a polylactide. This embodiment initially results in a clearance-free transverse locking of the medullary nail, which is then successively relieved again with increasing absorption of the polymer, so that the transverse locking screw is again movable relative to the medullary nail and thus also the supplied bone fragments. Thus, the bone fragments are dynamised after fracture consolidation.

p0015A further advantage of the bioresorbable material is that the chips which are produced by the nail when a locking screw is screwed through can be removed from the body.

p0016In a further embodiment, the nail has at least two transverse bores, preferably at least three transverse bores.

p0017One of the transverse holes can also be designed as a long hole with the cross-sectional profile F, the longer dimension "a" of the elongated hole being arranged in the axial direction of the nail.

p0018The material "m" of the insert also preferably has a lower density ρ₁ As the material M with the density ρ₂ , Wherein preferably ρ₁ &lt;0.8 ρ₂ Is.

p0019The nail can comprise a locking screw which can be inserted into the transverse bore (with the cross-sectional profile F) and through the insert or a locking bolt whose external thread or its helical shaft has an external diameter "d" which obeys the condition a> d <b.

p0020The diameter of the longitudinal bore of the nail in the direction of its central axis can be variable and the longitudinal bore preferably has a circular shoulder.

p0021In a further embodiment, the rod-shaped insert can also have a recess which extends radially, transversely to its longitudinal axis. Thanks to this recess, a locking screw or locking bolt can be more easily centered and drilled through the insert, resulting in less chips of material "m".

p0022The insert can also have a plurality of indentations which are arranged in the same way as the transverse bores of the nail.

p0023In a further embodiment, the rod-shaped insert can be designed conical. Thanks to this form, the insert can be inserted more easily from the distal into the longitudinal bore of the nail, and a press fit is also possible.

p0024In a further embodiment, such as the rod-shaped insert and the wall of the nail, co-operating means, preferably in the form of a groove and a mating projection which rotatably fixes the insert into a predetermined position relative to the nail.

p0025The rod-shaped insert can have one or more elevations running radially transversely to its longitudinal axis. These elevations can be arranged in the same way as the transverse holes in the nail. The elevations have a transverse expansion "x" which is advantageously in the ratio 1 &lt;x / q &lt;2, where "q" is the diameter of the insert (7). The advantage of this embodiment is that the elevations during insertion of the insert Into the longitudinal bore of the nail into the transverse holes so that the insert is clearly and securely positioned in the nail. In addition, the increased displacement volume results in an improved holding force, ie an increased angular stability.

p0026The nail can already be made available to the surgeon by means of an insert introduced into its longitudinal bore as far as the region of the transverse boreholes, or alternatively as separately packaged parts.

p0027The nail can be used together with a locking screw with a screw shank and an external thread, whereby the diameter d of the screw thread is> d <b, and "d" is preferably at least 5% smaller than the smaller of the two dimensions a, b.

p0028For producing the nail, a solid body made of a material "m" can be inserted into the longitudinal bore of the nail from the upper or lower end of the nail (of the material M) so that the solid body comes to rest at least in the region of one of the transverse bores of the nail .

p0029The invention and further developments of the invention are explained in more detail below with reference to the partial schematic representations of several exemplary embodiments.

p0030Show it:<ul><li><figref idrefs="f0001">FIG</figref> A longitudinal section through a hollow marker nail partially filled with a softer material;</li><li><figref idrefs="f0001">FIG</figref> A cross-section of the medullary nail in the region of the transverse bore;</li><li><figref idrefs="f0001">FIG</figref> An insert of biocompatible plastic for the introduction of distal into a hollow marker nail with radial countersinks, respectively, through-holes, corresponding to the position of the transverse bores in the nail nail;</li><li><figref idrefs="f0002">FIG</figref> A cross-section of the medullary nail in the region of the transverse bore with a rotational-securing insert;</li><li><figref idrefs="f0002">FIG</figref> A view of a rotationally securing insert of biocompatible plastic for the introduction of distal into a hollow nail with radial elevations corresponding to the position of the transverse bores in the nail;</li><li><figref idrefs="f0002">FIG</figref> A longitudinal section through an insert of biocompatible plastic for insertion from the proximal into a hollow marrow nail;</li><li><figref idrefs="f0002">FIG</figref> A longitudinal section rotated through 90 ° through the insert <figref idrefs="f0002">FIG</figref>; and</li><li><figref idrefs="f0002">FIG</figref> A view of an insert for insertion proximally over the entire length of the hollow marrow nail.</li></ul>

p0031The <figref idrefs="f0001">FIG</figref> Is a intramedullary nail for tubular bones with a central axis 2 which consists of a material M (metal or metal alloy) and has three transverse bore 5 with a diameter D and a transverse axis 6 extending transversely to the central axis 2.

p0032A fourth transverse bore is mounted proximally and is designed as a long hole 20, the longer dimension being arranged in the axial direction. Two of the three transverse bores 5 are arranged in the distal part of the marrow nail 1.

p0033The medullary nail has a longitudinal bore 3 running coaxially with the central axis 2 and thus a wall 4. A rod-shaped insert 7 (<figref idrefs="f0001">FIG</figref>) In the form of a one-piece solid made of resorbable polylactide, so that the longitudinal bore 3 is filled in the region of the two distal transverse boreholes 5 with a material m of lower strength, in particular a lower modulus of elasticity (compared to the material M of the intramedullary nail). However, a press fit of the material m is also possible.

p0034As in <figref idrefs="f0001">FIG</figref> A locking screw 21 with the shank 22 and the external thread 23 can be screwed into the transverse bore 5 and thus through the insert 7.

p0035The insert 7 has a continuous longitudinal bore 8 coaxial with its longitudinal axis 13 and, at its distal end, a hemispherical extension 11 with a stop 10 directed towards the proximal end. A secure axial positioning of the insert 7 in the longitudinal bore 3 occurs through the stop 10 of the enlargement 11 Of the marknagel.

p0036The insert 7 has four radial depressions 12 which extend transversely to the longitudinal axis 13 and are arranged axially such that they lie at the same height as the transverse holes 5 of the medullary nail when the insert 7 is inserted into the longitudinal bore 3 as far as the stop 10 Is. In order that the indentations 12 are also aligned radially with the bores 5, the insert 7, as shown in FIG<figref idrefs="f0001">FIG</figref> Has a profile 15 which corresponds to a profile 16 in the longitudinal bore 3 of the medullary nail so that the insert 7 can only be inserted into the longitudinal bore 3 in a specific rotational position.

p0037As in <figref idrefs="f0002">FIG</figref> The insert 7 and the longitudinal bore 3 of the medullary nail can also have two ribs / grooves 17, 18 instead of the profiles 15, 16 in the form of flattenings, which effect the same effect of the rotational blocking.

p0038In <figref idrefs="f0002">FIG</figref> An alternative to the insert 7 is then followed <figref idrefs="f0001">FIG</figref> In which, instead of the depressions 12, elevations 14 are present which, owing to their elasticity, can snap into the openings of the transverse bores 5 in the wall 4 so that an axial and rotational securing of the insert 7 can also be achieved. The transverse expansion x of the elevations 14 is in the ratio 1 &lt;x / q &lt;2, where q is the diameter of the insert 7.

p0039In the <figref idrefs="f0002">FIGS. 6 and 7</figref> A further alternative insert 7 is shown which can be introduced from the proximal to the longitudinal bore 3 of the marrow nail instead of from the distal direction. It has an axial longitudinal bore 8, as well as an elongated hole 19 corresponding to the long hole 20 in the marker nail 1. The elongated hole 19 is approximately elliptical with a long axis a and a short axis b.

p0040In <figref idrefs="f0002">FIG</figref> A further embodiment of an insert 7 is shown which has approximately the same length as the medullary nail and thus covers all transverse bores 5 (locking bores) of the medullary nail from proximal to distal. The insert 7 is fixed by a thread 24 in the proximal region of the insert 7 in the hollow marker nail. If necessary, the insert 7 can also be shortened intraoperatively.