Surgical nail

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

The locking of martens nails is a part of the prior art. The insertion of the locking screws, or locking bolts (in the following, only the term locking bolt is used but which also includes the term locking bolt) into the transverse boreholes of a 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.

This clearance defines the amount by which the bone main fragments, which are fixed by means of locking screws in the corresponding locking hole, relative to the nail and thus also due to the rigidity of the nail can also move relative to other bone main fragments fastened with the same nail. 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).

Even 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.

From the <patcit id="pcit0001" dnum="US6296645B"><text>US 6,296,645</text></patcit> HOVER ET AL. 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 easily pressed in 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.

Further marknails with inserts are from the <patcit id="pcit0002" dnum="WO9846169A"><text>WO-A-98/46169</text></patcit> and the <patcit id="pcit0003" dnum="US20020173792A"><text>US-A-2002/0173792</text></patcit> known.

The 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 can be eliminated without risk, and an improved holding force and an improved guiding effect between the locking screw and the nail nail can be achieved.

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

The following advantages are thus achievable:<ol><li>(A) the accuracy of the target during the insertion of the locking screw is unaffected;</li><li>B) the physician can still select whether or not to use an angularly stable locking of the locking screw, whereby the term "angularly stable" means a restriction of certain degrees of freedom;</li><li>C) the possibility of angularly stable fixation of the bone fragment in certain directions for a certain amount of the load; and</li><li>D) 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.</li></ol>

In a particular embodiment, the length L of the insert conforms to condition L&gt; 0.5 D and preferably L = D.

In a further embodiment, the insert is substantially congruent with the transverse bore.

In a particular embodiment, the insert may have a bore coaxial with its longitudinal axis to facilitate insertion of the locking screw.

Advantageously, material m of the insert has a tensile strength f_e.g., &lt;F_e.g.,, A compressive strength f_d &lt;F_d And an elastic modulus e &lt;0.8 E, preferably e &lt;0.7 E.

In one embodiment, the material m of the insert is a biocompatible plastic, preferably a polyethylene or a high molecular weight polyethylene (HMWPE), which has the advantage that no degradation of the plastic with unknown degradation products takes place.

A preferred embodiment consists in that the insert of a material of lower hardness is a bioresorbable polymer, 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. The bioresorbable material has the advantage that the chips resulting from the nail when a locking screw is screwed through can be removed from the body. A further advantage consists in the possibility of realizing a possibly temporally different strength of the angularly stable locking of the locking screw, ie achieving a gradual reduction in the holding force.

The cross-section of the mark nail can either be a circular bore, wherein the cross-sectional profile F has the maximum lengths a = b (ie a = b is the diameter of the cross-bore) or else as a long hole .

The material m of the insert advantageously also has a lower density ρ1 than the material M with the density ρ2, with ρ1 being preferably &lt;0.8 ρ2.

The locking bolt or locking bolt which can be passed through the insert should preferably have a shaft with the diameter d (maximum diameter, which also includes any external thread), which is subject to the conditions a&gt; d &lt;b. The diameter d of the helical thread should preferably be at least 5% smaller than the smaller of the two dimensions a, b.

In a special embodiment, the transverse bore expands towards the surface of the nail, preferably in the form of a conical portion. This has the advantage that an insert inserted therein with a corresponding conical section can no longer move axially in the insertion direction.

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

Show it:<ul><li>FIG. 1 is a perspective view of a perforated mark nail with a transverse bore and a suitable insert, as well as a transverse locking screw; FIG.</li><li>FIG. 2 is a longitudinal section through the medullary nail according to FIG. 1;</li><li>3 shows a longitudinal section rotated through 90 ° through the medullary nail according to FIG. 1; FIG.</li><li>FIG. 4 is an enlarged schematic view of the profile of the transverse bore of the medullary nail according to FIG. 1; </li><li>FIG. 5 shows a single-part insert with a longitudinal bore for the transverse bore in the nail nail, which, after insertion, is approximately aligned with the nail closure;</li><li>FIG. 6 shows a partial longitudinal section through a further, modified marker nail with a modified one-part insert; FIG. and</li><li>FIG. 7 shows a partial longitudinal section through a further, modified marker nail with a modified one-part insert.</li></ul>

The surgical nail 1 shown in FIGS. 1-3 is an intramedullary nail for tubular bones with a central axis 2 made of a metal or a metal alloy, ie, a material of relatively high strength (tensile strength F_e.g.,, Compressive strength F_d And modulus of elasticity E). The nail 1 has a transverse bore 3 extending with respect to the central axis 2 and configured as a long hole with the cross-sectional profile F with the transverse axis 4. As shown in FIG. 4, the transverse bore 3 has a cross-sectional profile F which has a maximum length a and, Perpendicular thereto a maximum width b. The nail can also have further cross-bores (circular or oval) which are not shown in the drawing.

As shown in FIG. 1, an insert 10 is provided for insertion into the transverse bore 3. The dimensioning of the insert 10 is congruent with the transverse bore 3, or is selected in such a way that a press fit results during the insertion, as a result of which the insert is prevented from falling out of the transverse bore 3. The insert 10 consists of material m of lower strength, in particular a lower modulus of elasticity (compared to the material M of the marker nail).

As shown in FIG. 5, the insert 10 can have a longitudinal bore 14 coaxial with its longitudinal axis 13 and a transverse bore 24 corresponding to its transverse cross-section 24, which corresponds perpendicularly to its cannulation after its insertion into the medullary nail.

FIG. 6 shows a variant of a one-part insert 10 which consists of a pin 17 with a conical enlarged head 18.

FIG. 7 shows a further variant of a one-part insert 10 which consists of a centrally pierced pin 19 with a plurality of peripheral, conical extensions 20 which extend into corresponding cavities 21 or respectively in the longitudinal bore 23 in the region of the transverse bore 3 in the form of a click closure Can intervene.