DE3201056C1 - Intramedullary nail - Google Patents

Description

The invention relates to an intramedullary nail according to the preamble of claim 1. As a material for In most cases, intramedullary nails are made of stainless steel. .

According to the prior art intramedullary nails usually have an open cross-section with a Form, which is reminiscent of a three-leaf clover and which is intended to prevent the opposite of the Bone drilling with a diameter of 0.5 to 1 mm larger intramedullary nails secured against rotation and nevertheless due to the cross-sectional elasticity resulting from the selected shape in large and whole can be easily inserted into the bone. Nevertheless, when you hit the The forces to be applied by the intramedullary nail are very large, which in individual cases even lead to the bone bursting can. In addition, there is the risk that bone tissue in the intramedullary nails described open longitudinal gap of the nail grows in, which means that the nail can be removed after the healing process has taken place can hinder. After all, there is no possibility of longitudinal anchoring with these intramedullary nails, so that after they have been introduced into the bone they sometimes not only proximally but also distally "hike".

Many attempts have therefore already been made to create an intramedullary nail that also has a Allows longitudinal anchoring after its introduction into the bone.

So for the first time from DE-AS 12 48 228 a device has become known that with one in the A hollow intramedullary nail to be introduced lengthways and one lengthwise of the same penetrating axial tensioner held on both sides of the fracture point works. In addition is for anchoring a screw that penetrates the hollow nail and is inserted in a further surgical procedure must be required.

Similar expansion bodies are also described in DE-PS 22 60 839. However, the spreading devices described there have the disadvantage that their removal can be hindered or even prevented by ingrown bone parts.
An intramedullary nail that can be spread over its entire effective length has also been proposed, which has thin-walled, lamellar, overlapping metal sheets which can be expanded either mechanically or by means of gas or a liquid (see DE-OS 25 58 584). The splitting of the nail wall into longitudinal lamellae, which is effective for the expansion, leads, however, to a considerable reduction in the torsional rigidity of the nail, so that the relative rotation of the fracture parts about the nail axis cannot be reliably prevented. In addition, the maintenance of the internal pressure is likely to cause difficulties, so that the compression of the fracture surface is too small, since it is only caused by the transverse contraction effect of the nail.

Finally, in DE-OS 28 21 785 a

so described compression nail in which the anchoring with a distal, extendable claw part, which is mounted axially displaceably in a proximal claw part is done. However, with these compression nails there is no frictional connection between Nail and bone wall possible.

Overall, the intramedullary nails described above have the main disadvantages that their insertion and application requires great forces, so there is a risk of bone damage that either no or insufficient anchoring of the intramedullary nail in the longitudinal direction of the bone it is possible that in many cases a strong drilling of the bone is necessary and thus the danger of a Fat embolism is given and that the contact pressures usually have to be chosen very high and after Insertion of the nail is uncontrollable, although a relative rotation of the fracture parts is not can be safely prevented. Some of them own

Intramedullary nails known to date also have too little strength, stiffness against bending and / or torsional stiffness. In addition, the intramedullary nails are sometimes complicated and laborious to handle.

It is also known that Ni - Ti alloys known as "memory alloys" Made of 55% Ni, the remainder Ti after appropriate pre-deformation through the application of heat. Mechanical work can perform. This effect based on structural transformation, which turns out to be a stress-induced, martensitic transformation, which can be explained reversible, is triggered when after a plastic one Deformation of these alloys back into theirs by heating them to a material-specific temperature return to the original shape they were in before the deformation. The conversion back takes place in a temperature range which depends very strongly on the alloy composition and which is different by adding iron, cobalt, manganese, aluminum, gold or zirconium.

The knowledge that through appropriate choice of alloy composition of memory alloys Thermally controlled forces can be triggered, one has already seen with a bone plate made use of the screwed on both sides of the bone fracture site and after heating through contraction by means of the memory effect, a tensile force is exerted on the pieces of bone on both sides and in the direction the breaking point exerts (US-PS 37 86 806). In DE-OS 27 03 529 implants have already been described such as intramedullary nails, osteosynthesis plates and prosthesis parts and the like made of memory alloys use. It has also been proposed to use bone nails from a "memory material" to be introduced into long bores as usual and these using the memory effect in the Expand bones. But these intramedullary nails also showed insufficient anchoring.

The invention is based on the object of creating a torsion-resistant intramedullary nail that is as can be introduced smoothly into the bone and is then easily and securely fixed in the bone can be.

The object is solved by an intramedullary nail with the described features of claim 1, wherein the 4 ^r> intramedullary nail from a Ni-Ti alloy with 54 to 56 wt .-% nickel, balance titanium.

The particular advantage of the intramedullary nail according to the invention is that, as a result of its closed Form has high torsional rigidity and no bone substance ingrowth into an intramedullary nail slot and also has the high transverse elasticity of the open cross-section. These advantages combine with the intramedullary nail according to the invention with the possibility of optimally using the memory effect exploit, so that after triggering the memory effect, the nail outer surface on the inner wall of the long bone fits tightly, while at the same time ensuring good stabilization and good compression. Compared to the previously proposed intramedullary nails made of a memory alloy, the inventive Cross-sectional shape of the intramedullary nail results in a significantly larger change in diameter by triggering the memory effect of the nail so that installation and removal can be carried out without any force.

According to a further embodiment of the invention, the intramedullary nail has a double-walled structure, in the cavity of which a molded part may be inserted between the double walls. This can be another Increase in the rigidity of the intramedullary nail, especially after it has been introduced into the bone will. The cavities created by double walls can also be used to in order to introduce gaseous and / or liquid bodies therein. The gases and / or liquids can both with a view to improving the mechanical properties of the intramedullary nail and for the targeted triggering of the memory effect inherent in this intramedullary nail, namely through suitable ones Preheating or cooling, can be used.

In order to be able to guide the intramedullary nail well during its introduction into the bone, the intramedullary nail tip has an axial, closable opening for receiving it a guide body. According to a further embodiment of the invention, this can consist of a skewer exist, which carries an attached plastic cone on its tip, with which when pulling out the Guide body, the opening in the intramedullary nail can be closed. According to a development of the invention Intramedullary nails have a fine, irregular outer wall, which is concave in cross-section Wave profile, which is formed by round sheet metal or wire parts attached to the outer walls of the intramedullary nail. A further improvement in the intramedullary nail stability is achieved if its edges are reinforced with material are.

Embodiments of the invention are shown in the drawings. Show it

F i g. 1 to 3 each have a medullary nail cross-section in the state before (each Fig. A) and after the triggering of the Memory effect (each F i g. B)

Fig. 4a, b an intramedullary nail with a pentagonal cross-section with reinforced edges,

5 shows a cross-section of an intramedullary nail with welded-on Round bars, before (b) and after triggering the memory effect (a),

6 shows a square intramedullary nail with welded round rods before the memory effect was triggered, which takes on a circular shape after triggering the memory effect (b) and

F i g. 7 shows a longitudinal section through an intramedullary nail with a guide body and a plastic cone attached and

F i g. 8 A longitudinal section of an intramedullary nail with the opening at the tip of the intramedullary nail from the inside with Plastic cone is closed.

The intramedullary nails according to the invention shown have in common that they have a closed jacket. This can be ensured on the one hand by a hollow cross-section, such as. B. a square tube, or in another expedient embodiment by a sheet metal wound into a circular shape, in which two or even more sheet metal layers can lie on top of one another on at least part of the circumference. At the ends of the nail, the cavity can be closed or open. The disadvantage of the closed cross-section when installing the nail is the strong resistance to compression on all sides in the radial direction, that is, a low transverse elasticity. This disadvantage is eliminated by the shape of the nail, the construction of the Nageltei- Is and by the choice of material. The in F i g. 1 shows the shape of the hollow intramedullary nail cross-section that the nail wall 1 is composed partially or entirely of concave circular arcs, so that a kind of star-shaped contour with a rotational

symmetry results. After rotating the cross-section by the angle 2π / η, where η is the number of edges 9 of the intramedullary nail, this shape comes back to coincide with itself. The choice of the circular cylindrical wall parts with the radius P ₀ in FIG. Ib has the advantage that these parts are subjected to a uniform, pure bending deformation when deformed in the radial direction (FIG. 1a) by means of an arcuate punch with a smaller radius Pi, that is, they are uniformly stressed and used. They then have the same edge expansion in the circumferential direction everywhere on the inner and outer fibers. The nail according to the invention is made of a metal alloy which consists of 55% Ni and 45% Ti, so that the intramedullary nail can be converted from the form shown in FIG. 1a into the configuration shown in FIG. Ib by supplying heat. The star-shaped cross-sectional shape makes it possible to produce a particularly large change in the diameter of the enveloping circle 10 or 10 'even with a closed nail. The achievable changes in diameter can be estimated by computer if a certain number of symmetry n, a certain radius Po and a permissible change in elongation of the edge fibers

of the sheet metal when changing from one to the other of the configurations shown and back will. In the estimate presented below, the sheet thickness is assumed to be negligibly small. In this case, the following relationships apply

15 tan -
η

a) for the change in diameter D = Ir

χ AD -. Pn .Yr. π ~ \ ρ, Γ η r / '"2 V

- = = 1 - - arcsin - sm - + - £ - ± - - (1 - -) "-

r D r \ _p ₀ nj r 2 \ nj

b) for the beam length, based on the radius r

■ 2- = & ■ arcsin \ j- sin ■ * -] - Jl-. JL Λ _1λ rr \ _p ₀ η Λ r 2 \ nj

Here r is the radius of the circle around the transverse ration. It is

section of the shape shown in Fig. Ib, χ = -

2

the reduction of this radius on transition to the configuration shown in Fig. la.

If the sheet thickness t is given, the change in strain in the edge fibers of the cylindrical parts in the central area is'

Pn ■ Y'r. π ~ \
- arcsin - sm -
r LPo η J

by

sin

Ue \ - L (^ -A
2 \ Pi P ₀

to replace.

As a special exemplary embodiment, the following are given a permissible change in strain, ie 40 cases shown below: z. B. before a change activated as a result of the memory effect, the radius can be determined for a given p ₀
Calculate P ₀ and thus the form shown in Fig. La.

As a limiting case is also p ₀ the case - *. °°, ie the polygon as illustrated in Figure Ib configurations t = 0.8 mm
D = 11 mm
A ε = 0.1 = 10%

(Polygon)

Symmetry
number η Case 1, P ₀ = r PiIr y / r x / r Case 2, P ^_0-00 PiIr y / r x / r 3 0.42105 0.82674 negative 0.72727 0.48523 0.09488 4th 0.42105 0.45471 0.12424 0.72727 0.13591 0.13682 5
6th 0.42105
0.42105 0.23149
0.08268 0.18899
0.18804 0.72727
0.72727 negative
negative 0.09665
0.00193 7th 0.42105 negative 0.14930 0.72727 negative negative

From the table above it follows that certain particular results for the case of the in Fig. La and b

Shapes are practically not feasible (with 65 star-shaped pentagonal nails shown in

negative values for - or y / r) and that other Po = pure change in diameter of almost 19%.

^r However, other intramedullary nail cross-sectional

deliver particularly large changes in diameter. Information such as B. the in F i g. la illustrated meander conveyor

Mige shape, which after completion of the heating in a circular shape IQ 'with the radius r according to Fig.2b, is possible. There are also large changes in diameter between the shapes shown in FIGS. 2a and b, even if they do not have the effect of the one shown in FIG. 1 achieved star shape with concave cross-sectional sides. The mandrel shape shown in FIG. 2a has six protuberances, each of which has a radius ρ ₂ and the connecting pieces of which uniformly have the radius ε> i.

Another intramedullary nail according to the invention is shown in FIG. 3 shown. The shape shown in FIG. 3b, in which the outer walls of the intramedullary nail are concave parts of a circular arc with the radius Po , can be converted into the shape shown in FIG. 3a by utilizing the memory effect. During this transition, leaf-shaped tips are formed at the medullary nail edges, between; tLenen the outer wall of the intramedullary nail each describes a partial circular arc with the Radius.ρι. The memory nail according to FIG. 3 takes particular account of the deformation behavior of the material in that a strong local deformation along the edges 9 is avoided by maintaining the angle <x, which is formed by lengthening the outer walls of the intramedullary nail which converge to a point. To stabilize the intramedullary nail, after the memory effect has been triggered, a molded part 14 has been inserted which defines the inner contour of the intramedullary nail as shown in FIG. 3b has.

The intramedullary nail cross-sections shown in FIGS. 4a and 4b differ from the previous intramedullary nail cross-sections in that they have reinforced corners and edges 2. Here it is both possible, according to FIG. 4a emboss the edges so that they broadened contact surfaces obtained, reducing the surface pressure between

AD D

= I-a / r.

the bone and the intramedullary nail is reduced, as well as larger radii of curvature at the edges of the intramedullary nail to be provided. As shown in Fig.4b, the edges can be reinforced both in the interior of the intramedullary nail as well as on the outer edge. In the simplest case, welded ones are used Pipe or wire pressure. The in F i g. The embodiment shown in 4a and b has the advantage the bending stiffness and load-bearing capacity of the nail by placing material on the furthest out to increase lying parts of the circumference while maintaining its transverse elasticity. This is also possible if an intramedullary nail is created as shown in FIG Edge area is strongly beaded and thereby the larger contact surface is achieved.

Another advantageous embodiment of the intramedullary nail is shown in cross section in FIG. The cross-sectional shape sketched in FIG. 5b with welded-on round bars 3 or thickenings with an enveloping circle radius r can be converted into the form shown in FIG results in an enveloping circle radius a. This is possible in that the intramedullary nail walls migrate radially inward at the weld lines 12 of the round rods 3 or thickenings, while the intervening intramedullary nail wall pieces 13 migrate outward, so that the cushion shape shown in FIG. 5a results. For the estimation of the in F i g. 5a and b and the associated change in diameter of the intramedullary nail envelope circle, the following geometrical relationships apply:

35

The values - and the angle β can be derived from the equations r

- cos

-f cos (± ₊ ß) - £ L

α Γ · η ■ ία, «Μ, Pi" fa.

- sin β - sin - + β I + ^ sm --—I-

r \ _ \ 2 / Jr \ 2

t ⁺ f) ⁺ 1 (t - f

can be calculated if p _x / r and p ₂ / r are known, so elongation from the memory effect is prescribed. Using these equations ensure the preservation of the arc of the abbreviation

length of the intramedullary nail tube at the transition from the in

Fig. 5b represented the form shown in Fig. 5a- * = I λ I- ^ ^r

provided form. From the calculation of the boundary ^ε t

elongations to the value A ε at this transition follow the conditions

\ Αε \

S - (- + -

2 \ Pi r

the limit values for the radii r _b Pi and P _{2 can} ^{then be} calculated from this. It applies

60

as well as accordingly

Λ - 1 Λ _

τ τ ν

Ud

65

Here / is the sheet metal thickness of the nail pipe and A ε is used as the permissible expansion value, e.g. B. as available

and thus

and ΐϊζλ

+ IA-A ₊ J_l

-V ¹ ε * ⁺ ε * ² ]

22 r

2 + ε * (1 - _Pl / r) "

The physically meaningful value for p ^ lr is to be selected from the two solutions. The line segment y is then off

10

to calculate.

A very rough estimate of the minimum value for the change in diameter can be determined very easily if one abandons the restriction of the elongations and demands p ₂ = 0, β = 0. ' ⁵

Then the undulating profile of the shape according to Fig. 5a degenerates into a polygon, and one can state (with a = π / 2 η)

1 + - tan

2n

2 _pl

tan-

π
η

2 «

^x - ι _ ^π

1 + - tan
η

π Tn

sin

1 + JL tan -5- n 2 «

The segment y is then

20th

25th

30th

35

y _ π r η

π
η

1 + JL tan Ji n 2n

40

The following numerical values are obtained as lower bounds for the change in diameter:

ΛΟ D

2 0.61102 0.38898 3 0.37679 0.24642 4th 0.24547 0.16192 5 0.16954 0.11227 6th 0.12304 0.08165

45

50

Only the arc length of the pipe wall has been retained. For / 3 = 4 is the corresponding form in Fig. 6a and 6b, respectively.

The particular advantages of the nail shape according to the invention are the greater torsional rigidity and the greater torsional load of the closed cross-section compared to the open one with the same Wall thickness, in preventing bone ingrowth into the interior of the nail through the closed cross-section and therefore easy to remove as well as in the large diameter change

tion of this hollow nail. This form also proves to be particularly favorable for ensuring the Rotational stability of the fragments. There is also the option of using a pneumatic or hydraulic internal pressure to expand the nail additionally. Also by introducing a molded part in the nail can have both an additional widening and an additional increase in load-bearing capacity and rigidity can be achieved.

There is also the possibility of making the nail very thin-walled, creating an even larger one Change in diameter is achievable, and then it is then closed by an insertable inner nail strengthen. The particular advantage is that when the nail is heated by means of hot liquid or hot gas of the nail without contamination of the surrounding tissue directly and with good heat transfer can be flushed inside. A special connection, e.g. in Form of a threaded hole can be provided.

As in Fig. 7, the intramedullary nail is advantageously introduced via a guide wire serving as a guide body 4, via which the respective to the form shown in Fig. Ib, 2b, 3b or 5b pre-deformed intramedullary nail is pushed. The guide wire has an attached one on its tip Plastic cone 5, which automatically opens the opening on the when pulling out the guide body 4 The tip of the intramedullary nail closes and engages in a locking groove. Corresponding to that shown in Fig.8 However, it is also possible to arrange the guide hole on the intramedullary nail tip 7 via a plastic cone 8 to close from the inside.

After checking that it is correctly positioned, the intramedullary nail is heated directly under an image intensifier, if necessary Liquid or heated by means of a contact heating probe or possibly inductively and then takes its expanded configuration according to Fig. Ib, 2b, 3b, 5b almost again, so that it is in the clamped the prepared medullary canal and stabilized the fracture. The posterior end of the intramedullary nail can then can also be closed by means of a plastic cone, but also remain open.

For the removal of the intramedullary nail is particularly advantageous that the intramedullary nail, if it consists of a Memory alloy is made, its envelope diameter is reduced again by cooling, so that the clamping effect loosened and the intramedullary nail can be easily removed.

But it is also possible to heat the intramedullary nail only partially along its length, so that the memory effect is only used in very specific places. This can be used in particular when about a compression in the longitudinal direction is desired. Here, the intramedullary nail is also stretched preformed in the longitudinal direction and can, for example, extendable or attached anchoring parts at its ends exhibit. The anchoring at the ends is first released after introduction and only Then the longitudinal compression is generated by heating in the central area. Similar advantages can also be achieved with intramedullary nails which, in one of the states, have an overlapping arrangement of the Have intramedullary nail walls.

In addition 8 sheets of drawings

Claims (8)

Patent claims: 1. Intramedullary nail, which is inserted into long tubular bones along the medullary cavity and used to fix fracture sites, consisting of a tubular hollow body made of a Ni-Ti alloy, which changes its shape permanently due to structural transformations when heat is supplied, whereby the intramedullary nail according to its plasticity Pre-deformation using the memory effect, depending on the temperature, has one of two possible shape states, characterized in that the shape states are defined by different radii (r \, r) of the smallest circle (10, 10 ') enveloping the cross-section of the intramedullary nail. distinguish and that the intramedullary nail has a polygonal, but at least square, star, meander or pillow-shaped cross-section with concave or flat outer walls (1), which after exceeding or falling below the temperature triggering the memory effect in a circular cross-section or a polygonal Cross section with concave outer walls n less curvature (go) is expandable. 2. intramedullary nail according to claim 1, characterized by a double-walled structure. 3. intramedullary nail according to claim 1 or 2, characterized in that in the through the intramedullary nail wall formed inner cavity or a molded part (14) between the double walls of the intramedullary nail is inserted. 4. intramedullary nail according to claim 3, characterized by closed cavities that have a Connection with gaseous and / or liquid bodies can be filled or flowed through. 5. intramedullary nail according to claim 1, characterized in that the intramedullary nail tip (6, 7) has an axial, has closable opening for receiving a guide body (4) for the nail. 6. intramedullary nail according to claim 5, characterized in that the guide body (4) is a skewer, which has an attached plastic cone (5, 8) on its tip, with which when it is pulled out of the guide body (4), the opening in the intramedullary nail can be closed. 7. intramedullary nail according to claim 1, characterized in that the outer walls concave in cross section have a fine, irregular wave profile, which is applied by on the outer walls Sheet metal or round wire parts (3) is formed. 8. intramedullary nail according to one of claims 1 to 7, characterized in that the intramedullary nail edges (2) are material-reinforced.