ZA200601384B - Intramedullary nail - Google Patents

Description

2017/PCT 23.8.2004

English translation of the specification of the International Patent Application No.

PCT/CH03/00591 “Intramedullary pin” in the name of Mathys Medizinaltechnik

AG

Intramedullary pin

The invention concerns an intramedullary pin according to the preamble of patent claim 1.

From CH-A5 668 173 Klaue an intramedullary pin is known, that has a longitudinal slot at its distal end. This known intramedullary pin is intended to be introduced into the medullary space only after the implantation of the associated locking element (a screw or a bolt), where with its slotted tip it contacts the locking screw, due to which the slot expands, so that the intramedullary pin can slide over the locking screw up to its end position. Thus the initially set locking screw serves as a targeting aid for the intramedullary pin to be subsequently implanted. To enable to do this, the longitudinal slot of this known intramedullary pin is relatively wide in comparison with the diameter of the locking screw, because the longitudinal slot could otherwise not open. However, the relatively wide longitudinal slot has two disadvantages: first the strength of the tip of the intramedullary pin is greatly reduced, and secondly it may happen anytime that the intramedullary pin would move axially relative to the locking screw.

This is where the invention wants to provide remedy. The object of the invention is to produce a slotted intramedullary pin, that after the introduction of the locking element does not permit relative axial movements.

This objective is achieved by the invention with an intramedullary pin having the features of claim 1.

The advantages of the intramedullary pin according to the invention are manifold: a) the reduced rigidity of the pin facilitates the implanting, b) when using locking bolts, the diameters of which are slightly greater than the transverse hole in the intramedullary pin, due to the elastic deformation of the pin the bolts can be clamped, leading to a better anchoring of the pin in the bone, c) due to the elasticity in the region of the slot, where the locking holes are also situated, in the case of small pin diameters locking bolts with larger diameters can be used (in the case of conventional pins this would lead to a reduction of the cross-section of the pin, due to large holes), d) due to the elasticity, caused by the slot, detrimental stress concentration can be reduced in the region of the locking holes, e) no relative longitudinal movement is possible between the intramedullary pin and the locking screw without a plastic deformation of the intramedullary pin or of the locking screw taking place, and f) the locking element(s) is (are) clamped without any clearance and are secured against angular misalignment or any movement.

Inthe case of a particular embodiment the width of the slot b of the intramedullary pin is maximum 0.5 times, preferably maximum 0.4 times that of the smallest defined diameter of the holes. By virtue of this the intramedullary pin is flexible in an optimum manner during the introduction and the locking elements are fixed and clamped angularly stable in an optimum manner.

In the case of another embodiment the number of holes 10, 11 is two, while the diameter d10 of the hole closer to the opening of the longitudinal slot is smaller than diameter d11 of the other hole. Due to this locking elements with larger dimensions can be used, resulting in fewer broken bolts.

The longitudinal slot of the intramedullary pin has a length of L, that is preferably 10 times, typically 15 times that of the smallest defined diameter d10 of the holes.

Due to this the intramedullary pin is flexible when being introduced.

The width b of the slot should preferably be constant over the entire length L of the slot. The result of this is a simplified manufacturing technology as well as a minimal weakening of the intramedullary pin with the smallest possible slot width.

The slot can be protected, for example in the form of a dovetail, that limits the expansion of the slot within reason. This will prevent a possible excessive expansion of the slot.

In the case of a particular embodiment the longitudinal slot commences at the proximal end of the intramedullary pin. In contrast to an intramedullary pin with the conventional distal slot, an intramedullary pin with a proximal slot has the advantage that it can be elastically pre-expanded by means of a suitable driving instrument, so that the locking element could be introduced into the intramedullary pin through the target yoke of the instrument. After removing the instrument the proximal slot closes again, due to which the locking elements are firmly clamped in the intramedullary pin.

In the case of a further embodiment the longitudinal slot terminates neither at the distal end nor at the proximal end of the intramedullary pin. This enclosed version has the advantage, that an unintentionally large expansion of the distal (or proximal) end of the intramedullary pin is prevented, particularly for intramedullary pins with a small diameter. Such an expansion may lead to stress concentration at the end of the slot. If the slot is closed at both ends, the locking elements can be clamped even firmer.

The intramedullary pin may have a hollow construction in the direction of the longitudinal axis.

The locking elements to be introduced into the holes of the intramedullary pin have a defined diameter, that are preferably greater than the defined diameter of the associated hole. The defined diameter of the locking element can, however, be the same as the defined diameter of the associated hole. The latter execution has the advantage, that the rigidity of the pin is reduced and the implanting is simplified.

The defined diameter of the locking element can, however, be at least 1.1 times, preferably 1.2 times that of the defined diameter of the associated hole. In the case of this execution larger locking elements can be used while retaining the cross-section of the pin and the breaking of the locking elements can be prevented in the case of small intramedullary pins.

The diameter of the locking element, introduced closer to the opening of the longitudinal slot, is preferably larger than the diameter of the other locking elements.

By introducing the locking element into the hole the intramedullary pin will be elastically expanded in the region of the longitudinal slot. The length L of the longitudinal slot should preferably be so chosen, that when the locking element is introduced the intramedullary pin is deformed only within the elastic range.

In the case of a further embodiment the intramedullary pin has an additional locking hole, extending at right angle to the plane of the holes. This results in an increase of the rigidity of the pin after its implanting and the setting of the locking elements in the plane of both holes. The elasticity of the pin is achieved by the longitudinal slot and simplifies the implanting of the pin. However, once the pin is implanted, the return of the rigidity is desirable, particularly in the case of thin pins.

The invention and developments of the invention are explained in detail below based on partly schematic illustrations of several embodiments.

They show in:

Fig.1 - a partial longitudinal section through an intramedullary pin slotted at the distal end,

Fig.2 - a partial longitudinal section according to Fig.1 with inserted locking elements,

Fig.3 - a partial longitudinal section according to Fig.2, rotated by 90°,

Fig.4 - a partial longitudinal section according to Fig.2 with an additional transverse hole,

Fig.5 - an enlarged section of Fig.4 in the region of the additional transverse hole, 5 Fig.6 - a partial longitudinal section through an intramedullary pin slotted in the proximal end, with a targeting yoke placed on it,

Fig.7 - a partial longitudinal section according to Fig.6, rotated by 90°, Fig.8 - a partial longitudinal section according to Fig.7 with an inserted locking element and the targeting yoke removed,

Fig.9 - a partial longitudinal section through an intramedullary pin having an unopened slot in the distal part,

Fig.10 - a partial longitudinal section according to Fig.7 with inserted locking elements, and

Fig.11 - a partial longitudinal section through an intramedullary pin slotted in the distal part, with a slot protection.

The distal end of the intramedullary pin 1, illustrated in Fig.1, has a longitudinal axis 2, a proximal end 3, a distal end 4, as well as two holes 10,11 extending transversely to the longitudinal axis 2 and at right angle to the plane of the drawing, having diameters d10 and d11, to accommodate the locking elements 12, 13 (Fig.2) in the form of locking screws, as well as a longitudinal slot 9 with a constant width b and a length L = (20 x d10), said slot commencing at the distal end 4 and extending parallel to the longitudinal axis 2 and at right angle to the plane of the drawing. At the same time the diameter d10 of the hole 10 situated closer to the open end of the longitudinal slot 9 is somewhat larger than the diameter d11 of the other hole 11.

In the region between the two holes 10, 11 the longitudinal slot 9 has a width p = (0.2 x d10), measured in the plane of the drawing.

Both holes 10, 11 have a centre 5, 6, respectively. The longitudinal slot 9 extends from its opening situated at the distal end 4 through both holes 10, 11 slightly further to the proximal end up to the base 8 of the slot in the form of a small hole having a very small diameter. The distance between the base 8 of the slot and the centre 6 of the hole 11 is L2. The greater L2, the more flexible the intramedullary pin.

The distance between the two centres 5, 6 of the two holes 10, 11 is L1. In this embodiment L1 is approx. 30 mm.

Furthermore, the intramedullary pin 1 has a continuous cannulation 7, extending coaxially with the longitudinal axis 2.

As illustrated in Fig.2, two locking elements 12, 13 can be introduced in the form of bone screws through the two holes 10,11. On this occasion an expansion of the longitudinal slot 9 takes place, so that at the open end of the longitudinal slot its width increases from b to b'>b.

As illustrated in Fig.3, the shaft of both locking elements 12, 13 has a diameter

D10, D11, corresponding to the 1.2-fold of the diameter of the corresponding holes 10, 11, so that after the introduction of the two locking elements 12, 13 into the holes 10, 11 the intramedullary pin 1 is elastically expanded in the region of its longitudinal slot 9, as this is illustrated in Fig.4.

Fig.4 illustrates a variation of the intramedullary pin 1, whereby an additional third hole 15 is provided between the two holes 10, 11. The hole 15 is 90° relative to the two other holes 10, 11.

Asitisillustrated in Figs.4 and 5, an additional locking element 14, in the form of a locking screw, can be introduced into this additional hole 15. In that segment of the intramedullary pin 1, which is removed from the entry side, an inner thread 16 is provided, that is engaged by the outside thread 17 of the locking element 14,

so that the intramedullary pin 1 is held together again in the slotted region by means of the locking element 14.

Figs.6-8 illustrate a variation of the intramedullary pin 1, whereby the longitudinal slot 9 is provided not at the distal end 4, but at the proximal end 3 of the intramedullary pin 1. In the case of this embodiment only a singie hole 10 is provided to accommodate a single locking element 13 in the form of a locking screw. Otherwise this execution corresponds to that according to Figs.1 and 2 for a distally slotted intramedullary pin 1.

As Fig.6 illustrates, the insertion of the locking element 13 into the hole 10 is carried out with the target yoke 18 placed on; on this occasion the slotted proximal end of the intramedullary pin 1 is expanded, as indicated by arrows 22 (Fig.7), by the connecting screw 19, so that the locking element 13, having larger dimensions than the hole 10, can be inserted in the hole without any problem.

The connecting screw 19 is subsequently released, so that the target yoke 18 can be removed. At the same time the slotted intramedullary pin 1 attempts to contract again at the proximal end 3 as indicated by arrows 21 (Fig.8), and consequently secures the inserted locking element 13 in the hole 10 in an angularly stable manner.

Figs.9 and 10 illustrate a further variation of the intramedullary pin 1, whereby the distal slot 9 is closed at both of its ends, i.e. it is not opened at the distal end 4 of the intramedullary pin 1 as is the case for the executions according to Figs.1-4.

By virtue of this construction the longitudinal slot 9 expands from its initial width b1 to a width of b1' when the locking elements 12 and 13 are introduced into the holes 10 and 11. Thus the expanded longitudinal slot 9 exerts a permanent clamping force on both locking elements 12 and 13 in the holes 10 and 11, so that they can be securely held in them. The longer L is, the more flexible the intramedullary pin and the simpler its insertion. L1 can be individually adapted to suit and has no influence on the function. The longer L2, the simpler the introduction of the locking elements 12 and 13 and the weaker is their angular stability. Otherwise this execution corresponds to the embodiment according to

Figs.1-4.

Fig.11 illustrates a further variation of the intramedullary pin 1, whereby the distal slot 9 is not continuously straight, i.e. extends coaxially with the longitudinal axis 2, but is bent shortly before the distal end 4, so that the slot 9 terminates laterally (on the right in this case). By reorienting the slot 9 a protection 23, 24 is realised of the "dovetail" kind that limits the expansion of the slot 9. When expanding the slot 9, the right portion 23 of the intramedullary pin 1 with its oblique end abuts against the correspondingly oblique end 24 of the left bent portion 24 of the intramedullary pin 1, and consequently prevents a further, excessive expansion of the intramedullary pin at its distal part.

Claims (18)

- $s English translation of the claims as amended under Article 19 PCT of the International Patent Application No. PCT/CH03/00591 “Intramedullary pin” in_the name of Mathys Medizinaltechnik AG S Patent claims

1. An intramedullary pin with a longitudinal axis , a proximal end , a distal end , at least one hole that extends transversely to the longitudinal axis and situated in a plane , having a defined diameter to accommodate a locking element , as well as a longitudinal slot extending in the plane parallel to the longitudinal axis , whereby in the unexpanded state of the intramedullary pin the longitudinal slot has a width b, measured perpendicularly to the plane in the region outside of the holes , said width b being maximum 0.6 times that of the smallest defined diameter of the holes, characterised in that the slot is either closed at the ends or has a protection so that the expansion of the slot is limited with regard to its amount.

2. An intramedullary pin according to claim 1, characterised in that the width b of the slot is maximum 0.5 times, that of the smallest defined diameter (d10) of the holes.

3. An intramedullary pin according to claim 1 or 2, characterised in that the number of holes is two, while the diameter d10 of the hole closer to the opening of the longitudinal slot is smaller than diameter d11 of the other hole .

4. An intramedullary pin according to any one of claims 1 to 3, characterised in that the longitudinal slot has a length of L, that is at least 10 times that of the smallest defined diameter of the holes .

5. An intramedullary pin according to any one of claims 1 to 4, characterised in that the longitudinal slot has a length of L, that is at least 15 times that of the smallest defined diameter of the holes.

6. An intramedullary pin according to any one of claims 1 to 5, characterised in that the width b of the slot is essentially constant over the entire length L of the slot.

7. An intramedullary pin according to any one of claims 1 to 6, characterised in that the longitudinal slot commences at the proximal end of the intramedullary pin

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8. An intramedullary pin according to any one of claims 1 to 7, characterised in that the longitudinal slot terminates neither at the distal end nor at the proximal end.

9. An intramedullary pin according to any one of claims 1 to 8, characterised in that it has a hollow construction in the direction of the longitudinal axis .

10. An intramedullary pin according to any one of claims 1 to 9, characterised in that it has at least one locking element with a defined diameter.

11. An intramedullary pin according to claim 10, characterised in that the defined diameter of the locking element is larger than the defined diameter of the associated hole.

12. An intramedullary pin according to claim 10, characterised in that the defined diameter of the locking element is the same as the defined diameter of the associated hole.

13. An intramedullary pinaccording to claim 10, characterised in that the defined diameter of the locking element is at least 1.1 times, that of the defined diameter of the associated hole .

14. An intramedullary pin according to any one of claims 10 to 13, characterised in that the diameter of the locking element, introduced closer to the opening of the longitudinal slot is larger than the diameter of the other locking elements .

15. An intramedullary pin according to any one of claims 10 to 14, characterised in that the locking element is introduced into the hole and the intramedullary pin is elastically expanded in the region of the longitudinal slot.

16. An intramedullary pin according to any one of claims 1 to 15, characterised in that the length L of the longitudinal slot is so chosen, that during the insertion

. A of the locking elements the intramedullary pin deforms only in the elastic range.

17. An intramedullary pin according to any one of claims 1 to 16, characterised in that it has an additional locking hole, extending at right angle to the plane.

18. An intramedullary pin substantially as herein described and as illustrated in Figures 1 to 3, Figures 4 to 5, Figures 6 to 8, Figures 9 and 10 or Figures 11.