EP0984732A1

EP0984732A1 - Retractable intramedullary nail

Info

Publication number: EP0984732A1
Application number: EP98920672A
Authority: EP
Inventors: Edward Craig Stevenson
Original assignee: University of Aberdeen
Current assignee: University of Aberdeen
Priority date: 1997-05-12
Filing date: 1998-05-12
Publication date: 2000-03-15
Also published as: GB9709509D0; AU7345998A; WO1998051228A1

Abstract

The present invention provides an intramedullary nail (1) comprising an elongate casing (3) adapted to interfit in an intramedullary space, at least one locking element (6) movable between a first position in register with the casing (3) and a second position extending outwardly therefrom and drive means (7 or 7'). The invention provides that the locking element (6) is actuatable by the drive means (7 or 7') to move the locking element to a second outward position, and wherein the locking element may be retracted, even having regard to bone overgrowth subsequently, for removal of the intramedullary nail from the bone.

Description

RETRACTABLE INTRAMEDULLARY NAIL

The present invention relates to a retractable intramedullary nail for the fixation of fractures particularly m long bones, and which incorporates a mechanism for expansion to achieve secure fixation of the nail in the intramedullary canal which fixation can be reversed if necessary to allow removal of the nail.

Intramedullary nails are commonly used to join fractured long bones to enable such fractured bones to unite. In order to perform this function, the nail must be securely fixed within the medullary space. However it may oe necessary to remove the nail subsequently, for example to treat infection at or around the fracture site. This has proved difficult to do with commonly utilized nails.

It is also known to provide devices which expand within a tubular construction to lock the device into position. Usually such devices comprise resilient means which are wholly inappropriate for the support of fractured limbs. Further, it is also a requirement that such expansion means not only expand from a first at rest position m register Vv--_th a casing to a second position m wnicn they have expanded tnerefrom, but also it is necessary mat such fins as may be expanded are contractible into register with the casing again by a drive means, preferably without the use of any resilient elements. It is also preferable that such fins are so formed that they allow a minimum of space for over growth of bone and that when such bone has been formed, the fins are sufficiently thin such that overgrown bone is crushed or cut readily during movement of the fin from the expanded or second position to the first or m register position during withdrawal of the nail.

Accordingly t is an ob ect of the invention to provide a retractable intramedullary nail which comprises expandable elements which may be driven into their expanded condition and driven from their expanded position into register with the casing in which they are housed. Further, it is an object of the present invention to provide fins which may be driven from the second expanded position to the first in register position even when bone overgrowth has occurred.

In the third object of the invention, there is provided a new method of fixing fractured long bones utilizing a intramedullary nail in accordance with the present invention.

According to the present invention therefore there is provided an intramedullary nail comprising an elongate casing adapted to interfit in an intramedullary space, at least one locking element movable between a first position in register with the casing and a second position extending outwardly therefrom, and a drive means therefor; characterized in that the locking element is actuatable by the drive means to move from the first to the second position and subsequently from the second to the first position .

Preferably, the locking element is generally fin shaped and may be caused to move between the first and second positions by axial movement of the drive means within the casing .

The drive means may comprise at least one block which is a close sliding fit within the casing and which is driven by a screw thread. Conveniently, the casing and the block are both of a circular cross section.

The fin may be pivoted to the drive means and may comprise an inclined plane which is in operative connection with the corresponding inclined plane in the casing. Axial movement of the drive means will then cause the inclined surfaces of the fin and the casing to slide over one another to cause the fin to move from its first to its second position .

In such an arrangement, the end of the fin remote from the inclined plane may be adapted, when the drive means 98/51228

- 3 - returns the fin to the first position, to come into contact with the casing so as to urge the inclined planes together again.

The drive means are conveniently placed either axially in the casing or are positioned perpendicular to the casing and generally intermediate the length thereof.

It will be appreciated that a number of blocks can be provided so as to provide an intramedullary nail of any unit length. In a particular aspect of the present invention, there is provided a method of positioning a intramedullary nail in a fractured bone which comprises :- forming intramedullary apertures to accommodate the nail generally along the axis of the parts to be joined; inserting an intramedullary nail as described above into both intramedullary apertures; and operating the drive means to cause locking elements in said nail to expand from the casing thereby to reversibly lock the nail into the intramedullary cavities. The present invention will now be described by way of illustration only with reference to the drawings accompanying this application.

Figure 1 shows a vertical cross section through an intramedullary nail in a first position in accordance with the present invention;

Figure 2 shows a vertical cross section through the intramedullary nail of Figure 1 in a second position.

Figure 3 shows an end view of the intramedullary nail of Figure 1; and Figure 4 shows a transverse cross section through a line AA of Figure 1.

With reference to Figure 1 particularly, a retractable intramedullary nail 1 is formed of a generally elongate casing

3 of a circular cross section. The casing 3 is hollow and is formed with a first end plate 4 and a second end plate 5 forming a unitary element. The casing and the element do not themselves expand or retract.

In the arrangement shown in Figure 1, two blocks, 2 and 2' are provided as a close sliding fit within the hollow casing. The blocks 2 are driven by means respectively of an outer screw threaded drive 7 and an inner screw threaded drive 7 ' , whereby each block is axially moveable over a short distance in either direction.

Each block 2 and 2' is formed with a pivot slot 13 extending transverse of the axis of the respective block.

In the at rest position of the device as shown in Figure 1 and adjacent each pivot slot 13, is a longitudinally extending slot through the casing 3 through which passes each fin 6. Three fins 6 are circumferentially spaced around the periphery of the casing 3 at the two axial locations shown in Figure 1. The shape of the fin 6 is shown in Figure 1 and comprises an elongate knife shaped member 6 to which is attached, a pivot 12 which cooperates in the pivot slot 13 in the block 2. The fin 6 terminates at one end in an inclined plane 15 which cooperates with a corresponding inclined plane

14 in the casing 3. Although the inclined planes 14 and 15 shown here are generally planar, the inclined plane of the fin

15 may be convex and correspondingly the inclined plane 14 of the casing may be concave in a preferred embodiment. Remote from the inclined planes 14 and 15 on the fins 6 are abutment surfaces of the casing 16 which in position of Figure 1 abut the cooperating surfaces 17 on the fins.

Although the arrangement to Figure 1 shows the two screw elements 7 and 7' extending into end plate 4, in another embodiment of the present invention a screw elements 7 is disposed perpendicular to the axis of the elongate casing and intermediate to the length thereof.

As will be appreciated, this screw threaded members are intended to move the blocks axially between fixed positions and this can equally well be achieved by normal mechanical means perpendicular to the axis, and indeed in some circumstances there is some virtue in this last arrangement.

In a particularly preferred embodiment of this type, a drive means is positioned intermediate the length of the casing and is provided with a worm drive element (not shown) .

The drive means 7 are replaced by a screw threaded bar which has oppositely handed screw threads in each direction.

The worm drive acts on one of these so as to cause rotation of the screw drive means 7 causing the blocks 2 to move apart and towards each other. This arrangement is also useful where more than two blocks are utilized since any number of blocks can be moved reciprocally utilizing this arrangement from one screw threaded drive means.

In use, an intramedullary apertura is formed in each fractured shank utilizing a surgical drill in accordance with usual surgical practice.

The intramedullary nail in accordance with the present invention is then slid into the aperture in which it is a tight but sliding fit. As can be seen from Figure 1, the left hand block 2' is driven by a screw 7' and accordingly with this end positioned in the intramedullary cavity or aperture, a screwdriver of a small diameter is applied to the head of the screw 7' and rotated such that the block 2' moves to the left of Figure 1 to the position shown in Figure 2. This causes the inclined plane 15 of the fin 6 to move up the inclined plane 14 of the casing 3.

Since the amount of travel of the fin 6 is relatively small in order to cause satisfactory fixation, the fin 6 is then fully deployed in the position shown in Figure 2 until only undue pressure on the screw head 7' will drive it further.

Similarly, the other end of the intramedullary nail 1 is positioned in a channel in the other shank and the screw head 7 is operated with a broader diameter screwdriver in the same way as previously described for block 2¹. Thus, the fully sterilized nail may be positioned between broken shanks of the bone and normally will stay in si tu while the bone grows thereover and incorporates this into the limb or upper portion of the body. Sometimes however, infection starts in the medullary cavity. In such circumstances, it is necessary to remove the intramedullary nail, a process which is currently done crudely.

In the present instance, it is only necessary to uncover the end plate 4 and engage screw head 7 and 7' to drive the fins 6 into the position as shown in Figure 1. As will be appreciated, the fins 6 are of a generally knife-like configuration and may indeed be provided with edge portions forming the inclined plane 15. This feature allows the fin portion 6 to cut through any ingrowing bone even sometime after the intramedullary nail has been positioned thereby ensuring that the expansion of the intramedullary nail in accordance with the present invention does not impeded its removal if necessary. As will be appreciated, the positioning of the drive head 7 and 7' can be inconvenient at the axial end of the device. In such circumstances, positioning of a single screw head with attendant single drive intermediate the length of the casing and extending generally perpendicular to the axis thereof may be considered appropriate. This may be used with a left and right handed threaded drive bar so that operation of the screw head in a first direction causes both blocks to move apart to cause expansion or together to cause retraction.

The invention therefore provides a retractable intramedullary nail and a method for its use.

Claims

CLAIMS : -

1. A intramedullary nail comprising an elongate casing adapted to interfit in an intramedullary cavity, at least one locking element movable between a first position in register with the casing and a second position extending outwardly therefrom, and drive means therefor; characterized in that the locking element is actuatable by the drive means to move reversibly from the first to the second positions.

2. A nail according to claim 1 wherein the locking element is generally fin shaped and cooperates in a corresponding slot in the casing.

3. A nail according to either of claims i or 2 wherein the locking element is caused to move by axial movement of the drive means in the casing. . A nail according to any preceding claim wherein the drive means comprises at least one block which is a close sliding fit within the casing and which is driven by a screw thread.

5. A nail according to claim 4 wherein the fin is pivoted to the drive means and wherein the fin comprises an inclined plane which is in operative connection with the corresponding inclined plane within the casing, whereby axial movement of the drive means causes inclined surfaces of the fin and the casing to slide over one another to cause the end of the fin to move outwardly from the casing.

6. A nail according to either of claims 4 or 5 wherein the end of the fin remote from the inclined plane is adapted, when the drive means returns the fin to its first position, to come into contact with the casing to urge the inclined planes together.

7. A nail according to any preceding claim wherein the drive means are positioned axially in the casing. 8. A nail according to any of claims 1 to 7 wherein the drive means comprise a screw head portion positioned perpendicular to the axis of the casing and intermediate the length thereof.

9. A nail according to claim 8 wherein the drive means comprises a worm drive and an oppositely handed screw thread device driven by the worm drive and operative to cause the blocks to move apart on a rotation in a single direction thereby to cause the fin to move to its second position.

10. A method for positioning an intramedullary nail in a fractured bone which comprises :- forming intramedullary apertures to accommodate the nail along the axis of the bone parts to be joined; inserting a intramedullary nail as claimed in claim 1 into both the intramedullary spaces so formed and operating the drive means to cause the locking elements to expand outwardly from the casing thereby to reversibly lock the nail into the intramedullary cavities.