Humeral nail

A humeral nail includes an elongated body, a plurality of interlocking devices and a locking device. The elongated body is at least partially insertable into a medullary canal of a humerus and has a proximal part with a plurality of orifices. The interlocking devices are insertable into the orifices to interlock initially split humeral fragments. The locking device is capable of locking the interlocking devices within the orifices. The locking device is free to move relative to the body between a free passage position in which the locking device enables free passage of the interlocking devices through the orifices, and a locking position in which the locking device locks the interlocking devices in position with respect to the orifices. The locking device has a plurality of openings, each of which has a free passage portion in alignment with a corresponding orifice when the locking device is in the free passage position, and a locking portion in alignment with the corresponding orifice and in engagement with a corresponding interlocking device when the locking device is in the locking position.

This invention relates to a humeral nail.

When a fracture occurs, the proximal part of the humerus can break into several pieces. It is known that these different fragments can be brought together using a humeral nail like that according to the invention.

A nail of this type, for example like that disclosed in U.S. Pat. No. 5,472,444, includes an elongated body that is inserted in the medullary canal of the humerus. This body is hollowed out with various drillings through which screws can pass to mutually interlock the nail and the humeral shaft.

This body is terminated by a proximal end in which at least three orifices are formed, offset at angles from each other. These different orifices house corresponding screws that interlock the different bone fragments that were initially split.

However, this known solution has some disadvantages. Interlocking screws for bone segments tend to become unscrewed, such that their position is modified after implantation, which can cause pain for the patient. Furthermore, if this unscrewing takes place shortly after the surgical operation, consolidation of the humerus assembly may be completely deficient.

To overcome this disadvantage, WO-A-2004/100810 proposes a humeral nail with a main body, different interlocking screws and an internal sheath capable of sliding within the volume inside the body. This sheath has various orifices formed in it, through which the above-mentioned screws can pass.

The first step in placing the nail is to place the sheath inside the body of the nail, and then penetrate the screws through the various orifices formed in the body and in the sheath, respectively. The sheath is then moved along the main axis of the body so as to interlock the screws using the walls of the orifices in the sheath, which stop in contact with the surfaces facing the screws.

However, this alternate solution has disadvantages. In particular, the reliability of the attachment of the nail in the humerus is not always satisfactory.

Having said this, the invention is aimed at proposing a humeral nail capable of overcoming these various disadvantages.

Consequently, the present invention is a humeral nail including an elongated body that can be at least partially inserted into the medullary canal of the humerus, the body including a proximal part with housing orifices into which interlocking devices, such as screws, are inserted to interlock the initially split humeral fragments, the nail also includes a locking device capable of locking the interlocking devices, the locking device being free to move relative to the body between a position in which the interlocking devices are free to move, in which the locking device enables free passage of the interlocking means through the orifices, and a locking position of the interlocking devices in which the locking device locks the interlocking devices relative to the walls of the orifices, characterised in that the locking device includes several openings, each of which includes a free passage part extending in front of a corresponding orifice in the free passage position, and a locking part, the walls of which stop in contact with a corresponding interlocking device, in the locking position.

FIG. 1shows a humeral nail according to the invention, denoted as a whole by reference2. The nail2is used to consolidate a fracture that occurred at a humerus100that includes a shaft102and a head104. The initially split fragments1061to1063of the humerus100, for which the nail2is used for consolidation, can also be seen inFIG. 1.

As shown particularly inFIG. 2, the nail2includes an elongated body4with a straight stem shape. The body4is inserted into the medullar canal108of the humerus and is provided with a tapered tip41at its distal end. Furthermore, two through holes42are formed in its median part, through which screws20will pass. The screws20interlock the body4relative to the humeral shaft102in a known manner.

The body4is provided with a proximal part43opposite the tip41which is cylindrical in shape and has a circular cross-section. The proximal part is hollowed out with three through orifices44that are circular in shape, and are arranged vertically in line with each other. The orifices44may advantageously be offset at angles from each other in pairs according to the information given in U.S. Pat. No. 5,472,444.

The humeral nail2also includes a sheath6open at both its ends that is visible particularly inFIG. 3. The sheath6is cylindrical in shape and has a slightly greater diameter than the proximal part43of the body4. Thus, the sheath6is free to slide around the external surface of the proximal part43.

Three through openings61pass through the sheath6, the locations of which correspond approximately to the locations of the orifices44. As shown more precisely inFIG. 3, which shows the orifices44and the openings61side by side, the openings61have a circular part611, the diameter of which corresponds approximately to the diameter of the orifices44. The circular part611is prolonged by an elongated slot612, the cross-section of which decreases towards the closed end (i.e. the upper end) of the slot612.

As shown particularly inFIGS. 5 and 6, the sheath6is also hollowed out with a notch62that opens up at its lower end, namely towards the tip41of the body4. The notch62defines two housings621and622that are oval and circular in shape, respectively, separated by a neck623with a smaller through dimension. The lower circularly-shaped housing622is prolonged by a canal624opening up at the lower end of the sheath6.

Furthermore, the body4is provided with a stud45with a substantially circular section with through dimensions globally corresponding to the dimensions of the housings621and622. As will be seen in the following, the stud45can fit selectively into either of the two housings621and622.

Finally, the humeral nail2according to the invention comprises a hollow cylindrically-shaped cap8with the same diameter as the sheath6. This cap8can be blocked as will be seen in the following, using a screw10.

Placement of the nail2in the humerus100described above will now be explained in the following.

One objective is to add the sheath6around the proximal part43so that the orifices44coincide with the circular parts611of the openings61. The assembly formed from the body4and the sheath6is then inserted into the medullary canal108of the humerus100. As a variant, the body4can be inserted into the medullary canal108first, and the sheath6can then be added around the proximal part43. Furthermore, the stud45of the body4fits into the lower housing622of the notch62formed in the sheath6, which corresponds to the layout inFIG. 5.

Under these conditions, it is possible to pass interlocking screws22through the orifices44, the interlocking screws22being visible particularly inFIGS. 1 and 4. As is known particularly from U.S. Pat. No. 5,472,444, the screws22are used to interlock the initially fractured fragments1061to1063, in order to consolidate them.

The sheath6is made to slide relative to the body4for example either manually or using an appropriate tool. In the example considered, the objective is to push the sheath6towards the distal part41of the body4, using the cap8and the screw10.

More precisely, the cap8is added around the proximal part43of the body4, the screw10is inserted in the inner volume of the cap8, and the screw10is then made to cooperate with an inner thread (not shown) formed in the proximal part43of the body4. This screwing of the screw10contributes to moving the cap8and consequently the sheath6along the main axis of the body4, which is materialised by the arrow F inFIG. 4.

Therefore, it can be seen that the head101of the screw10forms a stop for the cap8such that the cap8is immobilised axially relative to the body4. Consequently, the cap8also contributes to axially locking the sheath6with respect to the body4.

When the displacement mentioned above regarding the sheath6and the body4is terminated, the circular parts611are no longer coincident with the orifices44, and the walls of the slots612are then in contact with the surfaces facing the screws22. The walls of the slots612then act as a stop for the screws22and prevent any movement of the screws22, particularly an unscrewing movement. The circular parts611thus form free passage parts for the screws22, while the slots612form parts locking the screws22.

It should be noted that the through dimensions of the circular parts611are larger than the dimensions of the screws22, such that the screws can slide freely. On the other hand, the through dimensions of the slots612decrease towards the closed end of each slot. Consequently, when the sheath moves, the walls of these slots612cap the surfaces facing the screws22so as to lock them and keep them in position.

Furthermore, sliding of the sheath6with respect to the body4causes displacement of the stud45from the lower housing622towards the upper housing621, which corresponds to the position inFIG. 6. It will be noted that this movement that takes place through the neck623is enabled by the nature of the material from which the sheath6is made.

It can be imagined that in the position shown inFIG. 6, the sheath6is locked with respect to the body4. The presence of the neck623with a small through dimension prevents the stud45from moving back towards the lower housing622, unless a large force is applied on the sheath6. Consequently, this measure prevents any unexpected movement of the sheath6with respect to the body4. It should be noted that the screws22are not shown inFIG. 6, for reasons of clarity.

The invention is not limited to the example described and shown.

The sheath6extending outside the body4can be replaced by a locking device installed free to slide inside the hollow body. The locking device has a smaller diameter and is also provided with openings through which the interlocking screws22can be selectively locked.

Furthermore, the slots can extend in different directions from the direction shown. Thus, they can extend the circular parts downwards, obliquely or laterally.

Furthermore, several types of sheaths can be used, the openings of which have different spacings and/or orientations. The most suitable sheath can be chosen for this purpose as a function of the configuration of the bone fragments to be brought together.

Finally, more than one locking notch can be provided to lock the sheath6with respect to the body4, such as62described with reference toFIGS. 5 and 6.

The invention provides a means of achieving the objective mentioned above.

The Applicant realised that the solution described in WO-A-2004/100810 is not very satisfactory, because it does not assure that the interlocking screws are reliably held in position. Thus, these screws are locked by the walls of circular orifices, which necessarily have a larger cross section than the screws since the screws need to slide through these orifices in the free passage position. Under these conditions, the locking force generated by the walls of these orifices is relatively low, such that the screws tend to move away from their initial position.

On the other hand, according to the invention, the sheath6reliably locks the interlocking screws22which prevents any accidental unscrewing. In this respect, it should be noted that the free passage part of each opening that has large dimensions enables easy sliding of the screws. Furthermore, the different locking parts that are smaller in dimension reliably hold these screws in position.