Abstract:
The invention relates to a locking ring ( 20 ) for a threaded holding pin ( 18 ) to be screwed into a part of a bone ( 14 ), said ring including a first portion ( 22 ) having an axial bore ( 24 ) for receiving said holding pin, the periphery of said first portion being threaded so as to interact with a holding plate ( 12 ), wherein said ring in characterized in that the same further comprises, as an extension to said first portion, a second portion ( 28 ), said second portion being deformable and thus capable of blocking said ring on said pin by deformation.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/813,971, filed Jun. 11, 2010, which is a continuation-in-part of International Application No. PCT/FR2008/001732, filed on Dec. 12, 2008, which designated the United States and published in French, which claims priority to French Patent Application No. 0708686, filed on Dec. 13, 2007. The entire teachings of the above applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a lock ring for a fixing pin designed to be screwed into a bone part. It also relates to an assembly comprising not only such a ring but also a collar designed to be inserted into a hole in a fixing plate. Lastly, it relates to an osteosynthesis device. 
     BACKGROUND OF THE INVENTION 
     An osteosynthesis device comprises a fixing plate, at least two pins designed to be screwed into two bone parts, and lock rings for anchoring the pins and thus fastening the fixing plate to the two bone parts. 
     A major problem in this technical field is to devise an osteosynthesis device offering both efficient locking of the pins, to prevent them coming unscrewed when subjected to mechanical stresses or vibrations, and easy unscrewing of the pin when the practitioner wishes to remove the osteosynthesis device. 
     EP 1 583 478 discloses an osteosynthesis device in which the axis of the pin and that of the lock ring are at an angle relative to each other. In that osteosynthesis device the holes of the fixing plate are threaded and receive an intermediate ring containing a threaded bore to receive a pin and a lock ring. 
     In order to fit the osteosynthesis device, the practitioner first drills the fixing plate at least two points selected to enable it to be anchored to the bone part, and then drills this bone part with a drill bit guided perpendicular to the fixing plate. Next, he fits the intermediate ring and screws the threaded pin into the bone part to the desired length. He then places the lock ring onto the pin and screws this lock ring into the intermediate ring. 
     It can be seen that, because of the angular difference between the axis of the pin and that of the lock ring, the lock ring becomes increasingly wedged into the intermediate ring as it is screwed down. This provides an irreversible locking of the pin relative to the fixing plate. 
     That device is effective but has a number of drawbacks. 
     In the first place, there is little tolerance in the angular interval between the pin axis and the lock ring axis. Accurate manufacture of the intermediate ring is therefore required, resulting in a high cost of manufacture. 
     In addition, although this angular interval results in effective locking, it has the disadvantage that this locking action begins as soon as the lock ring begins to be screwed down. The lock ring can therefore sometimes fail to penetrate sufficiently into the fixing plate. 
     Lastly, in the case of a thin plate (less than 3 mm, for example), the intermediate ring and the lock ring must be inserted partially into the bone part if the device is to be properly anchored. This means that this prior art device cannot be used on the upper bones (arm, forearm, hands, wrist, face), which are too thin. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to overcome the limitations of prior art osteosynthesis devices. 
     The present invention achieves its object by providing a lock ring for a threaded fixing pin designed to be screwed into a bone piece, said ring comprising a first part having an axial bore to receive said fixing pin, and the periphery of said first part being threaded to engage with a fixing plate; said ring being characterized in that it further comprises, continuing on from said first part, a second part that is thinner than the first part and has a similar axial bore, this second part being deformable and thus able to lock, by deformation, said ring to said pin. 
     In a preferred embodiment, the bore of the first part of the ring is threaded. 
     Advantageously, the first part of the ring has a cylindrical or frustoconical external form. 
     The invention also relates to an assembly comprising a ring according to the invention and a collar, said collar being designed to be inserted into a hole in a fixing plate, the collar having a threaded frustoconical bore corresponding to the thread on the ring. 
     The collar advantageously comprises a radial slot. 
     In one particular embodiment, the collar has a convex periphery designed to engage with a concave hole in a fixing plate. 
     Lastly, the invention relates to an osteosynthesis device comprising a fixing plate having at least two holes, pins designed to be inserted into said holes for screwing into a bone piece, and lock rings or assemblies according to the invention. 
     Other features and advantages of the invention will become apparent on reading the description given below of one particular embodiment of the invention, given by way of indication, without implying any limitation, with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows schematically an osteosynthesis device. 
         FIG. 2  is a longitudinal section through part of an osteosynthesis device mounted on a bone part comprising a ring in a first embodiment of the invention. 
         FIG. 3  shows the same device as in  FIG. 1  following shearing of the lock ring and pin. 
         FIG. 4  is a longitudinal section through part of an osteosynthesis device mounted on a bone part comprising a ring in a second embodiment of the invention. 
         FIG. 5  is a view along D of the device shown in  FIG. 4 . 
         FIG. 6A  is an external view of an embodiment of the lock ring of the invention. 
         FIG. 6B  is a longitudinal section through the lock ring depicted in  FIG. 6A . 
         FIG. 6C  is a view along axis A of the device shown in  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows schematically an osteosynthesis device for fastening two bone parts  2   a ,  2   b  to a fixing plate  4 . The fixing plate  4  has holes for pins  6   a ,  6   b ,  6   c ,  6   d , to pass through, on at least part of which is a thread  8   a ,  8   b ,  8   c ,  8   d  for screwing the pin into one of the bone parts. The osteosynthesis device has two pins per bone part but it will be understood that it could have only one pin per bone part in certain cases. It will be noticed that the pins can be screwed in a direction perpendicular to that of the plane of the fixing plate  4 . Pin  8   b  is an example of this. They can also be screwed at an angle to this perpendicular direction. Pins  8   a ,  8   c  and  8   d  are examples of this. 
     Lock rings  10   a ,  10   b ,  10   c ,  10   d  are placed in the holes of the fixing plate  4  to fasten the pins to this fixing plate. 
     Embodiments of a lock ring according to the invention will now be described with reference to  FIGS. 2-6 . 
       FIG. 2  illustrates part of an osteosynthesis device comprising a ring in a first embodiment of the invention. This figure shows only one pin, but it will be understood that an osteosynthesis device preferably comprises at least two pins in order to unite two bone parts. 
     In  FIG. 2 , a fixing plate  12  is placed over a bone part  14 . The fixing plate comprises a hole  16  to receive a pin  18  and a lock ring  20 . 
     According to the invention the lock ring  20  comprises a first part  22  which has an axial bore  24  for the passage of the pin  18 , which bore may or may not be threaded, the periphery of the first part  22  of the lock ring comprising a thread  26  to enable it to be screwed into the hole in the fixing plate, and a second part  28 , continuing on from the first part  22 . 
     In preferred embodiments, the second part is more readily deformed than the first part. In an embodiment, the second part of the lock ring is thinner than the first part. In an embodiment, the second part has a sufficiently thinner wall than the first part that the second part is more easily deformed than the first part. In an embodiment, the first and second parts have substantially similar external diameters, but the wall of the second part is thinner than the wall of the first part. In an embodiment, the second part has an axial bore  30  similar to that of the first part. In an embodiment, the axial bore of the second part has a diameter which is substantially the same as the diameter of the axial bore of the first part. 
     In an embodiment, the second part is thinner than the first part and has an axial bore similar to that of the first part. 
     In an embodiment, the end of the first part proximal to the second part (the distal end) is adapted to engage a screwdriver, wrench or other tool suitable for removal of the pin by the practitioner. Preferably, the first part comprises an external driving feature adjacent to the second part. In one embodiment, the external driving feature has an external diameter or dimension which is greater than that of the remainder of the first part. The external driving feature can be a polygonal casing, such as a square or hexagonal casing, for engaging a tool, such as a screwdriver or wrench. The external driving feature can also comprise two or more notches or slots in the periphery of the distal end of first part. In one embodiment, the distal end of the first part comprises three notches separated by 120°. In another embodiment, the external driving feature comprises more than three notches, for example, four, five or six notches. The notches are preferably evenly spaced; that is, for n notches, adjacent notches are preferably separated by 360/n degrees. 
     The thickness of the second part  28  is selected to suit the material of which the ring  20  is made, so that when the pin and the second part are sheared, the remaining part of the second part deforms and is pushed down against the top of the remaining pin, thus locking the pin relative to the fixing plate. In an embodiment, the second part is made of 316L surgical steel and has a wall thickness of about 0.05 mm to about 1.5 mm, more preferably between about 0.1 mm and about 0.6 mm. In one embodiment, the second part is made of 316L surgical steel and has a wall thickness of about 1 mm. 
     In an embodiment, the lock ring is made of titanium, titanium alloy, or steel, preferably surgical steel, such as 316L surgical steel. In an embodiment, the lock ring is made of a biodegradable material, such as polylactide (PLA) or another biodegradable polymer. 
     The osteosynthesis device is installed in the following manner. The practitioner provides or selects a plate comprising at least two holes sufficient for affixing the plate to the bone parts. Alternatively, the practitioner drills holes in the fixing plate at least two points selected to enable it to be fixed to the bone parts. He then drills each bone part, using a drill bit guided perpendicular to the fixing plate. He next pre-positions the lock ring  20  by screwing it part of the way into the hole  16 . He can also screw the lock ring  20  all the way into the hole  16 , if for example the axial bore of the first part  22  of the lock ring is not threaded. The pin  18 , whose bottom part comprises a thread  32 , is then screwed into the bone part to the desired length, the lock ring  20 , or at any rate its second part, now having a secondary sighting function for guiding the pin as it is screwed in. If the lock ring  20  has merely been pre-positioned, it is now screwed fully into the hole  16 . 
     The practitioner then shears off the pin  18  and the ring  20  approximately at the base of the second part  28 —that is, at the junction between the first part  22  and the second part  28 . A mark such as a slight groove can be provided at the periphery of the ring in order precisely to define the position of the shearing tool. 
     The remaining part  34  of the second part  28  of the lock ring  22  is deformed toward the pin  18  by the shearing action. The pin  18  is thus locked relative to the lock ring  22 , and hence relative to the fixing plate  12 , by a crimping action. Consequently, when the practitioner shears the pin  18  and the ring  20  at the junction between the first part  22  and second part  28 , using suitable pliers, the jaws of the pliers initially tend to squeeze the lock ring  20 . As the jaws come together, they deform it and finally cut off both the lock ring  20  and the pin  18 . A sheared free edge of the second part is thus formed, making a remaining part  34  attached to the first part. Two diametrically opposite portions of this free edge are now pushed toward each other by the shearing action and roughly cover the sheared free end of the pin  18 . Thus deformed tightly around the pin  18 , the remaining part  34  of the second part  28  of the lock ring  22  locks the pin  18  relative to the lock ring  22  by a crimping action. 
     The situation now is that shown in  FIG. 3 , where elements identical to those in  FIG. 2  are given the same references. 
     The lock ring according to the invention is particularly advantageous in that it offers excellent locking efficiency for small-diameter pins, with diameters of for example from 0.8 to 1.8 mm, which corresponds to the type of pin used on bone parts in the wrist, hand and face. 
     Thus, experiments have demonstrated a resistance to tension of more than 200 kg on a testing machine able to measure no more than 200 kg with a 4 mm diameter pin and a ring made of 316L surgical steel in which the second part has a thickness of 1 mm. In this test, the ring had no internal thread. It will be appreciated that the resistance to tension would be greatly increased with an internally threaded ring. This would provide in particular excellent resistance to tension, even with small-diameter pins. 
     Clearly, the lock ring according to the invention is also usable and effective with larger-diameter pins. 
       FIG. 4  shows a cross section through part of an osteosynthesis device that has a lock ring in accordance with a second embodiment of the invention, and  FIG. 5  is a top view along a direction D parallel to the direction of the pin axis. 
     The lock ring  36  comprises a threaded (thread  40 ) frustoconical first part  38  provided with an axial bore  42  and a second part  44 , continuing on from the first part, comprising an axial bore  46  similar to that of the first part  38 . According to the invention the thickness of the second part is chosen to suit the material used so that this second part is deformable and thus locks the pin, by deformation, when sheared off. 
     The second embodiment of the invention differs from the first embodiment essentially in that the lock ring is mounted on a collar  48  whose orientation in the orifice  50  of the fixing plate can be adjusted. For this purpose the collar has a convex edge  52  and the hole in the fixing plate  12  has a corresponding concave edge  54 . Preferably, the collar has a radial slot  50 . 
     The pin is installed in the same way as in the device described with reference to  FIGS. 2 and 3 . In one embodiment, the practitioner first selects a plate with at least two holes positioned to be attached to the two bone parts. Preferably the holes have concave edges. In another embodiment, the practitioner introduces the holes into the plate by drilling the plate at least two points. He next forms the concave edge of the hole to permit the subsequent insertion of the collar. He then drills the bone part at the chosen angle using a drill bit. The collar  48  is next placed in the hole in the fixing plate, its insertion being facilitated by the radial slot  50  in the collar  48 . The lock ring  36  is screwed at least part of the way onto the collar  48  to immobilize its orientation and thus guide the pin  18 . When the pin has been screwed in to the desired length, and the lock ring has been screwed fully down onto the collar  48 , the practitioner shears off the lock ring  36  and the pin  18  at the lower part of the second part  44  of the lock ring  36 , thus deforming the residual part of this second part and thereby locking the pin  18 . 
     The pin ( 18 ) is preferably provided as a headless pin. As can be seen in  FIG. 5 , shearing of the pin and the second part forms a screw head comprising the remaining end of the pin, the remaining part of the second part and the external driving feature, shown in the figure as three notches ( 56 ). The practitioner thus cuts the pin to the required length upon installation of the device. Thus, the invention eliminates the need for a stock of pins of varied lengths. 
     Another embodiment of the lock ring of the invention is illustrated in  FIGS. 6A-C .  FIG. 6A  presents an external view of the lock ring, which comprises first part  22  and second part  28 . First part  22  comprises external driving feature  31 , represented in the figure by an hexagonal casing of which three faces are visible in the figure. First part  22  further comprises external threading  26 , which is intended to engage with the threading of a hole in a fixing plate.  FIG. 6B  is a longitudinal cross-section of the lock ring of  FIG. 6A . The lock ring comprises inner bore  30  of second part  28  and inner bore  24  of first part  22 . Inner bore  30  and inner bore  24  are cylindrical. First part  22  comprises internal threading  33 . It is to be understood that in  FIGS. 6A and 6B , the first part includes external driving feature  31 , external threaded region  26  and the region, if any, between external driving feature  31  and external threaded region  2 . Second part  28  is cylindrical. The portions of first part  22  other than external driving feature  31  are cylindrical.  FIG. 6C  is a view along axis A as shown in  FIG. 6A  and shows cylindrical second part  28 , inner bore  30  and the hexagonal external driving feature  31 . 
     The plates, lock rings and pins used in the devices of the invention can be provided in a range of sizes. For example, the plates can have a range of thicknesses such as is typical for osteosynthesis plates. For example, in certain embodiments the plates are from about 1 mm to about 2 mm thick. Moreover, the plates can have a range of lengths. In certain embodiments, the plates range from about 5 cm to about 15 cm in length and from about 2.5 cm to about 8 cm in width. In certain embodiments, the width of the plate varies along its length, in certain embodiments having a width from about 2.5 cm to about 3.5 cm near a hole and from about 5 cm to about 7 cm between two holes. The pins can have diameters which are typical for pins used in osteosynthesis devices. In certain embodiments, the pin has a diameter from about 1 mm to about 3 mm, preferably a diameter of from about 2 mm to about 2.5 mm. In certain embodiments, the lock ring has a diameter ranging from about 2 cm to about 5 cm. In certain embodiments, the lock ring has a diameter of about 3 cm. Those of skill in the art can readily select the appropriate plate, lock ring and pin size for the bone parts to be joined. 
     The osteosynthesis device of the invention preferably comprises a plate with at least two holes configured to join two bone parts, two lock rings as described herein and two pins. However, in certain embodiments, the osteosynthesis device comprises a plate comprising a first means of attachment to a bone part comprising at least one hole, at least one lock ring as described herein and at least one pin. In this embodiment, the device further comprises a second means of attachment to a bone part which is different from the first means. In one embodiment, the second means does not include the lock ring of the invention. The second means can be any means known in the art for attaching a fixing plate to a bone part, for example, a prior art lock ring and pin, a staple, or a pin which is directly screwed into the bone through the plate. 
     In an embodiment, the invention provides a method of attaching a fixing plate ( 12 ) to a bone part ( 14 ) in a subject in need of osteosynthesis. The method comprises the steps of:
         (a) providing:
           (i) a fixing plate ( 12 ) comprising a hole ( 16 );   (ii) a threaded fixing pin ( 18 ) designed to be screwed into the bone part; and   (iii) a lock ring ( 20 ,  36 ) comprising a first part ( 22 ,  38 ) having an axial bore ( 24 ,  42 ) to receive the fixing pin ( 18 ), and the periphery of said first part being threaded to engage with a hole of the fixing plate; said ring being characterized in that it further comprises, continuing on from said first part, a deformable second part ( 28 ,  44 );   
           (b) positioning the fixing plate ( 12 ) over the bone part ( 14 ) such that the at least one hole ( 16 ) of the plate ( 12 ) overlays the bone part ( 14 );   (c) drilling a hole in the bone part ( 14 ), wherein the hole in the bone part ( 14 ) is aligned with the hole in the fixing plate ( 12 ) of step (c);   (d) partially or completely screwing the lock ring ( 20 ,  36 ) into the hole of the fixing plate ( 12 );   (e) inserting the fixing pin ( 18 ) through the axial bore ( 24 ,  42 ) of the lock ring ( 20 ,  36 ) and screwing the fixing pin ( 18 ) into the hole in the bone part ( 14 ) to a depth sufficient to secure the pin in the bone part;   (f) if the lock ring ( 20 ) was only partially screwed into the fixing plate ( 12 ) in step (e), screwing the lock ring ( 20 ) completely into the hole of the fixing plate ( 12 ); and   (g) shearing the fixing pin ( 18 ) and the second part ( 28 ,  44 ) of the lock ring ( 20 ,  36 ), thereby deforming a remaining part ( 34 ) of the second part ( 28 ,  44 ) toward the fixing pin ( 18 ) and locking the fixing pin ( 18 ) relative to the fixing plate ( 12 );
 
thereby affixing the fixing plate ( 12 ) to the bone part ( 14 ).
       

     Preferably, in step (g), the pin ( 18 ) and the second part of the lock ring ( 28 ,  44 ) are sheared simultaneously. 
     In an embodiment, the process comprises the steps of identifying first and second bone parts in the subject in need of osteosynthesis. In this embodiment, the fixing plate comprises at least two holes, each hole being configured for attachment to one of the bone parts. In this embodiment, steps (a)-(g) are conducted for attachment of the plate to each of the bone parts, thereby fixing and joining the ends of the bone parts. The plate can be affixed to the two bone parts serially or in parallel. In certain embodiments, the plate comprises more than two holes, and the plate is attached to at least one of the bone parts by installation of two or more lock rings and pins according to steps (a)-(g). 
     In one embodiment, the hole in the fixing plate has a concave edge and is modified prior to step (d) by insertion of a collar as described above, where the collar is oriented within the hole at the desired angle. 
     The patent and scientific literature referred to herein establishes the knowledge that is available to those with skill in the art. All United States patents and published or unpublished United States patent applications cited herein are incorporated by reference. All published foreign patents and patent applications cited herein are hereby incorporated by reference. All other published references, documents, manuscripts and scientific literature cited herein are hereby incorporated by reference. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.