ZA200507665B - Bone fixation device - Google Patents

Description

1999/pCT 14.4.2003

English translation of the International Patent Application

No. PCT/CH03/00253 ,Bone fixation device“ in the name of

Mathys Medizinaltechnik AG

Bone fixation device 1¢ The invention relates tc a bone fixaticn device as claimed in the precharacterising part of claim 1.

The most widespread, known spinal column stakilisaticn systems use rigid connecting rods to connect the elements anchored in the spinal column. These rigid ccnnections make it possiple to fix the spinal column adjustments made by the surgeon in a desired position. The disadvantage cf such rigid connections lies in thelr intra-operative handling. Cnly In excepticnal cases will the surgeon succeed in attaching a plurality of anchorage elements in such a way to the spinal column that they can be connected to one another by means of a straight, rigid rod. For this reason the rigid rod will have to be shaped during the operation so as to match the form of the spinal column.

Such shaping 1s time-consuming and may lead to unwanted stress concentrations in the anchorage elements. In order to improve the inoperative handling of these systems, anchorage elements have been developed which are provided with polyaxially pivectable rod connecting members. Said pivotability, while facilitating the insertion cf the rigid rod, since the latter does not need to be pre-shaped with “he same aeyree ci exactness, presents the disadvantage of a massive volume occupied py these polyaxial connecting

: 2008/C7665

Z members. The great demerit of such solutions, regardless whether ordinary or polyaxially pivotable anchorage elements are used, lies in the fact that once the connection with the rigid rod has been established, tre possipilities of making further spinal column corrections are very limited.

Frem US-A 2,997,138 CROCK ET AL., a spinal column bone fixation device is known in which twec pedicle screws are implanted respectively in two adjacent vertebral bodies and connected to each other by means of two rods which may be fastened by clamping in closed channels formed in the heads of scald pedicle screws. The disadvantage of this aevice lies in the fact that when flexible rods are used, “he device in its entirety will still remain flexible, even after tne fastening of the connecting rods, and will thus not pe sufficiently rigid.

From US-A 4,041,939 HALL another spinal column bone fization device 1s known in which a series of pedicle screws are implanted respectively ir the vertebral bodies cf tre concerned segment of the spinal column and connected to each other by means of two rods which may be fastened by clamping in closed channels formed in the heads cf said pedicle screws. This device therefore shows the same disadvantage as CROCK ET AL., since subsequent to the fixation ct the caple in the heads of the pedicle screws the entire assembly will still remain flexible and will lack the necessary rigidity.

Trus, tne known, flexible connecting members shaped in the fcrm of thin wires, thin rcds, cr special, flexible cables extending between the ancnorage elements all have the disadvantage of not being able - except for adjustments in the direction of tensile strain - to satisfactorily keep in place a correction made by the surgeon. It is therefore not possikle to use said known, flexible rcd systems in order tc relieve the spinal column, to make positional corrections, or to stabilise bone fractures.

The invention is intended to provide a remedy fcr this. It is accordingiy an object of the invention to create a bone fixation device which 1s, on the one hand, capable of fiexibly adapting tc a patient's anatomy and to the surgical results achieved during the implantation of the device and, on the other hand, can be made to become completeiry rigid by simply blocking the elements of the device movable relative to one ancther. An additicnal ochjective 1s to achieve a minimally invasive treatment of the spinal column. rccording to the invention, this cbject is achieved by means of a device which shows the features cf claim 1.

Further advantageous embodiments of the invention will be characterised in the dependent claims. z5 The advantages achieved by the present invention consist ezsentially in the fact that the apparatus according toe the invention makes it possible to dispense with the complicated end time-consuming activity of adapting the rigid lcrgitudinal support members to a patient's anatcmy 3C without having to accept the disadvantages related with the use of flexible :cngitudinal support members. In addition, cnce tne pone fixaticn elemenls on the spinal column have successfully been connected, it is still possible tc modify the position of the individual bone fixation elements relative to one anctrner. The new pcsitions of the ccncerned vertebral bodies relative to one another (spinal column correction) may be kept in place by blocking the flexible connecting members within the bone fixaticn elements. The elasticity of the flexible connecting members permits them te be inserted through an operative approach limiting soft- tissue lnjury to a minimum.

In a particular embodiment of the invention, the bone fixation elements are provided with a blocking element by reans of which the mobility oi connecting members inserted in their passage may optionally be fixed and released. By clocking the flexible connecting members in the passages of two adjacent bone fixation elements, their displaceability within the passages is inhibited, which results in conveying rigidity to the whole device.

The bone fixation elements may be selected from the 720 following group: bone screws, bone retractors, and bone clates.

In one particular embodiment, the passage 1s realised as a peripherally closed channel. A closed channel has the advantage of making 1t possible to reduce the dimensions cf the bone fixation elements and to simplify their design. Typicaily, Lhe passage is realised as a ceripherazly open channel, preierapdly In the form of a groove having a U-shaped profile. The U-shaped prcfile advantageously allows the f[:exible connecting members to be inserted therein via the opening of said U-shaped prefile, sn that they no lcnger need to be threaded through the iraividual holes. DMorecver, it is possible, once the fiexibple connecting members have been assembled, to eccessorily attach an additional bone fixation element.

Ir a particular empodiment, the connecting members are 5 preferably rod-like, i.e. provided with a round cross- secticnal profile.

Preferably, the number of connecting members is fcur, five, six, or seven.

In a particular embodiment, the «c¢ross section of the passages ard the cress secticn cf the connecting members are adapted to each other in such a way that the connecting members are received by positive engagement In the passages. “he cross section cof the passages 1s suitably polyhedral, preferably square, rectangular, cr triangular. The polyhedral form of the passage profile has the advantage that the connecting members inserted therein will be disposed in a defined position. Thus, it 1s pcssible to predefine the maximum flexural strength of the connection cf two connecting members and/or of the whole device in cne direction.

Z5 In a particular embodiment, the connecting members ir the passage are in contact with one ancther. Due to this arrancement, the bleccking of the device will inhibit the longitudinal aisplaceability and rotational mobility of the connecting mempers relative to one another, which results in conveying the desired rigidity to the whole device. } in yet another embodiment, tre bone fixation elements are realised as bone screws and the porticn te be anchored

RE ‘ within the bone 1s shared in the form of a Lhreaded screw shank, the bone screw being provided with a screw head in which 2a passage in the fcrm of a U-shaped groove is realised which may be closed by means of a blocking element realised in the form of & cap, sc that the displaceability of connecting mempers placed 1n said groove can be inhibitea.

In & particular embodiment, the surface of the ilexible connecting members is previded with a roughened or microstructured pattern. In this way, the adhesion by friction between the connecting members may be enhanced.

In a further empodiment, the surface of the flexible cecnnecting members 1s provided with a macrostruccured pattern. This will ecually result in an enhancement of the adhesicn by fricticn between the connecting members.

In yet another embodiment, the surface of the passage is provided with a roughened cor microstructured pattern. This will result in an erhancement of the adhesion by friction tetween itself and the connecting members.

For a better understanding of the invention, the fecllowing description discloses a bone fixation method which ccnsists of the “ollowing suralcal procedure steps: al cne pene fixation element provided with a passage is anchored py means of 1ts anchoring porticn on or 1n each of a nurber of bones or bone fragments; lol TWO cr more lergitudinal, flexibie connecting frevpers are inserted in the passages of two adjacent bene fixation elements; and

Cc) the passages of the twec adjacent bene fixation elements are closed using a biocking element by means of which =the mcbility of the connecting members inserted in the passage relative to the bone fixation eiement is inhibited, thus conveying rigidity to the whole device.

The advantages achievable by using this method are manifold: (1) Possible devieticns from the cptimal positicn of Lhe two bone fixation elements do not represent a problem any longer since the flexible connecting members admit a wide range of variability (unlike the rigid, longitudinal suppcrt members according te the state of the art which, 1in a case like tnis, will first have to be removed from the patient's bedy and bent to shape by the surgeon using a special apparatus; ; (2) due tc the blocking of the connecting members their flexipility 1s inhibited, which results in conveying rigidity to the whole device, so that the final state equals that obtained by using a rigid, longitudinal support member; and (2) the position of the individual bone fixation elements relative to cone another may be changed and the latter may pe fiwed in a new position without necessity tc remove the connecting members inserted therein.

Tn rhe fcllicwing, the invention and improvements oI the invention will pe illustrated in greater detail with reference te the partially diagrammatic representations of several embodimonts.

In the drawings:

Fig. 1 1s a perspective view of a device according to the ‘nvention provided with two pedicle screws and four flexible, Longitudinal rods in a necn-blocked, flexible state;

Flg. 2 is a cross section of the head cf a pedicle screw cf the device according to Fig. 1; and

Fig. Zz 1s a cress secticn of a variant of a pedicle screw head provided with a cicsed passage.

The bone fixation device 1 represented in Fig. 1 comprises twe bone fixation elements 2 in the form of pedicle screws and four longitudinal, flexible connecting members 5 shaped in the form of thin, flexible rods that are connectable with the bone fixation elements Z. lc this end, the bone fixation elements 2 are provided with a porticn 2 in the ferm of a threaded shank which may be anchored in the bone, and with a head 7 having a U-shaped passage 4. The passages 4 of the rene fixation elements 2 may be closed by means of a blocking element 6 shaped in the form of a hollow cap 6 having an internal screw thread 10 (Fig. 2} and a hexagon socket &. The head 7 cf each of the bone fixation elements 2 is provided with a corresponding externa! screw thread 9 to which the blocking element 6 may be screwed cn in such a way that tne leongitudina:., flexible connecting members 5 inserted in the passage 4 are fixed in thelr pcsition both relative to one another and relative to the respective bene . fixation element 2. This fixed state of the device 1 is representoa Ln Fig. 2.

Fig. 3 shows a variant of a bene fixation element 2 in wnich instead cf an open, U-shaped passage 4 a closed, channel-like passage 4 with an apprcrimately sauare profile is used.

In crder to firmly fasten the connecting members 5 inserted in the passage 4, a locating screw 11 is provided which may be screwed in through the bore 12 until 1t exerts pressure cn the connecting members 5 so that they will pecome plocked.

Claims (15)

Claims

1. A bone fixation device having at least two bone fixation elements which are both provided with a portion to be anchored on or in the bone and with a passage, whereby the device comprises at least two longitudinal, flexible connecting members which may be inserted in the passages of two adjacent ones of a number of bone fixation elements and fastened therein, characterized in that the device comprises at least two longitudinal, flexible connecting members which may be inserted in the passages of two adjacent ones of a number of bone fixation elements and fastened therein.

2. The device as claimed in claim 1, characterised in that the bone fixation elements are provided with a blocking element by means of which the mobility of connecting members inserted in the passage relative to the bone fixation element may optionally be fastened and released.

3. The device as claimed in claim 1 or 2, characterised in that the bone fixation elements are selected from among the following group: bone screws, bone retractors, and bone plates.

4, The device as claimed in claims 1 to 3, characterised o in that the passage is a peripherally closed channel.

5. The device as claimed in claims 1 to 3, characterised in that the passage is a peripherally open channel.

6. The device as claimed in any of the claims 1 to 5, characterised in that the connecting members are rod- like, i.e. provided with a round cross-sectional profile.

7. The device as claimed in any of the claims 1 to 6, characterised in that the number of connecting members is four, five, six, or seven.

8. The device as claimed in any of the claims 1 to 7, characterised in that the diameter of the passages and the diameters of the connecting members are adjusted to one another, so that the connecting members may be received in the passages in positive engagement.

9. The device as claimed in any of the claims 1 to 8, characterised in that the cross section of the passages is polyhedral.

10. The device as claimed in any of the claims 1 to 9, characterised in that the connecting members inserted in the passage are in contact with one another.

11. The device as claimed in any of the claims 1 to 10, characterised in that the bone fixation elements are bone screws and the portion to be anchored in the a bone is a threaded screw shank, the bone screw being provided with a head in which a passage in the form of a U-shaped groove is realised which may be closed by means of a blocking element realised in the form of a cap, so that the displaceability of connecting members placed in the groove can be inhibited.

12. The device as claimed in any of the claims 1 to 11, characterised in that the surface of the flexible connecting members is provided with a roughened or microstructured pattern.

13. The device as claimed in any of the claims 1 to 12, characterised in that the surface of the flexible connecting members is provided with a macrostructured pattern.

14. The device as claimed in any of the claims 1 to 13, characterised in that the surface of the passage is provided with a roughened or microstructured pattern.

15. A bone fixation device substantially as herein described and as illustrated in Figures 1 and 2 or in Figure 3.