DE29724708U1 - one fastener and instrument for replacing portion of cranial vault during craniotomy - has threaded stud projecting from fastener and std threaded into collar which allows for opposing fastener to be brought closer together - Google Patents

Abstract

The fastener (10) has first and second fastening members (12a,12b), with an elongated, externally threaded stud (68) projecting from the first fastening member, while an elongated internally threaded collar projects from the second fastening member. The stud is rotationally threaded into the collar, with the collar extending between the fastening members. The collar fits through the burr hole (12) of a craniotomy incision, and each fastening member is wider than the collar and the burr hole to provide clamping surfaces above and below the burr hole that engage the internal and external surfaces of the bone cover and surrounding cranium. One of the fastening members is a base which includes a disc having a flat inner face and a flat outer face. A number of raised barbs (14) extend from the inner face of the base to provide frictional engagement between the disc and bone. The other fastening member is a cap (60) with an outer face that may be flat or convex (62), and a recess is provided in the outer face for engaging a drive member that rotates the cap. An externally threaded stud projects from an inner face of the base and an internally threaded collar projects from an inner face of the cap. The stud is approximately as long as the collar, and may be screwed partially or entirely into the collar, depending on the thickness of the bone cover.

Description

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Applicant: Walter Lorenz Surgical Inc.

Designation: Chin-bone fixing device and instrument for inserting the
Bone fixation device

Background of the invention Field of the invention

The invention relates to a fastening device for securing a bone plate to the surrounding bone when, for example, a portion of the skull cap that has been removed during a skull opening for a neurosurgical procedure is re-inserted. The invention also relates to an instrument for joining two parts, each with a thread. The instrument can be used during neurosurgical procedures or as a mechanical tool in numerous other applications.

General discussion of the background

A craniofacial flap is a surgical procedure in which a portion of the skull cap is removed or folded back as a flap to allow surgical access to the interior of the skull (for example, the brain). To perform the craniofacial flap, several holes are drilled through the skull cap. The number and location of these holes varies depending on the shape of the bone being removed. For example, three drill holes are drilled at corner points if a triangular bone flap is desired. The drill holes are then connected using osteotomic cuts, for example using a flexible saw passed inside between the drill holes. The saw is then moved back and forth to cut the skull along a dividing line (defined by the connecting osteotomies) to connect the adjacent drill holes. The bone cap is then detached from the underlying tissue to expose the brain. The bone cap can either be completely removed from the surgical site or folded back as a flap along an uncut edge of the flap.

After the operation is completed, the bone cover must be reattached to its original position to protect the brain underneath.

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In the case of conventional cranial openings, closure requires that holes be drilled in the bone plate and surrounding skull bone along the osteotomic lines, and stainless steel wire or silk sutures are then passed through the holes to hold the plate in place. Unfortunately, drilling the holes is very time consuming and potentially dangerous because of the risk of introducing infection. The sutures are also unstable and prone to tearing. Instability or tearing of the sutures can cause dangerous displacement of the skull plate against the brain, causing damage similar to that caused by a skull fracture. The sutures used to close the osteotomic lines are not particularly aesthetic, as they may leave irregularities on the overlying surface of the face or head. This irregularity is particularly unsightly if the surface of the bone plate is not held reasonably flush with the surrounding bone.

Various attachments have been proposed to secure the bone cover to the surrounding skull. US Patent 5,201,737 discloses a flexible plate having a plurality of tabs with holes to receive bone screws. The plate is placed over a drilled hole in the skull and near the osteotomy lines to provide external attachment of the bone cover to the surrounding skull.

Other external bone plates are shown in US 4,651,724, US 4,923,471, US 5,139,497 and US 5,372,498. All of these plates are designed for external use on broken bones and require the insertion of a large number of screws through the plates. As with the plate in US 5,201,737 discussed above, the insertion of numerous screws into the plates is time consuming and prone to fatal infections and is difficult to remove.

Numerous fixing devices are also known for the repair of broken bones. An example of such a device is US 2 511 051, in which a bolt with an external thread is screwed into a shaft with an internal thread. The movement of the bolt into the shaft is carried out by means of a hexagon wrench which is inserted through the shaft into a recess which can receive the tip of the threaded bolt.

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US 3 875 936 shows a fixture for replacing the ball head on the femur by providing a mandrel-equipped spacer between the femur and the ball head joint. US 5 098 433 uses a winged pressure pin to fix broken bones together. US 5 196 016 and US 5 433 719 disclose fixation nails or screws to hold bone fragments together.

Given the use of a variety of fasteners in orthopedic and neurosurgical procedures, improved techniques are still sought for securing a skull cap to the surrounding skull bone following cranial opening. Improved methods and apparatus for securing the fasteners to the skull are also disclosed.

It is therefore an object of the invention to provide a fastening device which is particularly suitable for closing skull openings.

A further object is to provide such a fixation device which can be applied quickly and effectively and which can be easily removed in the event that subsequent access to the interior of the skull is required for further neurosurgical intervention.

Furthermore, it is an object of the invention to provide such a fastening device which avoids the aesthetic disadvantages of conventional fastening devices, such as large indentations in the skin covering the skull.

Finally, it is an object of the invention to provide such a fastening device and such an instrument for manipulating the fastening device that allows the fastening device to be easily inserted and removed, thereby providing a possible permanent and detachable fastening of the skull cap, and thereby avoiding the possible disastrous neurological consequences that can result from the removal or compression of the bone cap.

Ultimately, it is an object of the invention to provide an instrument which is suitable for engaging ci'sLe and second parts with each other, in particular when the

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Intervention must occur between two opposing surfaces and one of the surfaces is not easily accessible.

Summary of the invention

These and other objects are achieved by the bone cover fastening device according to the invention, which has a first and a second fastening part. An elongated externally threaded bolt extends from the first fastening part, while an elongated internally threaded sleeve extends from the second fastening part. The bolt is threaded into the sleeve by turning, with the sleeve extending between the two fastening parts. The sleeve fits through the drill holes from a skull opening, and each fastening part is wider than the sleeve and the drill hole to allow for clamping of the surfaces above and below the drill hole so that the inner and outer surfaces of the bone cover and the surrounding bone merge into one another. Screwing the threaded bolt into the internally threaded sleeve brings the opposing fastening parts closer together and presses them against the inner and outer surfaces of the bone cover and the surrounding skull bone. The fastening parts overlie the side edges of the drill hole and adjacent osteotomic lines to securely attach the bone cover to the surrounding bone.

In a disclosed embodiment, one of the fasteners is a socket that includes a disk having a flat inner surface and a flat outer surface. A plurality of raised barbs extend from the inner surface of the socket to facilitate adhesion between the disk and the bone. The other fastener is a cap having an outer surface that may be flat or convex, and a recess is formed in the outer surface for receiving a drive member that rotates the cap. An externally threaded bolt extends from an inner surface of the socket and an internally threaded sleeve extends from an inner surface of the cap. The bolt is approximately as long as the sleeve. The bolt may be fully or partially threaded into the sleeve depending on the thickness of the bone covering. Consequently, the fastener has the versatility of

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versatility to be used in different parts of the skull where the bone cover varies.

The fastening device is used for a method of fastening a bone plate, for example a bone cover in a bone defect such as a skull opening. The bone plate has opposing inner and outer surfaces which must be held in position substantially flush with the inner and outer surfaces of the surrounding bone. The method comprises the steps of placing the socket and the cap of the fastening part on opposing inner and outer surfaces of the bone plate, with the sleeve extending into the hole and a portion of the socket and a portion of the cap covering the line of connection between the bone plate and the surrounding bone. The socket and the cap are then rotated together until the cap and the socket firmly grip the opposing surfaces of the bone plate and the surrounding bone to clamp the bone plate in place. In particularly preferred embodiments, the fastening device is placed through a craniotomic drill hole, with the cap and the socket covering and closing the drill hole.

In another embodiment, the socket is positioned adjacent the drill hole and against the inner surface of the bone plate by a positioning instrument. The instrument includes a disk-shaped platform preferably having flat top and bottom surfaces. A projection extending upwardly from the socket is configured to engage the mounting socket and hold it in a desired position on the platform. The positioning instrument allows the socket to be moved to a desired position against the inner surface of the bone plate and to be raised against the bone plate to embed the barbs on the socket into the inner surface of the bone. The positioning instrument is particularly useful for neurosurgical procedures because it allows the socket to be positioned between the brain and the skull, minimizing brain trauma.

In a further embodiment of the invention, a fastening instrument is provided for securing first and second parts together. The instrument comprises a sleeve, a shaft or rod which slides within the sleeve, a fastening

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mechanism on the sleeve to engage the first part with the instrument, and a recess on the shaft which receives the second part and engages it with the first part. In particularly preferred embodiments, the sleeve includes a handle extending from the sleeve and the rod includes a handle which allows the rod to be rotated and inverted relative to the sleeve. There is a threaded tip on the rod which engages an internally threaded socket of the first part to screw the first and second parts into engagement with each other.

In a particularly preferred embodiment, the instrument comprises a sleeve having a handle (e.g., a rod or disk) extending from the sleeve. A rod slides within the sleeve and has a threaded tip at the distal end of the rod, and a handle (e.g., a disk or curved handle) near the proximal end of the rod. The handle extends perpendicular to the rod and allows an operator to rotate the rod within the sleeve, and also to translate it axially. A distal tip of the sleeve surrounding the threaded rod has a plurality of locking members or prongs extending from the tip of the sleeve and fitting into complementary receptacles in one of the fasteners to close the fastener to the tip of the sleeve, e.g., by adhesion of the prongs to one of the fasteners.

The instrument is designed to engage two threaded fasteners. The fastener includes a cap and a base, and a receptacle in the cap engageable with prongs on the sleeve to close the cap to the sleeve. The cap also includes an opening through which the rod can slide. The base of the fastener includes a rod having an internal thread and an external thread, and the threaded tip of the rod has a thread complementary to the internal thread of the rod. The cap has a socket having an internal thread complementary to the external thread of the rod.

The fasteners are joined together by engaging the fastener cap with the socket by inserting the prongs into the recesses of the cap. The rod then extends through the cap and the socket is secured to the rod by inserting the threaded tip of the rod into the

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internal thread of the base rod. The sleeve is then slid axially over the rod until the external thread of the base rod makes contact with the internal thread of the sleeve cap. The rod and sleeve are then rotated relative to each other (e.g. by rotating the shaft) to screw the externally threaded tip of the rod on the base into the internally threaded sleeve of the cap. The threaded rod tip is then unscrewed from the internally threaded rod of the base. The connected fasteners can then be released from the instrument, for example by sliding the instrument away from the fasteners to release the locking elements from the fasteners. Alternatively, axial displacement of the rod against the fasteners brings the threaded tip of the rod into contact against the internal thread of the rod and slides fasteners onto the locking elements to release the fasteners from the instrument.

The instrument according to the invention can be used with many different types of fastening devices in many situations where two fastening devices must be joined together in a difficult to access area. The instrument is particularly useful when the fastening devices on opposite sides of an obstacle that blocks access to both sides of the obstacle must be joined together. A special fastening device with which the instrument can be used is the bone cover fastening device according to the invention.

Short description of the drawings

Fig. 1 is a schematic view of a portion of the human skull in which a cranial opening has been made and the fastening device according to the invention has been applied to secure the cranial cap to the surrounding cranial bone.

Fig. 2 is an enlarged perspective view of one of the fastening devices according to the invention, with the cap and the base separated from each other.
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Fig. 3 is a plan view of the cap of the fastening device according to Fig. 2.

Fig. 4 is a plan view of the base of the fastening device according to Fig. 2.

Fig. 5 is a sectional view taken along section line 5-5 of Fig. 1.

Fig. 6 is a sectional view of the fastening device shown in Fig. 2.

Fig. 7 is a sectional view of the fixture showing placement of the fixture base with one embodiment of the positioning instrument.

Fig. 8 is a plan view of another embodiment of the positioning instrument.
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Fig. 9 is an exploded side view, partially in section, showing an arrangement of the positioning instrument according to Fig. 8 and an embodiment of the base having a notch into which the extension fits.

Fig. 10 is a top perspective view of an embodiment of the positioning instrument shown in Fig. 7 in which a peripheral flange extends upwardly from the platform.

Fig. 11 is an exploded side view of the positioning instrument shown in Fig. 10, partially in section, demonstrating the arrangement of the peripheral flange and mounting base.

Figure 12 is a perspective view of a skull opening in which a flap of skull bone has been folded back to expose the brain, illustrating the use of the positioning instrument.

Fig. 13 is a sectional view of a fastening instrument suitable for engaging another embodiment of fastening devices with others.

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Fig. 14 is a plan view of the fastening instrument according to Fig. 13.

Fig. 15 is an enlarged perspective view of another embodiment of the fastening device according to the invention suitable for use with the fastening instrument, with the upper and lower parts detached.

Fig. 16 is a side view of the base of the fastening device according to Fig. 15.

Fig. 17 is a plan view of the base of the fastening device shown in Fig. 16.

Fig. 18 is a plan view of the cap of the fastener shown in Fig. 15.
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Fig. 19 is a sectional view through a skull opening showing the instrument of Fig. 13 with the cap and base of the fastening device engaged.

Fig. 20 is a view of the mounting cap attached to the instrument. Fig. 21 is a view of the mounting base attached to the instrument.

Fig. 22 is a view showing how the instrument is operated to rotate the fixing base relative to the fixing cap to connect the base and the cap together.

Fig. 23 is a view showing the instrument being removed from the fixture

is solved.
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Fig. 24 is a side view showing another embodiment of the fastening instrument in which the handle of the sleeve is a disk and the handle of the rod is a curved handle.

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Fig. 25 is a plan view of another embodiment of the base showing the distribution of the barbs on the inner surface of the base.

Fig. 26 is a side view of the base of Fig. 25 showing the profiles of the barbs.

Detailed description of a preferred embodiment

The invention includes fastening devices for securing two tabular structures together. The invention also includes a positioning instrument particularly useful for positioning the fastening devices in a surgical wound, and a fastening instrument for securing the fastening devices together. This detailed description illustrates several embodiments of the fastening devices, as well as an instrument that can engage the fastening devices together. The instrument can be used to secure many different types of fastening devices together, but for purposes of illustration it is shown in connection with neurosurgical fastening devices.

In the drawings there is shown a cranial opening closure clamp 10 (Fig. 1) which is a special type of panel-like structure. As is known in the art, cranial opening is performed by incising the skull and muscle, which is cut diathermically in the line of an imaginary bone flap. An incision is not made internally, where a strand of bone tissue or temporal muscle is often left uncut to allow some blood supply to the bone and the overlying tissue to remain intact. Alternatively, the bone tissue and muscle may be completely detached from the planned bone flap.

The craniocerebral opening is performed by making a series of drill holes 12 through the skull, approximately 6 or 7 cm apart, with a conventional drill. The underlying dura mater is separated from the bone using a periosteal chisel, which covers the osteotomy site ("the bone cover"). The osteotomies 14 between the drill holes 12 are then closed with a

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The bridge is made using a flexible Gigli saw which is passed between two adjacent drill holes and moved back and forth to make the bone opening from the inner to the outer surface of the skull. The base of the flap, as shown in Fig. 1, is not worked with a saw. A bone forceps (such as a de Vilbis forceps) is used to cut between the drill holes until the bridge breaks at the base 16, into which the flap is raised.

After placing the drill holes and making the osteotornias, a bone plate 18 is severed from the surrounding skull along a dividing line formed by the osteotornias 14. Each drill hole 12 has a plate portion 12a and a complementary skull portion 12b which together form the complete hole 12. The drills come in staggered sizes, e.g., between 0.5 and 2 inches (13 to 51 mm) in diameter, to drill drill holes of sizes varying within this usual range.

The bone plate 18 may be removed completely if the osteotomy connects all of the drill holes 12. However, it is often preferred to leave an intact edge of the skull bone (such as 16) to preserve the blood supply to the bone (as shown in Fig. 1). In either case, the bone plate or flap is referred to as the skull cap.

After the neurosurgical procedure is performed, the bone defect must be repaired by placing the cranial vault 18 back into the defect with opposing inner surface 20 and outer surface 22 (Fig. 5) substantially flush with the inner surface 24 and outer surface 26 of the surrounding skull 28 (Fig. 5). A transverse side 30 of the cranial vault 18 must also be secured opposite a transverse side 32 of the skull 28 along a boundary line defined by the osteotomy 14 between the cranial vault 18 and the surrounding skull bone 28.

Structure of the fastening device

In one embodiment, the fastening device 10 comprises a base 38 (Figs. 2, 4 to 6) comprising a solid disk 40 having a flat inner surface 42 and

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has a flat outer surface 44. The inner surface 42 defines an elongated cylindrical sleeve 46 which projects outwardly from the center of the inner surface 42. An internally threaded bore 48 extends longitudinally through the sleeve 46 but does not extend through the disc 40. Thus, in this embodiment, the bore 48 communicates only with a circular opening 50 at the upper end of the sleeve 46 and does not extend through the disc 40 which has a flat solid lower surface 44. In other embodiments, the bore 48 may extend through the base.

A plurality of ascending, conical or pyramidal barbs 52 are integral with the disc 40 and extend upwardly from the inner surface 42 thereof. As clearly shown in Figure 4, four barbs are arranged on the side 42, evenly spaced circumferentially of the disc 40 and spaced inwardly from the perimeter of the disc. The barbs 52 taper to sharp points 54 to engage the bone against which the barbs are placed and into which the barbs can be embedded by pressing the barbs against the bone. Due to its nature, the skull bone is particularly suitable for embedding the barbs therein.

A cap 60 is secured to the base 38 to form a fastening device which secures the bone cover 18 in the predetermined location and closes the drill holes. The cap 60 is a solid disk 61 (Figs. 5-6) having a convex outer surface 62 which is smooth except for a recess 64 for receiving a complementary drive member (not shown) which rotates the cap 60. The recess 64 shown is hexagonal and is designed to receive the tip of a surgical instrument similar to an Allen wrench. However, an elongated notch in the surface 62 may alternatively be used to receive the tip of an instrument similar to a screwdriver.

The cap 60 has a flat annular inner surface 66 from which an externally threaded bolt 68 projects to engage the internally threaded bore 48 of the sleeve 46. The bolt 68 projects from the center of the side 66 and the external thread is helically formed and machined to complement and screw into the internal helical thread of the sleeve 46. Consequently, the sleeve resembles a nut into which the cap fits like a bolt.

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zen. The bolt 68 preferably has a length (extending perpendicularly from the side 66 along a longitudinal axis of the fastener 10) approximately as long as the threaded bore 48 of the sleeve 46. The greatest width of the cap 60 (as measured with the diameter of the disk 61) and the greatest width of the base 38 (as measured with the diameter of the disk 40) are both wider than the outer diameter of the cylindrical sleeve 46. The outer diameter of the cylindrical sleeve 46 is smaller than the diameter of the bores 12, but the diameters of the disks 40 and 61 are larger than the diameters of the bores 12. The cap 60 and the base 38 each have a symmetrical longitudinal axis so that the fastener is symmetrical when assembled.

In an alternative embodiment, the base 38 may have a cross-shaped or x-shaped part instead of the disk 40.
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Method for use in closing a cranial opening

The fixation device 10 is used for a procedure to replace a bone plate, such as the cranial vault 18, after cranial opening. As previously described, cranial opening is performed by providing a plurality of craniotomic holes, such as the drill holes 12 through the skull. The drill holes are subsequently connected by the osteotomies 14 to create a dividing line for the cranial vault (which may be a plate that is removed or a flap that can be folded back along one edge). The cranial opening therefore includes a portion 12a of the drill hole 12 formed in the cranial vault 18 and a complementary portion 12b of the hole formed in the surrounding cranial bone 28.

The bone cover 18 has an inner side 20 and an outer side 22 which are substantially flush with the inner side 24 and the outer side 26 of the surrounding skull bone 28, respectively, once the skull opening is closed. Opposing transverse sides 30, 32 of the bone cover and the surrounding bone face each other along the dividing line when the bone cover is in place. The sides 30, 32 are substantially parallel to each other when facing each other.

. essentially parallel to each other when facing each other

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In the method of the invention, the bone cap 18 is folded back along a web 16 or removed entirely as a plate to expose the underlying dura mater and brain. After surgery within the skull and prior to insertion of the bone flap into its original orientation within the skull opening, the socket 38 is positioned beneath each drill hole with the inner surface 42 of the socket 38 against the inner surface 24 of the skull 28 so that one or more barbs 52 engage the inner surface 24. The socket 38 covers the edges of the hole 12 and the dividing line between the skull cap and the surrounding bone (as shown in Fig. 1). The sleeve 46 extends upwardly within or through the area 12b of the hole, but preferably does not extend outside the outer surface. The skull cap 18 is then reinserted into the skull opening, for example by folding the bone flap back into the skull opening along the web 16.

Once the skull cap 18 is reinserted into its original position in the skull opening, the complementary portions 12a and 12b again form the hole 12. The sleeve 46 is centered in the hole 12 with the barbs 52 engaging the inner surfaces 20 and 24 of the skull cap 18 and skull 28 (Fig. 5). The cap 60 is then positioned over the reformed hole 12 with the externally threaded bolt 68 above the opening 50. The bolt 68 is inserted into the sleeve 46 through the opening 50 and a driving member (such as a surgical instrument similar to an Allen wrench) is inserted into the hexagonal recess 64 to rotate the cap 60 and insert the bolt 68 into the threaded bore 48. The continued rotation of the cap 60 reduces the distance between the socket 38 and the cap 60 to compress the inner surfaces 42, 66 of the socket and cap against the inner and outer surfaces of the skull and cranial vault. The cap and socket are thereby stictionally engaged against opposite sides of the cranial vault 18 and surrounding bone 28 so as to clamp the cranial vault and surrounding bone together. The barbs 52 of the socket 38 anchor the socket to the cranial vault and surrounding bone to prevent rotation of the socket as the cap is threaded into the socket. The socket is secured to the bone as the barbs 52 penetrate the bone by being pushed by the fastening device.

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The fastening device is used to lock the cranial vault to the surrounding bone at one or more drill holes, preferably at all of the drill holes as shown in Figure 1. Therefore, prior to reinsertion of the cranial vault 18, a socket 38 is positioned under each drill hole 12 with the sleeve 46 extending upwardly in the hole. A cap 60 is then screwed into each internally threaded sleeve until the cap and socket securely clamp the cranial vault 18 and surrounding bone together. The cap and socket are secured together as determined by the degree of advancement of the externally threaded bolt 68 in the internally threaded sleeve 46 so that movement of the bone plate is substantially prevented. The bone plate and surrounding bone are held firmly in position relative to one another, preventing back pressure of the cranial vault (with attendant adverse neurological consequences).

The smooth convex upper exterior surface 62 of the cap 60 reduces the aesthetic problem of visible depressions on the skull or face above the craniotomic drill holes. The closed socket 44 tightly engages the inner surface of the cranial vault and the surrounding cranial bone, allowing ideal coverage of the hole to help prevent infection or trauma. The fixation device also quickly locks the cranial vault into place, thus reducing the amount of time the brain must be exposed and also reducing medical costs associated with prolonged time in the operating room. The fixation device is easily removed, for example, by inserting an instrument into the receptacle 64 of the cap 60 and rotating the cap away from the fixation device to allow the bone flap to be subsequently removed if subsequent neurosurgical intervention is required.

The fastening device 10 is made of a biocompatible material and includes stainless steel, titanium alloy, polyglycolic acid, silicone rubber, Teflon or nylon. Titanium is a particularly preferred material. The biocompatibility of these and other materials can be enhanced by treating the surface of the fastening device. Plasma gas deposition and corona treatment with reactive groups applied to polymeric surfaces are known as methods.

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to modify biomaterial surfaces (see Lee et al., Biomaterials 12:443, 1191 and Lee et al, J. Colloid Interface Sci. 151:563, 1992).

The fastener 10 can be manufactured in many different sizes. For purposes of illustration, the diameter of the bolt 68 here can be 7 mm (the same diameter as the cylindrical bore 48); the outside diameter of the sleeve 46 can be 8 mm; the diameter of the disc 61 can be 20 mm; the diameter of the disc 40 can be 20 mm. In a preferred embodiment, the bolt 68 has a length of 6 mm, which is the same length as the sleeve 46 and its inside bore 48.

The fastener according to the invention is adjustable when used to repair cranial openings for bone of varying thickness. For example, the pterion (in the temporo-parietal region) is quite thin and requires a fastener with a 3 mm bolt and a 3 mm sleeve, with the advancement of the cap and socket against each other until the bolt 68 is fully screwed into the sleeve 46 and the face 66 of the disc 61 contacts the sleeve 46. However, the 3 mm bolt and 3 mm sleeve would equally enable the fastener to clamp bone up to 6 mm thick (if the bolt is only slightly screwed into the sleeve). However, the parietal or frontal bone may be 10 mm to 20 mm thick. A fastener with a 6 mm long bolt 68 (and a 6 mm long internally threaded sleeve) can clamp bone varying in thickness between 6 mm and 12 mm. A longer bolt and sleeve (for example, the bolt and sleeve are each 12 mm long) could clamp together bone that is approximately between 12 mm thick (when the fastener is fully tightened) and 24 mm thick (when the cap and socket are initially engaged but before several turns of the cap into the socket).

Other variations of the disclosed fastening device are possible. For example, the sleeve with the internal screw thread can depend on the cap, while the bolt with the external screw thread can extend from the socket. The cap and socket can have many shapes other than circular, for example square or triangular. Bone plates that are not part of the skull can be attached to the surrounding bone, for example

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for example, a relatively flat bone such as the carpal bone, mandibular bone, maxillary bone or the bones of the eye socket. The convex side of the cap 60 may also be flat, particularly in areas of the skull (e.g., the temporal bones) with relatively flat external surfaces.

Positioning instrument

Two embodiments of a positioning instrument 70 for use with the invention are shown in Figs. 7-12. In the first embodiment, shown in Figs. 7 and 10-12, the instrument includes a low profile disk-shaped platform 42 having a flat inner surface 74 and a parallel flat outer surface 76 (Fig. 11). The inner surface 74 is surrounded by a continuous circular flange 78 (Figs. 10-11) that extends upwardly from the platform 72. An inner diameter of the peripheral flange 78 is approximately equal to an outer diameter of the base 38 so that the base 38 sits within the flange 78. The peripheral flange prevents transverse displacement of the base 38 from the platform 72.

An elongated handle 80 extends generally upwardly from the platform 72 to enable the instrument to be grasped and manipulated. The handle 80 includes a first portion 82 extending upwardly from the platform 72 at approximately a 45° angle and a second portion 84 inclined from a normal to the plane of the platform 72 such that the angle between the second portion 84 of the handle 80 and a normal to the platform 72 is approximately 30°. This angled, substantially upright orientation of the handle 80 enhances the ease of manipulating the mounting base 38 and pushing the base 38 upwardly against the inside of the skull bone. In a preferred embodiment, the platform 72 is about 1 mm thick and the height of the flange 78 above the platform 72 is about 1 mm above the inner surface 74 of the platform 72. The thickness of the base disk 40 is 1 to 2 mm in this disclosed embodiment. Although many different dimensions may be used, these small dimensions are particularly useful in performing delicate neurosurgical procedures.

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As shown in Fig. 11, the disk 40 of the base 38 fits snugly onto the top surface 74 of the platform 72 within a 1 mm deep well formed by the peripheral flange 78, with the continuous peripheral edge of the base 40 force-

. fits snugly against the peripheral edge of the socket disk 40. With the socket in position on the instrument 70, the handle 80 is manipulated by a surgeon (not shown) and moved to the location of the skull opening (Fig. 12). The flat platform 72 of the instrument is then carefully inserted between the skull bone and the underlying brain to insert the disk 40 between the brain and skull bone 28. The mounting base is moved against the bore hole 12 until the sleeve 46 rests against the surface 12b of the bore hole with the tab 18 shown in the open position in Fig. 12. This process is then repeated until all of the desired number of mounting devices are in place. Thereafter, the bone tab 20 is folded back to the position shown in Fig. 1 and the caps 60 are screwed into the sockets to firmly secure the bone cover in place.

Another embodiment of the positioning instrument is shown in Figs. 8 and 9, wherein a cylindrical extension knob 90 is provided at the center of the platform 72. A corresponding receptacle 92 of similar size and shape to the knob 90 is provided on the outside of the base disk 40. In a disclosed embodiment, the knob is about 1 mm high and 2 mm in diameter. The receptacle 92 is similarly 1 mm high and about 2 mm in diameter. The base 38 is placed on the platform 74 of the base 72 with the knob 90 located in the receptacle 92 to prevent transverse displacement of the base relative to the flat platform. The mounting bases are positioned below the bore hole with the sleeve 46 extending through the hole in the same manner already described in connection with Fig. 12.

The receiving trough 92 according to Figs. 8 to 9 is shown as a recess in the outside of the base plate 40. In other embodiments, however, the receiving trough can be formed continuously with the internally threaded bore 68 through the sleeve.

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Fastening instrument

An instrument 100 for assembling the fasteners is shown in Figs. 13 to 22, which includes an elongated tubular sleeve 102 (see particularly Fig. 13) having a proximal end 104 (near the surgeon or other user) and a distal end 106 (farther from the surgeon or other user). Two tubular handle portions 108, 110 extend diametrically from each other, perpendicular to the axis of the sleeve 102. The distal end 106 has two small rods 112, 114 (Figs. 13, 14 and 19) that protrude 1 to 3 mm (e.g. 2 to 3 mm) from the flat surface 116 of the distal end 106. The rods 112, 114 are spaced approximately 180° apart and serve as prongs that hold the fastener to the instrument.

An elongated rod 120 (Fig. 13) slides within the sleeve 102. A tubular guide member 107 can be placed within the sleeve 102 to fill the empty space and prevent relative transverse movement between the sleeve 102 and the rod 120, which slides freely axially within the sleeve. The rod 120 includes a proximal end 122 and a distal end 124. A disk 126 is attached to the proximal end 122 of the rod 120 by means of a hex nut 127 and extends perpendicular to the longitudinal axis of the rod 120. The disk 126 forms a handle on the instrument that can be manipulated by a user to invert or rotate the rod 120 within the sleeve 102.

The distal end 124 of the rod 120 has an externally threaded cylindrical tip 128 and a reduced diameter. In one embodiment, the sleeve 102 is about 14 cm long, with the span of the arms 108, 110 being about 9 cm. The rod 120 is longer than the sleeve 102, with the total length from the tip 128 to the disk 126 being about 16 mm. The disk 126 is a solid cylindrical disk having a diameter of about 3Vi cm. The dimensions of the instrument may vary.

The instrument 100 is used to engage the first and second fastening members. In this disclosed embodiment, the first fastening member 130 is a cap having the shape of a disk. Two openings 132, 134 through the disk are complementary in size and oriented to the location of the rods 112, 114 on

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the sleeve 102. Consequently, the openings 132, 134 form recesses into which the rods 112, 114 can be inserted and suitably received in order to fasten or close the cap 130 to the instrument 100, for example by static friction between the rods 112, 114 and the recesses of the cap 130.
5

A central opening 136 is formed through the center of the cap, along the axis of rotation of the cap 130. The central opening 136 has a diameter only slightly larger than the diameter of the rod 120 so that the rod can slide through and be guided by the walls of the central opening 136. An internally threaded sleeve 138 (has a helical internal thread) projects downwardly from the cap 130 around the central opening 136, and the central opening 136 is connected to and can extend through the sleeve 138.

The second fastening part is a base 140 which is in the form of a plate or disk with a central bolt 142 which projects upwardly. The bolt 142 is formed with a helical external thread 144 which is complementary to the helical internal thread of the sleeve 138 so that the sleeve 138 can be rotated to draw the cap 130 towards the base 140.

Three sharp projections 150, 152, 154 extend upwardly from the disk of the socket 140 to assist in closing the socket against a supporting surface. These projections 150-154 are located on the edge of the socket 140 and are evenly spaced 60° apart (so that all projections are on one half of the socket, preferably all are within a 120° angle). These projections are substantially triangular and each has a sharp apex suitable for embedding in a supporting surface (such as the inner surface of the skull).

The use of the instrument 100 to rotate the cap and base relative to each other to engage them is illustrated in Figs. 20 to 23. Fig. 20 shows the first step in which the rod 120 is inserted through the opening 136 of the cap 130 until the closing rods 112, 114 are inserted into the openings 132, 134 and the cap 130 is secured in place on the end 106 of the sleeve 102. The adhesion between the closing rods 112, 114 and

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the recesses formed by the openings 132, 134, the cap 130 holds the end 106

Next, as shown in Fig. 21, the socket 140 is joined to the rod 120 by inserting the threaded tip 128 (Fig. 20) into the internally threaded bolt 142 of the socket 140 (while securing the socket in place on the inside of the bone plate). Thereafter, the rod 120 is rotated in the direction of arrow 146 (Figs. 14 and 21) to screw the threaded tip 128 into the internally threaded bolt 142 of the socket. The rod 120 is rotated by inverting the disk 126 until the socket 140 is secured to the tip. The step of screwing the socket 140 onto the tip 128 is preferably performed with the rod 120 fully extended (as shown in Fig. 21) by applying axial pressure against the disk 126.

The rod 120 is then axially retracted relative to the sleeve 102 (or the sleeve 102 is advanced relative to the rod 120) (Fig. 22) to insert the external helical thread 144 on the bolt 142 into the internal helical thread 138 of the cap 130. When the rod is in the fully retracted position shown in Fig. 16, the sleeve 102 is rotated by turning the handle 110 in the direction shown by arrow 146 (Figs. 14 and 22). The socket 140 remains stationary because the barbed projections 150-154 on the socket engage the bone and block rotation of the socket. Consequently, rotation of the sleeve 102 screws the internally threaded sleeve 138 onto the externally threaded bolt 142 in the direction shown by arrow 146.

After the sleeve 138 has been fully screwed onto the base 140, the turntable 126 is then rotated in the direction of arrow 147 (the opposite direction of arrow 146) to unscrew the threaded tip 128 of the shaft 120 from the internal thread of the bolt 142. When the tip 128 is fully unscrewed from the bolt 142 and the sleeve 138, the tip is axially retracted from the opening 136 to fully release the instrument 100 from the fastening device. When used in a surgical procedure, the instrument can then be withdrawn from the surgical wound leaving the fastening device firmly in place with the opposite

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lying sides of the bone plate and the surrounding bone are involved.

The fastening instrument 100 may also be used for non-surgical applications, e.g., for attaching a fastener to two opposite sides of a workpiece, such as a wall or adjacent pieces of wood. Variations in the method of using the instrument may also be applied in surgical and non-surgical applications. For example, the base 140 may be rotated to screw it to the threaded tip 128, rather than rotating the threaded tip 128 to screw it to the base. Only relative rotation between the base and the sleeve is necessary. Similarly, the socket of the base may be screwed into the socket of the cap by performing relative rotation between the cap and the base, without necessarily rotating the cap by inverting the sleeve 102. Rather than being rotated (in a direction 147) to screw the base into the cap, the rod may be moved by relative rotation between the base and the cap.

The relationships of various parts of the instrument to the fastening device are shown in Fig. 19. The arrangement of parts in this drawing corresponds to the instrument shown in Fig. 22, wherein the rod 120 has been axially retracted and the cap 130 has been rotated relative to the socket 140 to fit the cap and socket together by the engagement of the helical threads. As shown in Fig. 19, the socket disk 140 has a smaller diameter than the cap 130. In the disclosed embodiment, the socket disk 140 has a diameter of about 11 mm, while the cap 130 has a diameter of about 13 mm. The bolt 142 has a height of about 9 mm, while the height of the sleeve 138 is about 4 mm. The smaller diameter of the socket disk 140 helps the socket to better fit the inside of the cranium, which has a steeper curvature than the curvature of the outer cranium.

The barbs 150, 152 and 154 are all located within a 120° sector of the base disk 140. This allows the barbs to be placed in the intact area of the skull bone without becoming embedded in the removable area of the skull cap. Consequently, the skull cap can be removed if desired,

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by releasing the cap and socket without having to disengage the barbs from the bone of the plate to be removed.

Alternative design of the fastening instrument

Another embodiment of the fastening instrument is shown in Figures 24-26 and is referred to as instrument 200. This instrument is similar to instrument 100 shown in Figures 13-23 so that similar parts have the same reference numerals plus 100 to identify similar parts, beginning with instrument 200. This embodiment differs, however, in that the handle 226 on the rod is not a disk, but instead is a handle with a semi-spherical exterior. Alternatively, the handle 226 may be of a semi-spherical or spherical shape. The advantage of this shape is that it provides a surface that can be easily grasped by hand with the fingers directed slightly inward (towards the long axis of the instrument 200). The handle 226 provides a fastening handle that can be easily rotated during use of the instrument.

The sleeve handle 210 is also different from the vertical rods 108, 110 that serve as the sleeve handle in the instrument 100. Rather than a disk, the sleeve handle encloses the sleeve 202 and extends perpendicularly outwardly therefrom. The peripheral side 211 of the disk 210 is ridged or otherwise roughened to increase the static friction between the side 211 and the hand of a surgeon or other user of the instrument. The improved adhesion between the handle and the hand is particularly useful, for example, during surgical procedures during which blood or other bodily fluids can contaminate the handle and make it slippery.

The friction rods 212, 214 have been extended to 2 to 3 mm (e.g. 3 mm) to provide prongs that more securely hold the mounting cap on the instrument. The receiving holes have been extended accordingly and firmly engage the rods 212, 214 to selectively hold and secure the instrument to one another. Fig. 24A also shows an alternative embodiment of the rods or prongs in which a coil spring or O-ring 215 (at the location of the rod

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212) is secured in an annular notch (shown as 217) on each rod. The coil spring is of such a spring force that the spring is easily compressed and the rods 212, 214 are inserted into the recesses of the cap. These compression springs provide improved engagement of the rods to the cap so that the cap is less likely to be torn away from the instrument during use. Secure engagement of the cap to the instrument is important to enable the instrument to be operated with one hand if desired.

Another embodiment of the mounting base is shown in Figs. 25 and 26. The base 340 is shown with six barbs 350, 352, 354, 356, 358 and 360 evenly spaced around the periphery of the base 340 and extending from the inner side 341 thereof. The barbs have a sharp profile, for example the tip of the barb forms an angle α which is about 30° or less (Fig. 26).

Each barb extends 2 to 3 mm in height above the surface of the inner surface 341. It has been found that this height allows the barb to penetrate into the bone (e.g., a bone plate) to a depth that specifically provides the maximum engagement between the attachment socket and the bone plate. The distribution of the barbs around the socket (instead of arranging the barbs in only one sector of the socket, e.g., in a 60° or 120° sector) allows the barbs to engage the bone plate even if the socket rotates slightly from its original position.

The fastening device and the instrument according to the invention are preferably made of a metallic material suitable for sterile use in surgical procedures. Titanium or stainless steel are examples of such materials. The invention also includes a fastening device, a positioning instrument and a fastening instrument which have been sterilized, for example in an autoclave or by irradiation (for example by irradiation with UV rays) or by chemical sterilization (for example with disinfectants or antibiotics).

Although the principle of the invention has been illustrated and described in several preferred embodiments, it is obvious to a person skilled in the art that the invention

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can be modified in its arrangement and in detail,
to leave.

without these principles

Claims (12)

1. A bone fixation device for securing a bone plate to adjacent bone, the fixation device comprising: - a first part having a cap, - a second part which has a base, - a bolt extending from an inner side of the base, - wherein the bolt has a plurality of concentric grooves along the bolt, - the cap has an opening through which the bolt extends, and - means are provided in the opening which can be brought into engagement with the concentric grooves of the bolt, and wherein - the cap can be moved along the bolt towards the base. 2. Bone fixation device according to claim 1, characterized in that the base comprises a disc having a flat inner side and a flat outer side. 3. Bone fixation device according to claim 1 or 2, characterized in that a plurality of standing barbs extend from the inside of the base. 4. Bone fixation device according to one of the preceding claims, characterized in that the opening through which the bolt projects has a sleeve, the first part and the second part being wider than the sleeve. 5. Bone fixation device according to one of the preceding claims, characterized in that a recess is provided in the outside of the cap for engagement of an engagement part. 6. Bone fixation device according to one of the preceding claims, characterized in that the bolt is fixed with respect to the base. 7. An instrument for engaging a first and a second part, the instrument comprising: - a sleeve, - a shaft that can slide within the sleeve, - a part on the instrument to engage the first part with the instrument, and - an engagement part on the shaft for gripping the second part and for engaging the second part with the first part. 8. An instrument according to claim 7, characterized in that the instrument has an extension extending from the sleeve and a further extension extending from a rod to enable the rod to be rotated and reciprocated relative to the sleeve. 9. Instrument according to claim 8, characterized in that the extension extending from the sleeve has a handle extending from the sleeve. 10. Instrument according to claim 8, characterized in that the extension on the rod has a handle. 11. Instrument according to one of claims 7 to 10, characterized in that the instrument further comprises a fastening device having a first part and a second part. 12. Instrument according to claim 11, characterized in that the fastening device is designed according to one of claims 1 to 6, wherein the first part comprises the base and the bolt and the second part comprises the cap.