Percutaneous bone screw device and method

Embodiments of the invention provide a bone screw device including a bone screw with a temporary encasement. In some embodiments, the temporary encasement comprises a biocompatible material that may be an osteoinductive, a hemostatic and or a bacteriocide. Some embodiments include a temporary encasement including a therapeutic. In some embodiments, the temporary encasement comprises a wax. In some embodiments, the screw head is substantially U-shaped. In some embodiments, the screw includes an extension tip extending from the screw shaft. Some embodiments of the invention include a system for percutaneous implantation of a bone screw including a screwdriver shaft rotatably coupled to a screw that includes a temporary encasement. In some embodiments, the screw shaft can be at least partially rotated by the screwdriver shaft. Some further embodiments further include a retractable sleeve at least partially surrounding the screwdriver shaft and the bone screw.

BACKGROUND

Bone screws generally comprise an implantable screw capable of internal fixation or anchoring, and can be used to surgically correct many types of injuries or deformities including scoliosis or kyphosis. Bone screws can be used to repair a fracture, or to secure rods, plates or nails, and can be permanent, semi-permanent or bio-degradable. For example, a bone screw may be left in place after a patient heals, or the bone screw may be surgically removed.

Different types of implants (e.g., screws, pins, rods) are sometimes used in spinal surgery to help fix the spine into a more normal position and stabilize a specific area of the spinal column. For example, a cortical screw is a type of bone screw designed to screw into bony prominences of the posterior vertebra or other bone where dense cortical bone is predominantly present, whereas a cancellous bone screw, which has a different thread pattern, is sometimes used during surgery to secure the anterior vertebra or other bone where porous cancellous bone is present in greater quantity. Functioning as firm anchor points, two or more bone screws can be interconnected using locking rods, allowing a spinal segment to be fixated for stabilization or fusion.

Screws for internal fixation can be surgically inserted either open or percutaneously. If they are inserted open, the skin, muscle, and connective tissue are split and retracted surgically, providing open exposure to the underlying bone. Screws and other hardware (e.g., to interconnect the screws) are then implanted, after which the muscle and skin are re-approximated and surgically closed (using sutures or other method).

The most common method for percutaneous insertion of screws for internal fixation is the use of cannulated screws with surgical guide wires. The guide wire, which has a sharp tip that may also be threaded, is mounted to the end of a drill and surgically inserted under fluoroscopic guidance or image guidance until it penetrates through skin and muscle and anchors into bone. Small diameter (1.5 mm or less) guide wires are typically used so that they can be disengaged and repositioned without substantially damaging bone if they do not strike the bone in the desired target. Tools such as dilators, drills, and taps that are cannulated are then positioned over the anchored guide wire and forced down into contact with the bone. These tools are used to prepare the hole to accept the screw. A cannulated screw is then positioned over the guide wire and a cannulated screwdriver is used to insert the screw into bone while the guide wire stays in position. After screw insertion, the guide wire is removed and the puncture required to place the guide wire and screw is sealed.

Pins, screws, and rods can also be used for external fixation. In this case, a portion of the screws and pins reside outside of the body, but pass through the skin and muscle to connect to bone, usually at some distance from the injury or surgical region.

Whether used for internal or external fixation, percutaneous insertion and placement of a bone screw can result in tissue injury. For example, during the insertion procedure, the tap passed over the guide wire or the screw threads may become entangled with connective tissues between the entry point and a bone fixation region which may lead to trauma and/or infection. Moreover, the percutaneous placement of screws can result in the entanglement, entrapment, laceration or compression of one or more nerve fibers that may lead to severe pain, nerve palsy and/or paralysis.

In some cases, using a dilator tube through which the screw is inserted can mitigate this problem. A tube (or sequence of successively larger tubes) is inserted through muscle and connective tissue to form a channel to a position on a bone. A screw can then be passed through the tube and driven into the bone without contacting soft tissues. However, this method can be tedious and it can be difficult to introduce the tube, which must have an inside diameter adequate to pass the screw and screw head, and a substantial wall thickness for tube strength.

SUMMARY

Some embodiments of the invention include a bone screw device comprising a screw including a screw shaft, a screw head and screw tip coupled to the screw shaft. The screw shaft includes a screw thread, and a temporary encasement at least partially covering the screw. In some embodiments, the temporary encasement envelops substantially all of the screw thread. Some embodiments include a temporary encasement comprising a substantially symmetrically curved surface extending over the screw tip.

In some embodiments, the temporary encasement comprises a biocompatible material. The biocompatible material can be an osteoinductive, a hemostatic, and/or a bacteriocide. Some embodiments include a temporary encasement comprising a therapeutic, and in some embodiments, the therapeutic is dispersed within the temporary encasement. In some embodiments, the temporary encasement comprises a wax.

In some embodiments, the screw shaft further includes a proximal end and a distal end, and the screw head is substantially U-shaped and coupled to the proximal end. In some embodiments, the screw includes an extension tip comprising a shaft including a screw thread, a tip proximal end coupled to the screw distal end, and a tip distal end extending from the distal end of the shaft.

Some embodiments of the invention include a system for percutaneous implantation of a bone screw. In some embodiments, the system can include a bone screw comprising a proximal end and a distal end, a screw shaft, a screw head, and screw tip coupled to the screw shaft. The screw shaft can comprise a shaft proximal end and a distal shaft end and can include a screw thread, and a temporary encasement at least partially covering the screw. In some embodiments, the screw shaft is configured and arranged to be at least partially rotated by a screwdriver.

In some embodiments, the screw head is substantially U-shaped and coupled to the proximal shaft end, and the screwdriver is coupled to an inner surface of the screw head. Some embodiments include a sleeve at least partially surrounding the screwdriver shaft. In some embodiments, the sleeve is at least partially coupled with the temporary encasement. In some further embodiments, the sleeve is at least partially retractable away from the screw. In some embodiments, a coupling of the sleeve with the temporary encasement occurs at a transition region, and comprises a substantially smooth tubular shell at least partially surrounding the screwdriver and bone screw.

DETAILED DESCRIPTION

Some embodiments of the invention provide a modified bone screw100to ease percutaneous insertion. For example, some embodiments of the invention provide a bone screw100with a temporarily altered outer surface.FIG. 1Aillustrates a screwdriver150coupling to an encased bone screw100in accordance with at least one embodiment of the invention, andFIG. 1Billustrates an encased bone screw100in accordance with a further embodiment of the invention. As shown inFIG. 1A, and in more detail inFIG. 1B, in some embodiments, the bone screw100can be manufactured with a temporary encasement110providing an encased bone screw100. In some embodiments, the temporary encasement110can provide a temporarily altered outer surface surrounding the screw shaft105that may result in a temporarily modified length to diameter ratio. In some embodiments, the shape, symmetry and/or volume of the bone screw100is temporarily altered using the temporary encasement110covering the bone screw shaft105in order to at least partially reduce soft tissue interaction during insertion into a patient (e.g., when using a bone screwdriver150).

For example, in some embodiments, the encasement110can be shaped to provide a spear-shaped volume around the bone screw shaft105. In some other embodiments, the temporary encasement110can be shaped to provide volumes around the bone screw shaft105that can be rod-shaped, bullet-shaped, or knife-shaped. In some embodiments, the temporary encasement110can be shaped around the bone screw shaft105to form a volume of the bone screw100with a substantially symmetrically pointed curved outer surface.

As depicted inFIG. 1A, in some embodiments, a screwdriver150can be coupled with an encased bone screw100. In some embodiments, the screwdriver150can include a screwdriver shaft120including a distal end120aand a proximal end120b. As shown, the screwdriver150can include a handle125coupled to the proximal end120bof the shaft120. In some embodiments, the distal end120aof the screwdriver shaft120can be coupled with the screw shaft105at a screw head105a. In some embodiments, a temporary encasement110can at least partially envelop the screw shaft105. For example, as shown inFIG. 1B, in some embodiments, a temporary encasement110can at least partially envelop the screw100covering at least the screw shaft105including the screw thread105c, the screw head105a, and the screw tip105b.

In some further embodiments, the temporary encasement110may envelop more or less of the screw100. For example, in some embodiments, a temporary encasement110can at least partially envelop the screw100covering at least the screw shaft105including the screw thread105c, and the screw tip105b, without enveloping the screw head105a. In other embodiments, a temporary encasement110can at least partially envelop the screw100covering at least the screw shaft105including the screw thread105c, and the screw head105awithout enveloping the screw tip105b. In some further embodiments, the temporary encasement110can at least partially envelop the screw thread105conly.

In some embodiments, the thickness of the temporary encasement110can be substantially constant. For example, in some embodiments, the thickness of the temporary encasement110can form a substantially constant thickness envelope over the screw100covering at least the screw shaft105including the screw thread105c, the screw head105a, and the screw tip105b. In some other embodiments, the thickness of the temporary encasement110may be substantially non-uniform. In some embodiments, the thickness of the temporary encasement110may be substantially constant over at least one region of the screw100but different from another region of the screw100. In some other embodiments, the thickness of the temporary encasement110may be substantially non-uniform within a region of the screw100. For example, in some embodiments, the thickness of the temporary encasement100may be substantially non-uniform over the screw shaft105including the screw thread105c, the screw head105a, and the screw tip105b.

In some embodiments, the material properties of the temporary encasement110(including, but not limited to, the density, hardness, and brittleness) can be substantially constant. For example, in some embodiments, the material properties of the temporary encasement110can be substantially constant over the screw100covering at least the screw shaft105including the screw thread105c, the screw head105a, and the screw tip105b. In some other embodiments, the material properties of the temporary encasement110may be substantially non-uniform. In some embodiments, the material properties of the temporary encasement110may be substantially constant over at least one region of the screw100, but different from another region of the screw100. In some other embodiments, the material properties of the temporary encasement110may be substantially non-uniform within a region of the screw100. For example, in some embodiments, the material properties of the temporary encasement110may be substantially non-uniform over the screw shaft105including the screw thread105c, the screw head105a, and the screw tip105b. In some further embodiments, the material properties of the temporary encasement110can be most dense, hard, and brittle at the screw tip105band less dense, hard, and brittle in regions of the temporary encasement enveloping other portions of the screw100.

In some embodiments, the temporary encasement110may comprise a coating that forms a smooth, substantially bullet-shaped surface over at least the screw threads105c. In some embodiments, the temporary encasement110can include a substantially smooth outer surface110a. In some embodiments, the temporary encasement110may have sufficient hardness to allow the bone screw100to penetrate through soft tissues such as muscle substantially intact, but soft and/or brittle enough to allow at least a portion of the temporary encasement110to crumble and/or substantially depart from one or more of the screw shaft105, the screw thread105cand the screw tip105b, and the screw head105aduring penetration into bone. For example,FIG. 1Cillustrates an encased bone screw100bone insertion in accordance with some embodiments of the invention. In some embodiments, when the screwdriver150is coupled with the bone screw100(as depicted inFIG. 1A) and driven into a patient, the temporary encasement110may crumble and/or extrude away as the screw penetrates bone leaving encasement debris140. In some embodiments, substantially all the temporary encasement110may be stripped from any region of screw100that enters the bone.

In some other embodiments, the temporary encasement110may be at least partially removed from the screw100upon entering the bone (i.e., at least some fraction of the temporary encasement110may remain at an interface between the bone and the screw100). In some embodiments, when the temporary encasement110comprises a material that comprises an osteoinductive, and/or hemostatic, and/or bacteriocidal, after driving the screw into bone, the presence of residual material (debris140), derived from the encasement110in and around the screw-bone interface, may provide therapeutic value. Moreover, in some embodiments, at least some of the temporary encasement110may remain on the screw100, and may provide some lubricating effect.

Some embodiments can include bone screws with alternative geometries. For example,FIG. 2Aillustrates a bone screw200in accordance with another embodiment of the invention, andFIG. 2Billustrates the bone screw205(the bone screw200including temporary encasement217). As shown, screws200,205can be especially suited to percutaneous implantation. For example, in some embodiments, screws200,205can include a leading small-diameter tip220bthat can penetrate bone and more easily hold a desired trajectory on a contoured complex surface (i.e., without wandering across the bone surface) than a standard screw tip (e.g., a screw200without the extension tip220). The screws200,205can then be advanced and inserted into bone, either with or without a previously drilled pilot hole. As shown, in some embodiments, the bone screws200,205comprising a distal end202aand a proximal end202b, and the bone screw205comprising a distal end207aand a proximal end207b, can include a screw shaft210comprising a distal end210aand a proximal end210bcoupled to a U-shaped screw head212including an inner surface212a. In some embodiments, screws200,205also comprise a screw thread215coupled to an extension tip220with tip end220b, and a shaft220dand a proximal end220a. As shown, in some embodiments, the U-shaped screw head212is wider than the shaft220d, as is typical for standard top-loading pedicle screws into which interconnecting rods are locked after the screw has been inserted.

In some embodiments, the tip end220bcan include a tip taper220c, and the shaft220dcan comprise a screw thread220e. In some embodiments, the screws200,205can comprise a standard diameter between about 3.5 mm and 7 mm. In some embodiments, the shaft220dcan be between about 1 mm to about 2 mm in diameter and the tip end220bcan extend between about 2 mm and about 4 mm from the proximal end220a. In some other embodiments, the screw200,205may have a diameter greater than about 7 mm, whereas in other embodiments, the screw200,205may have a diameter less than about 3.5 mm. In some embodiments, the shaft220dmay have a diameter less than about 1 mm, whereas in other embodiments, the diameter may be greater than about 2 mm. Some embodiments include a tip end220bthat can extend up to about 2 mm, whereas in other embodiments, the tip end220bcan extend further than about 4 mm from the proximal end220a.

In some embodiments, the leading small-diameter tip220bcan penetrate bone and hold the desired trajectory on a contoured complex surface more easily (i.e., without wandering across the bone surface) than a standard screw tip (e.g., a screw200,205without the extension tip220). The screw200,205can then be advanced and inserted into bone, either with or without a previously drilled pilot hole.

As shown inFIG. 2B, the bone screw205can include a temporary encasement217to aid in streamlining insertion. The wide screw head architecture illustrated by the screw head212can be difficult to insert percutaneously because the screw head212can become entangled with body matter while being driven The temporary encasement217can envelop the screw205covering at least the shaft210, and can facilitate insertion, making it unnecessary to first insert a tubular retractor. In some embodiments as shown, the temporary encasement217can gradually taper toward the tip220, ending at the distal end210aof the shaft210, and flaring to a larger diameter toward the head212. In some further embodiments, the temporary encasement217may envelop more or less of the screw205. For example, in some embodiments, a temporary encasement217can at least partially envelop the screw205covering at least the screw shaft210including the screw thread215, and the distal end210a. In other embodiments, the temporary encasement217can at least partially envelop the screw200covering at least the screw shaft210including the screw thread215, and the screw head212without enveloping the inner surface212a. In some further embodiments, the temporary encasement217can at least partially envelop the screw thread215only. In some other embodiments, the temporary encasement217can at least partially envelop the extension tip220.

In some embodiments, the thickness of the temporary encasement217can be substantially constant. For example, in some embodiments, the thickness of the temporary encasement217can be a substantially constant thickness envelope over the screw205, covering at least the screw shaft210including the screw thread215, the screw head212, and the distal end210a. In some other embodiments, the thickness of the temporary encasement217may be substantially non-uniform. In some embodiments, the thickness of the temporary encasement217may be substantially constant over at least one region of the screw205, but different from another region of the screw205. In some other embodiments, the thickness of the temporary encasement217may be substantially non-uniform within a region of the screw205. For example, in some embodiments, the thickness of the temporary encasement217may be substantially non-uniform over the screw shaft210, including the screw thread215, the screw head212, and the distal end210a.

In some embodiments, the material properties, including but not limited to density, brittleness, and hardness, of the temporary encasement217can be substantially constant. For example, in some embodiments, the density of the temporary encasement217can be substantially constant over the screw205, covering at least the screw shaft210including the screw thread215, the screw head212, and the distal end210a. In some other embodiments, the density of the temporary encasement217may be substantially non-uniform. In some embodiments, the density of the temporary encasement217may be substantially constant over at least one region of the screw205, but different from another region of the screw205. In some other embodiments, the density of the temporary encasement217may be substantially non-uniform within a region of the screw205. For example, in some embodiments, the density of the temporary encasement217may be substantially non-uniform over the screw shaft210including the screw thread215, the screw head212, and the distal end210a. In some embodiments, the density of the temporary encasement217is most dense at the screw tip and less dense in other portions of the screw205.

In some embodiments, the temporary encasement110,217can comprise a wax. In some embodiments, the temporary encasement110,217may be soft and/or brittle enough that the temporary encasement110,217crumbles away as the screw penetrates bone. In some embodiments, the temporary encasement110,217can comprise a material that is biocompatible, osteoinductive, and/or hemostatic, and/or bacteriocidal. Further, in some embodiments, a therapeutic compound may be dispersed within the temporary encasement110,217, or the temporary encasement110,217may comprise a therapeutic compound.

In some embodiments, the wax can comprise a hydrocarbon-based wax. Some embodiments include wax comprising an ester of a monohydric long-chain fatty alcohol and a long chain fatty acid. In some embodiments, the temporary encasement110,217can comprise natural waxes, including, but not limited to animal-derived waxes such as lanoline, spermaceti wax, and wool fat, insect waxes such as bees wax, and vegetable-derived wax such as candelila wax, carnauba wax or castor wax. In some other embodiments, the temporary encasement110,217can comprise a synthetic wax. For example, some embodiments can include poly-ethylene glycol-based wax, hydrogenated or partially hydrogenated vegetable oil based wax. Some embodiments of the invention include a temporary encasement110,217comprising at least one biocompatible wax. For example, some embodiments can include at least biodegradable or bio-absorbable wax. Some embodiments include a temporary encasement110,217comprising a non-waxy biocompatible semi-crystalline or amorphous polymer.

In some embodiments, the temporary encasement110,217includes a coating with a melting temperature of about 98° F. (i.e., body temperature). In some other embodiments, the temporary encasement110,217includes a coating with a melting temperature greater than 98° F., whereas in other embodiments, the temporary encasement110,217includes a coating with a melting temperature of less than 98° F. In some embodiments, the temporary encasement110,217comprises a material with a melting or softening point that is selected based on the length of time of the procedure. For example, in some embodiments, the temporary encasement110,217comprises a material that is substantially solid at room temperature prior to entering patient, but later becomes softer and/or enters a melting phase as its temperature is raised by the body of the patient during the procedure. In some embodiments, the temporary encasement110,217comprises a material that is substantially solid at room temperature prior to entering the patient and during percutaneous insertion, but becomes softer and/or enters a melting phase as its temperature is raised as the bone screw100enters the bone of the patient.

In some embodiments of the invention, the bone screw100,200,205can comprise a biocompatible metal. In some embodiments, the biocompatible metal can be stainless steel, such as a surgical stainless steel. In other embodiments, other metals or metal alloys can be used based on at least one of iron, chromium, nickel, molybdenum, titanium or other group IV metal. In other embodiments, the bone screw100,200,205can comprise a polymer, a ceramic, a glass, a metal-matrix composite, or combinations thereof.

FIG. 3Aillustrates a screwdriver300and bone screw200assembly in accordance with at least one embodiment of the invention, andFIG. 3Billustrates a blown-up region A of the assembly ofFIG. 3Ain accordance with at least one embodiment of the invention.FIG. 3Bshows shaft312coupled with the inner surface212aof the screw head212. In some embodiments, the shaft312can pass through a plastic or metal sleeve310. In some embodiments, the plastic or metal sleeve310can couple with the temporary encasement217at a transition region315to form a smooth tubular shell surrounding the screwdriver300and bone screw205. In some embodiments, the plastic or metal sleeve310is at least partially retractable away from the bone screw200and the transition region315.

In some embodiments, any one of the bone screws100,105,200,205described above and illustrated inFIGS. 1A-1C, 2A-2B, and 3A-3Bmay be driven by a medically qualified individual such as a surgeon, physician, or a physician assistant. In some further embodiments, any one of the bone screws100,105,200,205described above and illustrated inFIGS. 1A-1C, 2A-2B, and 3A-3Bmay be driven by a surgical robot (and optionally an imaging system) that utilizes a Cartesian positioning system that allows movement of a surgical instrument to be individually controlled in an x-axis, y-axis and z-axis. A surgical robot suitable for this task has been described in U.S. Provisional Patent Application No. 61/662,702 filed on Jun. 21, 2012, U.S. Provisional Patent Application No. 61/800,527 filed on Mar. 15, 2013, and Non-Provisional patent application Ser. No. 13/924,505 filed on Jun. 21, 2013, the entire contents of which are hereby incorporated by reference. As described, the surgical robot can include a base, a robot arm coupled to and configured for articulation relative to the base, as well as an end-effectuator coupled to a distal end of the robot arm. The effectuator element can include the surgical instrument or can be configured for operative coupling to the surgical instrument, and the roll, pitch and yaw rotation of the end-effectuator and/or surgical instrument to be controlled without creating movement along the x-axis, y-axis, or z-axis. The system can be configured to automatically position and rigidly hold the end-effectuator and/or the surgical instrument in accurate alignment with a required trajectory, such as, for example, a selected trajectory of a pedicle screw during pedicle screw insertion procedures. In case of movement of the patient, the system can be configured to automatically adjust the position of the robot to maintain desired alignment relative to an anatomical region of interest.

In some embodiments, when the screwdriver300is coupled with the bone screw205(as depicted inFIG. 3A) and driven into a patient, the temporary encasement217may crumble and/or extrude away as the screw205penetrates bone leaving encasement debris (illustrated by140inFIG. 1C). In some embodiments, substantially all the temporary encasement217may be stripped from any region of screw205that enters the bone. In some other embodiments, the temporary encasement217may be at least partially removed from the screw205upon entering the bone. In some embodiments, when the temporary encasement217comprises a material that comprises an osteoinductive, and/or hemostatic, and/or bacteriocidal, after driving the screw205into bone, the presence of residual material (debris140), derived from the encasement217in and around the screw-bone interface, may provide therapeutic value. In some embodiments, some of the temporary encasement217remains on the screw205and provides some lubricating effect.

In some embodiments, any one of the bone screws100,200,205described above and illustrated inFIGS. 1A-1C, 2A-2B, and 3A-3Bcan be used for therapy within any one of the cervical region of the human spine, the thoracic region of the human spine, the lumbar region of the human spine, and the sacral region of the human spine.

As described earlier, in some embodiments, when any one of the bone screws100,200,205described above and illustrated inFIGS. 1A-1C, 2A-2B, and 3A-3Bis turned and driven into bone, the temporary encasement110,217can be at least partially shed (i.e., the material may at least partially crumble, if the material is brittle, or the material may at least partially flow if material is softening or entering a melting phase). In some other embodiments, the temporary encasement110,217can be removed by thermal-induced melting and/or softening. For example, in some embodiments a conventional heating element can be included in the screwdriver150,300just proximal to the screw100,205to heat the screw100,205to induce melting and/or softening of the temporary encasement110,217on the screw100,205. In some other embodiments, an electrical current can be used to heat the screw100,205to induce melting and/or softening of the temporary encasement110,217on the screw100,205.

Some other embodiments can include chemically-induced removal of the temporary encasement110,217. For example, some embodiments can include injection of a chemical through a cannulation in a shaft of the screwdriver150,300, and/or fenestrations or porosity in the screw100,200,205. In some embodiments, the chemical may at least partially dissolve and/or penetrate at least some fraction of the temporary encasement110,217. In some other embodiments, the chemical may at least partially react with at least some fraction of the temporary encasement110,217. In some embodiments, the chemical may soften the temporary encasement110,217. In some embodiments, contact between any fraction of the temporary encasement110,217may cause the temporary encasement110,217to at least partially separate from the screw100,200,205.