System and method of osteodistraction

Systems, devices, and methods for osteodistraction are provided. The systems and devices comprise ellipsoidal cams for providing controlled distraction of adjacent bone structures using a rotational force to produce displacement of the bone structures. An implantable distraction cam system is provided, along with instruments for achieving progressive osteodistraction with reduced risk to a patient.

FIELD

The present disclosure relates to systems and methods of distracting adjacent bone tissue, and more specifically, systems and methods for predictably and progressively increasing a dimension of distraction between two bone tissue surfaces while reducing the risk of slippage or an abrupt return of a bone to its native position, thereby reducing the risks associated with various surgical procedures.

BACKGROUND

Various surgical procedures require the distraction of two bones or other hard anatomical features. For example, a cervical laminoplasty procedure requires distraction of the lamina of the spine away from the lateral mass of the vertebra.FIGS. 1A-1Cillustrate a cervical vertebra in various stages of a cervical laminoplasty procedure. With reference toFIG. 1A, a vertebra100with a compression of spinal cord101. A distraction of the lamina is frequently initiated by cutting lamina102on one side of the vertebra to create a gap103in the lamina. An incomplete kerf104on the contralateral lamina may serve as a hinge. Distraction of the lamina increases the dimension of the gap103, thereby elevating the lamina and opening the spinal canal, as shown inFIG. 1B. Distraction of the lamina can relieve spinal stenosis and pressure on the spinal cord101or surrounding nerve roots. As shown inFIG. 1C, an implant105may be placed in the enlarged laminar gap103following distraction and secured to the vertebra100using a plate106.

An osteodistraction procedure can present risks to a patient. In a cervical laminoplasty, various common approaches to engaging and distracting the lamina present risks to the patient. The instruments that may be used, the force vectors and movements applied to the lamina using the instruments, and the manner in which they engage the surfaces of the bones involve risks of over-insertion and slippage, which can lead to direct and/or indirect trauma to the spinal cord. For example and as illustrated inFIGS. 2A and 2B, a curet210may be used to distract lamina202of vertebra200. Curet210may first be inserted into laminar gap203(FIG. 2A). Such insertion involves directing curet210with force toward spinal cord201, with a risk of overinsertion of curet210and injury to the spinal cord. Following insertion of curet210into laminar gap203, curet210can be used to distract lamina202, such as with a prying or lifting movement (FIG. 2B). Distraction using this or similar instruments and techniques presents a risk that lamina202will slip from the distraction instrument and return to its original position abruptly or forcefully and in an uncontrolled manner, causing injury to spinal cord201.

The present disclosure provides systems and methods of osteodistraction that provide more predictable and/controllable distraction of two bone structures, thereby decreasing the risks to the patient associated with osteodistraction procedures.

DETAILED DESCRIPTION

As used herein, the terms “proximal” and “distal” refer to portions of a tool or device located nearer to and further from an operator, respectively.

As used herein, the term “ellipsoidal” means having at least a portion of the form of an ellipse, including a generally oblong shape partially defined by one or more convexly curved boundary profile segments. As used herein, an object can have an “ellipsoidal” cross-section, notwithstanding that the boundary profile of that cross-section may include non-ellipsoidal features, such as indentations (e.g., a notch or concave boundary profile segment), straight lines, or other boundary profile segment features or irregularities.

In various embodiments, a kit for performing an osteodistraction can comprise a distraction driver. With reference now toFIGS. 3A-3C, various views of a distraction driver300are illustrated. A distraction driver can comprise an elongated instrument with handle320at a proximal end. A shaft321may extend distally from the handle, and the shaft may terminate in a cam322at the distal end of distraction driver300. Distraction driver300can further comprise a protective plate323located proximally to cam322. With reference specifically toFIG. 3C, a view of the distal end of distraction driver300is shown to illustrate the configuration and relative dimensions of cam322and protective plate323in accordance with various embodiments. As illustrated, cam322can comprise an ellipsoidal cross-section or profile having an insertion dimension x and a distraction dimension y that is greater than insertion dimension x. Protective plate323can comprise a diameter z that is greater than the distraction dimension y and configured to prevent over-insertion of distraction driver300into a gap between two adjacent bone or other structures, such as a laminar gap, kerf or trough.

The cam of a distraction driver such as distraction driver300can have any of a range of possible insertion dimensions and distraction dimensions. For example, in various embodiments, insertion dimension x of cam322can be any dimension in the range of from about 1 mm to about 20 mm, such as about 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, and so forth, up to about 20 mm, or any other dimension with a non-integer value therebetween. Similarly, distraction dimension y of cam322can be any dimension in the range of from about 2 mm to about 30 mm, such as about 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, and so forth, up to about 30 mm, or any other dimension with a non-integer value therebetween, provided that distraction dimension y is greater than insertion dimension x.

Similarly, the cam of a distraction driver can be configured with any suitable cam depth dimension. The depth dimension of a cam is the distance from the distal surface of protective plate323to the distal end of cam322. In various embodiments, the depth dimension of cam322can be any suitable dimension to permit the radial walls of cam322to engage adjacent bone structures in use without extending into a gap between two bone structures, such as a laminar gap. For example, the depth of a cam may be any dimension in a range of from about 4 mm to about 15 mm.

The protective plate of a distraction driver may be configured with a circular, ellipsoid, or other rounded shape cross-section or profile. For example, protective plate323of distraction driver300can be configured with a substantially circular profile having a diameter dimension z. In accordance with various embodiments, diameter dimension z is greater than distraction dimension y so that protective plate323extends radially from shaft321beyond the radial profile of cam322. In various embodiments, diameter dimension z can range from about 4 mm to about 14 mm, dependent on the insertion dimension x and the distraction dimension y of cam322. For example, protective plate323may be configured with a diameter dimension z that extends radially about 1 mm beyond cam322on each side in the distraction dimension axis. In this manner, protective plate323may provide a positive stop for insertion of cam322in an axial direction into gap between adjacent bone or other structures that may provide a clearance fit for cam322in either the insertion dimension x orientation or the distraction dimension y orientation. Any dimension of protective plate323diameter dimension z suitable to provide a positive stop relative to the dimensions of cam322may be used.

A distraction driver can be manufactured from any material suitable for surgical instrumentation, such as titanium, stainless steel, tungsten carbide, or other suitable materials. A distraction driver can be manufactured as a unitary device, or a distraction driver can be assembled from separate components, such as by joining a separate handle, shaft, protective plate, and/or cam.

In various embodiments, the ellipsoidal cross-sectional profile of cam322may be configured to facilitate conversion of rotational motion of distraction driver300about the long axis of the driver into substantially linear displacement of two adjacent bone structures between which cam322is inserted, thereby increasing the dimension of a gap from a dimension approximating the insertion dimension x of cam322to a dimension approximating the distraction dimension y of cam322. In operation, cam322of distraction driver300may be inserted into a gap between two adjacent bone structures. The cam may be inserted until the distal surface of protective plate323comes into contact with an opposing surface of one or more bone structures. The dimension of the gap may provide a clearance fit for cam322in the insertion dimension orientation. Rotation of the driver300causes the walls of cam322to slide smoothly at the points of contact with the surrounding bone structures on either side of the gap, while the cross-sectional profile of cam322functions as a disc-cam, converting the rotational motion of the cam to linear motion of the adjacent bone structures in a direction substantially perpendicular to the axis of distraction driver300.

In this manner, distraction of the adjacent bone structures can be achieved while substantially reducing the forces directed along a vector oriented toward potentially sensitive, underlying tissue and the attendant risk of instrument slippage and intrusion into such tissue. For example, in a cervical laminoplasty, distraction of the lamina using distraction driver300as described above produces linear distraction of the lamina in a direction substantially parallel with the axis of the lamina, without relying on a prying action and instrument force vectors that intersect with the spinal cord, such as those involved in the prior art process illustrated inFIG. 2B. Moreover, distraction is achieved in a controlled manner, with cam322of distraction driver300contacting surfaces of both adjacent bone structures and occupying the gap between the adjacent bone structures throughout the distraction. This approach substantially reduces the risk associated with slippage of a distraction instruments and procedures that rely on instrument contact with the bone structure on only one side of the gap and/or do not occupy the gap between the adjacent bone structures. Using distraction driver300, the distraction force can be released in a controlled manner by either reversing the rotation of driver300, or by advancing rotation of driver300if rotation during distraction had proceeded to the point of maximal distraction with the dimension of the gap approximating the distraction dimension y of cam322.

In various embodiments, a plurality of distractions drivers comprising cams having a range of different insertion dimensions, distraction dimensions, and cam depth dimensions may be provided in various permutations. In this manner, a distraction driver may be operator-selectable based on the particular application, such as the particular distraction procedure to be performed, variations in patient anatomy, and/or accommodation of different desired surgical procedure outcomes and associated sets of surgical instruments or implants. Operator-selection of a distraction driver having a cam depth less than the dimension of the bone structures defining a gap to be distracted affords a further safety feature of the distraction driver device disclosed herein, with the radial dimension of protective plate323extending beyond the radial dimensions of cam322providing a positive stop for insertion of cam322into a gap having a clearance fit for the cam. The positive stop provided by protective plate323can thereby serve to prevent overinsertion of a distraction driver having an appropriately selected cam dimensions.

In various embodiments, a kit for performing an osteodistraction can comprise a plurality of distraction drivers. A plurality of distraction drivers can comprise, for example, 2, 3, 4, 5, or more distraction drivers having complementary cam dimensions suitable to provide progressively increasing distraction dimensions y. For example, a kit in accordance with various embodiments can comprise 3 distraction drivers providing distraction dimensions of 4 mm, 6 mm, and 8 mm, thereby providing a distraction dimension delta of about 4 mm between the largest and the smallest distraction driver. The insertion dimensions of the drivers in a kit may be the same. In other embodiments, the insertion dimensions of the drivers in a kit may increase in size in various embodiments. For example, the insertion dimensions of the kit described above could be 2 mm, 3 mm, and 4 mm, respectively, to provide progressively increasing insertion dimensions configured to be compatible with the progressively increased distraction achieved with each distraction driver in the kit. In various embodiments, a kit can comprise any number of distraction drivers having any suitable combination of insertion dimension and distraction dimension, including kits in which each distraction driver has the same insertion dimension but progressively greater distraction dimensions.

In various embodiments, a kit for performing an osteodistraction can comprise an implantable distractor cam device. An implantable distractor cam device can comprise a modular system for osteodistraction that is further comprised of separate, operator-selectable and operator-assembled components. With reference now toFIGS. 4A-4E, an implantable distractor cam device400is illustrated. In various embodiments, modular implantable distractor cam device400can comprise a distraction component such as distractor cam431, a fixation component such as fixation plate430, and an attachment component such as attachment device532(FIG. 5). The fixation plate may be configured to be adjustably coupled to the distractor cam using the attachment device to produce an assembled implantable distractor cam device400.

In various embodiments, a distractor cam431can have a configuration similar to that described above with respect to cam322of distraction driver300(FIGS. 3A-3C). For example, in various embodiments, a distractor cam can have an ellipsoid, disc-cam shape. The distractor cam may be substantially symmetrical about one of an axis in the first dimension and an axis in the second dimension of the ellipsoid shape. Other configurations of a distractor cam are possible. In various embodiments, a distractor cam can comprise features that facilitate stable engagement of the distractor cam comprising a component of the implantable distractor cam device400with the adjacent bone structures at the site of implantation. For example and as illustrated inFIG. 4E, distractor cam431E comprises grooves located near the ends of ellipsoid shape that may more positively engage adjacent bone structures when implanted. Any of another of other surface configurations or features are possible and may be used in a distractor cam in accordance with the present disclosure.

In various embodiments, distractor cam431can comprise an implantable material, such as an allograft material comprising human cortical bone and/or cancellous bone. Other implantable materials can be used, such as metals including titanium and stainless steel, polymers including polyetheretherketone (PEEK), polyactic acid, and polyglycolic acid, ceramic materials including aluminum oxide and hydroxyapatite, and other biocompatible materials.

Pre-distraction, for example, using the distraction drivers described above, facilitates achieving final distraction with an implantable distractor cam device400having an implantable distractor cam431comprising a relatively soft allograft, PEEK, titanium, stainless steel, ceramic, or other implantable material. In addition, performing final distraction with an implantable distractor cam device400may provide for enhanced efficiency of an osteodistraction and implant placement procedure such as a laminoplasty by providing for simultaneous distraction and implantation of implantable device400, as compared to achieving the desired distraction with other instruments followed by placement of an implant in the distracted gap. Moreover, fixation plate430can serve a similar function to protective plate323of distraction driver300, with fixation plate430having an oversized configuration relative to the cross section of distractor cam431suitable to prevent overinsertion of distractor cam431into the gap between adjacent bone structures.

In various embodiments, an implantable distractor cam device can comprise a fixation component such as fixation plate430. A fixation plate can be configured to approximate the contours of a distracted anatomical structure, as illustrated and described below with respect to fixation plate430D. An implantable distraction cam device can also comprise an attachment component such as attachment device532(FIG. 5). Attachment device532can comprise, for example, a screw that threadedly engages the distraction cam, such as by driving a self-drilling screw into an allograft distraction cam or a bolt configured to engage a pre-threaded plate or insert in the distraction cam. In various embodiments, fixation plate430can be configured to be adjustably coupled to distractor cam431. For example, a fixation plate can comprise a slot433through which attachment device532may be inserted, with slot433providing for slidable adjustment of the relative position of cam431and fixation plate430. Other attachment components, fastening mechanisms, and adjustable coupling configurations are possible and within the scope of the present disclosure. Tightening or otherwise securing attachment device532can secure cam431to fixation plate430. Fixation plate430can also comprise surface features such as teeth or protrusions that provide for a positive engagement between the adjacent surfaces of fixation plate430and cam431. Attachment device532may be configured to engage fixation plate430in a manner that prevents over-engagement or stripping of the distraction cam by the attachment device, such by a distal screw head that positively engages the corresponding surface of the fixation plate. In various embodiments, implantable distractor cam device400can comprise features that facilitate engagement of an implantation driver, such as implantation driver slots435, described in more detail below.

In various embodiments, fixation plate430can further comprise fixation apertures434. Fixation apertures434can be used to secure fixation plate430to the adjacent bone structures following placement of implantable distractor cam device400, such as by inserting screws through fixation apertures434into the underlying adjacent bone structures.

The modular configuration of implantable distractor cam device400can permit selection and attachment of a suitably configured fixation plate to a selected distractor cam431. For example, a fixation plate may have a planar profile, such as that shown for fixation plate430inFIG. 4B, or a fixation plate may be pre-bent to conform to the features of the implantation site, such as fixation plate430D shown inFIG. 4D. Likewise, fixation plates may have a range of possible lengths and widths to further enhance an operator's ability to obtain an optical configuration of an implantable distractor cam device.

In various embodiments and with reference now toFIGS. 5 and 6, a kit for performing an osteodistraction can comprise an insertion component such as implantation drivers500and600. An implantation driver can comprise an elongated shaft with a handle at the proximal end. The distal end of the implantation driver can be configured to securely and reversible engage one of an assembled implantable distractor cam device or a distractor cam. Implantation driver500can be configured to engage assembled distractor cam device540. Implantation driver500can have a driver head541configured to selectively engage corresponding receptacle542in the head of attachment device532. Driver head541can further comprise a locking pin543configured to releasably engage a corresponding receiver in the side wall of receptacle542, thereby securing the assembled distractor cam device to the implantation driver. Implantation driver500can further feature lateral pins544configured to be received by implantation driver slots535. The interface between lateral pins544and fixation plate530at implantation driver slots535can provide for enhanced torque transfer from implantation driver500to assembled implantable distractor cam device540for actuation of the distractor cam and distraction of the gap while minimizing risk of over-engagement or stripping of attachment device532in the distractor cam, or loosening of attachment device532from the distractor cam with rotation in the opposite direction. In various embodiments, implantation driver can be released from the implanted distractor cam device540by operator actuation of locking pin543, such as with a button or lever located on the handle of implantation driver500, disengagement of a threaded screw, or any other device which may be used to attach the driver to the implantable distractor cam device.

Implantation driver600illustrated inFIG. 6includes similar features to implantation driver500. However, implantation driver600is configured to engage distractor cam631directly. Driver head641may be configured to engage a receptacle in distractor cam631such as a threaded insert or tapped hole645that may later be used to receive an attachment device for securing a fixation plate to distractor cam631. Distractor cam631may include sockets646configured to receive lateral pins644. In the illustrated embodiment with a cylindrical driver head641and tapped hole645, the interface between the sockets and lateral pins may provide for substantially all of the torque transfer from implantation driver600to distractor cam631. In various embodiments, other interfaces and retention mechanisms, such as slots or other non-round driver shapes or configurations (e.g., torx, cross, hex, etc.) may be used between an implantation driver and an assembled implantable distraction device or a distractor cam.

In various embodiments, a method of implanting an osteodistraction device is provided, for example, in connection with what is known to those skilled in the art as “open door” or “French door” laminoplasty procedures. A method can comprise inserting a distal end of a distraction driver700into a gap having a gap dimension between a first bone surface and a second bone surface (FIGS. 7A and 7B). The distraction driver can be inserted into the gap until a distal surface of a protection plate contacts a surface of the bone structure. The method can further comprise rotating the distraction driver in a first direction about a longitudinal axis to produce a distraction force (i.e., by controlled distraction) on the first bone surface and the second bone surface. The amount of rotation can be about 90 degrees, or more or less than 90 degrees based on the particular application and/or the desired distraction. The distraction force can produce linear displacement of the first bone surface and the second bone surface to produce a first distracted gap dimension between the bone structures. The first distracted gap dimension may be greater than the gap dimension and may approximately correspond to a second cam dimension. The method can further comprise further rotating the distraction driver in one of the first direction or a second direction opposite the first direction to controllably reduce the distraction force on the first bone surface and the second bone surface. The method can further comprise removing the distal end of the distraction driver following controllably reducing the distraction force.

As used herein, “controlled distraction” means producing displacement of two surfaces or structures by means of a mechanical device that maintains contact with both surfaces or structures throughout the distraction process and relies on forces and movements substantially parallel to the direction of displacement, such as the rotational movement and forces of a disk cam device inserted between two surfaces to be displaced from one another by rotation of the disk cam. A distraction device suitable to provide controlled distraction in accordance with various embodiments described and illustrated herein minimizes risk of slipping during engagement and operation of the device, and further minimizes the risk of an abrupt loss of distraction due to insertion into the gap between surfaces to be distracted and the manner in which the device fully occupies the gap. In contrast, a simple lever, forceps, spreader or other device may include techniques, forces and directions of movement associated with an increased risk of slippage and/or an abrupt return of the displaced structures to an undistracted position. Such an abrupt return of the displaced structures may produce undesirable consequences.

In various embodiments, sequential controlled distraction may be performed using a plurality of distraction drivers comprising distraction cams with increasing distraction dimensions. Sequential controlled distraction may produce progressive increases in the distracted gap dimension. This sequential controlled distraction can comprise a predistraction process to prepare for final distraction using an assembled implantable distraction device in accordance with various embodiments.