SURGICAL BONE RIVET

A bone rivet is provided that may be used as an alternative to a bone screw for bone fixation. The bone rivet includes a head and a threaded shaft that can be expanded upon installing the bone rivet into bone. A channel extends through the bone rivet and is shaped corresponding to a bulb of a mandrel used for installing the bone rivet. A first section of the channel has a smaller width than the mandrel's bulb to enable the bulb to expand the threaded shaft and a second section is sized to have a greater width. The installation process eliminates the task of rotating a typical bone screw during its installation. The threaded shaft also includes a cutting flute, which cuts a thread path for the threaded shaft into the bone thereby reducing the amount of torque needed to rotate and remove the bone rivet from bone.

BACKGROUND

Bone screws are typically the gold standard fracture fixation device for providing reliable and solid fixation of a fractured bone during the healing time period. In various examples, bone screws may be used as a stand-alone device to affix a bone fragment to a larger bone segment or as a lag screw, with multiple variations such as compression screws, cannulated screws, etc. Bone screws are also often used in conjunction with plating or intramedullary device technologies. Typical bone screws may be headed or headless and may employ numerous thread technologies and driver interface technologies.

Bone screw installation often requires rotating the screw to advance it into bone. Such an installation process can be time-consuming and can be especially arduous for a surgeon in some instances, such as when installing long screws with small pitches. One alternative bone fixation device to bone screws is a bone rivet. Installing typical bone rivets, however, may still require rotation of a component, and in some instances, may result in a portion of a deployment tool being left in a patient. It can also be difficult to remove typical bone rivets once installed, among other drawbacks.

Accordingly, a need exists for an alternative bone fixation device to bone screws that addresses the above drawbacks of typical bone screws and typical bone rivets.

SUMMARY

The present disclosure relates generally to bone fixation devices. More specifically, the present disclosure provides new and innovative bone rivets for bone fixation that may be used as an alternative to bone screws. The present disclosure also provides insertion systems and methods for installing the provided bone rivets.

In an example, a bone rivet includes a body portion having a head and a threaded shaft. At least a portion of the threaded shaft is deformable such that a width of the deformed at least a portion of the threaded shaft is greater than a width of the threaded shaft prior to deformation. A channel extends through the body portion, the channel including a first portion having a greater width than a second portion. The first portion of the channel extends through the head of the body portion. The body portion is constructed of a material such that the at least a portion of the threaded shaft deforms upon forced expansion of the at least a portion of the threaded shaft and subsequently maintains that deformation. The threaded shaft includes a cutting flute.

In another example, a bone rivet installation system includes a mandrel and the above example bone rivet. The mandrel includes a rod and a bulb. The bulb is at a distal end of the mandrel and has a greater width than the rod. The width of the bulb is greater than the width of the second portion of the bone rivet's channel and less than the width of the first portion of the bone rivet's channel.

In another example still, a bone rivet installation method includes drilling, via a drill, a hole into at least a first cortex of a bone. The above example bone rivet loaded with the above example mandrel is inserted into the drilled hole. The mandrel is then translated through the bone rivet's channel and out of the bone rivet thereby deforming the at least a portion of the bone rivet's threaded shaft such that the bone rivet is installed in the bone.

DETAILED DESCRIPTION

The present disclosure provides a bone rivet that may be used as an alternative to a bone screw for bone fixation. For example, a surgeon may use the provided bone rivet as a stand-alone device to affix a bone fragment to a larger bone segment instead of using a bone screw. In some instances, a surgeon may use the provided bone rivet with plating or intramedullary device technologies.

The provided bone rivet includes a body having a head and a threaded shaft. The threaded shaft can be expanded upon installation of the bone rivet into bone so that the bone rivet provides holding power in the bone. In some examples, the threaded shaft can be constructed of a material such that the threaded shaft as a whole deforms to provide this expansion. In other examples, the threaded shaft can include one or more slits that separate the threaded shaft into two or more wings. In such other examples, the threaded shaft can be constructed of a material that enables the two or more wings to bend away from one another and maintain that bent position. The at least one thread on the threaded shaft provides increased holding power when the at least one thread is compressed into bone, as compared to a rivet with a shaft that is not threaded, and allows for controlled rotational removal of the rivet if so desired.

The provided bone rivet also includes an interior channel shaped corresponding to a bulb of a mandrel used for installation of the bone rivet. The bone rivet may be loaded with the mandrel during insertion of both into a bone hole, and then the mandrel may be translated through the bone rivet's interior channel and out of the bone rivet to install the bone rivet. A section of the interior channel is sized to have a smaller width (e.g., diameter) than the mandrel's bulb such that the bulb forces the portion of the bone rivet including this interior channel section to expand as the bulb is translated through this interior channel section. This interior channel section is within the threaded shaft. A different section of the interior channel is sized to have a greater width (e.g., diameter) than the mandrel's bulb such that the bulb can be translated through this different interior channel section without affecting the bone rivet. This different interior channel section is within the bone rivet's head, and at least in some instances, a portion of the threaded shaft.

Accordingly, the provided bone rivet can be installed by inserting the bone rivet loaded with a mandrel into a pre-drilled bone hole and removing the mandrel from the bone rivet. This installation process eliminates the time-consuming, and sometimes arduous, task of rotating a typical bone screw during its installation to drive the bone screw into bone. The provided bone rivet can therefore help reduce operative time and help reduce physical strain for a surgeon. In some aspects, the provided bone rivet and/or mandrel may be adapted to be used with a powered drill such that the bone rivet and/or mandrel are used to drill the bone hole, thereby eliminating the pre-drilling step and further reducing operative time.

Once the bone rivet is installed, it is also a requirement in orthopedic applications that a bone fixation device can be removed from the bone. The at least one thread of the threaded shaft helps enable removal of an installed bone rivet. The bone rivet's head may also include a driver interface that a surgeon may engage with a drive instrument during removal. For example, the surgeon may rotate the installed bone rivet with the drive instrument to remove the bone rivet in a similar fashion as removing a screw. Because the provided bone rivet is inserted and installed without rotating the bone rivet, however, a thread path does not exist in the bone, which can result in an undesired amount of torque being needed to remove the bone rivet. To help reduce the amount of torque needed to remove the bone rivet, the threaded shaft of the provided bone rivet may include a reverse cutting flute. The cutting flute cuts the thread path for the threaded shaft into the bone as the bone rivet is rotated thereby reducing the amount of torque needed to rotate and remove the bone rivet. The provided bone rivet is therefore easier to remove from bone once installed than at least some typical bone rivets.

FIGS. 1 to 3illustrate various views of an example bone rivet100. The bone rivet100includes a body having a head102and a threaded shaft104. A channel110extends through the body of the bone rivet100from a trailing end of the bone rivet100to a leading end of the bone rivet100. The trailing end includes the head102and the leading end includes the threaded shaft104. In at least some aspects, the head102of the bone rivet100includes a driver interface114that may engage with a drive instrument. The driver interface114is illustrated as a hexagon interface in the example ofFIG. 3, though in other examples the driver interface114may have any other suitable shape for engaging with a drive instrument (e.g., hexalobe, slotted, phillips, etc.)

The threaded shaft104of the bone rivet100includes a thread106. In some examples, the threaded shaft104may include more than one thread106such that the threaded shaft is double-threaded, triple-threaded, etc. The thread106of the threaded shaft104may be of any suitable thread form, such as trapezoidal, curved, sawtooth, etc. In one aspect of the present disclosure (e.g.,FIGS. 8A and 8B), the threaded shaft104may continuously extend around the channel110. In such an aspect, the thread106may extend continuously on the threaded shaft104. In other aspects of the present disclosure (e.g.,FIGS. 1-4), the threaded shaft104may include a slit108such that at least a portion of the threaded shaft104is split into a wing120and a wing122. In such other aspects, the thread106is discontinuous on the threaded shaft104due to the slit108. In some examples, the threaded shaft104may include more than one slit108such that at least a portion of the threaded shaft104is split into three or more wings120,122. For instance, the threaded shaft104may include two slits108perpendicular to one another thereby splitting the threaded shaft104into four wings120,122. In another instance, the threaded shaft104may include three slits108at an angle of 120° from one another and joining at a central axis of the bone rivet100, thereby splitting the threaded shaft104into three wings120,122.

In at least some aspects, the threaded shaft104includes a cutting flute112. The cutting flute112cuts into bone to form a thread path for the thread106when an installed bone rivet100is rotated, such as to remove the installed bone rivet100from bone. By forming the thread path for the thread106, the cutting flute112helps reduce the amount of torque needed to rotate and remove an installed bone rivet100from bone. For instance, without a thread path in the bone, an undesirable amount of torque would be required to rotate an installed bone rivet100, which could cause the driver interface114to strip or a drive instrument to break. In some examples, the cutting flute112may be located at an edge of the wing120or the wing122and adjacent the slit108. The example illustrated in the figures shows the cutting flute112located at an edge of the wing120and adjacent the slit108. In other examples, the cutting flute112may be located on the wing120or the wing122, and away from the slit108.

The threaded shaft104may be constructed of a material that enables at least a portion of the threaded shaft104to deform upon a sufficient force being applied to the threaded shaft104, and to thereafter maintain that deformation. For example, the wing120and the wing122may be forced away from another such that they bend away from one another (FIG. 6C) and permanently maintain that bend against forces that may be experienced within the bone. Suitable materials for enabling the wing120and the wing122to bend and permanently maintain that bend include, for example, stainless steel, titanium, cobalt chrome, and some plastics such as PEEK, etc. In some aspects, the head102may also be constructed of this material such that the bone rivet100as a whole is constructed of a single material. In one aspect, the head102may be constructed of a different material than the threaded shaft104.

In aspects in which the threaded shaft104includes one or more slits108, the one or more slits108may determine the portion of the threaded shaft104that is deformed. Stated differently, the portion of the threaded shaft104including the one or more slits108, which is the wings120and122, may be the only portion of the threaded shaft104that deforms. In various aspects, a portion of the threaded shaft104that does not include the one or more slits108, and therefore is not split into wings120and122, does not deform upon installation of the bone rivet100.

As mentioned above, in one aspect of the present disclosure, the threaded shaft104may continuously extend around the channel110. Stated differently, in such an aspect, the threaded shaft104does not include the slit108.FIG. 8Aillustrates an example bone rivet800that includes a threaded shaft104that extends continuously around the channel. In this example, the cutting flute112is formed in the threaded shaft104without the slit108. In such an aspect, when the example bone rivet800is installed, the threaded shaft104deforms so that a diameter of at least a portion of the threaded shaft104increases and the increased diameter is permanently maintained against forces that may be experienced within the bone.FIG. 8Billustrates the example bone rivet800with a deformed portion802of the threaded shaft104that has a greater diameter than a remaining portion of the threaded shaft104. Suitable materials for enabling the threaded shaft104to deform and maintain that deformation in this way include, for example, stainless steel, titanium, cobalt chrome, and some plastics such as PEEK, etc. In at least some aspects, the head102may also be constructed of this material such that the bone rivet100as a whole is constructed of a single material. In one aspect, the head102may be constructed of a different material than the threaded shaft104.

FIG. 4illustrates a cross-sectional view of the bone rivet100, along a central plane of the bone rivet100, showing the channel110that extends through the body of the bone rivet100. The channel110includes a first portion116and a second portion118. The first portion116has a greater width than the second portion118. In some aspects, the channel110may be cylindrical. In such aspects, the widths of the first portion116and of the second portion118are diameters. In other aspects, the channel110may be non-cylindrical (e.g., square, hexagonal, etc.). In some examples, such as the illustrated one, the width of the channel110may gradually increase from the second portion118to the first portion116. In other examples, the width of the channel110may abruptly increase from the second portion118to the first portion116.

FIG. 5illustrates an example bone rivet insertion system500that includes the bone rivet100and a mandrel502. The example mandrel502includes a rod504and a bulb506. The bulb506is located at a distal end of the mandrel502. A proximal end (not illustrated) of the mandrel502, in at least some aspects, may be adapted to be used with a bone rivet deployment tool (not illustrated). The bulb506has a greater width than the rod504. In some aspects, the rod504and/or the bulb506of the mandrel502may be cylindrical. In such aspects, the widths of the rod504and/or the bulb506are diameters. In other aspects, the rod504and/or the bulb506of the mandrel502may be non-cylindrical (e.g., square, hexagonal, etc.). In some examples, such as the illustrated one, the width of the mandrel502may gradually increase from the rod504to the bulb506. In other examples, the width of the mandrel502may abruptly increase from the rod504to the bulb506.

The bone rivet100and the mandrel502are each adapted to be used in conjunction for installing the bone rivet100in bone. For instance, the bone rivet100may be loaded with the mandrel502such that the rod504is positioned through the channel110and a leading end of the bone rivet100is adjacent the bulb506. The bone rivet100is shown loaded with the mandrel502inFIG. 6Bdiscussed below. From the loaded configuration, the bulb506of the mandrel502may be translated through the channel110to install the bone rivet100. Returning toFIGS. 4 and 5, the width of the bulb506is sized according to the widths of the first portion116and the second portion118of the channel110of the bone rivet100. More specifically, the width of the bulb506is greater than the width of the second portion118, but less than the width of the first portion116. As such, when the bulb506is translated through the channel110from the loaded configuration, the bulb506forces the threaded shaft104to deform as the bulb506translates through the second portion118since the bulb506has a greater width than the second portion118. For example, the wing120and the wing122may bend away from one another as the bulb506translates through the second portion118.

A difference between the width of the bulb506and the width of the second portion118can determine an amount that the threaded shaft104deforms. For instance, the larger the width of the bulb506as compared to the width of the second portion118, the more that the threaded shaft104will deform as the bulb506is translated through the second portion118. In at least some aspects, the width of the bulb506is therefore more than marginally greater than the width of the second portion118so that the threaded shaft104deforms sufficiently for the bone rivet100to provide sufficient holding power in bone. An upper limit of the width of the bulb506corresponds to a width of the first portion116, which is limited by the widths of the threaded shaft104and the head102.

As the bulb506is translated through the channel110and reaches the first portion116, the bulb506no longer forces the threaded shaft104to deform since the width of the bulb506is less than the width of the first portion116. In at least some aspects, the width of the bulb506is marginally less than the width of the first portion116such that the bulb506maintains axial alignment with the first portion116as the bulb506is translated through the first portion116.

In various aspects, the first portion116and the second portion118of the channel110may be arranged relative to the slit108. In the example illustrated inFIG. 4, the first portion116of the channel110begins near (e.g., just prior to) a termination point124of the slit108relative to the leading end of the bone rivet100. This example arrangement of the first portion116and second portion118of the channel110may help maintain the integrity and strength of the bone rivet100upon installation. For instance, the second portion118ending, and therefore the first portion116beginning, near (e.g., just prior to) the termination point124of the slit108helps prevent undesired deformation or breakage of the threaded shaft104outside of the wings120and122, which could reduce the holding strength or fatigue life of the bone rivet100.

In another example, the first portion116of the channel110may begin at a middle portion of the slit108, away from the termination point124. In this example, only a portion of the wings120and122would deform since only a portion of the wings120and122include the narrower second portion118of the channel110. It is also contemplated that, in one example, the first portion116of the channel110may begin after the termination point124of the slit108relative to the leading end of the bone rivet100. In such an example, the material of the bone rivet100may deform or fracture at the termination point124of the slit108to accommodate the bulb506translating through the second portion118. Despite the deformation or fracture at the termination point124, the bone rivet100in this example maintains sufficient strength for bone fixation.

FIGS. 6A to 6Cillustrate steps of an example method for installing a bone rivet (e.g., the bone rivet100) into bone. In some instances, the bone rivet100may secure a plate600to bone as shown inFIGS. 6A to 6C, though the example method may apply similarly to other instances in which the plate600is not present. A surgeon may drill a bone hole606into bone through the first cortex602A of the bone. In some aspects, the surgeon may drill the bone hole606through the first cortex602A, the medullary canal604, and the second cortex602B of the bone.

In at least some instances, the surgeon may determine a desired size of the bone rivet100using a suitable measuring tool. The bone rivet100of the desired size may then be loaded with a mandrel502if not already loaded. As mentioned above, the bone rivet100is loaded with the mandrel502when the rod504is positioned through the channel110and the leading end of the bone rivet100is adjacent the bulb506. In various aspects, the surgeon may insert the bone rivet100having a loaded mandrel502into the bone hole606. In some examples, the bone rivet100having the loaded mandrel502is loaded into a bone rivet deployment tool, such as a bone rivet gun, and the tool is used to insert the bone rivet100having the loaded mandrel502into the bone hole606.

In one aspect of the present disclosure, the mandrel502and/or the bone rivet100may be constructed such that they can be used to form a hole in a bone under the power of a drill without the need for pre-drilling prior to insertion. For instance, a tip of the bulb506of the mandrel502may be a trocar tip or a pointed tip with cutting flutes. In some aspects, the threaded shaft104of the bone rivet100may include an additional cutting flute at the leading edge of the threaded shaft104to aid in drilling.

In an example of such various aspects, the bone rivet100with a loaded mandrel502may be coupled to a powered drill that drives the bone rivet100and loaded mandrel502to form the bone hole606. In some instances, the bone rivet100with the loaded mandrel502may be removed from the bone hole606after formation, de-coupled from the powered drill, and then re-inserted into the bone hole606. In other instances, the bone rivet100remains in the bone hole606after formation (i.e. it is not removed) and only the mandrel502is removed to install the bone rivet100. In some aspects, a bone rivet deployment tool may be used with the bone rivet100and loaded mandrel502to install the bone rivet100in bone hole606. Because the drilling is done under high rotational speeds, the bone hole606formed by the bone rivet100and loaded mandrel502is smooth and therefore does not include a thread path despite the threaded shaft104of the bone rivet100being inserted in the bone hole606during formation. Accordingly, this aspect of the provided method still provides the advantage of aiding the removal of the installed bone rivet100from bone once installed as compared to at least some typical bone rivets. Additionally, this aspect of the provided method has the advantage of eliminating the need for pre-drilling, thus reducing operative time further.

With the bone rivet100and loaded mandrel502inserted in the bone hole606, the surgeon may translate the mandrel502through the channel110and out of the bone rivet100in the direction of the arrow608to install the bone rivet100. In at least some aspects, the surgeon translates the mandrel502through the channel110and out of the bone rivet100using the bone rivet deployment tool. As the surgeon translates the mandrel502through the channel110, the bulb506initially passes through the second portion118of the channel110. Since the bulb506has a greater width than the second portion118, as described above, the bulb506forces the threaded shaft104of the bone rivet100to deform as the bulb506passes through the second portion118of the channel110. In this example, the bulb506forces the wing120and the wing122to bend away from one another. The thread106on each of the bent wings120and122presses into the bone and provides holding power for the bone rivet100. Once the bulb506reaches the first portion116of the channel110as the mandrel502is translated out of the bone rivet100, the bulb506no longer forces the bone rivet100to deform, as described above. In various aspects, the entire mandrel502is removed from the bone rivet100and the patient, and can be disposed of or cleaned for later use.

Although it can be beneficial to remove the entire mandrel502from the patient so that there are no potentially loose pieces in the patient, it is also contemplated in one aspect of the present disclosure, that a portion of the mandrel502could remain between the wings120and122after installation of the bone rivet100to help maintain the bend in the wings120and122. For instance, the mandrel502may include a reduced portion at which the rod504is configured to break upon a force being applied, such as a twisting force. In one example, this reduced portion may be where the rod504meets the bulb506. In such an example, once the mandrel502has been translated through the channel110to sufficiently bend the wings120and122, a surgeon may twist the rod504to separate it from the bulb506thereby leaving the bulb506between the wings120and122.

In some aspects, the example method may include removing the installed bone rivet100from the bone hole606. In such aspects, the surgeon may engage the driver interface114of the bone rivet100with a drive instrument and rotate the bone rivet100so that the thread106drives the bone rivet100out of the bone hole106. As described above, the cutting flute112cuts into the bone as the surgeon rotates the bone rivet100with the drive instrument to form an interior thread in the bone, thereby reducing an amount of torque the surgeon must apply to rotate and remove the bone rivet100.

The inventors have demonstrated that the bone rivet100of the present disclosure provides a pull out strength on the same order of magnitude as a typical, comparably-sized bone screw.FIG. 7Aillustrates a bar graph700showing an average magnitude of the pullout force (in Newtons) for eight 8 mm bone screws (shown by the bar702) as compared to the provided bone rivet100(shown by the bar704). A standard deviation is also shown for each the bar702and the bar704. The inventors have additionally demonstrated that the torque required to remove the bone rivet100of the present disclosure from a bone is on the same order of magnitude as the torque required to insert a typical, comparably-sized bone screw.FIG. 7Billustrates a bar graph710showing an average magnitude of the torque (in Newton-meters) required to insert eight 8 mm bone screws (shown by the bar712) as compared to that required to remove the provided bone rivet100(shown by the bar714). A standard deviation is also shown for each the bar712and the bar714.

Without further elaboration, it is believed that one skilled in the art can use the preceding description to utilize the claimed inventions to their fullest extent. The examples and aspects disclosed herein are to be construed as merely illustrative and not a limitation of the scope of the present disclosure in any way. It will be apparent to those having skill in the art that changes may be made to the details of the above-described examples without departing from the underlying principles discussed. In other words, various modifications and improvements of the examples specifically disclosed in the description above are within the scope of the appended claims. For instance, any suitable combination of features of the various examples described is contemplated.