VARIABLE-ANGLE LOCKING SCREWS, AND BONE PLATE SYSTEMS THAT INCLUDE VARIABLE-ANGLE LOCKING SCREWS

A bone plate system may include a combination of one or more of a bone plate, non-locking screws, standard locking screws, and variable-angle locking screws. The bone plate may have threaded holes and non-threaded holes. Variable-angle locking screws may have a threaded shank and a threaded head. The threading on the head may be discontinuous, which allows the variable-angle locking screw to be inserted into a threaded hole on the plate at an angle relative to the axis of the threaded hole.

BACKGROUND

Bone plates are used to provide structural support for fixation of various types of bone fractures. Bone plates are secured to the bone to “reduce” the fracture, i.e., bring bone fragments into alignment and close proximity to facilitate the body's natural bone growth and healing. Bone reduction is generally accomplished using non-locking screws. Non-locking screws have threaded shafts and are anchored through holes in the bone plate and into the various bone fragments, which upon tightening pull the bone fragments together under a compression load against the plate. However, due to dynamic loading caused by physiological movement, the non-locking screws may back out over time.

Locking screws may be anchored both to the bone plate and to the bone to reduce the incidence of loosening and provide a fixed angular relationship between the bone plate and the locking screws. A locking screw has a threaded head which mates with corresponding threads of a threaded hole in the bone plate, and a threaded shaft which anchors to the bone. Thus, because a locking screw is secured to both the bone and the bone plate, movement between the bone plate and the locking screws is reduced. As the relationship between the locking screws and the bone plate is fixed, locking screws provide a high resistance to shear or torsional forces. However, locking screws have a limited capability to compress bone fragments.

Thus, a combination of non-locking and locking screws may be employed with a bone plate to promote reduction of bone fractures while also preventing loosening and movement between the bone plate and the screws. Accordingly, bone plates may be configured with a combination of threaded and non-threaded holes. Standard locking screws may be inserted into a threaded hole at a fixed angle. However, it may be desirable to have a locking screw that is able to be inserted into the threaded hole at different angles.

SUMMARY

Described herein is a variable-angle locking (VAL) screw insertable into a threaded hole, the VAL screw comprising a head having a first end, a second end, and an outer surface extending between the first end and the second end, and a shank extending from the first end of the head along a longitudinal axis of the VAL screw, wherein the outer surface of the head includes a plurality of thread segments, wherein the outer surface of the head includes engaging portions that engage the threaded hole and non-engaging portions that do not engage the threaded hole, and wherein the plurality of thread segments extend across the engaging portions and do not extend across the non-engaging portions.

A bone plate system is also described, the system comprising a plate having a threaded hole, wherein the threaded hole comprises a substantially continuous thread extending about an axis of the threaded hole, and a variable-angle locking (VAL) screw comprising a head having a first end, a second end, and an outer surface extending between the first end and the second end, and a shank extending from the first end of the head along a longitudinal axis of the VAL screw, wherein the outer surface of the head includes a plurality of thread segments, wherein the outer surface of the head includes engaging portions that engage the threaded hole and non-engaging portions that do not engage the threaded hole, wherein the plurality of thread segments extend across the engaging portions and do not extend across the non-engaging portions, wherein the VAL screw is insertable into the threaded hole of the plate.

Also described herein is a variable-angle locking (VAL) screw insertable into a threaded hole, the VAL screw comprising a head having a first end, a second end, and an outer surface extending between the first end and the second end, and a shank extending from the first end of the head along a longitudinal axis of the VAL screw, wherein the outer surface of the head comprises one or more discontinuous threads.

A bone plate system is also described, the system comprising a plate having a threaded hole, wherein the threaded hole comprises a substantially continuous thread extending about an axis of the threaded hole, and a variable-angle locking (VAL) screw comprising a head having a first end, a second end, and an outer surface extending between the first end and the second end, and a shank extending from the first end of the head along a longitudinal axis of the VAL screw, wherein the outer surface of the head comprises one or more discontinuous threads, and wherein the VAL screw is insertable into the threaded hole of the plate.

DETAILED DESCRIPTION

This disclosure uses various terms relating to threads on screws and on threaded holes. When an external surface of an item is threaded, this may be referred to as a male thread. On a male thread, the root is the point that is closest to the longitudinal axis of the thread, and the crest is the point that is farthest from the longitudinal axis of the thread. The major diameter is calculated by doubling the distance from the longitudinal axis to the crest. The minor diameter is calculated by doubling the distance from the longitudinal axis to the root. These distances are measured on a plane perpendicular to the longitudinal axis of the thread, which may also be referred to as a gauge plane.

When an internal surface of an object is threaded, this may be referred to as a female thread. On a female thread, the crest is the point that is closest to the longitudinal axis of the thread, and the root is the point that is farthest from the longitudinal axis of the thread. The major diameter is calculated by doubling the distance from the longitudinal axis to the root. The minor diameter is calculated by doubling the distance from the longitudinal axis to the crest. These distances are measured on a plane perpendicular to the longitudinal axis of the hole, which may also be referred to as a gauge plane.

Internal fixation of bone fractures may be achieved using a plating system001shown inFIGS. 16-17. The plating system may include a plate100, one or more non-locking screws300, and one or more locking screws200,400. The locking screws included in the plating system001may be standard locking screws400, variable-angle locking screws200, or a combination thereof. The plate100may be used to bridge the fracture and temporarily provides fixation as the bone heals, and may be attached to the bone by one or more screws. Non-locking screws300may be used to provide tension or compression by pushing the plate100and bone fragments relative to one another. Non-locking screws300may also be used neutrally to buttress the fracture and hold fragments in place, but they may back out of the hole over time. Standard locking screws400and/or variable-angle locking screws200may be used to anchor the plate100to the bone or hold small bone fragments in place. The exemplary embodiment shown inFIGS. 16-17includes a plate100, two non-locking screws300, two standard locking screws400, and two variable-angle locking screws200. However, any number of non-locking screws300, standard locking screws400, and variable-angle locking screws200may be used. Furthermore, the standard locking screws400are optional, as variable-angle locking screws200may be used in their place.

A bone plate, such as the plate100shown inFIGS. 7-9, may be used as part of an internal fixation system001for bone fractures. The bone plate100may be fabricated in any number of sizes and configurations in order to provide plates for use on different types of fractures. The plate100may be substantially planar, or it may be curved, angled, or otherwise formed to align with the patient's anatomy. The plate100may have a first surface102that faces the bone and a second surface103opposite the first surface102.

The plate100may include one or more holes120,130. The holes120,130may extend between the first surface102and the second surface103. Some of the holes may be threaded holes120, while other holes may be non-threaded holes130. Typically, locking screws200,400may be inserted into a threaded hole120and non-locking screws300may be inserted into a non-threaded hole130.

One or more threaded holes120may be included on the plate100. Each threaded hole120may have a first opening122on the first surface102of the plate100and a second opening123on the second surface103of the plate100. An axis124of the threaded hole120may extend along a line passing through the center of the first opening122and the center of the second opening123. Each threaded hole120may have one or more female threads121. The one or more threads121may be substantially continuous.

The threaded hole120may be a tapered hole, or it may have another configuration. Preferably, the threaded hole120may be tapered such that the first opening122on the first surface102of the plate100is smaller than the second opening123on the second surface103of the plate100. If the threaded hole120is tapered, each thread121may form a truncated conical helix following the taper of the threaded hole120. Alternatively, the threaded hole120may be substantially straight (cylindrical), and each thread121may form a cylindrical helix.

The one or more female threads121may form a series of alternating crests126and roots125. The major diameter128of a thread121may be calculated by doubling the distance from the axis124of the threaded hole120to the root125of the thread121. Likewise, the minor diameter127of a thread121may be calculated by doubling the distance from the axis124of the threaded hole120to the crest126of the thread121. A theoretical major diameter may be calculated by extending the two edges of adjacent windings of the threads121until they intersect at a theoretical root, and doubling the distance from the axis124to the theoretical root to arrive at a theoretical major diameter. A theoretical minor diameter may also be calculated by extending the two edges of a thread121until they intersect at a theoretical crest, and doubling the distance from the axis124to this theoretical crest to arrive at a theoretical minor diameter. For the threaded hole120shown inFIG. 9B, the major diameter128is also the theoretical major diameter because two adjacent windings of the threads121intersect at a point to form the root125. The minor diameter127is also to the theoretical minor diameter because the threads121have a triangular cross-section, so the two edges of a thread intersect at a point to form the crest126. A pitch diameter may be calculated by taking the average of the theoretical major diameter and the theoretical minor diameter. In the threaded hole120shown inFIG. 9B, the pitch diameter129is the average of the minor diameter127and the major diameter128.

The plate100may be manufactured using any materials that are commonly used in orthopedic fixation systems. For example, the plate100may be manufactured from a metal or polymeric material, or combinations thereof.

The system001may include one or more standard locking screws400, shown inFIG. 15. A standard locking screw400may have a head410and a shank460. The head410may have a first end411, a second end412, and an outer surface extending between the first end411and the second end412. The shank460may extend from the first end411of the head410along a longitudinal axis401of the screw400. A driving feature450may be included on the second end412of the head410. The longitudinal axis401may intersect the center points of one or more of the first end411of the head410, the second end412of the head410, and the driving feature450of the head410. Preferably, the longitudinal axis401may intersect the center points of all of the first end411of the head410, the second end412of the head410, and the driving feature450of the head410.

The shank460of the standard locking screw400may include one or more male threads462extending along at least part of the outer surface of the shank460. The threads462on the shank460allow the screw400to interlock with the bone. The threads462may extend substantially helically about the longitudinal axis401of the screw400.

The outer surface of the head410may also include one or more male threads421which allow the screw400to interlock with a threaded hole120on the plate100. The threads421on the outer surface of the head410of the standard locking screw400may be substantially continuous, such that the threads421fully engage the threads121on the threaded hole120of the plate100.

The system001may include one or more variable-angle locking screws200, shown inFIGS. 10-14. A variable-angle locking screw200may have a head210and a shank260. The head210may have a first end211, a second end212, and an outer surface extending between the first end211and the second end212. The shank260may extend from the first end211of the head210along a longitudinal axis201of the screw200. A driving feature250may be included on the second end212of the head210. The longitudinal axis201may intersect the center points of one or more of the first end211of the head210, the second end212of the head210, and the driving feature250of the head210. Preferably, the longitudinal axis201may intersect the center points of all of the first end211of the head210, the second end212of the head210, and the driving feature250of the head210.

The shank260of the variable-angle locking screw200may include one or more male threads262extending along at least part of the outer surface of the shank260. The threads262on the shank260allow the screw200to interlock with the bone. The threads262may extend substantially helically around the longitudinal axis201of the screw200.

The outer surface of the head210may also include one or more male threads221which allow the variable-angle locking screw200to interlock with a threaded hole120on the plate100. Unlike standard locking screws400which have substantially continuous threads421, the threads221on the head210of the variable-angle locking screw200may be discontinuous, such that each thread221is separated into a plurality of thread segments220.

The head210may have engaging portions230that interlock with the threaded hole120of the plate100, and non-engaging portions240which do not interlock with the threaded hole120of the plate100. Each engaging portion230comprises at least one thread segment220, and may further comprise a series of thread segments220. When the variable-angle locking screw200is inserted into a threaded hole120of a plate100, the thread segments220at the engaging portions230of the head210interlock with the threads121on the threaded hole120of the plate100. The thread segments220of the engaging portions230do not extend across the non-engaging portions240, and therefore the non-engaging portions240do not interlock with the threads121on the threaded hole120of the plate100. The non-engaging portions240may extend from the first end of the head to the second end of the head. The engaging portions230and non-engaging portions240may alternate around the outer surface of the head210, forming alternating columns around the outer surface of the head210. Each column may be formed by some of the thread segments220. The thread segments220on the engaging portions230may be aligned such that, if the thread segments220were extended across the non-engaging portions240, they would form substantially continuous threads221extending helically around the head210, as shown by the dashed lines inFIG. 13A. In other words, a curve extends along a trajectory formed by a crest223of a first thread segment220on a first engaging portion230, and the curve follows the trajectory across a non-engaging portion240and also extends along a trajectory formed by a crest223of a second thread segment220on an adjacent engaging portion230.

Each engaging portion230of the head210of the variable-angle locking screw200may comprise a series of alternating crests223and roots222that form the thread segments220. The number of thread segments220present in a particular engaging portion230may be counted by counting the number of crests223present in that engaging portion230. Each engaging portion may have at least one crest223. The engaging portions230may each have a substantially similar number of crests223.

The minor diameter224of a thread221may be calculated by doubling the distance from the longitudinal axis201to the root222of the thread221. Likewise, the major diameter225of a thread221may be calculated by doubling the distance from the longitudinal axis201to the crest223of the thread221. A theoretical major diameter (225t) may be calculated by extending the two edges of a thread segment220until they intersect at a theoretical crest (as shown inFIG. 13B), and doubling the distance from the longitudinal axis201to this theoretical crest to arrive at a theoretical major diameter. A theoretical minor diameter may also be calculated by extending the edges of two adjacent thread segments220until they intersect at a theoretical root, and doubling the distance from the longitudinal axis201to this theoretical root to arrive at a theoretical minor diameter. For the screw200shown inFIG. 13B, the minor diameter224is also the theoretical minor diameter because two adjacent thread segments220intersect at a point to form the root222. However, the major diameter225is not equal to the theoretical major diameter (225t) because the thread221has a trapezoidal cross-section. A pitch diameter may be calculated as the average of the theoretical major diameter and the theoretical minor diameter. In the screw shown inFIG. 13B, the pitch diameter226is the average of the minor diameter224and the theoretical major diameter (225t).

The non-engaging portions240may be formed in a variety of shapes. Typically, the non-engaging portions240are substantially unthreaded. In some embodiments, the surface of the non-engaging portions240may follow the shape of the head210of the variable-angle locking screw200to minimize the amount of material that is removed from the screw200to create the non-engaging portions240. For example, if the head210is tapered, then the surface of the non-engaging portion240may also be tapered. Alternatively, the non-engaging portions240may be substantially planar surfaces that extend between the adjacent engaging portions230.

The border228between an engaging portion230and an adjacent non-engaging portion240may be formed substantially along an intersection between the outer surface of the head210and a plane in which the longitudinal axis201lies. As such, each border228between an engaging portion230and an adjacent non-engaging portion240may be coplanar with the longitudinal axis201.

The following equation may be used to determine the angulation of the variable-angle locking screw200in the threaded hole120of the plate100.

The screw angle (x), shown inFIG. 3, is the angle between the longitudinal axis201of the variable-angle locking screw200and the axis124of the threaded hole120of the plate100. The screw angle (x) is greater than or equal to 0°. As the axis201of the screw200moves away from being coaxial with the axis124of the threaded hole120, the screw angle (x) increases.

The nominal screw head protrusion height (H), shown inFIG. 6, is the distance between the center of the second end212of the head210of the variable-angle locking screw200and a plane containing the second opening123of the threaded hole120of the plate100. The nominal screw head protrusion height (H) is measured when the screw200is inserted into the threaded hole120coaxially, such that the screw angle (x) is zero.

The screw head protrusion height (y), shown inFIG. 3, is the distance between the center of the second end212of the head210of the variable-angle locking screw200and a plane containing the second opening123of the threaded hole120of the plate100. If the screw200is coaxially inserted into the threaded hole120, then the head protrusion height (y) equals the nominal screw head protrusion height (H). The nominal screw head protrusion height (H) will be greater or equal to zero. In general, the screw head protrusion height (y) may increase as the screw angle (x) increases.

The segment angle (θseg), shown inFIG. 14, is the angle between the borders228on either side of an engaging portion230of the variable-angle locking screw200, if the borders228were each extended to intersect the longitudinal axis201of the screw200, as shown inFIG. 14.

The number of engaging portions (Nseg) is the total number of engaging portions230on the head210of the variable-angle locking screw200.

The engagement ratio (R) is the number of engaging portions230having at least one thread segment220that engages the threaded hole120on the plate100divided by the total number of engaging portions (Nseg). The engagement ratio (R) may range from 0 (if none of the thread segments220are engaged with the threaded hole120) to 1 (if each engaging portion230has at least one thread segment220on engaged with the threaded hole120). Preferably, the engagement ratio (R) is greater than zero.

The hole pitch diameter (Phole) is the pitch diameter of the threaded hole120of the plate100. If the threaded hole120of the plate100is not cylindrical, the hole pitch diameter (Phole) is measured on a gauge plane at the widest part of the threaded hole120. For example, if the threaded hole120of the plate100forms a truncated cone, wherein the second opening123is larger than the first opening122, as shown inFIG. 9A, then the hole pitch diameter (Phole) would be determined based on the theoretical minimum thread diameter and theoretical maximum thread diameter on a gauge plane at the second surface103of the plate100. Increasing the hole pitch diameter (Phole) may allow for a greater screw angle (x).

The plate thickness (T) is the distance between the first surface102of the plate100and the gauge plane at the widest part of the threaded hole120. InFIG. 9A, the plate thickness (T) is the distance between the first surface102of the plate100and the second surface103of the plate100adjacent the threaded hole120because the gauge plane is at the second surface103of the plate100. Increasing the plate thickness (T) may limit the screw angle (x). If a thicker plate is desired, a counter bore or relief area may be added to the first opening122of the threaded hole120of the plate100to offset an increase in thickness.

The screw pitch diameter (Pscrew) is the pitch diameter of the head210of the variable-angle locking screw200. The screw pitch diameter (Pscrew) may be measured on a gauge plane at the widest part of the head210of the screw200. For example, if the head210of the screw200forms a truncated cone, wherein the second end212is larger than the first end211, then the screw pitch diameter (Pscrew) would be determined based on the theoretical minimum thread diameter and theoretical maximum thread diameter on a gauge plane at the second end212of the head210of the screw200. Increasing the screw pitch diameter (Pscrew) may limit the screw angle (x).

In Equation 1, the screw angle (x) and segment angle (θseg) are measured in degrees; however, the equation could be modified to accommodate other units of measurement, such as radians. The plate thickness (T), nominal screw head protrusion height (H), screw head protrusion height (y), hole pitch diameter (Phole), and screw pitch diameter (Pscrew) may be measured in millimeters, inches, or any unit of distance, so long as the same unit is used for all of these variables (or the equation is modified to accommodate different units of measurements). The number of engaging portions (Nseg) and engagement ratio (R) do not have units.

Equation 1 assumes that, if the threaded hole120of the plate100and the head210of the screw200have a tapered conical shape, a similar taper angle is used on the threaded hole120of the plate100and the head210of the screw200.

The variable-angle locking screw200may have a plurality of engaging portions230and a plurality of non-engaging portions240. The number of engaging portions230(also referred to as (Nseg) in Equation 1) and the number of non-engaging portions240may vary based on the dimensions of the screw200. In some embodiments, the screw200may have at least two engaging portions230and at least two non-engaging portions240. In other embodiments, screw may have between two and ten engaging portions230and between two and ten non-engaging portions240. In preferred embodiments, the screw200may have at least three engaging portions230and at least three non-engaging portions240. In other preferred embodiments, screw may have between three and ten engaging portions230and between three and ten non-engaging portions240.

Each engaging portion230and non-engaging portion240may cover a percentage of the outer surface of the head210. The percentage of the outer surface of the head210covered by each engaging portion may be calculated as

In some embodiments, each engaging portion230may cover approximately the same percentage of the outer surface of the head210. Each non-engaging portion240may cover approximately the same percentage of the outer surface of the head210. However, the percentage of the outer surface of the head210covered by each engaging portion230is not necessarily the same as the percentage of the outer surface of the head210covered by each non-engaging portion240.

The total percentage of the outer surface of the head210covered by all of the engaging portions230may be calculated by adding together the percentage of the outer surface of the head210that each engaging portion230covers. If each engaging portion230covers the same percentage of the outer surface of the head210, then the total percentage of the outer surface of the head210covered by all of the engaging portions230combined may be calculated as

The total percentage of the outer surface of the head210covered by all of the engaging portions230may vary. In some embodiments, the total percentage of the outer surface of the head210covered by all of the engaging portions230may be at least about 25%. In other embodiments, the total percentage of the outer surface of the head210covered by all of the engaging portions230may range from about 25% to about 99%. In other embodiments, the total percentage of the outer surface of the head210covered by all of the engaging portions230is at least half of the outer surface of the head210and less than the entire outer surface of the head210. In other embodiments, the total percentage of the outer surface of the head210covered by all of the engaging portions230may be at least about 50%. In other embodiments, the total percentage of the outer surface of the head210covered by all of the engaging portions230may range from about 50% to about 99%. However, increasing the total percentage of the outer surface of the head210that is covered by the engaging portions230may limit the screw angle (x) that can be achieved.

The sum of the percentage of the outer surface covered by the engaging portions230and the percentage of the outer surface covered by the non-engaging portions240may equal 100%. Therefore, in some embodiments, the total percentage of the outer surface of the head210covered by all of the non-engaging portions240may be less than about 75%. In other embodiments, the total percentage of the outer surface of the head210covered by all of the non-engaging portions240may range from about 1% to about 75%. In other embodiments, the total percentage of the outer surface of the head210covered by all of the non-engaging portions240may be less than about 50%. In other embodiments, the total percentage of the outer surface of the head210covered by all of the non-engaging portions240may range from about 1% to about 50%.

In an exemplary, non-limiting example, the variable-angle locking screw200may have six engaging portions230and six non-engaging portions240. Each engaging portion230may cover about 8.3% of the outer surface of the head210. Therefore, when added together, the engaging portions230may cover a total of about 50% of the outer surface of the head210. Each non-engaging portion240may cover about 8.3% of the outer surface of the head210. Therefore, when added together, the non-engaging portions240may cover a total of about 50% of the outer surface of the head210.

If the thread segments220were extended across the non-engaging portions240of the head210, they may form one or more substantially continuous threads221, each thread221being shaped as a helix around the longitudinal axis201of the variable-angle locking screw200. Preferably, the head210may be tapered such that the head210is narrower near the first end211and wider near the second end212. Accordingly, the threads221may also be tapered, such that each thread221forms a truncated conical helix.

The thread segments220on the head210of the variable-angle locking screw200, may be arranged such that, if extended across the non-engaging portions240of the head210, they would form any number of substantially continuous male threads221. For example, the thread segments220may be arranged to create a single-start thread forming a single helix, if they were extended to form a substantially continuous thread221. However, the thread segments220, if extended, could also form multiple threads. The number of threads221formed on the head210of the screw (if the thread segments220were extended across the non-engaging portions240) may be the same as the number of threads121on the threaded hole120in the plate100. In some embodiments, both the threaded hole120in the plate100and the head210of the screw200may have double-start threads in which the threads121,221form a double helix. In some embodiments, the threads121,221may form in a truncated conical double helix.

A number of manufacturing techniques may be used to make a variable-angle locking screw200. One manufacturing method may include obtaining a standard locking screw (with a substantially continuously-threaded head), and removing material from the outer surface of the head to form the non-engaging portions240. Alternatively, the material at the non-engaging portions240may be removed from the outer surface of the head210and then the threads in the engaging portions230may be formed. The screw200may also be made using injection molding, 3D printing, or various other known techniques.

The system001may include various sizes of screws200,300,400, with varying lengths and diameters. Any size of screw may be used. The screws may be sized appropriately for use in orthopedic fixation systems.

The screws200,300,400may be manufactured using any materials that are commonly used in orthopedic fixation systems. The screws200,300,400may be manufactured from a metal or polymeric material, or combinations thereof. The plate100and the locking screws200,400may be manufactured from the same (or similar) materials having the same (or similar) properties, or they may be manufactured from different materials having different properties.

As discussed above, the locking screws200,400may include a driving feature250,450. The non-locking screw300may also include a driving feature. The driving feature may be designed to receive a driving tool (for example, a screw driver, socket, or any other drive type known in the art) which can be used to drive the shank of the screw into the bone. In the case of locking screws200,400, the driving tool may also be used to thread the head210,410of the screw into the threaded hole120in the plate100. The driving feature may be a slot, cruciate, square, hex, hexalobe, or any other drive type known in the art. All of the screws200,300,400in the system001may use the same type of driving feature, or different driving features may be used on different screws.

A variety of cross-sectional shapes may be used to form the threads described in this application, including triangular, trapezoidal, rectangular, or a variety of other cross-sectional shapes. For example, any of the threads described in this application may have a triangular cross-sectional shape similar to the threads121on the threaded hole120of the plate100shown inFIG. 9B. Any of the threads described in this application may also have a trapezoidal cross-sectional shape similar to the threads221on the head210of the screw200inFIGS. 13A-13B.

In some situations, a locking screw may be inserted coaxially into a threaded hole120of a plate100as shown inFIGS. 4-6. To achieve coaxial insertion, the surgeon may use either a variable-angle locking screw200or a standard locking screw400. The longitudinal axis201,401of the screw200,400may be substantially parallel to the axis124of the threaded hole120on the plate100. Using a standard locking screw400for coaxial insertion into the threaded hole120on the plate100may provide increased engagement between the screw and the plate because both the head410of the standard locking screw400and the threaded hole120on the plate100may have substantially continuous threads421,121. However, standard locking screws400are optional in system001because the threaded holes120on the plate100are able to interchangeably receive the variable-angle locking screw200and the standard locking screw400. Variable-angle locking screws200may also be inserted coaxially into threaded holes120on the plate100.

In other situations, instead of inserting the locking screw coaxially, a surgeon may wish to insert a locking screw into a threaded hole120of a plate100at an angle as shown inFIGS. 1-3. In this case, a variable-angle locking screw200may be inserted into the threaded hole120on the plate100at an angle to the axis124of the threaded hole120. The screw200may be inserted into the threaded hole120on the plate100such that the screw angle (the angle between the longitudinal axis201of the screw200and the axis124of the threaded hole120) may vary from about 0° (substantially coaxial) to about 20° or more in any direction, thereby forming a theoretical, substantially cone-shaped region in which the longitudinal axis201of the screw200may lie.FIGS. 1-3show an exemplary configuration of the system001wherein a variable-angle locking screw200is inserted into a threaded hole120of a plate100at an angle of 10°. No modifications are required to the threaded hole120of the plate100in order to insert the variable-angle locking screw200at an angle to the threaded hole120.

The system001described in this application achieves variable-angle insertion of locking screws by modifying the threads on the head of the locking screw and providing a plate100having standard threaded holes120with substantially continuous threads121. Alternatively, variable-angle insertion of locking screws may be achieved by modifying the threaded holes120on the plate100and providing a locking screw having substantially continuous threads on the head. However, modifying the threaded holes on the plate to achieve variable-angle insertion of locking screws may be disadvantageous because such modifications typically require the removal of material from the plate, which may weaken the plate.

A system which is able to achieve variable-angle insertion of locking screws using a plate100having standard threaded holes120with substantially continuous threads121may provide increased flexibility compared to systems which achieve variable-angle insertion of locking screws by modifying the threaded holes on the plate. In a system which uses a plate100having standard threaded holes120, the plate100is more versatile because any threaded hole120on the plate100is capable of receiving a standard locking screw400or a variable-angle locking screw200. If a variable-angle locking screw200is selected, it may be inserted into any threaded hole120either coaxially or at an angle. Furthermore, if coaxial insertion is desired, a standard locking screw400may be selected to increase engagement between the locking screw and the plate100, which may increase engagement between the threaded hole and the head of the locking screw. In contrast, if the threaded holes on the plates had discontinuous threads, increasing engagement between the plate and the locking screw during coaxial insertion would be more difficult because it would involve modifying an existing plate or custom-designing a plate with some threaded holes specifically designed for coaxial insertion.

The foregoing description is provided to enable any person skilled in the art to practice the various example implementations described herein. Various modifications to these variations will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations. All structural and functional equivalents to the elements of the various illustrious examples described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference.