Patent Description:
Spinal pathologies and disorders such as scoliosis, kyphosis and other curvature abnormalities, degenerative disc disease, disc herniation, osteoporosis, spondylolisthesis, stenosis, tumor, and fracture may result from factors including trauma, disease and degenerative conditions caused by injury and aging. Spinal disorders typically result in symptoms including deformity, pain, nerve damage, and partial or complete loss of mobility.

Non-surgical treatments, such as medication, rehabilitation and exercise can be effective, however, may fail to relieve the symptoms associated with these disorders. Surgical treatment of these spinal disorders includes correction, fusion, fixation, discectomy, laminectomy and implantable prosthetics. As part of these surgical treatments, implants such as bone fasteners, plates, connectors and vertebral rods are often used to provide stability to a treated region. These implants can redirect stresses away from a damaged or defective region while healing takes place to restore proper alignment and generally support the vertebral members. For example, the plates, connectors and/or rods may be attached via the fasteners to the exterior of one or more vertebral members. This disclosure describes an improvement over these prior technologies.

From the <CIT> a coupling member is known which comprises a shaft defining an axis and including at least one thread having an external thread form, the external thread form having a leading flank and a trailing flank, the external thread form defining a pitch and a crest, wherein the leading flank and the trailing flank are angled in a proximal orientation relative to the thread axis, wherein the external thread form is configured to interlock with an internal thread form of an implant receiver, and wherein the leading flank is disposed at a first angle relative to a transverse axis of the at least one thread and the trailing flank is disposed at a second angle relative to the transverse axis, the first angle being greater than the second angle.

The invention provides a coupling member according to claim <NUM>, a spinal implant according to claim <NUM>, and a spinal implant system according to claim <NUM>.

The embodiments of a surgical system and related methods of use (the methods not claimed) disclosed are discussed in terms of medical devices for the treatment of musculoskeletal disorders and more particularly, in terms of a spinal implant system including a bone fastener.

In some embodiments, the present spinal implant system includes a spinal implant, such as, for example, a bone fastener having a receiver and a set screw. According to the invention, the set screw is configured to facilitate engagement of the set screw with the receiver. According to the invention, the set screw is configured to contact a receiver and interlock with the receiver to reduce splay of the receiver.

According to the invention, the set screw includes a thread form having a crest, the crest includes a selected thickness, the thickness includes a percentage of the thread pitch. In some embodiments, the thickness of the crest is about <NUM> percent of the thread pitch. The thickness at the crest is configured to provide an increase in strength of the setscrew or mating receiver. The present surgical system includes a set screw configured to tolerate an increased load capacity. The set screw is configured to resist and/or prevent splaying of the arms of the receiver that may occur from excessive loading. Splaying is due to the set screw shifting off axis within the receiver resulting in overloading of the threads due to a decreased thread contact and thinning crest width. The angles of the trailing flank and the leading flank are disposed in a proximal orientation relative to a thread axis. The thread geometry provides for a thicker crest width on the minor diameter of the tulip head and the major diameter of the set screw. The an increase in crest width facilitates resisting and/or preventing shear forces produced by a clamping force generated during engagement of the set screw with the receiver. The set screw is configured to matingly engage the receiver.

In some embodiments, the receiver includes an internal thread having smooth rounded corners configured to eliminate binding and/or cutting into the set screw. During engagement of the set screw with the receiver, the rounded corners become load bearing surfaces. The arcuate configuration of the corners resist and/or prevent the corners from cutting into the setscrew. This configuration is beneficial when the receiver includes a harder material than the set screw.

According to the invention, the thread includes a leading flank and a trailing flank. The angles of leading flank and the trailing flank form the selected thickness of the crest. The leading flank is disposed at an angle greater than the angle of the trailing flank. The angle of the leading flank is about <NUM> degrees greater than the angle of the trailing flank.

According to the invention, the leading flank is disposed at an angle relative to a transverse axis. The leading flank angle is about <NUM> degrees relative to the transverse axis. The trailing flank is disposed at an angle relative to the transverse axis. The trailing flank angle is about -<NUM> degrees relative to the transverse axis i.e. a reverse angle of about <NUM> degrees. The leading flank angle is greater than the trailing flank angle by about <NUM> degrees.

In some examples, the present disclosure may be employed to treat spinal disorders such as, for example, degenerative disc disease, disc herniation, osteoporosis, spondylolisthesis, stenosis, scoliosis and other curvature abnormalities, kyphosis, tumor and fractures. In some examples, the present disclosure may be employed with other osteal and bone related applications, including those associated with diagnostics and therapeutics. In some examples, the disclosed surgical system may be alternatively employed in a surgical treatment with a patient in a prone or supine position, and/or employ various surgical approaches to the spine, including anterior, posterior, posterior mid-line, direct lateral, postero-lateral, and/or antero lateral approaches, and in other body regions. The present disclosure may also be alternatively employed with procedures for treating the lumbar, cervical, thoracic, sacral and pelvic regions of a spinal column. The surgical system of the present disclosure may also be used on animals, bone models and other non-living substrates, such as, for example, in training, testing and demonstration.

The present disclosure may be understood more readily by reference to the following detailed description of the embodiments taken in connection with the accompanying drawing figures, which form a part of this disclosure. As used in the specification and including the appended claims, the singular forms "a," "an," and "the" include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" or "approximately" one particular value and/or to "about" or "approximately" another particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. It is also understood that all spatial references, such as, for example, horizontal, vertical, top, upper, lower, bottom, left and right, are for illustrative purposes only and can be varied within the scope of the disclosure. For example, the references "upper" and "lower" are relative and used only in the context to the other, and are not necessarily "superior" and "inferior".

The following discussion includes a description of a surgical system including one or more spinal and related components in accordance with the present invention. Alternate embodiments are disclosed. Reference is made in detail to the embodiments of the present disclosure, which are illustrated in the accompanying figures. Turning to <FIG>, there are illustrated components of a spinal implant system <NUM> including a coupling member and a bone fastener.

For example, the components of spinal implant system <NUM>, individually or collectively, can be fabricated from materials such as stainless steel alloys, commercially pure titanium, titanium alloys, Grade <NUM> titanium, super-elastic titanium alloys, cobalt-chrome alloys, superelastic metallic alloys (e.g., Nitinol, super elasto-plastic metals, such as GUM METAL®), ceramics and composites thereof such as calcium phosphate (e.g., SKELITE™), thermoplastics such as polyaryletherketone (PAEK) including polyetheretherketone (PEEK), polyetherketoneketone (PEKK) and polyetherketone (PEK), carbon-PEEK composites, PEEK-BaSO<NUM> polymeric rubbers, polyethylene terephthalate (PET), fabric, silicone, polyurethane, silicone-polyurethane copolymers, polymeric rubbers, polyolefin rubbers, hydrogels, semirigid and rigid materials, elastomers, rubbers, thermoplastic elastomers, thermoset elastomers, elastomeric composites, rigid polymers including polyphenylene, polyamide, polyimide, polyetherimide, polyethylene, epoxy, bone material including autograft, allograft, xenograft or transgenic cortical and/or corticocancellous bone, and tissue growth or differentiation factors, partially resorbable materials, such as, for example, composites of metals and calcium-based ceramics, composites of PEEK and calcium based ceramics, composites of PEEK with resorbable polymers, totally resorbable materials, such as, for example, calcium based ceramics such as calcium phosphate, tri-calcium phosphate (TCP), hydroxyapatite (HA)-TCP, calcium sulfate, or other resorbable polymers such as polyaetide, polyglycolide, polytyrosine carbonate, polycaroplaetohe and their combinations.

Spinal implant system <NUM> includes a coupling member, such as, for example, a set screw <NUM> configured for engagement with a bone screw <NUM>, as described herein. Set screw <NUM> includes a portion, such as, for example, a head <NUM> and a portion, such as, for example a shaft <NUM>. Head <NUM> includes a tool engaging portion <NUM> configured to engage a surgical tool or instrument (not shown), as described herein. In some embodiments, portion <NUM> includes a hexagonal cross-section to facilitate engagement with a surgical tool or instrument. In some embodiments, head <NUM> may have alternative cross-sections, such as, for example, rectangular, polygonal, hexalobe, oval, or irregular. In some embodiments, portion <NUM> may have a cruciform, phillips, square, polygonal or star cross sectional configuration configured for disposal of a correspondingly shaped portion of a surgical tool or instrument. In some embodiments, head <NUM> includes a hollow breakoff setscrew and an internal drive mechanism for removal of the setscrew.

Shaft <NUM> extends between an end <NUM> and an end <NUM>, and defines an axis X1, as shown in <FIG>. An axis X2 extends transverse, such as, for example orthogonal, to axis X1, as shown in <FIG>. In some embodiments, axis X2 may be alternatively oriented relative to axis X1, such as, for example, angular orientations such as acute or obtuse. Shaft <NUM> includes an outer surface <NUM>. Surface <NUM> includes threads <NUM>. In some embodiments, surface <NUM> includes one or a plurality of threads <NUM> configured to enhance fixation with a receiver <NUM>, as described herein. In some embodiments, threads <NUM> are continuous along surface <NUM>. In some embodiments, threads <NUM> may include a single thread turn or a plurality of discrete threads. In some embodiments, penetrating elements may be located on shaft <NUM>, such as, for example, a nail configuration, barbs, expanding elements, raised elements, ribs, and/or spikes to facilitate engagement of shaft <NUM> with bone screw <NUM>.

Threads <NUM> include a minor diameter D1 and a major diameter D2, as shown in <FIG>. Threads <NUM> include an external thread form <NUM>. External thread form <NUM> defines a shape of a contour of one complete thread <NUM>. Thread form <NUM> includes a leading flank <NUM> and a trailing flank <NUM>, as shown in <FIG>. External thread form <NUM> is angled in a proximal and/or reverse angle orientation relative to axis X1, as shown in <FIG>, <FIG> and <FIG>. For example, thread form <NUM> e.g., the leading and/or trailing flanks <NUM>, <NUM> is angled toward end <NUM>.

Leading flank <NUM> includes a surface <NUM> disposed at an angle α1 relative to axis X2, as shown in <FIG> and <FIG>. According to the invention, angle α1 is about <NUM> degrees relative to axis X2. In some embodiments, surface <NUM> may be oriented in another manner relative to axis X2, such as, for example, by being perpendicular to axis X2 and/or having another angular orientations such as acute or obtuse relative to axis X2.

Trailing flank <NUM> includes a surface <NUM> disposed at an angle α2 relative to axis X2, as shown in <FIG> and <FIG>. According to the invention, angle α2 is about -<NUM> degrees relative to axis X2. In some embodiments, surface <NUM> may be alternatively oriented relative to axis X2, such as, for example, perpendicular and/or other angular orientations such as acute or obtuse.

According to the invention, angle α1 is greater than from angle α2 by a difference Δ1, as shown in <FIG>. In some of these embodiments, angle α1 is greater than angle a2. In examples, angle α1 is less than angle a2 (not claimed). The difference Δ1 is in a range of about <NUM> to about <NUM> degrees. The difference Δ1 is about <NUM> degrees.

Threads <NUM> define a pitch P1 having a length L1 extending between adjacent trailing flanks <NUM>, as shown in <FIG>. Leading flank <NUM> and trailing flank <NUM> merge at crest surface C1. Crest surface C1 extends along major diameter D2. Crest surface C1 includes a width W1 along major diameter D2. Width W1 is a percentage of length L1 of pitch P1. According to the invention, width W1 is percentage of length L1 in a range of about <NUM> to about <NUM> percent of length L1. In some embodiments, width W1 is about <NUM> percent of length L1. The value for width W1 is selected to disperse a load applied by shear forces during engagement of set screw <NUM> with receiver <NUM>. As such, width W1 is configured to resist and/or prevent effects of shear forces on set screw <NUM> and receiver <NUM> during tightening.

In some embodiments, width W1 bears a pre-determined relationship to pitch P1. In various embodiments, the relationship includes bone screw <NUM> being configured such that width W1 is a pre-set percentage of pitch P1, such as by width W1 being between about <NUM> and about <NUM> percent of pitch P1. In various embodiments, width W1 is any of between about <NUM> percent and about <NUM> percent of pitch P1, between about <NUM> and <NUM> percent of pitch P1, and about <NUM> percent of pitch P1.

Crest surface C1 is disposed at a length L2 from minor diameter D1, as shown in <FIG>. In various embodiments, crest surface C1 includes a substantially planar configuration. In various embodiments, crest surface C1 is disposed parallel relative to axis X1. In some embodiments, crest surface C1 may be alternatively oriented relative to axis X1, such as, for example, transverse, and/or other angular orientations such as acute or obtuse.

End <NUM> and head <NUM> form a section, such as, for example, a neck <NUM> with head <NUM>, as called out in <FIG> and shown also in <FIG>, <FIG>, and <FIG>. In some embodiments, end <NUM> includes a reduced diameter portion <NUM> at neck <NUM>. In some embodiments, portion <NUM> is frangibly connected to head <NUM>. In some embodiments, portion <NUM> is fabricated from a fracturing and/or frangible material such that manipulation of head <NUM> relative to shaft <NUM> can cause fracture at portion <NUM> to separate head <NUM> from shaft <NUM> at a predetermined force and/or torque limit, as described herein. In some embodiments, as force and/or torque is applied to head <NUM> and resistance increases, for example, due to fixation of shaft <NUM> within the receiver <NUM>, as described herein, the predetermined torque and force limit is approached.

In some embodiments, head <NUM> can fracture from neck <NUM> and separate at a predetermined force or torque limit, which may be in a range of approximately <NUM> Newton meters (Nm) to approximately <NUM>. In some embodiments, head <NUM> and/or shaft <NUM> may be fabricated from a homogenous material or heterogeneously fabricated from different materials, and/or alternately formed of a material having a greater degree, characteristic or attribute of plastic deformability, frangible property and/or break away quality to facilitate fracture and separation of head <NUM> from the shaft <NUM>. In some embodiments, head <NUM> includes an inner diameter that facilitates a desired breakoff torque.

End <NUM> includes a surface <NUM> that includes a penetrating element <NUM> extending distally from surface <NUM>. Element <NUM> is configured to engage a spinal implant, such as, for example, a spinal rod <NUM>, as shown in <FIG> and <FIG>. Element <NUM> is configured to apply a force to spinal rod <NUM> to fix spinal rod with bone screw <NUM>, as described herein.

Bone screw <NUM> includes receiver <NUM>, as shown in <FIG>. Receiver <NUM> includes a pair of spaced apart arms <NUM>, <NUM> that define an implant cavity <NUM> therebetween configured for disposal of spinal rod <NUM>. Arms <NUM>, <NUM> each extend parallel to an axis X3. In some embodiments, arms <NUM>, <NUM> may be disposed at alternative orientations, relative to axis X3, such as, for example, transverse, perpendicular and/or other angular orientations such as acute or obtuse, coaxial and/or may be offset or staggered.

Cavity <NUM> is in various embodiments substantially U-shaped. In some embodiments, all or only a portion of cavity <NUM> may have alternative cross section configurations, such as, for example, closed, V-shaped, W-shaped, oval, oblong triangular, square, polygonal, irregular, uniform, non-uniform, offset, staggered, and/or tapered.

Receiver <NUM> includes an inner surface <NUM>, as shown in <FIG>. Surface <NUM> includes threads <NUM>. Threads <NUM> include a minor diameter D3 and a major dimeter D4, as shown in <FIG>. Threads <NUM> include an internal thread form <NUM>. Internal thread form <NUM> defines a shape of a contour of one complete thread <NUM>. Internal thread form <NUM> is angled in a distal orientation relative to axis X3, as shown in <FIG>. For example, internal thread form <NUM> is angled toward a distal end of receiver <NUM>.

Internal thread form <NUM> includes a flank <NUM> and a flank <NUM>, as shown in <FIG>. Threads <NUM> define pitch P2 having a length L4 extending between adjacent flanks <NUM>, as shown in <FIG>. In some embodiments, pitch P1 (<FIG>) is approximately equal to pitch P2. In some embodiments, pitch P1 is greater than pitch P2. In some embodiments, pitch P1 is less that pitch P2.

Flank <NUM> includes a surface <NUM> that extends transverse to axis X3. Surface <NUM> is disposed in an orientation to facilitate engagement with leading flank <NUM> for interlocking set screw <NUM> with receiver <NUM>. In some embodiments, surface <NUM> may be alternatively oriented relative to axis X3, such as, for example, perpendicular and/or other angular orientations such as acute or obtuse.

Flank <NUM> includes a surface <NUM> that extends transverse to axis X3. Surface <NUM> is disposed in an orientation to facilitate engagement with trailing flank <NUM> for interlocking set screw <NUM> with receiver <NUM>. In some embodiments, surface <NUM> may be alternatively oriented relative to axis X3, such as, for example, perpendicular and/or other angular orientations such as acute or obtuse.

Crest C2 extends between flank <NUM> and flank <NUM> and extends along minor diameter D3. Crest surface C2 includes a width W2 along minor diameter D3. Width W2 is a percentage of length L4 of pitch P2. In some embodiments, width W2 is a percentage of length L1 in a range of about <NUM> to about <NUM> percent of length L4. In some embodiments, width W2 is about <NUM> percent of length L4. Width W2 is configured to disperse a load applied by shear forces during engagement of set screw <NUM> with receiver <NUM>. As such, engagement of set screw <NUM> with receiver <NUM> is configured to resist and/or prevent effects of shear forces on set screw <NUM> and receiver <NUM> during tightening.

In some embodiments, width W2 bears a pre-determined relationship to pitch P2. In various embodiments, the relationship includes bone screw <NUM> being configured such that width W2 is a pre-set percentage of pitch P2, such as by width W2 being between about <NUM> and about <NUM> percent of pitch P2. In various embodiments, width W2 is any of between about <NUM> percent and about <NUM> percent of pitch P2, between about <NUM> and <NUM> percent of pitch P1, and about <NUM> percent of pitch P2.

Crest surface C2 is disposed at a length L3 from major diameter D4, as shown in <FIG>. In some embodiments, distance L3 is greater than distance L2 by a difference Δ2. The components are configured such that the difference Δ2 is sufficient to provide clearance between crest surface C1 and a surface defining major diameter D4, as shown in <FIG>. The clearance between crest surface C1 and major dimeter D4 facilitates expansion of threads <NUM> during engagement of set screw <NUM> with receiver <NUM>. The space between crest surface C1 the surface defining major diameter D4 is configured to resist and/or prevent set screw <NUM> splaying arms <NUM>, <NUM> during engagement of set screw <NUM> with receiver <NUM>.

In various embodiments, flank <NUM> merges with crest surface C2 at a surface <NUM>. Surface <NUM> can include an arcuate configuration relative to minor diameter D3, such that surface <NUM> is rounded.

Flank <NUM> merges with crest surface C2 at a surface <NUM>. Surface <NUM> includes an arcuate configuration relative to minor diameter D3, such that surface <NUM> is rounded. In some embodiments, one or both of surfaces <NUM>, <NUM> includes an arcuate configuration.

The arcuate configuration of surfaces <NUM>, <NUM> prevent to surfaces <NUM>, <NUM> from cutting into setscrew <NUM>. For example, as set screw <NUM> is engaged with receiver <NUM>, surfaces <NUM>, <NUM> are load bearing surfaces. The arcuate configuration of surfaces <NUM>, <NUM> resists and/or prevents surfaces <NUM>, <NUM> from cutting into setscrew <NUM> when the load is applied. In some embodiments, this configuration is especially beneficial when receiver <NUM> includes a harder material than set screw <NUM>.

Bone screw <NUM> includes a shaft <NUM>, as shown in <FIG> and <FIG>. shaft <NUM> is configured for fixation with tissue of a patient (not shown). In some embodiments, shaft <NUM> has a cylindrical cross-section configuration and includes an outer surface having threads that define an external thread form. In some embodiments, the threads may include a single thread turn or a plurality of discrete threads. In some embodiments, engaging structures may be located on shaft <NUM>, such as, for example, a nail configuration, barbs, expanding elements, raised elements and/or spikes to facilitate engagement of shaft <NUM> with tissue, such as, for example, vertebrae.

In some embodiments, all or only a portion of shaft <NUM> may have alternate cross section configurations, such as, for example, oval, oblong, triangular, square, polygonal, irregular, uniform, non-uniform, offset, staggered, undulating, arcuate, variable and/or tapered. In some embodiments, the outer surface of shaft <NUM> may have alternate surface configurations to enhance fixation with tissue such as, for example, rough, arcuate, undulating, mesh, porous, semi-porous, dimpled and/or textured. In some embodiments, all or only a portion of shaft <NUM> may be disposed at alternate orientations, relative to axis X4, such as, for example, transverse, perpendicular and/or other angular orientations such as acute or obtuse, co-axial and/or may be offset or staggered. In some embodiments, all or only a portion of shaft <NUM> may be cannulated.

In some embodiments, one or more of bone screws <NUM> and/or bone fasteners, as described herein, may include, for example, multi-axial screws, sagittal angulation screws, pedicle screws, mono-axial screws, uni-planar screws, facet screws, fixed screws, tissue penetrating screws, conventional screws, expanding screws, wedges, anchors, buttons, clips, snaps, friction fittings, compressive fittings, expanding rivets, staples, nails, adhesives, posts, fixation plates and/or posts.

In assembly, operation and use, spinal implant system <NUM>, similar to the systems and methods described herein, includes set screw <NUM> and bone screw <NUM>, as described herein, and is employed with a surgical procedure for treatment of a spinal disorder affecting a section of a spine of a patient, as discussed herein. In some examples, the components of spinal implant system <NUM> may be employed with one or a plurality of vertebral levels of a spine. In some embodiments, the components of spinal implant system <NUM> may include one or a plurality of bone fasteners, spinal rods, plates, connectors and/or interbody devices.

In use, to treat the affected section of the spine, a medical practitioner obtains access to a surgical site in any appropriate manner, such as through incision and retraction of tissues. In some examples, the components of spinal implant system <NUM> may be used in any existing surgical method or technique including open surgery, mini-open surgery, and minimally invasive surgery including percutaneous surgical implantation. Once access to a surgical site(s) is obtained, the particular surgical procedure is performed for treating the spinal disorder. The components of spinal implant system <NUM> including set screw <NUM> and bone screw <NUM> are employed to augment the surgical treatment. The components of spinal implant system <NUM>, as described herein, are delivered or implanted as a pre-assembled device or can be assembled in situ. The components of spinal implant system <NUM> may be completely or partially revised, removed or replaced. For example, shaft <NUM> is fastened with tissue, such as, for example, vertebrae, such that spinal rod <NUM> is disposed with receiver <NUM> for attachment with the vertebrae.

Set screw <NUM> is coupled with bone screw <NUM> adjacent a top surface of receiver <NUM>. Set screw <NUM> is rotated in a clockwise direction, in a direction shown by arrow C in <FIG>, via a surgical instrument or tool and translated, in a direction shown by arrow D in <FIG>, such that threads <NUM> mate with threads <NUM> to couple set screw <NUM> with bone screw <NUM>. As such, external thread form <NUM> simultaneously mates with internal thread form <NUM>.

Translation of set screw <NUM> causes element <NUM> to engage spinal rod <NUM> such that set screw <NUM> provides a closure mechanism to dispose spinal rod <NUM> with cavity <NUM> and fix spinal rod <NUM> with receiver <NUM>, and attach spinal rod <NUM> with the vertebrae. Width W1 at crest surface C1 and width W2 at crest surface C2 disperse the load applied by shear forces during engagement of set screw <NUM> with receiver <NUM>. As such, widths W1, W2 are configured to resist and/or prevent effects of shear forces on set screw <NUM> and receiver <NUM> during tightening. Arcuate surfaces <NUM>, <NUM> resist and/or prevent threads <NUM> from cutting and/or biting into the surface of setscrew <NUM> during engagement with receiver <NUM>.

Upon completion of a procedure, as described herein, the surgical instruments, assemblies and non-implanted components of spinal implant system <NUM> are removed and the incision(s) are closed. One or more of the components of spinal implant system <NUM> can be made of radiolucent materials such as polymers. Radiomarkers may be included for identification under x-ray, fluoroscopy, CT or other imaging techniques. In some examples, the use of surgical navigation, microsurgical and image guided technologies may be employed to access, view and repair spinal deterioration or damage, with the aid of spinal implant system <NUM>.

Claim 1:
A coupling member (<NUM>) comprising:
a shaft (<NUM>) defining an axis and including at least one thread (<NUM>) having an external thread form, the external thread form having a leading flank (<NUM>) and a trailing flank (<NUM>), the external thread form defining a pitch (P1) and a crest (C1), the crest (C1) having a width (W1) in a range of about <NUM>% to about <NUM>% of the pitch (P1) of the external thread form,
wherein the leading flank (<NUM>) and the trailing flank (<NUM>) are angled in a proximal orientation relative to the thread axis,
wherein the external thread form is configured to interlock with an internal thread form of an implant receiver (<NUM>),
wherein the leading flank (<NUM>) is disposed at a first angle (a1) relative to a transverse axis of the at least one thread (<NUM>) and the trailing flank (<NUM>) is disposed at a second angle (a2)
relative to the transverse axis, the first angle being greater than the second angle, and
wherein the first angle is about <NUM> degrees relative to the transverse axis and the second angle is about -<NUM> degrees relative to the transverse axis.