Patent ID: 12207849

DETAILED DESCRIPTION

As used herein, when referring to the femur or the intramedullary nail, the term “proximal” means the end of femur or the intramedullary nail that is closer to the heart when the intramedullary nail is implanted within the medullary canal of a patient in its intended manner. The term “distal” means the end of femur or the intramedullary nail that is further from the heart when the intramedullary nail is implanted within the medullary canal of the patient as intended. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. When referring to the neck screw, the term “rear” means closer to the user, whereas the term “front” means further from the user. Also as used herein, the terms “substantially,” “generally” and “about” are intended to mean that slight deviations from absolute are included within the scope of the term so modified.

Throughout this disclosure, a fracture refers to a femoral neck fracture, however, the devices described hereinafter can be used to fixate associated fractures of the femoral shaft as well as factures in other long bones such as the tibia or the humorous, whether the fracture be naturally occurring or surgeon-induced.

FIG.1illustrates a femur10and its six anatomical regions: a diaphysis or midshaft12, proximal metaphysis14, distal metaphysis16, proximal epiphysis or head18, distal epiphysis20, and a femoral neck22. The femur10includes a hard cortex24and a medullary cavity26. The medullary cavity26includes a medullary canal28which runs through the center of shaft12, proximal and distal metaphyseal areas30,32, and the proximal and distal epiphyseal areas34and36.

FIG.2is an anterior-posterior view of a proximal portion of femur10having a fracture38extending along femoral neck22. Fracture38separates the proximal femur into a first bone portion40located adjacent the proximal metaphysis14and a second bone portion42located adjacent the proximal epiphysis or head18. Fracture38is an exemplary illustration of an unstable, extra-articular fracture, i.e., the fracture is located outside of a joint. This type of fracture, if not treated, can lead to long-term complications including comminution (i.e., pulverization of the bone), which may result in shortening of femoral neck22and severe pain.

FIG.3illustrates an intramedullary intertrochanteric fracture fixation device100according to an embodiment of the present disclosure. The device100is designed to compress first bone portion40and second bone portion42(shown inFIGS.1and2) and maintain rotational stability between the first and second bone portions during healing of fracture38. Device100includes an intramedullary nail102having an angulated opening104(shown inFIG.4) extending through the nail in the lateral to medial direction, a neck screw106that is insertable through the angulated opening for compressing the fractured bone portions together and a set screw200for rotationally stabilizing the neck screw within the angulated opening of the intramedullary nail.

With reference toFIG.4, intramedullary nail102includes a rod-shaped body having a proximal portion108, a distal portion110and an intermediate portion112located between and connecting the proximal and distal portions. The rod-shaped body of intramedullary nail102may be anatomically shaped to allow the intramedullary nail to be inserted into the medullary canal28of femur10(shown inFIG.1). For this reason, intermediate portion112may be bent and tapered in the proximal to distal direction.

The rod-shaped body of intramedullary nail102is cannulated and defines a channel114that is configured to receive a surgical wire, such as a K-wire, for guiding the intramedullary nail into a proper position within the medullary canal28of the femur10(shown inFIG.1). Intramedullary nail102may have a substantially circular cross-section over its entire length such that proximal portion108and distal portion110are substantially cylindrical. The proximal portion108of intramedullary nail102has a diameter sufficient to accommodate angulated bore104. The distal portion110of intramedullary nail102has a diameter that is smaller than the diameter of proximal portion108, and that is anatomically shaped to the medullary canal28of femur10to facilitate the insertion of the distal portion of the intramedullary nail into the medullary canal of the femur. For the same reason, the distal portion110of intramedullary nail102has a conical tip116at its distal end. The distal portion110of intramedullary nail102may also define an aperture118configured to receive a bone fastener such as a locking screw for fastening the intramedullary nail to the shaft12of femur10after implantation.

As shown inFIGS.5A and5B, intramedullary nail102has an axial bore122that extends along a longitudinal axis L of the proximal portion108of the nail between the proximal end of the nail and angulated opening104. Axial bore122includes internal threading126configured to mate with corresponding threading provided on set screw assembly200(shown inFIG.3).

Angulated opening104defines a bore axis124that is transversely angled with respect to the longitudinal axis L of proximal portion108such that the bore axis of the angulated opening has an oblique extension relative to an axial extension of the proximal portion. In other words, bore axis124of angulated opening104is oriented obliquely with respect to the longitudinal axis L of the proximal portion108. Thus, the bore axis124of angulated opening104is inclined at an angle α with respect to the longitudinal axis L of the proximal portion108. Angle α may be between approximately 90° and approximately 140°, and may be, for example, about 126°.

Returning toFIG.3, neck screw106extends through angulated opening104in a lateral to medial direction. As will be explained in more detail below, neck screw106is coupled to intramedullary nail102, via set screw200, in a manner that prevents the neck screw from rotating in angulated opening104and in a manner that allows the neck screw to limitedly slide along bore axis124(shown inFIG.5A) to account for load shifting.

Neck screw106includes a rear end128and a front end130. The rear end128of neck screw106includes a recess132, for example, a hexalobular internal driving feature configured to receive a tool tip such as a screw driver or wrench. The front portion of neck screw106includes a thread134, such as a coarse thread, for anchoring the neck screw into intertrochanteric bone. The peripheral surface of neck screw106defines a plurality of grooves136that extend in a direction generally parallel to the longitudinal axis of the neck screw. For example, neck screw106may include four grooves136circumferentially spaced about the peripheral surface of the neck screw at intervals of 90°. Each groove136defines a rising ramp having a shallow end and a deep end. The rising ramp extends from the rear portion of neck screw106toward the front portion of the neck screw. Because the longitudinal axis of neck screw106is substantially coaxial with the bore axis124of angulated opening104, the neck screw is configured to transfer loads placed on the femoral head to the intramedullary nail102, and at the same time, bridge the fracture38and compress first bone portions40and second bone portion42together.

Set screw assembly200, as shown inFIGS.6A-8, is cannulated and thus overcomes the drawbacks associated with the set screws described in the prior art, namely the difficulties associated with intraoperative assembly. Because set screw assembly200is cannulated, the set screw assembly can be pre-operatively assembled within intramedullary nail102and configured to receive a guidewire while disposed within the nail. That is, during operation, a surgeon may insert intramedullary nail102, in which set screw assembly200is housed, over the guidewire and into position within the medullary canal of the patient. As used herein, the term “pre-operatively assembled” means that set screw assembly200is assembled within intramedullary nail102by the manufacturer before intertrochanteric fracture fixation device100is shipped, or alternatively, that the set screw assembly is assembled within the nail by a user before the nail is implanted into the medullary canal of a patient.

Set screw assembly200includes a housing202and a set screw204. As shown inFIGS.6B and8, a cannulation206extends along a longitudinal axis of set screw assembly200and completely through the housing202and the set screw204of the set screw assembly such that when the set screw is disposed within the housing and pre-operatively assembled within intramedullary nail102, the set screw assembly is configured to receive a guidewire.

With reference toFIG.7, housing202includes an upper portion208and a lower portion210. The upper portion208of housing202includes a first end wall212, a second end wall214spaced a distance from the first end wall, and a sidewall216that extends between the first and second end walls and partially surrounds the cannulation206of the upper portion. Put another way, sidewall216only partially surrounds the longitudinal axis of set screw assembly200. In this manner, the combination of the first end wall212, the second end wall214and the sidewall216of upper portion208defines a cavity218sized and configured to receive set screw204. In a preferred embodiment, the first end wall212includes a lip219, as shown inFIG.8, for retaining set screw204within cavity218.

The upper portion208of housing202has a transverse cross-section that is greater than a transverse cross-section of the lower portion210of the housing such that a ledge220is formed at the junction of the upper and lower portions. Additionally, the transverse cross-section of the upper portion208of housing202may be polygonal in shape. As used herein, the term “polygon” or “polygonal” is defined as any shape that is not completely circular and that includes one or more vertices222. The vertices222may form a sharp point or be rounded. For example, as shown inFIG.6B, the transverse cross-section of the upper portion208of housing202may be substantially triangular and include rounded vertices.

With additional reference toFIG.5B, the proximal portion108of intramedullary nail102includes a seat138extending inwardly from the wall that defines the axial bore122of the intramedullary nail. The wall that defines axial bore122also defines a longitudinal slot140that extends substantially parallel to a longitudinal axis of the axial bore. Longitudinal slot140is shaped and sized to receive the corresponding vertices222of housing202and thus may act as a track for stabilizing set screw assembly200as the set screw assembly is loaded into intramedullary nail102. Moreover, after set screw assembly200has been secured to intramedullary nail102, the positioning of the vertices222within longitudinal slot140will inhibit unwanted post-operative rotation of the set screw assembly within axial bore122.

The lower portion210of housing202is substantially cylindrical in shape and includes one or more protrusions224extending from a distal end226of the housing. Protrusion224is sized and shaped to extend into the angulated opening104, and into one of the grooves136of neck screw106. The distal end226of lower portion210may be angled obliquely with respect to the longitudinal axis of set screw assembly200. In a preferred embodiment, the angle is approximately equal to a (e.g., the angle between the bore axis124of angulated opening104and the longitudinal axis L of the proximal portion108of nail102) such that only protrusion224extends into the angulated opening104of intramedullary nail102when the ledge220of housing202contacts seat138. In other words, the distal end226of the lower portion210of housing202does not extend into the angulated opening104of intramedullary nail102and will not contact a peripheral surface of neck screw106.

Set screw204has a substantially cylindrical body228provided with an external threading230disposed about the body. Set screw204is sized to be at least partially received within the cavity218of housing202in a manner that allows the threading230of the set screw to protrude from the cavity (as shown inFIG.6B) and to engage the internal threading126of intramedullary nail102(as shown inFIG.8) to threadably mate set screw assembly200to the intramedullary nail.

Set screw204includes an elastic member232that is transitionable between an expanded condition (e.g., uncompressed) and a compressed condition. In the compressed condition, set screw204has a length in the axial direction that is equal to or less than the distance between the first and wall212and the second end wall214of housing202. Thus, when elastic member232is in the compressed condition, set screw204can be inserted into cavity218. On the other hand, when elastic member232is expanded, the axial length of set screw204is greater than the distance between the first end wall212and the second end wall214of housing202. As a result, when set screw204is disposed within cavity218and elastic member232is expanded into a friction fit engagement with the first end wall212and the second end wall214of housing202, the set screw is securely coupled to the housing, and lateral movement of the set screw relative to the housing is prevented. The engagement between set screw204and housing202also prevents the set screw from unintentionally rotating within the housing and requires increased torque to intentionally rotate the set screw.

Elastic member232may have a transverse cross-section that is smaller than a transverse cross-section of the body228of set screw204such that a retaining step242is formed about the elastic member. Retaining step242may engage with the lip219of the housing to inhibit lateral movement of set screw204relative to housing202and aid in securely coupling the set screw within cavity218.

As shown inFIG.7, elastic member232is a flange that is integrally formed, or otherwise attached, to a terminal end of set screw204. The flange has a first or attached end234, and a second or unattached end236. The first end234of the flange extends from a terminal end of the body228of set screw204on a first lateral side of cannulation206, and the flange extends across the cannulation of the set screw such that the second or unattached end236is disposed over the terminal end of the set screw on an opposing lateral side of the cannulation. Because the second end236of the flange is not attached to the body228of set screw204, a gap238is formed between the second end (e.g., the unattached end) of the flange and the terminal end of the body to form a cantilever.

The flange may be formed of any material that exhibits elasticity such as a metal, a metal alloy or a rubber. In this manner, when a distally directed force is applied to the second end236of the flange, for example, by the first end wall212of housing202during insertion of set screw204into cavity218, the second end of the flange will compress toward the terminal end of the body228of set screw204, thereby decreasing the size of gap238and the axial length of the set screw202. After set screw204has been inserted into cavity218, beyond lip219, the elastic material will expand to secure the set screw within the cavity.

The above described flange is merely an example of elastic member232and it will be understood that any other elastic member such as a spring, rubber, silicon or the like may be substituted in place of the flange. Moreover, elastic member232may be integrally formed as a component of a monolithic set screw204or otherwise attached to a separate body of set screw204or housing202, so long as the compression and expansion of the elastic member securely couples the set screw within the cavity218of the housing, and permits the set screw to rotate within the cavity when a rotational force is applied to the set screw.

Referring toFIG.6B, elastic member232and/or the cannulation206of set screw204defines a driving feature240, such as a recessed hexalobular internal driving feature, adapted to receive a tool tip, for example, a screw driver or a hex key (not shown), to rotate the set screw in a first direction and thread set screw assembly200into axial bore122in a distal direction and into connection with intramedullary nail102. Of course, the tool tip may also be inserted into driving feature240and rotated in a second direction, opposite to the first direction, to move set screw204thorough axial bore122in a proximal direction to unthread the set screw from intramedullary nail102.

Use of intramedullary intertrochanteric fracture fixation device100to heal fracture38is now described. First, set screw assembly200is assembled by inserting set screw204into the cavity218of housing202. During insertion, the elastic member232of set screw204will transition from the uncompressed condition to the compressed condition when the elastic member contacts the first end wall212of housing202. More particularly, the first end wall212of housing202will apply a distally directed force to the unattached end236of flanged elastic member232and compress the unattached end toward the terminal end of the body228of set screw204. This compression reduces the size of gap238and, in turn, the axial length of set screw204(e.g., measured from the unattached end236of the flange to an opposing terminal end of body228), and allows the set screw to enter cavity218. After set screw204has passed beyond the lip219of the upper portion208of housing202, the elastic member232elastically expands. In the uncompressed condition, lip219sits within retaining step242and frictionally secures set screw204within cavity218. The engagement between lip219and retaining step242inhibits lateral movement of the set screw204relative to housing202, while permitting the set screw to rotate about its longitudinal axis within cavity218when a rotational force is applied to the set screw.

Set screw assembly200may then be pre-operatively assembled within the proximal portion108of intramedullary nail102. To begin, the manufacturer or another user may position one of the vertices222of housing202into the longitudinal slot140of intramedullary nail102. Once positioned, set screw assembly200may be slid in a distal direction until the external threading230of set screw204engages the internal threading126of intramedullary nail102. Sliding set screw assembly200into the axial bore122of intramedullary nail102as described will prevent the set screw assembly from tilting relative to the longitudinal axis and thus assists in properly aligning the external threading230of set screw204and the internal threading126of the intramedullary nail. The likelihood that either thread will be damaged during threading of screw204to intramedullary nail102is thereby reduced.

A driving tool (not shown) may then be inserted into the recessed driving feature240of set screw204and rotated in a first direction (e.g., clockwise) to threadably mate the set screw and intramedullary nail102and cause set screw assembly200to move in a distal direction within axial bore122. During rotation of the set screw204, components of set screw assembly200and intramedullary nail102may interact in several ways: 1) the engagement between the vertices222of housing202and the longitudinal slot140of the intramedullary nail prevents the housing from rotating within the axial bore; 2) the engagement between expanded set screw204and the housing (including the engagement between the lip219of the housing and the retaining step242of the set screw) prevents the set screw from moving in an axial or lateral direction relative the cavity218of the housing (while permitting rotational movement of the set screw within the cavity); and 3) the engagement between the external threading230of the set screw204and the internal threading126of the intramedullary nail102causes the set screw and, in turn, the housing202to move in a distal direction within axial bore122. Rotation of set screw204may be ceased before the protrusions224of lower portion210extend into the angulated opening104of intramedullary nail102.

With intramedullary intertrochanteric fracture fixation device100prepared for surgery, a surgeon may then advance the intramedullary nail102over a guidewire244, through the cannulated set screw assembly200(as shown inFIG.8), and into position within the medullary canal28of the patient. After intramedullary nail102has been positioned within the medullary canal28of femur10, the surgeon may remove guidewire244and insert neck screw106through the angulated opening104of the intramedullary nail in order to compress the fractured bone portions together.

After the surgeon has confirmed that neck screw106is appropriately positioned within the intertrochanteric bone, the driving tool may then again be used to rotate set screw204and drive set screw assembly200in the distal direction until the ledge220of housing202engages the seat138of intramedullary nail102such that protrusion224extends into the angulated opening104of the intramedullary nail, and into one of the grooves136of neck screw106. Once positioned within groove136, protrusion224prevents neck screw106from rotating about bore axis124, and effectively prevents neck screw106from rotating within angulated opening104.

The surgeon may then optionally choose to limit the axial movement of neck screw106relative to intramedullary nail102. In order to set this limit, the surgeon may intraoperatively use the driving tool to rotate set screw204until the desired limit has been reached. If the surgeon desires to decrease the axial movement of neck screw106, the surgeon may rotate the driving tool in a first direction (e.g., clockwise) causing set screw assembly200to move distally within axial bore122as described above. As a result, protrusion224will project further into the ramped groove136of neck screw106and limit the distance that the neck screw is able to slide. If protrusions224are secured into firm engagement with a surface of the neck screw106that defines groove136, movement of the neck screw may be prevented all together.

On the other hand, if the surgeon desires to allow or increase the axial sliding of neck screw106, the surgeon may intraoperatively rotate set screw204in a second direction (e.g., counter clockwise) causing set screw assembly200to move in a proximal direction. Such movement will result in the retraction of protrusion224away from neck screw106and permit the neck screw to slide relatively further in the axial direction before contacting the ramped grooves136of the neck screw.

FIGS.9A-9Cillustrate a variant intramedullary nail102′ and a variant set screw assembly200′. Intramedullary nail102′ and set screw assembly200′ include all of the features described above with respect to intramedullary nail102and set screw assembly200of intramedullary intertrochanteric fracture fixation device100and are further modified as described below. The sidewall216′ of housing202′, for example, includes a pair of concave cutouts that define apertures225′ which allow the external threading230′ of set screw204′ to extend through the apertures and into direct engagement with the internal threading126′ of intramedullary nail102′ when set screw assembly200′ is disposed within axial bore122′. With specific reference toFIG.9B, housing202′ has a substantially triangular and three-leaf clover cross-section shape taken orthogonal to the longitudinal axis.

The lower portion of housing202′ may be formed substantially similar to housing202shown inFIGS.6A-8. Alternatively, as shown inFIGS.9D-9H, the lower portion210′ of housing202′ may be cylindrical in shape and include a distal end226′ formed by one or more outwardly tapered surfaces223′ that facilitate insertion of the k-wire through set screw assembly200′. The distal end226′ of housing202′ also includes a medial protrusion224a′ and a lateral protrusion224b′. Medial and lateral protrusions224a′,224b′ are curved and, more specifically, parabolic in shape when viewed from a medial-lateral perspective. The curved shape is designed to reduce stress on protrusions224a′,224b′ when the protrusions engage neck screw106′.

Lateral protrusion224b′ extends further in a distal direction than medial protrusion224a′. Thus, when the fracture fixation device is assembled as shown inFIG.9Hand the medial and lateral protrusions224a′,224b′ are disposed within the groove136′ of neck screw106′, the lateral protrusion engages a bottom surface of the groove and causes the medial protrusion to float above the bottom surface of the groove. Put differently, medial protrusion224a′ extends partially into groove136′ to prevent neck screw106′ from rotating within the axial bore but does not engage the bottom surface of the groove and, therefore, will not necessarily slide against the bottom surface of the groove as the neck screw limitedly slides along the bore axis. Consequently, medial protrusion224a′ will not deform.

Lateral protrusion224b′ includes a chamfer246′ extending in the lateral-to-medial direction. The chamfer246′ of lateral protrusion224b′ is designed to anticipate and prevent plastic deformation of the lateral protrusion as the protrusion slides laterally against the bottom surface of the groove136′ of neck screw106′.

Referring toFIG.9C, it will be understood that the axial bore122′ of intramedullary nail102′ may be modified (relative to the axial bore122of intramedullary nail102) to correspond to the three-leaf clover shape of housing202′. For example, axial bore122′ may include three longitudinal slots140′ shaped and sized to receive a respective leaf or vertices222′ of housing202′. Like longitudinal slot140, each of longitudinal slots140′ may act as a track for stabilizing set screw assembly200′ as the set screw assembly is loaded into intramedullary nail102′ and inhibiting unwanted post-operative rotation of the set screw assembly after the set screw assembly has been positioned within axial bore122′. Moreover, axial bore122′ includes an internal threading126′ disposed between each adjacent pair of longitudinal slots140′. In this manner, the alignment and threading of set screw assembly200′ to intramedullary nail102′ may be improved. The modified fracture fixation device shown inFIGS.9A-9Hcan be used as described above with respect to intramedullary intertrochanteric fracture fixation device100and, therefore, is not described again in detail herein.

FIGS.10A-10Care top elevation views of example set screw assemblies200A-200F in accordance with other embodiments of the present disclosure. Each one of set screw assemblies200A-200F includes all of the features of set screw assembly200and/or set screw assembly200′ with the only difference being the shape of the housing. The term “shape,” as used below with respect to housings202A-202F, refers to the shape of the cross-section of the housing taken orthogonal to the longitudinal axis.

Each set screw assembly200A-200F is preferably designed to be used with a different intramedullary nail (not shown) having an axial bore that corresponds in shape to the shape of the respective housing202A-202F. More specifically, each housing202A-202F has a polygonal shape with a number of vertices that is equal to the number of longitudinal slots within the axial bore of the corresponding intramedullary nail. In this regard, each one of the vertices can be positioned within a respective one of the longitudinal slots to stabilize the set screw assembly when the set screw assembly is loaded into the corresponding intramedullary nail and to inhibit unwanted post-operative rotation of the set screw assembly after the set screw assembly has been positioned within the axial bore of the intramedullary nail.

FIG.10A, for example, illustrates a set screw assembly200A having a housing202A shaped substantially as an oval and, more specifically, an ellipse with two diametrically opposed vertices222A. Thus, the axial bore of its corresponding intramedullary nail (not shown) may be formed with two longitudinal slots positioned on opposite sides of the axial bore from one another.

The housing202B of set screw assembly200B, as shown inFIG.10B, is similar in shape to the housing202′ of set screw assembly200′. That is, the housing202B of set screw assembly200B is shaped substantially as a three-leaf clover and, includes three vertices222B. The housing202B of set screw assembly200B, however, has a slightly thicker sidewall216B compared to the sidewall216′ of set screw assembly200′. Nevertheless, the corresponding intramedullary nail may be formed substantially as shown inFIG.9Cwith three longitudinal slots angularly spaced about the axial bore.

FIG.10Cillustrates a third example housing202C that is substantially triangular in shape and similar to the housing202of set screw assembly200. The primary difference being that the sidewall216C of housing202C defines an arcuate cutout between each one of the three vertices222C. Therefore, the intramedullary nail that corresponds to set screw assembly200C may have an axial bore provided with three longitudinal slots angularly spaced about the axial bore.

Referring now toFIG.10D, the shape of the housing202D is substantially rectangular and, more specifically, square. The sidewall216D of housing202D may define an arcuate cutout between any one of the adjacent four vertices222D. In this regard, the intramedullary nail corresponding to set screw assembly200D will define four longitudinal slots spaced 90 degrees from one another about the axial bore.

As shown inFIG.10E, the housing202E of set screw assembly200E is shaped approximately as an ellipse with two diametrically opposed vertices222E. The sidewall216E of housing202E may define two arcuate cutouts positioned along the minor axis of the housing. Therefore, the corresponding intramedullary nail may define two longitudinal slots positioned on opposite sides of the axial bore from one another.

Turning toFIG.10F, the housing202F of set screw assembly200F is shaped substantially as a rectangle with four vertices222F and a thickened sidewall216F along its width and a thinner sidewall along its length. Of course, the thickness of sidewall216F may be altered and/or varied along the width and/or along the length of housing202F. The corresponding intramedullary nail thus preferably has four longitudinal slots spaced 90 degrees about the axial bore from one another.

AlthoughFIGS.10A-10Fillustrate the housings as specific shapes, it will be understood that the shape of the housing may be alternatively formed as any polygonal shape. Moreover, while the number of vertices of the respective housings is preferably equal to the number of longitudinal slots formed within the axial bore of a corresponding intramedullary nail, it will be appreciated that the number of vertices of the respective housings need not be equal to the number of longitudinal slots defined in the axial bore of a particular intramedullary nail. So long as one of the plurality of vertices of the housing is positioned within a single longitudinal slot of the intramedullary nail, the set screw assembly will exhibit some degree of stabilization during loading and the ability to withstand post-operative rotational forces, albeit to a lesser degree than if the number of vertices is equal to the number of longitudinal slots.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present disclosure as defined by the appended claims.