Flexible intramedullary nail

A flexible intramedullary nail is disclosed that is manufactured from a biocompatible rigid material and having a substantially cylindrical hollow body, a leading segment with an entry hole at a distal end and at least one securing means and a trailing segment having a trailing edge and an attachment mechanism. The body has at least one flexible center section, each having at least one slot to provide flexibility. In one embodiment the at least one slot follows a sinuous, serpentine path to form a plurality of interlocking teeth that can follow a helical or a concentric path. Each of the slots has a proximal end and a distal end, with the proximal end being spaced from the trailing segment and the distal end being spaced from the leading segment. When multiple slots are incorporated, the proximal end of a slot is spaced from a distal end of a subsequent slot. The first of the at least one flexible center section and a second of the at least one flexible center section can be separated by a non-slotted section. The nail can be used with a flexible insertion shaft or a locking shaft.

FIELD OF THE INVENTION

The present invention relates generally to the treatment of bone fractures and pertains, more specifically, to the fixation of fractures in long bones in the body.

BACKGROUND OF THE INVENTION

Long bones are those greatly elongated bones such as the femur or tibia that are found in a human or in an animal. When a long bone is fractured, the surgeon immobilizes the various bone segments relative to one another to promote healing of the fracture. The immobilization or fixation of the segments is accomplished by the use of one or more rigid devices that span the fracture site and are located either external to the body or internally on the bone surface or inside the bone canal.

This invention of a flexible intramedullary fixation device was first proposed and submitted to the National Institutes of Health as a Small Business Innovation Research proposal “Retrograde Femoral Reconstruction Fixation System” on Aug. 14, 1997 and assigned Application Number 1 R43 AR45345-01. A revised application, #1R43 AR45345-01A1 was resubmitted on Apr. 14, 1998. The applications describe a flexible intramedullary nail that is inserted into the medullary canal of a long bone to align and stabilize the fracture by providing proximal and distal locking.

External fixation devices are typically located outside of the body, with the only components that enter the body and bone being metal pins. One such external device is known as a Hoffmann device. Another such device is known as a Brooker frame. Both are characterized by plural pins lodged in each bone segment. The pins are oriented transversely to the bone and exit the body. Frames that are exterior to the body connect the pins together. External devices not only prohibit movement of the bone segments relative to one another, but they also provide longitudinal compressive force on the bone segments, causing the segments to contact one another at the fracture site. Such compressive contact between the bone segments is desirable because it creates a physiological stimulus to unite the bone segments. However, external devices have many problems. External devices are difficult to manipulate to achieve the desired compressive force. Also, once the devices are set in the desired position, they can be inadvertently manipulated. Furthermore, external devices are inconvenient for the patient and present an increased chance of infection along the metal pins that penetrate the skin and underlying tissue.

Internal fixation devices include either cortical plates which are located on the exterior of the bone cortex or intramedullary nails which are located in the bone's intramedullary canal. The cortical plates are implanted surgically in a single operation and usually require an extensive operative procedure and exposure of the bone. Cortical plates, which are fastened to the bone cortex by screws, can apply slight compression to the bone segments. However, cortical plates are applied at the fracture site, carry the risk of infection and excessive blood loss and require extensive surgical exposure. Intramedullary nails are stainless steel or titanium rods that are inserted within the central, medullary canal of the bone, span the fracture site and are locked in place above and below using screws. The nail can be either driven from the proximal end to the distal end (antegrade) or from the distal end to the proximal end (retrograde). Prior art nails include Schneider nails, Kuntscher nails and Ender nails. Schneider nails are longitudinally fluted rods with small teeth on the ends. The teeth allow a trough to be cut as the nail is driven down the canal. Kuntscher nails are hollow rods with longitudinal flutes. Intramedullary nails range in diameter from 9 to 16 millimeters in diameter. Ender nails are flexible rods 2 to 3 millimeters in diameter or diamond shaped rods that may be curved. Intramedullary nails reduce the risk of infection since there is no continued penetration of the skin and are inserted away from the fracture site. Intramedullary nails also prevent inadvertent manipulation. However, prior art intramedullary nails fail to provide compressive force along the length of the bone.

The use of intramedullary nails or rods has become the standard method for the treatment of fractures, malunions and non-unions of long bones, i.e., the femur and tibia in the lower extremities and the humerus, radius and ulna in the upper extremities. The typical surgical procedure for such treatment involves the insertion or implantation of a nail or rod into the intramedullary canal of the subject bones such that the nail spans the fracture(s) and/or non-union or malunion. Interlocking screws are then placed through bores or apertures within the intramedullary nail, interlocking with the nail and extending through the bone on both sides of the treatment site. As such, the bone and/or bone fragments are stabilized and immobilized against rotational and lateral movement in order to allow the bone to properly set and heal, and to prevent displacement of the fracture during the healing process.

Moreover, intramedullary nails have consisted of relatively rigid structures inserted into relatively curved bones such as the femur, tibia, humerus and radius. These fixation rods have relationships between their bending and torsional rigidities that are substantially different from those of the intended intact long bone. This can result in shielding the fracture from the natural loading stresses and inhibiting callus formation. In addition, the intramedullary nails are manufactured in a pre-bent configuration to supposedly to match the curvature of the intended long bone but variation of natural curvature and there is typically a double curvature to the long bone cause a mis-match in curvature. This mis-match in curvature can cause great difficulty for the surgeon to insert the nail down the intramedullary canal or causes the bone to conform the curvature of the nail leading to malreduction or unsatisfactory positioning of the fracture fragments.

Retrograde intramedullary nailing, first described by Harris in 1980, has become common recently. For critical patients with multiple injuries, femoral shaft fractures can be stabilized quickly and efficiently, and bilateral lower extremity injuries can be treated simultaneously in the supine position. Although the absolute indications for the use of retrograde nails are still the subject of some debate, relative indications include morbid obesity, multisystem trauma, ipsilateral floating knee and/or tibia injuries, bilateral femur fractures, ipsilateral acetabulum and/or femoral neck fractures, uncontaminated traumatic knee arthrotomies, through-knee amputations, pelvic ring injuries, pregnancy, gross contamination around the insertion point for antegrade nailing, unstable spine injuries, and multiple fractures. For properly selected cases, limited use of retrograde nailing is recommended by most researchers. Retrograde insertion of a reamed intramedullary titanium nail through an intercondylar approach within the knee joint is used for femoral shaft fractures in most applications. The nail is introduced along an *inserted guide pin and countersunk under the intercondylar notch to preclude the possibility of damage to the patellofemoral joint or other articular structures and resultant late degenerative joint disease. Potential complications associated with retrograde nailing, including knee stiffness or impaired function, quadriceps atrophy, articular or cruciate ligament damage, and septic joint. Researchers have concluded that antegrade and retrograde nailing appear to be comparable as far as union rates and bony fusion latency are concerned.

One of the methods of fixation is fixation with locking retrograde intramedullary nail. It is used in intertrochanteric fractures,FIG. 2. Longer locking retrograde intramedullary nail can be used to fixate complex fractures, combined of distal and middle femoral fractures, or in fractures of the middle and lower parts of the femur, where access with a locking antegrade intramedullary nail is not possible (e.g. in patients with total hip arthroplasty, in non-union proximal femur fractures with implanted osteosynthetic material). The method is very good for fixation of fractures in older patients with a weak bone structure, in cases of pathological factures, and in poly-traumatized patients whose condition allows complete treatment. Locking retrograde intramedullary nail is also used for fixation of corrective supracondylar osteothomy and for fixation of supracondylar fractures in patients with total knee arthroplasty.

SUMMARY OF THE INVENTION

The disclosed nail is flexible to follow the natural curvature of a bone thereby preventing unwanted penetration, increased erosion of the cortex or insertion difficulties. Because of the difference in curvature between the natural bone and the intramedullary nail, insertion of the nail can become very difficult, preventing complete insertion of the nail into the bone, and potentially causing additional fractures of the bone.

All bones have a natural curvature to them in both the anterior/posterior and medial/lateral planes such that a straight intramedullary nail cannot be inserted into a bone. As a result of the natural curvature, all intramedullary nails possess a radius of curvature imparted to them during their manufacturing process or are of a flexible nature that conforms to the curvature of the bone. However, the radius of curvature of the pre-bent nails is not necessarily the curvature of the bone as each individual bone will have a slightly different curvature. In the case of the human femur, the radius of curvature is typically 1 meter whereas the radius of curvature of IM nails are typically in the 2 meter range. For an antegrade nail, the starting or entry hole in the prymifossa of the femur is not necessarily along the curvature arc of the femur and will affect how the nail will proceed down the canal. For a retrograde nail the entry point is usually on the lateral aspect of the femur above the femoral condyle of the knee or the at the intercondylar notch within the knee joint. This entry requires a different curvature for the intramedullary nail for positioning within the medullary canal.

The complications associated with the prior art rigid nail inserted into a curved bone are thus overcome. The disclosed nail uses a modification of the flexible shaft technology as taught by Krause et al in U.S. Pat. Nos. 6,053,922 and 6,447,518 and pending application U.S. Ser. No. 12/712,174 by imparting a serpentine or sinuous, helical slot along a segment or segments of the component. Preferably, the flexible nail is formed by laser cutting an elongated tubular member of substantial wall thickness, to form the slot around and along the tubular member. A serpentine or sinuous path can also be superimposed on a circumferential slot about the circumference of the shaft in the form of a generally sinusoidal wave. Preferably, the sinusoidal wave forms dovetail-like teeth, which have a narrow base region and an anterior region that is wider than the base region. Thus, adjacent teeth interlock. The teeth can have a configuration as illustrated in U.S. Pat. Nos. 4,328,839, and 6,053,922 the disclosure of which is incorporated herein by reference, as though recited in detail.

A flexible intramedullary nail is disclosed that is manufactured from a biocompatible rigid material and has a substantially cylindrical hollow body. The nail has a leading segment with an entry hole at a distal end and at least one securing means and a trailing segment having a trailing edge and an attachment mechanism. The body has at least one flexible center section, each having at least one slot to provide flexibility. In one embodiment the at least one slot follows a sinuous, serpentine path to form a plurality of interlocking teeth. The serpentine path can follow a helical path or a concentric path. The helical path of said at least one slot is about 0.25 to about 5 cycles per diameter length and the helical angle ranges from about 5 degrees to about 20 degrees The ratio of the amplitude of the path to the pitch of the slot is in the range from greater than 0.1 to about 0.8. The width of each slot between about 0.5% and about 5.0% of the diameter of said flexible nail. The at least one slot can alternatively follow a helical path. Each of the slots has a proximal end and a distal end, with the proximal end being spaced from the trailing segment and the distal end being spaced from the leading segment. When multiple slots are incorporated, the proximal end of a slot is spaced from a distal end of a subsequent slot. The first of the at least one flexible center section and a second of the at least one flexible center section can be separated by a non-slotted section.

The securing means of the leading and trailing segments can be selected from at least one from the group comprising securing slots, holes, threads, deployable fins, talons, expandable cages, and the use of deployable bone cement.

Each of the at least one slot can have a varied flexibility in relationship to another of slot from the group comprising increased flexibility, decreased flexibility, equal flexibility. Each of the slots can have sufficient width to form an unbound joint permitting limited movement in any direction upon application of tensile, compressive, and/or torsion forces. Alternatively, each slot can have an increased width in a first direction compared to a second direction to provide increased flexibility in said first direction. The varied flexibility can be achieved by varying the pitch of the helical slot and helix angle, said helical angle being in the range of about 10 degrees to about 45 degrees. The flexibility can also be achieved by varying the width of the helical slot.

The flexible intramedullary nail can have an elastomeric material from at least one of the group comprising: filling at least one of the at least one slot; filling within at least one portion of the inside core adjacent to at least one flexible center section; filling the insider core; extend through, and fill, at least one slot; encompass at least a portion of the exterior diameter of the spinal element; encompass the exterior diameter extend through, and fill, at least one slot; encompass at least a portion of the exterior diameter.

A flexible insertion shaft can be used with the flexible intramedullary nail or other nail. The insertion shaft has a body with a serpentine slot along its length that is dimensioned to fit within the hollow body of the flexible nail The leading end has a threaded leading end segment that has one or more cutting recesses with an attachment hub connecting the threaded leading segment to the body. The trailing end has a trailing end locking bolt with an end hub that comprises an attachment member for receiving a driving mechanism, threads dimensioned to receive the flexible nail and fingers dimensioned to receive and compress the flexible insertion shaft upon threading and tightening the end hub on the trailing end of the nail.

A locking shaft can also be used in conjunction with the flexible nail or other flexible devices. The locking shaft has a flexible rod and multiple roller sets. Each of the multiple roller sets comprises at least a pair of rollers and spacers with a receiving hole off set from center and dimensioned to receive the rod. The outer diameter of the roller sets is dimensioned to be received within the flexible intramedullary nail. Rotation of the rod rotates the multiple roller sets to wedge them against the interior of the flexible intramedullary nail. In one embodiment the spacers are non-rotatably affixed to the rod and the rollers are rotatable on the rod. In an alternatively embodiment both the spacers and the rollers are non-rotatably affixed to said rod.

In use for the stabilization of long bones the flexible intramedullary nail can be combined with the flexible locking shaft. The bone is prepared to receive an insert. A flexible intramedullary nail, having a hollow body, is inserted into the fractured bone with the leading edge being secured beyond the fracture. The flexible locking shaft, consisting of a flexible rod and multiple roller sets dimensioned to be received within the nail. Each roller set comprises at least a pair of rollers and spacers with receiving holes offset from their center dimensioned to receive the rod. The spacers can be non-rotatably affixed to the rod with the rollers being rotatable on the rod. Alternatively, both spacers and rollers can be non-rotatably affixed to the rod. When rotated within the flexible intramedullary nail the multiple roller sets are wedged against the interior of the nail thereby locking the nail in the desired configuration. The locking shaft is then locked in place with a trailing end locking bolt.

In use for the stabilization of long bones the flexible intramedullary nail can be combined with a flexible locking shaft having a serpentine slot along its length. A threaded leading edge, having one or more cutting recesses, is attached to the flexible locking shaft with an attachment hub. An end hub at the trailing end has attachment means for receiving a driving mechanism, threads dimensioned to receive the flexible nail and fingers. The flexible locking shaft is inserted, through use of the driving mechanism, into the bone. The leading edge of the locking shaft is secured beyond the fracture and the flexible intramedullary nail is then passed over the flexible locking shaft and the leading segment secured to the leading end of the insertion shaft at the attachment hub. The flexible intramedullary nail is in place with the flexible locking shaft using a trailing end locking bolt. The locking bolt is placed over the trailing end of the insertion shaft to secure the trailing end of the nail. The fingers of the locking bolt compress and grip the insertion as the bolt is tightened.

This invention of a flexible intramedullary fixation device was first proposed and submitted to the National Institutes of Health as a Small Business Innovation Research proposal “Retrograde Femoral Reconstruction Fixation System” on Aug. 14, 1997 and assigned Application Number 1R43 AR45345-01. A revised application, #1R43 AR45345-01A1 was resubmitted on Apr. 14, 1998. The applications describe a flexible intramedullary nail that is inserted into the medullary canal of a long bone to align and stabilize the fracture by providing proximal and distal locking.

The present invention overcomes the deficiencies and problems evident in the prior art as described herein above by combining the following features into an integral, longitudinally, laterally and torsionally flexible segment of the component.

A slot of substantial length and width extends in a generally serpentine or sinuous or other predetermined path, either continuously or intermittently, around and along the tubular member. The slot or series of slots can extend in a circumferential manner around the tubular member. Advantageously, the slot is cut at an angle normal to the shaft using a computer controlled cutting technique such as laser cutting, water jet cutting, milling or other means. Additionally, this slot may be cut at an angle to the normal so as to provide an undercut slot; preferably the angle is in the range from about 5 to about 45 degrees from the normal.

A plurality of slots can be employed thereby increasing the flexibility of the component, relative to a shaft having a single slot of identical pattern. The serpentine or sinuous path forms a plurality of teeth and complimentary recesses on opposite sides of the slot. The slot has sufficient width to form an unbound joint permitting limited movement in any direction between the teeth and the recesses, thereby providing limited flexibility in all directions upon application of tensile, compressive, and/or torsion forces to said component. In a similar manner the slot can have increased width in one direction compared to another direction thus providing increased flexibility in one direction.

The flexible segment can have different degrees of flexibility along the length of said shaft. The varied flexibility can be achieved by having the pitch of the helical slot vary along the length of the shaft. The varied flexibility corresponds to the variation in the pitch of the helical slot. The helical path can have a helix angle in the range of about 10 degrees to about 45 degrees, and the helix angle can be varied along the length of the shaft to produce correspondingly varied flexibility. Alternatively, the width of the helical slot can vary along the length of the shaft to provide the varied flexibility. The rigidity of the flexible shaft can be achieved through the design of the slot pattern, thereby enabling the use of thinner walls than would otherwise be require to produce equivalent rigidity. In a preferred embodiment, the ratio of the amplitude of the path to the pitch of the slot is in the range from greater than 0.1 to about 0.8.

In one embodiment the slot can be filled with a resilient material, partially or entirely along the path of the slot. The resilient material can be an elastomer compound which can be of sufficient thickness to fill the slot and to encapsulate the entire shaft thus forming an elastomer enclosed member. The elastomer can be a resilient material such as a urethane or a silicone compound. The rigidity of the flexible shaft can be further achieved or varied through the use of filler material having different stiffness properties, thereby enabling the use of thinner walls than would otherwise be require to produce equivalent rigidity. The use of an elastomer is disclosed in co-pending application Ser. No. 12/069,934 and 61/077,892 expired, and U.S. Pat. Nos. 6,053,922 and 6,447,518 the disclosures of which are incorporated herein as though recited in full.

Preferably, the flexible segment is formed by laser cutting an elongated tubular member of substantial wall thickness, to form the slot around and along the tubular member in a helical manner. A serpentine or sinuous path can be superimposed on a helical wave in the form of a generally sinusoidal wave. This sinuous path provides interlocking recesses and appendages to provide torsional and axial limitations to bending of the nail.

Preferably, the sinusoidal wave forms dovetail-like teeth, which have a narrow base region and an anterior region which is wider than the base region. Thus, adjacent teeth interlock. The teeth can have a configuration as illustrated in U.S. Pat. No. 4,328,839, the disclosure of which is incorporated herein by reference, as though recited in detail.

An important aspect of this invention therefore lies in providing a nail for insertion in a curved bone that follows the curvature of the bone.

An additional important aspect of this invention is a mechanism that causes the flexible nail to become rigid to provide additional support to the fractures bone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes herein the term “intramedullary rod”, also known as an “intramedullary nail” (IM nail), means a metal rod forced into the medullary cavity of a bone to align and stabilize fractures. IM rods are primarily inserted into the bone marrow canal in the center of the long bones of the extremities (e.g. femur, tibia, fibula, humerus, ulna and radius).

For the purposes herein the terms “slit” and “slot” are used interchangeably, consistent with their definitions, as follows:slot n. 1. A narrow opening; a groove or slit: a slot for coins in a vending machine; a mail slot.2. A gap between a main and an auxiliary airfoil to provide space for airflow and facilitate the smooth passage of air over the wing.

For the purposes herein the term pitch as used herein is defined as:pitch-n.1. The distance traveled by a machine screw in one revolution.The distance between two corresponding points on adjacent screw threads or gear teeth. (American Heritage Dictionary, 3rd Edition, Copyright 1994)

For the purposes herein the term “cycle” shall refer to:Cycle-1. An interval of time during which a characteristic, often regularly repeated event or sequence of events occurs: Sunspots increase and decrease in intensity in an 11-year cycle.2.a. A single complete execution of a periodically repeated phenomenon: A year constitutes a cycle of the seasons.2b. A periodically repeated sequence of events: cycle includes two halves of the sine-wave like undulation of the slot path. (American Heritage Dictionary, 3rd Edition, Copyright 1994)

For the purposes herein the term “amplitude” shall refer to the maximum absolute value of the periodically varying quantity of the slot.

For the purposes herein the term “serpentine” shall refer to:3 a: winding or turning one way and another <a serpentine road>b: having a compound curve whose central curve is convex. (Merriam-Webster online dictionary)

For the purposes herein the term “sinuous” shall refer to:1. a: of a serpentine or wavy form: winding,2. b: marked by strong lithe movements. (Merriam-Webster online dictionary)

For the purposes herein the term “serpentine” and “sinuous” are interchangeable and shall refer to a winding or turning one way and then another so as to not follow a straight line, except for brief instances.

For the purposes herein the term “helical”, “helix” and “spiral” are interchangeable and shall refer to:1 a: winding around a center or pole and gradually receding from or approaching it <the spiral curve of a watch spring> b: helical c: spiral-bound <a spiral notebook>2: of or relating to the advancement to higher levels through a series of cyclical movements. (Merriam-Webster online dictionary)

For the purposes herein the term “frequency” shall refer to the number of times a specified phenomenon occurs within a specified interval:

1a. Number of repetitions of a complete sequence of values of a periodic function per unit variation of an independent variable.

1b. Number of complete cycles of a periodic process occurring per unit time.

1c.: Number of repetitions per unit time of a complete waveform, as of an electric current. The number of times the cycles form a repetitive pattern in one unit of length is the frequency of the slot pattern. The number of cycles “C” of the slot undulations superimposed upon the circumferential path which are present in one revolution around the shaft, is referred to as the cycles per revolution. (American Heritage Dictionary, 3rd Edition, Copyright 1994)

The terms antegrade and retrograde indicate the direction of introduction of the nail from proximal and distal portals, respectively.

While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which particular embodiments and methods of implantation are shown, it is to be understood at the outset that persons skilled in the art can modify the invention herein described while achieving the functions and results of this invention.

Flexible, intramedullary fixation devices are useable in many applications to provide fracture fixation to a number of different bones. Although usable in many forms of bone connection, the flexible nails disclosed are particularly useful in the intramedullary fixation of fractured or severed long bones.

Accordingly, the descriptions that follow are to be understood as illustrative and exemplary of specific structures, aspects and features within the broad scope of the present invention and not as limiting of such broad scope.

The invention in one embodiment relates to a flexible nail or rod having one or more flexible segments within a central section of the device. The flexible nail can also contain a segment, or segments, that also include threads or cross holes used for the placement of interlocking screws with the bone. The flexibility is created through the use of at least one sinuous helical slot formed in the center segment of the element. In other embodiments, additional flexible segments also have at least one sinuous helical slot in either the same helical rotation and pattern or in an opposite rotation and/or different pattern. In another embodiment the flexible section or sections has a flexible segment that has at least one helical, sinuous slot within a section of the element that is embedded within a polymer or other flexible material so as to fill the slot with the flexible material as disclosed in U.S. Pat. Nos. 6,053,922 and 6,447,518 which are incorporated herein as though recited in full. In an additional embodiment the flexible nail uses a hollow flexible element that encompasses a polymer or other flexible material within its central core without extending into the sinuous slot(s). A further embodiment uses a flexible slotted segment within the element that contains a polymer or other flexible material within the central core with the flexible material extending radially outward through the sinuous slot(s). The flexible nail can further incorporate a flexible slotted segment that contains a polymer or other flexible material within the central core of the flexible segment that extends radially outward through the slot and encompasses the outer surface of the element and/or the flexible segment.

In applications where additional fracture stability is required after implantation of flexible intramedullary nail; bone cement or other materials can be injected in the cannulation hole. The slotted flexible section of the nail provides flow-through mechanism for bone cement that is used for production of a bone cement jacket around the nail, such that nail will be anchored in a highly stable manner after being implanted in the bone and specially after being implanted in a bone of reduced quality.

InFIG. 1, the described flexible intramedullary nail100comprises leading end segment111and a trailing end segment112axially spaced apart by a substantially cylindrical, flexible center segment120. The leading end segment111is furnished with an entry hole113to the central core115(see alsoFIG. 7B) of the nail100and one or more transverse locking holes114′,114″. The trailing end segment112has a trailing edge119with an attachment mechanism109and transverse slot118and/or transverse locking hole117. The center section120in this embodiment has two flexible sections, although one or more can be used and dimensioned accordingly, proximal flexible section124′, and distal flexible section124″ in which a serpentine, spiral slot128′,128″, respectively is superimposed on a helical path about the shaft121of the center section120. The flexible section124″ extends, in this embodiment, generally from the proximal end of the leading end segment111about one third the length of the nail100. Spaced slightly from the proximal end of the distal flexible section124″ is the proximal flexible section124′ which extends to the distal end of the trailing segment112. Through the nail100is a hollow cavity115extending from the leading edge113to the trailing edge119. In this, and other illustrated embodiments, the leading edge113is slightly beveled, however whether there is a bevel and the degree to which there is a bevel, will vary depending upon end use.

As illustrated inFIG. 2, current practice includes the management of certain fractures of the femoral shaft26and in the supracondylar region40of the femur20through the use of intramedullary nails in the form of retrograde nails inserted through a relatively small incision at the knee. Thus, an intramedullary nail in the form of a conventional retrograde nail42has been inserted longitudinally into the femur20through intercondylar notch30and has been advanced into the femoral shaft26. A fracture44in the femoral shaft26and a fracture46in the supracondylar region40are stabilized by fixation screws48and49extending through retrograde nail42at50and51, respectively. Retrograde nails, such as that illustrated by retrograde nail42, ordinarily are not extended beyond the lesser trochanter52, shown in the vicinity of subtrochanteric region38, and always have been confined to treatment of fractures in the femoral shaft26or the supracondylar region40, as shown inFIG. 2. Because the insertion of a retrograde nail requires only a relatively small incision, usually no more than one to two inches long, and no muscular dissection, blood loss is minimal and recovery is accelerated. These retrograde nails are used in conjunction with locking screws, such as fixation screws48, which are inserted percutaneously and require incisions of one centimeter or less, thereby further minimizing blood loss and reducing recovery time. Moreover, intercondylar notch30is accessed readily for the insertion of a retrograde nail however it requires opening the knee joint and associated risk and damage to the articular cartilage of the joint.

Current practice also includes the management of certain fractures of the femoral shaft66, as shown inFIG. 3, in the mid shaft region60of the femur66through the use of intramedullary nails in the form of antegrade nails inserted through a relatively small incision at the hip region of the patient. Thus, an intramedullary nail in the form of a conventional nail62has been inserted longitudinally into the femur60through pyriforma fossa notch61and has been advanced into the femoral shaft66. A fracture64and a fracture64′ in the femoral shaft66are stabilized by fixation screws68,68′ and68″ extending through nail62at69,69′ and69″, respectively. Because the insertion of an antegrade nail requires only a relatively small incision, usually no more than two to four inches long, and no muscular dissection, blood loss is minimal and recovery is accelerated. Antegrade nails are used in conjunction with locking screws, such as fixation screws68,68′ and68″, which are inserted percutaneously and require incisions of one centimeter or less, thereby further minimizing blood loss and reducing recovery time.

Current practice can also include the management of certain fractures of the tibia76, as shown inFIG. 4, in the mid shaft region70through the use of intramedullary nails in the form of an antegrade nail inserted through a relatively small incision at the knee region of the patient. Thus, an intramedullary nail in the form of a conventional nail72has been inserted longitudinally into the tibia76in the area known as the tibial tuberosity71and has been advanced into the tibial shaft76. A fracture74and74′ in the tibial shaft76are stabilized by fixation screws78,78′,78″,78′″ and78″″ extending through nail72at79,79′,79″,79′″, and79″″, respectively. The insertion of an antegrade nail requires only a relatively small incision, usually no more than two to four inches long, however the patellar tendon must be split and knee joint opened. As in femoral nailing, blood loss is minimal and recovery is accelerated. Antegrade nails are used in conjunction with locking screws, such as fixation screws78,78′,78″,78′″ and78″″ which are inserted percutaneously and require incisions of one centimeter or less, thereby further minimizing blood loss and reducing recovery time.

FIG. 5is a diagrammatic illustration of a long bone demonstrating current prior art practice in the treatment of certain fractures in the femur using multiple Ender nails.FIG. 5Adepicts an intertrochanteric fracture84in a femur bone86with multiple Ender nails82, and82′ inserted retrograde from a point of entry88on the medial aspect of the femur86and nails82″,82′″ and82″″ inserted retrograde from an entry point88′ on the lateral aspect of the femur86.FIG. 5Bdepicts an subtrochanteric fracture94in a femur bone96with multiple Ender nails92, and92′ inserted retrograde from a point of entry98on the medial aspect of the femur96and nails92″,92′″ and92″″ inserted retrograde from an entry point98′ on the lateral aspect of the femur96.

FIG. 6is an additional embodiment of the intramedullary nail which has a leading end segment130for securing the nail150to the bone. In this embodiment the leading end segment130is a threaded ended segment but other means, as known in the art, of securing the leading end to the bone may be employed. Such means includes, but not limited to, deployable fins, talons, expandable cages, and the use of deployable bone cement. The flexible section,152, as with the embodiment illustrated inFIG. 1, contains a distal flexible section156and a proximal section158having differently dimensioned serpentine patterns. The trailing end154is configured to receive a locking section.

FIG. 7aandFIG. 7bare exploded views of section D inFIGS. 1 and 6showing the serpentine slot128within the shaft121′ of the flexible section124′ of nail100. The slot128, having a width129, is cut with a general helix angle127of about 10 to 80 degrees with respect to the longitudinal axis of the section124″. In this embodiment the slot128is cut in a serpentine pattern having an amplitude122and interlocking teeth126,125with a pitch123.

It should be noted that the serpentine slot128can be used on all embodiments herein. Although length and width can vary dependent upon end use, the basic concepts as illustrated in this embodiment are consistent. The slot128is representative of all the slots disclosed herein in that way that it is cut through the shaft121into the core115. Although the slots disclosed herein are of different patterns, this is purely a function of flexibility and all have the same basic construction. In the following description of the criteria of the slots, no reference numbers specific to other figures are used, as the criteria are applicable to all slot configurations.

FIG. 8illustrates the threaded leading end segment130of the flexible nail150ofFIG. 6in which a leading threaded end segment130, is furnished with a shank139for attachment with the nail100, an end132, screw thread134and a thread cutting recess135at the end132and cutting recess135′ on the shank139.

A variety of slot patterns are illustrated inFIG. 9A-K. The patterns are representative of patterns that can be used and are not intended to be all inclusive. As illustrated inFIG. 9A, and indicative of all patterns, the pattern has a cycle length C, which includes a neck region NA. The wider the neck region the greater the strength of the connector, that is, the greater the torsional forces which the flexible shaft can transmit. The ability of the device to interlock is dependent in part upon the amount of overlap or dovetailing, indicated as DTA forFIG. 9Aand DTB forFIG. 9B. The patterns illustrated inFIGS. 9C and 9G-9Kdo not provide dovetailing, and require a helix angle that is relatively small. Pattern9F is another interlocking dovetail pattern that can be used with a larger helical angle than non-dovetailing patterns The patterns ofFIGS. 9H-9Kis an interrupted spiral in which the slot follows the helical path, deviates from the original angle for a given distance, and then resumes the original or another helix angle. Patterns, as shown inFIGS. 9D, 9E, 9F, 9H through 9Kcan have a configuration as illustrated in U.S. Pat. No. 6,447,518, the disclosure of which is incorporated herein by reference, as though recited in detail.

The helical path of the slot128is about 0.25 to about 5 cycles per diameter length. In order to provide the desired flexibility, while maintaining support, the width of the slot128should not exceed about 0.075 of an inch in a nail or shaft having a diameter in the range from about 0.10 to about 0.750 inches, with a general width of about 0.005 to about 0.025 inches. Or alternatively stated, the slot128width is between about 0.5% and about 5.0% of the diameter of the element. The helical angle ranges from about 5 degrees to about 20 degrees.

FIG. 10is a diagrammatic illustration of an additional embodiment of the intramedullary nail150positioned retrograde in a femur156with the leading thread end segment130positioned in the femoral head151as would be used for a fracture of the femoral neck152, the intertrochanteric153, the subtrochanteric154or mid shaft155region.

FIG. 11is a diagrammatic illustration of the intramedullary nail150being positioned retrograde in a tibia160at an entry point161on the medial aspect of the tibia with the leading thread end segment130positioned in the tibia below the point of entry161.

FIG. 12is a diagrammatic illustration of the intramedullary nail150fully positioned retrograde in a tibia160from the entry point161on the medial aspect of the tibia with the leading thread end segment130positioned in the tibia.

In another embodiment of the invention as shown inFIGS. 13 through 17, a flexible insertion shaft170, with the threaded leading end segment175attached, is used in conjunction with the IM nail100.FIG. 14further illustrates Section A of the threaded leading end segment175that is incorporated with the small diameter flexible insertion shaft170. The end segment175is affixed to the insertion shaft170through use of an attachment hub180. The leading end segment175has one or more cutting recesses181in the hub180adjacent to the thread184and leading tip183. The leading end segment175and insertion shaft170form a unit that is initially inserted in a fractured bone over which the flexible intramedullary nail100is passed and locked in place with a trailing end locking bolt190,FIG. 15. The trailing locking bolt190has an end hub191with a hexagonal or other shape recess194, for attachment of a driving mechanism such as a screw driver, threads192for engaging the flexible nail100and fingers193

The insertion shaft170has the serpentine slot128along its length to conform to the curvature of the bone and the threaded end segment130can be screwed into the bone past the fracture site in an appropriate position. The flexible nail100is then slide over the insertion shaft170until the leading edge113of the nail100engages the leading end segment130as shown inFIG. 16. The trailing end locking bolt190is slide over the insertion shaft170and engages the trailing end of the nail119. As the locking bolt190is screwed into the flexible nail170with the threads192, the fingers193of the bolt190are compressed and grip the insertion shaft170.FIG. 17illustrates the fully assembled insertion shaft170and IM nail100as it would be in the bone.

FIG. 18illustrates another embodiment of the flexible compression nail210intended to apply compressive action when inserted; and therefore the pitch P1of thread214is slightly greater than the pitch P2of thread216. The threads214and216, as are all threads disclosed herein, are like-handed such that the variation in thread pitch, when the nail is inserted into a bone and rotated in place results, in movement of the distal bone segments towards each other and compresses the fracture. Sections D and B-B are described in more detail inFIGS. 19 and 20, respectively. Section D is illustrated inFIG. 7.

FIG. 19is a sectional view of axis B-B seen inFIG. 18to illustrate the passage of the central opening220from the leading edge218extending though the nail210to the trailing edge219. The trailing end219of the nail210is furnished with a threaded or similar receiving recess to receive a screwdriver, other rotational force device or attachment device for insertion.

FIG. 20illustrates another embodiment of the flexible nail270in which a flexible leading end segment271with serpentine slot278′ and a non threaded trailing end segment272are axially spaced apart by a substantially cylindrical, flexible center segment273having a slot278. The leading end segment271is furnished with a first screw thread274, a thread cutting recess275and a serpentine slot278′.

FIG. 21is an exploded view of section A inFIG. 20. In this instance, the serpentine slot278is formed on the minor diameter D2of the threaded segment271. The slot can extend partially up the side of the thread274or up and over the thread274.

FIG. 22illustrates another embodiment of the flexible compression nail280in which a leading threaded end segment284, a threaded trailing end segment282, are axially spaced apart by a substantially cylindrical, flexible center segment283with one or more concentric slots288. The concentric slot288has an amplitude A and spacing C from the previous slot. Between the leading end segment284and the center segment283is a collar289from which secondary cutting recess285′ is cut. The trailing segment287has a recess222, as shown inFIG. 19as a means of driving the nail285.

InFIG. 23the central segment283ofFIG. 22generally consists of a hollow tube having an outer surface354and a hollow central core351as illustrated inFIG. 25. Slots360,360′,360″, . . .360nare cut through the wall352, shown inFIG. 25, of section of the central segment283to provide flexibility. Multiple circumferential slots360,360′,360″, . . .360nare situated continually at prescribed or varying intervals over all or most of the length of the segment283enabling the majority of the element283to flex. The number of slots “n” can vary dependent upon the flexibility desired. The flexibility will be dependent upon the spacing “C” as well as the amplitude “A” of the serpentine slot360and the solid section354between slots360. In this embodiment the slots360,360′,360″, . . .360nallow for flexibility only within the flexible segment. The sections330and328of the central segment283that are not slotted remain relatively rigid and are used for attachment with the leading and trailing segments.

In the embodiment illustrated inFIGS. 24, 25, and 26, the serpentine pattern of slot360n+1is offset or staggered a rotational distance OFS from the adjacent slot360nBy staggering the serpentine pattern as illustrated, the bending characteristics, i.e. the bending strength and flexibility, can be changed to provide differences or uniformity with respect to the rotational axis.

The sectional view24-A24A of central segment283ofFIG. 24is shown inFIG. 25. A magnified view25B of the slot360nis illustrated inFIG. 26. The slot360nis representative of all the slots disclosed herein in the way that it is cut through the wall352into the core351. Although the slots disclosed herein are of different patterns, this is purely a function of flexibility and all have the same basic construction. The criticality to the disclosed invention lies in the ratios and dimensions rather than the process of placing a rod or tube. In the following description of the criteria of the slots, no reference numbers specific to other figures are used, as the criteria are applicable to all slot configurations.

In the embodiment illustrated inFIGS. 27, 28 and 29, a biocompatible resilient flexible or elastomeric material370fills only the slot360of the central segment. The exterior surface354of the central segment remains uncovered by the material370as does the interior surface353. The addition of the elastomeric material370to the slot360provides resistance to the flexibility of the segment283as well as preventing tissue and scar ingrowth into the slot. It should also be noted that the elastomeric material does not necessarily have to fill all slots in the rod, with the placement of filled and unfilled slots affecting the flexibility.

InFIGS. 30, 31, and 32the elastomeric material370encapsulates the central segment283as well as filling the slots360. In this embodiment, the interior surface430and exterior surface328are covered with the elastomeric material370and the slots360are filled to prevent tissue ingrowth into the slots360and increase the stiffness of the nail. The core355, of the encapsulated segment350, however, remains hollow as seen in section30A-30A inFIG. 31. Although in these figures the elastomeric material370also fills the slots360passing through wall352as shown inFIG. 32of the enlarged section31A, it should be noted that the elastomeric material370can alternatively only encapsulate the segment without filling the slots360. Additionally, just the interior or exterior of the segment can be covered with the elastomeric material with the slots being either filled or unfilled. The encapsulation can be only at the portion of the nail that is flexible or can extend the entire length of the nail. As noted above, the addition of the elastomeric material370increases the resistance to flexing and is not reflective of the advantages of encapsulating segment350with the elastomeric material370.

As can be practiced, any of the segments of the flexible nail can be either non-flexible or can be made flexible by the incorporation of a slot with a serpentine path along a helical or concentric path within the segment.

In another embodiment of the invention, a rod or similar type device can be inserted in the central core115to lock the curvature the flexible nail100in a shape matching the natural curvature of the bone. One such locking shaft400is illustrated inFIGS. 33 and 34which is comprised of sets of spacers420and movable rollers410. Sets of these spacers420nand rollers410nare positioned along a rod401at multiple intervals, determined at time of manufacture. In most embodiments the spacers420nare fixed to the rod401while the rollers410nare free to rotate about the rod401, although both spacers420and rollers410can rotate. The number and size of the sets, as well as the spacing in between is depend on end use and will be obvious to those skilled in the arts. At the driving end, or trailing section, of the locking shaft400is an attachment end405that is used to insert the locking device400and rotate the locking device400when required.

The locking bolt190ofFIG. 15can also be used to secure the locking shaft400to the flexible nail100.

In at least the spacer420, and in some embodiments both spacer420and roller410, the receiving hole for the rod401is offset from its center. This locks, upon rotation, the spacers420against the interior wall of the nail100creating the desired rigidity. The dimensioning between the outer diameter of the spacers420and rollers410and the inner diameter of the nail100must be such as to prevent the spacers420and rollers410from freely rotating within the interior of the nail100.FIG. 35shows the relative orientation of the spacer420nand roller410nwhen initially inserted into the central core of the flexible nail100.FIG. 36shows the relative orientation of the spacer420nand roller420nafter the rod401has been rotated after insertion. When rotated, the rollers410nact as a wedge to push the spacers420up against the opposite wall thus locking the two in the interior diameter of the nail100. With the multiple spacers420all locking within the interior of the nail100, the nail100will become rigid in the desired shape, matching the shape of the bone. The locking shaft can also be placed into a transfer sleeve prior to insert into the nail100. The transfer shaft, known in the art, aligns the rollers410and spacers420, making insertion easier. As known, the transfer shaft is removed prior to rotation of the attachment end405.

In another embodiment, illustrated inFIG. 37, the locking shaft450can have a threaded leading end segment475, as described for flexible insertion shaft170, at the distal end. As described for the flexible insertion shaft170, the locking shaft450is inserted prior to the flexible nail100insertion which is inserted over the locking shaft450. The enlarged view of37A is illustrated inFIG. 38.

Broad Scope of the Invention

While in the foregoing we have disclosed embodiments of the invention in considerable detail, it will understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.