CANNULATED TELESCOPIC FEMORAL NECK SCREW DEVICE AND RELATED FIXATION METHOD
A screw assembly and method developed for the fixation of femoral neck fractures without interruption of the growth process is disclosed. The screw assembly includes a male component that is attached to the lateral cortex and a female component that is attached at the proximal epiphysis. Anchorage of the components is achieved through screw-type fixation. The screw has a built-in feature that allows for free extension of its length as the fracture site or the slipped capital physeal plate heals and normal patient growth continues. Stable fixation and rotational stability are created at the fracture (slip) site while avoiding compression forces, thus avoiding premature closure of the physeal plate.
The present document generally relates to a screw assembly system and method for the fixation of fractures along the femoral neck, and in particular to an improved cannulated bone screw assembly that enables the implant to be used for the fixation of bone fractures through the physeal plate (growth plate).
BACKGROUNDCannulated screws have been used for internal fracture fixation, and a single screw placement through the femoral neck has become the preferred treatment for fractures through the physeal plate. Fractures through the physeal plate are more commonly referred to as Slipped Capital Femoral Epiphysis.
Generally, such a fixation device comprises a hollow shaft having a predetermined cross-section and provided with threaded sections beginning at the medial end of the device spanning a predetermined length of the shaft. The fixation device is placed parallel to the neck of the femur and secures the fracture with compressive force applied by the spherical lateral screw head at the lateral cortex. The prior art typically describes a variety of screw systems comprising different shaft diameters, shaft lengths, thread pitches and thread lengths in order to offer a fixation device for all possible locations and extents of the fracture sites. The general configuration of cannulated screws is well illustrated in U.S. Pat. No. 7,207,994. Such described screws are non self-adjustable in length and, therefore incapable of providing a surgical fixation to stabilize fractured bones during the healing process without disrupting the normal bone growth particularly in pediatric patients.
In another example described in U.S. Published Patent Application No. 20070260248, an adjustable feature is incorporated into the screw allowing extension of the shaft length along a predetermined range. The screw has an outer member and an inner member connected together by a spring-like component. Once the shaft length is selected and the device is stabilized in said position, the device is inserted into the prepared canal of the femoral neck to fixate the bone segments, just as previously described for cannulated screws, in order to promote healing.
Other prior art include an intramedullary nail described as an adjustable solution for long bone fixation in U.S. Pat. No. 6,524,313. However, no prior art device has shown adjustable screw solutions for this regard. Therefore, there is a need in the art for an extendable screw system for surgical fixation of femoral neck fractures in pediatric patients.
Given the present design of cannulated screws used for the fixation of femoral neck fractures, including Slipped Capital Femoral Epiphysis, the compressive loads created by the medially threaded shafts and the lateral spherical screw heads inhibit the normal growth in young patients. Premature closure of the physeal plate is a reoccurring condition widely documented in the literature as a result of pinning and fixation via cannulated screws. Telescoping devices such as the Fassier-Duval Intramedullary Nail, whose fixation features do not thread into the physeal plate, have shown successful internal fixation of fractures and osteotomies in long bones without compromising the integrity of the physeal plate and thus allowing the continuation of normal patient growth.
SUMMARYIn one aspect, a cannulated screw assembly is provided that is self-extendable in length for surgical fixation of fractured femoral necks or slipped femoral epiphysis in a young patient.
In another aspect, a cannulated screw assembly is provided which requires minimally invasive instrumentation and a relatively straightforward surgical technique.
Hence, in accordance with one aspect of the screw assembly, a screw assembly for fixation of femoral neck fractures may include a telescopic assembly having two opposed ends and including a male component and a female component. The interconnected components permit axial movement of each end relative to each other. Anchorage of the female and male components is achieved through screw-type fixation of each end of the telescoping screw to the lateral cortex of the femur and the head of the femur. The smooth shaft design and lack of compression element allow free longitudinal extension of the length of the screw so that the screw is extendable as the bone heals and normal patient growth occurs.
According to one embodiment of the screw assembly with a beveled head design, the screw assembly is provided with an elongated tube having one end formed with an external self-tapping thread that has a diameter greater than the external diameter of the tube, and a cannulated rod having one end formed with an external self-tapping thread as large as the external diameter of the tube. The cannulated rod is adapted for insertion through a drilled canal into the bone until the self-tapping end is anchored in the medial end of bone (the epiphysis of the femoral head) and the rod spans the fracture site. The elongated tube is adapted for insertion into the bone, over the cannulated rod, until the external fixation thread at the lateral end of the tube is anchored within the lateral cortex of the bone. The screw assembly creates a stable fixation and inhibits radial displacements of the fractured segments of the bone while permitting longitudinal extendibility as the bone structures heals and normal patient growth occurs.
This embodiment of the screw assembly provides a relatively easy method of implantation because anchorage of the screw assembly is as would be anchorage of a single cannulated screw, wherein the action is achieved through rotating the respective rod and tube components until the threads anchor in the bone structures with the use of detachable driving tools. The position of the screw assembly is final when beveled head is parallel to surface of the lateral cortex.
According to another embodiment with a triblobe design, the screw assembly is provided with a male component with an elongated rod having one end formed with an external self-tapping thread that has a diameter greater than the external diameter of the tube, and a female component having one end formed with an external self-tapping thread that is the same diameter as the tube. The female component is adapted to be inserted through a drilled canal into the bone until the self-tapping end is anchored in the medial end of bone (the epiphysis of the femoral head) and the rod spans the fracture site. The male component is adapted to be inserted into the bone, inside the female component, until the external fixation thread at the lateral end of the rod is anchored within the lateral cortex of the bone.
An additional characteristic of this embodiment is to provide a cannulated screw assembly for surgical fixation of fractures bones which prevents rotational instability of the femoral epiphysis by preventing the rotation of the male and female components along the central axis. Rotation is hindered by interlocking of a non-circular feature (e.g. one or more flat surfaces, trilobe, cloverleaf, etc.) on the outer surface of the male component and the inner surface of the female component. The male component must be placed into the female component according to the specific mating pattern dictated by the interlocking feature on the components of the assembly. The screw assembly inhibits both radial displacements of the fractured segments of the bone and axial rotation of the segments around the axis of the screw assembly, while permitting longitudinal extendibility as the bone structures heal and normal patient growth occurs.
Moreover, the screw assembly provides a relatively easy method of implantation because the design allows anchorage of the screw assembly as would the anchorage of a single cannulated screw. The male and female components are assembled as per presented in the embodiment in order to screw in simultaneously both medial and lateral threading through a simple continuous rotation action with the use of a driving tool detachably connected to the male component, which in turn serves as the driving tool for the female component. Device position is final when all threads on tube have fully tapped into bone beyond the physeal plate within the femoral epiphysis.
In all embodiments, the screw assembly has a unique feature of self-adjustment in length after its implantation to provide a stable fixation of the fractured bone segments without the use of compressive forces to promote healing without disrupting normal patient growth, which is particularly advantageous when the screw assembly is used in children. In addition, rotational stability can be achieved by the incorporation of a non-circular design feature to block rotation between male and female components. Furthermore, retrieval features incorporated into the lateral ends of the embodiments of the present invention allow retention of the screws during insertion and removal procedures. Finally, a cap-like component completes the screw assembly, which inserts into the proximal end of the screw assembly at the lateral cortex in order to prevent bone in-growth for eased retrieval of the screw assembly once the fracture site is healed or patient growth is complete.
Additional objectives, advantages and novel features will be set forth in the description which follows or will become apparent to those skilled in the art upon examination of the drawings and detailed description which follows.
Corresponding reference characters indicate corresponding elements among the view of the drawings. The headings used in the figures should not be interpreted to limit the scope of the claims.
DETAILED DESCRIPTIONReferring to the drawings, various embodiments of the screw assembly are illustrated and generally indicated as 100, 200 and 300 in
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It should be understood from the foregoing that, while particular embodiments have been illustrated and described, various modifications can be made thereto without departing from the spirit and scope of the invention as will be apparent to those skilled in the art. Such changes and modifications are within the scope and teachings of this invention as defined in the claims appended hereto.
Claims
1. A screw assembly comprising:
- a female component including a hollow elongated shaft defining a medial threaded portion at one end of the hollow shaft and a lateral end opening at the opposite end thereof, wherein the lateral end opening is in communication with a non-cylindrically shaped channel formed along the hollow shaft;
- a male component configured to be received within the non-cylindrically shaped channel of the female component, the male component including a non-cylindrical shaped shaft defining a lateral threaded portion at one end; and
- a cap configured to engage the male component;
- wherein the non-cylindrical shaped channel of the female component defines substantially the same cross-sectional configuration as the non-cylindrical shaped shaft of the male component such that the male component is freely slidable relative to the female component along a longitudinal axis defined by the screw assembly.
2. The screw assembly of claim 1, wherein the male component is not rotatable relative to the female component when the female component is engaged to the male component.
3. The screw assembly of claim 1, wherein the non-cylindrical shaped shaft of the male component and the non-cylindrical shaped channel of the female component each have a three sided cross sectional configuration or a double flat cross-sectional configuration.
4. The screw assembly of claim 1, wherein the non-cylindrical shaped shaft of the male component and the non-cylindrical shaped channel of the female component each have a triangular, square, rectangular, or oblong cross-sectional configurations.
5. The screw assembly of claim 1, wherein the lateral threaded portion of the male component defines a cortical-shaped profile.
6. The screw assembly of claim 1, wherein the medial threaded portion of the female component defines a cancellous-shaped profile.
7. The screw assembly of claim 1, wherein the medial threaded portion of the female component includes a self-tapping feature defining a flat surface area.
8. The screw assembly of claim 1, wherein a diameter of the medial threaded portion is as large as an external diameter of the hollow elongated shaft.
9. The screw assembly of claim 1, wherein the male component further includes a drive feature defining a hexagonal-shaped recess formed proximate the lateral threaded portion.
10. The screw assembly of claim 9, wherein the male component defines a second lateral threaded portion formed proximate the drive feature, wherein the second lateral threaded portion is configured to engage the cap and a drive mechanism.
11. The screw assembly of claim 1, wherein the cap comprises a middle portion with a cap portion formed at one end of the middle portion and an external threaded portion formed at the opposite end thereof.
12. The screw assembly of claim 1, wherein the lateral threaded portion of the male component includes a self-tapping feature that defines a flat surface area.
13. The screw assembly of claim 1, wherein the medial threaded portion of the female component defines an axial opening in communication with the non-cylindrical shaped channel.
14. The screw assembly of claim 9, further comprising a drive mechanism configured to engage the drive feature for inserting the screw assembly into a bone.
15. A screw assembly comprising:
- a female component including a hollow elongated shaft defining a lateral threaded portion at one end of the elongated hollow shaft and a medial end opening at the opposite end thereof, wherein the medial end opening is in communication with a cylindrically shaped channel formed along the elongated hollow shaft; and
- a male component configured to be received within the cylindrically shaped channel of the female component, the male component including a cylindrical shaped shaft defining a medial threaded portion at one end;
- wherein the cylindrical shaped channel of the female component defines substantially the same cross-sectional configuration as the cylindrical shaped shaft of the male component such that the male component is freely slidable and rotatable relative to the female component along a longitudinal axis defined by the screw assembly.
16. The screw assembly of claim 15, wherein the lateral threaded portion of the female component defines a beveled profile.
Type: Application
Filed: Jan 25, 2013
Publication Date: Jul 31, 2014
Inventors: Fady Rayes (Vaudreuil-Dorion), Ariel Ricardo Dujovne (Cote St Luc), François Fassier (Outremont), Marie Gdalevitch (Montreal)
Application Number: 13/750,881