PROSTHETIC DEVICE AND METHOD OF MANUFACTURING THE SAME
A knitted prosthetic device has at least two knitted sections, where each knitted section has at least one row of fiber. The knitted prosthetic device also has at least one intra-articular section disposed between the at least two knitted sections. In addition, the at least one intra-articular section has at least one single continuous fiber traversing the at least one intra-articular section and the at least two knitted sections, where the at least one single continuous fiber forms a plurality of traverses extending between the at least two knitted sections. In particular, embodiments may be used as ligament prostheses by anchoring each of the at least two knitted sections to a bone section of a patient. Such embodiments may be constructed from a strong polymer, preferably, but not limited to, silk, where the polymer provides ligament support but bioresorbs as load bearing responsibilities are transferred to tissue resulting from ingrowth.
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This application is a continuation of U.S. patent application Ser. No. 12/052,719, filed Mar. 20, 2008, which claims the benefit of U.S. Provisional Application No. 60/919,126 filed Mar. 20, 2007, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a prosthetic device for ligament reconstruction, and more particularly, to a fabric prosthetic device used for reconstruction of ligament tissue.
2. Description of the Related Art
Every year, hundreds of thousands of people sprain, tear, or rupture ligaments and tendons of the knee, elbow, hand, shoulder, wrist and jaw. One such ligament is the anterior cruciate ligament (ACL) of the knee. More than 200,000 people in the U.S. alone, tear or rupture their ACL each year. The ACL serves as a primary stabilizer of anterior tibial translation and as a secondary stabilizer of valgus-varus knee angulation, and is often susceptible to rupture or tear resulting from a flexion-rotation-valgus force associated with sports injuries and traffic accidents. Ruptures or tears often result in: severe limitations in mobility; pain and discomfort; and an inability to participate in sports and exercise. Failures of the ACL are classified in three categories: (1) ligamentous, in which ligament fibers pull apart due to tensile stress; (2) failure at the bone-ligament interface without bone fracture; and (3) failure at the bone-ligament interface with bone fracture at the attachment site of bone and ligament. Ligamentous failure is the most common type of ACL failure.
It is widely known that the ACL has poor healing capabilities. Total surgical replacement and reconstruction are required when the ACL suffers a significant tear or rupture. The most common practice is to reconstruct a tom ACL by substituting the tom ligament with the patient's own tissue, also known as an autograft. The middle third of the patellar tendon or the hamstring tendons are commonly used as autografts. Other options for substitute ligaments include donor tissues from a cadaver, also known as allografts, as well as synthetic grafts.
Conventionally, the techniques for reconstructing the ACL involve drilling tibial and femoral tunnels and pulling the autograft, allograft, or artificial ligament through the tunnels. The substitute ligament is then anchored to bone by a mechanical fixation device. Anchors may include the suspensory fixation, staples, as well as interference screws and cross pins. Often, the graft is folded in half to create a double bundle to more closely mimic the native human ACL. The size of the drilled bone tunnels depends on the size of the graft, which in turn depends on the strength of the graft material.
Although the use of auto grafts is common, the technique is disadvantageously accompanied by morbidity at the second surgery site from which the autograft is taken. For example, stress fracture of the patellar or weakness in the quadriceps muscle may occur, and a long rehabilitation period may be required. Furthermore, harvesting and preparation of autogeneous tissue prolong surgery time and cause additional trauma to the patient.
In-growth in the bone tunnels and about the device improves the device's strength and functionality over time. In addition, if sufficient in-growth does not occur, conventional devices may not be able to maintain proper flexibility, integrity, or tension in the long term.
In order to restore the stability of the knee with a replacement ligament, correct tensioning of the graft must also be established and maintained. A common mode of failure for conventional devices occurs when the devices loosen due to bone erosion and degradation around the implant site. In such cases, sufficient in-growth can fail to occur around the device within the bone tunnels. This then results in a slackening of the ligament and an eventual return to a dysfunctional knee.
Another disadvantage with conventional devices includes the release of debris from a failed ligament resulting in chronic inflammation of the joint. A further disadvantage includes osteolysis of bone, in and around the area of ligament attachment. Moreover, device abrasion may occur at the bone tunnel apertures.
SUMMARY OF THE INVENTIONIn view of the foregoing, embodiments according to aspects of the present invention address the disadvantages of conventional devices and provide an improved device for reconstruction of ligament tissue.
Advantageously, embodiments provide a reconstruction or prosthetic device having multiple bundles of fibers that closely mimic the natural structure of ligament tissue, such as a native ACL, and allow for new tissue in-growth. In addition, embodiments provide sufficient flexibility to enable implementation in a large range of anatomies.
Furthermore, embodiments may be compatible with conventional anchoring systems and may be implanted into the same footprint as the native ligament tissue. Additionally, embodiments enable equal tensioning and distribute load evenly across a reconstructive device while it sustains a physiologic load. Another aspect of embodiments is the minimization of abrasion at bone tunnel apertures or elsewhere. Embodiments also endure surgical procedures without sustaining damage, such as unraveling or changes in critical dimensions, when being pulled through bone tunnels.
A particular embodiment provides a knitted prosthetic device with at least two knitted sections, where each knitted section has at least one row of fiber. The knitted prosthetic device also has at least one intra-articular section disposed between the at least two knitted sections. In addition, the at least one intra-articular section has at least one single continuous fiber traversing the at least one intra-articular section and the at least two knitted sections, where the at least one single continuous fiber forms a plurality of traverses extending between the at least two knitted sections.
Another embodiment provides a knitted prosthetic device with a plurality of knitted sections and an intra-articular section disposed between two consecutive knitted sections. The knitted sections and the intra-articular sections have at least one single continuous fiber, where the at least one single continuous fiber forms a plurality of traverses extending between at least two knitted sections.
Embodiments may have three sections, i.e. two knitted sections separated by one intra-articular section, or five sections, i.e. three knitted sections separated by two intra-articular sections. Furthermore, embodiments of a knitted prosthetic device according to the present invention may be used by anchoring each of the at least two knitted sections to a bone section of a patient. For example, embodiments may include features, such as loops and/or button holes, that accommodate device tensioning and/or a variety of fixation or anchoring devices that act to keep the prosthetic device in position.
Additionally, embodiments may be constructed from a strong polymer, preferably, but not limited to, silk, where the polymer is bioresorbable to allow substantial in-growth, both in the device itself and within and around the bone tunnels to maintain or improve the strength of the device-tissue construct over time. Embodiments employing such a polymer exist long enough in the joint to support the knee prior to tissue in-growth, but bioresorb as load bearing responsibilities are transferred over to the newly developing tissue.
Although some embodiments described herein may be specifically applied as prosthetic ligaments for reconstructing an ACL, it is understood that embodiments according to aspects of the present invention may be employed for other tendons and support structures. Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, by illustrating a number of exemplary embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive.
Aspects of the present invention are described herein with reference to exemplary embodiments directed to a multi-section graft, or prosthetic device, that is used to reconstruct an ACL. In particular,
Preferably, ligament prosthesis 100 is generally formed of polymers, such as protein biomaterials. In particular, embodiments may be formed from silk, such as Bombyx mori silkworm silk fibroin. The raw silk fibers have a natural globular protein coating known as sericin, which may have antigenic properties and must be extracted before implantation. Accordingly, the yarn is taken through an extraction process. The extraction of sericin is further described, for example, by Gregory H. Altman et al., “Silk matrix for tissue engineered anterior cruciate ligaments,” BIOMATERIALS 23 (2002), pp. 4131-4141, the contents of which are incorporated herein by reference. As a result, the silk material used in the device embodiments contains substantially no sensitizing agents, in so far as can be measured or predicted with standardized biomaterials test methods.
The sericin may be extracted, or removed, from the fibroin fibers before alignment into a yarn or at a higher level in the hierarchical geometry of the fiber construct. The yarn is preferably handled at low tension, i.e. the force applied to the construct does not exceed the material's yield point during any processing step. However, if the yarn is to be employed as a non cyclic-load bearing yarn in the device, the material's yield may be exceeded. Moreover, the yarn is handled with care after the sericin is removed. Processing equipment is likewise configured to reduce abrasiveness and sharp angles in the guide fixtures that contact and direct the yarn during processing to protect the fragile fibroin fibers from damage. For example, extraction residence times may range approximately from instantaneous submersion to ten hours. In general, the extraction is slow enough to minimize damage to the exposed filaments and is determined by the configuration of the yarn being treated. When a silk fiber construct with multiple fibers organized in parallel has been extracted under these conditions, a “single” larger sericin free yarn resulted. In other words, individual fibers cannot be separated back out of the construct due to the mechanical interaction between the smaller fibroin filaments once exposed during extraction. Furthermore, due to the mechanical interplay between the sericin-free micro filaments, extraction of twisted or cabled yarns typically results in less “lively” yarns and structures. As a result, a greater degree of flexibility exists in the design of the yarns and resulting fabrics; for example, one may employ higher twist per inch (TPI) levels, which may normally create lively yarns that are difficult to form into fabrics. The added benefit of higher TPIs is the reduction in yarn and fabric stiffness, i.e. matrix elasticity may be increased.
It should be appreciated that the prosthetic devices of the present invention, are not limited to the use of silk, and may be formed from a strong polymer that is capable of being knitted. In particular, the polymer is preferably bioresorbable to allow substantial in-growth, both in the device itself and within and around the bone tunnels to maintain to improve the strength of the device tissue construct over time. The process of in-growth is discussed in further detail hereinbelow.
Moreover, embodiments may be processed with a surface treatment, which increases material hydrophilicity, biocompatibility, and handling for ease of cutting and graft pull-through, as well as anti-microbial and anti-fungal coatings. Specific examples of surface treatments include, but are not limited to, plasma modification, fibronectin, denatured collagen, collagen gels, peptides with a hydrophilic and a hydrophobic end, covalently linked proteins and peptides, physically bound and chemically stabilized peptides and gels, DNA/RNA aptamers, Peptide Nuclei Acids, avimers, modified and unmodified polysaccharide coatings, carbohydrate coating, anti-microbial coatings, anti-fungal coatings and/or phosphorylcholine coatings. The preferable concentration range for smaller proteins and peptides (in the range of 1000 kDa to 20,000 kDa) is from 0.01 μg/mg device to 100 μg/mg device. For larger proteins, a preferred concentration range is from 0.01 mg/mL to 5 mg/mL.
In general, embodiments of the present invention employ materials which that have undergone extensive biocompatibility testing in accordance with the ISO-10993 recommendations for a permanent implantable device. Generally, the materials are biocompatible, non-cytotoxic, nonirritating, non-toxic, non-pyrogenic, non-mutagenic, non-c1 astogenic, nonhemolytic, and non-antigenic with no evidence of sensitization or complement activation.
Referring again to
A single continuous weft insertion yarn 123 in ligament prosthesis 100 refers to a single yarn that traverses the intra-articular section 122 and the knitted sections 112 and 114 to form a plurality of traverses extending between the knitted sections 112 and 114. For instance, the continuous yarn 123 may be laid in and traversed in a repetitive S-shaped or Z-shaped pattern, extending from the first knitted section to the second knitted section where it pivots and returns back to the first knitted section where it may pivot again and repeat the sequence several times. Examples of an S-shaped or Z-shaped pattern are described further below. In other words, each traverse of the single continuous yarn 123 is a continuation of the previous traverse extending in the opposite longitudinal direction. In this way, a single continuous yarn 123 with more than one traverse may connect the two knitted sections 112 and 114 and form the intra-articular section 122. The pivot points are not limited to anyone location.
Of course, the ligament prosthesis 100 may contain more than one single continuous yarn 123 laid in and traversed in a repetitive pattern extending between the first knitted section and the second knitted section, thereby connecting the two knitted sections 112 and 114 with more than one traverse from more than one single continuous yarn 123. The traverses of the multiple single continuous yarns 123 may extend in the same direction, opposite directions, or any combination thereof.
The one or more single continuous yarns 123 form a plurality of parallel, non-discrete, and non-independently translatable elements which are organized into bundles, i.e. a plurality of longitudinal fibers. Advantageously, non-independently translatable fibers enable equal tensioning of all of the parallel elements of the ligament prosthesis 100 when a force acts to draw the knitted sections 112 and 114 apart.
If the ligament prosthesis 100 is a weft knitted fabric, each traverse of a single continuous yarn 123 is laid into a course of at least one knitted section and tucked, or secured, at least one time in the course. The tucking effectively locks the continuous yarn 123 into the knitted section, minimizing sliding of the yarn with respect to the knitted section, or vice versa, and minimizing any changes in the dimensions of the intra-articular section 122. One or more traverses of the single continuous yarn 123 may be laid into and/or tucked into a single course of the knitted section to form bundles of said traverses, before transitioning to the next course, or row, of the knitted section. In general, the knitted sections 112 and 114 may contain one or more rows, where each row has one or more traverses from a single continuous yarn.
Although the embodiments described herein may include a yarn tucked at each knit section, it is noted that knits that are not made on a weft knitting machine do not necessarily require that each yarn be tucked in each knit section. As such, embodiments of the present invention are not limited to those that tuck the continuous yarn at each knit section.
As further depicted in
As illustrated in
Another embodiment of a device of the present invention is shown in
The knitted sections 212, 214, and 216 may be formed from a weft-knitted fabric or a warp-knitted fabric. As shown in
As with ligament prosthesis 100, described previously, the ligament prosthesis 200 may be formed from a strong polymer capable of being knitted, such as Bombyx mori silkworm silk fibroin, which has the characteristics described previously.
A single continuous weft insertion yarn 223 in ligament prosthesis 200 traverses the intra-articular sections 222 and 224, as well as the knitted sections 212, 214, and 216 to form a plurality of traverses extending between the knitted sections 212, 214, and 216. For instance, the continuous yarn 223 is laid in and traversed in a repetitive S-shaped or Z shaped pattern, extending from the first knitted end section, through the knitted intermediate section, and to the second knitted end section where it pivots and returns back through the knitted intermediate section to the first knitted end section where it may pivot again and repeat the sequence several times. Examples of an S-shaped or Z-shaped pattern are illustrated by the insertion yarn 223 in
Of course, the ligament prosthesis 200 may contain more than one single continuous yarn 223 laid in and traversed in a repetitive pattern extending between the first knitted end section and the second knitted end section, thereby connecting the knitted sections 212, 214, and 216 with more than one traverse from more than one single continuous yarn 223. The traverses of the multiple single continuous yarns 223 may extend in the same direction, opposite directions, or any combination thereof.
Each traverse of a single continuous yarn 223 is laid into a course of a knitted section and tucked, or secured, at least one time in the course. The tucking effectively locks the continuous yarn 223 into the knitted section, minimizing sliding of the yarn with respect to the knitted section, or vice versa, and minimizing any changes in the dimensions of the intra-articular sections 222 and 224. One or more traverses of the single continuous yarn 223 may be laid into and/or tucked into a single course of the knitted section to form bundles of said traverses, before transitioning to the next course, or row, of the knitted section. In general, the knitted sections 212, 214, and 216 may contain one or more rows, where each row has one or more traverses from a single continuous yarn.
As with the ligament prosthesis 100, the pivot points for single continuous weft insertion yarn 223 are not limited to anyone location.
As further depicted in
A graft, such as the five-section ligament prosthesis 200 was employed for ACL reconstruction in a GLP large animal study, involving 43 goats. In particular, the ligament prosthesis 200 was applied in the following manner. The right ACL of each of animal was removed and replaced in an arthroscopically-assisted procedure. The ACL was sharply excised. A guide pin was driven into the femur and antegrade drilling is performed with a 6 mm drill. The tibial tunnel was drilled under direct visualization. The five-section ligament prosthesis 200, designed to mimic hamstring grafts, was anchored extra-articularly around a post and washer on the femur. The graft was then tensioned to about 50 N, and the knee was cycled approximately 30 times before the prosthesis was fixed at the tibial bone with a spiked staple backed up with sutures around a post.
In the study, all animals were allowed to ambulate immediately after the operation. The study evaluated the five-section graft 200 for ACL replacement in the goat model at 3, 6 and 12 months after the operation. Animals were necropsied at 3, 6 and 12 months and the knees were evaluated histologically and mechanically. Additional metrics including Lachmann, x-ray, gait analysis, and comprehensive necropsies were performed.
The study showed that the animals were able to bear weight at 3, 6 and 12 months. Greater than 95% were able to return to normal gait by 6 months with maintenance at 12 months. Lachmanns show the majority of knees were clinically stable at all points. No gross cartilage damage was observed on the articular surfaces or menisci. No synovitis was observed within the synovium as a result of the device and synovial fluid was of good viscosity and color. Collagen formation and remodeling in and around the graft increased with time. Conversely, inflammation necessary for device bioresorption decreased with time. The device bioresorption rate was shown to be predictable. X-rays indicated no abnormal findings within or around the bone tunnels which was confirmed histologically with no reaction to the device observed within the tunnels with active surface modeling. Preliminary AP laxity data showed that the majority of knees were stable. Implant abrasion was observed to varying extents due to goat knee mechanics and graft placement. Single-pull-to-failure testing revealed in-growth supports increased load bearing over time.
Therefore, the results of the study indicates that the five-section ACL graft 200 supported autologous development of a mechanically robust, biologically viable ligament which stabilized the joint over a 12 month period. As such, the implant offers an ACL replacement graft without the deleterious side-effects associated with donor-site morbidity and allogenic and xenogenic grafts.
Another embodiment of a five-section ligament prosthesis is illustrated in
In addition,
An exemplary application of a five-section ligament prosthesis is provided with reference to ligament prosthesis 300, shown in
As shown in
Note that in other embodiments, such as ligament prosthesis 200, the ligament prosthesis, during application, may be folded transversely in half at the intermediate knit section, e.g. section 214, while no folding occurs along the longitudinal axis, e.g. longitudinal axis 201.
As shown in
In another exemplary installation procedure, a single 8.5 mm diameter tibial tunnel may be drilled with or without a tunnel placement guide. A single 7.5 mm diameter femoral socket may be positioned transtibially or through the medial portal, according to the surgeon's preference, with or without an over-the-top guide and drilled to an appropriate depth based on total tunnel length. The total length of the tunnel and the minimum native ACL length may be measured. The appropriate size ligament device may be identified from a sizing guide. The ligament device may be prepared as would a hamstring tendon graft; the graft may be looped over standard suspensory fixation, a sock device (described in detail below) placed over the femoral section and sutures applied to the tibial ends through whip stitching or insertion of the suture through the device loops. The device may be inserted into the bone tunnels, tensioned and anchored with standard fixation.
Additionally, the ligament prosthesis may be installed by either: (i) placing the ligament device through the tibial tunnel, into the intra-articular space and then through the femoral tunnel; (ii) placing the ligament device through the femoral tunnel, into the intra-articular space and then through the tibial tunnel; or (iii) through the medial portal and into the tunnels from the intra-articular space.
The knitted sections 312, 314, 316 of the ligament prosthesis 300 serve to tension the fiber bundles that make up the intra-articular sections 322 and 324. Moreover, the knitted sections 312, 314, 316 distribute the yarns throughout the cross-section of the bone tunnels. As shown in
Additionally, varying lengths may be employed for the ligament prosthesis 300 may be available to accommodate variations in patient anatomy.
The combined intra-articular sections 322 and 324 serve as a functional ligament when the tibial sections 312 and 316 are anchored opposite to the femoral sections 314 in the knee 10. The combined intra-articular sections 322 and 324 of the prosthesis allow full functioning of the knee joint 10 while providing the necessary scaffolding and void volume for organized tissue in-growth and remodeling. As described above, advantageously, the intra-articular section 322 is formed by one or more single continuous yarns 323 connecting the tibial sections 312 and 316. The one or more single continuous yarns 323 form a plurality of parallel, non-discrete, and non-independently translatable elements which are organized into bundles, i.e. a plurality of longitudinal fibers. Advantageously, non-independently translatable fibers enable equal tensioning of all of the parallel elements of the ligament prosthesis 300 when a force acts to draw the tibial sections 312 and 316 apart from the femoral section 314.
In an alternative application of the ligament prosthesis 300, two femoral tunnels may be drilled opposite a single tibial tunnel. As such, the aligned femoral sections 312 are anchored in one of the femoral tunnels, while the aligned femoral sections 316 are anchored in the other femoral tunnel. Meanwhile, the aligned tibial sections 314 are anchored in the single tibial tunnel. The ligament prosthesis may be implanted in any of the following configurations: (i) single tibial tunnel and single femoral tunnel, (ii) single tibial tunnel and double femoral tunnels, (iii) double tibial tunnels and single femoral tunnels, (iv) double tibial tunnels and double femoral tunnels, and (v) single tibial tunnel and over-the-top positioning on the femur.
Designed to serve as a transitory scaffold that provides immediate knee joint stabilization following surgical repair, embodiments, such as the ligament prosthesis 300, leverage the patient's own internal repair machinery and growth environment to engineer new viable ligament tissue. While conducting the body's own regenerative processes at the implant site, the transitory nature of the graft is designed to allow for tissue healing and rejuvenation as the scaffold becomes less necessary and is bioresorbed through natural and localized tissue remodeling. This approach anticipates and utilizes the body's own inflammatory, revascularization, healing, mechanical and remodeling cascades which follow graft implantation without notice to the patient.
As described above, embodiments may be may be formed from a strong polymer, such as Bombyx mori silkworm silk fibroin. As such, the ligament prosthesis 300 has mechanically robust parallel fiber bundles. The excellent strength of the material permits less material to be employed in the ligament prosthesis 300, while still meeting the mechanical requirements of functional ACL tissue. Correspondingly, large void volumes in excess of 50% for tissue in-growth may be created. Void volumes in excess of 50% are preferred; however, any void resulting from a device that fits properly within anatomically positioned tunnels is acceptable.
A particular embodiment of ligament prosthesis 300 may employ individual bundles 322 or 324 that are individual yarns no greater than 400 μm in diameter in order to overcome mass transport limitations in the initial postoperatively avascular environment of the knee joint-diffusion of metabolites and nutrients can support ˜200 μm of cellular in-growth without active transport from a vascular network. While bundles no greater than 400 μm in diameter are preferred, ligament devices with bundles up to 2 mm in diameter are acceptable. The multi-bundle structure of the intra-articular sections 322 and 324 also promote organized tissue in-growth along the longitudinal axis of the ligament.
A variety of techniques are available for characterizing physical, mechanical, and chemical properties of embodiments of the present invention. ISO 10993 recommended biocompatibility testing and shelf-life stability studies may be also applied. Substantial pre-clinical animal trials, such as the study described previously, may be conducted to establish device biocompatibility and safety. Additionally, cadaver device implantation may be performed to determine device compatibility with standard anchors and surgical technique.
As an example, test methods and results for key parameters regarding embodiments of the ligament prosthesis are provided hereinbelow. TABLE 1 provides exemplary physical measurements including length, width and thickness for a ligament prosthesis 300. In this example, the total length and width of the ligament prosthesis 300 is approximately 170 mm by 20 mm, respectively.
Other physical attributes of embodiments of the present invention may also be determined. Gauge diameter may be determined for the embodiment through a graft sizing block. The prosthetic ligament 300, for example, may fit through an 8 mm diameter sizing block. Additionally, each sample may be visually inspected for color, presence of defects and distribution within an 8 mm tunnel. Such visual inspection preferably reveals that the ligament prosthetic is physically intact with no defects. Moreover, the prosthetic ligament 300 may be potted in epoxy in an 8 mm tunnel and the cross-section may be imaged using a device, such as a SZX7 Stereomicroscope (Olympus Corporation, Melville N.Y.) to determine distribution of the ligament through the tunnel.
Embodiments of the present invention may also be characterized mechanically by employing tests that measure single pull to failure tensile mechanics, cyclic fatigue, and anchor pull-out. Samples of embodiments may be incubated in phosphate buffered saline (PBS) for 2±0.5 hours at 37±2° C. prior to mechanical analysis to provide characteristics in a wet environment. Mechanical testing may be performed on a servo-hydraulic Instron 8871 mechanical testing system under ambient conditions with Blue Hill and WaveMaker-Runtime Software (Instron Corporation, MA, USA).
For tensile testing, samples, following incubation, may be cut in half longitudinally and each half may be tested independently. The samples may be folded around a metal bar and anchored in a pneumatic fabric clamp. Samples may then be loaded through displacement controlled testing at a strain rate of 100% per second. Mechanical properties determined may include (1) ultimate tensile strength (UTS), (2) linear stiffness, (3) percent elongation at UTS, (3) yield strength, and (4) mode of failure. Ultimate tensile strength results may be combined from each half of the same device in order to determine overall UTS. For example, measurements for a ligament prosthesis 300 may include: a UTS of 4338±286 N; an offset yield strength of 2330±195 N; a stiffness over a 30 mm length, the native ACL length, of 721±38 N/mm; and a percent elongation at UTS of 29.7±2.5%.
For tensile cyclic fatigue testing, samples, following incubation, may be cut in half longitudinally and anchored in pneumatic fabric clamps. Samples are preferably kept wet with PBS at room temperature during cycling. Tensile sinusoidal cyclic fatigue testing may be conducted at 60% and 80% of mean UTS. As such, cycles to failure and failure mode may be determined. Cyclic fatigue life is preferably approximated for average ACL stresses in the knee joint. For instance, a prosthetic ligament 300 may fail through complete rupture after 1549±784 cycles at 60% UTS, and 173±40 cycles at 80% UTS. A logarithmic trend between the number of cycles at failure and cycling amplitude may be observed. As shown in
Anchor pull out testing may be performed with the EndoButton® CL (Smith & Nephew, Andover, Mass.) or equivalent suspensory or interference fixation for femoral fixation and the Intrafix™ (Depuy Mitek, Raynham, Mass.) or equivalent interference or suspensory fixation for tibial fixation. Biomechanical solid rigid polyurethane testing foam block (20 pcf), laminated with 2 mm foam (40 pcf) (Sawbones, Vashon, Wash. 98070), may be utilized for femoral anchor pull out testing to mimic the cortical fixation achieved with the EndoButton®. Cellular rigid polyurethane testing foam block (10 pcf) may be utilized for tibial anchor pull out testing to mimic the cancellous bone fixation achieved with the Intrafix. Accordingly, UTS and failure mode may be determined. For example, a UTS of 1130±56 N may be observed during femoral anchor pull out testing with failure occurring through EndoButton fracture. A UTS of 1202±30 N may be observed during tibial anchor pull out testing with failure occurring through sawbone failure. Tibial anchor testing of interference screws, buttons, cross-pins, staples, extra-osseous post and combinations thereof may achieve pull-out strengths of 200N to 4000N.
Embodiments of the present invention may be ethylene oxide (EO) sterilized. Animal studies and biocompatibility testing, such as those conducted for prosthetic ligament 200 above, have shown no deleterious effects of EO sterilization; no results indicative of high EO residuals have been observed. In vitro characterization has shown that significant mechanical integrity is present following sterilization. Sterilization may be achieved through single lot release using an “overkill” sterilization process. Packaging may consist of a double Poly/Tyvek peel-seal pouch; 48 gauge PET/LDPE, PE0001 mated to Tyvek 1059B (Peel-Master Niles, Ill.). The overkill sterilization process requires that strategically placed biological indicators (Bls of 1.0×106 population) are all killed in a half exposure sterility cycle. The half exposure dwell sterilization delivers a SAL of 10−6 as preferably required for embodiments of the present invention, after which the embodiments are subjected to a full exposure sterility cycle. EO residual testing may be performed following sterilization. The maximum allowable residuals on embodiments of the present invention may be established as: 250 ppm Ethylene Oxide, 250 ppm Ethylene Chlorohydrin, and 5,000 ppm Ethylene Glycol.
The effect of EO sterilization may be determined by testing ultimate tensile strength and surface treatment concentration for the prosthetic devices prior to sterilization, after 1× sterilization, and after 2× sterilizations. Preferably, no significant difference in UTS is observed between all three groups. For instance, exemplary values for UTS for non-sterilized, 1× sterilized, and 2× sterilized may be 100±1.5%, 101.8±5.4%, and 100.1±4.2%, respectively.
Shelf life stability studies may also be performed on embodiments of the present invention. In particular, testing may be applied for devices that have been packaged and sealed in paper-film pouches, subjected to thylene oxide (EO) sterilization, and stored at ambient conditions in intermittent light. Moreover, single pull to failure testing may be applied to measure tensile strength. TABLE 2 provides example values for such shelf life stability tests for a prosthetic ligament 200. In this case, the results indicate no significant deleterious changes in mechanical integrity were observed following real-time ambient storage for 18 months. As such, it may be concluded in this case that mechanical integrity is stable for 18 months under ambient storage conditions following EO sterilization.
Although particular sterilization techniques are described in detail herein, it is understood that other approaches for sterilization may be employed, such as gamma, steam, e-beam, chemical, ozone, vaporized hydrogen peroxide or the like. Indeed, certain approaches, such as the “overkill” sterilization process, may be only applicable for clinical trials and other techniques may be required for sterilizing products that are used commercially, for example.
Bench studies may be conducted to model graft bioresorption for correlation to observed trends in an in vivo model. In particular, in-vitro bioresorption characterization may be evaluated with embodiments that have been implanted to replace the ACL in goats, such as the study for prosthetic ligament 200 described previously. The embodiments may be incubated in 0.25 mg/ml Protease XIV (Sigma, Mo.) at 37° C. and washed 3 times per week to remove adsorbed protease. Percent mass loss and single pull to failure mechanics of the ligament prosthesis may determined over time. For example, mass loss may be measured three times per week for nine weeks. Single pull to failure may also be conducted as previously described throughout the first 14 days.
Embodiments of a prosthetic device according to the present invention may be knitted on a fine gauge crochet knitting machine. The following is a list of crochet machines capable of manufacturing the five-section graft used in the study: Jakob Muller; Comez Acotronic; Zhangjiagang Kingkangda; Kyang Yhe; Ledmak Makina; Skytex Enterprise; Valentin Rius Clapers; Zhangjiagang Victor Textile; Suzhou Textile; Dah Heer Industrial; Jiangsu Victor; Taesin Co.; Arushi Consultancy & Engineering; Jiangsu Hongyaun Textile; Zhangjiagang City Tianjiang; Taiwan Giu Chun; P. K. International; Alfamatex; Wenli Weaving & Zipper; and Ningbo Poli.
An exemplary system for making embodiments of the present invention is described with reference to the general five-section ligament prosthesis 200 shown in
As discussed above, embodiments may be formed from silk, such as Bombyx mori silkworm silk fibroin. In a particular embodiment, for instance, the silk is a twisted yarn made from 20 denier raw silk fibers approximately 40 to 60 μm in diameter. Preferably, raw silk fibers of 10 to 30 denier may be employed; however, any fiber diameters that will allow the device bundles to be less than 2 mm and provide sufficient strength to stabilize the knee joint when used as an ACL device or sufficient to suspend or replace the intended tissue structure of organ are acceptable.
In one example, for the knitted sections 212, 214, and 216, manufacturing of the silk yarn involves two steps: i) four of the 20 denier fibers are twisted in the counterclockwise direction (S-direction), at 6 twists per inch (tpi); and ii) three plies from the first step are twisted together in the clockwise direction (z-direction) at 3 tpi. The result is a 12-filament yarn with a diameter of approximately 220-323 μm.
For weft insertion yarns 223, manufacturing of the silk yarn involves three steps: i) four of the 20 denier fibers are twisted in the clockwise direction (z-direction) at 10 tpi; ii) three plies from the first step are twisted together in the counterclockwise direction (s-direction) at 19 tpi; and iii) three plies from the second step are twisted together in the clockwise direction (z-direction) at 9 tpi. The result is 36-filament yarn with a diameter of approximately 350-400 μm.
The yarn size for a particular type of section, i.e. knitted sections 212, 214, and 216 or intra-articular sections 222 and 224, preferably does not vary in a given device or within a given section of a given device. Advantageously, a substantially constant yarn size may maximize the uniformity of the yarn's mechanical properties, e.g. stiffness, elongation, etc., throughout the sections of the ligament prosthesis. However, in other embodiments described further below, the size of yarn may be varied in particular sections of the same graft, or within any single section of a graft, in order to achieve different mechanical, physical and/or biological characteristics in different locations when implanted. For instance, areas of the graft that are closer to tunnel apertures may have larger yarn sizes in order to maximize abrasion resistance. On the other hand, areas that are farther from the bone tunnel may have smaller yarn sizes to increase flexibility. Additionally, yarn size may be varied in order to enable a certain section or sections of the graft to fit a particular type of fixation device or to achieve a press fit in a bone tunnel. Knit yarns may be different for each of the bone tunnel sections to allow the device to fit in two different diameter tunnels.
Factors that may influence the size of the yarn include, but are not limited to: ultimate tensile strength (UTS); yield strength, i.e. the point at which yarn is permanently deformed; percent elongation; fatigue and dynamic laxity (creep); bioresorption rate; transfer into and out of the graft (cells/nutrients); the ability to size the prosthetic device for implantation in the available bone tunnel; the ability to distribute fibers across a bone tunnel; and smoothness of stiffness profile, which is preferably not “stepping” as typically found in a braided yarn.
Using the knit pattern design 400 of
With further reference to the exemplary knit pattern design 400 of
Once the 14 rows have been created and one unit of a prosthetic device has been completed, the weft insertion is stopped. However, six additional courses of atlas stitches and closed tricot stitches are then performed simultaneously to separate the individual units of prosthetic devices.
Furthermore, the stitch density is increased, e.g. from 9 to 15 stitches per cm, to create a tighter fabric in the separation section 205. This provides a mechanically locked section so that the units of prosthetic devices may be cut from the series without causing any unraveling of the knit. The result is a type of finished edge, as described previously.
The combination of atlas and closed tricot stitches described above may be preferred because it minimizes unraveling while minimizing the density of knitted construction and maximizing porosity. However, any combination of stitches created with at least two independent bars, each one forming loops over two or more adjacent, or non-adjacent, needles, may effectively create a fabric structure that does not unravel when cut. The choice of stitch combination depends on desired density, abrasion resistance, etc.
The number of courses and the number weft yarns inserted per course indicated in the present example result in 56 parallel elements organized into bundles for the intra-articular sections 222 and 224. However, the same number of parallel elements may be achieved by employing different number combinations of courses per prosthetic device and yarns per weft bar (yarns per course). For example, TABLE 4 shows different combinations that produce 56 parallel elements. TABLE 4 assumes that each weft bar employs the same number of weft yarns and that the weft insertion yarns are laid-into every course to create an even fabric across its entire width.
TABLE 4 is not an exhaustive list of combinations. For example, it is understood that varying the number of weft yarns per weft bar may result in 56 overall parallel elements in a prosthetic ligament. In one alternative embodiment of the manufacturing system, 56 parallel elements may be achieved if the one weft bar lays in 29 weft yarns and a second weft bar lays in 27 weft yarns into a prosthetic ligament with one course. Meanwhile, other exemplary embodiments may employ only one weft bar, or as many as 12 weft bars, to layin the yarn. Thus, many possible combinations may achieve the desired number of parallel elements in the prosthetic ligament. Ranges of possible combinations are illustrated in TABLE 5.
Furthermore, if more than one weft bar is employed, it may be preferable to vary the number of yarns each weft bar lays in, while varying the number of weft bars which lay in yarn in any given course. Such a configuration alters the cross-sectional geometry of the prosthetic device. For instance,
It is understood that the range of course numbers described herein is provided merely as an example, and the number of courses is not limited to a particular range. For instance, one particular embodiment employs approximately 208 courses. The range of course numbers is from 0 to 6000 courses where the 6000 course device may be a ligament device comprised of enough single filament or greater courses to stabilize the knee joint when used as an ACL device or sufficient strength to suspend or replace the intended tissue structure or organ. For a bioresorbable ligament device, a strength of 1000 N to 5000 N is preferred. For a non-bioresorbable ligament device, a strength of 1000 N to 4000 N is preferred.
Another factor that may alter the cross-sectional geometry of a graft is the size of yarn used, as described previously. Correspondingly, another factor is the size of the needles on the manufacturing machine, e.g. a 20 gauge compound needle. Thus, the combination of yarn size, number of weft bars, and number of weft yarns per weft bar determines the diameter of the laid-in parallel elements per course. This diameter may range from 10 μm to 8,000 μm (e.g., 4 parallel elements of 2 mm diameter each).
Advantages may be associated with variations in cross-sectional geometry of a graft. For instance, more weft insertion yarns per course may be employed so that when the graft is implanted within a bone tunnel, more weft insertion yarns are present in certain regions. In particular, more weft insertion yarns may be employed at the outer end of femoral bone tunnel, where bioresorption rates tend to be higher for the graft. In addition, varying cross-section geometry may enable the weft insertion yarn bundles to be distributed more effectively within a bone tunnel diameter, depending on whether the graft is folded, rolled, etc. when implanted.
It is understood that the teachings provided for the five-section ligament prosthesis 200 can be applied to make the three-section ligament prosthesis 100, as described with reference to
Although the three-section ligament prosthesis 100 or the five-section ligament prosthesis 200 may be preferable for certain applications, the present invention is not limited these particular embodiments. Accordingly, embodiments may have any number of knitted sections, where one or more single continuous weft insertion yarns are laid into the knitted sections and form a plurality of longitudinal elements separating the knitted sections.
The alternative knit pattern design of
Initially, referring to the actual guide numbers on machine, Guide 8 of the machine is set up with SSUPY yarn (Shima Start Up Yarn) 308, as shown in
Guide 6 is set up with a “draw thread” yarn, which is looped in between the waste yarn and the first unit of the ligament prosthesis, and in between successive units. Accordingly, pulling the draw thread 306 separates each unit from the others. As described previously, a unit of the ligament prosthesis 300 includes two bundles 302, each having knitted sections 312, 314, and 316 as well as intra-articular sections 322 and 324. Therefore,
TABLE 7 provides the details of the Intarsia yarn guide set up, in order from left to right. The yarn supplied to each Intarsia guide is measured out by a digitally controlled stitch cam. The length of the knit loops is adjustable to 10 μm and the cam continually adjusts the yarn unwind so that the length of each knit loop in every row remains consistent throughout the entire product.
The alternative knit pattern for the five-section ligament prosthesis is performed on the flat bed knitter. After the SSUPY yarn 308 is hooked on the appropriate needles and grabbed by the comb, waste fabric 309 is knitted in tubular single jersey knits from the waste yarn across several rows. Towards the end of the waste fabric 309, a row of waste yarn is laid in ½ gauge tubular single jersey stitches, after which all front stitches are transferred to the back needle bed. One course of tubular single jersey knits are made with the waste yarn, followed by two more courses with the “draw-thread” yarn. Next, the knit loops in the area of sections 312 and 314 are transferred to the front needle bed. The machine then carries in Guide 4 and transfers the knit loops in the area of section 314 to the back needle bed. Next, the machine carries in Guide 3 and transfers the knit loops in the area of section 312 to the back needle bed. Now all three 12 filament yarn guides, Guides 2, 3 and 4, are in position to create the three knitted sections 312, 314, and 316. One course of double jersey stitches is performed in each section, followed by two courses of single jerseys on the front needle bed and one more single jersey on the back needle bed. Next, two courses in Y2 gauge are performed to create an interlock. The interlock knit loops are held on the needles while the 36t insertion yarn is laid along the width of the two courses of the interlock from left to right and back again across all three knitted sections and the spaces in between for a total of eight traverses. During the course of each traverse, the insertion yarn is “tucked,” or pulled in and held by a needle on either the front or back needle bed, so that after the eight traverses and the interlock is released, the tucked portions of the 36t yarn are secured along with the loops 76 of the interlock.
One exemplary technique for tucking the insertion yarn in each ligament prosthesis 300 may be achieved in the following manner. From left to right, starting in section 312, the insertion yarn is immediately tucked by a back needle, and several needles later (approximately 5-20 needles), tucked by a front needle. A few needles later (approximately 1-5 needles), it is tucked again to a front needle, for a total of three tucks in section 312. The insertion yarn lays freely across the separation between sections 312 and 314. The insertion yarn is laid-in to section 314. The insertion yarn lays freely across the separation between sections 314 and 316. Once the insertion yarn enters section 316, the insertion yarn is tucked by a back needle twice in a short distance (in a mirror image to section 312 described above). Then, after spanning section 316, the yarn is front tucked by the last needle before the yarn guide reverses and traverses right to left back across to section 312. The insertion yarn is tucked in a similar fashion as the previous traverse, except that the front and back tucks are reversed.
It is noted that tucking may affect the ability to distribute load evenly across the continuous weft yarn as the tuck acts as an anchor point. Hence, it may advantageous to limit the amount of tucks. For instance, a minimum of two tucks may be employed in sections 312 and 316, i.e. each tibial section, while no tucks are employed in section 314, i.e. the femoral section. This technique minimizes sliding by each knitted section while also enabling even tensioning.
Further describing the alternative knit pattern design for the five-section ligament prosthesis, two new courses are knitted to create the next interlock after eight traverses of the insertion yarn. This fully captures the previous eight traverses of insertion yarn, while providing a bed for the next eight traverses which are laid in and tucked in a similar fashion. This process is repeated to create eight series of interlocks, each with eight organized, parallel traverses, or bundles, of insertion yarns.
The alternative knit pattern concludes with a “bind-off” row for each ligament prosthesis 300. Starting from the farthest left in section 312, an exemplary bind-off technique transfers a knit loop from the back needle bed to the opposite needle on the front bed. A knit loop is then laid onto the vacated needle on the back bed with the draw thread. The back bed is then racked and the knit loop on the front needle is transferred to the back bed one needle to the right. The sequence is repeated across all three knitted sections 312, 314, and 316. Accordingly, each five-section ligament prosthesis 300 is successfully closed off with a finished edge and can be simply detached from the other units with the draw-thread.
It is understood that the teachings provided for this alternative knit pattern can be applied to make the three-section ligament prosthesis 100, as described with reference to
As discussed with reference to
Another embodiment of a five-section ligament prosthesis is illustrated in
In alternative embodiments, the two bundles 602′ and 602″ may be joined by a knit between corresponding knitted section 612′ and 612″ and/or 616′ and 616″, as illustrated for example by connecting knit sections 604 and 605 in
In addition,
As
As illustrated in
As
As
The knit structure of the tubular structures 613 and 617 may include the weft bundles formed by the single continuous yarns 623′/623″. As such, the tubular structures 613 and 617 do not interfere with the weft bundles but actually provide a way to organize the weft bundles in parallel orientation. In addition, because the weft bundles extend through the tubular structures 613 and 617, a load applied to sutures 650 passing through the tubular structures 613 and 617 results in even tensioning and/or anchor load distribution of the weft bundles.
In an example technique, the tubular structures 613 and 617 may be formed by employing the following knitting sequence on a 16 gauge Shima Seiki SES122si flat bed knitting machine configured with Intarsia yarn guides as described above. Starting from left to right, Guide 2 lays the 18t yarn to form a series of loops on every other needle on the back needle bed within a predetermined section of the prosthetic ligament 600 that will include an tubular structure 613. After spanning the width of the tubular structure section 613, Guide 2 reverses and traverses right to left back across the tubular structure section 613, laying the 18t yarn to form a series of loops on the needles on the front needle bed opposing the previously loaded needles. After returning to the original starting point, the 18t yarn reverses and traverses left to right across the tubular structure section 613 laying the 18t yarn to form a series of loops on the remaining needles not loaded in the first pass. After spanning the width of the tubular structure section 613, Guide 2 reverses and transverses right to left, back across laying the 18t yarn forming a series of loops on the front needle bed opposing the needles loaded in the previous position on the back needle bed. The above sequence may be repeated one or more times to stabilize the bottom of the section 613. The same sequence is repeated for knitted section 617. In knitted sections 612′/612″ and 616′/616″, i.e., sections outside the tubular structures 613 and 617, the 18t yarn may secure the 36t yarn with interlock loops. In the tubular structure 613 and 617, the 18t yarn may form single jersey stitches to secure the 36t yarn.
Following the formation of the tubular structures 613 and 617 with the 18t yarn, the weft insertion yarn may be tucked in the knitted sections 612′/612″ and 616′/616″ in a manner similar to the sequence described for the ligament prosthesis 300. In the tubular structures 613 and 617, the weft insertion yarn may be tucked on the same needle bed as the yarn guide moves from left to right and may be tucked on the opposite needle bed as the yarn guide moves from right to left. Preferably, before a row of single jersey stitches with the 18t yarn is formed, no more than one 36t yarn is tucked and held by the same needle to prevent damage to the 36t yarn and to the needle.
Alternative techniques are contemplated for producing a prosthetic ligament with one or more tubular structures. For example,
To facilitate alignment of the knitted sections 612′, 612″, 616′, and 616″ when the ligament prosthesis 600 is in the folded configuration, the knitted section 614′ of the bundle 602′ may have a shorter longitudinal length than the corresponding knitted section 614″ of the other bundle 602″. When the ligament prosthesis 600 is folded transversely at the knitted sections 614′ and 614″, the bundle 602″ with the longer knitted section 614″ may be folded over the bundle 602′ with the shorter knitted section 614′ to form an outer bundle of the ligament prosthesis 600. Due to the larger fold for the outer bundle 602″ with the longer femoral sections 614″, corresponding sections 612′/612″ and 616′ 1616″ of both bundles 602′ and 602″ are more easily aligned. Preferably, the inner bundle will be shortened by the radius of curvature of the ligament device when folded which is calculated as 1.5×π× the graft thickness. The range of length differences between the two bundles of a ligament device may be from no difference to 30 mm, where larger differences may be desired to accommodate variations in anchor design. Additionally, the bundle 602′ may be transversely narrower than the bundle 602″, so that the bundle 602″ can more easily form an outer bundle over the bundle 602′ and better conform to the anchor and/or tunnel. Preferably, to create a balanced knit pattern, an odd number of weft insertion groups (where each insertion group may contain multiple yarns) may be included in each bundle of the device. In an example implementation, in a device with twenty-six weft insertion groups where each group contains four weft bundles/yarns, preferably, the wider device bundle will contain fifteen insertion groups and the narrower bundle eleven. In this example, it would be acceptable to have any combination of odd numbers that add to the total twenty-six insertions with a range from twenty-five insertions in the wider bundle and one insertion in the narrower bundle to thirteen insertions in both device bundles.
In an example implementation, the femoral knit section 620 formed by knitted sections 614′ and 614″ is pulled through the tibial bone tunnel 13 before being anchored in the femoral bone tunnel 15. As described previously, the femoral knit section 620 is disposed in a sock device 700 with a collar 720. To facilitate the movement of the femoral knit section 620 and the sock structure through the tibial bone tunnel 13, the tibial bone tunnel 13 may be larger than the femoral bone tunnel 15. For example, the tibial bone tunnel 13 may be approximately 8.5 mm in width or diameter, while the femoral bone tunnel 15 may be approximately 7.5 mm in width or diameter.
By using a larger yarn size for the knitted sections 612′, 612″, 616′, and 616″, a thicker tibial knit section 619 may be formed so that the fit of the tibial knit section 619 in the larger tibial bone tunnel 13 is comparable to the fit of the femoral knit section 620 in the smaller femoral bone tunnel 15. In other words, rather than having a gap between the tibial knit section 619 and the tibial bone tunnel 13, the tibial knit section 619 plugs the tibial bone tunnel 13 to achieve a press-fit and seal the tunnel 13. For example, the tibial knit section 619 may be formed with yarn ranging from 12t to 36t, while the femoral knit section 620 may be formed with 12t yarn to fit within a 8.5 mm tibial tunnel and a 7.5 mm femoral tunnel with 208 wefts. For other larger and smaller tunnel diameters in humans and/or canine stifles, the knit yarn within the smaller diameter may range from 5 μm to 2 mm and within the larger diameter may range from 5 μm to 2 mm as a function of tunnel diameter, desired void volume, and weft number and size. (In an alternative embodiment, the graft may be installed in the reverse direction, i.e., the tibial section may be pulled through the femoral bone tunnel 15 before being anchored in the tibial bone tunnel 13, in which case the femoral bone tunnel 15 may be larger than the tibial bone tunnel 13.)
Alternatively, a desired fit between either knit section 619/620 and the bone tunnels 13/15 may be achieved by adjusting the length of the knitting loops in the knit sections 619/620. In particular, increasing the length of the loops provides a tighter fit while allowing the same yarn size, e.g., 12t yarn, to be used for both the tibial knit section 619 and the femoral knit section 320 when the tibial tunnel is a larger diameter than the femoral tunnel. In addition, employing longer loops may cause the knit sections 619/620 to conform to the shape of the bone tunnels 13/15 more easily. The loops lengths may be adjusted in increments as small as 10 μm. Table 8 contains the range of loop lengths that may be used. An example of the difference in conformity of a knit section 619/620 to a bone tunnel 13/15 is shown in
As another alternative, a desired fit between the tibial knit section 619 and the tibial bone tunnel 13 may be achieved by varying the inter-axis between two adjacent loops in combination with using a compensating knitting yarn size. For example, the same 16 gauge knitting machine may be employed in half gauge to produce a 8 gauge knit, while using a knitting yarn for the tibial section that is 1.5 or 2 times larger, for example, than the size of the yarn for the femoral section 620. Advantageously, this technique may provide a press fit and tunnel seal while allowing free area for bone ingrowth, anchor interface, and/or suture positioning.
As described previously, the femoral knit section 620 is disposed in a sock device 700.
In one example, initially, referring to the guide number on the machine, Guide 8 of the machine is set up with SSUPY yarn (Shima Start Up Yarn) 701, as shown in
TABLE 9 provides the details of the Intarsia yarn guide, in order from front to back as they are set up on the flat bed knitting machine. The yarn supplied to each Intarsia guide is measured out by a digitally controlled stitch cam. The length of the knit loops is adjustable to 10 μm and the cam continually adjusts the yarn unwind so that the length of each knit loop in every row remains consistent throughout the entire product.
After the SSUPY yarn 701 is hooked on the appropriate needles and grabbed by the comb, waste fabric is knitted in tubular single jersey knits from the waste yarn 702 across several rows. Towards the end of the waste fabric, the additional needles necessary to provide the correct comb tension are cast off 704. Two courses of tubular single jersey knits are made with the waste yarn 702, followed by two more courses with the “draw-thread” yarn 703. Next, the Guide 5 lays the 36t yarn to form a series of loops on every other needle across section 711 on the back needle bed. Then, the 36t yarn reverses and traverses right to left back across the section 711, laying the 36t yarn to form a series of loops on the needles on the front needle bed opposite to the previously loaded needles. After returning to the original starting point, the 36t yarn reverses and traverses left to right across section 711 laying the 36t yarn to form a series of loops on the remaining needles not loaded in the first pass. Then, the 36t yarn reverses and traverses right to left, back across section 711 laying the 36t yarn forming a series of loops on the front needle bed opposing the needles loaded in the previous position on the back needle bed. The sequence may be repeated one or more times to stabilize the bottom of section 711. Next, two course of single jerseys on the front and back needle bed are formed with the 36t yarn to complete section 711. Following this, a total of 31 courses of front and back needle bed single jersey are formed by the 18t yarn. Then, the furthest right needle of the front needle bed transfers to the second needle from the right on the back needle bed while the furthest right needle of the back needle bed transfers to the second needle from the right on the front needle bed. The resulting tubular knit fabric is now one needle narrower per needle bed than at start up resulting in a structure that follows the contour of the prosthetic ligament. This shaping procedure is repeated for a total of three times alternating between right side and left side and separated by one to three courses of single jersey on the front and back needle bed. The shaping procedures alternate from the left side, to the right side in sequence. For example, the furthest front right loop will transfer to the second left back needle and the furthest back left loop will transfer to the second front loop. After completion of ten courses single jersey, in the front and back needle bed, with the 12t yarn, eight more shaping steps as described above occur with the 18t yarn reducing the width of the tubular fabric to four needles on the front needle bed and four needles on the back needle bed. The final needle quantity is chosen based on the flat bed knitting machine gauge to allow the passage of a preferred fixation device through the end of the tubular section 714.
The formation of the sock device 700 concludes with a “bind-off” row for the front and back tubular structure. An exemplary bind-off technique starts from the farthest left in section 714, racks the back needle bed one needle position to the right, and transfers the first left loop of the front needle bed to one needle position to the left on the back bed. A new knit loop is then laid onto the first loop on the back needle bed and is subsequently transferred to the corresponding empty needle on the front bed. The back bed is then racked one needle position to the left and the first knit loop on the front needle is transferred to the back bed one needle to the right. The sequence is repeated across until the end of the section 714.
The bind off procedure direction is reversed to bind off all the remaining loops on the back needle bed as the draw thread is inserted. A knit loop is transferred from the back needle bed to the opposite needle on the front bed. A new knit loop is then laid onto the vacated needle on the back bed with the 15t draw thread. The back bed is then racked and the knit loop on the front needle is transferred to the back bed one needle to the left. The sequence is repeated across until only one loop remains and the sock device 700 is successfully closed off with a finished edge and can be simply detached from the other units with the draw-thread.
The teachings provided for the pattern for the sock device 700 can be applied to fit the range of dimensions, for example, indicated in TABLE 8 for the Length of 2nd Knitted Section corresponding to the femur section length of the ligament prosthesis as well as a range of diameters of the ligament device. Additionally, the number of regions forming the sock device 700 may vary in number from the four sections 711, 712, 713, and 714 described previously, for example to a single section. The sock device 700 may or may not have an opening for suspensory fixation. To knit the sock device 700, yarn diameters ranging from approximately 5 μm to 2 mm may be used as a function of the bone tunnel and graft diameters
The loop size used in knitting sections 711, 712, 713 and 714 may be varied according to the function of each section. To achieve increased abrasion resistance and increased fabric rigidity, a smaller loop size may be employed. On the other hand, a larger loop size may be employed to achieve increased elasticity and increased porosity. For example, a larger loop size in section 713 allows the sock device 700 to stretch more easily, particularly when it is being handled for anchoring. For example, when using an Endo-Button® to anchor the prosthetic ligament 300 described above, the fixation device must be toggled as it exits the femoral tunnel 15 and section 711 is secured at the entrance of the femoral tunnel 15. This technique provides a means to allow the sock to pass through the tunnels and to strength to allow the anchor to be seated while maintaining structural and dimensional integrity of the sock. In addition, the knit pattern can be maintained to allow bone ingrowth. The loop size in section 713 is larger than section 711, because a lower filament yarn is used and abrasion resistance must be higher in this area. Meanwhile, the loop size in section 714 is higher than section 713, because it is necessary to increase rigidity in order to prevent the ligament prosthesis from breaching the sock device 700 as the combination passes through the tunnels 13 and 15.
Alternatively, the ligament prosthesis 600 may be folded longitudinally, passed through a suspensory fixation device 660 and folded transversely at knitted sections 614′ and 614″ over the fixation device 660, as described above. The thread leader 662 that has previously been threaded through the suspensory fixation device 660 may be fed into the closed end of the laso-like yarn 715 (as shown in
Accordingly,
Furthermore the different variations described demonstrate the ability to tailor the fabric construction by varying the tibial knit density, shape and size for current and possibly future anchor design. For example tapering the anchor end of the tibia will allow a press fit anchor, while extending all of the weft insertion or part of the weft insertion beyond the end of the tibia will provide distribution of the load to each bundle.
It is contemplated that the sock device 700 may include additional features. For example,
In addition,
Although some embodiments described herein may be specifically applied as prosthetic ligaments for reconstructing an ACL, it is understood that embodiments according to aspects of the present invention are not limited to such applications. Embodiments may be employed for all soft tissue support and replacement, including, but not limited to, ligaments and tendons of the knee, stifle, ankle, foot, elbow, shoulder, wrist, hand and spine, bladder and urethra slings, neck and face lift support, body wall repair, restore pelvic floor, hernia repair, paravaginal repairs, reinforcement and buttressing of staple lines, closure of an abdominal incision, repair of anorectal fistulas, dural substitute for repairing dura mater, and organ repair or suspension.
Additionally, the prosthetic devices may be used in humans, primates and/or any quadrupeds including canines. For example,
While the present invention has been described in connection with a number of exemplary embodiments, and implementations, the present inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of prospective claims. All dimensions, measurements, and the like, provided herein are exemplary.
Claims
1. A prosthetic device comprising a knitted section, wherein the knitted section comprises sericin extracted silk fibroin fibers in the form of a yarn, and the silk fibroin fibers are substantially nonantigenic.
2. The prosthetic device of claim 1, wherein the prosthetic device further comprises at least two knitted sections.
3. The prosthetic device of claim 2, wherein each knitted section including at least one row of fiber.
4. The prosthetic device of claim 3, there is at least one section disposed between the at least two knitted sections.
5. The prosthetic device of claim 4, the at least one section disposed between the at least two knitted sections comprises at least one single continuous fiber traversing the at least one section disposed between the at least two knitted sections and the at least two knitted sections.
6. The prosthetic device of claim 5, wherein the at least one single continuous fiber forms a plurality of traverses extending between the at least two knitted sections.
7. The prosthetic device of claim 6, wherein the at least two knitted sections and the at least one single continuous fiber comprise the sericin extracted silk fibroin fibers in a form of a yarn.
8. The prosthetic device of claim 7, wherein the plurality of traverses extending between the at least two knitted sections are substantially parallel.
9. The prosthetic device of claim 8, wherein the at least one single continuous fiber is received into the at least one row of each knitted section.
10. The prosthetic device of claim 9, wherein the at least one single continuous fiber is tucked in the at least one row of each knitted section.
11. The prosthetic device of claim 10, wherein the at least one single continuous fiber is tucked to at least one loop in each knitted section.
12. The prosthetic device of claim 11, wherein the at least one loop is formed by the at least one single continuous fiber.
13. The prosthetic device of claim 12, wherein the at least one loop is formed in each knitted section.
14. The prosthetic device of claim 13, wherein the at least one row of the at least two knitted sections comprises a plurality of rows, and the at least one single continuous fiber traverses, at least once, each of the plurality of rows.
15. The prosthetic device of claim 14, wherein the at least one single continuous fiber is received into the plurality of rows.
16. A support structure for soft tissue support and replacement comprising a knitted section, wherein the knitted section comprises sericin extracted silk fibroin fibers in the form of a yarn and the silk fibroin fibers are substantially nonantigenic.
17. An implantable reconstructive device comprising a knitted section, wherein the knitted section comprises sericin extracted silk fibroin fibers in the form of a yarn and the silk fibroin fibers are substantially nonantigenic.
Type: Application
Filed: Mar 22, 2012
Publication Date: Jul 12, 2012
Applicant: Allergan, Inc. (Irvine, CA)
Inventors: Gregory H. Altman (Arlington, MA), Enrico Mortarino (Hickory, NC), David J. Horan (Westfield, MA)
Application Number: 13/426,906
International Classification: A61F 2/08 (20060101);
