Patent Application
20080183291
The present invention pertains to prosthetic devices. More particularly, the invention pertains to knee joint prosthesis, which may be surgically implanted between the femoral condyle and tibial plateau of the knee joint.
A meniscal cartilage provides the mobile weight bearing surfaces of the knee joint. Damage to these surfaces is generally due to genetic predisposition, trauma, and/or aging. The result is usually the development of chondromalacia, thinning and softening of the articular cartilage, and degenerative tearing of the meniscal cartilage. Various methods of treatment are available to treat these disease processes. Each option usually has specific indications and is accompanied by a list of benefits and efficiencies that may be compared to other options.
The healthy knee joint has a balance of joint cartilage across the four surfaces of this bi-compartmental joint (medical femoral condyle, medial tibial plateau, lateral femoral condyle and lateral tibial plateau). In patients with osteoarthritis, knee degenerative process typically leads to an asymmetric wear pattern that leaves one compartment with symmetrically less articular cartilage covering the distal portions (or weight bearing area) of the tibia and the femur than the other compartment. Most commonly, the medial compartment of the knee joint is affected more often than the lateral compartment.
As the disease progresses, large amounts of articular cartilage are worn away. Due to the asymmetrical nature of the erosion, the alignment of the mechanical axis of rotation of the femur relative to the tibia becomes tilted down towards the compartment which is suffering the majority of the erosion. This results in VARUS (bow-leg) deformity in the case of a medial compartment disease predominates, or a VALGUS (knock-kneed) deformity in a case of lateral compartment disease predominance. Factors such as excessive body weight, previously traumatic injury, knee instability, the absence of meniscus and genetic predisposition, all affect the rate of the disease.
It is important to understand that the disease manifests itself as periodic continuous pain that can be quite uncomfortable for the patient. The cause of this pain is subject to many opinions, but it is apparent that, as the joint compartment collapses, the collateral ligament on the side of the predominant diseased area becomes increasingly slack (like one side of a pair of loose suspenders), and the tibial and femoral axis move, for example, from a VALGUS to VARUS condition. This increases the stress of the opposing collateral ligament (and cruciate ligaments as well) and shifts the load bearing function of this bi-compartmental joint increasingly towards the disease side. This increasing joint laxity is suspected as causing some of the pain one feels. In addition, as the bearing loads are shifted, the body responds to the increased loading of the diseased compartment with increased production of bony-surfaced areas in an attempt to reduce the ever-increasing area unit loading. All of the shifting of the knee component geometry causes a misalignment of the mechanical axis of the joint. The misalignment causes an increase in the rate of degenerative change to the diseased joint surfaces causing an ever-increasing amount of cartilage debris to build up in the joint, further causing joint inflammation and subsequent pain.
Currently there is a void in options to treat the relatively young patient with moderate to severe chondromalacia involving mainly one compartment of the knee. Current treatments include cortisone injections, hyaluronic acid (HA) injections and arthroscopic debridement. Repeated cortisone injections actually weaken articular cartilage after a long period of time. HA has shown promising results but is only a short-term solution for pain. Arthroscopic debridement alone frequently does not provide long-lasting relief of symptoms. Unfortunately, the lack of long-term success of these treatments leads to more invasive treatment methods. Osteochondral allografts and micro fracture techniques are indicated for small cartilage defects that are typically the result of trauma. These procedures are not suitable for addressing large areas of degeneration. In addition, osteochondral allografts can only be used to address defects on the femoral condyle. Tibial degeneration can not be addressed with this technique.
The only true solution is to rebuild the defective joint by (filling) the joint space with more articular bearing material through complete resurfacing of the existing femoral condyle and tibial plateau. By replacing the original cartilage to its pre-disease depth, the joint mechanical axis alignment is restored to its original condition. Unfortunately these natural articular materials and surgical technology required to accomplish replacement tasks do not yet exist.
Therefore, what is needed is a uni-compartmental interpositional spacer, which by effectively replacing worn articular material, restores normal joint alignment and provides an anatomical correct bearing surface for the femoral condyle to articulate against.
The present invention is directed toward the method of performing surgery and various implants that may be used during knee reconstruction or surgery. In one aspect of the present invention, the method of performing surgery may include forming a groove in a tibial plateau. Next, an implant having a bone-securing element and an articulation element is provided and placed within the groove. Specifically, the bone securing element of the implant is positioned within the groove such that the articulation element is disposed adjacent a tibial plateau. In one aspect, the groove extends from the anterior of the tibia to the posterior. While forming a groove, at least some damaged cartilage may be removed from the tibial plateau.
The groove may include a first side extending from the medial to lateral side and a second width extending in the same direction. And the first width may be larger than the second width. The bone-securing element of the implant may include a corresponding geometric shape that is similarly shaped to the geometric shape of the groove.
In yet another aspect of the present invention, the implant may include an intermediate portion that is attached to both the bone-securing element and the articulation element such that the intermediate portion connects the articulation element to the bone-securing element.
Another aspect of the present invention, a meniscus implant may include a compressible bearing element having an articulation surface and a bone-securing element extending downwardly from the bearing element and configured to be engaged within a channel created within a tibial plateau.
At least a portion of the compressible bearing element may be embedded within a portion of the bone-securing element. And the bone-securing element may have a porosity that promotes bone ingrowth. The bone-securing element may include a first side wall and a second side wall. Each of the side walls may include a transitional portion that transitions the first side and second side walls from a separation that is equal to a first distance to a separation that is equal to a second distance.
The prosthesis meniscal devices of the subject invention are uni-compartmental devices suitable for minimally invasive, surgical implantation. By the term “meniscal” it is meant that the devices are positioned within a compartment in which a portion of the natural meniscus is ordinarily located. The natural meniscus may be maintained in position or may be wholly or partially removed, depending upon its condition. Under ordinary circumstances, pieces of a natural meniscus, which have been torn away, are removed, and damaged areas may be trimmed as necessary. In somewhat rare instances, the entire portion of the meniscus residing in meniscal cavity may be removed. Thus, the term “meniscal device” is descriptive of the location of the device rather than implying that it is a replacement for or has the shape of the natural meniscus. In most cases, the meniscal device of the present invention does not have the same shape as the natural meniscus and will not entirely replace the meniscus.
By the term “uni-compartmental” it is meant that each device is suitable for implantation into but one department defined by the space between the femoral condyle and it's associated tibial plateau. In other words, the device is not a “bi-compartmental” device which, in one rigid device, could be inserted into both of the two femoral condyle/tibial plateau compartments, unless it is specifically called out that the device is bi-compartmental. In many, if not most cases, a device will be inserted into one compartment only, generally the medial compartment, as meniscus and associated articular surfaces in these components (left knee medial and right knee medial compartments) are most subject to wear and damage. However, it is possible to insert two separate devices into the medial and lateral compartments of the same knee, or to use two such devices that are mechanically but not rigidly bi-compartmental.
With reference to
The articulation portion 20 is generally flexible and is preferably made from a polymer such as polyurethane, Delrin, Ultem, PVA, PEEK, and/or polyethylene. The articulation portion 20 thus uses a flexible, low profile layer of smooth material to create a smooth articulating surface as defined by the femoral facing surface 14. The femoral facing surface 14 is designed to slide against mating cartilage, bone, and/or additional implants. Preferably the new artificial joining surface created by the femoral facing surface 14 supports any type of motion that naturally occurs within the older joint surface prior to the damage that was incurred.
The meniscus implant 12 further includes a securing element such as a keel 30. Keel 30 is preferably comprised of a three dimensional titanium mesh having a predetermined porosity. The keel includes a bone anchoring portion 32 and an intermediate portion 34. The keel 30 may be constructed using various methods known to those in the art. And in certain preferred environments, the keel 30 may be formed using methods as described and commonly assigned U.S. patent application Ser. Nos. 11/448,954 entitled “Flexible Joint Implant”; 10/704,270 entitled “Laser-Produced Porous Surface”; 11/027,421 entitled, “Gradiant Porous Implant”; 11/295,008 entitled “Laser-Produced Porous Surface”, the disclosures of which are hereby incorporated by reference herein.
As discussed in U.S. patent application Ser. No. 10/704,270, the keel 30 may be constructed using a selective laser melting or sintering process, which hereby grows the structure in a layer by layer process. In an alternate process, the keel 30 may be built using a method described in U.S. patent application Ser. No. 10/704,270, wherein the intermediate portion 34 acts as a base or substrate on which the bone-anchoring portion 32 is built, also in a layer by layer fashion. Additional techniques for constructing metalized structures i.e., keel 30, may also be constructed employing methods as disclosed in commonly assigned in U.S. patent application Ser. No. 10/071,667 entitled “Porous Metallic Scaffold for Tissue”, the disclosure of which is hereby incorporated by reference herein, as well as additional methods as known to those in the art such as that disclosed in Patent Cooperation Treaty Application 2005/023118 entitled “Porous Metal Articles Formed Using an Extractable Particulate” filed on Jul. 22, 2004 the disclosure of which is hereby incorporated by reference herein.
The keel 30 generally has a height from a first end 36 of the keel to a second end 38 of the keel of approximately 4 mm to 20 mm The bone-engaging portion 32 of the keel 30 preferably has a height of between 2 mm and 18 mm.
As shown in
With reference to
In
In a method of assembly, the keel 30, including the bone-anchoring portion 32 and intermediate portion 34 may be constructed using the various processes described herein. Once the keel 30 has been constructed, the keel may be placed within a mold cavity as discussed in U.S. patent application Ser. No. 11/448,954 and the other various references of which are incorporated by reference herein or known to those in the art. The mold cavity may include a forming area that enables a polymer material to be disposed therein. The polymer material is introduced into the forming area of the mold cavity and is allowed to cure into a desired shape so as to form the articular portion of the meniscal implant 12. During this process, the polymer material is also allowed to creep into the intermediate portion 34 of the keel 30. The intermediate portion 34 of the keel 30 preferably has a porosity that enables the polymer to adhere to the various metal lattice constructed within the intermediate portion. Once cured, the combination the polymer locked within the metal lattice of the intermediate portion 34 secures the articulation portion 20 to the bone-engaging portion 32 of the keel 30.
As described in the various references disclosed herein, the keel 30 may include areas with various gradient porosities as well as barrier layers and other features described in the references incorporated, which aid the keel in promoting bone ingrowth and the like including a desirable porosity and pore size.
In a method of implantation, a small trough 60 of bone may be removed from a central section of the tibia adjacent to the tibial spine as shown in
Once the small trough 60 has been created within the tibial plateau by methods known to those in the art, the meniscus implant 12 may be introduced to the tibial plateau. As shown in
Since the keel includes a narrow portion and a wide portion, the keel is designed to fit into the small trough or key-way in a key like fashion so as to lock the meniscal implant 12 into the bone and prevent loosening. Therefore, the key way allows the meniscal device to be implanted into the proximal end of the tibia using a anterior to posterior approach. Once the keel 30 is positioned within a small trough or key-way, the tibial facing surface 16 of the implant is disposed adjacent and against the tibia. Thus the meniscus device sits atop the tibia condyle thereby providing a low profile articulation surface. Besides the various key and key-way method of locking the meniscus implant 12 within the bone, other short and/or long-term fixation methods may be used. Some of these methods include the use of bone screws, nails, staples, sutures, and/or hooks. In addition, porous metal or poly pegs, sheets, rectangles or other geometric shapes could be used by itself or in combination to fix the implant in place to allow for bone ingrowth. Further, bone cement could also be used to hold the implant to the bone; and ultrasonic waves may be used to cause protrusions on the backside of the implant to melt while being driven into the underlying bone. This would force the molten material to infuse and harden into the surrounding bone. The protrusions could be made of a homogenic material or other porous or solid metal reinforced plastic. Any additional property of the plastic protrusions could have the ability to be reabsorbed into the body and allow soft tissue or bone to grow into the implant for fixation. The metal reinforcements could be hollow, slotted or porous.
Another option may be to use small metal tubes or pegs that are slotted or porous and filled with a polymer material that could be melted or forced outside of the metal tubes after insertion into the bone. UV curing adhesives could be injected through openings in the implant after it is inserted into the bone and allowed to harden by inserting fiberoptic cables into the openings and activating the adhesive. A mesh could also be disposed on the tibia facing surface 16 to help secure the articulation portion 20 of the meniscus implant 12 to the tibial plateau. In yet another alternate embodiment as shown in
The meniscal implant 112 also includes a keel 130, similar to keel 30 of meniscal implant 12. Although the keel 130 may have many different geometrical configurations as may keel 30, keel 130 is shown in
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
