Patent Application
20170086981
Field of the Invention
This application relates to a femoral hip stem that optimizes conforming proximal medial geometry with a minimally invasive insertion and subsidence resistance.
Description of the Related Technology
Hip arthroplasty or replacement refers to a surgical procedure in which the hip joint is replaced by a prosthetic implant. Total hip arthroplasty has been used since the 1960s for the treatment of destructed hip joints and replaces both the femoral component and the acetabular surface of the joint. Artificial hip joints are generally ball and socket joints, designed to match as closely as possible to the natural joint function. Generally, the artificial socket is implanted in one bone, and the artificial ball articulates in the socket. A stem structure attached to the ball is implanted in another of the patient's bones, thereby securing the ball in position. In total hip replacement surgery, a patient's natural hip is replaced by an acetabular cup component that replaces the acetabular socket, and a femoral component, or the stem-and-ball component, which replaces the femoral head.
The ball and socket join of the human hip unites the femur to the pelvis, wherein the ball-shaped head of the femur is positioned within a socket-shaped acetabulum of the pelvis. The head of the femur or ball fits into the acetabulum, forming a joint which allows for leg movement in a range of directions.
Traditionally, total hip replacement surgery involves the use of a posterior approach in which the surgeon accesses the hip joint through an incision close to the buttocks. These hip replacement techniques can require significant disturbance of the joint and connecting tissues and typically involve a relatively large incision.
During a total hip replacement, the surgeon will take a number of measurements to ensure proper prosthesis selection, limb length, and hip rotation. After making the incision, the surgeon works between the large hip muscles to gain access to the joint. The femur is pushed out of the socket, exposing the joint cavity.
In order to install the acetabular cup, the surgeon prepares the bone by reaming the acetabular socket to create a surface for accepting a cup. The cup may be held in place by bone cement or an interference or press fit, or it may have a porous outer surface suitable for bony ingrowth. The new acetabular shell is implanted securely within the prepared hemispherical socket. The plastic inner portion of the implant is placed within the metal shell and fixed into place. Then, the femur is prepared to receive the stem. The proximal end of the femur is at least partially resected to expose the central portion of the bone. Generally, at least part of the greater femoral trochanter is resected to gain access to the central portion of the femur, specifically, the medullary canal. In the central portion, a cavity is created that matches the shape of the implant stem, utilizing the existing medullary canal. The top end of the femur may be planed and smoothed. If the ball is a separate piece, the proper size is selected and attached. Finally, the ball is seated within the cup so that the joint is properly aligned, and the incision is closed.
Many efforts have been made to provide a patient with less trauma during hip arthroplasty. Utilizing an anterior approach can be advantageous. However, the anterior approach used with some traditional instruments, such as straight femoral reamers, may result in extensive trauma to the patient's tissues. Therefore, there is an unrealized need for instruments and techniques that reduce the incision size and trauma to tissues without jeopardizing preparation of the cavity of the largest appropriate size, which provide for proper sizing and alignment of the femoral component's stem, and which will improve restoration of hip function and reduce the risk of the prosthesis loosening and failing.
Moreover, there is a current unrealized need for improved devices, systems and procedures adapted for use in minimally invasive hip arthroplasty. Improved devices are desired that are adapted for introduction and operation through a smaller surgical incision than conventionally available devices. Also needed are improved devices, systems, and procedures that would minimize the damage to the flesh, muscle, and other soft tissues during insertion, operation, and withdrawal. At the same time, there is a need for improved devices, systems, and procedures that would improve sizing and aligning of the femoral components and reduce the risk of their loosening. There is a need for devices that have increased fixation both in the short and long term.
In general, devices and systems are needed that are easy to use and manufacture, minimize tissue damage, simplify surgical procedures, are versatile, allow for faster healing with fewer complications, require less post-surgical immobilization, and are less costly to produce and operate.
In general, devices and systems are needed that are easy to use and manufacture, minimize tissue damage, simplify surgical procedures, are versatile, allow for faster healing with fewer complications, require less post-surgical immobilization, and are less costly to produce and operate.
A new design for a femoral hip stem optimizes conforming proximal medial geometry with anterior approach insertion and subluxation resistance. The new design improves on existing designs by optimizing the proximal geometry. The optimization uses computer-generated models of actual femur geometry to shape the geometry of the proximal body to produce a highly conforming symmetric surface while minimizing the difficulties of inserting a highly conforming surface. More specifically, the overall length of the device is reduced to allow insertion through a smaller wound, and the conforming geometry is tapered such natural variations in bone geometry won't cause high stress contacts with the highly conforming surfaces.
In one aspect, a tapered femoral prosthetic implant for use in total hip replacement is provided. The implant advantageously has a first taper portion configured to receive and attach to a femoral head element; and a stem portion. The stem portion may include a proximal stem region and a distal stem region, wherein the proximal stem region includes a 12 degree anterior proximal taper; and wherein the distal stem region has a 4 degree distal taper. The implant further includes an exterior surface, which may include a porous coating.
The stem portion may include a distal tip. In certain aspects, the distal tip includes a beveled configuration. The distal tip may facilitate insertion of said implant during implantation.
An improved method for treating osteoarthritis and fractures of a hip of a patient through replacement of the hip with a femoral hip stem is likewise described. The femoral hip stem facilitates insertion of the stem and visual confirmation of fit of the stem while also reducing trauma to tissue and femur of the patient. The method may include providing the femoral hip stem wherein as dimensions of the femur increase in both an anterior and posterior dimension from a diaphysial region of the femur to a proximal metaphysial region of the femur, dimensions of a proximal end of the stem also increase in both an anterior and posterior dimension relative to a distal end of the stem to provide a stem shape congruent to the femur of the patient and optimize proximal geometry of the stem for insertion of the stem. The method may further include making an incision in the patient and removing a portion of the femur to create a cavity. Advantageously, the stem is positioned in the cavity such that the proximal geometry of the stem is visible at a resection plane of the stem to allow visual feedback of the fit of the stem.
Advantageously, the stem shape is most congruent to the femur of the patient at the resection plane of the stem. The distal end of the stem may include a beveled tip to protect a lateral cortical bone of the patient. The proximal end of the stem may include a plurality of contact points at the resection plane to allow visual feedback that the plurality of contact points are congruent with the patient anatomy. The dimensions of stem decrease in both a medial and a lateral dimension from the proximal end of the stem to the distal end of the stem. The dimension of the stem decreases in a distal dimension from the proximal end of the stem to the distal end of the stem. Optionally, the incision is between about 5 and 10 cm in length.
The method may be employed utilizing an incision that is either a posterior, anterior, or lateral incision.
In yet another aspect, an improved method for treating osteoarthritis and fractures of a hip of a patient through replacement of the hip with a femoral hip stem is provided. The method minimizes subsidence risk, reduces trauma to tissue and femur of the patient, and improves recovery time, the method includes providing the femoral hip stem wherein the stem has both a distal taper and a proximal taper. The distal taper is configured to reduce the incidence of stress shielding and the proximal taper increases fixation and rotational stability through increased surface area contact with cortical bone structures. The improved method may further include making an incision in the patient; removing a portion of the femur to create a cavity; and setting the stem in the cavity. Preferably, the distal and proximal taper limit micromotion between the stem and the femur in both a medial and lateral dimension. The incision may be an anterior incision that reduces soft tissue damage. Optionally, a surface of the stem may be coated with a porous coating to facilitate rapid bone in-growth. In still other aspects, the distal taper is a 4 degree distal taper. The proximal taper may include a 12 degree proximal taper.
A kit for an improved treatment of osteoarthritis through replacement of a hip is likewise contemplated. The kit may include a femoral hip stem wherein as dimensions of a femur increase in both an anterior and posterior dimension from a diaphysial region of the femur to a proximal metaphysial region of the femur, dimensions of a proximal end of the stem also increase in both an anterior and posterior dimension relative to a distal end of the stem to provide a stem shape congruent to the femur and optimize proximal geometry of the stem for insertion of the stem; and instructions for positioning and setting the femoral hip stem in a cavity of the femur through an anterior incision. In certain aspects, the femoral hip stem includes a porous coating. The instructions may include a guide to visually confirm correct positioning and setting of the femoral hip stem.
After reading this description, it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, all the various embodiments of the present invention will not be described herein. It is understood that the embodiments presented here are presented by way of an example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the invention as set forth below.
Embodiments of this application relate to the optimization of proximal fit in a hip stem implant having a shorter stem. An anterior approach during total hip surgery can be advantageous for its less invasive technique as compared to a more traditional posterior approach. The anterior approach for total hip replacement is a tissue-sparing alternative to traditional hip replacement surgery that provides the potential for less pain, faster recovery, reduced hospital stays, and improved mobility because the muscle tissues are spared during the surgical procedure. The technique allows the surgeon to work between muscles and tissues without detaching the muscles from either the hip or thighbones, thereby sparing the tissue from trauma. Keeping the muscles intact may also help to prevent dislocations. With an anterior approach, the surgeon can employ a relatively small incision on the anterior of the hip as opposed to the side or back. Accordingly, with a front incision, a patient can avoid the pain of sitting on the incision site.
Minimally invasive arthroplasty techniques may further benefit a patient by providing reducing soft-tissue exposure and minimizing trauma to the muscle and ligament mechanisms. However, the less invasive technique necessarily results in a surgical window with restrictive geometry which complicates insertion and placement of longer femoral components. Disclosed herein is a femoral hip stem with a shortened overall length to facilitate insertion with an anterior approach and an anatomically congruent, tapered profile to maintain stability and prevent subsidence. Features of the invention include, without limitation, a device which is inserted with greater ease due to its stem size, increased fixation stability afforded by the proximal body conformity as well as optional coating as will be described in greater detail below, a reduced risk of initial subsidence, and a lower fracture risk as compared to highly conforming devices without regard to anatomical variation. Disclosed herein is a tapered hip system which provides increased stability and reduced trauma in less invasive hip approaches. The invention is based, in part, on the surprising discovery that the disclosed tapered implant performs so well for both the surgeon and the patient receiving the implant. As will be described in greater detail below, the implant, designed using anthropomorphic data and a unique algorithm to optimize fit and performance of the device, is a boon to femoral hip prostheses.
Features of the femoral hip system include its tapered design and integration of a filling proximal geometry, which provides superior congruency with the patient's cortical bone and prevents subsidence. Turning to
With less invasive approaches to total hip surgery, often the surgical window has a more restrictive geometry which can complicate insertion and placement of traditional length femoral components. Notably, the stem portion 16 of the implant 10 has significant advantages at least in part due to the reduced stem size and tapered profile. More particularly, the tapered profile provides ease of insertion, prevention of subsidence, and stability enhancement while allowing for a shortened femoral stem. The shape of the stem 16, having both a rounded portion and tapered profile, increases support during the initial implantation of the device when bone in-growth has not occurred. Despite the shorter stem as compared with many prior art devices, stability is achieved by promoting superior congruency with the cortical bone upon implantation such that micromotion and subsidence is decreased while promoting faster bone ingrowth. With specific reference to
Optionally, the exterior surface of the implant 10 may include a porous coating to aid in the apposition of bone to promote superior in-growth results. One such porous coating is the P2 coating from DJO Surgical (Austin, Tex.). Advantageously, the coating is a titanium porous coating having small, three-dimensional beads. The porous material may be commercially pure titanium or CoCr alloy. Advantageously, the coating includes non-spherical beads to provide greater points of contact and a substantially rougher surface area to promote fixation and may include a “lava rock” appearance. More specifically, the coating can create instant micro-fractures in the trabeculae upon initial bite to the bone, which causes a relatively quick bone in-growth reaction. The pore sizes of the porous coating may be variable, including an inter-bead pore size of between about 200-525 microns and an intra-bead pore size of between about 25-65 microns. The average porosity of the coating is preferably greater than 50%. In a preferred embodiment, the average porosity is around 60%. Preferably, the porous coating provides a high surface roughness than spherical beads, thereby providing for greater bone apposition and percent bone in-growth than an uncoated implant.
By employing a metaphysial fill and biological fixation (i.e. bone growth into the implant), stability is greatly increased over prior art devices, allowing for solid long-term endurance of the disclosed implant. Moreover, in optimizing conforming proximal medial geometry, subsidence resistance is improved. Features of the tapered hip system 10 include a relatively short stem length as compared to prior art devices and a tapered shape to facilitate insertion and visualization as compared to other currently available tissue sparing designs. In one embodiment, the stem of the disclosed hip system is approximately 30 mm shorter than the stem of the Linear™ hip system. The hip system is constructed and shaped to avoid material interfering with insertion or version correction as well as to avoid cortical overlap at resection. A further feature of the tapered hip system includes the ability to engage substantially more proximal bone than prior art hip systems. The primary fixation of the tapered hip system is medial/lateral. Secondary fixation is anterior/posterior (hereinafter A/P) proximal while reducing cortical bone interference and allowing for version placement. Prior art devices such as the Linear™ hip stem include an uncemented stem having stability based on three point fixation, citation on fit and fill, and AML on distal fixation. The rectangular stem of the Linear™ device, however, does not conform with a patient's bone geometry. By contrast, the disclosed hip system includes fixation at the metaphysial/diaphysial junction, the region of the femur that has the strongest bone and is shaped like a funnel. This type of fixation approach capitalizes on the anatomy and physiology of this area inasmuch as fixation at this level provides excellent stability to subsidence, varus/valgus, and rotational forces akin to a cork in a bottle. The tapered design and proximal body shape of the hip system disclosed herein allows the bone to be loaded proximally, yielding positive bone remodeling and eliminating stress shielding as well as promoting diaphysial and metaphysial engagement.
With reference to
The relatively shorter stem of the hip system 10 described herein allows for ease of insertion as well as addresses proximal and distal mismatches. The average incision length of a standard total hip prosthesis is traditionally 22 cm long to accommodate the stems of prior art devices. The surgical window for less-invasive techniques such as an anterior approach insertion is generally between about 5-10 cm in length. Thus, a shorter stem allows for easier insertion into the bone without stressing the muscles and avoiding undue trauma to a patient as compared with prior art. Moreover, the relatively short stem eliminates distal modulus of elasticity mismatches that can cause thigh pain, helps to preserve the endosteal blood supply, and facilitates future revision surgery. The tapered design with short stem preserves bone and thus decreases the need to lateralize, which better accommodates the anterior approach. Finally, the tapered tip prevents diaphysial engagement but nevertheless allows the surgeon to fit the stem into the cavity.
The design of the hip stem is thus facilitated, in some embodiments, by a geometry optimization algorithm that provides detailed criteria to optimize stem geometry. The resulting hip system includes a highly conforming symmetric surface while minimizing the challenges of insertion. The overall length of the device is reduced to allow insertion through a smaller wound, and the conforming geometry is designed such that natural variations in bone geometry do not cause high stress contacts with the highly conforming surface
The proximal body shape was designed to optimize fit along the medial-anterior aspect of the proximal femur. To generate and evaluate the design, CAD files were virtually implanted into femur geometry represented by ADaMs standardized femur models for 5 sizes: mean, ±1 standard deviation from the mean, and ±2 standard deviations from the mean. The ADaMs models were constructed from a database of 73 male and female femur CT scans (mean age 67.5) taken from Northern Europe. Three of the individual femur scans used in the data base were selected for validating the fit of the proposed implant geometry.
An evaluation of the concept designs was also performed to evaluate the initial mechanical stability of the concept designs. The mean femur model was first virtually broached to form a cavity that was the negative of the proposed design concept. The implant geometry was fit into the cavity and the assembly transferred to Ansys where a frictionless contact analysis was defined. A single load vector corresponding to the peak load magnitude and direction during gait was used to load the implant neck. Deformation of the implant and cancellous bone cavity at a point medial and a point lateral were used to measure the relative implant-bone micromotion as an indication of implant stability. The results of this analysis are depicted below in Table 1.
Due to variations in bone geometry with size, concepts built using the mean sized model were not always best fits for the other sizes, but by scaling the design concepts for the ±1, ±2 sizes, optimal shapes were developed to provide maximum congruency without interference across all sizes. To accommodate an anterior approach, a reduced length stem was desired, but it was recognized that simply cutting the stem on an existing implant could decrease initial stability thereby delaying or inhibiting bone growth.
Using the cross sectional plots, three dimensional designs were developed that had reduced overall length, were congruent with the cortical bone in the medial-anterior aspect of the femur, and consisted of a tapered design to minimize subsidence risk. The implant was designed to make use of increased proximal body congruency and tapered approach to maximize initial stability. Using the FEA model, micromotion between the implant and the broached bone was assessed for peak loading during the gait cycle. The clinically successfully Linear™ stem was used to benchmark excellent performance while a fictitious stem (Linear™ that was artificially shortened) was used as an indicator of minimal performance. The present implant, with its proximal conforming, tapered design had predicted micromotion less than one-third of Linear™.
While a highly congruent implant shape was a design goal, the most highly congruent shape was not necessarily the optimal shape. A design that is highly congruent below the resection may present problems during insertion as the surgeon would be unable to visually confirm proper sizing and placement of the implant at the resection plane. The final hip stem design had a congruency that was 57.3% better than the Linear™ stem, easier to insert with an anterior approach, and provides visual feedback to the surgeon for sizing and placement as reflected in
After optimizing fit and angles of the tapered design, the disclosed femoral prosthetic device provides even greater customization by offering numerous sizing options. In certain aspects, the disclosed hip system may include a plurality of both standard and lateralized offset stem sizes. The tapered design of the hip system provides immediate stable fixation with more physiologic loading proximally and promotes decreased risk of intraoperative complications, restoration of proper hip biomechanics and offset, intraoperative stability and expanded implant sizing options. As set forth with reference to
A method of treating a patient suffering from a hip disability is likewise contemplated. As used herein, the term “disability” includes without limitation non-inflammatory degenerative joint disease such as osteoarthritis and avascular necrosis of the natural femoral head, rheumatoid arthritis, correction of functional deformity, revision procedures where other treatments or devices have failed, treatment of non-union, and hip fractures. Utilizing the embodiments disclosed herein, a hip stem facilitates insertion than longer stem such as the Linear™ stem. The disclosed embodiment further provides increased fixation stability due to the proximal body conformity and a reduced chance of initial subsidence by providing tapered features. The inventive embodiments further provide for lower fracture risk, relative to highly conforming implants without regard to anatomical variation because of the intentional biasing of conformity to be maximum and consideration of the resection level where surgeon gets visual feedback of stem fit.
It will be appreciated that one of the features of the disclosed prosthetic device is its tapered profile and shorter stem. The configuration is particularly well suited for providing enhanced congruency with the cortical bone of the patient while allowing for visual feedback to the surgeon at the resection plane when the implant is inserted. The combination of a highly congruent device with a short stem allows for increased support during implantation as well as facilitating insertion, despite the congruency between the device and cortical bone. Enabling visual feedback to the surgeon at the resection plan prevents weakening of the patient bone caused by the surgeon trying to force the implant position beyond contact with the cortical shell. While the implant can be used with any number of incision approaches, it is particularly well-suited for use in an anterior approach because of the reduced incision length of such an approach coupled with the shorter stem of the disclosed device and opportunity for visual feedback for the surgeon at the resection plane.
An improved method for treating osteoarthritis and fractures of a hip of a patient through replacement of the hip with a femoral hip stem that facilitates insertion of the stem and visual confirmation of fit to patient's anatomy while also reducing trauma to tissue and femur of the patient is provided. The method includes providing a femoral hip implant as disclosed herein. The femoral hip implant is dimensioned such that as dimensions of the femur increase in both an anterior and posterior dimension from a diaphysial region of the femur to a proximal metaphysial region of the femur, dimensions of the proximal end of the stem also increase in both an anterior and posterior dimension relative to a distal end of the stem to provide a stem shape congruent to the femur of the patient and optimize proximal geometry of the stem for insertion of the stem. The tapered design of the implant includes at the distal stem region, a tapering of the stem medially/laterally at an angle of approximately 4°. As detailed above, this reduced distal taper avoids stress shielding common with prior art devices. Moreover, the 4 degree distal taper helps account for proximal/distal mismatch. The proximal stem region 18 comprises a proximal anterior/posterior (AP) taper angle of approximately 12° to enhance the stability of the device upon insertion. The distal tip is beveled and likewise angled to secure the device in the cavity of the femur.
The method further includes making an incision in the patient. The incision is advantageously less than the standard hip replacement surgery of between about 20-22 cm. In some aspects, the incision is instead between about 5 and 10 cm. Once an incision has been made, a portion of the femur is removed to create a cavity. The stem of the implant is positioned in the cavity, wherein the proximal geometry of the stem is visible at a resection plane of the stem to allow visual feedback of the positioning of the stem.
The implant as described herein is useful in hip replacement surgery whether the incision is a posterior, anterior, or lateral approach. In certain aspects, the implant is particularly well suited for an anterior approach to hip replacement.
In another aspect, an improved method for treating osteoarthritis and fractures of a hip of a patient through replacement of the hip with a femoral hip stem that minimizes subsidence risk, reduces trauma to tissue and femur of the patient, and improves recovery time is provided. The method includes providing a femoral hip stem wherein the stem has both a distal taper and a proximal taper, the distal taper minimizing stress shielding and the proximal taper increasing fixation and rotational stability through increased surface area contact with cortical bone structures. The method further includes making a 5-10 cm incision in a patient, removing a portion of the femur to create a cavity, and setting the stem in the cavity, wherein the proximal body shape and the distal and proximal taper limit micromotion between the stem and the femur in both the medial and lateral dimensions. The incision may be an anterior incision that reduces soft tissue damage. Optionally, the surface of the stem of the implant is coated with a porous coating to facilitate rapid bone in-growth. The tapers of the femoral implant include the distal taper of about 4 degrees and a proximal taper of about 12 degrees.
A kit for an improved treatment of osteoarthritis through replacement of a hip is likewise contemplated. The kit may include a femoral hip stem wherein as dimensions of a femur increase in both an anterior and posterior dimension from a diaphysial region of the femur to a proximal metaphysial region of the femur, dimensions of a proximal end of the stem also increase in both an anterior and posterior dimension relative to a distal end of the stem to provide a stem shape congruent to the femur and optimize proximal geometry of the stem for insertion of the stem; and instructions for positioning and setting the femoral hip stem in a cavity of the femur through an anterior incision; wherein the instructions include a guide to visually confirm correct positioning and setting of the femoral hip stem.
The above description of disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to the embodiments will be readily apparent to those skilled in the art; the generic principles defined herein can be applied to other embodiments without departing from spirit or scope of the invention. Thus, the invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
This application is a continuation of and claims priority to PCT Application PCT/US2015/020275 filed on Mar. 12, 2015, which claims priority to U.S. Provisional Application No. 61/952,094, filed on Mar. 12, 2014, the disclosure of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61952094 | Mar 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2015/020275 | Mar 2015 | US |
| Child | 15263002 | US |
