Patent Publication Number: US-2021186710-A1

Title: Bone density scan result-matched orthopedic implants and methods of use

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 16/995,256, filed on Aug. 17, 2020, which is a continuation of U.S. patent application Ser. No. 15/840,697, filed on Dec. 13, 2017, now U.S. Pat. No. 10,779,954, which claims priority from U.S. Provisional Patent Application Ser. No. 62/433,345 filed Dec. 13, 2016, all of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     This invention relates generally to the field of orthopedic surgery involving orthopedic implants to correct or repair damaged bones, cartilage, vertebral discs and other musculoskeletal structures. Such surgery may include implants such as interbody cage implants (fusion or non-fusion) for spinal surgery to replace damaged or diseased vertebral discs, interspinous fixation implants, full or partial knee replacement implants, full or partial hip replacement implants and the like. 
     A bone density test is used to measure bone mineral content and density (sometimes referred to herein as “BMD”). It may be done using X-rays, dual-energy X-ray absorptiometry (DEXA or DXA), or a special CT scan that uses computer software to determine bone density of the hip or spine. For various reasons, the DEXA scan is considered the “gold standard” or most accurate test. 
     This measurement tells the healthcare provider whether there is decreased bone mass. This is a condition in which bones are more brittle and prone to break or fracture easily. A bone density test is used mainly to diagnose osteopenia and osteoporosis. It is also used to determine a patient&#39;s future fracture risk. 
     In patients scheduled to undergo orthopedic surgery, bone quality in the area of surgical intervention and implantation affects the safety and longevity of the prosthetic implant. For example, in patients undergoing joint arthroplasty of the hip, the bone quality around the joint affects the safety and failure rate and useful life span of the implant. BMD can also affect strategies employed in spinal fusion in osteoporotic spines. 
     BMD is a clinical marker for bone strength. Bone mineral density varies among different body regions and also varies as a result of age, disease, injury, general health, weight, demographic, and use of certain medications or hormones. 
     Although BMD at the site of intervention is correlated with long-term results, bone density scans of the diseased or damaged site are not always performed and even when they are performed, they do not affect the course of treatment in terms of the specific implant that is used. Thus, there is a one size fits all standard of care when it comes to orthopedic implants as they relate to the bone density of the area surrounding the implant. 
     The gold standard for bone densitometry or bone density scans is the dual energy x-ray absorptiometry (“DEXA” or “DXA”) scan. A DEXA scan is a means of measuring bone density by directing two x-ray beams with different energy levels at the patient&#39;s bone at the diseased or injured site or the site of diagnosis for age-related routine scans to determine BMD. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by the bone. DEXA scans are the most widely used and most thoroughly studied bone density measurement technology for determining the density of bone. 
     Bone density scans prior to an orthopedic implant are not always the standard of care. For example, in one study, orthopedic surgeons were asked if BMD is important to them in performing hip arthroplasty (Maier G S, Kolbow K, Djorde L, Maus U. The Importance of Bone Mineral Density in Hip Arthroplasty: Results of a Survey Asking Orthopaedic Surgeons about Their Opinions and Attitudes Concerning Osteoporosis and Hip Arthroplasty. Adv. In Orthopedics. 2016, Article ID 8079354). 72% of all asked orthopaedics reported to use cementless implants as a standard in hip arthroplasty, and over 60% reported that low BMD is a reason to reconsider operation strategies, such as using cement if the patient has low BMD. However, only 4% performed BMD measurement preoperatively. 
     Another example where BMD is an important factor, albeit one that is not typically considered, in patient treatment is spinal fusion implants, including those that employ PEEk or titanium cages. Especially in older patients with osteoporosis, low BMD at the site of fusion is associated with poor fusion rate and bone stability. Various interventions have been proposed to address this problem, but most interventions focus simply on poor screw fixation or screw loosening and fixation failure. Many techniques have been employed to enhance the pullout strength of the pedicle screws that fix cages to the vertebrae. The preparation for screw hole or minimization of tapping hole can affect the pullout strength in osteoporotic bone and, although the anatomical constraints vary with patients, bigger and longer screws have been used to improve fixation to fragile bones. Other solutions involve the angulation of the screws and screw positioning in areas of higher BMD, either of which may increase pullout strength. These techniques may enhance fixation, but they still don&#39;t address the core problem of implant failure that results from poor bone BMD around the implant. 
     In fact, the current standard of care considers BMD around the site of intervention mainly as a factor to determine whether or not to perform a procedure, and sometimes, as discussed above, BMD is used as a factor to alter fixation methods, such as the screws. Otherwise, BMD is mostly used as a means of diagnosing the progression of osteoporosis in older patients, and is not a factor in the use and type of orthopedic implants. 
     Clinically, stiffening of the functional spinal unit (FSU) is a consequence of surgical intervention for fusion. While such a condition is unavoidable, Applicants believe that more focus is needed on developing a mechanical configuration that will provide sufficient stability yet not result in stress shielding due to an overly stiff construct. For example, as it relates to titanium cage interbody spinal fusion implants, the modulus of elasticity for trabecular bone has been reported to be approximately 0.10 GPa, while titanium displays a modulus of 110 GPa, and reinforced PEEK has a modulus of approximately 18 GPa. In short, the implants and the surrounding bone don&#39;t match, and there has been no focus in the clinic or the scientific literature on this mismatch and whether it leads to a higher than necessary incidence of failure in implants over time. 
     For example, in the case of spinal fusion, Applicants believe that interbody cage stiffness can affect surgical outcomes, particularly in osteoporotic bone. Unwanted subsidence or collapse of the vertebral endplates is an unfortunate result that happens too frequently. The patient&#39;s bone density scan is able to reveal the level of osteoporosis in the subject patient but no bone scan density result-matched interbody cage with semi-customized interbody implant is available at the present time, nor has such a matched method of intervention been contemplated until the present invention. Certainly there has been no effort to match a patient&#39;s DEXA scan with an implant that closely approximates the DEXA scan so that the implant and the surrounding bone at the site of intervention are similar in density. Nor has such a method been considered as a means of improving long-term outcome for patients with orthopedic implants, such as interbody spinal fusion cage implants or hip implants, among others. 
     There is a need to improve results in orthopedic implants. There is a need to customize implants based on the health and strength of the bone at the site of intervention. There is a need to improve fusion and minimize failure at the site of fusion. There is a need to deliver implants that match the mechanics of the surrounding tissue so that the new and the old are adapted to one another and one is not prone to cause the failure of the other. These are needs that have not been addressed until now. 
     SUMMARY 
     One object of the invention is to provide a spine surgery fusion product that has variable stiffness designs in order to match patients&#39; bone density and be as close as possible to the modulus of the patient&#39;s own bone modulus. The modulus of elasticity variation of one embodiment of the current invention can be achieved by making the design hollow to create a “soft-cage” that has lower, medium or higher material density, and the various optional densities can be used to best match the implant to the bone at the site of intervention. 
     In various embodiments, the implants described herein can be manufactured from implantable metal, plastic, reinforced plastic, titanium, titanium cobalt, stainless steel, cobalt-chromium alloys, titanium and cobalt mixed metal, ceramic, PEEK or carbon fiber. The interbody cages described herein can be manufactured employing well known traditional manufacturing methods or newer methods such as 3-D printing. 
     In one embodiment, a kit for orthopedic surgical procedures is provided. The kit has two, three, four or more orthopedic implants of the same type. In one embodiment, there are two implants, and one of the implants has a first density that is less than the density of the second implant. In another embodiment there are three implants. The first implant has a first density, the second implant has a second density that is lower than the first density, and the third implant has a third density that is lower than the first and second densities. Other than the density of the implants, the three implants are the same in outer dimension and will otherwise fit within the same space of a surgical site of intervention. The kit also includes instructions for use during a surgical procedure on a patient. The instructions include the following steps: determine the DEXA scan T-score of the patient&#39;s native bone at a site of surgical intervention;
         i. if the DEXA scan T-score of the patient&#39;s native bone is −1 or higher, then retrieve the first implant and introduce it to the patient&#39;s native bone to the exclusion of the second and third implants;   ii. if the DEXA scan T-score of the patient&#39;s native bone is between a −2.5 and −1.0, then retrieve the second implant and introduce it to the patient&#39;s native bone to the exclusion of the first and third implants; and   iii. if the DEXA scan T-score of the patient&#39;s native bone is lower than −2.5, then retrieve the third implant and introduce it to the patient&#39;s native bone to the exclusion of the first and second implants.       

     In one embodiment, the implants are interbody cages. In one particular embodiment, the interbody cages are for spine fusion, and in another embodiment, the cages are not for spine fusion. In other embodiments, the implants are femoral stems of a hip implant or acetabular components of a hip implant. 
     In another embodiment, a method of treating a patient who requires surgical implantation of an orthopedic implant is described. The method includes the steps of: determining the DEXA scan T-score of the patient&#39;s native bone at a site of surgical implantation where the implant will be in contact with the patient&#39;s native bone; retrieve an implant that has a density that is closest to the density of the patient&#39;s native bone at the site of surgical implantation based on the DEXA scan T-score of the patient&#39;s native bone; and implanting the retrieved implant in the patient. In one embodiment, the implants are interbody cages, which may or may not be for spine fusion. In other embodiments the implants are femoral stems of a hip implant or acetabular components of a hip implant. 
     In another embodiment, an interbody cage implant that has about the same density as natural bone that has a T-score of −1.0 or higher as measured by a DEXA scan is described. The interbody cage implant has an identifier that identifies it as having a density that is about the same as natural bone having a T-score above −1.0. The interbody cage implant can have a density of about 1.10 g/cm 3  or greater. In one embodiment, the identifier can be the color green, and the whole cage can be green or just a portion of the cage can be green. 
     In another embodiment, an interbody cage implant that has about the same density as natural bone that has a T-score of between −2.5 and −1.0 as measured by a DEXA scan is described. The interbody cage implant has an identifier that identifies it as having a density that is about the same as natural bone having a T-score of between −1.5 and −1.0. The interbody cage implant can have a density of between about 0.90 g/cm 3  and about 1.10 g/cm 3 . In one embodiment, the identifier can be the color yellow, and the whole cage can be yellow or just a portion of the cage can be yellow. 
     In another embodiment, an interbody cage implant that has about the same density as natural bone that has a T-score lower than −2.5 as measured by a DEXA scan is described. The interbody cage implant has an identifier that identifies it as having a density that is about the same as natural bone having a T-score below −2.5. The interbody cage implant can have a density of below about 0.90 g/cm 3 . In one embodiment, the identifier can be the color red, and the whole cage can be red or just a portion of the cage can be red. 
     In yet another embodiment, a method of treating a patient in need of an orthopedic implant is described. The method includes obtaining the T-score or bone density of the patient&#39;s native bone at a site of implantation, said T-score or bone density being determined by a DEXA scan or other means of determining a T-score or bone density. The method further includes selecting an orthopedic implant that has about the same density as the native bone at the site of implantation, and implanting the orthopedic implant at the site of implantation. 
     Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, various embodiments of the present invention are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention. 
         FIG. 1  is a perspective view of a kit of three interbody cage implants. 
         FIG. 2  is a perspective view of one of the interbody cage implants from the kit of  FIG. 1  with anchors and an anchor plate. 
         FIG. 3  is a side view of the interbody cage implant of  FIG. 2 . 
         FIG. 4  is a perspective view of an anchor used in the interbody cage implant of  FIG. 2 . 
         FIG. 5  is a perspective view of an anchor plate used to secure the anchors of the interbody cage implant of  FIG. 2 . 
         FIG. 6  is a top side view of the anchor plate of  FIG. 5 . 
         FIG. 7  is a DEXA Scan T score chart of the prior art. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the invention are shown in the accompanying figures and described below. 
     A bone mineral density (BMD) test provides a snapshot of bone health by providing a value associated with bone density. The more dense the bone, the healthier and stronger it is. The test is typically performed to identify osteoporosis, determine risk for fractures (broken bones), and measure response to osteoporosis treatment. It is not presently used to determine the appropriate density of an orthopedic implant for a patient undergoing an orthopedic surgical procedure requiring an implant. 
     The most widely recognized BMD test is called a central dual-energy x-ray absorptiometry, or central DEXA scan. The DEXA scan can measure bone density at the hip, spine and other bones. A DEXA scan measures BMD and compares it to that of an established norm or reference standard to give the patient a DEXA Scan score. The DEXA scan score is called a T-score, which is a value that compares the patient to an ideal or peak bone mineral density of a healthy 30-year old adult. A score of 0 means the BMD is equal to the norm for a healthy young adult. Differences between the patient&#39;s BMD and that of the healthy young adult norm are measured in units called standard deviations (SDs). The more standard deviations below 0, indicated as negative numbers, the lower the patient&#39;s BMD, meaning the less dense the bone. A DEXA scan T-score between +1 and −1 is considered normal or healthy. A DEXA Scan T-score between −1 and −2.5 indicates low BMD, although not low enough to be diagnosed with severe osteoporosis. A DEXA scan T-score of −2.5 or lower indicates osteoporosis and means that the BMD is very low. The greater the negative number, the more severe the osteoporosis and the less dense the bone. Thus, when the DEXA scan T-score is between +1 and −1 (or is higher than −1), the BMD of the bone is normal. When the DEXA scan score is between 1 and 2.5 SD below the young adult mean (−1 to −2.5 SD), then the BMD is lower than normal and indicates bone that is less dense than normal bone for that location. When the DEXA scan score is 2.5 SD or more below the young adult mean (−2.5 SD or lower) this indicates bone density that is significantly below normal for bone in that location and is an indicator of osteoporosis. These scores are typically associated with a DEXA scan chart, such as the one shown in  FIG. 7 , in which the normal range of +1 to −1 (or greater than −1) is represented in green, the below normal range of −1 to −2.5 is represented in yellow, and the very low range below −2.5 indicating osteoporosis is represented in red. This is a standard method of depicting the DEXA scan T-score in the medical community. 
     DEXA scan T-scores of the spinal column are typically matched to BMD as follows. BMD in g/cm 3  of about 1.10 and higher are associated with a normal bone density and are therefore given a DEXA scan T-score of at least −1 or higher (meaning 0, +1 and higher), i.e., in the green range. BMD in g/cm 2  of about 0.90 to about 1.10 are associated with low bone mass and are therefore given a DEXA scan T-score of between −1 and −2.5, i.e., in the yellow range. Finally, BMD below about 0.90 g/cm 3  are associated with very low bone mass and osteoporosis and are therefore given a DEXA scan T-score of below 2.5, i.e., in the red range. 
     The present invention provides methods of treatment and orthopedic implant kits that allow physicians to best match the implant with their patient&#39;s DEXA Scan T-score such that the implant that most closely approximates the density of the bone at the site of implantation relative to other implants is the one that is implanted to the exclusion of the other implants of the same type. When given the choice of two, three or more implants of the same type that only differ by density, surface area, and porosity, the surgeon can choose the implant that most closely approximates the patient&#39;s native bone at the site of implantation based on the patient&#39;s DEXA Scan T-score. 
     One embodiment of the invention is illustrated in  FIG. 1 .  FIG. 1  shows three interbody spinal cage implants that are part of a kit  1 . The interbody spinal cage implants may be fusion implants may or may not be fusion implants. Kit  1  may have two interbody cage implants instead of three. Kit  1  may have four or more interbody cage implants instead of three. Interbody cage implants are well known in the art and they come in various sizes and shapes to fit within the lumbar, thoracic or cervical spine. One example of an interbody cage is the Discovery™ minimally invasive cervical interbody spinal fusion cage made by Aurora Spine. There are many other examples made by many other manufacturers from many different shapes, sizes and materials. 
     In one embodiment, kit  1  contains cage  10 , cage  11 , and cage  12  (although in other embodiments it may contain only cage  10  and  11 , cage  10  and  12 , or cage  11  and  12 . It can also contains an inserter  13  for inserting cages  10 ,  11  or  12  into the disk space in between two vertebral bodies in the spinal column of a patient, as well as instructions for use (not shown). Kit  1  may also include one or more sizers to determine the correct size of interbody cage implant to insert into the disk space. Kit  1  may also include graft material that is packed into the hollow space B in the center of cages  10 ,  11  or  12 . Each of cages  10 ,  11 , and  12  have outer dimensions that are virtually identical, meaning they are the same or about the same height, width, and depth. However, they are not the same weight, and they do not have the same density, porosity or amount of surface area. Cage  10  is the heaviest of the three cages, has the least porosity, the least surface area and the most density. Cage  11  weighs less than cage  10  but more than cage  12 . Cage  11  has more porosity, more surface area, and less density than cage  10  but less porosity, less surface area and more density than cage  12 . Cage  12  weighs less than both cage  10  and cage  11 . Cage  12  has more porosity, more surface area, and less density than both cages  10  and  11 . Cages  10 ,  11  and  12  can be manufactured from implantable metal, plastic, reinforced plastic, titanium, titanium cobalt, stainless steel, cobalt-chromium alloys, titanium and cobalt mixed metal, ceramic, PEEK or carbon fiber, or combinations of any of the above. In one embodiment, they are manufactured from titanium. The weight, density, surface area, and porosity of the three cages differs as a result of the number and positioning of various hollow channels A through the cages, which run through the solid surfaces of the cages. The cage with the most number of hollow channels running through it has the most porosity, is the lightest in weight, is the lowest in density, and has the most surface area. Cage  12  is has the most porosity, least density, lowest weight and highest surface area among the three cages in kit  1 , because it has the most number of hollow channels A running through its otherwise solid body. Cage  12  therefore has the least resistance to crush under load and is most similar to osteoporotic bone having a DEXA Scan T-score of −2.5 or lower (in the red range of a DEXA scan T-score) as compared to cages  11  and  10 . Cage  11  has fewer hollow channels A running through it than cage  12  but has more hollow channels A than cage  10 . Cage  11  is heavier, less porous, more dense, and has less surface area than cage  12 , but is lighter in weight, more porous, less dense, and has more surface area than cage  10 . Therefore, cage  11  is more dense than cage  12  but less dense than cage  10  and is most similar to low density bone at the T-Score range of −1 to −2.5 (in the yellow range of a DEXA scan T-score) as compared to the other two cages  10  and  12 . Cage  10  has fewer hollow channels A than both cages  11  and  12 , and is therefore the heaviest in weight, least porous, most dense, and have the least amount of surface area of cages  10 ,  11  and  12  of kit  1 . Cage  10  has the strongest resistance to crushing under load compared to cages  11  and  12 . Cage  10  is therefore the cage among cages  10 ,  11  and  12  that is most similar to healthy bone having a DEXA scan T-score range of −1 or higher (in the green range of a DEXA scan T-score) as compared to the other two cages  11  and  12 . 
     Turning to cage  10 , it has the highest density of the three cages. In one embodiment, it has a density of about 4.40 g/cm 3 , but can range from about 3.90 g/cm 3  to about 5.00 g/cm 3  in density. In another embodiment, it has a density of about 3.90 g/cm 3 . In another embodiment, it has a density of about 3 g/cm 3 , but it can range from about 2 g/cm 3  to about 4 g/cm 3  in density. In another embodiment, it has a density of about 1.40 g/cm 3 , but can range from about 1.10 g/cm 3  to about 1.80 g/cm 3  in density. 
     Turning to cage  11 , it has a density that is in between the densities of cage  10  and cage  12 , meaning it is less dense than cage  10  but more dense than cage  12 . In one embodiment, it has a density of about 3.80 g/cm 3 , but range from about 3.30 g/cm 3  to about 4.20 g/cm 3  in density. In one embodiment, it has a density of about 3.30 g/cm 3 . In another embodiment, it has a density of about 2.00 g/cm 3 , but can range from about 1.00 g/cm 3  to about 3.00 g/cm 3  in density. In another embodiment, it has a density of about 1 g/cm 3 , but can range from about 0.90 g/cm 3  to about 1.10 g/cm 3  in density. 
     Turning to cage  12 , it has a density that is lower than both cage  10  and cage  11  of the cages in kit  1 . In one embodiment, it has a density of about 3.20 g/cm 3 , but range from about 2.50 g/cm 3  to about 3.60 g/cm 3  in density. In one embodiment, it has a density of about 2.50 g/cm 3 . In another embodiment, it has a density of about 1.50 g/cm 3 , but can range from about 1.00 g/cm 3  to about 2.5 g/cm 3 . In another embodiment, it has a density of about 0.80 g/cm 3 , but can range from about 0.60 g/cm 3  to about 0.90 g/cm 3  in density. 
     In another embodiment, not shown in the figures, kit  1  may contain a fourth cage that is still lower in density than cage  12 , and is used to match DEXA scan T-scores that are lower than −3 suggesting not only osteoporosis but potentially a fracture. In one embodiment, the fourth cage has a density of about 2.50 g/cm 3 , but can range from about 2.00 g/cm 3  to about 3.00 g/cm 3  in density. In another embodiment, it has a density of about 1.00 g/cm 3  but can range from about 0.40 g/cm 3  to about 1.3 g/cm 3  in density. In another embodiment, it has a density of about 0.60 g/cm 3 , but can range from about 0.40 g/cm 3  and about 0.70 g/cm 3  in density. 
     In one embodiment, cages  10 ,  11  and  12  have identifying indicia that indicate whether they are the most dense (also heaviest, least porous and least surface area), middle density (middle heavy, middle porous and middle surface area), or least dense (least heavy, most porous and most surface area) of the 3 cages. For example, the cages can be numbered  1  for cage  10 ,  2  for cage  11  and  3  for cage  12  or the reverse etched into the cages. In another embodiment, their relative density/porosity/weight/surface area may be identified by a + − and = signs etched into the cages. In another embodiment, the cages may have a color painted on an area of the cage or the entirety of the cage. For example, cage  10  may be green, cage  11  may be yellow and cage  12  may be red to match the typical DEXA Scan color coded results. In another embodiment, each of cages  10 ,  11  and  12  is located within a sealed package of its own that itself has an identifier that indicates whether it is the most dense/least porous/heaviest/lowest surface area, middle density/porosity/weight/surface area or least dense/most porous/lightest/highest surface area of the cages. For example, cage  10  may be in a sealed package that is green or has green markings on it; cage  11  may be in a sealed package that is yellow or has yellow markings on it; and cage  12  may be in a sealed package that is red or has red markings on it. The purpose of this is so that the team of surgeons and staff that are involved in a surgical procedure can easily identify which of the cages  10 ,  11 , or  12  they should use based on the DEXA scan T-score of the patient&#39;s spinal column at the site of intervention, and they won&#39;t make a mistake by implanting the wrong cage. 
       FIG. 2  shows an exemplary embodiment of a cage  12  with anchors  21  and anchor plate  40 . The anchors  31  and anchor plate  40  also fit and are used with cages  10  and  11  in the same manner. Each of cages  10 ,  11  and  12  also has a center hole B where bone graft material can be packed prior to insertion into disk space within a spinal column of a patient. Anchors  21  have the same density as the cages with which they are associated. Anchors  21  can be made with the right amount of holes or channels A to give the anchors the density level that matches the density of the cage with which they are matched and packaged. Thus, anchors  21  can have the same density as cage  10 , the same density as cage  11 , or the same density as cage  12 . Anchors  21  that are matched with cage  10  in density have the least amount of holes or channels compared to anchors  21  that are matched with cages  11  or  12 . Anchors  21  that are matched with cage  11  in density have fewer holes or channels A than anchors  21  that are matched with cage  12  but more holes or channels A than anchors  21  that are matched with cage  10 . Anchors  21  that are matched with cage  12  in density have the most amount of holes or channels compared to anchors  21  that are matched with cages  11  or  12 . Anchors  21  can have the same indicia identifying their density level as cages  10 ,  11  and  12 , therefore indicating which of cages  10 ,  11  or  12  they match. In one embodiment, anchors  21  that are matched in density with cage  10  are located in a sealed package with cage  10 . As described above, the sealed package can be green in color or have green markings. And anchors  21  that are matched in density with cage  11  are located in a sealed package with cage  11 . As described above, the sealed package can be yellow in color or have yellow markings. And anchors  21  that are matched in density with cage  12  are located in a sealed package with cage  12 . As described above, the sealed package can be red in color or have red markings. This way it becomes more difficult to incorrectly match anchors  21  with the wrong counterpart cages  10 ,  11 , or  12 . 
     Anchors  21  are inserted through two upper holes  20  and two lower holes  30  on cage  10 ,  11  and  12  so that each of cages  10 ,  11  and  12  has four anchors, which can anchor the cage to a set of vertebrae in the spinal column of a patient. Anchors  21  that are inserted through anchor holes  20  are anchored to a first vertebra (superior), and anchors  21  that are inserted through anchor holes  30  are anchored or secured to a second vertebra (inferior) that is inferior to the first vertebra.  FIG. 3  is a side view that shows the orientation and angularity of the anchors relative to a cage, in this case cage  12 , although the same is true with cages  10  and  11 . 
       FIG. 4  shows an anchor of the present invention. When anchoring cages to vertebra, typically screws are used in the prior art. In the present invention, however, anchors  21  are used instead of screws. Anchors  21  have multiple ridges  24  that drive into bone and secure anchors  21  to the vertebral bone so that the anchors won&#39;t dislodge from the bone. The head of the anchor  22  can be struck to advance the distal end  23  of anchor into bone and lodge anchor  21  into bone. In alternative embodiments, screws instead of anchors  21  can also be used, although they may not be as effective in long-term stability within the bone. 
     Anchor plate  40  is shown in  FIG. 5 . Anchor plate  40  has a bayonet lock  42  that locks the anchor plate  40  to any one of cages  10 ,  11  or  12  when the bayonet lock  40  mates with an opening in the center of the faces of cages  10 ,  11 , and  12 . This prevents any anchors  21  from falling out or disassociating from cages  10 ,  11  or  12 . Front face  41  of anchor plate  40  can be tapped to engage and secure it to a cage  10 ,  11  or  12 . Guide posts  43  are used to engage with guide holes in the faces of cages  10 ,  11  or  12 . Like anchors  21 , anchor plate  40  can be matched to the density of cages  10 ,  11  or  12 . The interbody cage implants  10 ,  11 , or  12  may not be fusion implants that require anchoring, but may be cages that are implanted without anchoring. 
     In one embodiment, each kit  1  contains one or more of the following items: (i) a sealed green colored package containing cage  10 , four anchors  21  that are matched in density with cage  10 , and an anchor plate  40  that is matched in density with cage  10 ; (ii) a sealed yellow colored package containing cage  11 , four anchors  21  (optional) that are matched in density with cage  11 , and an anchor plate  40  (optional) that is matched in density with cage  11 ; (iii) a sealed red colored package containing cage  12 , four anchors  21  (optional) that are matched in density with cage  12 , and an anchor plate  40  (optional) that is matched in density with cage  12 ; (iv) an inserter  13  that is used to insert one of the cages into a disk space between two adjacent vertebrae; (v) instructions for use; and (vi) bone graft material (optional). 
     The instructions for use of kit  1  can include the following steps for use of the items found within kit  1 :
         i. determine the DEXA scan T-score of the patient&#39;s native bone at the site of surgical intervention in the spine (this can be done prior to the surgical procedure and be included in the patient&#39;s medical records or chart and confirmed by the surgical physician just prior to or during the surgical procedure;   ii. choose a cage from among the three cages  10 ,  11  or  12  that most closely matches the native bone&#39;s BMD based on the DEXA scan T-score of the patient&#39;s native bone at the site of implantation by doing the following:
           1. If the patient&#39;s native bone has a DEXA Scan T-score of −1 or higher, i.e., in the normal range of BMD indicated by a T-score that is in the green range, retrieve the green package containing cage  10 .   2. If the patient&#39;s native bone has as DEXA Scan T-score of between −1 and −2.5, i.e., in the low range of BMD indicated by a T-score that is in the yellow range, retrieve the yellow package containing cage  11 .   3. If the patient&#39;s native bone has a DEXA Scan T-score lower than −2.5, i.e., in the very low range of BMD indicated by a T-score that is in the red range, retrieve the red package containing cage  12 .   
           iii. Unseal the package that most closely matches your patient&#39;s DEXA scan T-score as indicated above, and do NOT unseal the other two sealed packages.   iv. Pack the bone graft material into the central hole B of the cage (optional) that you retrieved.   v. Take the cage from the unsealed package, which now has bone graft material in it (optional) and releasably couple it to the inserter.   vi. Use the inserter to guide the cage into the disk space at the site of intervention in the surgical procedure.   vii. Secure the cage within the spinal column using the four anchors that are in the same sealed package (now unsealed) as the cage that you used with this patient (optional).   viii. Secure the anchor plate over the exposed face of the cage by inserting the bayonet lock of the anchor plate into the opening on the face of the cage until it locks in place (optional).   ix. Once the procedure is completed, discard kit  1 .       

     Other embodiments of kits are also contemplated herein. For example, a kit that doesn&#39;t contain anchors and the cages are self anchoring as a result of being serrated or having other mechanisms that don&#39;t require anchors. In other embodiments, the kits contain only one of the implants, such as the most dense implant and not the others. In another embodiment, the kits contain two of the three implants set forth above and not all three implants. In another embodiment, the kits contain four or more implants, including the three implants set forth above and at least one more that is less dense than the least dense of the implants set forth above. 
     The same principals discussed above with respect to interbody spinal fusion cages can be applied to other types of orthopedic implants, such as knee implants and hip implants. In one embodiment, a hip implant kit is described, which contains at least three femoral stems, each having outer dimensions that are virtually identical. However, they are not the same weight, density, porosity, or surface area. The first one is the most dense, heaviest, least porous, and has the least surface area; the second is middle in density, porosity, weight and surface area; and the third is the least dense, lightest in weight, most porous, and has the most surface area. The stems can be manufactured from implantable metal, plastic, reinforced plastic, titanium, titanium cobalt, stainless steel, cobalt-chromium alloys, titanium and cobalt mixed metal, ceramic, PEEK or carbon fiber, or any combination thereof. In one embodiment, they are manufactured from titanium. 
     In one embodiment, each of the hip implant stems has identifying indicia that indicates whether it is the most dense, middle density, or least dense of the 3 stems. For example, the stems can be numbered  1 ,  2  and  3  or the reverse etched into the stems. In another embodiment, their density may be identified by a + − and = signs etched into the stems. In another embodiment, the stems may have a color painted on an area of the stem or the entirety of the stem. For example, the first stem that is the most dense may be green; the second stem in middle density may be yellow; and the third stem with the least density may be red to match the typical DEXA Scan color coded results. In another embodiment, each of the stems is located within a sealed package of its own that itself has an identifier that indicates whether it is the most dense, middle density or least dense of the stems. For example, the first stem of the highest density may be in a sealed package that is green or has green markings on it; the second stem in middle density may be in a sealed package that is yellow or has yellow markings on it; and the third stem of lowest density may be in a sealed package that is red or has red markings on it. The purpose of this is so that the team of surgeons and staff that are involved in a surgical procedure can easily identify which of the stems they should use based on the DEXA scan T-score of the patient&#39;s hip, and they won&#39;t make a mistake by implanting the wrong stem. 
     In yet another embodiment, a kit contains 3 or more acetabular components each having outer dimensions that are virtually identical. However, they are not the same weight, and they do not have the same density, porosity, or surface area. The first one is the most dense, heaviest, least porous, and has the least surface area; the second is middle in density, porosity, weight and surface area; and the third is the least dense, lightest in weight, most porous, and has the most surface area. The acetabular components can be manufactured from implantable metal, plastic, reinforced plastic, titanium, titanium cobalt, stainless steel, cobalt-chromium alloys, titanium and cobalt mixed metal, ceramic, PEEK or carbon fiber or any combination thereof. In one embodiment, they are manufactured from titanium. 
     In one embodiment, each of the acetabular components has identifying indicia that indicate whether it is the most dense, middle density, or least dense of the components. For example, the components can be numbered  1 ,  2  and  3  or the reverse etched into the components. In another embodiment, their density may be identified by a + − and = signs etched into the components. In another embodiment, the components may have a color painted on an area of the component or the entirety of the component. For example, the first acetabular component that is the most dense may be green; the second acetabular component in middle density may be yellow; and the third acetabular component with the least density may be red to match the typical DEXA Scan color coded results. In another embodiment, each of the acetabular components is located within a sealed package of its own that itself has an identifier that indicates whether it is the most dense, middle density or least dense of the components. For example, the first component of the highest density may be in a sealed package that is green or has green markings on it; the second component in middle density may be in a sealed package that is yellow or has yellow markings on it; and the third component of lowest density may be in a sealed package that is red or has red markings on it. 
     In one embodiment, kit  1  is associated with a specific demographic. For example, it may be associated with white females, black females, white males, black males, Hispanic females, Hispanic males, Asian females, Asian males, or other demographics based on gender, race, ethnic origin, height, weight, physical condition, medications the patient takes, history of illness or current illness, or other factor for which there may be a reference database for DEXA Scan T-scores. The specific kit that most closely matches a patient can be used, because the cages in that kit can have densities that are matched with the DEXA Scan T-score reference database that most closely matches that patient in terms of gender, race, ethnic origin, country of nationality or other factor. 
     Each of the kits described above can contain a instructions for use during a surgical procedure on a patient. The instructions can contain the following steps, which are described with respect to a kit containing 3 or more implants of the same type but different density/weight/surface area/porosity:
         i. determine the DEXA scan T-score of the patient&#39;s native bone at a site of surgical intervention in the spine (this can be done prior to the surgical procedure and be included in the patient&#39;s medical records or chart and confirmed by the surgical physician just prior to or during the surgical procedure in which an orthopedic implant is introduced into the patient;   ii. choose the implant from among the three implants that most closely matches the native bone&#39;s BMD based on the DEXA scan T-score;
           1. If the patient has a DEXA Scan T-score of −1 or higher, i.e., in the normal range of BMD indicated by a T-score that is in the green range, choose the implant that has a green indicia (or other indicia indicating highest density among the three cages) or is in green packaging;   2. If the patient has as DEXA Scan T-score of between −1 and −2.5, i.e., in the low range of BMD indicated by a T-score that is in the yellow range, choose the implant which has a yellow indicia (or other indicia indicating medium density among the 3 cages) or is in yellow packaging;   3. If the patient has a DEXA Scan T-score lower than −2.5, i.e., in the very low range of BMD indicated by a T-score that is in the red range, choose the implant, which has a red indicia (or other indicia indicating least density among the three cages) or is in the red packaging.   
           iii. Introduce the implant to the patient&#39;s native bone at the site of surgical intervention to the exclusion of the other two implants.   iv. Once the procedure is completed, discard the kit.       

     In another embodiment, a method of treating a patient who requires surgical implantation of an orthopedic implant is described. The method includes the steps of: determining the DEXA scan T-score of the patient&#39;s native bone at a site of surgical implantation where the implant will be in contact with the patient&#39;s native bone; choosing from among three or more otherwise identical implants an implant that has a density that is closest to the density of the patient&#39;s native bone at the site of surgical implantation based on the DEXA scan T-score of the patient&#39;s native bone; and using said implant in the surgical procedure to the exclusion of the other two or more implants. 
     In one embodiment, the method of treatment involves implanting an interbody spinal fusion cage in the spinal column. The physician or medical team performing the surgery may determine the patient&#39;s gender, race and/or ethnic origin or this step may be skipped. The physician may determine other factors unique to the patient as well, such as height, weight, physical condition, the medications the patient takes, history of illness or current illness. The physician or medical team performing the surgery then determines the DEXA scan T-score of the native bone at either or both the vertebra above and the vertebra below the location where the cage will be implanted. Once the DEXA scan T-score is determined, the physician or medical team performing the surgery will choose an interbody spinal fusion cage from among 3 or more cages that most closely matches the patient&#39;s DEXA scan T-score for either or both of the vertebrae that were scanned relative to the other two implants. The DEXA scan T-score may use a general reference such as a healthy person have peek bone at 30 years of age, or it may use a more specific reference, such as a black male. If a more specific reference is used, then a kit that is matched to that reference will be used rather than a kit that is matched to a general reference. If the DEXA scan T-score is in the green range or a score of −1 or higher indicating healthy bone in the normal range, then the cage having an indicia of highest density/weight and lowest surface area/porosity is chosen from among the 3 or more cages. That indicia may be a number, a sign, or a color on the cage or on the packaging of the cage. For example, the cage may be in a sealed package that is green or has green markings to indicate that it is the cage with the highest density/lowest porosity/greatest weight/lowest surface area. If the DEXA scan T-score is in the yellow range or a score of between about −1 and about −2.5 indicating bone that is lower than normal in density, then the cage having an indicia of medium density/porosity/surface area/weight is chosen from among the 3 or more cages. Again, that indicia may be a number, a sign or a color on the cage or on the packaging of the cage. For example, the cage may be in a sealed package that is yellow or has yellow markings to indicate that it is the cage with the medium amount of density/porosity/surface area/weight from among the three or more cages. If the DEXA scan T-score is in the red range or a score of −2.5 or lower indicating very low bone density and osteoporosis, then the cage having an indicia of low density/weight and high porosity/surface area is chosen from among the 3 or more cages. Again, this indicia may be a number, sign or color on the cage or on the packaging of the cage. For example, the cage may be in a sealed package that is red or has red markings to indicate that it is the cage with the lowest density/weight and highest porosity/surface area from among the three or more cages. Once the physician or medical team has chosen the interbody cage based on the DEXA scan T-score of the particular patient, that interbody cage is implanted in the spinal column at the site of intervention to the exclusion of the other two cages. This process may be repeated for any further cages that are to be implanted in the patient at other sites along the spinal column by matching the correct cage with the site of intervention based on the DEXA scan T-score for the additional site(s) of intervention along the spinal column. 
     In another method of treating a patient requiring an orthopedic implant, the medical team treating the patient first obtains information about the bone density of the patient&#39;s bone at the implantation site. The bone density can be determined with a DEXA (sometimes referred to as DXA) scan providing a T-score for the bone at the implantation site. Once the medical team (physician, surgeon, etc.) knows the T-score or the bone density of the bone at the implantation site as determined by DEXA scan or other means other than a DEXA scan, the medical team selects an orthopedic implant that is close in density to the bone at the site of implantation. The orthopedic implant has an identifier associated with it that provides an indication of the density of the implant. The identifier can indicate the actual density of the orthopedic implant or the relative density of the orthopedic implant compared to other orthopedic implants of the same type. For example, the identifier can indicate that a an interbody cage implant has a density of 1.10 g/cm3 or greater as an absolute measure of density. Or the identifier can indicate that among a number of interbody cage implants, the particular implant is more dense or less dense than other implants of the same type. For example, when using color as an identifier, the color green color on the interbody cage (or associated with the packaging of the interbody cage) may indicate that the interbody cage is more dense than another interbody cage having the color yellow as its identifier or yet another interbody cage having the color red as its identifier. Thus, the colors, green, yellow and red may be indicators of relative density among the three implants. The green may indicate that the implant is closest in density to natural healthy bone; the yellow may indicate that the implant is closest in density to bone having a low bone mass; and the red may indicate that the implant is closest in density to bone having the presence of osteoporosis; all relative to one another. 
     In one embodiment, if the bone of the patient at the site of implantation is healthy bone, the orthopedic implant selected by the medical team has about the same density as healthy natural bone having a T-score higher than −1.0 as measured by a DEXA scan (See  FIG. 7 ). The implant has an identifier that identifies it as having a density that is about the same as healthy natural bone having a T-score of −1.0 or higher. This makes it easy and convenient for the medical team to know that the implant they are using has a density that is about the same as natural healthy bone having a DEXA scan T-score of −1.0 or higher. The identifier can be a number, word, symbol, or color. In one embodiment, the identifier is a color, and the color is green, which is the color on a DEXA T-score chart that corresponds with healthy bone (see  FIG. 7 ). Thus, the orthopedic implant itself can be entirely green, or a portion or part of it can be green, indicating that the density of the implant is about the same as natural healthy bone or bone having a DEXA scan T-score of −1.0 or higher. The density of the implant having the green identifier can be about 1.10 g/cm 3  or greater, which generally corresponds with the density of healthy bone. 
     If the bone of the patient at the site of implantation has low bone mass, the orthopedic implant selected by the medical team has about the same density as natural bone having a T-score of −2.5 to −1.0 as measured by a DEXA scan, which corresponds with bone having a low bone mass (See  FIG. 7 ). The implant has an identifier that identifies it as having a density that is about the same as natural bone having a low bone mass and corresponding with a T-score of −2.5 to −1.0. This makes it easy and convenient for the medical team to know that the implant they are using has a density that is about the same as the bone at the site of implantation having the DEXA scan T-score of −2.5 to −1.0. The identifier can be a number, word, symbol, or color. In one embodiment, the identifier is a color, and the color is yellow, which is the color on a DEXA T-score chart that corresponds with low bone mass (see  FIG. 7 ). Thus, the orthopedic implant itself can be entirely yellow, or a portion or part of it can be yellow, indicating that the density of the implant is about the same as natural bone having low bone mass or bone having a DEXA scan T-score of −2.5 to −1.0. The density of the implant having the yellow identifier can be about 0.90 g/cm 3  to about 1.10 g/cm 3 , which generally corresponds with the density of bone having a low bone mass but not necessarily osteoporatic or having the presence of osteoporosis yet. 
     If the bone of the patient at the site of implantation has presence of osteoporosis (i.e., is osteoporatic), the orthopedic implant selected by the medical team has about the same density as natural bone having a T-score below −2.5 as measured by a DEXA scan, which corresponds with bone having a low bone mass (See  FIG. 7 ). The implant has an identifier that identifies it as having a density that is about the same as natural bone having the presence of osteoporosis and corresponding with a T-score below −2.5 (See  FIG. 7 ). This makes it easy and convenient for the medical team to know that the implant they are using has a density that is about the same as the osteoporatic bone at the site of implantation having the DEXA scan T-score below −2.5. The identifier can be a number, word, symbol, or color. In one embodiment, the identifier is a color, and the color is red, which is the color on a DEXA T-score chart that corresponds with the presence of osteoporosis (see  FIG. 7 ). Thus, the orthopedic implant itself can be entirely red, or a portion or part of it can be red, indicating that the density of the implant is about the same as natural bone having the presence of osteoporosis or bone having a DEXA scan T-score of below −2.5. The density of the implant having the red identifier can be below about 0.90 g/cm 3 ′ such as between about 0.60 gm/cm 3  and about 0.90 g/cm 3  or lower, which generally corresponds with the density of bone having the presence of osteoporosis. 
     Thus, if the patient&#39;s bone at the site of implantation is normal healthy bone, the medical team will select the orthopedic implant with the green identifier and implant that at the site of implantation. If the patient&#39;s bone at the site of implantation has low bone mass, the medical team will select the orthopedic implant with the yellow identifier and implant that at the site of implantation. If the patient&#39;s bone at the site of implantation has presence of osteoporosis, the medical team will select the orthopedic implant with the red identifier and implant that at the site of implantation. When the patient is undergoing a spinal procedure and requires an interbody cage implanted in between successive vertebrae, the implant can be an interbody cage or, alternatively, an interbody cage for spinal fusion. Interbody cages are placed between the bodies of 2 adjacent vertebrae—after removing the intervertebral disc that typically occupies this space. Interbody cages may be made of metal, polymer, ceramic, or a fusion of different materials. Two commonly used materials include titanium and polyetheretherketone (PEEK). The interbody cage can be coated with various materials, such as TiNANO®, a titanium plasma spray coating. The interbody cage will typically have a hollow center (such as shown in  FIG. 1 ), which is filled with a bone-growth promoting material, such as beta-tricalcium phosphate or the patient&#39;s own bone taken from a another location of the patient&#39;s skeletal anatomy. The interbody cage can also be expandable—a small cage is implanted (reducing the risk of nerve injury), which expands to a larger size after the implantation is done. The medical team can typically control the extent of expansion, to ensure that the surrounding nerves are not injured during the surgery. The interbody cage can be any size and variation described here or known in the art. However, the density of the interbody cage that is implanted will depend on the density of the patient&#39;s bone at the site of implantation as described here. 
     While the is susceptible to various modifications and alternative forms, specific examples thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.