MAGNETIC IMPLANTS WITH IMPROVED ANATOMICAL COMPATIBILITY
A distraction system includes a first distraction device having a first adjustable portion and a first distraction rod configured to telescope within the first adjustable portion, the first adjustable portion having contained therein a first rotatable magnetic assembly mechanically coupled to a first screw configured to axially telescope the first distraction rod. A second distraction device is provided and includes a second adjustable portion and a second distraction rod configured to telescope within the second adjustable portion, the second adjustable portion having contained therein a second rotatable magnetic assembly mechanically coupled to a second screw configured to axially telescope the second distraction rod. An adjustable joint connects one end of the first adjustable portion to one end of the second adjustable portion.
The field of the invention generally relates to medical devices for treating disorders of the skeletal system.
BACKGROUNDScoliosis is a general term for the sideways (lateral) curving of the spine, usually in the thoracic or thoracolumbar region. Often, there is also a rotation of the spine as well as curvature. Scoliosis is commonly broken up into different treatment groups, Adolescent Idiopathic Scoliosis, Early Onset Scoliosis and Adult Scoliosis.
Adolescent Idiopathic Scoliosis (AIS) typically affects children between ages 10 and 16, and becomes most severe during growth spurts that occur as the body is developing. One to two percent of children between ages 10 and 16 have some amount of scoliosis. Of every 1000 children, two to five develop curves that are serious enough to require treatment. The degree of scoliosis is typically described by the Cobb angle, which is determined, usually from x-ray images, by taking the most tilted vertebrae above and below the apex of the curved portion and measuring the angle between intersecting lines drawn perpendicular to the top of the top vertebrae and the bottom of the bottom. The term idiopathic refers to the fact that the exact cause of this curvature is unknown. Some have speculated that scoliosis occurs when, during rapid growth phases, the ligamentum flavum of the spine is too tight and hinders symmetric growth of the spine. For example, as the anterior portion of the spine elongates faster than the posterior portion, the thoracic spine begins to straighten, until it curves laterally, often with an accompanying rotation. In more severe cases, this rotation actually creates a noticeable deformity, wherein one shoulder is lower than the other. Currently, many school districts perform external visual assessment of spines, for example in all fifth grade students. For those students in whom an “S” shape or “C” shape is identified, instead of an “I” shape, a recommendation is given to have the spine examined by a physician, and commonly followed-up with periodic spinal x-rays.
Typically, patients with a Cobb angle of 20° or less are not treated, but are continually followed up, often with subsequent x-rays. Patients with a Cobb angle of 40° or greater are usually recommended for fusion surgery. It should be noted that many patients do not receive this spinal assessment, for numerous reasons. Many school districts do not perform this assessment, and many children do not regularly visit a physician, so often, the curve progresses rapidly and severely. In AIS, the ratio of females to males for curves under 10° is about one to one, however, at angles above 30°, females outnumber males by as much as eight to one. Fusion surgery can be performed on the AIS patients or on adult scoliosis patients. In a typical posterior fusion surgery, an incision is made down the length of the back and Titanium or stainless steel straightening rods are placed along the curved portion. These rods are typically secured to the vertebral bodies, for example with bone screws, or more specifically pedicle screws, in a manner that allows the spine to be straightened. Usually, at the section desired for fusion, the intervertebral disks are removed and bone graft material is placed to create the fusion. If this is autologous material, the bone is harvested from a hip via a separate incision.
Alternatively, the fusion surgery may be performed anteriorly. A lateral and anterior incision is made for access. Usually, one of the lungs is deflated in order to allow access to the spine from this anterior approach. In a less-invasive version of the anterior procedure, instead of the single long incision, approximately five incisions, each about three to four cm long are made in several of the intercostal spaces (between the ribs) on one side of the patient. In one version of this minimally invasive surgery, tethers and bone screws are placed and are secured to the vertebra on the anterior convex portion of the curve. Currently, clinical trials are being performed which use staples in place of the tether/screw combination. One advantage of this surgery in comparison with the posterior approach is that the scars from the incisions are not as dramatic, though they are still located in a visible area, when a bathing suit, for example, is worn. The staples have had some difficulty in the clinical trials. The staples tend to pull out of the bone when a critical stress level is reached.
Commonly, after surgery, the patient will wear a brace for a few months as the fusing process occurs. Once the patient reaches spinal maturity, it is difficult to remove the rods and associated hardware in a subsequent surgery, because the fusion of the vertebra usually incorporates the rods themselves. Standard practice is to leave this implant in for life. With either of these two surgical methods, after fusion, the patient's spine is now straight, but depending on how many vertebra were fused, there are often limitations in the degree of flexibility, both in bending and twisting. As these fused patients mature, the fused section can impart large stresses on the adjacent non-fused vertebra, and often, other problems including pain can occur in these areas, sometimes necessitating further surgery. Many physicians are now interested in fusionless surgery for scoliosis, which may be able to eliminate some of the drawbacks of fusion.
One group of patients in which the spine is especially dynamic is the subset known as Early Onset Scoliosis (EOS), which typically occurs in children before the age of five. This is a more rare condition, occurring in only about one or two out of 10,000 children, but can be severe, sometimes affecting the normal development of organs. Because of the fact that the spines of these children will still grow a large amount after treatment, non-fusion distraction devices known as growing rods and a device known as the VEPTR—Vertical Expandable Prosthetic Titanium Rib (“Titanium Rib”) have been developed. These devices are typically adjusted approximately every six months, to match the child's growth, until the child is at least eight years old, sometimes until they are 15 years old. Each adjustment requires a surgical incision to access the adjustable portion of the device. Because the patients may receive the device at an age as early as six months old, this treatment requires a large number of surgeries. Because of the multiple surgeries, these patients have a rather high preponderance of infection and other complications. A new magnetically controlled growing rod is now being used which allows adjustments to be done non-invasively, as reported in the article “Magnetically controlled growing rods for severe spinal curvature in young children: a prospective case series”, Cheung et. al., Lancet, 2012.
Returning to the AIS patients, the treatment methodology for those with a Cobb angle between 20° and 40° is quite controversial. Many physicians prescribe a brace (for example, the Boston Brace), that the patient must wear on their body and under their clothes 18 to 23 hours a day until they become skeletally mature, for example to age 16. Because these patients are all passing through their socially demanding adolescent years, it is quite a serious prospect to be forced with the choice of either wearing a somewhat bulky brace that covers most of the upper body, having fusion surgery that may leave large scars and also limit motion, or doing nothing and running the risk of becoming disfigured and possibly disabled. It is commonly known that many patients have at times hidden their braces, for example, in a bush outside of school, in order to escape any related embarrassment. The patient compliance with brace wearing has been so problematic, that there have been special braces constructed which sense the body of the patient, and keep track of the amount of time per day that the brace is worn. Patients have even been known to place objects into unworn braces of this type in order to fool the sensor. Coupled with the inconsistent patient compliance with brace usage, is a feeling by many physicians that braces, even if used properly, are not at all effective at curing scoliosis. These physicians may agree that bracing can possibly slow down or even temporarily stop curve (Cobb angle) progression, but they have noted that as soon as the treatment period ends and the brace is no longer worn, often the scoliosis rapidly progresses, to a Cobb angle even more severe than it was at the beginning of treatment. Some say the reason for the supposed ineffectiveness of the brace is that it works only on a portion of the torso, and not on the entire spine. Currently a 500 patient clinical trial known as BrAIST (Bracing in Adolescent Idiopathic Scoliosis Trial) is enrolling patients, 50% of whom will be treated with the brace and 50% of who will simply be watched. The Cobb angle data will be measured continually up until skeletal maturity, or until a Cobb angle of 50° is reached, at which time the patient will likely undergo surgery.
Though this trial began as a randomized trial, it has since been changed to a “preference” trial, wherein the patients choose which treatment arm they will be in. This is partially because so many patients were rejecting the brace. Many physicians feel that the BrAIST trial will show that braces are completely ineffective. If this is the case, the quandary about what to do with AIS patients who have a Cobb angle of between 20° and 40° will only become more pronounced. It should be noted that the “20° to 40° ” patient population is as much as ten times larger than the “40° and greater” patient population.
Currently, genetic scientists have found and continue to find multiple genes that may predispose scoliosis. Though gene tests have been developed, including a scoliosis score for risk of curve progression, some are still skeptical as to whether gene therapy would be possible to prevent scoliosis. However the existence of a scoliosis gene would no doubt allow for easier and earlier identification of probable surgical patients.
Scoliosis is also present in patients with mature spines. One type of malady in mature patients is known as adult idiopathic scoliosis. It should be noted for reference purposes that the spine is actually mature in girls as young as fifteen or sixteen years old. In boys the maturity often occurs at a slightly older age of about eighteen years. Adult idiopathic scoliosis should be differentiated from what is known as de novo scoliosis or degenerative scoliosis, and which is predominantly caused by degeneration of the disc and facets with age., often combined with poor bone quality from osteopenia and osteoporosis. Oftentimes, fusion surgery in patients having mature spines with deformities requires significantly invasive measures to straighten the spine. This includes performing osteotomies (cutting out sections of the vertebrae) performed either from a posterior access or from an anterior access to the spine. Some types of osteotomies include Smith-Peterson osteotomy (SPO), pedicle subtraction osteotomy (PSO), and vertebral column resection (VCR). Because these osteotomies require more time and more invasive surgical techniques, their use adds significant cost and complications to fusion surgery.
There is a large population of mature spine patients with untreated scoliosis, in extreme cases with a Cobb angle as high as or greater than 60°, or even higher than 90°. In some cases, straightening this spine during a single fusion surgery could be problematic, even causing severe neurological problems. Many of these adults, though, do not have pain associated with this deformity while untreated, and live relatively normal lives, though oftentimes with restricted mobility and motion. It is contemplated that the devices and methods described herein also have application in the treatment of adult scoliosis. Adult scoliosis can continue to worsen with time. Though the adult is skeletally mature, the Cobb angle may still continue to increase with time. The relaxation or slight reduction in height that occurs in adults may have some relation with this increase in Cobb angle. Curves above 100° are rare, but they can be life-threatening if the spine twists the body to the point where pressure is put on the heart and lungs. The magnetically controlled growing rod has been described before as a treatment method of adult scoliosis, e.g., allowing adult scoliosis to be treated with a minimally invasive and/or fusionless approach. In addition, gradual adjustment of the spine may be desired, especially in the cases of very high Cobb angles. For example, it may be desired to limit the amount of stresses on the bones or on the implant materials, by first adjusting an adult scoliosis patient so that their Cobb angle is reduced 50% or less, then 15% or less each few months, until the spine is straight. As one example, the initial surgical implantation may reduce the Cobb angle by 50% or more by the physician performing manual distraction on the spine. Post-implantation, the Cobb angle can be reduced in a non-invasive manner by application of a constant or periodically changing distraction force. A first non-invasive adjustment may result in a Cobb angle reduction of less than 50%. Additional non-invasive adjustments may be performed which result in even smaller Cobb angle reductions (e.g., less than 15% from original Cobb angle).
In this regard, the Cobb angle may be reduced by a smaller amount over the next few months (e.g., less than around 15% each month post-operation). The non-invasive adjustment of a fusionless implant made possible by the invention allows for a gradual adjustment scheme of this nature. Moreover, the distraction forces used over this period of time are generally low (e.g., distraction force less than 45 pounds) which means, among other things, less patient discomfort, and less chance of failure within the adjustable rods. Non-invasive adjustments may be periodically performed when the patient visits his or her physician. This may occur over a span of more than one week (e.g., a several week process). Of course, the number and periodicity of the adjustments is a function of, among other things, the Cobb angle of the patient.
Oftentimes, the adult spine has less dense or even osteoporotic bone, so it may be desirable to combine the sort of gradual adjustment described here with additional methods to strengthen the bone, for example the bone of the vertebral bodies. One method is to strengthen the vertebral body by performing prophylactic vertebroplasty or kyphoplasty, wherein the internal area of the vertebral body is strengthened, for example by injection of bone cement or Polymethyl Methacrylate (PMMA). Additionally, if pedicle screws are used for fixation, the surface of the screws may be treated with a biologic material that promotes bone growth, or a surface characteristic that improves bone adhesion. Any of these methods would further improve the possibilities that the distraction forces would not cause fracture or other damage to the vertebrae of the patient.
In use, magnetically controlled growing rods are often cut and bent in the desired curves prior to implantation in the patient. It is common practice then to test the magnetically controlled growing rod immediately prior to placing in the patient (for example after cutting and bending) to confirm that it is completely operational. This often involves placing a sterile cover over the external adjustment device that is used to lengthen the magnetically controlled growing rod. This additional operation is not ideal because of the extra effort to bring the external adjustment device into the operating room, the extra effort to maintain sterility, and the fact that the external adjustment device contains powerful magnets, which can attract structures of the surgical table as well as surgical instruments.
SUMMARYIn one embodiment, a distraction system includes a first distraction device having a first adjustable portion and a first distraction rod configured to telescope within the first adjustable portion, the first adjustable portion having contained therein a first rotatable magnetic assembly mechanically coupled to a first screw configured to axially telescope the first distraction rod. The system includes a second distraction device having a second adjustable portion and a second distraction rod configured to telescope within the second adjustable portion, the second adjustable portion having contained therein a second rotatable magnetic assembly mechanically coupled to a second screw configured to axially telescope the second distraction rod. The distraction system includes an adjustable joint connecting one end of the first adjustable portion to one end of the second adjustable portion.
In another embodiment, a distraction system includes a first distraction device with a first adjustable portion having contained therein a first rotatable magnetic assembly. The system includes a second distraction device with a second adjustable portion having contained therein a second rotatable magnetic assembly; and a common distraction rod having first and second opposing ends, wherein a first end of the common distraction rod is mechanically coupled to the first rotatable magnetic assembly and wherein a second end of the common distraction rod is mechanically coupled to the second rotatable magnetic assembly.
In yet another embodiment, a distraction system includes an adjustable portion having contained therein a rotatable magnetic assembly, the adjustable portion being at least one of curved or angled; and a distraction rod mechanically coupled to the rotatable magnetic assembly via a screw and configured for telescopic movement relative to the adjustable portion.
In still another embodiment, a distraction system includes an adjustable portion having contained therein a rotatable magnetic assembly; a screw operatively coupled to the rotatable magnetic assembly; and a distraction rod having a recess formed therein, the recess containing a nut having internal threads, the nut having first and second collared ends disposed on either side of the internal threads, wherein the screw interfaces with the internal threads of the nut and wherein rotation of the rotatable magnetic assembly effectuates telescopic movement of the distraction rod relative to the adjustable portion.
In another embodiment, a distraction system includes an adjustable portion having contained therein a rotatable magnetic assembly; a distraction rod mechanically coupled to the rotatable magnetic assembly via a screw and configured for telescopic movement relative to the adjustable portion; and a distraction tester including a body having a cylindrical cavity passing through the body, wherein the distraction tester has a first circumferential portion of the body that has a higher mass of magnetically permeable material than a second circumferential portion, spaced apart from the first circumferential portion.
In many Adolescent Idiopathic Scoliosis (AIS) patients with a Cobb angle of 40° or greater, spinal fusion surgery is typically the first option. Alternatively, non-fusion surgery may be performed, for example with the distraction device 200 of
Each vertebra is different from the other vertebra by its size and shape, with the upper vertebra generally being smaller than the lower vertebra. However, generally, the vertebrae have a similar structure and include a vertebral body 516, a spinous process 518, 520, laminae 526, transverse processes 521, 522 and pedicles 524. In this embodiment, the distraction device 200 includes a distraction rod 206 which is adjustable (lengthwise) via a coupled adjustable portion 208. The distraction device 200 also includes a lower extension 209 which may be a short rod segment. The distraction device 200 is fixated to the spine 500 via hooks 600, 601 at the upper end 202 of the distraction rod 206. Alternatively, a clamp may be secured around an adjacent rib (not shown) or rib facet. In still another alternative, a pedicle screw system may be used.
Referring back to
Because a scoliotic spine is also rotated (usually the center section is rotated to the right in AIS patients), the non-fusion embodiment presented here allows de-rotation of the spine 500 to happen naturally, because there is no fixation at the middle portion of the distraction device 200.
In order to further facilitate this de-rotation, the distraction device 200 may allow for free rotation at its ends. For example, the adjustable portion 208 may be coupled to the spine via an articulating joint. U.S. Patent Application Publication Nos. 2009-0112207 and 2010-0094302, both of which are incorporated by reference, describe various articulating interfaces and joints that may be utilized to couple the adjustable portion 208 to the connecting rods or the like. These Published Applications further describe various distraction rod embodiments and methods of use that may be used with inventions described herein.
As noted, the distraction rod 206 and the lower extension 209 may be bent by the user (or supplied pre-curved) with the typical shape of a normal saggital spine, but it should also be noted that the curve may be slightly different than standard scoliosis fusion instrumentation, because in the non-fusion embodiment described herein, the distraction device 200 is not usually flush with the spine but rather is placed either subcutaneous or sub-fascial, and thus is not completely below the back muscles. In these less invasive methods, the only portions of the distraction device 200 that are designed to be placed below the muscles are the hooks 600, 601 and the portion of the distraction rod 206 immediately adjacent the hooks 600, 601, the pedicle screw system 531 and the lower extension 209. Thus,
By design, the distraction rod 206 is configured to be distracted from the adjustable portion, increasing the total device length via magnetic adjustment. The preferred design for a distraction device 200, does not allow significant circumferential motion between the distraction rod 206 and the adjustable portion 208.
Annularly contained between the magnetic assembly 336 and the expanded portion 305 of the tubular housing 326 is a cylindrical maintenance member 303 made from a magnetically permeable material, such as 400 series stainless steel. The cylindrical maintenance member 303 can be seen in isolation in
The distraction device 700 of
Turning now to
Distraction device 900 in
While
As illustrated, the entire body of the manual distraction tester 1100 is monolithic and configured from a single material, for example 420 stainless steel, although other materials having magnetic permeability may be used. Thought the minimally magnetic circumferential portion 1059 has some attraction to magnet poles, the significantly larger mass of the maximally magnetic circumferential portion 1061 dominates. One way to achieve the difference in magnetic attraction between the two circumferential portions, if the manual distraction tester 1100 is made entirely from 420 stainless steel, is to make, for example the axial thickness of the minimally magnetic circumferential portion 1059 small (for example 2.5 mm) and the axial thickness of the maximally magnetic circumferential portion comparatively large (for example 19 mm). The manual distraction tester 1100 is axially slid onto the distraction device 1000 in the direction of the arrow 1065 in
The manual distraction tester 1100 is turned in a first direction 1069, magnetically causing the radially-poled cylindrical magnet to turn and in turn to cause lengthening of the distraction device 1000. A mark 1071 on the distraction rod 1006 can easily be seen moving in relation to an end 1073 of the adjustable portion 1008 of the distraction device 1000.
A distraction rod 1206 is shown in
When adjusting the length of the distraction device, the lead screw 360 turns within nut 1214 because protrusions 1222a of distraction rod 1206 and protrusions 1222b of nut 1214 are held within longitudinal grooves 224, 324 of the housing and so they remain rotationally static with respect to adjustable portion 308, while allowing distraction rod 1206 to axially adjust in relation to adjustable portion 308. This collared nut 1214 allows a stability of the distraction length of the distraction device that precludes the need for the cylindrical maintenance member 303 of
While embodiments have been shown and described, various modifications may be made without departing from the scope of the inventive concepts disclosed herein. The embodiments have application in many other medical conditions, including lengthening of bones by intramedullary placed distraction devices or by distracting plates placed on the exterior of bones. The invention(s), therefore, should not be limited, except to the following claims, and their equivalents.
Claims
1. A distraction system comprising:
- a first distraction device comprising a first adjustable portion and a first distraction rod configured to telescope within the first adjustable portion, the first adjustable portion having contained therein a first rotatable magnetic assembly mechanically coupled to a first screw configured to axially telescope the first distraction rod;
- a second distraction device comprising a second adjustable portion and a second distraction rod configured to telescope within the second adjustable portion, the second adjustable portion having contained therein a second rotatable magnetic assembly mechanically coupled to a second screw configured to axially telescope the second distraction rod; and
- an adjustable joint connecting one end of the first adjustable portion to one end of the second adjustable portion.
2. The distraction system of claim 1, wherein the adjustable joint comprises a first interfacing surface coupled to the first adjustable portion and a second interfacing surface coupled to the second adjustable portion, and a locking member configured to secure the first interfacing surface to the second interfacing surface.
3. The distraction system of claim 2, wherein the locking member comprises a screw.
4. The distraction system of claim 2, wherein the first interfacing surface and the second interfacing surface comprise circumferentially arrayed teeth.
5. The distraction system of claim 1, wherein the adjustable joint comprises a locking pivot joint.
6. A distraction system comprising:
- a first distraction device comprising a first adjustable portion having contained therein a first rotatable magnetic assembly;
- a second distraction device comprising a second adjustable portion having contained therein a second rotatable magnetic assembly; and
- a common distraction rod having first and second opposing ends, wherein a first end of the common distraction rod is mechanically coupled to the first rotatable magnetic assembly and wherein a second end of the common distraction rod is mechanically coupled to the second rotatable magnetic assembly.
7. The distraction system of claim 6, wherein the common distraction rod is bendable.
8. The distraction system of claim 6, wherein the common distraction rod is straight.
9. The distraction system of claim 6, wherein the common distraction rod is curved.
10. A distraction system comprising:
- an adjustable portion having contained therein a rotatable magnetic assembly, the adjustable portion being at least one of curved or angled; and
- a distraction rod mechanically coupled to the rotatable magnetic assembly via a screw and configured for telescopic movement relative to the adjustable portion.
11. The distraction system of claim 10, wherein the curve or angle of the adjustable portion defines an angle within the range of about 3° and 35°.
12. The distraction system of claim 11, wherein the adjustable portion comprises a bendable tube.
13. The distraction system of claim 10, further comprising a universal joint coupling the screw to the rotatable magnetic assembly.
14. A distraction system comprising:
- an adjustable portion having contained therein a rotatable magnetic assembly;
- a screw operatively coupled to the rotatable magnetic assembly; and
- a distraction rod having a recess formed therein, the recess containing a nut having internal threads, the nut comprising first and second collared ends disposed on either side of the internal threads, wherein the screw interfaces with the internal threads of the nut and wherein rotation of the rotatable magnetic assembly effectuates telescopic movement of the distraction rod relative to the adjustable portion.
15. The distraction system of claim 14, wherein the nut is bonded directly to the distraction rod.
16. The distraction system of claim 14, wherein the adjustable portion comprises a housing having a plurality of longitudinal grooves disposed along an inner surface thereof and wherein the nut comprises a plurality of protrusions configured to fit within the plurality of longitudinal grooves.
17. The distraction system of 14, wherein the distraction rod comprises a cavity disposed along the recess and the nut comprises a flange dimensioned to fit within the cavity.
18. The distraction system of claim 14, further comprising a gap formed between an outer diameter of the nut and an inner diameter of the recess.
19. A distraction system comprising:
- an adjustable portion having contained therein a rotatable magnetic assembly
- a distraction rod mechanically coupled to the rotatable magnetic assembly via a screw and configured for telescopic movement relative to the adjustable portion; and
- a distraction tester comprising a body having a cylindrical cavity passing through the body, wherein the distraction tester has a first circumferential portion of the body that has a higher mass of a magnetically permeable material as compared to a second circumferential portion of the body spaced apart from the first circumferential portion.
20. The distraction device of claim 19, wherein the first circumferential portion of the body is substantially thicker than the second circumferential portion of the body.
21. The distraction device of claim 1, wherein the first and second rotatable magnetic assemblies comprise at least one of a magnet or circumferentially arrayed magnetically permeable elements.
22. The distraction device of claim 6, wherein the first and second rotatable magnetic assemblies comprise at least one of a magnet or circumferentially arrayed magnetically permeable elements.
23. The distraction device of claim 10, wherein the rotatable magnetic assembly comprises at least one of a magnet or circumferentially arrayed magnetically permeable elements.
24. The distraction device of claim 14, wherein the rotatable magnetic assembly comprises at least one of a magnet or circumferentially arrayed magnetically permeable elements.
Type: Application
Filed: Jun 15, 2012
Publication Date: Dec 19, 2013
Inventors: Arvin Chang (Yorba Linda, CA), Blair Walker (Mission Viejo, CA), Scott Pool (Laguna Hills, CA), Peter P. Tran (Irvine, CA)
Application Number: 13/525,058
International Classification: A61B 17/70 (20060101);