Abstract:
A tool kit for performing biologic vertebral reconstruction has a drilling tool including a drill bit for forming a cavity in a vertebra to be reconstructed, a biologically active jacket sized for insertion into the cavity, an artificial bone injector attachable to the biologically active jacket, and an artificial bone material injectable into the biologically active jacket by the artificial bone injector. The biologically active jacket is inserted into a cavity formed in a vertebra to be reconstructed. The artificial bone material is inserted into the biologically active jacket and allowed to set.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/018,507, filed Jan. 23, 2008 now U.S. Pat. No. 8,292,961, the entire content of which is hereby incorporated by reference in this application. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     (NOT APPLICABLE) 
     BACKGROUND OF THE INVENTION 
     The invention relates to biologic vertebral reconstruction and, more particularly, to devices and methods for biologic vertebral reconstruction utilizing a biologically active jacket inserted into a cavity formed in a vertebra to be reconstructed. 
     Vertebral compression fractures are quite common in the elderly population. These fractures occur following minor injuries or spontaneously in the elderly osteoporotic spine. The other group of patients, usually middle aged, is those on long term steroid therapy for conditions such as chronic obstructive pulmonary disease. In the younger population with normal bone mineralization, vertebral fractures usually occur following high energy injuries such as motor vehicle accidents or a fall from heights. 
     Until recently, the elderly osteoporotic fractures were treated with pain control and bracing, depending on the severity of pain. However, over the last decade, there has been increasing use of minimally invasive procedures such as vertebroplasty and Kyphoplasty, whereby bone cement in a state of low viscosity is injected into the fractured vertebrae. As the bone cement sets it glues together the fragments of the fractured vertebra. Patients usually wake up from anesthesia with minimal discomfort. 
     As the use of this technique became more common, some adverse effects of the treatment have become apparent. At the time of surgery, patients may suffer from cardio-respiratory failure associated from infusion of large amounts of polymethylmethacrylate monomers into the circulation; in the case of vertebroplasty which requires injection of the cement at high pressures, extrusion of the cement into the venous channels and embolization into the pulmonary veins have been described; the cement may extrude through the cracks in the vertebrae into the spinal canal and compress the spinal cord or the spinal nerves with possible serious complications. 
     It is now being appreciated by surgeons that reinforcing an osteoporotic vertebra with bone cement may lead to fractures of the adjacent vertebra by compression against a very much hardened neighboring vertebra. The other concern is the fact that the bone cement will stay permanently in the vertebra because it is not resorbable. The long term consequence of this is not known, hence, its use is generally avoided in young vertebral fractures. 
     Treatments of young vertebral fractures are either conservative or surgical. The conservative approach is usually favored when the deformity of the vertebra is not severe and when there is no injury to neural elements. However, the biomechanical alterations caused even by an apparently minor deformity may lead to the development of chronic back pain. Surgical stabilization becomes imperative if there is spinal cord injury, usually associated with significant instability of the spine. The stabilization surgery usually involves massive surgical trauma through either or both anterior and posterior approaches. 
     BRIEF SUMMARY OF THE INVENTION 
     Significant aspects of the described embodiments include: (a) the technology involves implantation of a biologic material—artificial bone into the fractured vertebra such that the host bone will replace the artificial bone over a period of time making this a more suitable option than the currently used bone cement; (b) the implant is inserted into the vertebra in a biologically active jacket, to minimize its extrusion into the spinal canal and the paravertebral spaces; (c) because of its biomechanical characteristics, which approximate the host bone, there is relative protection of the neighboring vertebrae against fracture; and (d) the walls of the implant jacket may be impregnated with various substances to achieve various advantageous tasks. Examples of these include bone morphogenic proteins to stimulate incorporation of the artificial bone into the host bone, among others. 
     In an exemplary embodiment, a method of biologic vertebral reconstruction includes the steps of (a) forming a cavity in a vertebra to be reconstructed; (b) inserting a biologically active jacket in the cavity; and (c) injecting an artificial bone material into the biologically active jacket and allowing the artificial bone material to set. Step (a) may be practiced by drilling. In this context, the method may further include a step of collecting bone shavings during the drilling step. Preferably, step (a) is practiced by drilling in the vertebra to within five millimeters of the vertebra anterior cortex. 
     Prior to step (b), the method may include impregnating the biologically active jacket with a predetermined substance. The impregnating step may include impregnating the biologically active jacket with a catalyst to speed up the setting of the artificial bone material injected in step (c). Alternatively, the impregnating step may include impregnating the biologically active jacket with a bone morphogenic protein to stimulate incorporation of the artificial bone material into the vertebra to be reconstructed. As still another alternative, the impregnating step may include impregnating the biologically active jacket with an antibiotic as a prophylaxis against infection. 
     Prior to step (a), the method may include steps of inserting a trochar and a cannula into a target pedicle of the vertebra to be reconstructed, and removing the trochar, where step (a) is practiced by inserting a drilling tool through the cannula, drilling the cavity, and removing the drilling tool. In this context, step (b) may be practiced by inserting the biologically active jacket in the cavity through the cannula. 
     In another exemplary embodiment, a tool kit for performing biologic vertebral reconstruction, includes a drilling tool including a drill bit for forming a cavity in a vertebra to be reconstructed, and a biologically active jacket sized for insertion into the cavity. An artificial bone injector is attachable to the biologically active jacket. Additionally, an artificial bone material is injectable into the biologically active jacket by the artificial bone injector. The drilling tool may include a biopsy tool attachment for collecting bone shavings during drilling for a biopsy specimen. Preferably, the biologically active jacket is formed of various bioabsorbable synthetic materials. 
     In still another exemplary embodiment, a biologically active jacket for use in a biologic vertebral reconstruction includes expandable jacket walls and is sized for insertion into a cavity formed in a vertebra to be reconstructed. The biologically active jacket is formed of various bioabsorbable synthetic materials. For example, the biologically active jacket may be formed of polyglycolic acid. Generally, the biologically active jacket may be formed of a synthetic bioabsorbable woven fiber network. In one arrangement, the biologically active jacket is multi-loculated, where loculations include connecting valves made of overlapping wall fibers. The jacket walls may be formed as one of single layer, double layer, uni-compartmental, multi-compartmental, elastic, inelastic, etc. 
     The jacket may also be provided with a central fenestrated channel. In this context, the central fenestrated channel may be sealed at one end and may include a threaded connection at an opposite end, the threaded connection being configured to receive a cement injector. The jacket may additionally include concentric chambers disposed surrounding the central fenestrated channel, where each of the concentric chambers is partially loculated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects and advantages will be described in detail with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  show a longitudinal section view and a transverse section view of a biologically active jacket, respectively; 
         FIG. 2  illustrates a drill and biopsy tool; 
         FIG. 3  illustrates an artificial bone injector; 
         FIG. 4  illustrates the artificial bone injector coupled with the biologically active jacket; and 
         FIGS. 5A-5C  illustrate the steps in the vertebral reconstruction. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1A and 1B , a preferred embodiment includes a jacket  12  of synthetic bio-absorbable fiber network woven like cloth and may be uni-compartmental or multi-loculated. If multi-loculated the loculations  14  will have connecting valves  16  made of overlapping wall fibers acting as trap-doors that open up as the chamber is filled with artificial bone to allow filling of the neighboring chambers. The jacket  12  has a central fenestrated channel  18  that runs through the length of the jacket  12 . The channel  18  is sealed at its far end, and the near end is threaded  20  to allow a cement injector to be screwed on. 
     The multi-loculated design has concentric chambers with the central channel  18  running down the center of the innermost chamber. Each chamber may be partially loculated to reinforce the construct with multiple networks of fibers to minimize the risk of compression fracture of the implant itself. The artificial bone is injected into the central channel  18  from which the cement extrudes into the inner-most chamber. As the chamber  18  fills up, its wall stretches out to open up the valves  16  in its outer wall, which then fill up with the artificial bone, from the inner chamber, to open the valves in its outer wall, so on and so forth until all the chambers are full. The outer chambers  22  will also have fenestrations in the outer wall to allow some artificial bone to extrude and anchor into the host bone. The entire jacket  12  may be fitted with a network of channels extending into its interior from the outer wall. These channels will act as a conduit for vascular in-growth. 
     The fiber network of the jacket  12  may be used as a carrier for various factors by impregnating with a material suited for a particular purpose. For example, the material may be bone morphogenic proteins to stimulate osteo-induction and osteosynthesis within the artificial bone, antibiotics as a prophylaxis against infection, or the like. 
     The artificial bone  24  ( FIG. 3 ), in a preferred embodiment, is in a semi-liquid state which sets into a hard bone within a few minutes after injection into the implant jacket  12  in the vertebral body. A catalyst may also be impregnated into the walls of the jacket  12  to speed up the setting process. The ceramic bone (artificial bone)  24  may be made out of hydroxyapatite or other calcium compounds. 
       FIG. 2  illustrates a drill and biopsy tool  26  for creating a cavity in the vertebra to be reconstructed and for taking a biopsy sample. The device  26  includes a drill bit  28  at the tip, and immediately next to it is biopsy tool  30  for shaving of the host bone. The shaving tool  30  is hollow in its center for collection of bone shavings. At the conclusion of the drilling, enough bone shavings will have been collected for a biopsy specimen. The diameter of the shaving tool  30  is the same or slightly larger than the diameter of the unexpanded implant jacket  12 . 
     The artificial bone injector  32  is shown in  FIGS. 3 and 4 . The injector  32  includes a syringe with a plunger  34  that is operated by a screw mechanism  36 . As the handle  38  is turned clockwise, the plunger  34  goes deeper into the syringe and pushes out the artificial bone  24 . The nozzle  40  of the syringe is connected through a screw mechanism to an injection cannula  42 . The injection cannula  42  in turn includes a threaded connector  44  or the like that is engageable with the threads  20  on the biologically active jacket  12 . 
     The process of biologic vertebral reconstruction will be described with reference to  FIGS. 5A-5C . 
     The patient is placed on a radiolucent operating table in the prone or lateral position depending on the surgeon&#39;s preference. The skin is marked at the level of the target pedicles with the aid of fluoroscopic visualization. Through a small skin incision, a trochar and cannula are inserted under fluoroscopic visualization into the target pedicle. The position is checked in antero-posterior, lateral and oblique projections. The trochar is then inserted deeper into the vertebra to establish the preferred trajectory. The cannula  42  is then advanced until it is at least 3 mm deep to the posterior wall of the vertebra to be reconstructed. At this point, the trochar is removed leaving the cannula  42  in place. 
     The drill/biopsy tool  26  is inserted through the cannula, and hand drilling is performed by clockwise turning of the handle. See  FIG. 5A . Drilling is carried out to within 5 millimeters of the anterior cortex. The drill/biopsy tool  26  is then removed. 
     Subsequently, the unexpanded implant jacket  12  is attached to the injection cannula  42  and is inserted through the cannula  42  to the appropriate depth as determined by fluoroscopically reading the position of the radio-opaque marker at the advancing tip of the device. See  FIG. 5B . 
     The injection cannula  42  is attached to the syringe containing the artificial bone, and the artificial bone is injected while visualizing fluoroscopically. See  FIG. 5C . 
     Exemplary characteristics and properties of the device construction are outlined below. 
     1. Implant jacket: 
     a. Material—polymer of various bioabsorbable synthetic materials such as polyglycolic acid 
     b. Wall design
         i. Single layer   ii. Double layer wall   iii. Uni-compartmental   iv. Multi-compartmental   v. Elastic   vi. In-elastic, folded       

     c. Implantation mechanism
         i. Create void and then implant   ii. Implant to correct deformity as the artificial bone is injected       

     d. Filling mechanism 
     2. Artificial bone 
     a. Ceramic 
     b. Host bone 
     c. Host or ceramic impregnated with radio-opaque material for better visualization intra-operatively. 
     3. Instruments 
     a. Drill/biopsy tool 
     b. Artificial bone injection device 
     4. Technique 
     a. Prep 
     b. Insertion of jacket 
     c. Implantation of the artificial bone 
     The structure and method described herein provide for effective biologic vertebral reconstruction. The use of a biological material and artificial bone enables the host bone to replace the artificial bone over a period of time. Additionally, the structure of the biologically active jacket minimizes any impact into the spinal canal and the paravertebral spaces. Moreover, because of its biomechanical characteristics, which approximate the host bone, there is relative protection of the neighboring vertebra against fracture. Still further, the materials of the biologically active jacket may be impregnated with various substances to achieve various advantageous tasks. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.