Abstract:
A spinal implant in one embodiment includes an implant for insertion between two opposite spaced vertebrae of a spine, comprising an upper section having a substantially rectangular cross section and comprising a toothed top retaining member and a peripheral surface; a lower section having a substantially rectangular cross section and comprising a toothed bottom retaining member and a peripheral surface; an intermediate padding member for fastening the upper section and the lower section together; two three-dimensional matrix structures formed in the upper section and the lower section respectively and on the peripheral surfaces of the upper section and the lower section respectively as support; and a plurality of holes formed through at least one of three directions of each of the three-dimensional matrix structures.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The invention relates to surgical procedures for stabilizing the spine and more particularly to an improved implant having padded bone engaging projections for use in such procedure. 
         [0003]    2. Description of Related Art 
         [0004]    In human anatomy, the vertebral column (backbone or spine) is a column usually consisting of 24 articulating vertebrae (including 7 vertebrae in cervical region, 12 vertebrae in thoracic region, and 5 vertebrae in lumbar region) and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs. It houses and protects the spinal cord in its spinal canal. 
         [0005]    Intervertebral discs lie between adjacent vertebrae in the spine. Each intervertebral disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together. An intervertebral disc consists of an outer annulus fibrosus surrounding the inner nucleus pulposus. The annulus fibrosus consists of several layers of fibrocartilage. The strong annular fibers contain the nucleus pulposus and distribute pressure evenly across the disc. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel with the consistency of jelly. The nucleus of the intervertebral disc acts as a shock absorber, absorbing the impact of the body&#39;s daily activities and keeping the two vertebrae separated. 
         [0006]    Chronic low back pain is a perplexing problem facing the field of orthopedic surgery. Low back pain can be avoided by preventing relative motion between spinal vertebrae (commonly known as intervertebral stabilization). To abate low back pain, stabilization is directed to stabilizing contiguous vertebrae in the lumbar region of the spine. Surgical techniques seek to rigidly join vertebrae which are separated by a degenerated disc. One typical technique is to partially remove a degenerated disc and to insert a bone graft into the void formed by the removed disc. Spinal implants are also employed and are either acting along or in combination with bone fragments to replace the use of bone grafts. 
         [0007]    However, improvements of spinal implant are still desired in order to enhance patient safety and the probability of a satisfactory recovery. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore one object of the invention to provide an implant for insertion between two opposite spaced vertebrae of a spine, comprising an upper section having a substantially rectangular cross section and comprising a toothed top retaining member and a peripheral surface; a lower section having a substantially rectangular cross section and comprising a toothed bottom retaining member and a peripheral surface; an intermediate padding member for fastening the upper section and the lower section together; two three-dimensional matrix structures formed in the upper section and the lower section respectively and on the peripheral surfaces of the upper section and the lower section respectively as support; and a plurality of holes formed through at least one of three directions of each of the three-dimensional matrix structures. 
         [0009]    It is another object of the invention to provide an implant for insertion between two opposite spaced vertebrae of a spine, comprising an upper section having a substantially rectangular cross section and comprising a toothed top retaining member and a peripheral surface; a lower section having a substantially rectangular cross section and comprising a toothed bottom retaining member and a peripheral surface; an intermediate padding member for fastening the upper section and the lower section together; two three-dimensional matrix structures formed in the upper section and the lower section respectively and on the peripheral surfaces of the upper section and the lower section respectively as support; a plurality of holes formed through at least one of three directions of each of the three-dimensional matrix structures; a longitudinal channel formed in central portions of each of the three-dimensional matrix structures and the padding member and communicating with the holes; and an elastic device disposed in the channel. 
         [0010]    The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a spinal implant according to a first preferred embodiment of the invention; 
           [0012]      FIGS. 2 and 3  are sectional views taken along line  2 - 2  and line  3 - 3  of  FIG. 1  respectively; 
           [0013]      FIG. 4  schematically depicts a fixing of the spinal implant in a bore formed between opposing vertebrae of a spine; 
           [0014]      FIG. 5  is a perspective view of a spinal implant according to a second preferred embodiment of the invention; 
           [0015]      FIGS. 6 and 7  are sectional views taken along line  6 - 6  and line  7 - 7  of  FIG. 5  respectively; 
           [0016]      FIG. 8  schematically depicts a fixing of the spinal implant of  FIG. 5  in a bore formed between opposing vertebrae of a spine; 
           [0017]      FIG. 9  is a perspective view of a spinal implant according to a third preferred embodiment of the invention; and 
           [0018]      FIG. 10  is a perspective view of a spinal implant according to a fourth preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring to  FIGS. 1 to 4 , a spinal implant in accordance with a first preferred embodiment of the invention is shown. The spinal implant has a substantially rectangular cross section and comprises the following components as discussed in detail below. 
         [0020]    An upper section  10  is formed of a composite material being sturdy and highly resistant to chemicals. The composite material may be carbon fiber or PEEK (polyetheretherketone). Alternatively, the upper section  10  is formed of alloy such as stainless steel, cobalt-chromium-molybdenum alloy, titanium, or titanium alloy. Still alternatively, the upper section  10  is formed of polymer such as UHMWPE (ultra high molecular weight polyethylene), PMMA (polymethylmethacrylate), silicon rubber, or ultra high molecular polyethylene. Still alternatively, the upper section  10  is formed of ceramic such as aluminum oxide, calcium phosphate tri-basic, or fiber glass. 
         [0021]    The upper section  10  has a top surface  11  with a top retaining member  12  formed thereon. The top retaining member  12  is shaped as a plurality of rows of teeth (i.e., bone engaging projections), an engaging bottom  13 , and a three-dimensional matrix structure  15  formed between the top surface  11  and the engaging bottom  13  as support. The three-dimensional matrix structure  15  can provide mechanical properties such as enhanced resistance to pressure, enhanced resistance to stress, and enhanced resistance to tension to the upper section  10 . A plurality of holes  14  are formed through each of three directions of the three-dimensional matrix structure  15 . The holes  14  occupy about 1% to 90% of the volume of the upper section  10  depending upon engineering choice of design. Each hole  14  has a bore of about 150 μm to 1,000 μm. 
         [0022]    A lower section  20  is formed of a composite material being sturdy and highly resistant to chemicals. The composite material may be carbon fiber or PEEK (polyetheretherketone). Alternatively, the lower section  20  is formed of alloy such as stainless steel, cobalt-chromium-molybdenum alloy, titanium, or titanium alloy. Still alternatively, the lower section  20  is formed of polymer such as UHMWPE (ultra high molecular weight polyethylene), PMMA (polymethylmethacrylate), silicon rubber, or ultra high molecular polyethylene. Still alternatively, the lower section  20  is formed of ceramic such as aluminum oxide, calcium phosphate tri-basic, or fiber glass. 
         [0023]    The lower section  20  is an inverted mirror image of the upper section  10  and comprises a bottom surface  21  with a bottom retaining member  22  formed thereon. The bottom retaining member  22  is shaped as a plurality of rows of teeth (i.e., bone engaging projections). The lower section  20  further comprises an engaging top  23  and a supporting three-dimensional matrix structure  25  formed between the bottom surface  21  and the engaging top  23 . The three-dimensional matrix structure  25  can provide mechanical properties such as enhanced resistance to pressure, enhanced resistance to stress, and enhanced resistance to tension to the lower section  20 . A plurality of holes  24  are formed through each of three directions of the three-dimensional matrix structure  25 . The holes  24  occupy about 1% to 90% of the volume of the lower section  20  depending upon engineering choice of design. Each hole  24  has a bore of about 150 μm to 1,000 μm. 
         [0024]    A padding member  30  is formed of silicon rubber in this embodiment. The padding member  30  has excellent properties including great flexibility, oxidation resistant, corrosion proof, and water resistant. The padding member  30  comprises an engaging top  31  and an engaging bottom  32 . The engaging top and bottom  31 ,  32  are permanently secured to the upper section  10  and the lower section  20  respectively by subjecting to heat. 
         [0025]    As shown in  FIG. 4  specifically, a physician may insert the spinal implant into a bore formed between an upper vertebra  61  and a lower vertebra  62  of a spine. The teeth of the top retaining member  12  and the teeth of the bottom retaining member  22  thus grasp the upper vertebra  61  and the lower vertebra  62  respectively (i.e., the spinal implant being fastened). Moreover, an appropriate biocompatible material may filled in the voids of the holes  14  and  24  for stuffing and stabilization purposes. The biocompatible material may be calcium phosphate tri-basic (CaP) or hydroxyapattie (HA) (Ca 10 (PO 4 ) 6 (OH) 2 ). 
         [0026]    The holes  14  and  24  allow body tissues to grow therein for the health of spinal bone. Moreover, the fastening of the upper and lower vertebrae  61 ,  62  and the top and bottom retaining members  12 ,  22  is reliable so as to rigidly join the upper and lower vertebrae  61 ,  62 . As a result, intervertebral stabilization is carried out. 
         [0027]    In addition, the provision of the three-dimensional matrix structures  15  and  25  can significantly increase resistance to pressure, stress, and tension to the spinal implant. Moreover, the padding member  30  acts as a shock absorbing and buffering device. Therefore, the spinal implant is sturdy and a useful life of the spinal implant can be prolonged. 
         [0028]    Referring to  FIGS. 5 to 8 , a spinal implant in accordance with a second preferred embodiment of the invention is shown. The characteristics of the second preferred embodiment are substantially the same as that of the first preferred embodiment except the following: A longitudinal channel  50  of circular section is formed in central portions of the upper section  10 , the padding member  30 , and the lower section  20  and communicates with the holes  14  and  24 . An elastic device  40  is provided in the channel  50  and comprises a helical spring  43 , two cup-shaped caps  41  at both ends of the spring  43 , and the cap  41  having a peripheral shoulder  42  on an outer surface. Two stop members  60  each is provided on the top surface  11  of the upper section  10  or the bottom surface  21  of the lower section  20 . The stop members  60  are adapted to prevent from the caps  41  from being disengaging from the spring  43  when the caps  41  contact the stop members  60  due to expansion of the spring  43 . The provision of the elastic device  40  further increases the shock absorbing and buffering capabilities of the spinal implant. 
         [0029]    After inserting the spinal implant between the upper and lower vertebrae  71 ,  72  with the upper and lower vertebrae  71 ,  72  and the top and bottom retaining members  12 ,  22  being fastened together in a surgery, bone tissues may grow to fill in the holes  14 ,  24 . This has the benefits of carrying out intervertebral stabilization and increasing the probability of a satisfactory recovery of a patient. 
         [0030]    Referring to  FIG. 9 , a spinal implant in accordance with a third preferred embodiment of the invention is shown. The characteristics of the third preferred embodiment are substantially the same as that of the first preferred embodiment except the following: The peripheral surface of each of the upper section  10  and the lower section  20  has two relatively smooth, opposite sides. No holes are formed along the direction of the opposite sides of the peripheral surface of each of the upper section  10  and the lower section  20 . 
         [0031]    Referring to  FIG. 10 , a spinal implant in accordance with a fourth preferred embodiment of the invention is shown. The characteristics of the fourth preferred embodiment are substantially the same as that of the first preferred embodiment except the following: The peripheral surface of each of the upper section  10  and the lower section  20  has all of four sides being relatively smooth. No holes are formed transversely in each of the upper section  10  and the lower section  20  (i.e., both the upper section  10  and the lower section  20  having no transverse holes). 
         [0032]    While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.