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

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 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 a body having a substantially rectangular cross section and comprising a toothed top retaining member, a toothed bottom retaining member, and a peripheral surface; a three-dimensional matrix structure formed in the body and on the peripheral surface as support; and a plurality of holes formed through at least one of three directions of the three-dimensional matrix structure. 
         [0009]    It is another object of the invention to provide an implant for insertion between two opposite spaced vertebrae of a spine, comprising a body having a substantially rectangular cross section and comprising a toothed top retaining member, a toothed bottom retaining member, and a peripheral surface; a three-dimensional matrix structure formed in the body and on the peripheral surface as support; a plurality of holes formed through at least one of three directions of the three-dimensional matrix structure; and a longitudinal channel formed in a central portion of the body and communicating with the holes. 
         [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 comprises the following components as discussed in detail below. 
         [0020]    A body  10  has a substantially rectangular cross section and comprises a top surface  11 , a bottom surface  12 , and a peripheral surface  15  therebetween. The body  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 body  10  is formed of alloy such as stainless steel, cobalt-chromium-molybdenum alloy, titanium, or titanium alloy. Still alternatively, the body  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 body  10  is formed of ceramic such as aluminum oxide, calcium phosphate tri-basic, or fiber glass. 
         [0021]    An upper retaining member  111  is formed on the top surface  11  and shaped as a plurality of rows of bone engaging projections (i.e., teeth). A lower retaining member  121  is formed on the bottom surface  12  and shaped as a plurality of rows of bone engaging projections (i.e., teeth). A three-dimensional matrix structure  14  is formed in the body  10  and on the peripheral surface  15  as support. The three-dimensional matrix structure  14  can provide mechanical properties such as enhanced resistance to pressure, enhanced resistance to stress, and enhanced resistance to tension to the body  10 . A plurality of holes  13  are formed through each of three directions of the three-dimensional matrix structure  14 . The holes  13  occupy about 1% to 90% of the volume of the body  10  depending upon engineering choice of design. Each hole  13  has a bore of about 150 μm to 1,000 μm. 
         [0022]    As shown in  FIG. 4  specifically, a physician may insert the body  10  into a bore formed between an upper vertebra  21  and a lower vertebra  22  of a spine. The bone engaging projections of the upper retaining member  111  and the bone engaging projections of the lower retaining member  121  thus grasped the upper vertebra  21  and the lower vertebra  22  respectively (i.e., the body  10  being fastened). Moreover, an appropriate biocompatible material may filled in the voids of the holes  13  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 ). 
         [0023]    The holes  13  allow body tissues to grow therein for the health of spinal bone. Moreover, the fastening of the upper and lower vertebrae  21 ,  22  and the upper and lower retaining members  111 ,  112  is reliable so as to rigidly join the upper and lower vertebrae  21 ,  22 . As a result, intervertebral stabilization is carried out. 
         [0024]    In addition, the provision of the three-dimensional matrix structure  14  can significantly increase resistance to pressure, stress, and tension to the body  10 . Therefore, the body  10  is sturdy and a useful life of the spinal implant can be prolonged. 
         [0025]    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  16  of circular section is formed in a central portion of the body  10  and communicates with the holes  13 . After inserting the spinal implant between the upper and lower vertebrae  21 ,  22  with the upper and lower vertebrae  21 ,  22  and the upper and lower retaining members  111 ,  112  being fastened together in a surgery, bone tissues  30  may grow to fill in the channel  16 . This has the benefits of carrying out intervertebral stabilization and increasing the probability of a satisfactory recovery of a patient. 
         [0026]    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 second preferred embodiment except the following: The peripheral surface  15  has two relatively smooth opposite sides, an inner surface of the channel  16  has two opposite smooth portions substantially aligned with the two opposite sides of the peripheral surface  15 , and no holes  13  are formed along the direction of the opposite sides of the peripheral surface  15 . 
         [0027]    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 second preferred embodiment except the following: The peripheral surface  15  has all of four sides being relatively smooth, the channel  16  has a relatively smooth inner surface, and no holes  13  being formed transversely (i.e., the body  10  having no transverse holes  13 ). 
         [0028]    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.