Dynamic stabilization medical implant assemblies and methods

Abstract

Bone screw assemblies include longitudinal connecting members that provide for dynamic stabilization, some including non-uniform portions that are configured to flex, contract or expand. Composite longitudinal connecting members include longitudinal segments made from different materials having different flexibilities. Polyaxial bone screw assemblies include change-out receivers for cooperating with replacement longitudinal connecting members having a different flexibility. Bone screw shanks for cooperating with one or more open receivers include treatment or coating to provide biologically active interface with bone.

1 . In a medical implant assembly including at least two bone attachment structures, the improvement comprising: 
 a longitudinal connecting member having an axis and further having first, second and third integral portions extending along the axis, the third portion being disposed between the first and second portions, the first and second portions being substantially uniform and each receivable in an open receiver of a bone attachment structure, the third portion having first and second substantially parallel axially spaced sides and a plurality of curved strips, each curved strip integral with both the first side and the second side at either end thereof, the third portion being both compressible and expandable along the axis.    
   
   
       2 . The improvement of  claim 1  wherein each bone attachment structure has an open receiver for receiving the longitudinal connecting member and a shank, the shank having a surface altered by at least one of 
 i) a surface roughening treatment; and    ii) a coating    to provide a bioactive interface between the bone attachment structure and a vertebra.    
   
   
       3 . The improvement of  claim 2  wherein the shank surface is plasma coated.  
   
   
       4 . The improvement of  claim 2  wherein the shank surface is coated with hydroxyapatite.  
   
   
       5 . The improvement of  claim 1  wherein at least one of the first and second portions includes at least one elongate segment, the segment being made from a different material than a remainder of the first and second portions resulting in the elongate segment having a flexibility different than a flexibility of the remainder of the first and second portions.  
   
   
       6 . The improvement of  claim 1  wherein at least a length of the first portion measured along the axis is made from a different material than the second portion.  
   
   
       7 . In a medical implant assembly including at least two bone attachment structures, the improvement comprising: 
 a) a longitudinal connecting member having first, second and third integral and substantially coaxial portions, the third portion disposed between the first and second portions, the first and second portions being substantially uniform and receivable in an open receiver of a bone attachment structure, the third portion being hollow and substantially ellipsoid when under tension.    
   
   
       8 . The improvement of  claim 7  wherein each bone attachment structure has an open receiver for receiving the longitudinal connecting member and a shank, the shank having a surface altered by at least one of 
 i) a surface roughening treatment; and    ii) a coating    to provide a bioactive interface between the bone attachment structure and a vertebra.    
   
   
       9 . The improvement of  claim 8  wherein the shank surface is plasma coated.  
   
   
       10 . The improvement of  claim 8  wherein the shank surface is coated with hydroxyapatite.  
   
   
       11 . A polyaxial bone screw assembly comprising: 
 a) at least first and second bone attachment structures, each structure having an open receiver and a shank, the shank treated with at least one of 
 i) a surface texture; and  
 ii) a coating  
   to provide a bioactive interface between the bone attachment structure and a vertebra; and    b) a longitudinal connecting member receivable in the open receivers of the first and second bone attachment structures, the longitudinal member having at least one flexible portion for providing protected motion of the spine.    
   
   
       12 . The assembly of  claim 11  wherein when assembled, the longitudinal connecting member directly frictionally engages an upper portion of the shank.  
   
   
       13 . The assembly of  claim 11  wherein the shank surface is plasma coated.  
   
   
       14 . The assembly of  claim 11  wherein the shank surface is coated with hydroxyapatite.  
   
   
       15 . The assembly of  claim 11  wherein the longitudinal connecting member has first, second and third integral and substantially coaxial portions, the third portion disposed between the first and second portions, the first and second portions being substantially uniform and receivable in the open receiver of the bone attachment structure, the third portion having first and second substantially parallel axially spaced sides and a plurality of curved strips, each curved strip integral with both the first side and the second side at either end thereof, the third portion being both compressible and expandable in an axial direction.  
   
   
       16 . A medical implant kit comprising: 
 a) a polyaxial bone screw shank;    b) a first receiver having a first opening, the first receiver swivelably attachable to the shank and removable therefrom when the shank is implanted into a vertebra of a spine;    c) a first longitudinal connecting member closely receivable in the first opening of the first receiver, the first connecting member sized and shaped to allow protected motion of the spine;    d) a second receiver swivelably attachable to the shank when the shank is attached to the vertebra, the second receiver having a second opening of a different size than the first opening of the first receiver; and    e) a second longitudinal connecting member sized and shaped to be closely receivable in the second opening of the second receiver, the second longitudinal member having a different amount of flexibility than the first longitudinal member.    
   
   
       17 . The kit of  claim 16  wherein the bone screw shank includes at least one of 
 a) a surface roughening treatment; and    b) a coating    to provide a bioactive interface between the bone attachment structure and a vertebra.    
   
   
       18 . The kit of  claim 16  wherein the shank surface is plasma coated.  
   
   
       19 . The kit of  claim 16  wherein the shank surface is coated with hydroxyapatite.  
   
   
       20 . A surgical method comprising: 
 a) providing a polyaxial bone screw shank attachable to a first receiver;    b) implanting the shank and attached first receiver into a vertebra of a spine;    c) providing a first longitudinal connecting member sized and shaped to be closely receivable in the first receiver and to allow protected motion of the spine;    d) securing the first longitudinal connecting member in the first receiver; and    e) providing a second receiver attachable to the shank when the shank is implanted in the vertebra and sized and shaped to receive a second longitudinal connecting member, the second member having a different degree of flexibility than the first member.    
   
   
       21 . The method of  claim 20  comprising the subsequent steps of: 
 f) removing the first longitudinal connecting member from the first receiver;    h) replacing the first receiver with the second receiver without removing the bone screw shank from the vertebra; and    i) securing the second longitudinal connecting member to the second receiver.    
   
   
       22 . A longitudinal connecting member comprising at least first and second elongate segments wherein each of the segments is sized and shaped to be adapted to be received between a pair of bone anchors; the first segment being comparatively stiff and the second segment being comparatively flexible in comparison to the first segment.  
   
   
       23 . The longitudinal connecting member of  claim 22  wherein at least a portion of the first segment is made from a material different from the second segment.  
   
   
       24 . A longitudinal connecting member of substantially uniform cross section and being longitudinally divided into at least first and second integral segments wherein the first segment is substantially more flexible in comparison to the second section.  
   
   
       25 . The connecting member of  claim 24  wherein at least a portion of the first segment is constructed of material different from the second segment.  
   
   
       26 . The connecting member of  claim 24  wherein the uniform cross-section is substantially circular in shape.  
   
   
       27 . The connecting member of  claim 24  wherein both the first and second segments are substantially solid.