Expandable spacer and method for use thereof

Abstract

An expandable implant is disclosed having an adjustable height for insertion between two adjacent bony structures or joint surfaces, for example between two adjacent spinal vertebrae. The implant includes at least one gear associated with at least one threaded shaft. Rotation of the gear engages the threaded shaft to expand the implant. The implant can be inserted in a collapsed configuration and expanded in situ. The invention also provides methods for using the implant to facilitate arthrodesis or fusion of adjacent joint surfaces or spinal vertebrae.

What is claimed is: 
     
         1 . An expandable implant for insertion in a space between adjacent bony structures, comprising:
 a first threaded shaft;   a second threaded shaft;   a base plate coupled to the first and second threaded shafts;   a first gear operably coupled to the first threaded shaft and the base plate;   a second gear operably coupled to the second threaded shaft and the base plate, wherein each of the first and second gears includes an interior surface having threads matably engaged with respective ones of the first and second threaded shafts; and   a third gear disposed between and operatively engaged with the first and second gears, wherein rotation of the third gear causes rotation of the first and second gears which initiates displacement of the first and second threaded shafts within the base plate, wherein the first and second threaded shafts are extendable in a direction away the base plate,   wherein the base plate and the first and second threaded shafts are configured to engage bony structures to support or distract the bony structures relative to each other.   
     
     
         2 . The expandable implant according to  claim 1 , wherein the implant has a first, collapsed height prior to extension of the first and second threaded shafts and a second, expanded height after extension of the first and second threaded shafts. 
     
     
         3 . The expandable implant according to  claim 2 , wherein the second, expanded height is adjustable. 
     
     
         4 . The expandable implant according to  claim 1 , wherein the implant is operable to distract the adjacent bony structures. 
     
     
         5 . The expandable implant according to  claim 1 , wherein the space for insertion is an intervertebral space between two adjacent spinal vertebrae. 
     
     
         6 . The expandable implant according to  claim 1 , wherein each of the first and second threaded shafts has a hollow interior. 
     
     
         7 . The expandable implant according to  claim 6 , wherein a top end of each of the first and second threaded shafts includes an opening, the opening operable for insertion of material into the hollow interior. 
     
     
         8 . The expandable implant according to  claim 7 , wherein the material is a bone graft material selected from the group consisting of autograft, allograft, xenograft, artificial mixtures, synthetic mixtures, demineralized bone matrix, hydroxyapatite mixtures, and combinations thereof. 
     
     
         9 . The expandable implant according to  claim 8 , wherein the bone graft material further includes an effective amount of a growth factor or differentiation factor. 
     
     
         10 . The expandable implant according to  claim 9 , wherein the growth factor or differentiation factor is selected from the group consisting of bone morphogenic protein (BMP), transforming growth factor β1 (TGFβ1), insulin-like growth factor 1 (IGF-1), platelet-derived growth factor (PDGF), activin, parathyroid hormone, fibroblast growth factor (FGF), LIM mineralization protein (LMP), and combinations thereof. 
     
     
         11 . The expandable implant according to  claim 1 , wherein the implant is formed from a material selected from the group consisting of titanium, titanium alloys, stainless steel, chrome cobalt, nickel, ceramics, plastics, shape-memory alloys, bioactive glass, composites, bone, bone substitutes, and combinations thereof. 
     
     
         12 . An expandable implant for insertion in a space between adjacent bony structures comprising:
 a first threaded shaft:   a second threaded shaft;   a bottom plate having an exterior surface and an interior surface, the interior surface including a base configured for receiving the first and second threaded shafts; and   a pair of decoupled actuation gears, a first gear of the pair operably coupled to the first threaded shaft and a second gear of the pair operably coupled to the second threaded shaft; and   a wedge coupled to the base and configured to enable angular displacement of the base to preserve correct angular displacement of bone,   whereby rotation of the first gear in a first direction initiates rotation of the second gear in a second direction, opposite the first direction, initiating rotation of the first threaded shaft and then the second threaded shaft such that the shafts extend to engage adjacent bony structures.   
     
     
         13 . The expandable implant according to  claim 12 , wherein the first threaded shaft and the second threaded shaft are in a substantially parallel configuration. 
     
     
         14 . The expandable implant according to  claim 12 , wherein the base holds the first threaded shaft and the second threaded shaft in an angled configuration.