Connecting rod for bone anchors having a bioresorbable tip

Abstract

The invention provides a connecting rod for bone anchors such as pedicle screws. The rod is constructed to include a main shaft portion that is not bioresorbable and a tip portion that is bioresorbable. The tip facilitates percutaneous insertion into a patient's body. After placement of the rod, the bioresorbable tip is resorbed preventing post-operative complications such as impingement of adjacent spinal facet joints.

What is claimed is: 
     
         1 . An improved connecting rod for use on an animal subject, said connecting rod used in conjunction with an installation instrument having anchor extensions coupled to at least two pedicle screws, a portion of the instrument moveable through an arcing trajectory with respect to said pedicle screws to position said connecting rod to a position proximate said at least two pedicle screws, the improvement comprising:
 a connecting rod defined by a single piece non-bioresorbable shaft portion having a length sufficient to connect at least two pedicle screws, said shaft portion having a longitudinal centerline that is arced to substantially match said arcing trajectory, and an aperture that extends generally along said longitudinal centerline of said shaft portion;   a bioresorbable tip having a base end and an insertion end securable to a distal end of said shaft portion constructed and arranged for use in forming a path through animal tissue to facilitate installation of said shaft portion to said pedicle screws, said base end including a projection sized and shaped to enter said aperture, said projection having a side surface constructed and arranged to cooperate with said aperture for securing said tip to said main shaft to retain said tip in alignment with said arcing longitudinal centerline;   wherein when implanted in the subject, said connecting rod has a first overall length causing impingement with an adjacent boney structure and a second length after a predetermined time to eliminate said impingement with said boney structure, after resorption of said tip the non-bioresorbable shaft remains connecting pedicle screws between adjacent vertebrae without inhibiting movement.   
     
     
         2 . The improved connecting rod for use on an animal subject of  claim 2  wherein said bioresorbable material is selected from the group consisting of polylactic acid, polyglycolic acid, polycaprolactone, polyanhydrides, polydioxanone, polyamino acids, trimethylene carbonate, 1,5-dioxepan-2-one, copolymers of lactic acid, hydroxyapatite, alginates and bioresorbable metals. 
     
     
         3 . The improved connecting rod for use on an animal subject of  claim 1  wherein said insertion end of said tip includes a trocar shape. 
     
     
         4 . The improved connecting rod for use on an animal subject of  claim 1  wherein said base end of said tip and said aperture of said main shaft include mating helical threads. 
     
     
         5 . The improved connecting rod for use on an animal subject of  claim 1  wherein said base end of said tip and said aperture of said main shaft include mating locking tapers. 
     
     
         6 . The improved connecting rod for use on an animal subject of  claim 1  wherein said base end of said tip and said aperture of said main shaft include an interference fit. 
     
     
         7 . The improved connecting rod for use on an animal subject of  claim 1  wherein said base end of said tip and said aperture of said main shaft include a laser weld for securing said tip and said main shaft together.