Spinal fixation system

A load transmitting member for use with a spinal fixation system for engagement between the vertebrae and an elongated spinal plate for transmitting forces therebetween, the spinal plate having a top and a bottom side and an elongated slot defined therethrough between the bottom and top sides and extending substantially along the length of the plate, the slot having a lower edge at the intersection of the slot and the bottom surface and an upper edge at the intersection of the slot and the top surface, and a number of first concave depressions formed at the lower edge of the slot and a number of second concave depressions formed at the upper edge of the slot, said load transmitting member comprising:

• a first threaded portion having machine threads for engaging a nut;
• a second threaded portion having bone engaging threads;
• and
• an intermediate portion between and integral with said first and second threaded portions, said intermediate portion having a rigid upper arcuate surface adjacent said first threaded portion and an oppositely facing rigid lower arcuate surface adjacent said second threaded portion, wherein said upper arcuate surface is defined at a first radius of curvature and said lower arcuate surface is defined at a second radius of curvature that is substantially different from said first radius of curvature.

A spinal fixation system for maintaining vertebrae in a desired relationship comprising:

• an elongated plate having;
• a bottom side for facing the vertebrae;
• an opposite top side extending generally parallel to said bottom side;
• an elongated slot defined therethrough between said bottom side and said top side and extending substantially along the length of said plate, said slot having a lower edge at the intersection of said slot and said bottom surface and an upper edge at the intersection of said slot and said top surface, and
• a number of first concave depressions formed at said lower edge of said slot and a number of second concave depressions formed at said upper edge of said slot;
• and load transmitting means for engagement between the vertebrae and said elongated plate for transmitting forces therebetween, said load transmitting means including;
• pedicle screw means having a first threaded portion, a second threaded portion and an intermediate portion between and integral with said, first and said second threaded portions, said second threaded portion including a number of threads adapted to engage the bone of the vertebrae, said intermediate portion having a rigid upper arcuate surface facing toward said first threaded portion, and a rigid lower arcuate surface;
• and
• a nut having a threaded head portion for engaging said first threaded portion and a rigid lower arcuate surface,
• wherein said rigid lower arcuate surface of said nut, said rigid lower arcuate surface-of said intermediate portion of said pedicle screw means and said number of second concave depressions of said plate are each defined by a substantially equal spherical radius, and
• wherein said rigid upper arcuate surface of said intermediate portion of said pedicle screw means and said number of first concave depressions of said plate are defined by substantially different spherical radii relative to each other.