Spinal fixation system with modular receiver sub-assemblies for connecting with bi-spherical universal shank heads

Abstract

A spinal fixation system includes a plurality of bone anchors, each having an anchor portion and a shank head with an upper spherical surface having a first diameter extending downward to an inner edge of an annular shelf spaced below a hemisphere plane, and a lower spherical surface having a second diameter greater than the first diameter extending downward from an outer edge of the annular shelf toward a neck extending between the shank head and anchor portion. The system also includes both pivoting and non-pivoting receiver sub-assemblies, with each receiver sub-assembly including a receiver having a central bore with a seating surface adjacent a bottom opening and a channel for receiving a rod. Each receiver sub-assembly also includes one of a multiplanar retaining structure, a monoplanar retaining structure, or a monoaxial retaining structure positioned therein and slidably engageable with the seating surface after capturing the shank head upon its uploading through the bottom opening.