Multi-axial bone screw assembly

A bone fixation apparatus comprising:

• an elongated member configured for placement adjacent and along a length of at least one bone;
• a receiver member defining an opening therethrough from a top end to a bottom end, said opening having a lower aperture at said bottom end and an upper aperture at said top end, said receiver member also defining a groove around a portion of said opening, said groove being proximate to said lower aperture, said receiver member further including a channel communicating with said opening and said upper aperture, said channel being configured to receive said elongated member therein;
• a crown member insertable through said lower aperture and disposed within said opening, said crown member having a lower surface and an opposite upper surface contacting said elongated member;
• a bone anchor having a lower portion configured for engaging a bone and a head having a width dimension, said head being insertable through said lower aperture and adjacent to said crown member within said opening of said receiver member;
• a retaining member defining an aperture having a width dimension that is less than said width dimension of said head, said retaining member being positioned around a portion of said bone anchor and at least a portion of said retaining member being housed within at least a portion of said groove;
• and
• a compression member engaged within said opening proximate to said upper aperture, said compression member operable to press said elongated member against said crown member, thereby fixing said head of said fastener between said crown member and said retaining member.