Bone fixation assembly

An anchor assembly configured to couple a bone anchor to a spinal rod to stabilize bones or bone fragments, the anchor assembly comprising:

• a body having an upper end that defines an upper opening, and a lower end that defines a lower opening and that is spaced from the upper end, the body defining a bore that extends between the upper opening and the lower opening, and the body defining a first rod-receiving channel configured to receive the spinal rod;
• a sleeve disposed in the bore of the body, the sleeve defining a second rod-receiving channel configured to receive a portion of the spinal rod;
• and
• an insert member received in the bore of the body, the insert member including an upper end portion and a lower expandable portion that is expandable so as to receive a head of a bone anchor while the insert member is in an unlocked configuration, wherein the lower expandable portion is compressible against the head in a locked configuration so as to lock the head in the insert member,
• the insert member further comprising a first wing and a second wing, and the bore comprises an interference zone that comprises first and second channels, wherein the first wing is configured to be received in the second channel while the second wing is received in the first channel,
• wherein the sleeve is configured to receive a force, which causes the sleeve to bear against the insert member, thereby transitioning the insert member from the unlocked configuration to the locked configuration while the head of the bone anchor is received in the insert member, and
• wherein in the unlocked configuration, the bone anchor is poly-axially rotatable in the insert member with respect to the body, and in the locked configuration, the insert member prevents the bone anchor from rotating polyaxially with respect to the body.