Bone anchor assemblies

A bone anchor assembly comprising:

• a bone anchor having a proximal head and a distal shaft configured to engage bone,
• a receiver member for receiving a spinal fixation element to be coupled to the bone anchor, the receiver member having
• a proximal end having a pair of spaced apart arms defining a recess therebetween for receiving a spinal rod, the arms including a first inner thread,
• a distal end having a distal end surface defining opening through which at least a portion of the bone anchor extends, the bone anchor being movable relative to the receiver member,
• a compression member positioned within the receiver member, the compression member including a seat for receiving the rod and a distal surface for engaging the proximal head of the bone anchor,
• a outer set screw positionable between and engaging the arms, the outer set screw including a first outer thread for engaging the first inner thread, the outer set screw operable to act on the compression member to fix the bone anchor relative to the receiver member, the first inner thread and the first outer thread having a thread angle between 5° and 25°, the outer set screw having a central passage from a top surface of the outer set screw to a bottom surface of the outer set screw, the central passage having a second internal thread, and
• an inner set screw positionable within the central passage, the inner set screw having a second outer thread for engaging the second inner thread, the inner set screw operable to act on the spinal rod to fix the spinal rod relative to the receiver member.

A bone anchor assembly comprising:

• a bone anchor having a proximal head and a distal shaft configured to engage bone,
• a receiver member for receiving a spinal fixation element to be coupled to the bone anchor, the receiver member having
• a proximal end having a proximal end surface and a pair of spaced apart arms defining a recess therebetween for receiving a spinal rod, the arms including a first inner thread, the proximal end surface defining a first plane
• a distal end having a distal end surface defining an opening through which at least a portion of the bone anchor extends, the bone anchor being movable relative to the receiver member, the distal end surface defining a second plane, the first plane and the second plane intersecting one another,
• a compression member positioned within the receiver member, the compression member including pair of spaced apart arms defining a u-shaped seat for receiving the rod and a distal surface for engaging the proximal head of the bone anchor,
• an outer set screw positionable between and engaging the arms, the outer set screw including a first outer thread for engaging the first inner thread, the outer set screw operable to act on the compression member to fix the bone anchor relative to the receiver member, the first inner thread and the first outer thread having a thread angle between 5° and 25°, the outer set screw having a central passage from a top surface of the outer set screw to a bottom surface of the outer set screw, the central passage having a second internal thread, and
• an inner set screw positionable within the central passage, the inner set screw having a second outer thread for engaging the second inner thread, the inner set screw operable to act on the spinal rod to fix the spinal rod relative to the receiver member.