POLYAXIAL BONE SCREW
A polyaxial bone screw includes a shaft, a body member, and a toroidal member. The shaft includes a longitudinal axis and a proximal end with a head having a generally rounded surface. The body member has a bore disposed longitudinally therethrough and a groove defined by a luminal surface of the bore. The toroidal member has an elliptical cross-section with a major axis and disposed within the groove to engage the generally rounded surface of the head at a point of contact.
1 . A polyaxial bone screw, comprising:
a shaft including a longitudinal axis and a proximal end with a head having a generally rounded surface;
a body member having a bore disposed longitudinally therethrough and a groove defined by a luminal surface of the bore; and
a toroidal member having an elliptical cross-section with a major axis and disposed within the groove to engage the generally rounded surface of the head at a point of contact.
2 . The polyaxial bone screw of claim 1 , wherein the point of contact is distal to a point of intersection between the major axis and the head in a first position.
3 . The polyaxial bone screw of claim 1 , wherein the point of contact is proximal to a point of intersection between the major axis and the head in a second position.
4 . The polyaxial bone screw of claim 1 , wherein the toroidal member moves between a first position and a second position as the body member distally advances over the head.
5 . The polyaxial bone screw of claim 1 , wherein the body member removably attaches to the head by elastic deformation of the toroidal member.
6 . The polyaxial bone screw of claim 1 , wherein the body member removably attaches to the head by rotation of the toroidal member.
7 . The polyaxial bone screw of claim 1 , wherein the toroidal member comprises a coil spring.
8 . The polyaxial bone screw of claim 1 , wherein the toroidal member comprises a coil spring filled with an elastomer.
9 . The polyaxial bone screw of claim 1 , wherein the toroidal member comprises a toroidal sealing ring.
10 . The polyaxial bone screw of claim 1 , wherein the groove comprises a generally right angled internal shoulder.
11 . The polyaxial bone screw of claim 1 , further comprising a bushing with a pair of oppositely disposed proximally opening slots and distally depending tapered skirt adapted to abut a periphery of the head.
12 . The polyaxial bone screw of claim 1 , wherein the shaft includes a proximal portion with a circumference greater than a circumference the head to prevent proximal movement along the longitudinal axis by contact with the toroidal member.
13 . A method for attachment of a body member of a polyaxial bone screw onto a head of the polyaxial bone screw, comprising:
aligning a body member having a bore disposed longitudinally therethrough and a groove defined by a luminal surface of the bore relative to a shaft including a longitudinal axis and a proximal end with a head having a generally rounded surface;
advancing the body member over the head until a toroidal member having an elliptical cross-section with a major axis and disposed within the groove engages the generally rounded surface of the head at a point of contact, wherein the point of contact is distal to a point of intersection between the major axis and the head in a first position; and
continuing to advance the body member over the head until the point of contact is proximal to the point of intersection between the major axis and the head in a second position.
14 . The method of 13 , wherein continuing to advance body member moves the toroidal member between the first position and the second position as the body member distally advances over the head.
15 . The method of claim 13 , further comprising elastically deforming the toroidal member as the body member advances relative to the head.
16 . The method of claim 13 , further comprising rotating the toroidal member as the body member advances relative to the head.
17 . The method of claim 13 , further comprising inserting a bushing with a pair of oppositely disposed proximally opening slots and distally depending tapered skirt adapted to abut a periphery of the head.