Spinal stabilization device
A flexible connection unit for use in a spinal fixation device, including: a longitudinal member having first end portion, a second end portion and a flexible member interposed between the first end portion and the second end portion, at least one of the first end portion and the second end portion configured to be coupled to a first bone securing member; and a spacer located between the first and second end portions, wherein at least a portion of the flexible member passes through an axial channel of the spacer and wherein the spacer comprises a resilient element configured to be coupled to a second bone securing member.
1 . A flexible connection unit for use in a spinal fixation device, comprising:
a longitudinal member having first end portion, a second end portion and a flexible member interposed between the first end portion and the second end portion, at least one of the first end portion and the second end portion configured to be coupled to a first bone securing member; and
a spacer located between the first and second end portions, wherein at least a portion of the flexible member passes through an axial channel of the spacer and wherein the spacer comprises a resilient element configured to be coupled to a second bone securing member.
2 . The flexible connection unit of claim 1 wherein the spacer further comprises a ring element surrounding at least a portion of the resilient element and configured to be directly coupled to the second bone securing member.
3 . The flexible connection unit of claim 1 , wherein the resilient element comprises a first bumper section located on one side of the second bone securing member, a second bumper section located on the other side of the second bone securing member, and an internal bumper section interposed between the second bone securing member and the flexible member, each bumper section configured to provide resistance to translation of the second bone securing member in one or more directions.
4 . The flexible connection unit of claim 3 , wherein the resistances provided by the first, second and internal bumper sections are different from one another.
5 . The flexible connection unit of claim 4 , wherein the resistance provided by each bumper section is independently adjustable by changing a physical characteristic of the bumper section.
6 . The flexible connection unit of claim 5 , wherein the physical characteristic comprises at least one characteristic selected from a group consisting of: longitudinal length, thickness, diameter, material stiffness and material composition.
7 . The flexible connection unit of claim 3 , wherein the resistance provided by the bumper sections is adjustable by changing the length provided for the spacer between the first and second end portions.
8 . The flexible connection unit of claim 7 , wherein the length provided for the spacer between the first and second end portions is adjustable.
9 . The flexible connection unit of claim 8 , wherein the spacer is slidably constrained on the flexible member.
10 . The flexible connection unit of claim 3 , wherein the first bumper section is configured to deform when the ring translates in a first longitudinal direction and the second bumper section is configured to deform when the ring translates in a second, opposite longitudinal direction.
11 . The flexible connection unit of claim 10 , wherein the spacer is configured to move between a first compressed state, where a first end of the spacer is biased against the second end of the longitudinal member, and a second compressed state, where a second end of the spacer is biased against the first end of the longitudinal member.
12 . The flexible connection unit of claim 3 , wherein the internal bumper section is configured to provide resistance to motion of the second bone securing member orthogonal to the longitudinal axis of the longitudinal member.
13 . The flexible connection unit of claim 3 , wherein the internal bumper section is configured to provide resistance to angular rotation of the second bone securing member relative to the longitudinal axis of the longitudinal member.
14 . The flexible connection unit of claim 3 , wherein at least one of the bumper sections comprises a helical spring.
15 . The flexible connection unit of claim 1 , wherein the spacer provides nonlinear resistance to longitudinal translation of the second bone securing member.
16 . The flexible connection unit of claim 1 , wherein the resilient member provides a first level of resistance during longitudinal translation of the second bone securing member up to a first distance and a second level of resistance during longitudinal translation past the first distance.
17 . The flexible connection unit of claim 16 , wherein the first level of resistance is less than the second level of resistance.
18 . The flexible connection unit of claim 16 , wherein the first level of resistance is greater than the second level of resistance.
19 . The flexible connection unit of claim 1 , wherein the resilient element comprises at least one material selected from a group of biocompatible materials consisting of: elastomers, polymers, resins, plastics, metals and composites thereof.
20 . The flexible connection unit of claim 19 , wherein the at least one material consists of polycarbonate urethane.
21 . The flexible connection unit of claim 1 , wherein the resilient member is contoured to deform at a first predetermined location in response to a first compressive force.
22 . The flexible connection unit of claim 21 , wherein the resilient member comprises at least one predetermined deformation zone configured to buckle in response to a particular compressive force being applied to the resilient member.
23 . The flexible connection unit of claim 21 , wherein the resilient member is contoured to deform at a second predetermined location in response to a second, different compressive force.
24 . The flexible connection unit of claim 23 , wherein the resilient member has a first deformation zone that is configured to buckle in response to translation in a first longitudinal direction and the second bumper has a second deformation zone that is configured to buckle in response to translation in a second, opposite longitudinal direction.
25 . The flexible connection unit of claim 24 , wherein the first and second deformation zones have a reduced diameter at a respective center portion thereof.
26 . The flexible connection unit of claim 1 , wherein the connection unit provides stabilized motion of the second bone securing member relative to the first end in five degrees of freedom, excluding rotation about a longitudinal axis of the connection unit.
27 . The flexible connection unit of claim 1 , wherein the connection unit provides stabilized motion of the second bone securing member relative to the first end in six degrees of freedom.