Adjustable posterior spinal column positioner

1. A posterior element distraction system for implantation at a spinal motion segment comprising a superior vertebra, an inferior vertebra, each vertebra comprising a posterior element comprising a spinous process, laminal portions and a set of facet joints, and further comprising an interspinous space between the spinous processes, the system comprising: at least one lateral member for positioning on a side of the spinal motion segment and outside the interspinous space, wherein the at least one lateral member has an unexpanded configuration and an expanded configuration; and first and second transverse members extending transversely from the at least one lateral member, wherein the first transverse member has a concave upper bearing surface adapted for bearing against an upper posterior process, wherein the second transverse member has a concave lower bearing surface adapted for bearing against a lower posterior process, wherein when the system is operatively implanted at a spinal motion segment and the at least one lateral member is in an expanded configuration, the transverse members are caused to contact a portion of either the superior or inferior posterior elements thereby providing distraction between the superior and inferior posterior elements,

wherein the upper and lower bearing surfaces defining a height of the implant, and

wherein the unexpanded configuration and an expanded configuration define different heights of the implant.

2. The system of claim 1 , wherein the system comprises only one lateral member.

3. The system of claim 1 , wherein the at least one lateral member comprises a strut configuration.

4. The system of claim 1 wherein the upper bearing surface has a concave portion.

5. The system of claim 1 wherein the first transverse member extends from an upper body of the lateral member and the second transverse member extends from a lower body of the lateral member.