20. The system of claim 18 , wherein the opening is elongate.
18. A spinal fixation system, comprising: a bone anchor having a bone-engaging portion and a head; a connecting member having first and second ends with a spanning portion extending therebetween, the spanning portion extending at an oblique angle with respect to the first end and at an oblique angle with respect to the second end, at least one of the first and second ends having an opening formed therein, and a portion of the opening being configured to engage a portion of the head at a locked position such that the connecting member is at a fixed location with respect to the bone anchor; and a buttress extending distally from a portion of the distal surface of the connecting member that is substantially more proximate to the second end than the first end, the buttress extending towards the bone anchor when the connecting member is coupled to the bone anchor, wherein the buttress includes a substantially flat first sidewall configured to engage a posterior element of a vertebra and a second sidewall that is opposed to the first sidewall, each of the first and second sidewalls being more proximate to the second end than the first end.