Comparison of instrumented posterolateral fusion versus percutaneous pedicle screw fixation combined with anterior lumbar interbody fusion in elderly patients with L5-S1 isthmic spondylolisthesis and foraminal stenosis - Shim, J H; Kim, W S; Kim, J H; Kim, D H; Hwang, J H; Park, C K (J Neurosurg Spine, 2011)