Transsacral Interbody Fusion for L5S1 High Grade SpondylolisthesisOur Experience

Abstract : In high-grade spondylolisthesis the distorted anatomy due to forward slippage of L5 over S1, a high degree of sacral inclination, an unfavourable slip angle, and loss of normal lordosis make conventional approaches to 360 degree fusion difficult or hazardous.Traditional posterior instrumentation with posterolateral fusion is associated with a high rate of slip progression because the construct fails to provide anterior column axial load sharing and to restrict shear forces across the disc space. Interbody grafting is of marginal efficacy because of the limited endplate surface area available to create an interface with a graft.Several innovative techniques have been described to achieve successful arthrodesis in this setting .We present three cases of high grade , L5-S1 spondylolisthesis with sciatica and instability pain who were managed with three different techniques ,namely,transsacral intervertebral pedicle screw fixation ,transsacral intervertebral pedicle screw fixation and transvertebral fibular strut grafting,transsacral intervertebral pedicle screw fixation and transvertebral autograft filled cage. All three patients were operated by the same surgeon under intraoperative fluoroscopic guidance.Clinical and functional outcomes were analyzed using standard scores (ODI,SRS,VAS) preoperatively and during the recent follow up(26 months).Fusion was analyzed at the end of 14 months in all three patients. As fusion was inconvincing with conventional radiographs we analyzed fusion with a multislice helical topographic scan with multiplanar reconstruction with cage subtraction.Pain relief was good except with transvertebral fibular strut grafting.The ODI and SRS scores were significantly better with transvertebral cage fixation .3D- CT films showed a fracture of the fibular autograft ,whereas a solid anterior L5-S1 bridging fusion mass and intracage graft incorporation was evident with transvertebral cage.Transsacral intervertebral screw fixation with transvertbral cage provides a biomechanically stable construct capable of anterior column axial load sharing and resisting shear forces across the lumbosacral junction, given the anatomical constraints accompanying high-grade spondylolisthesis. The titanium cage will not be resorbed, as is the case with fibular allograft,and the autograft within it will enable an interbody fusion to occur.