Remain an effective technique to supplement S1 pedicle screws, especially as a salvage technique for those who cannot have iliac fixation, such as those who previously had substantial posterior iliac crest harvested for bone graft ¹⁾.

Commonly directed laterally abd superiorly into the ala of sacrum.

Three-dimensional image guidance allows for safe placement of large S2 sacral alar screws that can provide additional biomechanical stability to lumbosacral constructs or serve as an alternate point of sacral fixation when S1 pedicle screws cannot be salvaged or placed in a medial trajectory ²⁾.

Leong et al. ³⁾ found that a construct consisting of bicortical S1 pedicle screws in combination with bicortical S2 alar screws that were inserted 30 degrees anterolaterally was significantly stronger than constructs using bicortical S1 pedicle screws alone. In a study by Zindrick et al., ⁴⁾ second sacral pedicle is weakest location and screws aimed laterally into the ala of sacrum at 45 degrees resist larger axial pull-put loads than straight anteriorly into the ala. But, diagonal insertion of S2 screw did not tested and S2 screw is not embedded firmly than iliac screw. To overcome the iliac screw disadvantages, the diagonal S2 screw for lumbo-sacral fixation was described here. The diagonal S2 screw has many potential advantages compared with iliac screw fixation such as a lower profile, avoidance of extra soft tissue dissection, no competition with iliac bone graft harvest, and easier salvage if ever infected. But in patient with severe sagittal imbalance, authors thought iliac screw fixation is appropriate option for preventing pseudarthrosis. Authors used a 6.0-mm-diameter, 50-mm-long variable angle screw in most of the patients and it was sufficient for solid lumbo-sacral fixation. More larger screw is able to provide greater stability, but further biomechanical testing would have to be accomplished to come to any firm conclusion regarding the strength of S2 screws. In our cases, a posterolateral fusion was performed in 13 patients and there was no interbody fusion case. Interbody fusion provides mechanical advantages in terms of graft compression and a large, well vascularized fusion surface. But, only posterolateral fusion with S2 screw fixation provided high fusion rate (12/13) and authors think interbody fusion doesn’t need in our techniques. Authors suggest that the S1-diagonal S2 screw construct is an appropriate alternative to the S1-iliac screw construct and it presents certain clinical advantages. However, the short- and long-term effects of the diagonal S2 screw have not been completely evaluated. Further data are needed to fully evaluate the diagonal S2 technique.

The ability to place a diagonal S2 screw requires a thorough understanding of each individual patient’s anatomy. Standing anteroposterior and lateral lumbar radiographs and an anteroposterior pelvic radiograph should be obtained. The overall alignment of the spine and pelvis in Placing instrumentation into the ilium has been shown to increase the biomechanical stability and the fusion rates, but it has some disadvantages. The diagonal S2 screw technique is an attractive surgical procedure for degenerative lumbar deformity. Between 2008 and 2010, we carried out long fusion across the lumbosacral junction in 13 patients with a degenerative lumbar deformity using the diagonal S2 screws. In 12 of these 13 patients, the lumbosacral fusion was graded as solid fusion with obvious bridging bone (92%). One patient had a rod dislodge at one S2 screw and breakage of one S1 screw and underwent revision nine months postoperatively. So, we present alternative method of lumbopelvic fixation for long fusion in degenerative lumbar deformity using diagonal S2 screw instead of iliac screw. Keywords: Long fusion, Diagonal S2 screw, Iliac screw, Degenerative lumbar deformity both the coronal and sagittal plane should be evaluated carefully. Preoperative computerized tomography (CT) should be performed to evaluate for absent or small pedicles and congenital and other bony abnormalities. Depending on the experience, skill, and comfort of the operating surgeon, intraoperative fluoroscopy is recommended but not required ⁵⁾.

Two patients were treated by the senior author (FAS) who underwent surgery employing S2-AI fixation utilizing an electronic conductivity device (Pediguard cannulated probe, Spineguard, Paris, France). The surgical technique, case illustrations, and radiographic outcomes are discussed.

Stable and accurate fixation was attained in both patients. There were no peri-operative complications related to hardware placement.

To the authors' knowledge, this is the first reported literature combining S2-AI screws with electronic conductivity for immediate intraoperative feedback. This technique has the opportunity to provide surgeons with increased accuracy for placement of S2-AI screws while improving overall radiation safety. This feedback can be particularly helpful when surgeons are learning new techniques such as placement of S2AI screws ⁶⁾.