Durability and Failure Types of S2-Alar-Iliac Screws: An Analysis of 312 Consecutive Screws

BACKGROUND: S2-alar-iliac (S2AI) screws improve stability across the lumbosacral junction in spinopelvic fixation proceduresby crossing the cortical surfaces of the sacroiliac joint (SIJ), thereby increasing the biomechanical strength of the instrumentation. OBJECTIVE: To investigate the durability and failure types of S2AI screws after spinopelvic reconstruction surgery. METHODS: A single-center, single-surgeon consecutive series of patientswho underwent spinopelvic fixation using bilateral S2AI screwswith a >= 1-yr follow-up and at least 1 post-operative computed tomographic scan were retrospectively reviewed. Patient characteristics, radiographic parameters, operative data, clinical outcomes, and complications were analyzed. RESULTS: In total, 312 S2AI screws in 156 patients were evaluated (mean follow-up, 26.1 mo; range 12-71 mo). Therewere no significant differences in screwdiameter, length, or insertion angle between right-side and left-side screws. Visual analogue scale scores for back pain, ambulatory status, and Oswestry Disability Index scores significantly improved. A total of 10 patients (3.2%) experienced SIJ pain after S2AI screw installation. SIJ pain improved in 8 of them following SIJ block. In total, 7 screws (2.2%) showed partial periscrew lucency. Set screwdislodgement occurred in 7 screws (2.2%). Screwfracture occurred in 6 screws (1.9%): 5 neck fractures and 1 shaft fracture. A total of 5 patients (1.6%) underwent revision surgery for S2AI screw failure. Distal device (L4-pelvis region) breakage occurred in 5 patients. CONCLUSION: The radiographic and clinical outcomes of S2AI screw fixation were acceptable. However, S2AI screw fixation has several drawbacks, including screw fracture and dislodgement of the set screw. SIJ irritation symptoms after S2AI screw fixation occurred with considerable frequency.