Spinopelvic fixation with iliac screws provides biomechanical advantages of stable fixation and has increased usage in adult spinal deformity. We have previously described a technique of Subcrestal Iliac Screw (SCIS) placement where the iliac screw is inserted at the medial wall of the iliac crest, underneath the crest and above the SI joint at the level of S1 or between the S1/S2 foramen. This entry point allowed for a low-profile screw head, easy connection with the proximal construct without need of connectors, avoidance of SI joint violation and reduced radiation exposure during insertion with a freehand technique. This study reports the long term clinical and radiological outcomes of the SCIS in a larger cohort of patients.

Consecutive patients undergoing spinopelvic fixation for correction of spinal deformity were recruited. Patient demographics, operative details, pre and post op clinical scores, and presence of complications pertaining to the iliac screws were recorded. A total of 206 SCIS were inserted in 100 patients with a mean follow-up of 40.6 months±30.2 months. The mean age was 65.1±12.9 with 73 % females. The main cause of deformity was degenerative scoliosis (89%). Majority of procedures were performed open (72%). The median common diameter of iliac screws used was 8.5mm with mean length of 83.3mm. SCIS implant complications included iliac screw breakage (n=2), radiological loosening (n=14), implant prominence (n= 3), SI joint sclerosis (n=15). There were no SCIS related skin complications or infection. 2 patients underwent revision of the SCIS for loosening and breakage. Other non SCIS complications include rod breakage (n=15), rod screw detachment (n=2), surgical site infections requiring debridement(n=5), sacral fractures (n=2) and persistent post-operative back pain (n= 15). An additional 4 patients required revision surgery 2 for rod breakage, 1 for proximal pullout and 1 for proximal junctional kyphosis. In conclusion the SCIS is safe and easily with reproducible outcomes. It combines the advantage of traditional and traditional S2 alar iliac screw with minimal complications.