Extra-articular Portion of the Sacroiliac Joint—Between the Sacral and Pelvic Tuberosities: An Anatomical Guide for the S2-Alar-Iliac Screw Trajectory

Abstract

Study Design: A novel technique for S2-alar-iliac (S2AI) screw placement was analyzed. Objectives: Accurate confirmation of the S2AI screw trajectory with free-hand techniques is not simple, although some anatomical landmarks have been reported. To overcome the drawback, we aimed to introduce our technique for S2AI screw placement assisted with a guidewire using a new anatomical landmark. Methods: A total of 104 S2AI screws of 52 patients who underwent S2AI screw placement were investigated. Navigation software was used to simulate S2AI screw placement preoperatively. Screw placement was performed with the nonfluoroscopic free-hand technique. In this technique, a guidewire is inserted into the ilium from the extra-articular portion of the sacroiliac joint just lateral to the ideal screw entry point toward the tip of the greater trochanter and guides the screw trajectory. If the direction of the guidewire is satisfactory, all procedures of screw insertion are performed accordingly. The screw accuracy was assessed with computed tomography. Results: The modal size of the screw was 9.5 mm × 90 mm. The average horizontal angle was 42.0° (SD = 5.1°) on the right and 40.7° (SD = 4.7°) on the left. Of the 104 screws, 4 screws (3.9%) breached dorsally. No screw-related complication was observed. Conclusions: Because the guidewire can be inserted at an angle according to the individual morphology of the sacroiliac joint, it will be a reliable guide for the screw trajectory. This technique with a guidewire would help improve the accuracy of S2AI screw placement.

Changes in Lumbosacral Anatomy and Vertebral Numbering in Patients with Thoracolumbar and/or Lumbosacral Transitional Vertebrae

“…Similarly, in patients with Castellvi LSTVs, particularly those with type-IIIb LSTV, considering S1 (the vertebra below type-IIIb LSTV) as the true S2 would be clinically beneficial, even if this LSTV corresponds to the lowest lumbar vertebra. In a patient series analyzed by Tatara et al, preoperative planning with navigation software required S2-alar-iliac screws to be inserted from S1 in all patients with Castellvi type-IIIb LSTV 19 .…”

“…Similarly, in patients with Castellvi LSTVs, particularly those with type-IIIb LSTV, considering S1 (the vertebra below type-IIIb LSTV) as the true S2 would be clinically beneficial, even if this LSTV corresponds to the lowest lumbar vertebra. In a patient series analyzed by Tatara et al, preoperative planning with navigation software required S2-alar-iliac screws to be inserted from S1 in all patients with Castellvi type-IIIb LSTV 19 . Regarding vertebral numbering, TLTV was most frequently identified at T13, with the highest incidence of dysplastic rib types B and C. The most frequent combinations of presacral vertebral numbers were T13 and L5 in patients with type-III LSTV and T13 and L4 in patients with S6 LSTV.…”

Is the Greater Trochanter the Ideal Freehand Landmark for the S2AI Screw Angle in the Caudal Direction? Commentary on “Extra-articular Portion of the Sacroiliac Joint—Between the Sacral and Pelvic Tuberosities: An Anatomical Guide for the S2-Alar-Iliac Screw Trajectory” by Tatara et al

“…No screw-related complication was observed. 1 According to our knowledge, TGT is not the only reported anatomical landmarks of the S2AI screw angle in the caudal direction. In previous studies about freehand S2AI technique of both Shillingford, J. N. et.…”

“…The author introduced a novel freehand technique for S2AI screw placement assisted with a guidewire using a new anatomical landmark. 1 In this technique, a guidewire is inserted into the ilium from the extra-articular portion of the sacroiliac joint just lateral to the ideal screw entry point toward the tip of the greater trochanter(TGT) and guides the screw trajectory. Navigation software is used preoperatively to determine the ideal S2AI screw trajectory.…”