Radio-anatomical study of anterior-posterior placement sacroiliac screw channel.

Purpose: The outlet of the classic sacroiliac screw (SIS) cannot be precisely controlled by aiming devices, which may lead to malpositioned implants and neurovascular and visceral injury. This study aimed to radio-anatomically measure the parameters of the channel for anterior-posterior placement SIS (AP-SIS), which can be placed percutaneously with an aiming device.

Methods: Pelvic CT scan data of 80 healthy adults (40 males and 40 females) with an average age of 45 years (range 20-70 years) were collected. The length (L), width (W), height (H), cortical bone spacing (M), camber angle (E), anteversion angle (F), cross-sectional safety angle (P) and sagittal safety angle (Q) of the channel were measured by CT or Mimics software.

Results: The L, W, H, M, E, F, P and Q measures of S1 were 109.2 ± 8.0 mm, 18.5 ± 1.9 mm, 21.7 ± 1.7 mm, 8.1 ± 0.4 mm, 44.2 ± 3.2°, 42.4 ± 3.6°, 16.8 ± 1.1°, and 19.4 ± 2.0°, respectively, for S1, and 113.5 ± 9.4 mm, 18.2 ± 1.5 mm, 21.7 ± 1.7 mm, 7.7 ± 0.4 mm, 44.7 ± 3.2°, 31.2 ± 2.7°, 13.8 ± 1.0° and 15.4 ± 1.4°, respectively, for S2. Of the L measures, the intra-iliac segment was slightly longer than the intra-sacral segment. All parameters showed significant sex-related differences (p < 0.05).

Conclusion: The AP-SIS channels of S1-2 have sufficient width and length to accommodate a cancellous screw with a Φ 7.0-8.0 mm and a length 90-130 mm. The intra-iliac segment is a long channel screw with better mechanical properties over classic SIS.