Study on the relationship between pelvic landmarks on the body surface and S2AI screw path

English Keywords:S2AI screw  Pelvic body surface landmarks  Anterior superior iliac spine  Greater trochanter

English Abstract:

  【Abstract】 Objectives: To investigate the relationship between pelvic landmarks on body surface and the trajectory of S2 alar-iliac(S2AI) screws in populations of different genders and body mass indexes. Methods: A retrospective analysis was conducted on 150 patients who underwent pelvic CT scans in the Affiliated Hospital of Southwest Medical University between February 2022 and February 2024. Basic demographic data including age, gender, weight, and height were collected. Pelvic models were reconstructed by CT, and screw trajectories were simulated on the models. The screw trajectories were extended to intersect with the skin surface, and the intersection points of the safe trajectories with skin formed a safety zone on the body surface. The shortest distances from the anterior superior iliac spine(ASIS), anterior inferior iliac spine(AIIS), and greater trochanter(GT) to the safe zone were measured. The length of the line connecting ASIS and GT on the surface, length of such line intersecting with the safety zone, length from ASIS to the safety zone along such line, length from GT to the safety zone along such line were measured. Group comparisons were performed based on gender and BMI[underweight group(BMI<18.50kg/m2), normal group(18.50kg/m2≤BMI<24.00kg/m2), overweight group(24.00kg/m2≤BMI<28.00kg/m2), obese group(BMI≥28.00kg/m2)]. Results: In males, the shortest distances from ASIS, AIIS, and GT to the safe zone were 19.87±3.66mm, 33.66±3.33mm, and 39.53±3.56mm, respectively; In females, they were 19.31±3.41mm, 33.23±3.45mm, and 38.74±3.23mm, respectively. No statistically significant differences were observed between gender groups(P＞0.05). The shortest distance from ASIS, AIIS, GT to safety zone was 14.03±1.64mm, 26.79±1.15mm, 43.68±1.32mm in the underweight group,17.67±2.36mm, 31.73±1.77mm, 41.18±2.43mm in the normal group, 21.85±1.37mm, 35.78±1.76mm, 36.80±1.68mm in the overweight group, and 25.66±0.84mm, 38.75±0.88mm, and 36.80±1.68mm in the obese group, respectively. Intergroup comparisons between the four groups were statistically significant(P＜0.05), and pairwise comparisons within groups were statistically significant(P<0.05). In males, the length of the line connecting ASIS and GT was 129.43±6.42mm, the length of the line intersecting with safety zone was 30.72±5.27mm, the length from ASIS to safety zone along the line was 33.61±8.82mm, and the length from GT to safety zone along the line was 69.14±11.46mm; In females, such lengths were 109.83±8.99mm, 32.32±4.94mm, 35.77±11.26mm, and 43.75±7.62mm, respectively, with significant differences between the two gender groups(P<0.05); In the underweight group, such distances were 119.40±12.21mm, 30.72±3.83mm, 25.42±7.75mm, and 65.64±14.79mm; In the normal weight group, they were 122.98±10.91mm, 30.29±4.29mm, 35.01±10.22mm, and 60.58±13.43mm; In the overweight group, they were 117.52±13.70mm, 32.12±6.27mm, 36.92±8.27mm, and 51.42±18.38mm; In the obese group, they were 120.52±13.95mm, 35.65±3.29mm, 29.58±11.67mm, and 60.93±15.13mm. The length of the line connecting ASIS and GT showed no statistically significant difference between weight subgroups(P>0.05). However, the length of the line intersecting with the safety zone, the length from ASIS to the safety zone along the line, and the length from GT to the safety zone along the line exhibited statistically significant differences between subgroups(P<0.05). Conclusions: All the S2AI screw safety channels targets a specific area on the body surface, and the line connecting the anterior superior iliac spine and greater trochanter(GT) passes through this safety zone, which can serve as an auxiliary landmark for placing the S2AI screw.