Prevalence and severity of sacral dysmorphism and implications for safe transsacral screw placement in the Indigenous and non-Indigenous Australian population: A retrospective matched cohort study.

Objective: To compare prevalence and severity of sacral dysmorphism in Indigenous and non-Indigenous Australian populations.

Methods: We performed a single centre retrospective matched cohort study in consecutive Indigenous and non-Indigenous Australian patients who received a CT scan of the pelvis between January and March 2024 at our institution. Patients were excluded if they were under the age of 18 at the time of the scan or had a history of pelvic fractures or fixation. CT scans were assessed for both qualitative and quantitative features of sacral dysmorphism. The primary outcome of interest was the prevalence and severity of sacral dysmorphism in Indigenous and non-Indigenous Australian populations.

Results: 120 patients were included in the study - 60 Indigenous and 60 non-Indigenous Australians. All patients exhibited at least one characteristic of sacral dysmorphism. There was no difference in the prevalence of qualitative sacral dysmorphism between the two groups. Compared to their non-Indigenous counterpart, Indigenous patients demonstrated a lower S1 transsacral corridor coronal diameter (20.50 vs. 21.85 mm, p = 0.005), S1 oblique corridor axial diameter (17.90 vs. 19.60 mm, p = 0.028), S1 pelvic width (144.85 vs. 158.70 mm, p < 0.001), S2 transsacral corridor coronal diameter (13.70 vs. 14.95 mm, p = 0.013), S2 transsacral corridor axial diameter (10.60 vs. 11.55 mm, p = 0.013), and S2 pelvic width (126.60 vs 136.00 mm, p < 0.001). Additionally, in Indigenous patients, S1 and S2 transsacral and oblique S1 iliosacral fixation lengths were shorter. Where an S1 trans-sacral osseous corridor was not present, the S2 corridor was significantly larger in coronal, axial measurements across both groups (p < 0.001).

Conclusions: Indigenous Australian patients exhibited more severe forms of sacral dysmorphism when compared to their non-Indigenous counterparts. Additionally the overall prevalence of sacral dysmorphism across this Australian population was amongst the highest reported in the literature. This may present significant technical challenges and warrants consideration when performing percutaneous iliosacral screw fixation.