Radioanatomical study of the proximity of the sciatic nerve and the pelvic bone.

PURPOSE: Percutaneous thermal ablation of pelvic bone tumours carries a risk of iatrogenic injury to the sciatic nerve. This study aimed to determine the proximity of the sciatic nerve to the iliac bone as it exits the pelvis and evaluate its anatomical variability.

METHODS

This retrospective, non-interventional study reviewed consecutive MRI scans of the lumbar spine performed at our institution between September and October 2021. Two experienced musculoskeletal radiologists independently measured the shortest distance between the sciatic nerve and the adjacent bone at six predefined levels on coronal T2-weighted images: 1.5 cm above the acetabulum; at the acetabular roof; at the femoral head apex; at the fovea; at the acetabular notch; and at the ischio-pubic ramus apex. The nature of the interposed tissue and the anatomical variant of the sciatic nerve (according to the Beaton and Anson classification) were also recorded.

RESULTS

Ninety-six patients (192 sides) were included. The sciatic nerve was found to be closest to the bone at the femoral head apex (mean distance: 1.48 mm [95% CI: 1.11–1.86]), with no interposed tissue present in 53.1% of cases. The greatest nerve-to-bone distance was observed at the ischio-pubic ramus (mean distance: 16.42 mm [95% CI: 15.59–17.25]), where hamstring tendon interposition was present in 97.4% of cases. Anatomical variants (Beaton type B) were identified in 14.1% of hips but were not associated with greater nerve-to-bone proximity except at a distance of 1.5 cm above the acetabulum (p = 0.021). Inter- and intra-observer reliability were good to excellent.

CONCLUSION

The sciatic nerve is most vulnerable to thermal injury at the femoral head apex, where it lies within 1.48 mm of the greater sciatic notch and there is no interposed tissue in over half of cases. These findings suggest that hydrodissection may be technically challenging at this level and should be carefully planned during pelvic thermoablation procedures.