Background

Fragility fractures of the sacrum are increasing in prevalence due to osteoporosis and epidemiological changes and are challenging in their treatment. They exhibit specific fracture patterns with unilateral or bilateral fractures lateral to the sacral foramina, and sometimes an additional transverse fracture leads to spinopelvic dissociation. The goal of this study was to assess sacral bone mass distribution and corresponding changes with decreased general bone mass.

Methods

Clinical computed tomography (CT) scans of intact pelves in ninety-one individuals (mean age and standard deviation, 61.5 ± 11.3 years) were used to generate three-dimensional (3D) models of the sacrum averaging bone mass in Hounsfield units (HU). Individuals with decreased general bone mass were identified by measuring bone mass in L5 (group 1 with <100 HU; in contrast to group 2 with ≥100 HU).

Results

In group 1, a large zone of negative Hounsfield units was located in the paraforaminal lateral region from S1 to S3. Along the trans-sacral corridors, a Hounsfield unit peak was observed laterally, corresponding to cortical bone of the auricular surface. The lowest Hounsfield unit values were found in the paraforaminal lateral region in the sacral ala. An intermediate level of bone mass was observed in the area of the vertebral bodies, which also demonstrated the largest difference between groups 1 and 2. Overall, the Hounsfield units were lower at S2 than S1.

Conclusions

The models of averaged bone mass in the sacrum revealed a distinct 3D distribution pattern.