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RESEARCH PRODUCT

Bone Mass Distribution in the Sacrum

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description

The trabecular architecture and bone mass distribution of each bone follows biomechanical principles and is an adaption to the stress exhibited during lifetime. In patients with osteoporosis, the bone mass decreases and the bone microarchitecture changes. A distinct bone mass distribution in non-osteoporotic and osteoporotic individuals is demonstrated using statistical modelling in the sacrum. The authors studied the sacral bone mass distribution using a 3D statistical model based on clinical CT scans of 92 Europeans. In the group with worse general bone mass (less than 100 Houndsfeld Units (HU) measured in the body of L5), there were large areas of negative HU in the sacral alae. These “alar voids” describe a fatty sphere in the sacral ala, characterized by complete loss of trabecular bone. There was a distinct distribution of bone mass along the trans-sacral corridors. The most prominent decrease of bone mineral density was found in the sacral ala. The overall bone mass along the trans-sacral corridors was lower in the group with <100 HU in L5 compared to the group with generally higher bone mass. However, the largest difference was found in the vertebral bodies. The overall HU in S2 were lower than in S1. The underlying low bone mass in the sacral ala may explain the unique and consistent location of fractures in the sacral ala in fragility fractures of the sacrum. Loosening and backing out of iliosacral screws may be explained by the loss of bone mass in the sacral body. Trans-sacral implants traverse the sacrum and anchor in the cortical bone of the posterior ilium bilaterally. They do not depend on a good holding power in the trabecular bone of the sacrum.