The components and functionality of a new prototype system are described and its precision and accuracy evaluated. It was found to have an accuracy similar to other comparable systems in the literature.

The slices-to-volume ultrasound-CT registration significantly reduces the total registration time per vertebra, making this automated technique more practical intraoperatively.

Our registration technique demonstrates good accuracy and robustness under clinically realistic conditions and thus warrants further studies on its surgical application.

Postpartum sacral insufficiency fracture is an uncommon occurrence that is often under-diagnosed because its symptoms of low back, buttock and groin pains may initially be attributed to physiologic biomechanical changes caused by pregnancy or to intervertebral disc disease. We present a case of bilateral sacral insufficiency fractures in a 37-year-old postpartum woman with osteopenic bone mineral density confirmed by dual energy X-ray absorptiometry. The symptoms were initially suspected to be of discogenic cause, and the fractures were incidentally appreciated at the edge of a lumbar spine magnetic resonance image. Therefore, it is important to keep in mind this potential diagnosis when examining imaging studies of postpartum patients. For women who present other risk factors of osteoporosis, imaging of the entire sacrum should be part of the imaging studies. If sacral stress fractures are diagnosed, further evaluation for bone mineral density and underlying metabolic bone disease is recommended.