Findings: Following the intravenous administration of 26.1 mCi of Technetium 99m MDP, a delayed posterior image over the pelvis and lower abdomen was obtained. Increased activity is noted throughout the sacrum, more pronounced on the left. In addition, a linear area of increased activity is noted along the superior aspect of the L-1 vertebral body.

Diagnosis: Sacral insufficiency fracture and L-1 compression fracture.

Discussion: Stress fractures can be divided into two types. A fatigue fracture occurs with repeated stress on normal bone. The second is an insufficiency fracture, which occurs when normal stress is placed on abnormal bone.

Insufficiency fractures are most commonly secondary to osteoporosis. However, other associations include Paget's disease and fibrous dysplasia.

Compression fractures commonly occur in the thoracic and lumbar spine. They characteristically involve either the superior or inferior end plate. This in distinction to a metastatic focus, which can show increased activity throughout the vertebral body in addition to involvement of the pedicle.

Finally, osteomyelitis commonly involves the disc space.

References:
McAfee JG, Reba RC, Majd M. The Musculoskeletal System. In: Wagner,
HN, Szabo Z, Buchanan JW, et al., Eds. (Principles of Nuclear Medicine, Ed. 2)
Philadelphia, W.B. Saunders, 1995:986-1019.

Mettler FA, Jr., Gulberteau MJ. Essentials of Nuclear Medicine Imaging, 4th Edition,
W.B. Saunders, Philadelphia 1998:311-320.

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