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Findings: AP and lateral views of the lumbar spine.

1. Loss of disc height with adjacent irregularity and sclerosis of vertebral body
   endplates at L-3-4 and L-4-5 (more severe at L3-4).
2. Erosion and widening of the right sacroiliac joint.

Discussion: Osteomyelitis of the spine with disc space infection (infectious spondylitis) comprises 2-4% of osteomyelitis cases. Routes of contamination are (1) hematogenous, via arterial flow or by venous back flow through Batson's Plexus, (2) contiguous contamination from adjacent infection in soft tissue, (3) direct implantation during instrumentation or surgery, or from trauma.

Men are affected more than women, with the highest frequency in the fifth and sixth decades. Urinary tract infections, diabetes, and IV drug abuse are risk factors. There is often a recent history of primary infection (urinary tract, respiratory, skin), instrumentation or surgical procedure. The most frequently encountered organism is Staph aureus. Laboratory testing will show an elevated ESR; however, the leukocyte count may or may not rise. In addition to the spine, hematologic seeding may take place at the sternoclavicular, acromioclavicular, and sacroiliac joints, and the pubis symphysis. Sacroiliac infection is usually unilateral, seen as blurring of the subchondral osseous line and erosion which is most prominent at the inferoanterior aspect of the joint space.

Radiographic findings do not appear until 1-3 weeks following infection. Early changes are loss of disc height and endplate irregularity. Subsequently, spread to the adjacent vertebral body occurs. After 10-12 weeks, sclerosis is seen. Following treatment, there may be a radio-dense (ivory) vertebral body, focal ankylosis, and osteophytosis. MR findings of disc and endplate enhancement, and increase T2 signal intensity may predate the radiographic findings.

The differential diagnosis includes: (1) neuroarthropathy, (2) spondyloarthropathy of hemodialysis, (3) post-traumatic pseudoarthrosis of ankylosing spondylitis, (4) mechanical erosion found with rheumatoid arthritis, (5) osteoarthritis.

References:
Resnick D and Niwayama. Diagnosis of Bone and Joint Disorders,
2nd Edition, 1988. G. Chap. 72, Pages 2619-2643.

Sartoris D. Musculoskeletal Imaging: The Requisites. 1996:127-128.

Dahnert W. Radiology Review Manual, 2nd Edition, 1993. Page 133.

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