Osteitis condensans

This is a case of osteitis condensans (sometimes also described as hyperostosis triangularis). On X-ray, the condition is characterized by pronounced sclerosis that forms a triangular pattern extending caudally within the primary load-bearing zone. No X-ray was taken of our patient. Nevertheless, the diagnosis can be clearly established based on these three criteria:

• Bone marrow edema primarily in the ventral slices
• Marked sclerosis of the bone
• No erosions detectable

Osteitis condensans is the differential diagnosis for axial spondyloarthritis, which most frequently causes confusion and is sometimes treated for decades with various conventional and biologic disease-modifying antirheumatic drugs (DMARDs). The cause is instability of the pelvic ring, which leads to premature, severe osteoarthritis of the sacroiliac joints, sometimes involving the pubic symphysis.

The following factors are known to cause osteitis condensans:

• Pregnancy and childbirth
• Obesity
• Scoliosis
• Anatomical variations of the sacroiliac joints
• “Run-and-stop” sports, such as tennis, soccer, and handball
• Sports that place stress on the pelvis, such as horseback riding

Typically, inflammatory serology is negative, and the HLA-B27 test is negative.

Bone marrow edema in osteitis condensans can be very pronounced—as in our patient—and difficult to distinguish from that seen in axial spondyloarthritis. In such cases, analyzing the location of the changes in the ventrodorsal plane is helpful