Vertebral compression fracture with the vacuum cleft sign.

Vacuum cleft is seen usually in osteoporotic fractures in the thoracolumbar spine.
The cleft predict mobility of the fracture . The cleft fills with air or fluid depending on the posture. The sign is rarely seen in infection or neoplasms. The high specificity of the sign for the osteonecrosis or Kummell΄s disease is debated.

F. McKiernan , T. Faciszewski Arthritis & Rheumatism Volume 48, Issue 5, 2003

Theodorou DJ .The intravertebral vacuum cleft sign.
Radiology 2001 ; 221:787-9.