Ring apophysis is a narrow mound which more or less completely encircles the rims of the upper and lower surfaces of the growing ossific mass of the vertebral body.
In the developing spine, the outermost fibers of the annulus fibrosus(the Sharpey fibers) are embedded in the ring apophysis.
If intervertebral disc herniation occurs before fusion of the ring apophysis, avulsion fracture of the vertebral end plate may occur through a relatively weak point between the ring apophysis and the adjacent vertebral body.
Using the magnetic resonance image and computed tomography, we studied clinical and radiological features of this kind of fractures in 23 patients(25 fractures) from Dec. 1989 to Jul. 1994. The mean age at the time of diagnosis was 18.5
years(range
11.5
to 41 years). Seventeen patients(74%) were male, six patients were female (26%). Sixteen patients (70%) were related to a history of trauma. Most patients (21 patients, 91%) complained of low back pain radiating to lower extremities.
Simple X-ray revealed the lesion (bony fragment or defect at the posterior-vertebral margin) in only 6 cases (24%) and no associated anomalie. On CT scan or MRI studies, fourteen patients showed characteristic osteochondral fragment displaced
posteriorly into the spinal canal with defect at the posterior margin of the vertebrae, seven patients showed exophytic bony lesion at the posterior margin of the vertebrae, two patients showed concomittent fracture and exophytic bony lesion. All
patients had associated disc herniation at the affected level. The most commonly affected site was posterior cephalad margin of L5 in 11 cases(44%).
|