Ankylosing Spondylitis
represents a chronic inflammatory disease, primarily affecting the axial skeleton and secondarily affecting the appendicular skeleton. It typically presents in men, 15-35 years old. Remember it as the least erosive and most ossifying arthropathy. Joint ankylosis is the hallmark, as the name less than subtlely suggests. Some details on different pieces of anatomy: SI joints are radiographically invovled first, bilaterally and symmetrically. Joint edges have a serrated “postage stamp” appearance due to tiny erosions, which start on the iliac side, due to the thinner cartilage, then progress to the sacral side.
Here’s a CT example that gives you an idea of the fine nature of the erosions:
The synovial portion of the SI joint, i.e. the anteroinferior 1/2 to 2/3 of the joint, ankyloses first, follwed by the ligamentous portion. Ankylosis of the posterosuperior ligamentous portion is considered to look like a “star.” The first CT above gives an idea of the initial involvement of the anteroinferior SI joint portion, while the next CT shows the more diffuse involvement at a later stage. The end result is ankylosis, which we see starting here on CT:
Other findings one might see in the pelvis are ossification of ligamentous attachments in the iliac crests and ischial tuberosities, classically giving a purported “whiskered” look. The symphysis pubis can show tiny “serrated” erosions like the SI joints, before it ankyloses. Purportedly, ~25% of ankylosing sponylitis eventually has symphysis pubis involvement. Probably since SI joints are the first radiographic evidence of AS and the pelvis is being imaged for that, lumbosacral AS involvement is typically seen first, as we see on the above pelvis radiograph, although apparently the thoracolumbar junction can be the first site of invovlement in the spine for AS. Involvement progresses cranially to involve the entire spine. At first, there is slight erosion of the vertebral body corners with secondary sclerosis, giving a classic squared vertebral body with “ivory” corners.
The ivory corners disappear, not unlike true elephant ivory has, leaving simply square vertebral bodies. The outer portion of the annulus fibrosus, i.e. Sharpey’s fibers, ossify first. Apparently this may not always be seen radiographically, but decreased ROM will suggest this to an astute radiologist. The ossification progresses deeper to involve the longitudinal ligaments, resulting in the classic syndesmophyte seen with AS, linking adjacent vertebral bodies. Here we see a nice AP and lateral example of ‘dem syndesmophytes:
Disc spaces tend to remain normal at first, with no loss of height, but they may eventually calcify. Apophyseal joints in the spine can be involved, if they choose to, with resultant erosions followed by ankylosis. All spinal ligaments can eventually ossify giving the classic “bamboo” spine.
Once you get a bamboo spine, a classic sign is that of the “tram track,” namely the syndesmophytes and ossified ligaments between spinout processes look like “tram tracks.”
. Similarly, fracture in the thoracolumbar region can result in pseudoarthrosis. This can also result from an area that failed to ossify. At this area one can see DDD, erosion, and bony sclerosis. These findings can resemble severe DDD, discitis/osteomyelitis, or “neuropathic” spinal disease.
Moving beyond the axial skeleton, the hip is the most common appendicular joint involved. Two kinds of patterns can be seen when the hip is involved, i.e. nondestructive and destructive. Kind of reminds me of relationships. The former is fortunately more common, as hard as that is to believe sometimes. In AS the hips are involved bilaterally and symmetrically, with, surprise surprise, ankylosis being the characteristic feature. There can be no joint space loss, or uniform joint space loss with axial migration of the femoral head. Here’s a fine example of the uniform joint space loss and axial migration.
TREATMENT:
Appropriate treatment of ankylosing spondylitis is a combination of treatment prescribed by your Rheumatologist (Dr. Meera Oza in Orange Park Phone number (904) 276-0001) and your Physiatrist (Physical Medicine & Rehabilitation MD). The Physiatrist, such as Dr. Rehman, can prescribe a regimen of exercises and stretching program to lessen the crippling postural abnormalities that develop with AS. These exercises and stretches combined help the patient maintain a better posture and stay in better physical shape so that one does not get chest infections as easily as one can get in advanced AS. Also, avoiding of trauma is paramount in AS such as car accidents and falls as the brittle spine can crack under the stress of trauma and result in significant longstanding crippling pain and or catatrophic spinal injuries.