Ankylosing spondylitis of the thoracic spine

Patients complain of a chronic stiff back, especially early in the morning and easing with activity. Periods of worsening pain and stiffness come on spontaneously and are not provoked by activity or exercise. During the pain-free periods, the patient is effectively normal. Only slight radiation to the sides is present. Because several levels are usually involved and little referred pain is present, the pain is distributed in the vertical axis. All these are important differences from disc lesions, in which pain is usually referred horizontally, is worse during the daytime and is brought on by activity.

The findings on inspection depend on the duration of the disorder. Initially, a rigid lumbar segment is present, which later becomes flat, together with a slight accentuation of the thoracic kyphosis. This develops further to a thoracic hyperkyphosis with hyperextension of the upper cervical spine and flexion of the hip.⁴ Chest expansion may be diminished.

On functional examination, a clear capsular pattern is present with an equal amount of pain and limitation of both side flexions and rotations, more pain and limitation on extension, and only slight discomfort on flexion. The end-feel on rotation and extension is typically hard. The range of rotation has a significant negative correlation with the duration of the disease.⁵ Pain provoked by pressure on the spinous processes is usually much more severe than in an ordinary disc lesion.⁶ At a later stage, the vertebrae are much more vulnerable to fractures, because of loss of normal capsular and ligamentous elasticity.

The capsular pattern with hard end-feel, chronic prolonged morning stiffness and pain with periods of spontaneous exacerbations, together with other localizations of the same disorder, all in young patients (mainly 18–30 years), strongly indicates AS.

A radiographic examination should be done at once and must always include the sacroiliac joints.

Ankylosing spondylitis of the anterior longitudinal ligament

Involvement of the anterior longitudinal ligament gives rise to pain felt only at the sternum or in the epigastrium, without central dorsal pain. The pain has the same characteristics as in other localizations of AS at the thoracic spine.

Ankylosing spondylitis of the thoracic facet joints

The apophyseal joints are usually involved, together with the intervertebral joints. The former are mainly responsible for bilateral paravertebral pain. AS may lead to total fusion of the facet joints.

Ankylosing spondylitis of the costovertebral joints

Costovertebral and costotransverse joints are often affected in AS. Computed tomography (CT) scans usually show the classic lesions: erosions, sclerosis, joint widening and bridging.⁷

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