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Generel imaging aspects
Sacroiliitis - radiography
Sacroiliitis - MRI
Spine - radiography
Spine - MRI
Spinal fractures
Other joints

In patients with ankylosing spondylitis (AS) the spine gradually fuses through ligamentous ossification, syndesmophytosis and ankylosis of apophyseal joints resulting in a rigid hyperkyphotic deformity. Biomechanically the fused bone is more akin to a long bone and acts as a rigid lever incapable of appropriately dissipating the energy of a traumatic event. These altered spinal biomechanics combined with the brittle quality of the osteoporotic bone greatly increase susceptibility to vertebral column fractures, even after minor often trivial trauma.

Fracture types

Ankylosing spondylitis can result in two different types of fractures: compression fractures as part of osteoporosis and transverse fractures.

Osteoporotic compression fractures
May occur in all stages of the disease and contribute to the thoracic kyphosis often seen in AS. These fractures are usually stable and rarely cause spinal cord injury, though impingement of the cord may occur.

AS patient with thoracic kyphosis developed progressive pain in the lower thoracic region without preceding trauma. MRI of the thoracic and cervical spine (T1 and STIR sequence) shows pronounced osteoporotic collapse of Th12 with dislocation of the spinal cord.
The transverse fractures

Mainly occur in ankylosed spines in late stages of AS. They are caused by trauma; occasionally patients do not remember having had a trauma as they can be minimal and result from a fall from standing or seating position. Transverse fractures are most frequently located to the lower cervical and upper thoracic spine. They pass through ankylosed intervertebral spaces or vertebral bodies and will not always respect normal anatomical clivages. They may cross the spine horizontally or obliquely through several vertebral bodies. The posterior structures are usually involved, including the apophyseal joint region and ossified ligaments making the fracture site unstable. Thus, fractures of the stiff spine resemble fractures of tubular bones with a potential for dislocation. In the spine, this instability carries a risk for serious spinal cord or nerve injuries.
It is important to bear in mind that all movement occurs at the fracture site in an otherwise completely ankylosed spine. This can cause serious adverse events, particularly in the cervical region, if the fracture is attempted stabilized in a cervical collar which does not fit. The spinal cord can thereby be compressed, resulting in neurological lesions following the movement.


Fracture of C7 - before applying a cervical collar - with only slight dislocation of the fracture. The figure is shown with kind permission from Acta Orthop Belg (article 2010;76:413-5).


Fracture of the C7 – after applying a cervical collar. The fracture has been torn apart and there is angulation corresponding to the spinal canal potentially causing damage to the spinal cord. The figure is shown with kind permission from Acta Orthop Belg (article 2010;76:413-5).

Patient recommendation
The Danish (and other national) Ankylosing Spondylitis Society and the Ankylosing Spondylitis International Federation (ASIF) therefore recommend that patients carry information cards about their illness, including a photo showing the normal posture of the person. This must be considered by paramedics, emergency room physicians, radiographers etc. in cases of suspected fracture.

Information card recommended by The Danish Ankylosing Spondylitis Society.

Medical recommendations

When possible, it is important to diagnose fractures before they are dislocated and give rise to neurological deficits. Hence the following guidelines.

The possibility of spinal fracture must always be considered when an AS patient reports:

  • A direct or indirect spinal trauma, even minor trauma.
  • Newly onset of mechanical back pain that is triggered or worsened by activity and completely or partially relieved by rest.
  • Changes in posture; if necessary check photo of the patient on the information card.
  • Occurrence of new neurological symptoms (even weak). These can occur immediately after a trauma or be delayed for hours or days.

When substantive suspicion of fracture is present, the following is important:

  • Manage the patient as having an unstable fracture until the diagnosis is excluded.
  • Avoid the use of rigid cervical collar, if it does not immediately fit the patient's shape.
  • Do not attempt to correct a kyphotic spine.
  • When positioning and moving the patient, support the entire spine in the position present before the trauma.

Diagnostic Imaging:
Conventional radiography in at least two planes is often the initial examination. It can be used to diagnose o
steoporotic compression fractures and show obvious transverse fractures.


Obvious fracture through a discus and the posterior structures with dislocation of the lower part anterior to the upper part of the spine (arrow).


Altered anatomy with poorly defined discs, osteoporosis, calcified ligaments etc. often complicates interpretation of conventional radiographic images. A non-dislocated fracture can be difficult to diagnose with certainty by conventional radiography. There may only be a small osseous break at the discus (corresponding to syndesmophytes) although there is a potentially unstable fracture, which may dislocate and cause neurological deficits.


AS patient with pronounced pain after a tennis game. Radiography does not confirm the occurrence of a fracture. There is not visible malalignment or osseous breaks.


Supplementary CT scan shows fracture corresponding to syndesmophytes with increased height of the intervertebral space, signs compatible with a horizontal fracture.


Conventional radiography can thus only contribute diagnostically if there are positive findings such as slight misalignment between the vertebrae. A simple fracture of a spinosus process also points with high probability to the presence of a transverse fracture (Koivikko & Koskinen 2008; http://www.springerlink.com/content/32632r1h15140931/fulltext.pdf).


Standing radiography of the thoracic spine in a 64-year-old man with AS and persistent mechanical back pain during 3-4 weeks. There is slight displacement between Th9 and Th10 anteriorly (arrow), and the intervertebral space has reduced height both on the lateral and frontal view, all suggesting fracture.

CT performed in supine position, coronal and sagittal reconstructions clearly show the fracture through the intervertebral space and the posterior structures. In this position the intervertebral space opens anteriorly with concomitant space reduction of the spinal canal.

It is important to be aware that conventional radiography cannot exclude the presence of spinal fracture. Supplementary computer tomography (CT) and/or magnetic resonance imaging (MRI) may therefore be necessary.

Most fractures are cervical or at the cervico-thoracic transition where fractures can be difficult to detect by radiography due to overprojecting shoulders. Besides, the occasional occurrence of pronounced kyphosis can impede an optimal frontal view. In this region CT is therefore the preferable initial examination.

Computer tomography
Is often necessary to confirm the diagnosis of transverse fractures and/or delineate the osseous structure before surgical intervention. The examination should be conducted as a multi-slice CT (MSCT) with multiplanar reconstructions in relevant planes. MSCT is superior to conventional radiography in the diagnosis of fractures, especially if the scan is performed with high resolution (Harrop et al. 2005; http://www.ncbi.nlm.nih.gov/pubmed/16025019; Jacobs & Fehling 2008; http://www.ncbi.nlm.nih.gov/pubmed/18290738. Be aware that there may be more than one fracture, especially in patients with obvious trauma.

AS patient after a fall from a bicycle. Primary CT shows two transverse fractures in the cervical region (arrows).

Magnetic resonance imaging

Is always indicated in patients with neurologic deficits. It can visualize spinal cord injury and hemorrhages, most importantly epidural hemorrhage, often necessitating emergency surgery (Koivikko & Koskinen 2008; http://www.springerlink.com/content/32632r1h15140931/fulltext.pdf; Campagna et al 2009; http://www.ajronline.org/content/192/4/987.full.pdf + html).

Fracture in the cervical region causing neurological deficits (paresis). Besides the fracture there is hemorrhage in the spinal cord corresponding to the angulation area (arrow). Part of this may be caused by inappropriate stabilization in a position “not normal" for the patient; please see the first patient illustrated with transverse fracture.

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