Managing Fractures of the Ankylosed Spine

Trauma to the ankylosed spine represents a major challenge for spine surgeons, since changes in biomechanics render the spinal column prone to unstable fractures even after relatively trivial injuries. In a healthy flexible spine, the energy of a traumatic impact is distributed over multiple levels, due to the segmental configuration – i.e., alternating sequence of stiff vertebral body and deformable intervertebral disc (IVD). In the case of ankylosis, the spine becomes increasingly stiff due to the progressive formation of non-elastic bridges spanning multiple segments. This ankylosing process may lead to long mechanical lever arms on which traumatic forces can act, often resulting in patterns similar to traumatic fractures of long bones. Since stabilising structures, such as the longitudinal and interspinal ligaments, are often included in the ankylosing and ossifying process, these fractures are highly unstable and may lead to neurological deficit in case of dislocation. ¹


Patients affected by an ankylosing spinal disorder (ASD) have an increased lifetime risk of sustaining a spinal fracture, sometimes even after a low-energy impact such as a ground-level fall. The number of patients with ASD and a spinal fracture presenting with neurological deficits on admission is high compared with the general trauma population. Unfortunately, secondary neurological deterioration also often occurs because of patient/doctor delay, missed/occult fractures, unwarranted patient mobilisation and progressive post-traumatic myelopathy. Patients with ASD sustaining spinal fractures have considerably higher rates of morbidity and mortality than non-ankylosed trauma patients. ²

The optimal treatment strategy for patients with fractures of the ankylosed spine is not known. The available literature on this topic consists of case reports and retrospective small series only. The current paucity of data on the management of fractures of the ankylosed spine may lead to a suboptimal clinical outcome for patients. It is therefore important for healthcare professionals to be aware of the prevalent conditions leading to an ankylosed spine, i.e., ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH). This article will describe these two conditions, highlight the difficulties encountered when caring for an ASD patient with a spinal fracture and discuss the available treatment options.

Ankylosing Spondylitis
In AS, chronic inflammation leads to spontaneous fusion of the sacroiliac joints and vertebrae, eventually leading to multilevel bony fusion of the spinal column. AS is an autoimmune disease associated with the human leucocyte antigen-B27 (HLA-B27) gene and may coexist with Crohn’s disease, uveitis and psoriasis. Its worldwide prevalence is stable at around 0.1–1.4 %; it is more prevalent in males and typically starts in adolescence. ³ Clinical symptoms typically start with back pain and morning stiffness, evolving over the years into generalised stiffness of the entire spine until complete ankylosis.

In end-stage AS, thoracic hyperkyphosis combined with flexion contracture of the hips may lead to the characteristic ‘bent knees, stooped over’ posture. Decreased eyesight and disturbed postural balance may lead to an increased fall risk and, over the course of the disease, the spine becomes increasingly susceptible to fracture due to decreased elasticity. In advanced stages of AS, even a trivial trauma, such as a ground-level fall, may result in highly unstable spinal fractures (see Figure 1). Several authors have described that AS patients have a three- to fourfold increased lifetime risk of sustaining a spinal fracture compared with unaffected individuals. ⁴ This risk is proportionally related to the duration of the disease. ⁵ Not much is known about typical fracture patterns in AS, although some hypothesise that fractures occur most frequently through the IVD. ⁶ Chondroid metaplasia, and calcification of the annulus fibrosus and nucleus pulposus, lead to functional degradation of the IVD, possibly making this structure the weakest link in the AS-affected spine.