66-year-old male with back pain after falling in a wheelchair.
Hyperextension injury including a fracture of the bridging osteophytes at T9-T10 with an associated paravertebral hematoma. No ventral epidural hematoma. No cord signal abnormality.
There’s a super old Nature article that says “The stability of the spine depends on its ligaments and especially on the intervertebral discs and the common spinal ligaments. The bones, whether individually or as a group, contribute stability to the spine only by acting as anchorages for the ligaments.” Assuming that’s true, a traumatic injury that tears spinal ligaments stands a good chance of resulting in spinal instability. In patients with diseases that result in a rigid spine, there are varying degrees of calcification or ossification of the spinal ligaments, and even a low-energy impact can result in severe injuries. Essentially, the longer the fused vertebral segment, the longer the lever arm on which forces can act during a traumatic incident (i.e., because physics).
The first of these diseases is ankylosing spondylitis, in which T-cells attack the sites where the vertebra meet the joint capsule, tendons, and ligaments. These connections weaken, the bones become sclerotic and osteoporotic, and the inside of the spinal ligaments ossify around the annulus fibrosus, forming syndesmophytes, and the characteristic “bamboo spine” appearance. Importantly, this inflammatory, rigidity-inducing process can involve all three of the spinal columns – from the anterior longitudinal ligament through the posterior ligament complex. So, when there’s a traumatic injury, these tissues are significantly more likely to fracture, resulting in severe spinal instability. These patients are 11x more likely to have an associated spinal cord injury than someone in the general population, and around 20% have concurrent epidural hematomas, further increasing the risk of neurologic compromise.
Around 70% of spinal fractures in ankylosing spondylitis are hyperextension injuries and are most commonly located from C5-T1. Commonly, the fracture line is transverse and passes through the disk space instead of the vertebral body – probably because the discs become calcified and brittle, and represent the weakest link in the bamboo stick. Around 20% of people have multiple noncontiguous fractures too, so recommend a full spine CT if the initial study just shows you one spinal segment. You can use that study to see if you’ll need MRIs of those additional spinal segments.
The other principle cause of spinal rigidity is diffuse idiopathic skeletal hyperostosis, or DISH. It arises in people in their 50s-60s and is a bit more common in males. It’s characterized by extensive spinal ossification that occurs predominantly along the anterior aspect, including ossification of the anterior longitudinal ligament, producing its characteristic appearance of “flowing osteophytes.” Since DISH is typically asymptomatic, the history likely won’t tip you off to the presence of a rigid spine, as it would in someone with ankylosing spondylitis. Importantly, the fracture doesn’t have to occur within the region of spinal rigidity; it often occurs in the junctional zone beyond the fusion since there’s atypical stress transferred to the normal vertebrae from the abnormally long lever arm. When the fracture is nondisplaced, you’ve got to figure out the anterior-posterior extent of the fracture plane. If the DISH fracture doesn’t extend to the posterior elements (namely, the facets, lamina, and spinous process), then it can often be managed nonsurgically. If it does extend posteriorly, then it can be just as unstable as an ankylosing spondylitis fracture.
These fractures are a huge deal, particularly in the elderly population. For patients who are over 80-years-old with with ankylosing spondylitis and DISH, one study showed an 84% mortality, and a rate of 38% for those in their 60s (most commonly secondary to pneumonia/respiratory failure).
Management:
Neurosurgery consultation. Unstable fractures require surgical fixation while associated traumatic sequelae (e.g., epidural hematoma, central cord compression, etc.) may require decompression as well.