Posterior longitudinal ligament ossification describes a problematic degenerative condition in which one of the important spinal ligaments loses its soft and flexible structure and hardens into a bony tissue. Being that this ligament borders the central spinal canal, the resulting thickening and hardening is often a prime cause of spinal stenosis. While the posterior longitudinal ligament runs from the axis to the sacrum, virtually all cases of ossification occur in the upper cervical region, followed less commonly by the lower cervical and upper thoracic spinal zones. Lumbar OPLL is very rare, but does exist in some scenarios, although the consequences are usually not nearly as symptomatic.
This commentary defines OPLL and explains why this structural change in the spinal anatomy is a significant cause and contributor to central stenotic change, particularly in the cervical region.
What is Longitudinal Ligament Ossification?
Let us begin by examining the ligament itself. There are 2 longitudinal ligaments: the posterior and the anterior. The anterior ligament travels virtually the entire length of the spine, on the frontal side of the vertebral bodies. This is the surface that does not influence the spinal canal. Meanwhile, the posterior longitudinal ligament also runs virtually the entire length of the spine, but resides on the rear surface of the vertebral bodies. This makes the ligament the effective frontal border of the central spinal canal, residing on its anterior face.
The ligamentum flavum runs on the posterior of the central spinal canal, forming its posterior border.
Focusing on the PLL, ossification is the process by which a soft tissue becomes a bony one. Instead of a flexible fibrous ligament, areas of the PLL become skeletal, often growing attached to the vertebral bodies and the outer surface of the spinal canal membrane, called the dura mater.
In essence, the condition describes a process by which a soft tissue becomes skeletal, thickening and hardening against the frontal surface of the central spinal canal. As noted above, this transformation is most commonly seen in the cervical levels, followed by the upper thoracic levels. However, PLL hardening can occur virtually anywhere in the spinal anatomy.
Causes of Posterior Longitudinal Ligament Ossification
There are rarely well defined causes of OPLL. However, there are many factors that have been cited as being contributory to its development:
The condition is doubly more common in men than in women.
The condition is far more common in Northern Asian patients than in other ethnicities.
The condition definitely has genetic markers that can predispose a person to inherit a propensity to develop OPLL from their parents.
Ossification in this ligament is often part of a larger symptomatic process, such as those found in ankylosing spondylitis, diabetes and certain metabolic diseases.
Age is the most universal factor in accounting for OPLL. Most patients are passed middle age, and many are elderly, suffering from the typical spinal degeneration that comes about with ever-advancing age.
Just because the posterior longitudinal ligament hardens does not mean that symptoms will result. In fact, the majority of cases are mild and completely asymptomatic, as is par for the course when discussing many causes of spinal stenosis. However, most cases of OPLL will continue to progress and may cause pain and neurological deficits in the future, as the conditions worsens.
Treatment for Posterior Longitudinal Ligament Ossification
Like most cases of structural stenosis, the typical treatments for symptomatic cases of OPLL involve extremely invasive surgery. When the spinal cord has been compromised by ligamentous ossification, the usual approach is to provide surgical decompression using any number of possible approaches.
Regardless of the particular procedure utilized, including laminectomy, corpectomy and fusion, the cord must be freed up from the impingement, without causing more harm than good. Since ossification often bonds the dura mater to the PLL, this can be an extremely complex task.
In cases of asymptomatic ossification, no treatment is needed. However, some statistics show that physical therapy, or regular exercise of the area, may have positive long-term benefits in reducing the likelihood of experiencing symptomatic versions of the condition later in life.
Regardless of symptomatic expression, when ossification is present, the condition should be monitored by a spinal neurologist.
Posterior Longitudinal Ligament Ossification Summary
OPLL is shown to be a major factor is determining who will suffer significant neurological effects in the cervical spine. In fact, the condition is present in a substantial percentage of patients with spinal cord compression in the cervical region.
Treatment can be highly effective, but is often filled with complications, including cerebral spinal fluid leaks, neurological damage, failed fusions and the recurring regrowth of stenosis. Each approach to surgical treatment has positive and negative considerations, so be sure to research all possible procedural options before deciding on the ideal course of action. The best way to do this objectively is to discuss each variety of surgical technique with several doctors. Failure to consider all possible choices in surgical care might result in a poor postoperative outcome and a greater severity of complications.