Ossification of the posterior longitudinal ligament (OPLL) is a condition where the posterior longitudinal ligament, a strong, fibrous band along the back of the spinal column, gradually transforms into bone. This process, known as ossification, results in the hardening and thickening of the ligament. OPLL most frequently affects the cervical spine (neck region), though it can occur in other parts of the spine.
Development and Contributing Factors
The exact reasons why ossification of the posterior longitudinal ligament develops are not fully understood, but several factors are believed to play a role. A strong genetic predisposition exists, with the condition showing a higher prevalence in individuals of East Asian descent, affecting approximately 0.8% to 4.3% of Asian populations compared to 0.1% to 1.7% in Caucasians. Family studies indicate that OPLL prevalence can be as high as 26% in parents and 29% in siblings of affected individuals, suggesting a hereditary component.
Aging is another factor, as OPLL often manifests in individuals over 50 years old, with a notable male predominance. Certain metabolic conditions are also associated with its occurrence, including diabetes mellitus and diffuse idiopathic skeletal hyperostosis (DISH). Other linked conditions include hypophosphatemic rickets/osteomalacia, hypoparathyroidism, and acromegaly. Environmental influences such as obesity, a diet rich in vitamin A, and prolonged abnormal mechanical stress on the head are also considered potential contributing elements.
Associated Symptoms
Symptoms of OPLL vary depending on the extent and location of the bony growth. In early stages, OPLL often causes no symptoms or only mild discomfort, such as a dull ache or chronic pain and stiffness in the neck or back. Some individuals may experience tingling, numbness in their hands, or dysesthesia.
As the ossified ligament expands, it can press on the spinal cord, leading to myelopathy, or compress individual nerve roots, causing radiculopathy. Myelopathy symptoms often involve challenges with movement and coordination, including difficulty walking, balance problems, clumsiness, and impaired fine motor skills. In advanced cases, myelopathy may affect bladder and bowel control. Radiculopathy typically causes pain, tingling, numbness, or weakness radiating into the neck, shoulder, arm, or hand, depending on the compressed nerve root. While symptoms usually progress gradually, they can sometimes worsen suddenly after a minor injury.
Diagnostic Process
Confirming a diagnosis of OPLL typically begins with a thorough medical history and physical examination. Following this, various imaging studies are employed. Plain X-rays are often the first imaging step and can reveal bone formation along the spine. However, X-rays are less sensitive for detecting smaller ossifications, which can sometimes be obscured by other bony structures.
A computed tomography (CT) scan is generally considered the most effective imaging method for precisely evaluating the size, shape, and overall extent of the ossification. CT scans excel at showing bony detail and can detect ossifications that might be missed on X-rays, particularly segmental or localized types. This detailed view helps in assessing the morphology of the ossified mass and its occupation ratio within the spinal canal. Magnetic resonance imaging (MRI) is then utilized to assess the soft tissues, providing information on the degree of compression on the spinal cord and nerves. MRI can also reveal changes within the spinal cord itself, such as myelomalacia, which indicates cord injury. While MRI is valuable for soft tissue assessment, it can sometimes be challenging to differentiate ossification from simple ligament hypertrophy.
Management and Treatment Approaches
Management of OPLL is tailored to the individual’s symptoms and the degree of spinal cord or nerve compression. For patients with no symptoms or only mild discomfort, non-surgical management is recommended. This conservative approach includes careful observation, physical therapy to maintain spinal mobility and strength, and pain relief medications such as non-steroidal anti-inflammatory drugs (NSAIDs), anticonvulsants, or topical opioids. Lifestyle adjustments and activity modification are also advised to minimize stress on the spine and potentially slow ossification progression.
Surgical intervention is reserved for individuals who develop progressive neurological symptoms, particularly myelopathy, indicating significant spinal cord compression. The goal of surgery is to decompress the spinal cord and relieve pressure from the ossified ligament. Surgical strategies fall into two categories: posterior and anterior approaches.
Posterior Approaches
Posterior approaches, such as laminectomy or laminoplasty, are common for multi-level disease. A laminectomy involves removing a portion of the vertebral bone called the lamina to create more space for the spinal cord, and sometimes includes fusion to stabilize the spine. Laminoplasty involves creating a hinge in the lamina to expand the spinal canal, allowing the spinal cord to drift backward and decompress. Laminectomy with fusion may offer advantages in maintaining cervical lordosis.
Anterior Approaches
Anterior approaches involve accessing the spine from the front. Procedures like anterior cervical discectomy with fusion (ACDF) or anterior cervical corpectomy with fusion (ACCF) directly remove the ossified ligament and, if necessary, a portion of the vertebral body to relieve pressure. Anterior approaches are considered for single or dual-level ossification or very severe, localized compression. However, they can carry a higher risk of complications, such as dural tears or cerebrospinal fluid leakage, especially if the ossification has fused with the dura mater. The choice between anterior and posterior approaches depends on several factors, including the number of affected vertebral levels, the alignment of the spine, and the specific characteristics of the ossification.