In the spine, a disc or a nucleus pulposus is localized between vertebral bodies. It supports the spine by acting as a shock-absorbing cushion. A herniated disc in the spine is a condition during which a nucleus pulposus is displaced from intervertebral space. In some instances, a herniated disc can compress the nerve or the spinal cord that causes pain consistent with nerve compression or spinal cord dysfunction also known as myelopathy.
An intervertebral disc is composed of annulus fibrous which is a dense collagenous ring encircling the nucleus pulposus. Disc herniation occurs when part or all the nucleus pulposus protrudes through the annulus fibrous. The most common cause of disc herniation is a degenerative process in which as humans age, the nucleus pulposus becomes less hydrated and weakens. This process will lead to progressive disc herniation that can cause symptoms. The second most common cause of disc herniation is trauma. Other causes include connective tissue disorders and congenital disorders such as short pedicles. Disc herniation is most common in the lumbar spine followed by the cervical spine. A high rate of disc herniation in the lumbar and cervical spine can be explained by an understanding of the biomechanical forces in the flexible part of the spine. The thoracic spine has a lower rate of disc herniation.
The incidence of herniated disc is about 5 to 20 cases per 1000 adults annually and is most common in people in their third to the fifth decade of life, with a male to female ratio of 2:1
The pathophysiology of herniated discs is believed to be a combination of the mechanical compression of the nerve by the bulging nucleus pulposus and the local increase in inflammatory chemokines.
Herniation is more likely to occur posterolaterally, where the annulus fibrosus is thinner and lacks the structural support from the anterior or posterior longitudinal ligaments. Because of the proximity to the nerve roots, a posterolateral herniation is more likely to compress the nerve root and to produce radiculopathies in the associated dermatome. On the other hand, spinal cord compression and clinical myelopathy can occur if there is herniation of a large midline disc. The localized back pain is a combination of the herniated disc pressure on the longitudinal ligament, and chemical irritation due to local inflammation.
In the cervical spine, the C6-7 is the most common herniation disc that causes symptoms, mostly radiculopathy. History in these patients should include the chief complaint, the onset of symptoms, where the pain starts and radiates. History should include if there are any past treatments.
On physical examination, particular attention should be given to weaknesses and sensory disturbances, and their myotome and dermatomal distribution. The examiner should also pay attention at this point to any sign of spinal cord dysfunction.
Table 1: Typical findings of solitary nerve lesion due to compression by herniated disc in cervical spine
In the lumbar spine, herniated disc can present with symptoms including sensory and motor abnormalities limited to specific myotome. History in these patients should include chief complaints, the onset of symptoms, where the pain starts and radiates. History should include if there are any past treatments.
A careful neurological examination can help in localizing the level of the compression. The sensory loss, weakness, pain location and reflex loss associated with the different level are described in Table 2.
Table 2. Typical findings of solitary nerve lesion due to compression by herniated disc in lumbar spine
The straight leg raise test: With the patient lying supine, the examiner slowly elevates the patient’s led at increasing angle, while keeping the leg straight at the knee joint. The test is positive if it reproduces the patient’s typical pain and paresthesia.
The contralateral (crossed) straight leg raise test: As in the straight leg raise test, the patient is lying supine, and the examiner elevates the asymptomatic leg. The test is positive if the maneuver reproduces the patient's typical pain and paresthesia. The test has a specificity greater than 90%.
Over 85% patients with symptoms associated with acute herniated disc will resolve within 8 to 12 weeks without any specific treatments. However, patients who have an abnormal neurological examination or refractory to conservative treatments will need further evaluation and treatments.
X-rays: These are very accessible at most clinics and outpatient offices. This imaging technique can be used to assess for any structural instability. If x-rays show an acute fracture, it needs to be further investigated using CT scan or MRI.
CT Scan: It is preferred study to visualize bony structures in the spine. It can also show calcified herniated discs. It is less accessible in the office settings compared to x-rays. But, it is more accessible than MRI. In the patients that have non-MRI comparable implanted devices, CT myelography can be performed to visualize herniated disc.
MRI: It is the preferred and most sensitive study to visualize herniated disc. MRI findings will help surgeons and other providers plan procedural care if it is indicated.
Conservative Treatments: Acute cervical and lumbar radiculopathies due to herniated disc are primarily managed with non-surgical treatments. NSAIDs and physical therapy are the first-line treatment modalities. Translaminar epidural injections and selective nerve root blocks are the second line modalities. These are good modalities for managing disabling pain. Patients who fail conservative treatment or patients with neurological deficits need timely surgical consultation.
Surgical Treatments: As always surgical treatment is the last resort. Surgical treatments for a herniated disc include laminectomies with discectomies depending on the cervical or lumbar area. In addition, a patient with a herniated disc in the cervical spine can be managed via an anterior approach that requires anterior cervical decompression and fusion. This patient can also be managed with artificial disks replacement. Other alternative surgical approaches to the lumbar spine include a lateral or anterior approach that requires complete discectomy and fusion.
Thoracic spine herniated disc usually presents with radiculopathy symptoms or myelopathic symptoms depending on the compression of the nerve roots or spinal cord, respectively. As in the cervical and lumbar spine, patients initially are managed conservatively. A patient who has progressive myelopathic symptoms or does not respond to conservative treatment can be managed surgically. The surgical approach for thoracic spine includes the transthoracic or costotransversectomy approach for discectomies and fusion.