Adjacent Segment Disease after Cervical Fusion
Adjacent segment degeneration is the appearance of degenerative changes with or without clinical symptoms in the level up or below the fused cervical segment. Adjacent segment disease may lead to symptoms of radiculopathy or myelopathy. The initial treatment of adjacent level disease is conservative but a fusion surgery of the adjacent level may be needed in the case of continued symptoms.
The vertebrae are stacked upon each other connected by intervertebral disks and facet joints. Additionally, various ligaments provide stability to the spine during motion. The fusion of a segment may result in increased stress at the segment adjacent to the fused vertebrae as the adjacent segment tries to compensate for the loss of motion.
The increased compensatory motion and stress may cause accelerated intervertebral disc degeneration in the adjacent segment. The increased pressure in the adjacent segment may cause disc herniation and loss of disc height. As a result, there may be degenerative changes in the facet joint (facet joint syndrome) and formation of bone spurs.
The degenerative changes may cause cervical canal stenosis which may present as cervical radiculopathy or cervical myelopathy. The adjacent segment disease has also been attributed to damage to ligament and muscles during anterior cervical decompression surgery.
The adjacent segment degeneration is more common in the lower segments of the cervical spine, especially C5-C6. Female patients and patients under the age of 60 years are more susceptible for adjacent level degeneration after ACDF (anterior cervical decompression and fusion). Similarly patients with a history of smoking and pre-existing degenerative changes in the adjacent segments are at an increased risk of accelerated degeneration.
The chances of adjacent level degeneration increase after 10 years of ACDF surgery. The symptoms of adjacent level degeneration depends upon the level of encroachment of the space occupied by the neural structures.
The symptoms of radiculopathy include pain in the dermatome supplied by the adjacent level. There may be motor weakness in the corresponding adjacent segment. Cervical myelopathy presents as clumsiness in the hands and difficulty walking. In some cases, there may be loss of bladder and bowel control.
The diagnosis of adjacent segment disease in a patient with a prior history of ACDF is made after thorough history and physical examination. The surgeon may look for signs of motor and sensory weakness in all the four limbs. The physician may also inspect the walking pattern of the patient. Special tests may be done to localize the segment involved in the symptoms.
Radiological examinations include an X-ray as the first investigation which may be followed by an MRI or a CT scan. A CT scan provides a more detailed image of the bony structures as compared to an X-ray. A CT scan is particularly helpful to look for ossification of the posterior longitudinal ligament and formation of a false joint in the fused segment. The MRI provided a detailed image of the soft tissue structures including the degree of compression of the neural structures.
The investigations are aimed to diagnose and also differentiate other similarly presenting pathologies such as infection, degenerative changes at a non adjacent segment, pseudoarthrosis, etc.
The initial management of adjacent level degeneration is conservative treatment. The conservative treatment consists of modification of the activity, pain medications, physical therapy, epidural injections. Operative management is reserved for patients with no benefit from conservative management and symptoms of motor and sensory weakness.
The operative management is extension of the ACDF construct to the adjacent segment involved. A total cervical disc replacement may also be done in a case of adjacent segment degeneration.