Spondylolisthesis occurs when one vertebrae "slips" forward relative to the one below it. Spondylolisthesis is most frequently used to describe this process in the lumbar spine, but it may occur in the cervical or thoracic spine as well.
Spondylolisthesis can be caused by different pathological processes. In fact, spondylolisthesis has traditionally been divided into different categories based on the underlying pathology causing the slip (ie: the Wiltse classification). The categories are congenital, isthmic, degenerative, traumatic, pathologic, and post-surgical (aka: iatrogenic).
Regardless of the category, the end result is the same: one vertebrae slips forward relative to the one below it. Let's talk about each category in more detail...
Congenital spondylolisthesis occurs in children. It is usually caused by malformation of the superior articulating facet of the first sacral vertebrae (S1). The facet is a portion of bone that forms a joint with the vertebrae above or below it. Therefore, in congenital spondylolisthesis the malformed S1 facet joint is unable to form a stable joint with the lowest lumbar vertebrae (L5). The end result is that the L5 vertebrae is able to slip forward relative to the sacrum.
Isthmic spondylolisthesis occurs when there is a break in the bone that connects the facet of one vertebrae to the facet of the vertebrae immediately above (or below) it. This connecting bone is known as the pars interarticularis. The defect in the pars interarticularis is known formally as spondylolysis (see image below). Spondylolysis does not necessarily cause spondylolisthesis, but when it does it is classified as "isthmic". This type of spondylolisthesis is more common in those of Inuit heritage, as well as in athletes involved in repetitive hyperextension of the low back (ie: gymnastics, tennis, football, etc).
Traumatic spondylolisthesis is exactly what it sounds like. Injury to the facet joints, pars interarticularis, or ligaments of the spine can allow one vertebrae to slip forward/dislocate relative to the one above and/or below it.
Pathologic spondylolisthesis occurs when the slip is caused by some underlying pathology in the bone. This category is broad and may include tumors, osteoporosis, osteopetrosis, Paget's disease, or other diseases of bone formation/metabolism.
Post surgical (also known as iatrogenic) spondylolisthesis occurs after surgery. It most frequently develops after a "simple" laminectomy is performed. If too much bone is removed during a laminectomy it may cause instability and allow a slip to occur.
The last category, degenerative spondylolisthesis, affects people over the age of forty. It is unclear exactly what causes this type of spondylolisthesis, but it is believed to be secondary to a combination of arthritic changes in the facet joints, degenerative disc disease, and bony remodeling of the pars interarticularis. Degenerative spondylolisthesis, unlike isthmic or congenital, usually results in the fourth lumbar vertebrae (L4) slipping over the fifth lumbar vertebrae (L5).
Spondylolisthesis typically presents with a combination of low back pain with or without radiculopathy (ie: "zingers" down the legs). The radiculopathic symptoms are due to narrowing of the intervertebral foramen and pinching of the nerves as they exit the spinal column.
Neurological symptoms such as weakness, bowel or bladder problems, or sexual dysfunction are uncommon. These symptoms become more common as the severity of the slip increases.
Many patient's with spondylolisthesis also have significant hamstring tightness (ie: unable to touch their toes). Additionally, many patients will walk or stand with their torso or knees in a flexed position.
Diagnosis and Severity
Diagnosis of spondylolisthesis is based on x-rays, CT scans, and MRI imaging. X-rays and CT scans are best at delineating the bony anatomy. MRIs are frequently ordered to assess the amount of nerve compression (especially in patients with signs of neurologic dysfunction).
The severity of the slip is based on the Meyerding classification system. Type one slips occur when less than 25% of the diameter of the vertebral body slips forward relative to the one below it. Type two slips are between 26% and 50%. Type three slips are between 51% and 75% and type four slips are between 76% and 100%. If a slip is more than 100% it is referred to as a grade five slip or spondyloptosis.
Treatment for low grade slips (ie: less than 50%) presenting with only back pain and radiculopathy is usually conservative. Physical therapy, joint injections, ibuprofen (or other non steroidal anti-inflammatory medications), and bracing can be used for several months. Physical therapy should focus on lumbar flexion exercises with avoidance of lumbar extension. If symptoms continue or worsen then surgery is indicated.
Patient's who fail conservative treatment, have high grade slips (ie: greater than 50%), or have weakness, bowel/bladder issues, or sexual dysfunction should be offered surgery. The primary goal of surgery is to prevent further slippage by fusing the vertebrae together; realigning the spine is a secondary goal, but is not absolutely necessary. In fact, attempts to realign high grade slips have been shown to increase the risk of neurological injury.
The type of surgery offered to correct spondylolisthesis may be from the front (ie: anterior), from the back (ie: posterior), or a combination of both. As of now, there is no right surgical approach. It appears that patients who have combination approaches have higher rates of fusion; however, patients with anterior only approaches seem to have better overall outcomes (I know! It seems counter intuitive).
Spondylolisthesis is a fancy term that describes one vertebrae slipping forward relative to the one below. There are six categories based on the underlying pathology causing the slip. These categories are congenital, isthmic, degenerative, traumatic, pathologic, and post surgical/iatrogenic. Symptoms are typically low back pain with a component of radiculopathy. Weakness, bowel/bladder or sexual dysfunction is actually uncommon unless high grade slips are present. The Meyerding system is used to determine the severity of the slip. Treatment for low grade slips is usually conservative, but surgery may be necessary for high grade slips, patients that fail conservative management, or those with hard signs of neurological dysfunction.
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