Causes of Spondylolisthesis is a condition in which one vertebra slips forward over the one below it. It is a slipping of the vertebra that occurs, in most cases, at the base of the spine. Spondylolysis, which is a defect or fracture of one or both wing-shaped parts of a vertebra, can result in vertebrae slipping backward, forward, or over a bone below
Spondylolisthesis most commonly occurs in the lower lumbar spine but can also occur in the cervical spine and rarely, except for trauma, in the thoracic spine. Degenerative spondylolisthesis predominately occurs in adults and is more common in females than males with increased risk in the obese. Isthmic spondylolisthesis is more common in the adolescent and young adult population but may go unrecognized until symptoms develop in adulthood. There is a higher prevalence of isthmic spondylolisthesis in males. Dysplastic spondylolisthesis is more common in the pediatric population with females more commonly affected than males. Current estimates for prevalence are 6-7% for isthmic spondylolisthesis by the age of 18 years and up to 18% of adult patients undergoing MRI of the lumbar spine. Grade I spondylolisthesis accounts for 75% of all cases. Spondylolisthesis most commonly occurs at the L5-S1 level with anterior translation of the L5 vertebral body on the S1 vertebral body. The L4-5 level is the second most common location for spondylolisthesis.
Spondylolisthesis is where a bone in the spine (vertebra) slips out of position, either forwards or backward.
It’s most common in the lower back (lumbar spine), but it can also occur in the mid to upper back (thoracic spine) or the neck (cervical spine). Spondylolisthesis isn’t the same as a slipped disc, which is where one of the spinal discs between the vertebrae ruptures.
The word spondylolisthesis comes from the Greek words spondylosis, which means “spine” or “vertebra,” and listhesis, which means “to slip or slide
Classification / Types of Spondylolisthesis
Spondylolisthesis can be categorized by cause, location, and severity.
1. By causes
- Degenerative – spondylolisthesis (a.k.a. type 3) is a disease of the older adult that develops as a result of facet arthritis and joint remodeling. Joint arthritis, and ligamentum flavum weakness may result in slippage of a vertebra. Degenerative forms are more likely to occur in women, persons older than fifty, and African Americans.
- Traumatic – spondylolisthesis is rare and results from acute fractures in the neural arch, other than the pars.
- Dysplastic – spondylolisthesis (a.k.a. type 1) results from congenital abnormalities of the upper sacral facets or inferior facets of the fifth lumbar vertebra, and accounts for 14% to 21% of all spondylolisthesis.
- Isthmic – spondylolisthesis (a.k.a. type 2) is caused by a defect in the pars interarticularis but it can also be seen with an elongated par.
- Pathologic – spondylolisthesis (a.k.a. type 5) is caused by either infection or a malignancy.
- Post-surgical/iatrogenic – spondylolisthesis (a.k.a. type 6) is caused by complications after surgery.
2. By location
Spondylolisthesis location includes which vertebrae are involved, and may also specify which parts of the vertebrae are affected.
Isthmic spondylolisthesis is where there is a defect in the pars interarticularis. It is the most common form of spondylolisthesis; also called spondylolytic spondylolisthesis, it occurs with a reported prevalence of 5–7 percent in the US population. A slip or fracture of the intravertebral joint is usually acquired between the ages of 6 and 16 years but remains unnoticed until adulthood. Roughly 90 percent of these isthmic slips are low-grade (less than 50 percent slip) and 10 percent are high-grade (greater than 50 percent slip). It is divided into three subtypes
- A: pars fatigue fracture
- B: pars elongation due to multiple healed stress fx
- C: pars acute fracture
Overall Types 0f spondylolisthesis
There are different types of spondylolisthesis. The more common types include.
- Congenital spondylolisthesis — Congenital means “present at birth.” Congenital spondylolisthesis is the result of abnormal bone formation. In this case, the abnormal arrangement of the vertebrae puts them at greater risk for slipping.
- Isthmic spondylolisthesis — This type occurs as a result of spondylolysis, a condition that leads to small stress fractures (breaks) in the vertebrae. In some cases, the fractures weaken the bone so much that it slips out of place.
- Degenerative spondylolisthesis — This is the most common form of the disorder. With aging, the discs — the cushions between the vertebral bones — lose water, becoming less spongy and less able to resist movement by the vertebrae.
Less common forms of spondylolisthesis include
- Traumatic spondylolisthesis, in which an injury leads to a spinal fracture or slippage
- Pathological spondylolisthesis, which results when the spine is weakened by disease — such as osteoporosis — an infection, or tumor
- Post-surgical spondylolisthesis, which refers to slippage that occurs or becomes worse after spinal surgery
- Isthmic – spondylolisthesis refers to a defect within the pars interarticular is usually from repetitive microtrauma and accounts for the vast majority of cases in children and adolescents.
- Degenerative – spondylolisthesis is the most common form of spondylolisthesis seen in adults. It is due to chronic degenerative changes at the posterior elements resulting in the incompetence of the surrounding ligamentous structures, leading to elongation and slippage.
- Traumatic – spondylolisthesis can occur following a high-energy injury flexion/extension that causes a fracture-dislocation at the posterior elements.
- Dysplastic – spondylolisthesis which is a result of an abnormal formation of the posterior elements resulting in this subsequent instability.
Grading/Types of Spondylolisthesis
- Type I – This is also called dysplastic or congenital spondylolisthesis. Congenital means that you’re born with it. Type I spondylolisthesis, then, is a defect in the articular processes of the vertebra (the part that’s supposed to control the movement of the vertebra; your facet joints are made of the articular processes). It usually happens in the area where the lumbar spine and the sacrum come together, the L5-S1 area. The defect allows the L5 vertebra (your last vertebra in your lumbar spine) to slip forward over the sacrum.
- Type II – Also called isthmic, this is the most common kind of spondylolisthesis. With type II spondylolisthesis, there’s a problem with the pars interarticularis, a particular region of your vertebra. (You can see an illustration of this in Anatomy of Spondylolisthesis). Isthmic spondylolisthesis is divided further:
- Type II A – Gymnasts, weightlifters, and football linemen are especially prone to this kind of spondylolisthesis. It’s caused by multiple micro-fractures on the pars interarticularis—micro-fractures that occur because of hyperextension (overarching) and overuse. The pars fractures completely in type II-A.
- Type II B – This type is also caused by micro-fractures. The difference, though, is that the pars don’t fracture completely. Instead, new bones grow as the pars heal, causing it to stretch. Longer pars can then cause the vertebra to slide forward.
- Type II C – Like type II A, this type has a complete fracture. However, it’s caused by trauma. The impact in a car accident could fracture your pars, for example.
A pars fracture can lead to a mobile piece of bone – the detached inferior articular process can actually move around. This bone fragment, also called a Gill fragment, can pinch the exiting nerve root, so the bone may need to be removed. Problems with the pars interarticular are can also be called spondylolysis. The word looks like spondylolisthesis, and they are somewhat related. Micro-fractures in the pars interarticularis—the kind that gymnasts, football linemen, and weightlifters are prone to—are a form of spondylolysis. The fractures are called spondylolysis; if the vertebra slips forward because it’s not being held in place properly, it’s called spondylolisthesis.
- Type III – Aging can also cause spondylolisthesis. As you grow older, the parts of your spine can degenerate; they can wear out. Usually, your intervertebral discs change first. The older you get, the less water and proteoglycan content the discs have—and less fluid makes them less able to handle movement and shock. Less fluid can also cause the disc to thin, and a thinner disc brings the facet joints closer together. Without the disc acting as the cushion, the facets can’t control the spine’s movement as well, and they become hypermobile.
- Type IV – Similar to type II C, type IV involves a fracture. However, it’s a fracture of any other part of the vertebra other than the pars interarticular is. Your facet joints, for example, can fracture, separating the front part of your vertebra from the back part.
- Type V – Tumors on the vertebra can also cause spondylolisthesis because they weaken the bones and can cause fractures that split your vertebra, leading to instability and a potential slip.
- Type VI – You have this type of spondylolisthesis if surgery caused your vertebra to slip forward. It’s also known as iatrogenic spondylolisthesis, and it’s caused by a weakening of the pars, often as a result of a laminectomy (a typical back surgery, but type VI spondylolisthesis isn’t a typical result of the surgery).
Retrolistheses are found most prominently in the cervical spine and lumbar region but can also be seen in the thoracic area.
Causes of Spondylolisthesis
There are five main types of spondylolisthesis, each with a different cause. Spondylolisthesis can be caused by
- a birth defect in part of the vertebra – this can cause it to slip forward (dysplastic spondylolisthesis)
- repetitive trauma to the spine – this results in a defect developing in the vertebra, which can cause it to slip; this is known as isthmic spondylolisthesis and is more common in athletes such as gymnasts and weightlifters
- the joints of the vertebrae becoming worn and arthritic – this is known as degenerative spondylolisthesis and is more common in older people
- a sudden injury or trauma to the spine – such as a fracture, which can result in the vertebra slipping forward (traumatic spondylolisthesis)
- a bone abnormality – this could be caused by a tumor, for example (pathologic spondylolisthesis)
Long-term back pain
Possible causes of spondylolisthesis are
- Degenerative (arthritis)
- Congenital (birth defect)
- Isthmic, (having a spondylotic defect)
- Traumatic (stress fractures etc often caused by repetitive hyperextension of the back eg: gymnasts)
- Pathologic (bone disease)
Many people may not realize they have spondylolisthesis because it doesn’t always cause symptoms.
Symptoms of Spondylolisthesis
Symptoms depend on the amount of contact with the nerves. They may include:
- Local pain or radiating pain
- Pain in the leg or buttock
- Generalized numbness
- Tingling or weakness
- Difficulty controlling bowel and bladder functions
- Inability to control urine or stool, or to begin urination (This may indicate that the slippage is pushing on the spinal cord and is considered an emergency.)
- Lower back pain – which is usually worse during activity and when standing, and is often relieved by lying down
- Pain, numbness or a tingling sensation radiating from your lower back down your legs (sciatica) – this occurs if the slipped vertebra presses on a nerve
- Tight hamstring muscles
- Lower back tenderness
- Tight hamstring and buttock muscles
- Stiffness or tenderness in your back
- Excessive curvature of the spine (kyphosis)
The severity of these symptoms can vary considerably from person to person.
A radiologist determines the degree of slippage upon reviewing spinal X-rays. Slippage is graded I through IV:
- Grade I — 1 percent to 25 percent slip
- Grade II — 26 percent to 50 percent slip
- Grade III — 51 percent to 75 percent slip
- Grade IV — 76 percent to 100 percent slip
Generally, Grade I and Grade II slips do not require surgical treatment and are treated medically. Grade III and Grade IV slips might require surgery if persistent, painful, slips are present.
Early diagnosis of AS is important if fusion of the joints and permanent stiffening of the spine are to be avoided. It can be difficult to diagnose in the early stages as symptoms may be attributed to more common causes of back pain. A doctor will evaluate the following when diagnosing the condition:
- A full medical history, including any family history of AS
- Discussion of current symptoms including a history of back pain
- The age of the patient when the pain started
- Physical assessment
- MRI (magnetic resonance imaging)
- Blood tests – which may show the presence of the HLA-B27gene, a raised ESR (erythrocyte sedimentation rate) and a reactive protein which indicates inflammation.
In order for a diagnosis of AS to be made, a referral to a rheumatologist – who specialises in treating arthritis – may be recommended.