Spondylolysis and Spondylolisthesis
Description
Spondylolysis and spondylolisthesis are relatively common causes of low back pain, especially in young athletes. Spondylolysis refers to a fracture or other defect in a specific region of the vertebra called the pars articularis. These defects are most often caused by repetitive stress. Spondylolisthesis refers to anterior slippage (displacement) of the vertebrae. This is most often the result of bilateral spondylolysis, a so-called isthmic spondylolisthesis. Thus, spondylolysis and spondylolisthesis are separate yet inter-related conditions.
Besides isthmic spondylolisthesis, there are several other notable subtypes of spondylolisthesis as well. The two other most common forms are dysplastic (congenital) and degenerative spondylolisthesis. Less common forms include traumatic, pathologic, and iatrogenic/post-surgical.
Structure and Function
The human spine has 24 spinal vertebral bodies stacked one on top of the other: seven cervical, twelve thoracic and five lumbar. The lowest lumbar vertebra, L5, sits atop the sacrum. The vertebral bodies are separated by an intervertebral disc, which works as a shock absorber dissipating forces transmitted through the spinal column.
Behind the vertebral body lie the so-called posterior elements of the spine: the pedicles, the lamina and three processes, the transverse, the articular and the spinous processes (fFigure 1). The posterior elements connect to the vertebral body via the pedicles. At the dorsal limit of the pedicle is the pars interarticularis. The pars then extends cephalad to become the superior articular process and caudad to become the inferior articular process. The transverse process projects laterally from the pars in the thoracic and lumbar spine. Coursing dorsally from the pars, the lamina extend dorsally and medially to connect in the midline and complete the ring around the spinal canal. The spinous process is a dorsal extension from the junction of the two lamina at the midline.
Figure 1: Sschematic drawings of a lumbar vertebra, seen from above (axial view, on the left) and from the side (lateral view, right). VB: vertebral body; TP: transverse process (omitted from drawing on the right as it projects out of the plane); SP: spinous process. As seen from above, the central canal, behind the vertebral body, is surrounded by the pedicles (red), lamina (purple) and the superior and inferior articulating processes and the bone that connects them, the pars intraarticularis (gray).
Damage to the pars can incite an attempt at healing. The resultant fibrous tissue hypertrophy can cause foraminal stenosis with compression of the exiting nerve root.
On each side, left and right, the inferior articular processes of the vertebra above and the superior articular processes of the vertebra below, come together to form the facet joints. The function of the facet joint is to guide and also limit motion of the spine. Specifically, the facet joints in the lumbar spine permit flexion and extension while simultaneously preventing extremes of these motions (hyperextension and hyperflexion).
Because the pars bridges the articular processes to the body, damage to the pars (usually from repetitive hyperextension) can lead to structural instability of the facet joints. It is this loss of restraint that allows anterior displacement or “slippage” of the superior vertebral body: spondylolisthesis (Ffigure 2).
Figure 2: If there is a pars defect, the bodies above can slip forward relative to the body below.
In the vast majority of cases, spondylolysis occurs via the above mechanism of overuse resulting in stress and microfracture. In rare circumstances, however, a defect in the pars articularis can occur following an acute load or trauma.
While the progression from a pars stress reaction to spondylolisthesis is the mechanism of isthmic type spondylolisthesis, the pathophysiology of degenerative spondylolisthesis is different. In the most fundamental sense, the major difference between isthmic and degenerative forms is the absence of a defect in the pars articularis causing the anterior displacement in degenerative spondylolisthesis. Instead, the pathophysiology centers around degeneration of the facet joint and intervertebral discs, leading to instability and increased motion of the vertebra. Degenerative spondylolisthesis is most commonly seen at L4-L5. Because the pars is intact, the posterior elements of the sliding vertebra must also slide, leading to a greater risk of canal compression.
With respect to the other, rarer forms of spondylolisthesis, the dysplastic (congenital) type occurs secondary to abnormal spine development in utero, traumatic is the result of severe traumatic injury leading to vertebral displacement, and pathologic refers to the presence of a secondary disease process resulting in instability and displacement of the vertebra, including osteoporosis, malignancy, or infection.
Patient Presentation
The diagnosis of spondylolysis is oftentimes made upon incidental discovery on an x-ray without any clinical signs or symptoms. In fact, the majority of patients with evidence of spondylolysis are asymptomatic.
In patients with spondylolysis that have symptoms, however, the most common complaint is low back pain of gradual onset that is worsened with activity, especially activities which involve hyperextension of the lumbar spine. The quality of the pain is non-specific and may resemble that of an ordinary lumbar muscle strain. Impingement of the L5 nerve root (as it exits the neural foramen) may be seen.
The presentation of isthmic spondylolisthesis is similar to that in spondylolysis, with non-specific low back pain being the primary complaint. In spondylolisthesis, however, there is a higher occurrence of radicular symptoms (paresthesias or pain radiating to the legs). Impingement of the L5 nerve root (prior to exiting the canal) is most common.
In rare circumstances, patients with spondylolisthesis can experience a “listhetic crisis” characterized by severe back pain, neurologic deficits, and hamstring spasm, all which may be exacerbated by extension of the lumbar spine.
On physical examination of patients with spondylolysis and spondylolisthesis, there may be evidence of decreased lumbar lordosis (normal inward curvature of the spine), decreased range of motion of the spine, pain upon lumbar spine extension, or a palpable step off of the spinous process (representing anterior displacement in spondylolisthesis). They may also have sensory or motor findings on neurologic exam depending upon any underlying neural compression.
In degenerative spondylolisthesis, low back pain is the most common symptom as well. These patients, however, may experience neurogenic claudication and leg pain secondary to spinal stenosis, which is more common in the degenerative than the isthmic form.
Objective Evidence
The gold standard modality for the diagnosis of spondylolysis and spondylolisthesis are plain radiographs of the lumbar spine. The important views are anterior-posterior (AP), lateral, and posterolateral (oblique), each of which can provide useful information.
In the AP view, sclerosis of the pars articularis may be appreciated secondary to stress reaction. From the lateral view, a defect in the pars articularis is identifiable in 80% of patients (Ffigure 3).
Figure 3: A pars defect is shown in the red circle; a normal pars is seen above in the green circle. (Case courtesy of Radswiki, Radiopaedia.org, rID: 11967)
The oblique film is the most important view in the assessment of spondylolysis and spondylolisthesis. From this angle, the vertebra in the lumbar spine demonstrate the classic “Scottie dog” appearance (Ffigure 4), consisting of the superior articular process (ears of the dog), transverse process (head), isthmus (neck), lamina and spinous process (body), and inferior articular processes (foreleg and hindleg). In spondylolysis, the fracture through the pars articularis appears as a neck collar on the Scottie dog.
Figure 4: An oblique view of the lumbar spine, showing the “Scottie Dog”. The pars is represented by the dog’s collar, shown in faint red here. (Case courtesy of A.Prof Frank Gaillard, Radiopaedia.org, rID: 7552)
In spondylolisthesis, there is anterior displacement of the superior articular process relative, allowing the entire body to slip forward (fFigure 5).
Figure 5: At left is a lateral x-ray showing an anterolisthesis at the L5-S1 level. In the annotation at right, the sacrum is outlined in yellow and the lumbar vertebral bodies in purple. The faint red lines outline the correct anatomic position from which the lumbar bodies have slipped. (Modified from https://en.wikipedia.org/wiki/Spondylolisthesis#/media/File:SpondylolisthesisL5S1.jpg)
Spondylolisthesis can be graded based on magnitude of vertebral displacement. The superior endplate of the caudal vertebra is divided into 4 quarters. The grade is dependent on location of the poster-inferior corner of the vertebra above. Grade 1 represents a 0-25% displacement, grade 2: 25-50%, grade 3: 50-75%, and grade 4: > 75%. Grades 1 and 2 are considered ‘low grade’ and grades 3 and 4 are considered ‘high grade’, which will be important when developing an appropriate treatment strategy.
Advanced imaging may also a play a role in the assessment of spondylolysis and spondylolisthesis is select circumstances. CT scan is the best modality for revealing the specific anatomy of the underlying lesion in spondylolysis, and thus can be helpful for delineating subtle defects. In addition, CT or MRI are useful if there is suspicion for radiculopathy, cord compression, or a secondary cause of spondylolisthesis (pathologic). Bone scan (SPECT) is the most sensitive test, and can be utilized in patients with a high suspicion for a pars defect with normal or inconclusive radiographs.
Epidemiology
Children and adolescents are more susceptible to developing spondylolysis, given the weaker nature of the pars articularis in developing bone. The disease affects about 5% of the entire population, but can occur in as high as 45% of pediatric athletes involved in high risk sports such as gymnastics, Olympic weightlifting, football (especially linemen), dancing, figure skating, and wrestling. Ultimately, this is the most common source of identifiable low back pain in adolescents.
Progression of spondylolysis to spondylolisthesis occurs in only 15% of patients.
L5-S1 is the most commonly affected spinal segment in isthmic spondylolisthesis (90%), followed by L4-L5 (10%).
Spondylolisthesis (isthmic) is more common in older adolescents and adults. This is the most common cause of back pain in teenagers, as symptoms often arise upon the onset of the growth spurt.
Degenerative spondylolisthesis occurs in older adults. In the majority of cases, this occurs after the age of 40, though risk increases upon increasing age.
Isthmic spondylolisthesis is slightly more common in males, while degenerative spondylolisthesis is significantly more common in females (about 8eight times more prevalent) and occurs in approximately 10% of all women.
Differential Diagnosis
In the patient with unknown spondylolysis or spondylolisthesis presenting with low back pain, the differential diagnosis is broad. In the pediatric patient, this includes lumbar disc related pathology, lumbar muscle strain, Sheuermann’s kyphosis, scoliosis, sacroiliac joint instability, tumors (including especially osteoid osteoma), or infection (vertebral osteomyelitis or discitis). In the older patient, the differential diagnosis is similar but also includes degenerative disc disease or spinal stenosis without spondylolisthesis.
In a patient with confirmed spondylolisthesis, the differential diagnosis revolves around the specific etiology, and includes the six different types: dysplastic, isthmic, degenerative, traumatic, pathologic, and iatrogenic.
Red Flags
Night pain and so-called constitutional symptoms (fever, chills, unintended weight loss) is always a red flag for important diagnoses.
Signs or symptoms of spinal cord compression, which may represent a surgical emergency, include bowel or bladder involvement, saddle anesthesia, and progressive weakness. (Note that the cord terminates at approximately L1/L2, and thus a listhesis would affect the nerve roots within the canal, the cauda equina.)
Other red flags include any evidence of pathologic spondylolisthesis, especially signs or symptoms of malignancy or infection. Specifically, any constitutional symptoms (generalized fatigue, anorexia, unintended weight loss), fevers or chills, and night pain should warrant a broad differential diagnosis and subsequent work up.
Treatment Options and Outcomes
The primary goal of treatment of spondylolysis is symptom reduction, bone healing and prevention of progression to spondylolisthesis.
There are three general categories of management strategy for patients with spondylolysis and spondylolisthesis: observation with no treatment and no activity modification/limitation (benign neglect); activity modification/limitation with or without bracing; and surgical correction.
Benign neglect is typically appropriate only for asymptomatic patients with no more than low-grade (0-50% displacement) spondylolisthesis.
Activity modification is generally indicated for patients with spondylolysis or low-grade spondylolisthesis who are symptomatic. This strategy encompasses use of NSAIDs for pain control and physical therapy with a focus on stretching, lumbar spine flexion, core strengthening/stability as first-line.
For pain control that fails to improve with NSAID use, steroid injections may be a useful alternative.
Lumbar spine bracing may also be beneficial, particularly in the case of a failed trial of physical therapy or in an acute pars stress reaction spondylolysis, for which bracing is superior to activity restriction alone.
Surgical management is the final line of therapy for spondylosis and spondylolisthesis. Surgery is rarely required for isolated spondylolysis without spondylolisthesis. Broadly, the major indications for surgery include high grade (50-100% displacement) spondylolisthesis, progressive spondylolisthesis, and intractable pain or disability despite an adequate trial of non-operative management.
The goals of surgery for spondylolisthesis are to prevent progressive vertebral slippage/displacement and provide symptomatic relief. In both pediatric and adult patients, the primary surgical technique is instrumented posterolateral fusion of the affected vertebra. In degenerative spondylolisthesis, surgical options also include decompression (in the setting of neural impingement) with or without concurrent posterolateral fusion.
In general, the prognosis of spondylolysis and spondylolisthesis is very favorable. For symptomatic patients who undergo non-operative or operative treatment, the vast majority of patients experience total relief of their pain and regain full functionality.
For patients with symptomatic spondylolysis, the majority will improve with observation and conservative non-operative management. Only 15% of patients with spondylolysis will go on to develop spondylolisthesis.
For spondylolisthesis, the outcome is dependent upon grade/severity and specific subtype. Since most cases of spondylolisthesis are low grade, the overall prognosis is good. In these mild cases, non-operative conservative management is successful in about 80% of patients. With regard to risk for displacement progression, dysplastic portends the highest rate (over 30%), while the most common type (isthmic) progresses in less than 5% of cases.
Severe cases of spondylolisthesis portend a slightly worse prognosis, but is still favorable overall. There is a higher risk of neurologic damage secondary to nerve compression, in addition to the risks associated with surgery (below). There is also a higher likelihood of persistent low back pain and disability, though surgery is successful in 85-90% of cases.
Specific complications of surgery include mainly pseudoarthrosis, infection, dural tear, neurologic deficits, and hardware failure. The risk of complications is higher for patients with degenerative spondylolisthesis given their increased age and medical comorbidities.
Note that excessive avoidance of activity may also impose costs on patients including deconditioning, weight gain, osteoporosis, and psychic distress. It may be possible, thus, to be excessively conservative in recommending treatment.
Risk Factors and Prevention
The primary risk factor for spondylolysis and spondylolisthesis is overuse with frequent hyperextension of the lumbar spine (participation in high risk sports including gymnastics, football, weight-liftingweightlifting, dancing, figure skating, wrestling) which can weaken the pars articularis over time. Other risk factors include genetic susceptibility, osteoporosis (degenerative spondylolisthesis), young age (isthmic spondylolisthesis), white race, pre-existing spinal deformity, and weakness or tightness of the gluteal, hip flexor, and lumbar extensor muscles.
The best approach for preventing spondylolysis is through the avoidance of overuse activity and repetitive hyperextension of the lumbar spine, maintenance of adequate core strength and flexibility, and maintenance of good bone health (vitamin D and calcium, avoid smoking and excessive alcohol use, participate in regular weight bearing activity).
Key Terms
Spondylolysis, spondylolisthesis, facet joint, pars articularis, ‘Scottie dog’, spinal fusion
Skills
Understand the similarities and differences in the pathophysiology underlying spondylolysis and spondylolisthesis. Recognize the different subtypes and severity grading system for spondylolisthesis. Understand the non-operative and operative treatment modalities and their efficacy in the treatment of spondylolysis and spondylolisthesis
