Introduction
Background
Spondylolysis is a common clinical condition that can result in low back pain. Patients with spondylolysis have a defect in the pars interarticularis of the neural arch, that portion of the neural arch that connects the superior and inferior articular facets.1,2,3,4
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Pathophysiology
Spondylolysis is believed to be caused by repeated microtrauma, resulting in stress fracture of the pars interarticularis. Heredity also is believed to be a factor. Patients with spina bifida occulta have an increased risk for spondylolysis. Approximately 95% of cases of spondylolysis occur at the L5 level. Lyses can occur much less commonly at other lumbar or the thoracic levels. Involvement of multiple levels is rare. The process may be unilateral or bilateral.2,5
Patients with bilateral pars defects can progress to spondylolisthesis. The degree of slippage of adjacent vertebral bodies varies and can progress over time.6
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Spondylolisthesis
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Frequency
United States
Approximately 3-7% of the general population (14 million people) have spondylolysis. In certain athletes, the incidence increases to 23-62%.
Mortality/Morbidity
Spondylolysis can result in significant morbidity. This occurs most often in athletes who may be forced to stop competing and training in their sport for significant periods. A permanent inability to participate in a particular sport also is possible.2,7
Patients with bilateral spondylolysis can progress to significant spondylolisthesis.6
Sex
Spondylolysis is 2-4 times more common in men than in women.
Age
Spondylolysis can be seen in both children and adults. The reported incidence of spondylolysis at age 6 years is 4.4%. Most believe that the prevalence of spondylolysis increases with age and correlates with the high rate of failure of these fractures to heal.8
Anatomy
Spondylolysis is a defect seen in the pars interarticularis portion of the lamina. On oblique radiographs, the posterior elements form the appearance of a Scottie dog. A break in the pars interarticularis can have the appearance of a collar around the neck.
Presentation
Spondylolysis commonly is asymptomatic. Symptomatic patients often have pain with extension and/or rotation of the lumbar spine.1 Approximately 25% of individuals with spondylolysis have symptoms at some time. Athletes who participate in sports such as soccer, baseball, football, wrestling, gymnastics, and tennis are more likely to have symptomatic spondylolysis at some point.2,7
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Preferred Examination
Patients with suspected spondylolysis should be evaluated initially with plain radiography, consisting of anteroposterior, lateral, and oblique views of the lumbar spine. The lateral views are most sensitive for detection of pars fractures, and the oblique views are most specific.9,10
If plain radiographs are negative or inconclusive, further imaging may be warranted. MRI, CT, and single-photon emission computed tomography (SPECT) bone scintigraphy are used to further evaluate these patients. Controversy surrounds the designation of one of these tests as most useful in the evaluation of spondylolysis.11,12,13,14,15,16,17,18
Some investigators and practicing radiologists believe that after normal radiographs have been obtained, MRI of the lumbar spine should be next. However, the examination must be performed with thin-section images (3 mm) and at relatively high resolution (256 x 192 matrix). Imaging should be obtained in 2 planes, sagittal and axial. Obtain T1-weighted (short recovery time [TR]/echo time [TE]) and T2-weighted (long TR/TE) with fat suppression images. Usually, this type of MRI examination requires a high-field magnet (minimum of 1 T).11,12,17,19
CT of the lumbar spine can be performed after obtaining radiographs or after an equivocal MRI. Perform the examination with stacked thin (2 mm) axial sections through the portion of the spine in question. Perform sagittal reconstructions. However, even without reconstructions, pars fractures can be identified on CT because of the absence of a complete ring of bony structures at a given vertebral level.14,19
Nuclear medicine SPECT bone scintigraphy also can be obtained after plain radiographs. The nuclear medicine SPECT examination can provide images in the axial, coronal, and sagittal planes. The spatial resolution of SPECT bone scintigraphy is less than that of CT or MRI.18
Limitations of Techniques
Radiography of the lumbar spine is limited by its inability to detect stress reactions in the pars interarticularis that have not progressed to complete fracture.1,9,10,20,21,22
CT of the lumbar spine is not sensitive for detecting early acute stress reactions in the pars interarticularis where there is only marrow edema and microtrabecular fracture.17,20
These findings are not visible on CT but are observed easily on MRI; thus, MRI of the lumbar spine can easily identify acute stress reactions in the pars interarticularis. However, direct identification of pars defects may be slightly more difficult with MRI than with CT. The presence of facet osteophytes combined with volume averaging occasionally can obscure the presence of the pars defect in the sagittal plane.21
Nuclear medicine SPECT bone scintigraphy easily identifies acute stress reaction in the pars interarticularis; however, anatomic details such as the pars defect cannot be identified directly with bone scan. This means that old lyses usually are not seen.22
Differential Diagnoses
Osteoid Osteoma
Osteomyelitis, Acute Pyogenic
Stress Fracture
Other Problems to Be Considered
Facet arthritis
Congenital malformations of the posterior elements of the vertebral column
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References
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Ulmer JL, Mathews VP, Elster AD, et al. MR imaging of lumbar spondylolysis: the importance of ancillary observations. AJR Am J Roentgenol. Jul 1997;169(1):233-9. [Medline].
Ulmer JL, Elster AD, Mathews VP, Allen AM. Lumbar spondylolysis: reactive marrow changes seen in adjacent pedicles on MR images. AJR Am J Roentgenol. Feb 1995;164(2):429-33. [Medline].
Mofidi A, Tansey C, Mahapatra SR, Mirza HA, Eisenstein SM. Cervical spondylolysis, radiologic pointers of stability and acute traumatic as opposed to chronic spondylolysis. J Spinal Disord Tech. Aug 2007;20(6):473-9. [Medline].
Krupski W, Majcher P, Tatara MR. Computed tomorgaphy diagnostic of lumbar spondylolysis. Ortop Traumatol Rehabil. Oct 30 2004;6(5):652-7. [Medline].
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Masharawi Y, Dar G, Peleg S, Steinberg N, Alperovitch-Najenson D, Salame K. Lumbar facet anatomy changes in spondylolysis: a comparative skeletal study. Eur Spine J. Jul 2007;16(7):993-9. [Medline].
Sairyo K, Katoh S, Takata Y, Terai T, Yasui N, Goel VK. MRI signal changes of the pedicle as an indicator for early diagnosis of spondylolysis in children and adolescents: a clinical and biomechanical study. Spine. Jan 15 2006;31(2):206-11. [Medline].
Gregory PL, Batt ME, Kerslake RW, Webb JK. Single photon emission computerized tomography and reverse gantry computerized tomography findings in patients with back pain investigated for spondylolysis. Clin J Sport Med. Mar 2005;15(2):79-86. [Medline].
Belfi LM, Ortiz AO, Katz DS. Computed tomography evaluation of spondylolysis and spondylolisthesis in asymptomatic patients. Spine. Nov 15 2006;31(24):E907-10. [Medline].
Hession PR, Butt WP. Imaging of spondylolysis and spondylolisthesis. Eur Radiol. 1996;6(3):284-90. [Medline].
Lee J, Ehara S, Tamakawa Y, Shimamura T. Spondylolysis of the upper lumbar spine. Radiological features. Clin Imaging. Nov-Dec 1999;23(6):389-93. [Medline].
Saraste H, Nilsson B, Brostrom LA, Aparisi T. Relationship between radiological and clinical variables in spondylolysis. Int Orthop. 1984;8(3):163-74. [Medline].
Ben-Galim P, Reitman CA. The distended facet sign: an indicator of position-dependent spinal stenosis and degenerative spondylolisthesis. Spine J. Mar-Apr 2007;7(2):245-8. [Medline].
Further Reading
Keywords
pars defect, neural arch defect, pars interarticularis defect, spondylolisthesis
