Skeletal Radiol (2011) 40:683–700 DOI 10.1007/s00256-010-0942-0
REVIEW ARTICLE
Lumbar spondylolysis: a review Antonio Leone & Alessandro Cianfoni & Alfonso Cerase & Nicola Magarelli & Lorenzo Bonomo
Received: 25 January 2010 / Revised: 20 March 2010 / Accepted: 12 April 2010 / Published online: 4 May 2010 # ISS 2010
Abstract Spondylolysis is an osseous defect of the pars interarticularis, thought to be a developmental or acquired stress fracture secondary to chronic low-grade trauma. It is encountered most frequently in adolescents, most commonly involving the lower lumbar spine, with particularly high prevalence among athletes involved in certain sports or activities. Spondylolysis can be asymptomatic or can be a cause of spine instability, back pain, and radiculopathy. The biomechanics and pathophysiology of spondylolysis are complex and debated. Imaging is utilized to detect spondylolysis, distinguish acute and active lesions from chronic inactive non-union, help establish prognosis, guide treatment, and to assess bony healing. Radiography with satisfactory technical quality can often demonstrate a pars defect. Multislice CT with multiplanar reformats is the most accurate modality for detecting the bony defect and may also be used for assessment of osseous healing; however, as with radiographs, it is not sensitive for detection
A. Leone (*) : N. Magarelli : L. Bonomo Department of Bioimaging and Radiological Sciences, Catholic University, School of Medicine, Largo A. Gemelli, 1, 00168 Rome, Italy e-mail:
[email protected] A. Cianfoni Neuroradiology Section, Department of Radiology and Radiological Sciences, Medical University of South Carolina (MUSC), Charleston, SC, USA A. Cerase Unit Neuroimaging and Neurointervention (NINT), Department of Neurosciences, Azienda Ospedaliera Universitaria Senese, “Santa Maria alle Scotte” General Hospital, Siena, Italy
of the early edematous stress response without a fracture line and exposes the patient to ionizing radiation. Magnetic resonance (MR) imaging should be used as the primary investigation for adolescents with back pain and suspected stress reactions of the lumbar pars interarticularis. Several imaging pitfalls render MR imaging less sensitive than CT for directly visualizing the pars defects (regional degenerative changes and sclerosis). Nevertheless, the presence of bone marrow edema on fluid-sensitive images is an important early finding that may suggest stress response without a visible fracture line. Moreover, MR is the imaging modality of choice for identifying associated nerve root compression. Single-photon emission computed tomography (SPECT) use is limited by a high rate of false-positive and false-negative results and by considerable ionizing radiation exposure. In this article, we provide a review of the current concepts regarding spondylolysis, its epidemiology, pathogenesis, and general treatment guidelines, as well as a detailed review and discussion of the imaging principles for the diagnosis and follow-up of this condition. Keywords Spine . CT . MRI . Single photon emission computed tomography . Spondylolysis . Biomechanics
Introduction Spondylolysis is a unilateral or bilateral bony defect in the pars interarticularis (or isthmus) of the vertebra. The term derives from the Greek words spondylos (vertebra) and lysis (defect). The pars interarticularis represents the junction of the pedicle, articular facets and lamina. A pars lesion becomes bridged by tissue composed of a combination of fibrous, cartilaginous, or osseous material and may
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develop into a chronic non-union. At times, healing and bony union of the pars defects occur [1]. The incidence of lumbar spondylolysis in the general population is estimated to be about 6–8% [2, 3], but it reaches 63% in those engaging in certain sporting activities [4]. Upright posture and ambulation appear to play a role in the development of this condition because there are no known cases in non-ambulatory patients [5]. Spondylolysis in children occurs after the age of walking, but is rare in those under the age of 5 years; it is much more likely to be seen in patients older than 10 years [6]. The incidence of spondylolysis increases with age until adulthood, but not thereafter [6]. Despite a study by Sonne-Holm et al. [7] using lateral radiographs that suggested lumbar spondylolysis can develop in adulthood, Brooks et al. [3] found no significant increase in the prevalence of lumbar spondylolysis in patients older than 20 years using CT imaging. In the United States there are sexual and racial differences in the incidence of spondylolysis: the condition occurs in 6.4% of white men, 2.8% of black men, 2.3% of white women, and only 1.1% of black women [8]. Pathogenesis of spondylolysis is debated, but the most accepted theories postulate repetitive micro-trauma on congenitally predisposed anatomical conditions leading to stress fracture. Spondylolysis primarily involves the L5 vertebra (95% of cases) and the incidence decreases proceeding cephalad [9]. It almost always occurs bilaterally [10], thus dividing the vertebra into two segments. The anterosuperior segment consists of the vertebral body with the pedicles, transverse processes, and superior articular processes. The posteroinferior segment consists of the inferior articular processes, laminae, and spinous process. In one reported CT series, unilateral defects were observed in 16% of cases [11]. This may also reflect unilateral healing or union of a defect that was initially bilateral. If the defect is bilateral, anterior spondylolisthesis of the involved vertebral body or posterior displacement of the neural arch may occur. In the strictest sense, spondylolisthesis means that there is movement or translation of a vertebral body in relation to an adjacent vertebra. However, spondylolisthesis generally refers to the forward slippage (of any cause) of a vertebral body in relation to the vertebral body underlying it. Spondylolysis and spondylolisthesis are often asymptomatic, but may also be a cause of back pain, instability, and radiculopathy requiring treatment. Imaging is necessary for the diagnosis of spondylolisthesis. The primary objective of this article is to provide a review of the current concepts regarding spondylolysis, its epidemiology, pathogenesis, and general treatment guidelines, as well as a detailed review and discussion of the imaging principles for the diagnosis and follow-up of this condition.
Skeletal Radiol (2011) 40:683–700
Pathogenesis of spondylolysis The pathogenesis of lumbar spondylolysis remains controversial [4, 6, 12–17]. Several observations favor a hereditary predisposition to the pars defect. Numerous authors have reported a high rate of occurrence among family members with an incidence up to 69% [13–15] as well as a strong association with spina bifida occulta [6]. These reports lend credence to the theory of an underlying dysplasia, which may be characterized by hypoplasia and elongation or sclerosis of the pars interarticularis. Infrequently, spondylolysis can be the result of acute trauma. Developmental factors, such as posture or certain repetitive physical activities, may lead to a stress fracture of the pars interarticularis [16]. This is confirmed by the higher incidence of spondylolysis in young people engaged in certain sports or activities [4, 17]. The most probable mechanism of lumbar spondylolysis; however, is multifactorial with a stress fracture occurring through a congenitally weak or dysplastic pars interarticularis [18]. The mechanism of injury is usually a combination of repetitive flexion, extension, or rotation of the lumbar spine [14]. In particular, the pars interarticularis of L5 is sheared during extension by the inferior articular process of L4 and the superior articular process of the sacrum acting as a pair of wedges. This mechanism leads to stretching of the pars and eventually to a stress microfracture. With continued stress an overt but incomplete fracture occurs that may progress to complete fracture and chronic non-union (Fig. 1). This “bony pincers” theory was described by Capener in 1931 and is confirmed by the higher incidence of spondylolysis in athletes and those participating in strenuous exercise [4, 17]. Dysplasia would represent a factor that predisposes the patient to the occurrence of lysis, the actual onset of which would be triggered by the mechanical stresses described previously [18, 19]. This pathogenetic chain of events would seem to be confirmed by the fact that spondylolysis is found predominantly at the level of L5, which is the vertebra subjected to the greatest amount of static and dynamic stress associated with daily activities. Ward et al. [20], using anteroposterior radiographs, compared the transverse interfacet distances throughout the lumbar columns of 39 adult patients with L5 spondylolysis and 42 normal control individuals. Transverse interfacet distance normally increases proceeding caudally in the lower lumbar spine. Patients with spondylolysis exhibited a significantly smaller increase in interfacet distance from the L3–S4 to the L5–S1 facet joints compared with the control group, even relative to vertebral size. The authors postulated that insufficient interfacet distance increase, during hyperextension, results in adjacent (L4 and S1) articular process pinching of the L5 pars
Skeletal Radiol (2011) 40:683–700
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Fig. 1 a Unilateral spondylolysis of L5 in a 16-year-old boy complaining of back pain. Right oblique radiograph of the lumbosacral spine shows a narrow pars defect that appears as a radiolucent line around the “dog’s neck” (arrow). The edges appear jagged, and without much sclerosis. b, c A 37-year-old woman with chronic non-
union of the pars of the L5 vertebra. Right oblique radiograph (b) of the lumbosacral spine shows spondylolysis of L5 (white arrow). Note the gap as well as the smooth and rounded edges of the defect. Lateral view (c) shows L5–S1 spondylolisthesis (black arrows) and the wide osseous gap of the L5 pars interarticularis (white arrow)
interarticularis, contributing to bony resorption and increased likelihood of fracture. These results were also confirmed in a pediatric population [21]. Thus, individuals lacking sufficient increase in transverse interfacet distances in their lumbar spines could be at greater risk of developing and maintaining spondylolytic defects.
ments that can be regarded as a series of rotations about a moving axis. The axis of rotation at any instant is called the instantaneous axis of rotation. The point where the axis meets the plane of motion is called the instantaneous center of rotation, and is used as an indicator of lumbar kinematics [25]. Spino-pelvic balance
Principles of biomechanics Stability of the spinal motion segment The spinal motion segment, consisting of two vertebrae and the interconnecting soft tissue, can be considered the smallest functional unit in the lumbar spine [22]. Spinal stability and instability are respectively defined as the ability and the inability for the vertebrae to maintain their relationship and limit their relative displacements during physiological postures and loads [23]. Failure stress of the material In an elastic body that is subject to a system of loads in three dimensions, a complex three-dimensional system of stresses is developed. At any point, the combination of stresses (equivalent stress, as calculated by Von Mises formula) can result in structural failure of the material on which the stress is applied [24]. Instantaneous center of rotation Kinematically, continuous motion of the lumbar spine may be considered as a succession of infinitely small displace-
The human standing posture involves a delicate balance between the spine and pelvis. A balanced posture is obtained when these body segments are aligned in order to minimize energy expenditure. The spino-pelvic balance in normal children and adolescents was evaluated by Mac-Thiong et al. [26]. The sacral slope (SS) is the angle between the horizontal line and the cranial sacral endplate tangent. The pelvic tilt (PT) is the angle between the vertical line and the line joining the middle of the sacral endplate to the middle axis of the femoral heads. The pelvic incidence (PI) is the angle between the line perpendicular to the superior plate of the first sacral vertebra at its midpoint and the line connecting this point to the middle axis of the femoral heads (Fig. 2). The PI is a fundamental anatomical parameter that is specific and constant for each individual and independent of the three-dimensional orientation of the pelvis. Geometrically, the PI equals the sum of the SS and the PT. Therefore, as the PI is increased, the PT and/or SS will be increased. Generally, the normal range of the PT is very narrow, from 10 to 15°. Thus, if the PI is increased, the SS will be increased relatively much more than the PT and it will be the cause of increasing lumbar lordosis, that is, the angle between the cranial endplate of L1 and the caudal endplate of L5 [27]. Measuring the PI remains a technically
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Fig. 2 Lateral radiograph of the lumbosacral spine showing the following spino-pelvic parameters: the pelvic incidence (PI), the pelvic tilt (PT), and the sacral slope (SS). The PI is the angle formed by drawing a perpendicular line starting from the midpoint of the sacral end plate and a line connecting this point to the middle axis of the femoral heads. The PT is the angle between the vertical line and the line connecting the midpoint of the sacral plate to the axis of the femoral heads. The SS is the angle between the superior plate of the S1 and the horizontal line
difficult task. Imperfect radiographic incidence may compromise optimal conditions for measurement. Anatomical remodeling of the sacral plate can also have an impact on rigorous measurement of the PI. Blondel et al. [28], however, demonstrated that the PI is a reliable measure, even if the quality of the radiographs is not perfect.
Development of spondylolisthesis Spondylolysis diminishes the stabilizing ability of the posterior elements in the spinal motion segment and may lead to isthmic spondylolisthesis [29]. Thus, there is strong support to assume that spondylolysis can induce spinal segmental instability/hypermobility in the growing adolescent spine. A biomechanical study [30], using calf lumbar spines, evaluated the kinematic changes at the involved spinal motion segment before and after the creation of bony defects on the L4 pars interarticularis bilaterally. The authors demonstrated that bilateral spondylolysis increased the intervertebral mobility, not only at the involved level, but also at the upper adjacent level to the lysis. This increase was significant (p
