Pars Interarticularis Injury 

Updated: Jan 22, 2019
Author: Gerard A Malanga, MD; Chief Editor: Craig C Young, MD 


Practice Essentials

Lumbar spondylolysis, a unilateral or bilateral stress fracture of the narrow bridge between the upper and lower pars interarticularis, is a common cause of low back pain (LBP) in adolescent athletes.[1]  The lifetime prevalence of LBP in those aged 11-17 years has been reported to be as high as 30.4% among adolescents participating in sports.[2]  Although a variety of disorders are likely responsible for these cases, lumbar spondylolysis must be considered in the differential diagnosis of LBP in this population.

Lumbar spondylolysis is a radiographic finding that is believed to develop, in most cases, during early childhood.[90] Typically, it is not associated with any clinical symptomatology of significance, except in a particular subset of patients who are young and adolescent athletes participating in sports that involve repetitive spinal motion, especially lumbar flexion/extension, and to a lesser degree, rotation.

Athletes who are involved in gymnastics, diving, weight lifting, wrestling, rowing, figure skating, dancing, volleyball, soccer, tennis, and football have been found to have a higher incidence of spondylolysis.[3]  The pars interarticularis defect is believed by most authors to represent a fatigue fracture caused by repetitive loading and unloading of this region of the vertebrae from physical activity. The natural history of the fracture appears to be relatively benign, and in most cases, there is no significant progression of the pars defect.

See Common Pediatric Sports and Recreational Injuries, a Critical Images slideshow, to help recognize some of the more common injuries and conditions associated with pediatric recreational activities.

Spondylolysis can persist in some cases to become spondylolisthesis.[4]  Spondylolisthesis occurs when one vertebra slips forward in relation to an adjacent vertebra, usually in the lowest lumbar vertebral segment (L5). As a result, the L5 vertebral body slips forward on the S1 vertebral body. This also commonly occurs at the L4 and L5 levels. Spondylolisthesis is almost never due to trauma; however, it is usually discovered after a trauma or prolonged episode of back pain in an athlete prompts radiographic studies.

Most patients with either spondylolysis or spondylolisthesis have excellent clinical outcomes with conservative measures, and surgical intervention rarely is rarely necessary.[1, 4, 5]  In selected cases, those patients unresponsive to nonoperative measures may benefit from surgical management. The approach to surgical management is dictated by the age of the patient and the degree of associated spondylolisthesis.[6]

This article focuses on isthmic spondylolysis as an independent entity from spondylolisthesis and its relationship to athletes, as this type of spondylolysis is a primary focus of concern in athletic adolescents.

For patient education resources, see the patient education articles Back Pain and Slipped Disk.



United States

The incidence of isthmic spondylolysis varies according to different surveys, but it has been estimated to be approximately 3-6% in the general adult population. The incidence has been found to vary amongst different ethnic groups, possibly identifying genetic factors as having a degree of influence. Roche and Lowe examined 4200 cadaveric spines and found an overall incidence of 4.2%, with an incidence of 6.4% for white males, 2.3% for white females, 2.8% for black males, and 1.1% for black females.[7] Lifestyle differences among cultural groups undoubtedly account for at least part of the difference in incidence among ethnic groups, and these findings must be treated with a degree of caution.[8]

Most studies reveal that males are consistently affected 2-3 times as often as females, and whites are affected almost 3 times as often as blacks. Most studies also show no significant change in incidence in individuals aged 20-80 years. Based on these studies, spondylolytic lesions are generally believed to occur in the early school-age years.

A prospective study demonstrated a 4.4% incidence of spondylolysis in 500 first-grade children, which increased to an incidence of 6% in adulthood, with a follow-up interval of 45 years.[9] The prevalence of spondylolytic lesions among adolescent athletes appears to be much higher than the prevalence among the general population. According to large-scale radiographic studies, the prevalence among adolescent athletes ranges from 8-15%; among adolescent athletes referred for evaluation of back pain, this figure has been reported to be as high as 47%.[10]

A large screening study in Japan obtained from children who presented with LBP and who were participating in sports found that 32% of the patients younger than 19 years had at least one or more pars interarticularis defects.[11] Morita et al investigated 185 adolescents younger than 19 years with spondylolysis and found 180 to be currently active in sports.[11]

Within competitive sports, increasing age and training more than 15 hours per week correlates with a higher incidence of spondylolytic defects.[12] The most common level of a spondylolytic lesion is at the L5 level, estimated at 85-95%, followed by the L4 level, estimated at 5-15%.

Further evidence supporting the role of genetics as a significant factor was found by Fredrickson et al, who discovered an increased incidence of spondylolysis in fathers, mothers, and male siblings of affected people in their study.[13] In an earlier study, as many as 26% of the immediate relatives of those with a demonstrable spondylolysis were found to have a similar problem.[14]

A strong association exists between lumbar spondylolysis and the presence of spina bifida occulta, which has been found to occur in 5-10% of the general population.[7, 13, 15] One theory is that spina bifida occulta may lead to instability of the lower lumbar segment, predisposing an individual to the development of pars interarticularis defects.[16] Hyperlordosis of the lumbosacral spine, such as seen in Scheuermann kyphosis, has been associated with a higher incidence of spondylolysis.[17]

Spondylolysis is associated with spondylolisthesis in approximately 25% of cases; however, the progression of the spondylolisthesis to any significant degree is generally uncommon in those who participate in athletics and in those who do not participate in athletics. The tendency of progression of spondylolisthesis is correlated with the pubescent growth spurt; in a study involving a 20-year follow-up of 255 patients, the mean slip progression was 4 mm.[18] Only 11% of adolescents and 5% of adults had slip progressions of greater than 10 mm in this radiologic review.

A European retrospective analysis by Lemoine et al that included 717 pediatric abdominal and pelvic CT scans from 532 children who had a CT scan for a variety on non-lumber conditions reported that the prevalence of spondylolysis was 1% in children under age 3, 3.7% in children under age 6 and 4.7% total (editors note - the prevalence may have been affected by the inclusion of multiple CT studies on the same patient since it was unclear how the researchers handled these cases - other than noting that 3 of these patients had findings of spondylosis on all their studies). The study also found that unilateral spondylolysis was associated with a spinal malformation with normal pelvic incidence.[19]

Functional Anatomy

Spondylolysis is derived from the Greek word spondylo, which means vertebrae, and lysis, which means fracture. Spondylolysis is defined as a defect in the pars interarticularis of the vertebral arch. Often, it is described in association with spondylolisthesis, which can be found concurrently with spondylolysis. Spondylolisthesis is defined as the anterior or posterior displacement of a vertebral body on the one below it. These conditions are generally described according to the following classification of Wiltse, Newman, and Macnab[20] :

  • Type I (dysplastic): Congenital abnormalities of L5 or the upper sacrum allow anterior displacement of L5 on the sacrum, which can occur with the pars interarticularis remaining intact.

  • Type II (isthmic): A lesion in the pars interarticularis occurs. This type of spondylolysis is subclassified as a fatigue fracture (IIA), elongation (IIB), or acute fracture (IIC).

  • Type III (degenerative): This type of spondylolysis is associated with long-standing segmental instability and alterations in the articular processes with associated remodeling of the articular process.

  • Type IV (traumatic): Acute fractures of the vertebral arch occur in areas other than the pars.

  • Type V (pathologic): This type of spondylolysis is due to generalized or focal bone disease affecting the vertebral arch.

Sport-Specific Biomechanics

The pathogenesis of pars interarticularis injuries is likely multifactorial. This "pincer theory" hypothesizes that the inferior articular process of the superiorly adjacent vertebrae and the superior articular process of the inferiorly adjacent vertebrae act as wedges and create a shear force at the pars. For example, at the L5 pars, the inferior articular process of L4 and the superior articular process of S1 would create a shear force at the L5 pars during spinal extension.[21] Two studies assessing the intrafacet distance in the lumbar spine suggest that insufficient caudal increase in lumbar interfacet spacing could be another predisposing risk factor for this condition.[22, 23]




The clinical presentation and reported findings of the historical examination of patients with spondylolysis may include the following:

  • Although most patients with spondylolysis are asymptomatic, those who do develop symptoms typically present during the preadolescent growth spurt.[24]

  • Patients predominantly complain of focal LBP brought on by certain performance activities. Pain may be sharp and lancinating in the acute period or may become chronic, dull, and aching over time. The pain is usually of mild to moderate intensity. Pain may be located unilaterally or bilaterally, usually along the belt line. On occasion, the pain may radiate into the buttock or proximal lower extremity.

  • The onset of symptoms may be either insidious or acute. Often, mild symptoms may be present for a time period, but then the symptoms may become exacerbated by a specific incident.

  • Movements, particularly those involving spinal extension and, to a lesser extent, rotation, are typically described as exacerbating events. Pain is often improved with rest. One study showed up to 98% of adolescent patients with spondylolysis have pain with extension and rotation movements of the spine.[25]


Common findings during the physical examination of a patient with spondylolysis may include the following:

  • Upon inspection of the lumbar spine: A patient with LBP resulting from spondylolysis often exhibits a reduced lordotic posture with excessive hamstring tightness.

  • The classically described Phalen-Dickson sign (ie, a knee-flexed, hip-flexed gait) may be demonstrated in patients with spondylolysis. Although this sign is more often seen in those with concomitant spondylolisthesis, it may be present regardless of the degree of vertebral slippage.[26]

  • A gait pattern described as the pelvic waddle has also been described in association with spondylolysis. The hallmark of this gait abnormality includes a stiff-legged gait with a short stride length due to hamstring tightness.

  • The clinician should also note the presence or absence of skin dimpling in the lumbosacral region that may signify the presence of spina bifida occulta, thereby raising the clinical suspicion of spondylolysis.

  • Palpation of the overlying paraspinal region often produces tenderness, and there may be spasm of the paraspinal musculature that causes splinting in acute cases.[3] Take care to identify a possible "step-off" when palpating over the spinous process. This step-off is indicative of concomitant spondylolisthesis, particularly over the L5-S1 level.

  • In assessing lumbar range of motion (ROM), forward flexion is commonly diminished secondary to hamstring tightness. Flexion typically does not increase symptoms, and in many cases, it provides relief. However, extension and rotation commonly cause discomfort for the patient.

  • The preeminent physical examination maneuver thought to most reliably reproduce pain from spondylolysis is the one-legged, hyperextension maneuver, also known as the stork test.

    • The patient is asked to stand on one leg and is brought backward into lumbar extension. Pain due to spondylolysis is thought to be elicited in unilateral lesions by standing on the ipsilateral leg.

    • Although this maneuver is most often described in association with spondylolysis, it stresses other structures besides the pars interarticularis and can therefore be considered to be only suggestive of a pars interarticularis lesion within the context of the clinical picture.

  • The neurologic examination should include assessment of motor strength, sensation, and reflexes. The findings of the neurologic examination should be within normal limits. Typically, radicular findings are absent in patients with isolated spondylolysis.


Spondylolysis is considered by most to represent a fatigue fracture that results from repeated mechanical stress with microtrauma and eventual overload to the pars interarticularis rather than as a result of a single traumatic event.[27] However, a traumatic event may result in the completion of a developing fracture.[27] Studies have shown a remarkably low or absent rate of occurrence in newborns and very young children, as well as in those patients who have never been ambulatory.

Rosenberg et al studied 143 patients who had never walked, with an average age of 27 years, and found no cases of spondylolysis.[28] This finding appears to support the theory that loading of the pars interarticularis during upright, weight-bearing activities plays a role in the pathogenesis of these lesions.

Another study investigating the mechanical loading of the spine tested cadaveric lumbar vertebrae that were cyclically loaded at the inferior articular processes to simulate shear force.[27] The authors found 55 of 74 vertebrae to sustain pars fractures. They concluded that the pars interarticularis was particularly vulnerable to this type of repetitive loading. Further analysis of the vertebrae of those subjects without a fracture revealed a larger cross-sectional area of cortical bone in the pars compared with the control group.[27] This led Wiltse et al to hypothesize that a genetic predisposition may be related to the cortical bone density of the pars. This study also suggested that the strength of the neural arch may increase up to the 4th or 5th decade of life.[27]

In an experimental model, Dietrich and Kurowski found that the greatest mechanical loads occur at L5 and S1 with flexion and extension movements.[29] Furthermore, the greatest mechanical stress was found to occur at the region of the pars interarticularis. The investigators also noted that the loads and stresses across this region are related to the physical dimensions of the vertebrae, which may offer a partial explanation regarding the varying incidence among different races and the sexes. Repeated flexion and extension maneuvers, and to a lesser degree rotation, typically have been thought to be the movements that are responsible for generating the forces across the pars interarticularis that result in spondylolysis.[29, 30]

In a retrospective analysis of 213 young athletes, Gregory et al found left-sided lower lumbar pain was more common than the right side, and a marked increase in scintigraphic uptake was noted on the left side of the neural arch more often than the right side.[31] Unilateral spondylolysis was identified by reverse gantry computed tomography (CT) scanning on the left pars 36 times and on the right pars 16 times. These findings support the hypothesis that asymmetric repetitive movements associated with certain sports may be responsible for the development of unilateral spondylolysis.[31]

Green et al concluded from their cadaveric study on pars interarticularis stress, which investigated mechanical loading, that activities involving alternating flexion and extension movements cause large stress reversals in the pars interarticularis, thereby creating the highest risk for developing a pars defect.[32] The authors found compressive or axial loading to have little effect in generating these stresses likely responsible for spondylolysis.[32] Other anatomic studies have suggested that shear stresses on the isthmic pars are the greatest with lumbar spine extension.[33]

The specific cause of LBP associated with spondylolysis and spondylolytic spondylolisthesis has not been definitively established. Theories include nerve root compression by floating laminae, intervertebral disc pain, lumbar facet joint pain resulting from spinal instability, or a combination of these pathologies.[34] . A fibrocartilage mass of scar tissue forms at the site of lumbar spondylolysis and eventually develops into a structure frequently indistinguishable from a normal ligament by adulthood.

Eisenstein et al identified nerve fibers in the fibrocartilage masses histologically,[35] and Nordstrom et al detected the existence of the slow-conducting type C pain fibers and substance P in spondylolytic tissue obtained from patients who underwent resection.[36] Mechanoreceptors were later identified in these masses as well.

Hasegawa et al concluded that these fibrocartilage masses appear to be one source of pain, as LBP was induced by injecting hypertonic saline and was blocked by injecting lidocaine into these masses in all patients in their study before resection of the lesion.[37] The authors hypothesized that the fibrocartilage mass plays a protective role by sensing instability through the mechanoreceptor and then conveying this information through nociceptive fibers as pain, while at the same time, stabilizing this area of instability by acting as a ligamentlike structure across the defect.[37]

Given the high number of asymptomatic spondylolytic lesions, an important issue that is lacking in the literature and warrants further investigation is determining the factors that are responsible for producing pain in one patient but not another.





Laboratory Studies

Laboratory studies are not indicated for diagnosing lumbosacral spondylolysis.

Imaging Studies

Plain radiography

Traditionally, plain radiographs have been the hallmark of diagnostic imaging in cases of spondylolysis. The lateral oblique view, in which the pars interarticularis is best visualized, is described as having the appearance of a "Scotty dog." In isthmic spondylolytic lesions, the Scotty dog is described as having the appearance of a "collar" or a "broken neck," which is thought to be a pathognomonic finding.[5] In unilateral pars lesions, the contralateral region may demonstrate sclerosis secondary to the increased stresses in that area.[38]

In studies comparing the different views of plain radiographs, including anteroposterior (AP), lateral, and lateral oblique, 19% of pars interarticularis lesions were identified only on the lateral oblique view. Pierce reported the sensitivity of the AP view to be 32%, of the lateral view to be 75%, and of the lateral oblique view to be 77%.[39] The most sensitive view in one study was found to be the lateral spot view of the lumbosacral junction, which revealed 84% of pars interarticularis lesions.

Limitations of plain radiographs lie in the fact that to be optimally visualized, the lesion should ideally be aligned tangentially to the beam. Spondylolytic lesions are often not aligned within the plane of the standard 45º lateral oblique views. Although most authors support the belief that multiple views of the lumbosacral spine are necessary for optimal visualization of the pars interarticularis on plain radiography, the need for routine oblique radiographs has been questioned with concerns regarding increased radiographic exposure.[40] Additionally, spondylolytic lesions seen on radiographs are often believed to represent an old injury that may not be symptomatic.

Flexion and extension lateral radiographs may be obtained if spondylolisthesis or spine instability is suspected.

Based on a literature review, Tofte et al recommended two-view plain radiography as the initial imaging study in pediatric patients thought to have spondylolysis-related back pain. The recommendation was made based on the modality’s efficacy and relatively low cost, as well as the relatively low amount of radiation exposure involved (7-9 times less effective radiation dose than bone scanning and approximately half of that associated with four-view plain radiography and computed tomography [CT] scanning).[41]

Single-photon emission tomography scan (SPECT)

Radionuclide imaging studies, including planar bone scanning and, more specifically, SPECT bone scanning, have been found to be more sensitive than plain radiography in detecting pars lesions. Several authors comparing planar bone scan versus plain radiographs concluded that planar bone scans could potentially detect pars lesions earlier in the clinical course than could plain radiographs. Furthermore, it appears that bone scanning may be more sensitive in differentiating pain-producing pars lesions from incidentally found lesions.

In a study by Lowe et al, a group of patients found to have spondylolysis on plain films were further imaged with a bone scan.[42] A positive bone scan in each case correlated with the presence of LBP, whereas those with negative bone scans were all without pain. Similar results have been obtained in other studies, and it appears that bone scans may have a role in identifying those cases in which the spondylolytic lesion is the pain generator rather than just an incidental finding.

SPECT scanning has been found to be more sensitive than either plain radiography or planar bone scintigraphy in detecting spondylolysis and has, for the most part, replaced planar bone scanning as the radionuclide imaging study of first choice in suspected pars interarticularis lesions.

Studies carried out that compared plain radiography, planar bone scanning, and SPECT scanning by Bodner et al and Bellah et al, respectively, both found the SPECT scan to be more sensitive compared with the other 2 imaging studies.[43, 44] Furthermore, as with planar bone scans, SPECT scans may be helpful in detecting symptomatic pars lesions from asymptomatic lesions as they can identify metabolically active bone change.

A particularly interesting study comparing the clinical outcome following surgery for pars interarticularis defects with SPECT scanning found that patients who became pain free after surgery have positive preoperative SPECT scans, whereas those in whom pain persisted after surgery had negative preoperative scans. This finding implies that those with negative scans may have been experiencing their symptomatology from a source other than the pars lesion.

A Japanese study was performed to clarify the role of SPECT scans. In this study, plain radiographs and SPECT scans were obtained in young patients (mean age 15.6 y) who had LBP and were clinically suspected of having spondylolysis. This study concluded that the SPECT scan is primarily indicated in patients with no apparent abnormality seen on plain radiograph and/or CT scan and who are still suspected of having spondylolysis from their history and physical examination. A positive study was thought to represent a stress reaction in the pars interarticularis, which may be amenable to rest and immobilization. A negative study at this point strongly suggests that spondylolysis is not the likely source of pain and may warrant further imaging to evaluate for a different pathology that may be causing symptomatology.[45]

Herring and Standaert offer the opinion that considering the relatively high radiation exposure one is subjected to in undergoing multiple views on plain film, along with the increased sensitivity of SPECT scanning, the latter may be the most appropriate choice for the initial screening study.[46] The authors feel with the advantages of SPECT scanning, multiple plain radiographic views as an initial screening tool may not play a role in detecting spondylolytic lesions.[46] In cases in which plain radiographs do reveal pars lesions, SPECT scanning can be helpful in documenting the acuity of injury.

Interpretation of plain radiographs coupled with SPECT scan results

Below, table 1 outlines the interpretation of plain radiographs coupled with SPECT scan results.

Table 1 also offers treatment strategies based on these results, as followed by a British institution.[47] These treatment strategies were outlined in a study conducted jointly by the investigators' orthopedic and radiology departments, who investigated the role of SPECT scanning in the management of patients with back pain and spondylolysis.[47]

Although radionuclide imaging may have increased sensitivity in detecting pars defects compared with plain radiographs, they are not necessarily highly specific for this detection and have been found to yield positive results from pathologies other than spondylolysis, including a infection and tumor such as osteoid osteoma and osteoblastoma.

Table 1. Outline of the Treatment Strategy Based on Results of Plain Radiographs and SPECT Scanning in the Evaluation of Defects of the Pars Interarticularis in Patients Clinically Suspected of Having Symptomatic Pars Interarticularis Lesions (Open Table in a new window)

Plain Radiograph






Pathology other than pars defect should be suspected

Further investigation of cause of back pain should be performed (eg, MRI)



Early pars interarticularis fracture

Conservative management in form of rest, +/– bracing




Conservative management in the form of rest and bracing



Pseudoarthrosis or old unhealed fracture

Consider surgical intervention for stabilization to prevent spondylolisthesis and to relieve pain. Consider further investigation to rule out alternative pathology.

CT scanning

As with the above mentioned radionuclide studies, CT scanning has been found to be more sensitive than plain radiography in visualizing spondylolytic lesions.[48, 49]

In a study comparing plain radiography, CT scanning, and bone scintigraphy (either bone scan or SPECT), CT scanning was found to be more sensitive than plain radiographs, as well as more specific than radionuclide imaging. Both standard axial views and reverse gantry CT imaging were used for this study, and the authors noted that some pars interarticularis defects were seen more clearly with one versus the other, although a direct comparison of views was not made.

CT scanning has the added benefit of providing more detail about the nature of the pars interarticularis defect than bone scanning or SPECT scanning does. CT scanning has the advantage of visualizing other spinal pathologies, most notably intervertebral disc pathology, which is not seen on the other radionuclide imaging studies. The relationship between CT scanning and SPECT scanning has not been fully established, and it is presently unclear as to which is the more sensitive study. The role of CT scanning may be as an adjunctive study investigating the stage of healing in a pars fracture.

Yamane et al described a 4-stage grading system based on CT scan findings: nonlysis, prefissure, fissure, and pseudoarthrosis.[50]


MRI has not been studied as well as plain radiography, radionuclide scanning, and CT scanning. Initial studies revealed that MRI provides great difficulty in identifying a normal intact pars interarticularis, resulting in a low positive predictive value.

MRI may be useful in detecting spondylolysis earlier in the clinical course than plain radiography or CT scanning does; this makes MRI comparable to radionuclide scanning, whereas removing the disadvantages of radiation exposure. In 1993, a study evaluating MRI findings in pars interarticularis injury using a 0.5-T magnet suggested that MRI may show a hypointense area in the pars interarticularis area on T1-weighted images prior to the appearance of spondylolysis being visible on plain radiographs or CT scans. This study went on to explain that prior literature suggested that the hypointense area may be due to hemorrhage in the pars interarticularis area or edema of adjacent tissues and that hemorrhage appears hypointense on T1-weighted images owing to the presence of deoxyhemoglobin.[50]

Goda et al conducted a study that included 98 adolescent patients to investigate the discrepancy between MRI and computed tomography (CT) findings in the spinal level distribution of spondylolysis. The authors concluded that MRI revealed a higher prevalence of L3 or L4 spondylolysis than observed with CT.[51]

Improvements in the technical aspects of MRI have increased its usefulness in imaging pars interarticularis lesions. T1-weighted imaging with sagittal 3-mm slices has been shown to be most useful. Kobayashi et al published a study that assessed MRI with a 0.3-T magnet to evaluate for spondylolysis in patients who did not have clear spondylolysis diagnosed with plain radiographs. MRI showed active spondylolysis in 45.7% of the patients with negative findings on plain radiographs and in 91.7% of patients with unclear findings on plain radiographs.[52] They used a 5-stage classification system based on CT findings, and 70.6% of the pars injuries were in the nonlysis or very early stage, again confirming that MRI may be useful in detecting spondylosis earlier than plain radiography or CT scanning.[52]

MRI offers some advantages; this modality is the criterion standard of imaging in most other lumbosacral spine pathologies. The lack of ionizing radiation makes MRI especially attractive for use on adolescent athletes. A study comparing MRI findings found prevalent abnormalities of the lumbar spine in adolescents who were high-performance rowers; these abnormalities included disk disease and pars interarticularis stress reaction.[53]

The overall role of MRI has yet to be determined, as it is not clearly defined in the literature at this point. MRI is not a first-line imaging study in clinically suggested spondylolysis, but rather it is an adjunct study in evaluating for alternative pathologies (see Differentials).



Acute Phase

Rehabilitation Program

Physical Therapy

During the acute phase of rehabilitation for patients with spondylolysis, the focus is to reduce the pain. Instruction in posture and biomechanics with activities of daily living (ADL) can help to protect the injured pars, thus reducing symptoms and preventing further injury. A period of rest for an average of 2-4 weeks can provide beneficial effects by modulating pain, decreasing inflammation, and decreasing the risk for further progression of a pars stress reaction to a frank fracture.

Applying ice to the injured area for 20 minutes 3-4 times a day in conjunction with performing gentle ROM exercises and stretching of the quadriceps and hamstring muscles is strongly advised. Activity modification is recommended. The patient is advised to stop the activity or sport that evokes the back pain for an average of 2-4 weeks.[24, 46, 54] In particular, the patient should avoid any activities involving hyperextension.

A retrospective study by Selhorst et al found that in adolescent athletes with acute spondylolysis who were referred to physical therapy after less than 10 weeks of rest, the median period for full return to activity was almost 25 days shorter than it was for those referred to physical therapy after more than 10 weeks of rest, with no statistically significant difference in the risk of adverse reactions seen between the two groups.[55]


Indications for the use of a brace are lack of symptom improvement by 2-4 weeks, the presence of a true fracture, the presence of a spondylolisthesis, the need for pain control, and the lack of patient compliance to activity restrictions.[56]

There are no randomized, double-blinded studies of brace application in the treatment of spondylolysis; however, several authors have demonstrated good results. In 1985, a widely referenced study by Steiner and Micheli evaluated 67 patients with symptomatic spondylosis or low-grade spondylolisthesis via plain film or planar bone scan without a control group.[57] A rigid, antilordotic, modified Boston brace was applied for 23 hours per day for 6 months, followed by 6 months of weaning. Follow-up at an average of 2.5 years demonstrated good or excellent results, and 23% of patients showed bony healing on radiograph.

Furthermore, Blanda et al examined 62 patients with spondylolysis and found that 84% had excellent results with conservative treatment, which included using a lumbar brace, at an average follow-up of 4.2 years.[25] Overall, the results of bracing vary from complete healing with resolution of back pain to nonunion, persistence of pain, or progression to spondylolisthesis. Using return to sport as the end point, the success of bracing has ranged widely from 7-84%.[25, 58, 59, 60, 61]

In contrast to the above studies, several authors have reported on the treatment of patients with symptomatic spondylolysis using a soft brace or no brace instead of a rigid brace. Rigid braces do not have a stabilizing effect on the sagittal, vertical, and transverse intervertebral translations and provide gross limitation of body motion.

Morita et al studied 185 adolescents with spondylolysis and classified the pars defects into early, progressive, and terminal stages.[61] Conservative management included the use of a conventional lumbar corset for 3-6 months. Follow-up radiographs showed healing without the use of a rigid brace in 73% of the patients in the early stage, in 38.5% of those in the progressive stage, and in 0% of those in the terminal stage.[61]

Jackson et al also examined 7 athletes who had a positive bone scan with negative lumbosacral plain films and discovered that if the bony reaction was recognized early, healing at the subroentgenographic level could occur with rest and activity modification without the use of a brace.[62] Furthermore, Congeni et al examined 40 young athletes diagnosed with spondylolysis on bone scan and followed a treatment protocol of nonrigid bracing, specific educational guidelines instructing patients to avoid hyperextension activities, flexibility training, strengthening, and cardiovascular activities.[49] Only 2 of 40 patients needed to switch to a rigid brace after 4 weeks due to persistent pain. None of the patients required surgical intervention at a follow-up period ranging from 3 months to 5 years.[49]

Research on the biomechanical effects of bracing and its effect of immobilization on the spine has been performed. Axelsson et al studied 7 patients following posterolateral lumbosacral fusions without internal fixation.[63] These individuals were examined by roentgen stereophotogrammetric analysis in supine and erect positions 1 month postsurgery without lumbar support, with a molded rigid orthosis, and with a canvas corset with a molded plastic posterior support. Neither of the 2 types of lumbar support showed any evidence of a stabilizing effect on the sagittal, vertical, or transverse intervertebral translations.

Lantz and Schultz also reviewed 4 trunk movements in 5 young men wearing a lumbosacral corset, a chairback brace, and a molded plastic thoracolumbosacral orthosis (TLSO) in standing and sitting positions.[64] All 3 orthoses restricted some gross body motion, approximately one half to two thirds more than in patients without an orthosis. Both studies confirmed that a lumbosacral orthosis restricts gross motions of the trunk rather than intervertebral mobility in the lumbar spine.

Willems et al investigated whether plaster casts actually immobilize the lumbosacral joint. They studied 10 patients placed in a plaster cast and examined the lumbosacral joint of these patients, using a 3-dimensional (3-D) motion analysis system in static and dynamic test conditions. Willems et al found that plaster casting did decrease lumbosacral mobility during static test conditions and did not significantly decrease the mobility of the lumbosacral joint in dynamic test conditions.[65] Hence, the most consistent effect of the lumbosacral orthoses appears to be the limitation of gross body motion. The rigid bracing seems to be the most effective.

Sairyo et al assessed the efficacy of using a hard brace to restrict lumbar rotation and extension. They treated 37 patients younger than 18 years with incomplete pars interarticularis injury. They stratified the patients into 4 categories: early, progressive with high signal intensity, progressive with low signal intensity, and terminal defects. The union rates for early defect were 94%, progressive with high signal intensity were 64%, progressive with low signal intensity were 27%, and terminal were 0%. They also showed that based on CT findings, the mean time to heal was 3.2 months for the early-defects group, 5.4 months for the progressive with high signal intensity group, and 5.7 months for the progressive with low signal intensity group. They concluded that patients with early-stage defects are the best candidates for conservative treatment with a hard brace based on their findings.[66]

Based on current literature, the need for bracing is limited. Bracing can be considered in patients who continue to have symptoms despite a period of rest. For most of these patients, nonrigid bracing is adequate. The Sairyo et al study suggests that patients younger than 18 years with early defects on CT scan may be good candidates for rigid hard bracing for 3 months, owing to the high rate of union in their study.[66]

Surgical Intervention

During the acute phase, it is the general consensus in the medical community to attempt conservative management before implementing surgical intervention. Many studies support the nonsurgical approach.

Wiltse et al demonstrated that 12 of 17 young patients diagnosed with spondylolysis showed osseous healing with conservative treatment and no surgery.[27] Steiner and Micheli demonstrated radiologic healing in 18% of 67 patients with symptomatic spondylolysis or grade I spondylolisthesis.[57] Furthermore, Blanda et al examined 62 patients with spondylolysis and found 52 patients had excellent results with conservative treatment, with an average follow-up of 4.2 years.[25] In a longitudinal study of young athletes with early detected spondylolysis who were treated with conservative management, 29 of 32 respondents had good to excellent low back outcome scores at an average follow-up interval of 9 years.[67]

Early diagnosis is an important factor for a good prognosis in bone healing. Ciullo and Jackson studied gymnasts and found that the longer symptoms were present before treatment, the more likely that surgical intervention was needed.[68] Jackson also examined 7 athletes with positive bone scans and negative lumbosacral plain films.[62] Jackson discovered that if the bony reaction was recognized early, healing at the subroentgenographic level could occur with conservative treatment.

Furthermore, Morita et studied 185 adolescents with spondylolysis and classified the pars defects into early, progressive, and terminal stages.[11] Conservative management produced healing in 73% of the early stage cases, in 38.5% of the progressive stage cases, and in 0% of the cases with terminal defects.

These studies suggest that spondylolysis can successfully be treated using conservative treatment if diagnosed at an early stage.

Sairyo et al described a new minimally invasive technique to repair pars interarticularis defects in 2 adults, in which they modified the established pedicle screw and hook-rod system technique.[69] Percutaneous insertion of bilateral pedicle screws was performed with the Sextant system; then, an illuminated tubular retractor was inserted through a small skin incision into the pars defect, and the nearby bursa and fibrocartilaginous mass were removed. The pseudoarthrosis at the spondylolytic level was decorticated, followed by implantation of bone grafts and attachment of the hook portion of the hook-rod system to the lamina. The rod was secured at the pedicle screws' tulip head.[69] Sairyo et al reported resolution of the patients' low back pain immediately postsurgery, with postoperative return to their work or sports activities by 3 months.

Gillis et al described an application of a minimally invasive surgery pars repair technique on 8 athletes which attempts to recreate the normal anatomy rather than fusing across a motion segment. The study reported that minimally invasive surgery advantages include less muscle tissue disruption and restoration of the natural anatomy which leads to a more rapid recovery, decreased perioperative pain, minimal blood loss, earlier mobilization and decreased hospital length of stay. At one year follow-up, 6 of the 8 athletes had been able to return to their previous sport activity level.[70]

Other Treatment

The use of external electrical stimulation for the healing of spondylolysis has been reported in 2 cases in the literature. Electrical stimulation has been used to heal fractures in all areas of the body. Although the literature supports the efficacy of electrical stimulation in healing fractures, the use of electrical stimulation for healing of spondylosis is not well studied and generally not necessary.[71]

Recovery Phase

Rehabilitation Program

Physical Therapy

Once the LBP is controlled during the acute phase of treatment, a therapy program can be initiated. If the patient’s symptoms significantly decrease with rest and activity modification, a regimen of hamstring and hip flexor stretching, abdominal strengthening, lumbar flexion exercises, and cross-training with extension precautions can be instituted. If the patient requires the use of a brace, an initial program of hamstring stretching while wearing the brace can be started.

As the symptoms continue to decrease, lumbar flexion exercises, abdominal strengthening, and hip flexor and hamstring stretching can be instituted without the use of the brace. Cross-training in nonextension activities can be performed, such as the stationary bike and hydrotherapy.[3, 11, 27, 46, 49, 57, 59, 61, 62, 63]

These exercises are eventually incorporated into a more comprehensive rehabilitation program that includes spinal stabilization exercises that help the patient in finding the neutral position of the spine (ie, the position that produces the least amount of pain). This position is dependent on the specific individual and is determined by the pelvic and spine posture that places the least stress on the elements of the spine and supporting structures. In classic spondylolysis pain, the neutral spine has a flexion bias. Dynamic lumbar stabilization exercises may be used to help provide dynamic muscular control and to protect the spine from biomechanical stresses, such as tension, compression, torsion, and shear.[72]

Surgical Intervention

See Maintenance Phase.

Maintenance Phase

Rehabilitation Program

Physical Therapy

The maintenance phase represents the final phase of the rehabilitation program for those affected by spondylolysis, spondylolisthesis, or pars interarticularis injuries. A home exercise regimen is prescribed and should be performed on a daily basis. An analysis of variables should be performed for each individual athlete so that further injuries can be prevented. Such variables include biomechanical errors, anthropomorphic features, posture, cardiovascular fitness, psychosocial factors, level of training, specific activities, medical pathology, and sports participation.

Biomechanical errors should be assessed with the specific requirements of the sport in mind. For example, movements in ballet dancing require maximal hip external rotation; therefore, a deficit may cause stretching of the abdominal muscles and thereby increase lumbar lordosis. Consequently, increased stress on the posterior elements of the spine may occur.[72, 73]

Anthropomorphic features involve looking at predictive factors that may lead to back injury. For example, hypermobility of the spine in lumbar extension in female gymnasts may be predictive of back injuries.[74, 75, 76] The posture of the athlete in the specific sport is also important to analyze, because it is well known that hyperextension of the back can cause increased stress on the posterior elements of the spine. A tight hip flexor muscle can also cause increased stress on the spine because it arises from the sides of the intervertebral discs and the adjacent ends of the vertebral bodies from T12-L4 and from the transverse processes of all the lumbar vertebrae.[77]

Intramuscular electromyography (EMG) recordings have shown that the only lumbar movement that consistently recruits the hip flexor is a deliberate increase in lumbar lordosis while an individual is standing erect.[78] Therefore, if this muscle is tight, it can promote an increase in lumbar lordosis and, hence, increased stress on the posterior elements of the spine. Another study also showed an association of LBP with tight hip flexors.[79]

Cardiovascular fitness should also be stressed in order to increase endurance and decrease fatigue. Psychosocial factors are also important to incorporate into the maintenance phase, because pain can be magnified by depression.

Medical pathology should also be evaluated, especially in female athletes who are at risk for the female athlete triad, which includes disordered eating patterns, amenorrhea, and osteoporosis. Eating disorders include anorexia nervosa and bulimia nervosa. The prevalence of eating disorders in female athletes is 5-10% higher than in female nonathletes, and some reports indicate the prevalence is as high as 15-62%.[80] The prevalence of primary amenorrhea is reported to be as high as 4-66% in female athletes, compared with 2-5% in the general population.[80]

Amenorrhea is postulated to occur as a result of poor diet and excessive exercise, which can cause hormonal changes that inhibit ovulation. Consequently, with low estrogen levels, early osteoporosis can occur; therefore, the risk for fracture is increased in this population.

Sports participation should also be examined. For instance, the athlete may be involved in more than one sport. The above variables should also be carefully analyzed for the second sport. Regardless of the sport, maintenance of proper spine positioning during play should focus on spinal stabilization and maintaining a neutral spine. The program should progress to a functional exercise regimen and then to sport-specific training. In general, the abdominal, gluteal, and back extensor muscles are the key muscles to strengthen and build endurance.

Surgical Intervention

Indications for surgery include (1) persistent pain unrelieved by rest and immobilization for more than 6 months, (2) progression to spondylolisthesis, (3) spondylolisthesis of greater than grade II in a patient about to undergo the preadolescent growth spurt, and (4) any significant neurologic abnormalities.[3, 54, 81] As discussed above, the prognosis of bone healing is dependent on the stage of the spondylolytic lesion.[11] Dubousset reported that if treatment is delayed for 3 months or more after the fracture occurs, nonoperative treatment is unsuccessful.[82] Surgical options include direct repair of the spondylolytic defect, fusion in situ, reduction and fusion, and vertebrectomy.

Ideal candidates for direct repair of the pars defect are those with early lesions, with lysis but no listhesis, and with the lytic defect between L1-L4. L5 lytic defects have been reported to yield less predictable results due to the fact that many L5 defects occur because of a developmentally weakened and elongated pars.[24] Surgical techniques generally employ debridement of the lytic defect, application of large amounts of autogenous iliac crest cancellous bone graft, and tension band wiring or screw fixation from the cephalad portion of the posterior element to the free-floating caudal fragment. Bone healing of 75% to greater than 90% and symptomatic relief in 70-90% of the patients have been reported with the screw fixation technique.[83, 84] Tension band wiring with 73-100% bony union has been reported.[24, 85]

Ideal candidates for a fusion-in-situ procedure are patients with a low-grade spondylolisthesis that remains symptomatic despite nonoperative measures or those with a high-grade spondylolisthesis and acceptable sagittal balance. Reports of fusion rates of 83-95% and good or excellent results in 75-100% of the patients have been reported.[86, 87]

Decompression and fusion are indicated when severe neurologic signs of compression are present, such as radiating leg pain, numbness, and weakness with corresponding imaging studies demonstrating nerve root or thecal sac compression. Reduction is indicated to prevent the complications of progression of slip, pseudoarthrosis, and cosmetic deformity associated with in-situ fusion; hence, reduction of high-grade slips is often performed. Reduction (closed or open) serves to correct lumbosacral kyphosis and to diminish the sagittal translation seen in high-grade slips. Also, correction of lumbosacral kyphosis decreases the compensatory hyperlordosis above the fusion site.[24]

Spondyloptosis, complete slippage of one vertebra on the next lower vertebra, is an indication for vertebrectomy. This condition has a high rate of neurologic dysfunction, such as cauda equina syndrome. The Gaines procedure (stage 2) is commonly used. The first stage is anterior resection of the L5 vertebral body. Several days later, the second stage involves posterior resection of the remainder of the L5 pedicles and posterior elements after distraction via Harrington outriggers. Pedicle screws are placed in L4 and S1, and reduction is performed. This procedure is associated with iatrogenic neurologic deficits due to the preexisting neurologic dysfunction from the slipped vertebra. Reports of 25-30% of patients developing neurologic deficits postoperatively have been reported.[24]

Complications of surgery include disc degeneration adjacent to previously fused segments; however, Szypryt et al reported that disc degeneration, either at the disc or adjacent disc., was uncommon in patients younger than 25 years.[88, 89] In fact, the investigators found that patients who are older than 25 years and who are not treated developed a higher prevalence of disc degeneration at the deranged motion segment, as well as at the adjacent segment when compared with age-matched healthy patients.[88] Other complications include slip progression after surgery and iatrogenic neurologic deficit.[24]


A consultation with a spine surgeon may be indicated if conservative management is unsuccessful.



Medication Summary

Medications recommended for the treatment of pain in spondylolysis include nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and muscle relaxants. Before prescribing these medications, review the contraindications, adverse side effects, and mode of action.

Nonsteroidal Anti-inflammatory Drugs

Class Summary

NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. The mechanism of action of these agents is not known, but NSAIDs may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may include leukotriene synthesis inhibition, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation and various cell membrane functions.

Ibuprofen (Ibuprin, Motrin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis. The anti-inflammatory dose is higher than the analgesic dose. Newer generation NSAIDs have a lower risk of gastrointestinal risk because they selectively interact with COX–2 receptors. Prolonged use of the medication is generally not recommended.

Celecoxib (Celebrex)

Inhibits primarily COX-2. COX-2 is considered an inducible isoenzyme, induced by pain and inflammatory stimuli. Inhibition of COX-1 may contribute to NSAID GI toxicity. At therapeutic concentrations, COX-1 isoenzyme is not inhibited, thus, GI toxicity may be decreased. Seek the lowest dose of celecoxib for each patient.

Naproxen (Naprosyn, Naprelan, Anaprox)

For relief of mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing the activity of COX, which is responsible for prostaglandin synthesis.

Muscle Relaxants

Class Summary

Muscle relaxants help to relax tight muscles and can be used in conjunction with NSAIDs.

Cyclobenzaprine (Flexeril)

Muscle relaxants may be helpful in some patients with LBP and seem to have additional benefits when used in conjunction with NSAIDs. Muscle relaxants can be used as short-term adjunctive medications and should be taken hs to take advantage of their sedating side effects.


Class Summary

Pain control is essential to quality patient care. Analgesics ensure patient comfort and have sedating properties, which are beneficial for patients who have sustained trauma or who have sustained injuries.

Acetaminophen (Tylenol, Feverall, Tempra)

Offers pain relief without the increased risk of bleeding for patients with contraindications to the use of NSAIDs.



Return to Play

Return-to-play protocol depends on the individual's progress and the stage of the pars injury. Herring and Standaert recommended that the athlete progressively return to the sport if he/she is asymptomatic after 4-6 weeks with a mature corticated fracture on CT scan.[46] According to the investigators, if the CT scan shows an earlier stage lesion with either a stress reaction or minimal separation with noncorticated or cystic margins, the potential for true bone healing exists, and they recommend a more extensive rest protocol of 12 weeks, with no participation in sports and no extensive physical activity beyond that associated with normal daily activities. After a gradual rehabilitation program and no symptoms, the athlete can progressively return to the sport.[46]

Congeni et al recommended that after 8 weeks from the diagnosis, the athlete can return to play if he/she has been pain free during therapy, at rest, with hyperextension, and with the specific athletic activity.[49] Omey et al recommend that with early spondylolytic lesions, a rigid brace be applied for 6-9 months before returning to the sport.[81] The athlete must be pain free when playing the sport with the brace applied before discontinuing its use.

In general, there is no official time guideline for return to play in the literature; however, the general consensus for return to play is for the athlete to be asymptomatic at rest, with activity, with hyperextension, and when playing the specific sport.


See Maintenance Phase, Physical Therapy.


In general, early lesions have a greater chance for true bony healing. Early lesions usually yield good to excellent results. The chronic lesions have a decreased chance for true bony healing; however, even without complete bony union, the symptoms can resolve with proper therapy, rest, and sport-specific techniques.[1]


Overall, patient education in the prevention of low back injuries is important. Maintaining proper flexibility and spinal stabilization with a home exercise program are also strongly advised. Teaching proper technique in the specific sport can also prevent recurrence of back injury. Seasonal athletes should be encouraged to cross-train year round or undergo preconditioning before participation in the sport.


Questions & Answers


What is a pars interarticularis injury?

What is incidence of pars interarticularis injury in the US?

How are pars interarticularis injuries classified?

What is the pathogenesis of pars interarticularis injuries?


Which clinical history findings are characteristic of a pars interarticularis injury?

Which physical findings are characteristic of pars interarticularis injury?

What causes pars interarticularis injuries?


What are the differential diagnoses for Pars Interarticularis Injury?


What is the role of lab testing in the workup of pars interarticularis injury?

What is the role of plain radiography in the workup of pars interarticularis injury?

What is the role of SPECT in the workup of pars interarticularis injury?

How are the results of plain radiographs and SPECT used in treatment selection for pars interarticularis injuries?

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What is the role of physical therapy in the treatment of acute pars interarticularis injuries?

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What is the role of medications in the treatment of pars interarticularis injury?

Which medications in the drug class Analgesics are used in the treatment of Pars Interarticularis Injury?

Which medications in the drug class Muscle Relaxants are used in the treatment of Pars Interarticularis Injury?

Which medications in the drug class Nonsteroidal Anti-inflammatory Drugs are used in the treatment of Pars Interarticularis Injury?


How is return-to-play determined following treatment of a pars interarticularis injury?

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