Pars interarticularis defect (otherwise referred to as spondylolysis) represents a common cause of axial back pain in adolescents, especially in the case of young athletes. The pars interarticularis (pars) lies between the superior and inferior articular process bilaterally at each vertebral level. Anatomically, one can describe the pars as the region between two, one superior and one inferior, zygapophyseal joints. The definition of pars interarticularis defect is a unilateral or bilateral overuse or fatigue stress fracture involving the pars interarticularis of the posterior vertebral arch. This injury occurs almost exclusively in the lower lumbar region, most often at L5 . Though history can be suggestive, especially in the case of young athletes involved in higher risk sport (see below), diagnosis is made radiographically by the presence of fracture through the pars interarticularis. In cases of bilateral pars interarticularis defects, there is the potential for anterior or posterior spondylolisthesis (the slipping of one vertebral body relative to the adjacent segment). Spondylolisthesis can be graded based upon the percent degree of displacement of one vertebral body compared to the other. Grading of spondylolisthesis is included below in “staging.”
Two common clinical presentations of a pars defect include; imaging of an asymptomatic adolescent or adult in whom there is the incidental discovery of a pars defect. The second common presentation is an adolescent athlete involved in a sport requiring repetitive lumbar loading in extension and rotation, presenting with acute or insidious onset low back pain that is aggravated by continued lumbar loading. Although this history is typical, there is a broad differential diagnosis that might explain these symptoms, and as such, diagnosis of a pars interarticularis defect confirmation is only with radiographic support. Depending on the time of presentation and degree of injury, most cases of pars defects respond well to conservative treatment and relative rest from sport.
The exact cause is still unclear. Currently, the most accepted theory is repetitive mechanical stress, specifically lumbar extension and rotation, which results in overuse or stress fracture to the pars interarticularis. This theory garners support from the fact that, as noted below in epidemiology, research observed zero cases of pars defects in 500 newborns and zero cases of pars defects in 143 non-ambulatory patients, suggesting this pathology develops as a result of repetitive axial loading over time. Additionally, this theory is supported by the progression of unilateral pars defects into bilateral pars defects with age, again suggesting repetitive axial loading over time both leading to the initial injury as well as disease progression. As discussed, although generally thought to be the result of chronic repetitive stress to the pars region, these injuries can also occur due to a single acute overload injury.
The pars interarticularis is most susceptible to chronic axial loading injury because it is a weak point in the vertebrae and this region bears the highest stress load in extension/flexion. The weakness of the pars region is multifactorial, with a hereditary and an acquired mechanical component. Mechanical factors include the physically narrow structure of the pars interarticularis as compared to other regions of the vertebrae. Furthermore, the pars in the lower lumbar vertebra characteristically have uneven trabeculation and cortication. The inherent mechanical flaws of the pars interarticularis in combination with the high-stress loads seen in the lower lumbar region render this region prone to stress fractures.
Additionally, there has been a strong association reported with spina bifida occulta.
As previously noted, pars interarticularis defects or spondylolysis are generally thought to be the result of mechanical stress. Most commonly, fatigue or stress fractures result from repetitive loading and stress through the weak and high-stress load region of the pars. Extension and rotational loading place particular stress through this region. Though these injuries typically occur as a result of repetitive loading or movements, a single stressor or trauma can result in a pars defect. See “staging” below for details regarding the classification of pars defects. Though history and exam might be suggestive of diagnosis, imaging ought to be used to confirm and assess severity. Fracture through the pars interarticularis is classically described on oblique radiographs as the “collar sign” on the “Scottie dog.” See "evaluation" below for details.
Sagi et al. demonstrated, via histomorphic analysis, the pars interarticularis begins to ossify at 12 to 13 weeks gestation by endochondral ossification. In the lower lumbar vertebra, ossification center originates in the pars region resulting in uneven distribution of trabeculation and cortication in this region. As a result of this uneven distribution of isthmic ossification, this region is potentially more susceptible to fatigue fracture. In contrast, in the upper lumbar vertebra, the ossification center arises at the end of the pedicle which results in more uniform trabeculation throughout the pars.
As previously mentioned, there are two common clinical presentations associated with pars defects; First, imaging of an asymptomatic child or adolescent in whom there is an incidental finding of pars defect. In this case, the physical exam likely will not reveal any findings attributable to the pars defect. Incidental discovery of pars defects may additionally be visible on CT or MRI imaging of the abdomen.
The second common presentation is an adolescent athlete involved in a sport requiring repetitive lumbar loading in extension and rotation, presenting with acute or insidious onset low back pain that is aggravated by continued lumbar loading. The incidence of pars defect in this pediatric athlete population presenting with low back pain is as high as approximately 50%. In light of that, this particular population merits a high index of suspicion followed by appropriate diagnostic workup.
In the symptomatic patient, classic history will include a child or adolescent athlete playing a sport that requires repetitive lumbar extension and rotation. The onset of pain may be either acute or insidious over several weeks. Patients will report their low back pain increases with strenuous activity or hyperextension and improves with relative rest. Pain typically remains located in the low back with occasional radiation to the buttock and/or proximal lower extremities, while neurologic symptoms such as numbness/tingling in the lower extremities are uncommon.
Physical exam ought to include single leg hyperextension, otherwise known as Stork test (patient should be instructed to stand on one leg while simultaneously hyperextending the low back). A positive single leg hyperextension test is elicited by reproduction of pain during this maneuver, typically worse when standing on the leg ipsilateral to the side of the pars defect. This maneuver is the only potentially pathognomonic physical exam finding.
Potential additional physical exam findings include hyperlordotic lumbar curve and tight hamstrings. If clinically indicated, a complete neurologic exam should is necessary, though isolated pars defects typically present with no neurological findings.
Given the relatively nonspecific physical exam findings and the known high incidence in particular patient populations, if pars defect is suspected additional workup ought to include appropriate imaging studies. There is no universally accepted imaging standard for diagnosis of pars defect. Given the high-risk population includes children and adolescents, close attention to radiation exposure is warranted. With that in mind, initial workup generally begins with AP/lateral/oblique plain radiographs of the lumbar spine. AP/lateral radiograph is sufficient to detect most pars defects, though estimates are that 20% require oblique views to appreciate the lesion. Dynamic plain radiographs may additionally be indicated when there is a concern for instability in the case of spondylolisthesis.
On oblique plain radiographs, the common descriptive term for a fracture to the pars interarticularis is as the “collar” on the “Scottie dog.” (figure 1).
Plain radiographs can miss some lesions, especially acute injury. Other useful imaging modalities include CT, MRI, and bone scan. A bone scan is the most sensitive modality, and best detects early pars defects. This test should be utilized when there is high clinical suspicion for pars lesion, and initial imaging studies are equivocal. After plain radiographs, the imaging modality of choice is either MRI without contrast or CT scan without contrast. CT scan is the best imaging tool for determining fracture size and extent and is the most appropriate modality for follow-up assessment of healing. CT has the downside of additional radiation exposure, which is particularly concerning in the pediatric & adolescent population. Similar to a bone scan, MRI can be useful for early detection of acute lesions by the presence of bone marrow edema on T2 weighted sequences. Additionally, MRI has the benefit of no radiation exposure. MRI is somewhat limited though in its ability to adequately depict the cortical integrity of incomplete fractures.
There is insufficient evidence to support the natural course or treated pars defect as the preferred management. Management generally reflects the following treatment algorithm.
Additionally, on the discovery of the condition, vitamin D should be checked, and repleted levels are low.
Pars defects (Spondylolysis) subdivide into five categories according to the Wiltse-Newman Classification:
Classification of spondylolisthesis is according to the Meyerding Classification. This is a measure of the percent of antero or retro slippage/transitional displacement of one vertebral body on the vertebral body below observed on lateral radiographs.
The general prognosis for pars interarticularis defects is quite good. The overwhelming majority of cases are asymptomatic, estimated at 80%. The majority of these asymptomatic cases will not lead to a progressive lesion. In the case of symptomatic isthmic pars defect in adolescent patients roughly 75 to 95% will improve with appropriate conservative management. Estimates are that 9 to 15% of symptomatic pars defects will eventually require surgical intervention. Roche and Rowe’s study demonstrated between 20 and 80 years there is no evidence of increased incidence of pars defects, suggesting the highest risk is through adolescents after which time the bones have fully ossified and risk plateaus. Radiographically visualized spondylolysis is associated with spondylolisthesis approximately 25% of the time.
Seitsalo et al. found that 23% of their 272 children/adolescents demonstrated slip progression greater than 10% at approximately 16 years follow up. Another study, Danielson et al., found 3% of their 311 patients demonstrated slip progression greater than 20% at approximately 4 years follow up. Patients are likely most vulnerable to slip progression during growth spurts.
As previously discussed, in cases where physical therapy is warranted, a structured PT program should be carried out for roughly 6 months. This program should focus on hamstring stretching to offload additional extension forces, core strengthening, and pelvic tilts. Additionally, PT program should begin with a flexion based program with slow progression into extension exercises once these are no longer aggravating.
Consultation for possible spinal surgery is the recommendation for the cases described above in “Treatment / Management” section under “II. Operative.”
Pars defects are surprisingly common in the pediatric/adolescent population who participate in sports and present with low back pain (as high as 50%). With that in mind, approach these patients with an appropriate index of suspicion and work up with imaging. If initial radiographs are negative (AP/lateral/oblique), follow up with MRI or CT. Early identification correlates with a significantly improved outcome.
Pars interarticularis defects can pose both diagnostic and treatment challenges for healthcare providers. Diagnosis can be challenging because the typical patient is a child or adolescent who the clinician would prefer to spare from radiation exposure, yet confirmation of suspected pars defects relies on imaging support. Additionally, imaging in conjunction with symptoms should guide management. No universal algorithm for workup exists for this pathology; therefore workup must be approached in a case by case fashion. Challenges arise when treating the pediatric population; providers would especially like to spare these patients from unnecessary radiation exposure and know that the majority of pars defects can be managed conservatively, so many patients undergo management without a full workup. Generally, when pars defect is high on the differential, regardless of age, appropriate plain radiographs should be obtained. If initial imaging is equivocal, again regardless of age, imaging should progress to MRI or CT depending on the clinical history and provider preference. Patients and family must be educated on the importance of appropriate workup (including imaging) given outcomes are improved with early detection.
|||Fredrickson BE,Baker D,McHolick WJ,Yuan HA,Lubicky JP, The natural history of spondylolysis and spondylolisthesis. The Journal of bone and joint surgery. American volume. 1984 Jun; [PubMed PMID: 6373773]|
|||Berger RG,Doyle SM, Spondylolysis 2019 update. Current opinion in pediatrics. 2019 Feb; [PubMed PMID: 30531225]|
|||Rosenberg NJ,Bargar WL,Friedman B, The incidence of spondylolysis and spondylolisthesis in nonambulatory patients. Spine. 1981 Jan-Feb; [PubMed PMID: 7209672]|
|||Beutler WJ,Fredrickson BE,Murtland A,Sweeney CA,Grant WD,Baker D, The natural history of spondylolysis and spondylolisthesis: 45-year follow-up evaluation. Spine. 2003 May 15; [PubMed PMID: 12768144]|
|||Logroscino G,Mazza O,Aulisa G,Pitta L,Pola E,Aulisa L, Spondylolysis and spondylolisthesis in the pediatric and adolescent population. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery. 2001 Nov; [PubMed PMID: 11734982]|
|||Cyron BM,Hutton WC, The fatigue strength of the lumbar neural arch in spondylolysis. The Journal of bone and joint surgery. British volume. 1978 May; [PubMed PMID: 659472]|
|||ROCHE MB,ROWE GG, The incidence of separate neural arch and coincident bone variations; a survey of 4,200 skeletons. The Anatomical record. 1951 Feb; [PubMed PMID: 14811059]|
|||Rossi F, Spondylolysis, spondylolisthesis and sports. The Journal of sports medicine and physical fitness. 1978 Dec; [PubMed PMID: 745379]|
|||Micheli LJ,Wood R, Back pain in young athletes. Significant differences from adults in causes and patterns. Archives of pediatrics [PubMed PMID: 7827653]|
|||Morita T,Ikata T,Katoh S,Miyake R, Lumbar spondylolysis in children and adolescents. The Journal of bone and joint surgery. British volume. 1995 Jul; [PubMed PMID: 7615609]|
|||Standaert CJ,Herring SA,Halpern B,King O, Spondylolysis. Physical medicine and rehabilitation clinics of North America. 2000 Nov; [PubMed PMID: 11092019]|
|||Jackson DW,Wiltse LL,Cirincoine RJ, Spondylolysis in the female gymnast. Clinical orthopaedics and related research. 1976 Jun; [PubMed PMID: 132328]|
|||Libson E,Bloom RA,Dinari G, Symptomatic and asymptomatic spondylolysis and spondylolisthesis in young adults. International orthopaedics. 1982; [PubMed PMID: 6222997]|
|||Sagi HC,Jarvis JG,Uhthoff HK, Histomorphic analysis of the development of the pars interarticularis and its association with isthmic spondylolysis. Spine. 1998 Aug 1; [PubMed PMID: 9704368]|
|||Ralston S,Weir M, Suspecting lumbar spondylolysis in adolescent low back pain. Clinical pediatrics. 1998 May; [PubMed PMID: 9597294]|
|||Ramirez N,Flynn JM,Hill BW,Serrano JA,Calvo CE,Bredy R,Macchiavelli RE, Evaluation of a systematic approach to pediatric back pain: the utility of magnetic resonance imaging. Journal of pediatric orthopedics. 2015 Jan; [PubMed PMID: 24686297]|
|||Scavone JG,Latshaw RF,Weidner WA, Anteroposterior and lateral radiographs: an adequate lumbar spine examination. AJR. American journal of roentgenology. 1981 Apr; [PubMed PMID: 6784466]|
|||Jarvik JG,Deyo RA, Diagnostic evaluation of low back pain with emphasis on imaging. Annals of internal medicine. 2002 Oct 1; [PubMed PMID: 12353946]|
|||Bellaïche L,Petrover D, [Imaging in chronic low back pain: which one and when?]. La Revue du praticien. 2008 Feb 15; [PubMed PMID: 18536201]|
|||Crawford CH 3rd,Ledonio CG,Bess RS,Buchowski JM,Burton DC,Hu SS,Lonner BS,Polly DW,Smith JS,Sanders JO, Current Evidence Regarding the Surgical and Nonsurgical Treatment of Pediatric Lumbar Spondylolysis: A Report from the Scoliosis Research Society Evidence-Based Medicine Committee. Spine deformity. 2015 Jan; [PubMed PMID: 27927449]|
|||Sairyo K,Sakai T,Yasui N,Dezawa A, Conservative treatment for pediatric lumbar spondylolysis to achieve bone healing using a hard brace: what type and how long?: Clinical article. Journal of neurosurgery. Spine. 2012 Jun; [PubMed PMID: 22519929]|
|||McClellan JW 3rd,Vernon BA,White MA,Stamm S,Ryschon KL, Should 25-hydroxyvitamin D and bone density using DXA be tested in adolescents with lumbar stress fractures of the pars interarticularis? Journal of spinal disorders [PubMed PMID: 22134731]|
|||Kurd MF,Patel D,Norton R,Picetti G,Friel B,Vaccaro AR, Nonoperative treatment of symptomatic spondylolysis. Journal of spinal disorders [PubMed PMID: 18046167]|
|||Syrmou E,Tsitsopoulos PP,Marinopoulos D,Tsonidis C,Anagnostopoulos I,Tsitsopoulos PD, Spondylolysis: a review and reappraisal. Hippokratia. 2010 Jan; [PubMed PMID: 20411054]|
|||Seitsalo S,Osterman K,Hyvãrinen H,Tallroth K,Schlenzka D,Poussa M, Progression of spondylolisthesis in children and adolescents. A long-term follow-up of 272 patients. Spine. 1991 Apr; [PubMed PMID: 2047915]|
|||Danielson BI,Frennered AK,Irstam LK, Radiologic progression of isthmic lumbar spondylolisthesis in young patients. Spine. 1991 Apr; [PubMed PMID: 2047916]|
|||Blackburne JS,Velikas EP, Spondylolisthesis in children and adolescents. The Journal of bone and joint surgery. British volume. 1977 Nov; [PubMed PMID: 925059]|