Repetitive stress on the lumbosacral spine during sporting activity places the athletic patient at risk of developing symptomatic pars defect. Clinical history, physical examination, and diagnostic imaging are important to distinguish spondylolysis from other causes of lower back pain. Early pars stress reaction can be identified with advanced imaging, before the development of cortical fracture or vertebral slip progression to spondylolisthesis. Conservative management is first-line for low-grade injury with surgical intervention indicated for refractory symptoms, severe spondylolisthesis, or considerable neurologic deficit. Prompt diagnosis and management of spondylolysis leads to good outcomes and return to competition for most athletes.
Key points
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Pars injury is a common cause of back pain in the athletic population, particularly in adolescents and young adults.
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MRI is a potential alternative to computed tomography/single-photon emission computed tomography for initial diagnostic imaging of pars injury.
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Conservative management with rest and rehabilitation is the mainstay for treatment of pars defects.
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Surgical intervention may be considered after 6 to 12 months of failed conservative management or in cases of severe spondylolisthesis or progressive neurologic deficit.
Pathophysiology and incidence
Spondylolysis describes the fracture defect in the pars interarticularis of the lumbar vertebrae, which may be found as a unilateral or bilateral lesion. One or more vertebral levels may be involved, with the L5 vertebrae most commonly injured in spondylolysis. Bilateral pars defects may lead to progressive anterior translation of the involved vertebrae relative to the next caudal level, termed spondylolisthesis. Thus, the injury pattern of the pars exists on a spectrum, from stress reactions detected by advanced imaging methods to full anterior vertebral subluxation or spondyloptosis.
The pathophysiological development of pars injury may be multifactorial, as some studies suggest there is a genetic predisposition to spondylolysis. However, the predominant contributing factor, particularly relevant to the athletic individual, is the force exerted on the lumbar pars by repetitive hyperextension, axial loading, and rotational motion with sporting activities. The repetitive stress pattern initiates a cycle of microfracture and healing in the pars, until cortical defects arise from a failure of bony remodeling. The notion that physical activity contributes to the development of spondylolysis is supported by the 0% prevalence found in nonambulatory patients. Further, young athletes have a higher prevalence of pars defect compared with nonathletes.
The incidence of pars defects arising from such repetitive microtrauma in children is 4.4% by 6 years of age and increases to 6% by 18 years. Although many cases are asymptomatic, spondylolysis and spondylolisthesis are commonly identified as the cause of lower back pain in the adolescent population. , Pars injury has classically been associated with gymnasts, but athletes in other sports including wrestling, rowing, diving, weight-lifting, and throwing sports have also demonstrated a high prevalence of pars injury. In addition, multiple case series have reported on spondylolysis management for athletes competing in tennis, soccer, cricket, and volleyball, among other sports. For the athletic adolescent patient presenting with lower back pain, injury to the pars should be given strong consideration when working up the differential diagnosis.
Classification
The Wiltse-Newman classification was described in 1976, grouping spondylolisthesis into different categories. Type I, termed dysplastic spondylolisthesis, describes the abnormal congenital development of lumbosacral articulation, predisposing the L5 vertebral body to slip anteriorly relative to the sacrum over time. Type II, or isthmic, spondylolisthesis occurs as a result of a defect in the pars interarticularis and is subcategorized into 3 groups. Type IIA describes the isthmic fatigue fracture arising from repetitive loading and microtrauma to the pars interarticularis. Type IIB includes isthmic fractures that occur after elongation of the pars from the cyclic incidence of stress fractures and bony healing. Notably, this type of injury pattern can be difficult to distinguish from dysplastic spondylolisthesis. Type IIC describes pars fracture after an acute injury. Type I and II spondylolisthesis are more relevant for consideration in the athletic population, particularly for children and adolescents.
Several other classifications describing spondylolisthesis have been created without widespread adoption. Marchetti and Bartolozzi developed a separate classification system, which divides spondylolisthesis broadly into 2 categories, developmental or acquired. The Meyerding classification describes the percent slippage of the proximal vertebral body. More recent classifications were created by combining components of Wiltse-Newman with Marchetti and Bartolozzi to guide nonoperative treatment and surgical management.
Clinical evaluation
A thorough history and comprehensive physical examination should be conducted during the initial encounter with athletic patients. Patients with spondylolysis often present with insidious onset of lower back pain associated with motions required for sporting activity. The pain may occasionally radiate to the buttocks or lower extremities, although neurologic symptoms and deficits are rare findings with spondylolysis. Patients will report modifications in activity participation to accommodate the pain, and some may find their symptoms to interfere with other daily activities. Clarifying the timeline of symptomatic progression may assist with diagnosis in consideration of other organic causes for low back pain, including sacroiliac dysfunction or lumbar disk herniation. Other questions directed at dietary and nutritional intake may elucidate an increased risk for bony fracture. The implementation of social needs screening may also identify barriers to maintaining nutritional needs in the growing adolescent, which should be addressed with all families regardless of perceived socioeconomic status.
The physical examination begins with inspection for spinal deformity and other superficial abnormalities. Many reports have associated scoliosis and spina bifida occulta with an increased risk of lumbar spondylolysis. Tenderness and spasms over the paraspinal regions may also contribute to apparent spinal curvature. Lumbar range of motion may be limited particularly in lumbar flexion and extension, with pain often elicited with hyperextension. Single-leg hyperextension, or the stork test, can accentuate the pain. , Patients will frequently experience hamstring tightness, which may affect changes in gait. Spondylolisthesis may also be suspected in patients with a vertically oriented sacrum and visible or palpable vertebral step-off. No clinical maneuvers have demonstrated high sensitivity or specificity for the diagnosis of pars injury, , but a high index of suspicion from the clinical history and examination should prompt further investigation with diagnostic imaging modalities.
Diagnostic imaging
Radiography
Prompt diagnostic imaging plays an important role in the prognosis and treatment of athletes, as pars injuries identified in the acute phase of development have shown better healing with conservative management. Standard anteroposterior and lateral radiographic views are typically acquired as a part of initial screening to assess obvious bony pathology. The lateral view is also used to describe the severity of anterior slippage in spondylolisthesis, with less than 50% translation (Meyerding I or II) considered low-grade and Meyerding III–V as high-grade. However, standard radiographs have demonstrated a low sensitivity in the diagnosis of pars defects. Oblique spinal views ( Fig. 1 ) are often acquired to demonstrate the classic “Scotty dog sign,” although recent studies have demonstrated poor diagnostic utility of oblique views. , The lucent defect described as the dog collar is seen most reliably only in late-stage spondylolysis, such that a negative radiograph cannot exclude early stage stress fractures. Despite these limitations, radiographic imaging is frequently obtained because it remains a relatively affordable and accessible measure for initial screening.
Computed Tomography
Standard axial and sagittal computed tomography (CT) of the lumbar spine provides excellent resolution of the bony anatomy to characterize cortical defects, incomplete fractures, and sclerotic changes associated with pars injury. , Even modified protocols, with comparable radiation exposure to plain radiography, outperform standard radiographic imaging in the diagnosis of spondylolysis. Plain CT images are superior in demonstrating disruptions to bony cortex, with early pars fractures typically identified as defects in the inferior margin and subsequent extension to the superior margin found as the fracture progresses ( Fig. 2 A, B). CT imaging is also used to assess fracture healing. However, the limitation with CT, particularly in comparison with single-photon emission CT (SPECT) and MRI, is the inability to identify early stress reactions , and to distinguish acute from chronic injury patterns.
Single-Photon Emission Computed Tomography
The acquisition of single-photon emission computed tomography (SPECT) involves the intravenous injection of radioisotopes to identify regions with high rates of bony turnover. Metabolically active sites of stress fracture can be identified earlier in the progression of injury with SPECT compared with radiography or CT ( Fig. 2 C, D). However, radiotracer uptake in posterior elements of the spine is nonspecific for pars injury and may reflect an active secondary ossification center, vertebral pedicle fracture, infection, or developing neoplasm. , In the athletic population, asymptomatic patients with spondylolysis have had positive radionuclide imaging, and some symptomatic patients with positive SPECT have no demonstrated signs of pars injury on CT. Although some have advocated for the hybrid acquisition of SPECT and CT to increase the combined diagnostic utility, , , others find the false-positive and false-negative rate of SPECT too high to justify its use as a primary screening modality, particularly given the increased cost and radiation exposure to patients. , , ,
MRI
MRI has recently emerged as a potential alternative to CT or SPECT for initial diagnostic imaging of suspected lumbosacral spondylolysis. A major benefit with the use of MRI is the avoidance of radiation exposure, which is particularly relevant for young, skeletally immature athletes. MRI provides insight into anatomic structures, with better soft tissue visualization, and is able to characterize activity changes at the pars interarticularis. , Although abnormalities on MRI are detected in asymptomatic patients, MRI may be helpful in identifying other contributing factors to lower back pain besides spondylolysis. In addition, although CT is considered the gold standard for evaluation of osseous anatomy, recent data also suggest that specific MRI sequences can detect incomplete and complete pars fractures with high accuracy. ,
Hollenberg and colleagues used T1- and T2-weighted sagittal and T2-weighted axial sequences for lumbosacral MRI to generate a 5-grade classification system describing stress reaction at the pars interarticularis. The addition of a short-tau inversion recovery sequence also improves the sensitivity for bone marrow edema to detect early pars stress reactions. , , MRI has demonstrated a high sensitivity and specificity for distinguishing normal pars from grade 1 or higher injury, comparable to bone SPECT. , It should be noted that although there exists discrepancy between results using SPECT and MRI to detect stress reactions, the 2 imaging modalities identify distinctly separate biomarkers for bone stress.
With multiple options for advanced imaging of spondylolytic defects, there is little consensus on the appropriate diagnostic pathway. In recent years, there has been increasing momentum for the use of MRI as the first-line imaging test in suspected pars injury, as it reliably distinguishes early stage stress reactions from normal pars. , , Evaluation with CT and SPECT may be more warranted to guide treatment decisions in the case of refractory management or for athletes in high-level competition. Regardless of diagnostic modality, the ultimate goal of management for spondylolysis and spondylolisthesis is the alleviation of debilitating symptoms and the return to preinjury activity. Because osseous union on imaging has shown poor correlation with clinical outcomes, the use of follow-up imaging to demonstrate healing should be avoided in patients progressing with rehabilitation protocols and reserved for those with refractory symptoms.
Nonoperative management
Stress Reactions
Stress injuries of the pars interarticularis are commonly found in athletes. A retrospective analysis of adolescent athletes with acute low back pain found a spondylolytic stress fracture in 47% of their cohort. Another retrospective study compared lumbar pathology in high-level athletic and nonathletic adolescents, finding the radiographic incidence of stress reaction in athletes was 12% versus 2% in nonathletes ( P = .08), with spondylolysis occurring in 32% and 2% in respective cohorts ( P = .0003). Because cortical stress reactions are better delineated by CT or SPECT imaging, having a high suspicion with negative radiographic findings in an athlete should prompt further work-up with advanced imaging.
Athletes with pars stress reactions have shown a capacity to heal and return to sport with early rest from activity and immobilization. Jackson and colleagues reported on a case series of 7 athletes with pars stress reaction who returned to sport at an average of 7.3 months after initial resting and variable use of a form-fitting brace to limit lumbar hyperextension. Anderson and colleagues followed 34 patients with pars stress reaction and found that symptomatic alleviation and improvements on SPECT studies were more robust in the patients initiated on early bracing. Sys and colleagues initiated bracing for competitive athletes with spondylolytic defects identified by positive bone scan, leading to 5.5-month average return to competition for 25/28 of their cohort. Early recognition and therapy lead to better osseous healing and can prevent the progression of stress reaction to the development of spondylolysis. , ,
Despite a general consensus regarding restriction of activity to promote early bony healing and progressive return to play, specific protocols for management of pars stress reaction are likely derived from more prevalent literature on rehabilitation for spondylolysis and spondylolisthesis. The senior author’s approach to athletic patients with pars stress reactions involves 6 to 12 weeks of rest from activity, without external bracing for immobilization. Physical therapy is initiated after the initial period of rest with an individualized timeline for return to activity based on symptomatic resolution and other patient-specific factors. The physical therapy program is focused on strengthening of deep core musculature while limiting hyperextension of the lumbosacral junction.
Spondylolysis
Conservative management is the mainstay of treatment of diagnosed spondylolysis in the athletic patient. A period of rest from activity is indicated typically until, at least, the patient experiences alleviation of pain, although some investigators suggest a minimum 3 months of restriction from sport. , Targeted physical therapy is generally recommended, with exercises directed at deep abdominal musculature and lumbar multifidi contributing to improvements in pain and functional outcome. However, the timing for introduction of physical therapy is variable in the literature, with some advocating for early therapy and others recommending that rehabilitation start after the initial period of activity restriction. , Selhorst and colleagues conducted a retrospective analysis of adolescents who were referred to physical therapy before or after 10 weeks of rest from activity and found faster return to activity with earlier initiation of physical therapy. Recommendations on timing for rehabilitation are based on low-level evidence and generally derive from anecdotal physician practices.
The utility of bracing for spondylolysis remains a controversial topic. Several studies have reported on successful outcomes for return to activity with different braces, including thoracolumbosacral orthotics and lumbosacral orthotics. , , , , However, a meta-analysis of studies using lumbar bracing identified no difference in clinical outcomes associated with usage, and bracing did not prognosticate poor long-term outcomes. Biomechanical studies have suggested that lumbar bracing is less effective at stabilizing the lower intervertebral segments that are most commonly involved in isthmic spondylolysis. , True immobilization at L5 and S1 is achieved only with the use of a leg extension, and its use is rarely reported in the literature. Confounding the proposed benefits of spinal stabilization and motion restriction may be a general adherence to activity restriction. For these reasons, the senior author’s general approach is conservative therapy without bracing initially, with reconsideration for use in those patients whose symptoms are persistent after 6 to 12 weeks.
The concept of osseous union or healing of the spondylosis is an intuitively attractive one, but the rate of lysis healing is in actuality quite low. In a meta-analysis of 10 radiographic studies, Klein and colleagues found that only 28% of spondylolytic lesions healed. Furthermore, multiple studies have shown no correlation with osseus union and clinical outcomes. Therefore, the goal of treatment of spondylolysis is symptomatic alleviation, rather than osseous healing on imaging. For the clinically improving athlete, it is unnecessary to demonstrate radiographic healing, thereby avoiding radiation exposure and the associated costs of further imaging.
Spondylolisthesis
Nonsurgical management of low-grade isthmic spondylolisthesis in athletes is frequently treated similarly as spondylolysis. Several studies on conservative management of spondylolysis also included patients with grade-I spondylolisthesis in their cohort analysis. , , , Pizzutillo and Hummer demonstrated pain relief in two-thirds of patients with grade 2 or lower slippage, whereas all 28 patients in a case series by Bell and colleagues were pain free after brace treatment. , Similar to the strategy for patients with spondylolysis, rest from activity and rehabilitation should be prioritized to alleviate pain and hamstring spasm with progressive return to sport based on individual response to therapy.
Several studies on the natural history of spondylolisthesis demonstrate a low rate of progression in adolescent populations ( Fig. 3 ). However, the rate of slippage may be slightly increased in the athletic population that persists with sporting involvement. A retrospective analysis of asymptomatic adolescent athletes identified a progression in spondylolisthesis greater than 5° in 33 out of 86 patients. Although slip progression in the study did not disrupt training or activity participation, another study found that 5 of 20 athletes with symptomatic spondylolisthesis went on to undergo posterolateral fusion for slip progression after initial nonoperative therapy, with 5 more patients citing persistent pain as their surgical indication. These data suggest that a diagnosis of spondylolisthesis need not dictate a restriction from activity after achieving a pain-free condition from initial therapy. Even though increased deformity is not expected for most patients, a general awareness of the diagnosis may prompt further evaluation in the setting recurrent or persistent pain.
Surgical management
For athletic patients with spondylolysis or low-grade spondylolisthesis, surgical management is typically reserved for those without symptomatic improvement after conservative management for 6 to 12 months. Patients with high-grade spondylolisthesis or significant neurologic deficit may also respond to conservative measures, but many surgeons recommend earlier surgical intervention in these cases. Before surgery, the clinician should exclude other causes of back pain with a thorough history and physical examination and additional diagnostic modalities as indicated. Direct pars fixation and in situ fusion encompass the 2 broad categorizations for the surgical approach to spondylolysis and spondylolisthesis. Although both methods have good postoperative outcomes, direct pars repair obviates surgical extension to adjacent vertebrae, thereby retaining more physiologic mobility, which may be desirable for high-level athletes.
Direct Pars Repair
Direct pars repair involves addressing the direct level of pathology in the lumbar spine. Multiple techniques have been described to stabilize the pars, including Buck compression pedicle screw, Scott wire fixation, and other variations. The Buck procedure involves direct visualization with placement of a bone screw across the pars defect, with bony graft placement to promote osseous healing. Multiple studies on the use of Buck procedure in the athletic population demonstrate improvements in functional outcomes with successful return to sport for most patients.
Scott’s wire fixation technique involves passing a wire through the ipsilateral transverse process and back to the spinous process in a figure-of-8 configuration to compress the pars defect. Nozawa and colleagues studied the Scott wiring technique in athletes, with 18 returning to sport after an extended 12-month rehabilitation process and 3 complications involving the wire construct. Hioki and colleagues correlated improvements in midterm outcome measures by Japanese Orthopedic Association Score with bony union rates on CT, although their study demonstrated nonunion in nearly 20% of their cohort. Debnath and colleagues reported on 22 athletes, with 3 undergoing wire fixation and 19 receiving Buck procedure. Of the patients treated with Scott wiring, one showed no improvement in patient-reported outcome measures and the other two required posterolateral fusion for malunion. Of the patients treated with Buck procedure, 18/19 returned to sport within 7 months with an overall improvement in Short-Form 36 score and Oswestry Disability Index. Although these data suggest that Buck’s screw fixation is superior to Scott wiring, there is currently no high-level evidence directly comparing the 2 techniques.
There is also a growing body of literature on the use of minimally invasive approaches for repair of the spondylolysis, although few have reported specifically on athletic patients and outcomes ( Fig. 2 E, F). A systematic review comparing minimally invasive surgery to conventional pars repair techniques suggested that patients experienced greater symptomatic improvement in pain, despite an older patient population. With further improvements in surgical technique, tissue-sparing techniques to address spondylolysis may see increased utilization in the near future.
Fusion Techniques
Spinal fusion techniques may be indicated in athletes with spondylolysis and spondylolisthesis. Several variables may be considered when determining the specific method of fixation, including level of pars defect, degree of slippage, and patient-specific considerations. With the L5 pars most commonly injured in isthmic spondylolisthesis, in situ L5-S1 fusion with autogenous posterior iliac graft is commonly used. Extension to L4 may also be indicated with more severe vertebral slippage. Although studies on athletes are limited, studies on in situ fusion in the pediatric population demonstrate good improvement in pain and successful rates of bony union. Symptomatic alleviation persists on long-term follow-up of adolescent patients after in situ fusion, without significant degenerative changes in vertebrae proximal to the fixation site. , Posterolateral fusion is the classic technique described for isthmic spondylolysis, although anterior and circumferential in situ fusion approaches have also shown good functional and radiographic outcomes in high-grade spondylolisthesis ( Fig. 4 ).
