Injury of the pars interarticularis is among the most common causes of low back pain, especially in adolescent athletes. Sometimes these lesions develop in an asymptomatic manner, and they are detected in adulthood when the injury becomes chronic and symptomatic.
The spectrum of pathologies in the pars interarticularis ranges from bone stress, pars fracture (spondylolysis) to isthmic spondylolisthesis, which represents an anterior vertebral slippage. Bone stress is considered the earliest sign of disease. Repetitive bone stress causes bone remodeling and may result in spondylolysis, a non-displaced fracture of the pars interarticularis. Also, radiographically visualized spondylolysis is associated with spondylolisthesis about 25% of cases.
Spondylolisthesis, a related condition to spondylolysis, is defined by the forward displacement of the upper vertebra relative to the caudal vertebra. In 1976 Wiltse et al. classified spondylolisthesis into five types:
Type I or dysplastic: is attributed to congenital dysplasia of the superior articular process of the sacrum.
Type II or isthmic: is due to a lesion in the pars interarticularis; these subclassify as:
(a) Lytic, when a fatigue pars fracture is present
(b) Pars elongation due to multiple healed stress fractures
(c) Acute pars fracture
Type III or degenerative: originates from facet instability without a pars fracture.
Type IV or traumatic: the displacement is due to an acute posterior arch fracture other than pars.
Type V or pathological: is due to posterior vertebral arch bone disease.
Type VI or iatrogenic: it is a potential sequel to spinal surgery.
For this activity, the focus will be on type II or isthmic spondylolisthesis.
Spondylolisthesis was classified by Meyerding et al.  in five subtypes according to the magnitude of slippage on plain lateral lumbar radiograph measured in accordance to the inferior vertebra.
Grade I, less than 25% of displacement,
Grade II, between 25 and 50%,
Grade III, between 50 and 75%,
Grade IV, between 75 and 100% and
Grade V or spondyloptosis, when there is no contact between the vertebrae endplates. The commonly used Grade V, representing more than a 100% slip or spondyloptosis, is not part of the original grading system.
The majority of pars lesions or spondylolysis occur at L5 (85 to 95%), with L4 being the second most commonly affected vertebra (5 to 15%). The other lumbar levels are less often affected. The defect is unilateral in 22% of the cases.
Pars defect is an acquired condition that develops at a young age. However, there is a strong association between pars defects and congenital anomalies such as spina bifida occulta.
Congenital pars injury has never been described. Even though the acquired theory is the most accepted, there is evidence that a genetic component is likely to contribute. Wynne-Davies et al. found that first-degree relatives of those affected by spondylolysis had a higher incidence (19%) of spondylolysis compared to the general population.
Isthmic spondylolysis represents a fatigue fracture in the pars interarticularis isthmus; this is the weakest part of the posterior vertebral arch. Hyperextension and rotatory forces may result in repetitive stress in this region. An isolated traumatic event is less common as a cause of spondylolysis; however, it could potentially complete a developing pars fracture.
Athletes encompass the majority of patients presenting with spondylolysis. Sport-specific maneuvers with repetitive twisting rotation and extension increase the load on the spine and may result in stress injury. There are reports that the strength of the neural arch increases through adulthood until the age of 50. Children and adolescents are prone to a higher risk of fatigue pars fractures.
The incidence of spondylolysis is about 3 to 6%, being higher in elite adolescent athletes (8 to 15%), the male to female ratio is 2-3:1.  Divers, rowers, gymnasts, weight lifters, wrestlers, throwing track, and field athletes have higher rates within this group. Roche and Rowe reported an overall incidence of 4.2%, with rates of 6.4% for White males and 2.3% for White females, while the prevalence for African-American males was 2.8% and 1.1% for African-American females. Fredrickson et al. found an increased incidence in population sorted by age. The overall incidence at age six was 4.4%, 5.2% by age 12, and 6% by adulthood. No newborn within 500 studied patients showed radiographic evidence of spondylolysis. Family members of affected patients have a higher rate of spondylolysis than the rest of the population.
Approximately 80% of patients with spondylolysis at the L5 level have the isthmic type of spondylolisthesis, and 20% of these show slippage that exceeds 25%.
History and Physical
There is a fairly high incidence of radiographically identified spondylolysis among the general population. However, clinicians find the majority of these lesions in asymptomatic patients.
Symptomatic pars lesions appear to be a clinical problem in adolescents, especially in athletes. The mechanism of trauma, history, and physical examination findings may lead to suspicion of pars interarticularis injuries. The mechanism of injury involves hyperextension and twisting rotation activities such as weight lifting or aerobic gymnastics. However, any sporting activity may increase the risk of pars injury.
The most frequent complaint is low back pain; either localized or diffuse. Trunk hyperextension or rotation exercises usually exacerbate the pain and rest partially relieves it. It usually locates at the lower lumbar back. However, patients may complain about buttocks or irradiated pain, into one or both legs. The outset of pain can be gradual for a long period with mild symptoms or start sharply after acute trauma.
During the physical examination, patients tend to express a hyperlordotic posture. Tight hamstrings and knee contractures are common. Sometimes, patients may demonstrate a flattened lumbar lordosis, a palpable step off of the spinous process or limitation of lumbar flexion and extension.
The Stork test or one-legged hyperextension maneuver is thought to be the only pathognomonic finding during examination. It involves asking the patient to stand on one leg and to extend the low back. When properly done, the leg is straight and trunk tilted as a result of the lumbosacral extension. Concurrent ipsilateral knee flexion may produce trunk tilt without low back extension and subsequently, produce lower test sensitivity. Pain indicates possible spondylolysis on the ipsilateral side.
If patients present an isolated spondylolysis, the neurological examination should be normal. The most frequent neurological symptoms are radicular pain, weakness, tingling, and numbness in the lower limbs. They are related to spondylolisthesis rather that spondylolysis. Sometimes patients complain about symptom exacerbation when performing activities that involve low back extension. As a result, patients will express a kyphotic lumbar posture to relieve nerve roots by lumbar flexion and foraminal widening. If radicular pain is present, the L5 nerve root is the most commonly affected, and the straight leg raise test may be positive. Bowel and bladder symptoms or cauda equina syndrome are rare.
Multiple imaging studies may assist in the diagnosis of a pars lesion. Once pars injury is suspected from the history and physical examination, radiographic studies are the next step. Anterior-posterior and lateral lumbar X-rays must be requested. Although lateral lumbosacral radiograph may show the defect in pars in 80% of the cases, the classical oblique x-ray views have been mentioned as important studies to diagnose this condition. The defect in isthmic spondylolysis appears as a lucency in the region of the pars interarticularis. The common description of the radiographic appearance of the lesion on lateral oblique radiographs is commonly that of a collar or a broken neck on the “Scotty dog.” Radiographic studies have limited sensitivity to diagnose acute pars injury compared with other imaging modalities. When an X-ray is not diagnostic, further studies merit consideration.
Scintigraphy is an excellent screening tool for low back pain in children or adolescents. It has shown high sensitivity for the detection of acute injuries and bone stress reaction in the pars. However, some lesions may not display an increased contrast uptake.
Computed tomography scan (CT) may be helpful in some cases due to its higher specificity. The tomographic finding of an acute injury include the margin reabsorption in the pars; pars sclerosis may indicate chronic stress, and marginal sclerosis with widening may indicate a chronic condition. The identification of patients with a normal CT scan and abnormalities on bone scintigraphy or Single-photon emission computed tomography (SPECT) is important as these patients are presumed to be in a very early stage of the disease and have a higher chance of healing with timely conservative treatment.
SPECT is considered the best diagnostic adjunct when plain radiographs are negative. Several of the abnormalities identified on SPECT proved to represent spinal pathology other than spondylolysis, including infection and osteoid osteoma. Although these modalities may present with increased sensitivity in detecting pars lesions compared with plain film, they are not necessarily highly specific for this disorder. Repetitive stress causes local bone remodeling and abnormal uptake of scintigraphic tracer. SPECT has 10 to 20 times more contrast than planar bone scintigraphy; it is more sensitive than radiography and planar bone scans and improves anatomic localization of skeletal lesions without exposing the patient to additional radiation.
Magnetic resonance imaging (MRI) offers advantages in terms of visualizing other types of pathology present in the lumbar spine and may potentially detect pars edema secondary to stress in their clinical course. The lack of ionizing radiation with MRI may also make it a particularly desirable modality for studying pars lesions, especially in the female adolescent population. However, it is worth noting that MRI, like CT, does not assess whether a bony lesion is metabolically active and is less sensitive and specific than scintigraphy or SPECT.
The optimal diagnostic algorithm remains undefined in the current literature. When an acute pars injury is suspected, the recommendation is for X-ray to be the first diagnostic study, followed by scintigraphy or SPECT. If SPECT is positive, a CT scan should be run after SPECT to confirm the pars lesion suspicion and diagnose the stage of the lesion. If SPECT is negative, pars injury has almost certainly been ruled out as the cause of the low back pain, and MRI can be the next study to search for other possible entities.
The differential diagnosis for back pain is extensive and includes degenerative disease, infection, inflammation, tumors, and trauma.
Pediatric dogma suggests that children presenting with back pain may have serious pathology, including malignancy and infection. However, most instances of back pain are non-specific and self-limiting. The onset of symptoms will help differentiate between acute trauma and chronic overuse injury, postural, and developmental abnormalities.
Abdominal and pelvic pathologies may refer pain to the back; laboratory tests are necessary for evaluating patients presenting with back pain and high suspicion of infection or systemic disease. White cell count, erythrocyte sedimentation rate (ESR) or C Reactive Protein, blood, and joint cultures are necessary if an infection is suspected.
The following is a list of the most common differential diagnoses:
Pain originating from the posterior elements of the spine:
Spondylolysis and spondylolisthesis (revised in this article).
Posterior element overuse syndrome: It includes injuries to the ligaments, joint capsules, muscle-tendon units, and facet joints. It is also known as hyperlordotic back pain, spondylotic back pain or lumbar facet syndrome. Patients will present with extension-related low back pain, weak core muscles, decreased lumbar range of motion, and tight hamstrings with no evidence of spondylolysis. Conservative management with cryotherapy and non-steroidal anti-inflammatory drugs is indicated, including physiotherapy focusing on core strength and hamstring flexibility.
Sacroiliac joint (SI) pain:
This syndrome may be present in children with insidious onset of low back and buttock pain, worsened by extension, prolonged standing, or sitting. It can result from inflammation or stress fracture of the sacrum or SI joint. Rest, ice and non-steroidal anti-inflammatory drugs are indicated. A rheumatoid origin of the inflammation must be ruled out.
Pain originating from the anterior elements of the spine:
Scheuermann disease: This entity, with an incidence rate between 1 to 8%, is the most common cause of kyphotic deformity in adolescents. Both females and males are affected equally, and its etiology is unknown. The main difference between Scheuermann disease and postural kyphosis is that the first one is a fixed kyphosis during hyperextension and flexion of the spine.
Lumbar disk herniation is relatively uncommon in children and adolescents with a rate of 3.5%. Children complain about the low back or leg pain worsened by bending forward or Valsalva efforts (coughing, sneezing).
Idiopathic scoliosis demonstrates a Cobb angle above 10 degrees on a standing coronal radiograph. It affects 1 to 3% of the school-age population. However, it is usually painless in this group age.
Discitis and vertebral osteomyelitis are uncommon entities. Discitis is the result of a bacterial infection (most common germen isolated is Staphylococcus aureus) and usually affects the lumbar region, mainly in children under 5 years old. Children may present with unspecific symptoms, irritability, refusal to bear weight, back or abdominal pain. Fever is not constant. Vertebral osteomyelitis is yet more uncommon in children, representing only 1 to 2% of all cases of pediatric osteomyelitis.
Spondyloarthropathy includes juvenile idiopathic arthritis, psoriatic arthritis, reactive arthritis, and inflammatory bowel disease. They are more common in boys, and the genetic marker HLA-B27 should be ruled out.
Pain amplification syndromes:
These syndromes do not have an identified cause. They provoke severe chronic musculoskeletal pain and sometimes are associated with minor trauma, underlying chronic illnesses, and psychological distress.
Benign and malignant tumors require exclusion in every child presenting with low back pain, even though they are very rare. The physician should look for severe pain and night pain, fever, weight loss, or neurologic symptoms. The most common benign lesions are osteoid osteoma, bone cysts, osteoblastoma, and Langerhans cell histiocytosis. Malignant bone tumors include osteosarcoma, leukemia, Ewing sarcoma, and metastases from rhabdomyosarcoma or neuroblastoma.
Progressive spondylolisthesis is among the primary concerns in patients with pars defects. Overall, the risk of progression is small, running about 3 to 4%. Progressive slip was predominantly noted during the adolescent growth spurt and was associated with the presence of spina bifida occulta in this study. Progression after the age of 20 years is much less common; this is likely due to the ossification of the growth plate. Sietsalo et al. demonstrated an increased tendency to progress with an initial slip of greater than 20%.
In low-grade spondylolisthesis, the pelvic incidence is a significant predictor for the risk progression. while in high-grade spondylolisthesis, the pelvic incidence is always high, so sacral slope and pelvic tilt became more relevant.
The majority of adolescents return to activities after 6 months of conservative treatment. Skeletally immature children and adolescents who have bilateral spondylolysis or spondylolisthesis require standing lateral radiographs to assess the progression of slippage every 6 to 12 months until reaching skeletal maturity. Adolescents with over 50% slip (Grade 3 or 4) warrant orthopedic referral and possible surgical treatment.
Complications of this condition as well as from the postoperative course appear below.
A chronic pars defect or non-fusion is a possible evolution after the non-operative treatment as the potential of healing is decreased. This condition can be asymptomatic, or it can produce chronic low back pain.
Another possible evolution from a spondylolysis is the slippage of the lower vertebral body (spondylolisthesis). This problem can be associated with low back pain and neurologic symptoms.
Complications derived from surgical treatment are:
Neurologic deficit: L5 deficit resulting in motor weakness has been mentioned with a prevalence of 30% in cases of high-grade spondylolisthesis after reduction, most of the cases are transitory and resolve completely.
Isthmus non-union: Represents a failure in the consolidation process. It is more common in patients with progressive or terminal stages.
Progression of slippage
Deterrence and Patient Education
As a patient, it is crucial to have a general practitioner consultation in the presence of low back pain, particularly when it results from repetitive sports activities and is not relieved by rest. Pars interarticularis injury is a common cause of low back pain in young people, and prompt recognition and treatment may help to improve short and long term outcomes and avoid complications derived from wrong or delayed diagnosis.
Enhancing Healthcare Team Outcomes
The pars interarticularis injury is a common cause of low back pain, especially among the young population. It is frequently misdiagnosed and can potentially affect clinical outcomes and patient satisfaction. Thus, an interprofessional team approach is essential to make a prompt and accurate diagnosis. While the orthopedic surgeon usually manages the primary injury, other clinicians and nurses should coordinate the education of the patient on lifestyle changes and appropriate exercises. Patients need to perform stretching before any physical activity, maintain healthy body weight, discontinue smoking, and not lead a sedentary life.
Patients with low back pain, especially after repetitive sports activities require a general practitioner consultation. If the healthcare professional considers this diagnosis as a cause of low back pain, then a referral to a spine specialist is vital. Patients may also have this condition discovered by a chiropractor, who should work collaboratively with orthopedic specialists on a way forward.
Entering a rehabilitation program may be necessary for all patients to restore muscle strength and joint flexibility. Physical therapists need to keep the healthcare team informed regarding progress. The pharmacist should work with team by educating the patient on alternatives to opiates for pain control, and verify all dosing as well as performing medication reconciliation. Nursing can monitor progress at followup visits, monitor for treatment progress, and note any adverse medication effects. Only with such an interprofessional team approach can the morbidity of this disorder be reduced. [Level V]
(Click Image to Enlarge)
Oblique plain radiograph of the lumbar spine. Black arrow demonstrates normal pars interarticularis. The white arrow demonstrates lucency in the pars interarticularis, suggestive of fracture. The scottie dog features: transverse process being the nose, the pedicle forming the eye, the inferior articular facet being the front leg, the superior articular facet representing the ear, the pars interarticularis equivalent to the neck of the dog. The "collar" represents the pars fracture.
"Contributed by J Taylor Mansfield, DO"
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