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Pars Interarticularis – Causes, Symptoms, Diagnosis, Treatment

A pars interarticularis defect is a unilateral or bilateral fracture involving the pars interarticularis of the posterior vertebral arch. This injury occurs almost exclusively in the lower lumbar region, most often at L5. This activity highlights the interprofessional management of this condition. The pars interarticularis (pars) lies between the superior and inferior articular processes bilaterally at each zygapophyseal joint. Pars interarticularis defects also referred to as spondylolysis, are a common cause of axial back pain in adolescents, especially young athletes.

The pars interarticularis, or pars for short, is the part of a vertebra located between the inferior and superior articular processes of the facet joint.^[rx]

In the transverse plane, it lies between the lamina and pedicle. In other words, in the axial view, it is the bony mass between the facets that is anterior to the lamina and posterior to the pedicle. It is abnormal in spondylolysis, either due to fracture or congenitally.^[rx] Bilateral C2 pars fractures are known as a variant of the hangman’s fracture.

Stress fractures of the pars interarticularis are known to be associated with playing sports such as volleyball, although the mechanism is somewhat unclear.^[rx] Patients with spina bifida occulta have an increased risk for spondylolysis.^[rx]

Staging

Pars defects subdivide into five categories according to the Wiltse-Newman Classification[rx]:

Dysplastic: congenital abnormalities/attenuated pars (approximately 20%)
Isthmic: lesions in the pars resulting from a stress fracture or acute fractures (approximately 50%)
- Type II-A: pars fatigue fracture
- Type II-B: pars elongation due to a healed fracture
- Type II-C: pars acute fracture
Degenerative: degeneration of the intervertebral discs that results in segmental instability and alterations of the articular processes
Traumatic: an acute fracture that results in fractures to various regions of the neural arch
Pathological: bone disease such as tumors and infections that result in lesions to the pars

Classification of spondylolisthesis is according to the Meyerding Classification.[22] 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.

Grade I less than 25%
Grade II 25 to 50%
Grade III 50 to 75%
Grade IV 75 to 100%
Grade V greater than 100% (spondylosis)

Causes of Pars Interarticularis

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.[rx] This theory garners support from the fact that, as noted below in epidemiology, the 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.[rx][rx] 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.[rx] 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.[rx]

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.[rx] 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 certification. 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.[rx]

Symptoms of Pars Interarticularis

pain in the lower center back that might feel like a muscle strain
pain in the thighs and buttocks
stiff muscles and tenderness in the lower back region
muscle tightness, especially in the hamstring muscles
Pain radiating down one or both legs
Numbness, tingling, and weakness in the legs

Diagnosis of Pars Interarticularis

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.[rx][rx]

Symptomatic pars lesions appear to be a clinical problem in adolescents, especially in athletes.[rx] 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.

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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.[rx][rx][rx][rx] The outset of pain can be gradual for a long period with mild symptoms or start sharply after acute trauma.[rx]

During the physical examination, patients tend to express a hyperlordotic posture. Tight hamstrings and knee contractures are common.[rx][rx] 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.[rx][rx][rx]

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 than 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.

Lab Test and Imaging

Anterior-posterior and lateral lumbar X-rays – Multiple imaging studies may assist in the diagnosis of a pars lesion.[rx] 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.
A 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.[rx]
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.[rx] 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.[rx] 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.[rx]

Treatment of Pars Interarticularis

In most cases, pars defect is treated with medication, muscle relaxers and rest. However, sometimes surgery will be required. Your Physiotherapist may also prescribe a lumbar back brace in the acute stages of pars defect that will aid in the treatment process.

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Since a pars fracture is a break in the bone, only rest and time will promote healing. Most people with a pars defect do not require surgery with anti-inflammatory medications, Physiotherapy, and recovery the recommended means of dealing with a pars stress fracture.

Typically, the average recovery rate of Pars Fracture can be anything from between 6-12 weeks.

Recovery is the most important aspect for the initial stages of a pars stress fracture. With the guidance and implementation of Physiotherapy, individuals with a stress fracture should expect a series of strengthening exercises for the abdominal and low back muscles to combat the pain and rehabilitation from their Physiotherapist.

In some cases, a complete recovery from a pars stress fracture can take as long as 6 months.

When symptoms and pain are not relieved with nonsurgical treatments patients may require surgery. Surgical options for pars defect include a pars repair versus a lumbar fusion.

Injections are another alternative but more commonly used in the adult population. Injections might help control the pain enough to least keep you functional. In some cases, injections will have very little effect on some adults and if they do work, the injections do have the tendency to wear off. However, the positive implication of using injections is that they are very low risk and a less invasive technique to adopt.

The treatment regimen of brace varies widely; it usually consists of 23 hours a day usage for six months, with a subsequent six-month weaning period and physical therapy. TLSO bracing indications include when an acute pars stress reaction spondylolysis is present, for isthmic spondylolysis and low-grade spondylolisthesis that have failed to improve with physical therapy.

Physical therapy should be done for 6 months and include hamstring stretching, pelvic tilts, abdominal strengthening, and close follow-up of low-grade dysplastic lysis as there is a higher chance of progression.

Surgical treatment for spondylolysis has is generally only for patients who fail to respond to conservative treatment or those in the terminal stage. Surgery is necessary in about 9 to 15% of cases of spondylolysis and/or low-grade spondylolisthesis.[rx][rx] Other indications for surgical intervention include progressive slip, intractable pain, development of neurological deficits, and segmental instability associated with pain.[rx][rx]

The most common surgical options are direct repair at the pars defect or fusion of the lumbar segment. Direct repair is the preferred surgical treatment as it avoids a decreased range of motion and adjacent segment disease reported in fusion surgery with rates from 5.2 to 18.5%.[rx][rx] There are many surgical techniques; Buck´s technique with single lag screw,[rx] Scott´s technique with cerclage wire, Morscher´s technique that utilizes a hook screw fixation,[rx], Louis´s fixation technique with a butterfly plate,[rx] Tokuhashi´s technique based on pedicle screw hook fixation,[rx] and Ulibarri´s fixation technique with pedicle screw rod system.[rx]

Of the surgical treatment options listed here, the most favorable option is the pedicle screw hook technique and the pedicle screw rod technique. This success is due to the high success rate, low rate of hardware failure, the lack of required postoperative bracing, and sufficient maintenance of reduction during flexion, extension, torsion, and side bending.[rx]

L5-S1 in-situ posterolateral fusion with bone grafting is the recommended approach in patients with L5 spondylolysis or low-grade spondylolisthesis (Meyerding Grade I and II) that have failed nonoperative treatment or demonstrated progression, neurologic deficits, and dysplastic changes with a high propensity for progression. The fusion is possible with or without instrumentation. Postoperative immobilization in a TLSO is a suggested approach, and decompression is indicated if clinical symptoms of stenosis or radiculopathy are present.

L4-S1 posterolateral fusion, with or without reduction, is considered for high-grade isthmic spondylolisthesis (Meyerding Grade III, IV, V). The reduction is extremely controversial, with no accepted guidelines. It may take place with instrumentation or positioning. It is possible to restore sagittal alignment and reduce lumbosacral kyphosis, even though there is a significant risk of complications (8 to 30%) including L5 nerve root injury as the most common complication, sexual dysfunction or catastrophic neurologic injury. Fusion is usually an instrumented intervention.

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Lately, low-intensity pulsed ultrasound (LIPUS) in addition to conservative treatment appears to be very promising for achieving a higher rate of bony union. LIPUS requires more supporting studies but may prove to become a standard of care in the future.[rx] Arima et al. evaluated the use of LIPUS versus conventional conservative treatment in patients with the progressive stage of spondylolysis.[rx] The experimental group consisted of 9 adolescent patients that received a combination of LIPUS for 20 minutes every day in addition to conventional conservative treatment. The control group consisted of 10 adolescent patients who received only conventional conservative treatment. The experimental group treated with LIPUS achieved a union rate of 66.7% with a mean treatment time of 3.8 months. The control group treated with conventional conservative treatment achieved a union rate of 10% with a treatment time of 3.8 months.

How can you prevent the possibility of this fracture and pain in your spine?

There are actually a few things that you can do to avoid getting a pars stress fracture including;

Taking a break from sports every few days
Maintaining good physical condition during the offseason
Increasing high impact activities gradually
Increasing hours in sports gradually
Avoiding year-round participation in sports
Maintaining flexibility in the hamstrings and hip flexors
Increasing strength in the lumbar and core muscles.
Yoga movements and exercises.

Is a pars fracture serious?

It depends. Like any fracture, a pars defect is relatively serious and will require some form of treatment. However, it can be difficult to detect and makes things a bit trickier than when you break an arm or foot.

Since pars defect is common among children who are quite active or participate in a sport of some kind, the healing rate for bones is rather quick meaning that most children recover with not much more than a bit of downtime.

However, on some occasions, the symptoms of a pars defect won’t show up until later in life. Overall, yes, a pars fracture is serious but not life-threatening and can be treated.

How long does a pars defect take to heal?

A pars defect takes about six to 12 weeks to heal but it could take up to six months to see a full recovery. However, the rate at which you recover from a pars defect depends on variables such as:

Your current health
How you’ve managed your recovery (ie. working with a physiotherapist, taking enough time off from physical activity)
The severity of your pars defect

As with anything, there’s no one size fits all recovery time. It’s important to speak with your doctor and physiotherapist about how long recovery should take for your particular situation.

How do you sleep with a pars defect?

The best position to sleep with a pars defect is in a reclined position as if you were sitting in a recliner chair.

If you have a recliner, you might even try sleeping in the chair for a few nights to see if it helps relieve the back pain from your pars defect. If not, you might use a stack of pillows to prop yourself up in bed. You might also place a pillow under your knees to further the relief.

There are also adjustable beds where you can change your side to mimic the shape of a recliner whilst still sleeping next to your partner. So, if you find that it relieves your back pain to some extent, you might consider investing in one of these adjustable beds.

Keep in mind that these are only general guidelines and everyone’s body is different, therefore requiring different sleeping positions. Try out a few different options of pillows propping you up or placed underneath your knees to find your ultimate sleep spot.

How common is pars defect?

Pars defect is relatively common, affecting one out of every 20 people. The most common cause is repetitive stress on the lumbar vertebrae.

A pars defect is also more common in children since children tend to be more physically active than adults. However, you might not start experiencing the signs of a pars defect until you’re older, even if it actually occurred in childhood.

References