Surgical Techniques: Spondylolysis Repair



Fig. 11.1
Pedicle screw, rod, and laminar hook construct. (a) The lateral view of the construct. The appearance of the construct at the posterior view (b) and inferior view (c) of the vertebra



The reported incidence in the general population varies depending on the age group. Lumbar spondylolysis in newborn is rarely described [5]. It is reported in 4.4 % of preschool children. This increases to 6 % in adulthood [4]. A higher incidence of up to 15 % is noted among young athletes. Males are twice as commonly affected compared to females. This ratio becomes 1:1 in the symptomatic populations suggesting a higher proportion of females may become symptomatic. The underlying reason, however, is not well understood; it may reflect the more active participation in sports among young women. It represents the most common organic cause of low back pain in children, adolescents, and young adults. The rate of spontaneous healing with bone is thought to be extremely low, but fibrous unions can result in long-term pain relief without instability.

The pars interarticularis is normally an area under great stress posteriorly in a normal vertebra given its small area and frequent impaction with the inferior articular process at the level above in a lordotic lumbar spine in an erect position [6]. Acute trauma or chronic repetitive microtrauma, particularly hyperextension, is believed to place pathological shear stresses at the pars and results in lumbar spondylolysis [7, 8]. This probably explains the absence of such pathology in non-ambulatory adults and the higher incidence noted in young athletes involved in sports with repetitive hyperextension activities like gymnastics, diving, football, and now more commonly, soccer.

Many children and adolescents with spondylolysis are asymptomatic. The most common presentation is activity-related back pain, particularly in extension. The postulated causes of pain in spondylolysis include rich nociceptive nerve endings within the defect, hypermobility of the loose posterior arch with stimulation of the nerve endings within the defect, relative instability of the vertebral body, and excessive stress on the underlying disc. It is thus important to ascertain the primary pain generators prior to surgical intervention.



Diagnostic Imaging


Patients with suspected lumbar spondylolysis are investigated with an erect posterior–anterior (PA) and lateral radiographs of the lumbosacral spine. Some patients may have spinal bifida occulta associated with the pars defects. This has implications during the surgical approach. Oblique radiographs have increased X-rays exposure and have not been shown to add additional information [9]. The authors have virtually abandoned oblique X-rays and bone scans in favor of advanced imaging that is more diagnostic. Thin cut computed tomography (CT) with reverse gantry alignment to lumbar lordosis is recommended in cases that spondylolysis is suspected but not well demonstrated in radiographs to confirm the diagnosis [10]. Pre-operative CT scan is indicated to evaluate the size of the pars defect and degree of bony sclerosis (i.e., atrophic or hypertrophic non-union). Magnetic resonance imaging (MRI) is indicated for patients with an atypical presentation or with neurological symptoms. It may show a pre-lysis stage in patients with normal CT scan, by showing signal intensity in the pars or pedicle. It can also prognosticate the healing ability of a defect after a trial of conservative treatment. High signal intensity around the pedicle reveals remaining potential for bony union to occur [11]. MRI is performed pre-operatively to assess discal health at the spondylolytic segment.


Indications for Pars Repair


Careful patient-selection yields a better outcome: a few factors influence the decision to repair the pars (Table 11.1).


Table 11.1
Factors affecting patient selection in pars repair

















•  Duration of symptoms/adequacy of non-operative treatment

•  Concordance of pars injection with temporary symptom resolution

•  Age

•  Segmental instability

•  Lumbar disc health

•  Unilateral or bilateral involvement


Unremitting Pain/Increasing Pain Attributed to the Pars Defect


Non-operative treatment without adversely affecting quality of life is the mainstay of the management. More than 80 % of children and adolescents respond to this with near resolution of symptoms, or occasional recurrence of pain. Return to sports after rest and rehabilitation with core strengthening and flexibility exercises can be expected.

Generally, if recurrent pain with sports precludes their return, or patients have failed 6 months or more of non-operative treatment, then surgical repair can be an option. The non-responders who are considered for surgery should undergo a diagnostic injection with pars infiltration. This is done by injection of small volume of local anesthetic (e.g., bupivacaine) and a corticosteroid into the spondylolytic pars interarticularis under CT guidance. A concordant result in the pars injection should be at least 70 % improvement in pain and is a prognostic feature of good functional outcome postoperatively [1214].


Age


The correlation between age and clinical outcome is conflicting. Most authors state that patients in the age range of 20–30 years have worse clinical results than younger patients [8, 1517]. A more recent study did not find an association between patient’s age and post-operative VAS score [13]. The compounding factors in these studies include:

1.

Higher prevalence of disc degeneration in the population with spondylolysis at an age of more than 25 years compared to the normal control population [18]

 

2.

Functional outcome does not correlate with bony union [8]

 

Ideal patients for pars repair are younger than 20 years old. One should proceed with caution in an older patient.


Segmental Instability and Degenerative Disc


Better outcome is observed with fusion when compared to direct pars repair in patients with spondylolisthesis [19]. Up to grade 1 (<25 % slippage) spondylolisthesis is amenable for pars repair. Fixation can be used to compress the defect and reduce the slip, but results are variable.

Disc degeneration at the level below the spondylolytic segment may result in an independent pain generator and is a contraindication to pars repair. The disc degeneration does not correlate with the grade of vertebral slip [20]. The degeneration is demonstrated by structural changes, signal change, and height loss of the discs as classified by the Pfirrmann classification on MRI [21] (see Table 11.2). Pfirrmann grade 1 or 2 is an ideal indication; grade 3 or above is contraindicated for pars repair, and may benefit from fusion.


Table 11.2
Classification of disc degeneration (Pfirrmann)














































Grade

Structure

Distinction of nucleus and annulus

Signal intensity

Height of intervertebral disc

I

Homogeneous, bright white

Clear

Hyperintense, isointense to cerebrospinal fluid

Normal

II

Inhomogeneous with or without horizontal bands

Clear

Hyperintense, isointense to cerebrospinal fluid

Normal

III

Inhomogeneous, gray

Unclear

Intermediate

Normal to slightly decreased

IV

Inhomogeneous, gray to black

Lost

Intermediate to hypointense

Normal to moderately decreased

V

Inhomogeneous, black

Lost

Hypointense

Collapsed disc space


Unilateral vs. Bilateral Pars Defects


An acute unilateral pars defect has a good prognosis and may heal spontaneously. Longer conservative treatment is recommended prior to surgical intervention.


Surgical Treatment



The Evolution


The surgical strategy has evolved over time. Earlier surgical procedures involved arthrodesis of the motion segment by posterolateral or interbody fusion techniques. These procedures sacrificed the mobility of the involved motion segment and placed excessive mechanical stress at the adjacent levels, both of which are undesirable and potentially harmful in younger patients.

In 1968, Kimura described a direct repair of the isthmic defect of the pars interarticularis without instrumentation, as an alternative to segmental fusion [22]. This technique had the advantage of preserving segmental motion. Scott began using a wiring technique as a tension band with bone graft to augment the lytic defect in 1968. Many authors used the Scott wiring method, whereas others have modified the technique to include pedicle screws or cable instead of wire [23, 24].

In 1970, Buck [25] documented the use of a lag screw across the lytic defect, and many other authors have described their outcomes following this technique. In 1984, Morscher et al. [26] reported that the Buck technique of using a 3.5-mm lag screw did not work well with a thin or dysplastic lamina, and advocated using laminar fixation with a hook screw device specially made for this purpose. The major problem of this technique was screw placement and facet joint violation. A screw placement analysis showed that in 15 % of cases, there was screw penetration into the inferior articular process of the superior vertebra. Other authors have reported using pedicle screws to secure the lamina with either a rod-hook construct [27] or a U- or V-shaped rod under the spinous process [7, 28].

Other common contemporary techniques of pars repair are direct repair using a laminar/pars compression screw through the fractured pars (modified Buck’s technique) and compression of the fracture fragments using a pedicle screw, rod, and laminar hook construct within the same segment. They are shown to have the least amount of motion across the defect during flexion, extension, and rotation compared to the Scott wiring technique [29]. Adjacent segment mobility is not increased compared to untreated spondylolysis or pedicle screw-rod motion segment fixation in segmental arthrodesis [30]. These two constructs represent the most ideal anatomical constructs biomechanically and a relatively straightforward once the surgeon addresses the pseudarthrosis at the pars.


Surgical Technique



Positioning


Patient is placed prone on a radiolucent operating table with four posts (e.g., flat Jackson table or AMSCO table). All the pressure areas are adequately padded including the chest, anterior superior iliac spine and patella. The abdomen is hung free which otherwise would impede venous return and increase bleeding at the surgical site. Prophylactic antibiotics are administered according to the local guidelines.


Direct Laminar/Pars Compression Screw Fixation


Intra-operative fluoroscopy is used for localization prior to skin incision (Figs. 11.2, 11.3 and Table 11.3). A paraspinal approach, similar to Wiltse is employed for fascial incision. The longissimus–multifidus muscle interval is bluntly dissected with a finger in order to preserve the vascularity and prevent unnecessary tissue damage. A minimally invasive expandable retractor is used, and through this retractor, the pars interarticularis is subperiosteally dissected, leaving the adjacent facet capsules intact. The defect is located, and the fibrous tissue in the defect is removed with pituitary rongeurs. The sclerotic surfaces are prepared with a high-speed burr until bleeding bone surface is seen, but care is taken not to resect too much bone—this results in enlarging the defect. Gross motion is noted through the pars fracture. Great care is taken not to disrupt the joint capsule bilaterally. The entry point of the screw is made by creating a notch in the caudal margin of the lamina 10 mm lateral to the base of the spinous process. Then, using the Discovery or F2 cannulated screw system for facet fusion (DePuy Synthes Spine, Raynham, MA, USA), two guidewires are placed to provide adequate fixation across the pars defects from an ipsilateral infralaminar approach into the junction of the pars and transverse processes and pedicle cortex. The guidewire placement is confirmed via fluoroscopy in multiple planes. Alternatively, the guidewire placement could be aided by CT navigation (Fig. 11.4). The guidewire is then over drilled, and a cannulated screw is placed over the guidewire, providing compression and fixation across the defect. A 3.2-mm drill bit is used to drill the path of the screw with the trajectory angled 30° lateral to the sagittal plane, toward the ipsilateral pedicle, crossing the lytic defect. An appropriately sized, 4.5-mm titanium cortical screw is inserted along the path across the defect, but not tightened completely. Then cancellous bone graft obtained from the posterior iliac crest is packed in the lytic defect, and the screw is tightened completely to obtain a good purchase in the solid bone of the ipsilateral pedicle and compression across the defect. Radiographic AP and lateral views of the lumbar spine are taken (Fig. 11.5).
May 22, 2017 | Posted by in ORTHOPEDIC | Comments Off on Surgical Techniques: Spondylolysis Repair

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