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 [12–14].

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, 15–17]. 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:

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

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.

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

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.

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.

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).