Triple Procedure for Direct Pars Repair: An Innovative, Non-fusion Approach for Managing Spondylolysis in Late Adolescence or Early Adulthood

Introduction

Spondylolysis is a developmental defect or an acquired abnormality of the pars interarticularis, often attributed to repetitive microtrauma sustained by a neural arch ^[1,2]. The purported incidence of spondylolysis is approximately 6%, and 85–95% of these defects develop at the L5 level ^[2,3,4]. The bipedal ambulation in an erect posture predisposes the lordotic lumbar spine of the human beings to high degrees of static and dynamic stresses during routine physiological activities ^[5]. These abnormal forces have been implicated as the inciting events in unilateral (U/L) or bilateral (B/L) spondylolysis ^{[6, 7]}.

A majority of the acute pars interarticularis fractures are successfully managed in a conservative manner ^[8,9]. Symptomatic pediatric patients and young adults (especially with an athletic background) with chronic stress fractures or pars defects can benefit from non-fusion surgeries such as direct pars repair ^[10,11,12]. Although diverse techniques for pars repair have been described with varying success rates, there is considerable ambiguity in the relative efficacy of each technique, particularly in the relatively older cohort of patients in their late adolescence or early adulthood ^[13,14,15]. With the advent of modern imaging modalities, such procedures are increasingly performed through minimally invasive approaches ^{[16,17,18,19,20]}. The current case report discusses an uncommon presentation of a 19-year-old boy, who was treated with a novel “triple procedure” approach involving a combination of bilateral intralaminar screws, autogenous iliac crest bone graft and temporary intersegmental pedicle screw fixation. The case is reported for the relative rarity of the presentation; and the innovative approach employed in the management of this condition.

Case Report

A 19-year-old (tall and relatively well-built) boy presented with chronic mechanical low back pain over the past 2 years. The pain was progressively worsening in the last 6 months and was typically aggravated on hyperextension postures and heavy lifting activities (VAS: varying between 3/10 and 9/10). There was no radicular symptom or sensory involvement.

He underwent an initial, short course of conservative management; following which he was advised plain radiographs of his lumbar spine. His X-rays (Fig. 1a, Fig. 1b, c) revealed a defect in the pars interarticularis of the L5 vertebra with hypoplasia of the neural arch. There was minimal instability on dynamic radiographs. Further, he was advised a computed tomography (CT) and magnetic resonance imaging (MRI) scan of his lumbar spine (Fig. 1d, Fig. 1e, f, h). While the CT scan revealed bilateral L5 pars deficiencies and posterior neural arch hypoplasia; MRI revealed L5-S1 Pfirmann Grade 1 disk space degeneration. In addition, there was no hyperintense signal in the peri-pedicular region, suggesting that the lesion was a chronic pars defect.

Based on his clinico-radiological presentation, the possible treatment options were discussed. He was advised a course of conservative treatment including diverse interventions, namely anti-inflammatory medications, physiotherapeutic regimens, exercises (back and core strengthening exercises), and lifestyle modifications. Nevertheless, despite these conservative measures, his symptoms persisted. He was offered the option of diagnostic pars block. However, he did not consent to undergo the block and wished to go ahead with a definitive procedure.

The possible treatment options and their prognostic implications were discussed. Based on a detailed discussion with the patient and the family members, the plan to go ahead with direct pars repair (in the form of non-fusion surgery) was made. Considering his presentation at a relatively older age and larger physical build, the possibility of treatment failure, including non-union/ pseudoarthrosis, implant failure, iatrogenic neural arch fractures, progressive disk degeneration, and persistent instability, was discussed. In view of the poorer outlook in our patient, the “novel” triple approach involving a combined treatment strategy of intralaminar screw fixation (Buck technique), autologous iliac crest bone graft application and intersegmental pedicle screw stabilization was planned.

Discussion

Symptomatic patients with spondylolysis usually recover well with non-operative treatment ^[2]. Surgical management may benefit in situations of persistent symptomatology, despite a reasonable course of conservative measures ^[11]. In addition, early surgery may be considered in professional athletes, who may prefer timely return to heavy sporting activities. The goals of surgery include pain mitigation, promotion of healing of the pars deficiency, stabilization of the involved segment, and impeding the listhesis progression ^[9]. Broadly, the surgical treatment can be classified as fusion and non-fusion surgeries ^[9]. The latter procedures typically involve a wide array of intrasegmental fixation modalities, aimed at achieving repair of the pars deficiency ^{[1, 3, 5,12, 16, 17, 19]}.

Since inadvertent sacrifice of an intervertebral (IV) disk and motion segment are best avoided in pediatric patients and young adults without significant IV instability, pars repair techniques offer substantial benefit over fusion surgeries in this patient cohort ^[2]. The technique of pars repair has been likened to osteosynthesis, and its philosophy broadly includes debridement of the pars defect, bone grafting, and intrasegmental stabilization ^[15]. Diverse intrasegmental fixation methods include intralaminar screw fixation (Buck technique), pedicle screw-hook construct, intrasegmental wiring, pedicle screw-U-rod, and butterfly plate-screw technique ^{[2, 6, 8, 10, 11, 13, 14, 15, 20]}.

The intralaminar screw technique (Table 1) has been reported to provide successful pars healing in 82–100% of patients ^{[2, 8]}. In a recent meta-analysis by Tsai et al. ^[8] comparing Buck repair, Scott wiring, Morscher technique and pedicle screw repair, Buck repair was shown to result in excellent outcome with high union rate (effect size [ES]: 93%; 95% CI: 86–98%), positive functional outcome (ES: 85%; 95% CI: 86–97%); and lowest complication rates. The purported advantages of Buck repair include the use of a stable low-profile implant, ability to employ minimally invasive approaches, and excellent healing rates. Recently, studies have also utilized robotic- or navigation-guided approaches to enable mini-open or minimally invasive approaches in challengingly narrow or hypoplastic laminae ^{[9, 15]}. Some of the situations where Buck repair has been associated with poorer outcome include the presence of narrow lamina, association with spina bifida occulta (SBO), terminal or more-advanced stage of pars defect, wider or larger gap of the defect, and more advanced disk degeneration. Studies have shown that patients developing non-union after pars repair have substantially poorer clinical outcomes in comparison with those who were conservatively managed ^{[2, 9, 15]}.

Our patient was relatively old, as compared to the typical patient cohort for whom pars repair is recommended. In addition, he had SBO with hypoplastic neural arch, which can potentially compromise the purchase of the intralaminar screw. As evident from our imaging studies, he also had minimal instability at the L5-S1 level with some disk degeneration. As previously discussed, our patient also had a tall and well-built habitus. In view of these aforementioned reasons, we planned to additionally supplement our intralaminar screw fixation (along with bone grafting) with additional intersegmental stabilization using a unilateral pedicle screw-rod construct (Unilateral fixation through Wiltse approach was planned in order to minimize the soft-tissue dissection). Although we recommended the removal of the temporary pedicle screw-rod construct at the end of one year, due to personal reasons, the patient underwent the procedure at 2 years postoperatively.

Zhang et al.^[9] discussed the relative strengths of intra- and inter-segmental fixation techniques in the context of direct pars repair. They observed that L5 pars interarticularis is consistently stressed during extension and rotational moments, as a result of wedging between the inferior articular process of L4 and superior articular process of L5 vertebrae. They concluded that temporary intersegmental L5-S1 fixation could be an excellent technique in achieving stability and healing across pars defects at the L5 level, especially in specific scenarios such as SBO, disk degeneration, larger gap across the defect, Grade 1 spondylolisthesis, and higher segmental sagittal angular movements. Although Zhang et al. ^[9] recommended that the pars repair must always be preceded by a pars block (to confirm the causative association between the symptoms and pars defect), our patient opted to not undergo such blocks. Based on their experience with 5 patients (mean age of 19.2 ± 5.4 years), Ye et al. ^[15] described a successful outcome following pars repair using a combination of Buck repair, bone grafting, and bilateral temporary screw fixation. They argued in favor of supplementing the Buck repair with additional B/L temporary pedicle screw insertion, owing to their observation that intralaminar screw fixation alone fails to address abnormal stress concentrations at the L5 pars interarticularis (especially in the presence of sagittal imbalance or relative kyphotic alignment at the lumbo-sacral [L5-S1] junction). They suggested that temporary L5-S1 intersegmental fixation can thereby mitigate the incidence of complications like screw loosening, inadequate defect healing, and fracture, which have been reported after Buck repair.

In our patient, we performed a similar triple procedure; although we performed only a unilateral temporary intersegmental stabilization (so as to reduce the extent of soft-tissue dissection). Our patient had a satisfactory clinical outcome following this approach.

Conclusion

Triple procedure involving a combination of bilateral intralaminar screws, autogenous iliac crest bone graft and temporary intersegmental pedicle screw fixation can offer excellent clinical and radiological outcome in challenging situations of spondylolysis with minimal instability and early disk degeneration.

Clinical Message

• Direct pars repair remains a valuable non-fusion option for young patients with persistent spondylolysis symptoms despite conservative care.

• Buck intralaminar screw fixation achieves high union rates but may be compromised in hypoplastic lamina or spina bifida occulta.

• Supplementing pars repair with autologous bone graft enhances healing and reduces risk of non-union or pseudoarthrosis.

• Temporary intersegmental pedicle screw fixation can provide added stability in challenging cases with disk degeneration or minimal instability.

• A combined “triple procedure” approach – bilateral intralaminar screws, bone graft, and temporary fixation – can yield excellent clinical and radiological outcomes in complex spondylolysis.

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About the Authors

• 

  Vibhu Krishnan Viswanathan

• 

  Malmarugan Ramachandran

• 

  Sathish Muthu

• 

  S Gopalakannan

• 

  Annamalai Devadoss

• 

  Sathish Devadoss