Posterior lumbar interbody fusion (PLIF) combined with pars repair using a U-shaped rod technique for two-level lumbar spondylolysis: case report and technical note

Introduction

Spondylolysis is a defect of the pars interarticularis that is often associated with lower back pain. Isthmic spondylolisthesis is a condition in which a spinal vertebra slips forward, below it, due to spondylolysis, causing radiculopathy. Past reports have demonstrated that lumbar spondylolysis incidence is 4–7.68%, and multilevel spondylolysis occurs in 0.3–1.8% of cases, an even rarer phenomenon (1-4). Patients often require surgical intervention in cases where conservative therapy fails to achieve satisfactory outcomes. Two broad surgical treatment categories exist: decompression with or without fusion, and direct reduction and repair. Nonetheless, the optimal surgical method for treating multilevel spondylolysis remains controversial. Clinically, it is selected on a case-by-case basis. Here, we report a case treated with a novel surgical strategy that integrated posterior lumbar interbody fusion (PLIF) and direct pars repair using a U-shaped rod. We present this article in accordance with the CARE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-242/rc).

Case presentation

The patient was a 47-year-old male. He experienced pain in the lower back, the right buttock, and the lateral surface of the left lower leg. One year earlier, he underwent a full endoscopic discectomy for L4-5 lumbar disc herniation, which resulted in satisfactory symptom relief. Nevertheless, the symptoms recurred following the subsequent spondylolisthesis development. He had no other medical or family history. At the first visit to our hospital, pain was rated as 8 on a numeric rating scale (NRS) ranging from 0 (“no pain”) to 10 (“extremely painful”). Neurological examination revealed no motor weakness. His preoperative Japanese Orthopedic Association (JOA) score was 15. Radiography revealed mild Grade 2 (Meyerding classification) spondylolisthesis at L4-5 due to L4 spondylolysis with instability; dynamic radiographs demonstrated a slip angle greater than 10° (Figure 1A,1B). Computed tomography (CT) revealed bilateral L4 and L5 pars interarticularis defects (Figure 1C,1D). Magnetic resonance imaging (MRI) identified L4 nerve root compression caused by right L4-5 foraminal stenosis (Figure 1E-1G). His symptoms were attributed to L4-5 pathology, and fusion surgery was considered the most appropriate treatment option. Nonetheless, in L4-5 fusion, potential future complications related to pre-existing L5 spondylolysis are a concern. Therefore, we selected a surgical approach consisting of an L4-5 PLIF, bilateral pedicle fixation, and L5 spondylolysis repair with a U-shaped rod.

Figure 1 Preoperative images. (A,B) X-ray imaging shows L4 and L5 spondylolysis and L4-5 spondylolisthesis with instability. (C,D) CT reveals L4 (C) and L5 (D) spondylolysis. (E-G) MRI demonstrates that the right L4 nerve root is compressed by right L4-5 foraminal stenosis. CT, computed tomography; MRI, magnetic resonance imaging.

A conventional posterior midline approach to the lumbar spine was used. A 6-cm skin incision allowed adequate exposure of the L4 lamina and L5 lamina’s upper half, including the pars interarticularis defect. The supraspinous and interspinous ligaments at L5-S1 were preserved. The L4-5 PLIF was performed according to the standard technique. The L4 lamina, including the abnormally increased synovium in the pars defect, was completely resected, and the L4 nerve was decompressed. After L4-5 intervertebral disc curettage, the cage and autologous bone tips were inserted into the interbody space. Open pedicle screw insertion was performed at both L4 and L5, using the O-arm navigation system. For the L5 pars defect, the granulation tissue was removed, followed by decortication and autologous bone grafting. A rod approximately 200 mm in length was bent into a U-shape. The length was determined to be twice the distance from the L4 screw to the inferior margin of the L5 spinous process, the inter-screw distance between the left and right screws, and an additional margin. In the coronal plane, the 5.5 mm titanium rod was bent into a U-shape to pass beneath the inferior aspect of the L5 spinous process from the L5 screw head. In the sagittal plane, the straight portion corresponding to L4-5 and the U-shaped portion were contoured to create lordosis and match the L5 lamina, respectively. The rod was placed caudal to the L5 spinous process, passing through the L5-S1 interspinous ligament and attaching to the heads of the L4 and L5 pedicle screws bilaterally. To firmly reduce the floating lamina, L5 screws were inserted while a rod pusher pressed the bent rod against the base of the spinous process (Figure 2A,2B). L5 pars repair followed the principles of the smiley face rod technique (5). After tightening the L5 set screws, L4-5 spondylolisthesis was reduced by elevating the L4 screw and achieving lordosis through compression between the L4 and L5 screws (Figure 2C,2D).

Figure 2 Intraoperative lateral fluoroscope images. (A) Before reduction of L5 pars defect (arrow). (B) After reduction of L5 pars defect (arrow). (C) Before reduction and compression between L4-5 (black line, vertebral posterior wall line; blue line, vertebral endplate line; arrow, inter-screw heads distance). (D) After reduction and compression between L4-5 (black line, vertebral posterior wall line; black dotted line, vertebral endplate line; arrow, inter-screw heads distance).

No perioperative or postoperative complications were observed. Postoperative imaging confirmed satisfactory correction of the L4-5 slip and L5 defect and decompression of the L4-5 foramen (Figure 3). The patient improved symptomatically and was discharged after approximately one week. At 6 months postoperatively, imaging still demonstrated no bony union at the L5 defect; however, stabilization had been achieved and L5-S1 mobility was preserved. Clinically, the patient maintained marked improvement in daily activities and favorable outcomes, with a JOA score of 28 (improvement rate, 92.8%) and an NRS score of 0 (improvement rate, 100%).

Figure 3 Postoperative images. (A) Anteroposterior radiographic. (B) Neutral lateral radiographic. (C) Flection lateral radiographic. (D) Extension lateral radiographic. (E,F) Parasagittal CT view demonstrating decompression of the L4-5 foramen and correction of the L5 pars defect (E, right side; F, left side). (G) Six-month postoperative CT revealing the bony union at the L5 defect. (H) Parasagittal view, (I) coronal view, and (J) axial view of MRI exhibiting right L4 nerve root decompression. CT, computed tomography; MRI, magnetic resonance imaging.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

We reported a rare L4-5 spondylolytic spondylolisthesis case, presenting with L5 spondylolysis neurological symptoms, treated with L4-5 PLIF combined with pars repair using the U-shaped rod technique. Generally, single-level spondylolysis treatment can be divided into two categories; pars repair and fusion surgery (6,7). For multilevel lumbar spondylolysis, previous reports have described some surgical strategies, including multilevel fusion and multilevel pars repair techniques such as the smiley-face rod (SFR) method (8-10). Multilevel spondylolysis often exhibits complex pathomechanics, making treatment selection challenging. This novel technique is sufficient and appropriate for achieving therapeutic goals in such cases.

This combined strategy of L4-5 PLIF and L5 pars repair offers a major advantage over two-level PLIF by achieving secure stabilization of the symptomatic level while preserving L5-S1 mobility. Avoiding fusion at an asymptomatic adjacent segment helps maintain physiological motion and reduces the risk of future adjacent segment disease (11,12)—an especially important consideration when spondylolysis already exists at the neighboring level. A similar concept was reported by Tatsumura et al., who combined TLIF with the SFR technique (13); however, their method required dual-headed screws to apply separate compression forces. In contrast, our technique accomplishes the same goals—pars compression and slip reduction—using only standard pedicle screws and a conventional rod. This eliminates the need for specialized implants, simplifies the procedure, and enhances practical applicability. Accordingly, this method represents a minimally invasive, efficient and reliable option for managing multilevel spondylolysis.

Attention is warranted to the complications associated with conventional fusion procedures and pars repair techniques, especially the potential for rod breakage, which may represent a limitation. Previous studies have suggested that the risk of fixation fracture associated with the SFR technique is lower than that observed with interbody fusion procedures; however, implant-related complications remain a potential concern even with the SFR method (14). Compared with the standard smiley-face configuration, our technique requires the rod to pass through pedicle screw heads across two levels, necessitating approximately 180° of bending. These factors may impose greater mechanical stress compared to traditional SFR constructs. Therefore, bending the rod gradually over a broad area, rather than producing a sharp angulation at a single point, is necessary. Additionally, titanium rods are advantageous. Titanium has a lower elastic modulus and greater flexibility than cobalt–chromium alloys, reducing stress concentration and allowing safer contouring. Therefore, we think that meticulous rod contouring and appropriate material selection may reduce mechanical complications.

The only disappointing aspect of the postoperative course in this case was the absence of radiographic evidence of bony union at the L5 pars defect at 6 months. Preoperative CT revealed sclerosis of the defect and marked atrophy, particularly on the right side. Previous studies indicate that this morphological subtype is less likely to achieve bony union, suggesting an inherently unfavorable biological environment for healing in this patient (15). Although the SFR technique provides symptomatic improvement regardless of bony union and bone healing is not an absolute requirement for clinical success with this method, careful long-term follow-up is essential. Persistent nonunions may predispose patients to future spondylolisthesis or segmental instability, and vigilance is required to detect such changes at an early stage. Based on these considerations, the indications for pars repair in this technique should be regarded as comparable to those of the SFR method, namely cases without spondylolisthesis or disc degeneration, or with only mild involvement. Because the fusion rate associated with this approach has not yet been established, further investigation is warranted. Accordingly, careful case-by-case decision-making that takes into account the morphological characteristics of the pars defect is essential when applying this technique.

Conclusions

We report a novel technique for treating L4 isthmic spondylolisthesis and L5 spondylolysis. L4-5 PLIF combined with L5 pars repair using a U-shaped rod provided stable fixation for L4-5 slip and L5 defects while preserving L5-S1 mobility. In such cases, the U-shaped rod method is the most appropriate treatment option as it is readily available, simple, and effective.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-242/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-242/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-242/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Ganju A. Isthmic spondylolisthesis. Neurosurg Focus 2002;13:E1. [Crossref] [PubMed]
2. Standaert CJ, Herring SA. Spondylolysis: a critical review. Br J Sports Med 2000;34:415-22. [Crossref] [PubMed]
3. Sakai T, Sairyo K, Takao S, et al. Incidence of lumbar spondylolysis in the general population in Japan based on multidetector computed tomography scans from two thousand subjects. Spine (Phila Pa 1976) 2009;34:2346-50. [Crossref] [PubMed]
4. Sharma B, Panta OB, Thapa BR, et al. Spondylolysis among patients without low back pain in a diagnostic center: a descriptive cross-sectional study. JNMA J Nepal Med Assoc 2023;61:123-6. [Crossref] [PubMed]
5. Tatsumura M, Okuwaki S, Gamada H, et al. A Novel Technique for Pars Defect Direct Repair with a Modified Smiley Face Rod for Spondylolysis and Isthmic Spondylolisthesis. Spine Surg Relat Res 2023;7:396-401. [Crossref] [PubMed]
6. Linton AA, Hsu WK. A Review of Treatment for Acute and Chronic Pars Fractures in the Lumbar Spine. Curr Rev Musculoskelet Med 2022;15:259-71. [Crossref] [PubMed]
7. Beutler WJ, Fredrickson BE, Murtland A, et al. The natural history of spondylolysis and spondylolisthesis: 45-year follow-up evaluation. Spine (Phila Pa 1976) 2003;28:1027-35; discussion 1035. [Crossref] [PubMed]
8. Liu X, Wang L, Yuan S, et al. Multiple-level lumbar spondylolysis and spondylolisthesis. J Neurosurg Spine 2015;22:283-7. [Crossref] [PubMed]
9. Park KH, Ha JW, Kim HS, et al. Multiple levels of lumbar spondylolysis—a case report. Asian Spine J 2009;3:35-8. [Crossref] [PubMed]
10. Takeuchi M, Tezuka F, Chikawa T, et al. Consecutive double-level lumbar spondylolysis successfully treated with the double “smiley face” rod method. J Med Invest 2020;67:202-6. [Crossref] [PubMed]
11. Cheh G, Bridwell KH, Lenke LG, et al. Adjacent segment disease followinglumbar/thoracolumbar fusion with pedicle screw instrumentation: a minimum 5-year follow-up. Spine (Phila Pa 1976) 2007;32:2253-7. [Crossref] [PubMed]
12. Ji J, Tang W, Sun H, et al. Preventing adjacent segment disease after lumbar fusion: a new perspective emphasizing individualized factors. Quant Imaging Med Surg 2026;16:17. [Crossref] [PubMed]
13. Tatsumura M, Ikezawa S, Okuwaki S, et al. Combined Transforaminal Lumbar Interbody Fusion and Smiley Face Rod Technique Using Dual-Headed Pedicle Screws for L4 Isthmic Spondylolisthesis and L5 Spondylolysis. Cureus 2024;16:e60756. [Crossref] [PubMed]
14. Dong QY, Yang XF, Wu HL, et al. Comparison of the smiley face rod method versus intervertebral fusion for the treatment of L5 spondylolysis in adults. Front Med (Lausanne) 2024;11:1499773. [Crossref] [PubMed]
15. Okuwaki S, Tatsumura M, Gamada H, et al. Association of Pars Defect Type with Clinical Outcome after Smiley Face Rod Methods for Terminal-Stage Spondylolysis. Spine Surg Relat Res 2024;8:58-65. [Crossref] [PubMed]