Surgical treatment of double-level spondylolysis of the L4 and L5 vertebrae using custom-made implant

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INTRODUCTION

Spondylolysis is a defect of the pars interarticularis of the vertebral arch and a common cause of low back pain in adolescents and young adults [1, 2]. Bilateral spondylolysis is of particular clinical relevance. Its prevalence in the general population ranges from 6% to 8% [2–6].

Spondylolysis most frequently occurs at the L5 level and less commonly at L4. Based on the published data, multilevel spondylolysis is considered rare. Reports describing this condition in the scientific sources are limited to isolated case studies [7, 8]. In 1980, Ravichandran reported that multilevel spondylolysis was found in 1.48% of patients with low back pain [9]. In a 2011 review, Hersh confirmed this observation, referencing earlier data [10]. Peng et al. (2015), citing previous studies, reported the prevalence of multilevel spondylolysis to be between 1.2% and 5.6% of all cases of spondylolysis [2]. According to Skryabin, two-level spondylolysis accounts for approximately 1% of cases [8]. The low prevalence and associated diagnostic challenges contribute to the lack of a standardized treatment approach.

The use of additive manufacturing technologies for the production of patient-specific implants is an emerging field in spinal surgery [11]. Compared with off-the-shelf implants, custom-designed devices offer several advantages that support their successful use in the surgical management of spondylolysis as well [12]. This article presents a case report of successful surgical treatment of two-level spondylolysis in an adolescent using customized implants, along with a review of the relevant published data.

CASE DESCRIPTION

Patient P., aged 16 years, was admitted to the N.N. Priorov National Medical Research Center of Traumatology and Orthopedics (Russia) in 2024 with complaints of severe low back pain during exercise, running, and playing soccer. The patient had been playing amateur soccer. Three months prior to admission, he experienced acute lumbar pain during a match, which forced him to stop playing. Outpatient evaluation, including lumbar spine X-ray and computed tomography (CT), revealed bilateral two-level spondylolysis at L4 and L5. Conservative management was initiated, including cessation of sports, restriction of spine axial load, use of a lumbosacral orthopedic brace, physiotherapy, massage, and therapeutic exercise. Pain symptoms significantly regressed with conservative treatment and reduced physical activity. However, two months later, upon resuming active sports, including running and jumping, the patient experienced recurrent lumbar pain.

With these complaints, the patient presented to the consultation and diagnostic department of the same healthcare facility. Clinical examination revealed moderate paraspinal muscle tension and increased lumbar pain during trunk flexion and extension. Palpation indicated localized tenderness in the lumbosacral region along the paraspinal muscles. Neurological examination showed no focal deficits; tension signs were negative, and there was no evidence of paresis, pathological reflexes, sensory disturbances, or pelvic organ dysfunction. The Pediatric Quality of Life Inventory (PedsQL) score was 88.9; the visual analog scale (VAS) score was 6.

Postural spinal X-ray confirmed the diagnosis of bilateral two-level spondylolysis. A left-sided lumbar scoliotic curve with an apex at L1–L2 was observed (Cobb angle: 15°). Sagittal alignment parameters were within normal limits (PI = 50°, PT = 9°, SS = 39°, LL = 60°, TK = 43.6°) (Fig. 1a, b). Dynamic lateral X-rays in flexion and extension revealed no significant changes at the L4 lamina defect, while the L5 defect appeared to widen in flexion (Fig. 1c, d).

 

Fig. 1. Postural and functional X-ray of the lumbar spine: (a) lateral view; (b) anteroposterior view; (c) flexion; (d) extension. Arrows indicate areas of spondylolysis.

 

Multislice CT confirmed bilateral pars defects at L4 and L5. According to the Fujii classification [13], both lesions corresponded to the terminal stage (Fig. 2). Additionally, dysplastic changes in the posterior elements of L5 were noted, including lamina asymmetry and altered morphology of the spinous process. MRI showed no signs of spinal stenosis, and intervertebral disc hydrophilic properties were preserved (Pfirrmann grade 1) (Fig. 3).

 

Fig. 2. Lumbar spine CT scans: (a) sagittal slice, right side; (b) sagittal slice, left side; (c) axial view at L4 lamina; (d) axial view at L5 lamina.

 

Fig. 3. Lumbar spine MRI, sagittal view.

 

Based on clinical and imaging findings, a diagnosis of bilateral two-level spondylolysis at L4 and L5 was established.

Given persistent pain limiting physical and sports activity, failure of conservative therapy, and imaging data, surgical intervention was recommended. A decision was made to perform indirect reconstruction of the L4 and L5 pars interarticularis using patient-specific implants.

A 3D CT-based spinal reconstruction from L4 to S1 was created in collaboration with engineers from Conmet LLC. A full-scale stereolithographic model of the L4–L5–S1 segment was produced. Based on the model, custom implants were designed to restore the integrity of the L4 and L5 arches (Fig. 4). The devices comprised contoured plates matching the dorsal surface of the laminae and undersurface of the L4 and L5 spinous processes, each featuring two hook-like projections for sublaminar fixation. Lateral extensions transitioned into 5.5-mm rods for pedicle screw fixation. The design ensured no impingement between the constructs at L4 and L5 during motion. Standard pedicle screws were used with customized selection of length and diameter based on CT data. The construct was manufactured from Ti-6Al-4V ELI alloy by Conmet LLC using additive manufacturing technology (Fig. 5).

 

Fig. 4. Design model of the patient-specific implant.

 

Fig. 5. Full-scale 3D model of the lumbosacral segment and the custom metal implant.

 

Surgical procedure: Under endotracheal anesthesia with the patient in prone position, a midline incision in the skin and subcutaneous fat was made from L4 to S1. Subperiosteal exposure of L4 and L5 laminae was performed, preserving the supraspinous ligament. Hemostasis was achieved. Under fluoroscopic guidance, pedicle screws were inserted bilaterally at L4 and L5 pedicles, sparing the transverse processes. The interspinous ligaments at L4–L5 and L5–S1 were excised using Kerrison rongeurs. Using a curved raspatory, the laminae were exposed at the planned sublaminar fixation sites. The custom L4 plate was inserted between the L4 and L5 spinous processes and secured to the L4 lamina. Similarly, the L5 plate was positioned between L5 and S1 spinous processes and fixed to the L5 lamina. Locking nuts secured the implant rods to the screw heads. Intraoperative fluoroscopy confirmed correct implant positioning (Fig. 6). The wound was irrigated with antiseptic solution and closed in layers, with a cosmetic intracutaneous suture. Blood loss was 100 mL. The patient was mobilized on postoperative day 1. He reported moderate pain at the surgical site, which resolved within three days on NSAIDs. Postoperative CT and X-ray confirmed appropriate implant position and defect fixation (Fig. 7). The patient was discharged on postoperative day 4, with wound healing by primary intention.

 

Fig. 6. Intraoperative fluoroscopic control.

 

Fig. 7. (a, b) Postural X-ray images of the lumbar spine showing correct implant positioning, stable fixation at the sites of spondylolysis, and preserved sagittal alignment; (c) Lumbar spine CT, 3D reconstruction; (d) axial view at L4; (e) axial view at L5.

 

At 3-month follow-up, the patient had resumed full physical activity without lumbar pain (PedsQL score: 96; VAS: 0). Dynamic X-ray images showed correct implant placement, stable fixation, and preserved mobility of the treated motion segments (Fig. 8).

 

Fig. 8. Functional X-rays of the lumbar spine: (a) extension; (b) flexion.

 

DISCUSSION

Two-level spondylolysis is an exceedingly rare pathology of the lumbar spine [2, 7, 8]. Its etiology is similar to that of single-level lesions. Some studies suggest a genetic predisposition to the development of multilevel spondylolysis. For instance, Yurube et al. (2017) reported L4 and L5 spondylolysis in three biological brothers, while their father had L4 spondylolysis and L5 spondylolisthesis [14]. The high incidence of vertebral developmental anomalies, such as spina bifida and other dysplastic changes, among patients with this condition further supports the role of hereditary factors [5, 15].

Athletic activity is a major contributing factor in both single- and multilevel spondylolysis [8, 16]. Most reports concern young athletes, with defects in the pars interarticularis believed to result from repetitive stress to the lumbosacral spine. These mechanical loads may cause stress fractures of pars interarticularis, eventually leading to spondylolysis [1, 17–20].

Although there are reports of successful conservative management, including in athletes [21], the requirement to restrict physical activity during and after treatment remains a key limitation. When conservative treatment fails, surgery becomes a reasonable alternative. The surgical approach should aim to stabilize the defect while preserving motion at the affected segment, potentially allowing patients to return to their prior level of physical activity—an especially important goal for athletes.

Due to the rarity of two-level spondylolysis, no standardized surgical protocol exists. However, most authors agree that surgical principles align with those for single-level lesions. The primary goal is to restore the integrity of the lamina and maintain motion in the functional spinal unit whenever possible [2, 22–24].

Several techniques have been described for pars repair, including direct fixation using wires, screws, or laminar hooks placed across the defect [25–27].

One of the first Russian studies on direct pars repair using bone grafting was published by Nadulich et al. (2011) [28]. Based on our experience, outcomes with or without bone grafting do not differ significantly. Currently, indirect repair using pedicle screws combined with laminar hooks is the most common technique [29]. This method has also been successfully applied in multilevel cases. For example, Peng et al. (2015) reported on three patients: two had bilateral spondylolysis at L3–L5, and one had left-sided defects at L3–L5 and right-sided defects at L4–L5. Li et al. (2021) also described a four-level spondylolysis case treated with a similar metal construct [2, 24, 30, 31]. Khominets et al. (2020) reported two young military servicemen (aged 18 and 19) with two-level spondylolysis (L2, L4 and L4, L5) successfully treated with a screw–rod–hook system and autologous bone grafts for pars defects. Both experienced resolution of pain within a month post-surgery and complete defect healing within 8–12 months [7].

Another reported technique is “smiley face rod,” which involves pedicle screws connected by a U-shaped rod passed beneath the spinous process [32]. Yamashita et al. (2017) detailed this approach in a 13-year-old baseball player with bilateral L5 spondylolysis and back pain, showing favorable outcomes [33]. Takeuchi et al. (2020) applied the same technique in a 29-year-old patient with chronic lumbar pain lasting for 6 years. The pain was unresponsive to conservative therapy. Based on CT imaging, L4–L5 spondylolysis was diagnosed. The outcomes of the smiley face rod surgery were favorable, with pain regression [22].

Use of curved rods may be indicated when laminar hooks cannot be placed due to dysplastic posterior elements. Severe dysplasia and arch clefts can preclude the use of standard fixation devices. In such cases, patient-specific implants produced with additive manufacturing offer a compelling solution. Custom-designed fixators, designed by 3D modeling and anatomically contoured to the dorsal surface of the lamina, provide optimal implant–bone congruence. Our method allows for stable fixation even in cases of marked laminar dysplasia or vertebral arch cleft, including in multilevel involvement.

Preserving motion in the spinal segment is a major advantage of pars repair in spondylolysis. However, multilevel fixation carries the risk of implant interference between adjacent levels. Arai et al. (2013) described such a case in a patient with L3–L5 spondylolysis for which pedicle screws and hooks were placed. In early postoperative period, the patient developed marked discomfort and pain when flexing and extending the trunk. The examination revealed that the contact between the laminar hook heads at L3 and pedicle screw heads at L4 was causing the symptoms. A revision surgery was required to remove the L3 construct [31].

Patient-specific implant design allows for preoperative virtual planning of both implant geometry and placement relative to anatomy and adjacent constructs. This ensures optimal positioning and prevents implant contact during lumbar motion in multilevel spondylolysis, as demonstrated in our case. Furthermore, these custom devices can be used with standard pedicle screws, allowing for the use of convenient reduction tools and controlled compression across the defect. To our knowledge, no previous publications have described this type of custom-made implant for spondylolysis. The novelty and advantages of our technique have been confirmed by a patent registered in the Russian Federation [34].

The described approach enabled successful surgical treatment of a patient with bilateral two-level spondylolysis, facilitating early mobilization and return to physical activity.

CONCLUSION

Surgical management of bilateral two-level spondylolysis at L4–L5 with indirect reconstruction of the pars interarticularis and preservation of motion in the functional spinal units can be successfully achieved using patient-specific implants fabricated via additive manufacturing technologies. One of the key advantages of employing custom-made fixation devices in multilevel spondylolysis is the ability to perform preoperative computer-assisted planning, which helps prevent implant interference during spinal motion.

ADDITIONAL INFO

Author contribution. All authors have approved the final version before publication and have also agreed to be responsible for all aspects of the work, ensuring that issues relating to the accuracy and integrity of any part of it are properly addressed and resolved.

Funding sources. No funding.

Disclosure of interests. The authors declare that they have no competing interests.

Consent for publication. The authors received written informed voluntary consent from the patient to publish personal data in a scientific journal, including its electronic version (date of signing August 16, 2024). The scope of published data was agreed with the patient.

Provenance and peer-review. This paper was submitted to the journal on an initiative basis and reviewed according to the usual procedure. Two external reviewers, a member of the editorial board and the scientific editor of the publication participated in the review.

About the authors

Alexander A. Kuleshov

Priorov National Medical Research Center of Traumatology and Orthopedics

Email: cito-spine@mail.ru
ORCID iD: 0000-0002-9526-8274
SPIN-code: 7052-0220

MD, Dr. Sci. (Medicine)

Russian Federation, 10 Priorova str., 127299 Moscow

Anton G. Nazarenko

Priorov National Medical Research Center of Traumatology and Orthopedics

Email: NazarenkoAG@cito.priorov.ru
ORCID iD: 0000-0003-1314-2887
SPIN-code: 1402-5186

MD, Dr. Sci. (Medicine), professor of RAS

Russian Federation, 10 Priorova str., 127299 Moscow

Marchel S. Vetrile

Priorov National Medical Research Center of Traumatology and Orthopedics

Author for correspondence.
Email: vetrilams@cito-priorov.ru
ORCID iD: 0000-0001-6689-5220
SPIN-code: 9690-5117

MD, Cand. Sci. (Medicine)

Russian Federation, 10 Priorova str., 127299 Moscow

Vladislav A. Sharov

Priorov National Medical Research Center of Traumatology and Orthopedics

Email: sharov.vlad397@gmail.com
ORCID iD: 0000-0002-0801-0639
SPIN-code: 8062-9216

MD

Russian Federation, 10 Priorova str., 127299 Moscow

Vitaly R. Zakharin

Priorov National Medical Research Center of Traumatology and Orthopedics

Email: zakhvit@gmail.com
ORCID iD: 0000-0003-1553-2782
SPIN-code: 2931-0703

MD, Cand. Sci. (Medicine)

Russian Federation, 10 Priorova str., 127299 Moscow

References

Supplementary files