Safety and Efficacy of Three-Dimensional Printed Patient-Specific Drilling Templates for Expansive Open-Door Laminoplasty
Expansive open-door laminoplasty (EOLP) is a widely utilized surgical technique for treating multi-level cervical myelopathy caused by conditions such as cervical spondylosis, ossification of the posterior longitudinal ligament, and spinal stenosis. While effective, traditional EOLP carries risks of complications, including displaced complete fractures on the hinge side of the lamina and lamina re-closure, both of which may lead to neurological deterioration. Previous studies have explored modifications to reduce these risks, such as the use of mini-plates instead of sutures for lamina fixation. However, even with these advancements, the incidence of hinge-side complete fractures remains high, reported at approximately 56.8%. Accurate positioning of the trough during laminoplasty has been identified as a critical factor in minimizing hinge fractures. This study investigates the safety and efficacy of three-dimensional (3D) printed patient-specific drilling templates to guide trough placement during EOLP, aiming to reduce complications and improve surgical outcomes.
Methodology
Patient Cohort and Study Design
A retrospective review was conducted on 22 patients (13 males, 9 females; median age 57.1 years) who underwent EOLP from C3 to C7 using 3D printed patient-specific drilling templates at West China Hospital between July 2016 and February 2018. All procedures were approved by the institutional ethics committee, and informed consent was obtained.
Template Design and Fabrication
Preoperative computed tomography (CT) scans of the cervical spine were reconstructed using Mimics 17.0 software (Materialise, Belgium). Two cutting paths were digitally simulated at the junction of the lamina and lateral mass on both the open and hinge sides. A 3D model of the lamina surface was created to design a customized template. The template body incorporated channels corresponding to the planned cutting paths. The final design was fabricated using stereolithography with acrylate resin (Beijing AK Medical Co., Ltd.). After sterilization with ethylene oxide, the templates were stored in sterile packaging until surgery.
Surgical Technique
During surgery, the lamina was exposed via a posterior approach. The 3D printed template was firmly positioned on each lamina from C3 to C7. On the open side, a burr was guided through the template channel to create a full-thickness trough. On the hinge side, a partial-thickness trough was created by sliding the burr along the template channel, preserving the inner cortical layer to maintain a “greenstick” fracture. The lamina was then gently elevated, and adhesions between the dura and ligamentum flavum were released. Decompression was confirmed visually, and a Centerpiece mini-plate (Medtronic Sofamor Danek) was fixed to the lamina and lateral mass to stabilize the expanded lamina.
Clinical and Radiographic Evaluation
Clinical outcomes were assessed preoperatively and at 1 week, 3 months, 6 months, and 12 months postoperatively. Neurological function was evaluated using the Japanese Orthopedic Association (JOA) score, while neck pain was quantified via the visual analog scale (VAS). Complications, including wound infection, cerebrospinal fluid (CSF) leakage, axial symptoms, and C5 palsy, were recorded.
Radiographic parameters measured included:
- Anteroposterior spinal canal diameter
- Pavlov ratio (ratio of spinal canal diameter to vertebral body diameter)
- C2–C7 Cobb angle (sagittal alignment)
- C2–C7 range of motion (ROM)
Postoperative CT scans at 1 week were analyzed to classify hinge-side fractures as either incomplete (greenstick) or complete. Lamina re-closure was defined as a ≥10% reduction in the Pavlov ratio during follow-up.
Results
Surgical Outcomes
A total of 110 laminae (C3–C7 in 22 patients) were operated on. The mean operative time was 130.10 ± 11.83 minutes, with an average blood loss of 225.40 ± 92.69 mL. No template-related intraoperative complications occurred.
Clinical Improvements
Significant improvements in neurological function and pain reduction were observed:
- JOA scores increased from 8.55 ± 2.10 preoperatively to 14.32 ± 1.29 at 12 months (P < 0.0001).
- VAS scores decreased from 5.74 ± 1.08 preoperatively to 2.82 ± 0.79 at 12 months (P < 0.0001).
Complications
- Three patients developed axial symptoms (intense neck/shoulder pain), resolving within 1 month with physical therapy.
- One patient experienced CSF leakage, managed successfully with drainage.
- One case of transient C5 palsy resolved spontaneously within 1 month.
- No instances of wound infection or lamina re-closure occurred.
Radiographic Outcomes
- Anteroposterior canal diameter increased from 10.82 ± 2.50 mm preoperatively to 17.09 ± 3.07 mm at 12 months (P < 0.0001).
- Pavlov ratio improved from 0.44 ± 0.11 to 0.89 ± 0.15 (P < 0.0001).
- C2–C7 Cobb angle decreased from 19.21° ± 5.71° to 14.88° ± 4.40° (P = 0.0142), indicating slight loss of cervical lordosis.
- C2–C7 ROM reduced from 48.48° ± 12.45° to 39.86° ± 13.97° (P = 0.0129), reflecting postoperative stiffness.
Hinge-Side Fracture Analysis
Of 110 hinge-side troughs, 16 (14.5%) exhibited complete fractures on postoperative CT. Fracture distribution across levels was uniform (C3: 3; C4: 2; C5: 3; C6: 4; C7: 4; P = 0.9061). All complete fractures showed progressive fusion: 81.3% at 3 months, 93.8% at 6 months, and 100% at 12 months. No fractures displaced into the spinal canal.
Discussion
This study demonstrates that 3D printed patient-specific drilling templates enhance the precision of trough placement in EOLP, reducing the incidence of hinge-side complete fractures compared to historical controls. The 14.5% complete fracture rate observed here is markedly lower than the 56.8% reported in previous studies using freehand techniques. The templates enabled consistent positioning of the hinge trough at the lamina-lateral mass junction, minimizing medial displacement—a known risk factor for fractures.
The high fusion rate of complete fractures (100% at 12 months) suggests that even when fractures occur, they do not compromise long-term stability. The absence of lamina re-closure further supports the durability of mini-plate fixation when combined with accurate trough placement.
Postoperative reductions in cervical ROM and lordosis are consistent with known sequelae of laminoplasty, attributable to scar formation and natural aging. However, these changes did not negate the significant neurological improvements achieved.
Limitations
This study is limited by its retrospective design and small sample size. Longer follow-up is required to assess late complications, such as adjacent segment degeneration. Additionally, the cost and time required for template fabrication may limit widespread adoption.
Conclusion
3D printed patient-specific drilling templates improve the accuracy and safety of EOLP, reducing hinge-side fractures without increasing operative risks. This technique represents a promising advancement in cervical spine surgery, particularly for patients at high risk of complications.
doi.org/10.1097/CM9.0000000000000476
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