C-Arm Oblique View–Assisted Screw Placement Method for Extremely Small Lumbar Pedicles in Thoracolumbar Vertebral Body Fractures

Discussion

With the growth of modern industry and transportation, the incidence of high-energy trauma is rising yearly.10 Falls from heights and traffic accidents are common causes of spinal fractures. Patients with unstable fractures or foreign body intrusion into the spinal canal, leading to spinal cord injury symptoms, are now mostly treated surgically.11 Posterior short-segment internal fixation surgery has become the mainstream approach for thoracolumbar fracture reduction and internal fixation. It involves fixing the injured vertebrae and adjacent upper and lower vertebrae using longitudinal bracing force to restore the injured vertebrae to their normal height for corrective effect,12 thereby maximizing the preservation of thoracolumbar motion segment mobility and minimizing surgical trauma.

Short-segment internal fixation surgery has specific requirements. The pedicle, providing most of the holding force and axial stiffness for screws, is crucial, as cancellous bone contributes only 15% to 20% of the holding force. This indicates that an intact pedicle structure is essential for sufficient screw fixation.13 Studies indicate that pedicle morphology varies with age, gender, and region.6 In normal adults, the pedicle width can reach 1 cm, accommodating screws and providing adequate holding force. Common pedicle screw diameters are 6 mm and 6.5 mm, with a transverse pedicle diameter below 7 mm often used as the implantation threshold in literature. However, some patients have congenitally small pedicles (diameter between 5 mm and 7 mm). While smaller diameter screws can be used, they may compromise holding power and increase the risk of poor positioning and medial cortex penetration. Emerging technologies like the Renaissance spinal robot and preoperative 3D printing simulation planning help ensure surgical safety and reduce damage.14

However, some patients have pedicles narrower than 4 mm in diameter.7 Conventional posterior pedicle screw implantation risks include penetrating the bone cortex, fracturing the pedicle, and invading the spinal canal. The complex adjacent tissues and neurological structures around the screw path can lead to cerebrospinal fluid leakage, neurological dysfunction, and other complications. Currently, standardized methods for safely, accurately, and effectively placing screws in extremely small pedicles are lacking. Recently, intraoperative navigation and robotic technologies have been developed to enhance the accuracy of pedicle screw placement. The use of O-arm navigation systems in spinal implanting is increasing, offering surgeons a relatively easy and safe pedicle screw access option.8 However, these systems expose patients to higher doses of CT-like radiation than C-arm x-ray machines and are too costly for many tertiary hospitals.15 Thus, most spine surgeons still rely on C-arm x-ray machines alone to perform spinal implant-rod internal fixation in patients with very thin pedicles.

In 1993, Dvorak et al16 developed the technique of thoracic pedicle screw placement to maximize screw numbers and enhance correction in scoliosis surgery. In 2011, Lee et al17 further promoted this technique. However, the literature rarely reports the incidence of very small lumbar pedicles and their screw placement methods. The presence or absence of ribs creates significant structural differences between thoracic and lumbar spines. Therefore, we introduced an external lumbar pedicle pinning method. In this method, the screw is inserted into the transverse process from the pedicle midline at a high level from the lateral paracentral articular synchondrosis joint. During the puncture process, the transverse process cortex is bilaterally penetrated, and then the screw tip is pressed tightly against the pedicle edge and advanced toward the lateral vertebral wall to the anterior vertebral bone cortex. Here, the lumbar transverse process cortex and the vertebral body outer margin cortex provide the screw with holding force, establishing a robust “3-point fixation.” In a quantitative study of lumbar cortical bone, Odeh et al18 reported that the transverse process cortical thickness averaged 0.68 ± 0.16 mm, slightly less than the 0.94 ± 0.16 mm measured at the pedicle. However, the cortical bone mineral density of the transverse process (478 ± 84 mg HA/cm³) was virtually identical to that of the pedicle (481 ± 71 mg HA/cm³), indicating that the transverse process cortex can provide comparable mechanical anchorage despite its marginally thinner dimension.

Accurately positioning the pedicle of the injured vertebra is crucial for surgical success. The surgeon must be well versed in spinal anatomy and rely on tactile feedback and intraoperative fluoroscopy for screw placement. Traditional C-arm machines provide planar fluoroscopic imaging, requiring surgeons to confirm screw position in the lateral aspect of the pedicle and their depth and position in the lateral view. Repeated imaging disrupts surgical continuity, reduces implant placement accuracy, and prolongs operation time. Moreover, fluoroscopy exposes the surgical team and patient to harmful radiation. To address these issues, our team developed and applied an angled C-arm fluoroscopy technique. Preoperatively, the C-arm’s head-tail tilt was adjusted to align endplate shadows, determining the puncture needle’s head-tail angle. The internal inclination angle and puncture depth were established via 3D CT reconstruction, and the C-arm x-ray machine’s oblique angle was adjusted to match. The screw puncture site was on the outer side of the pedicle’s circular projection. The insertion path was perpendicular to the upper endplate’s shadow, near the outer edge of the projection to avoid pedicle contact and damage, and was gradually inserted to the predetermined depth. Idler et al demonstrated that using the pedicle axis view for puncture positioning preserves the pedicle’s circular projection area, preventing pedicle damage and neurological dysfunction during pedicle screw placement.19 In conventional C-arm fluoroscopy, pedicle screw insertion is typically accomplished through an iterative trial-and-error paradigm that mandates repeated intraoperative image acquisitions and positional corrections. By contrast, the proposed method rigidly co-registers preoperative 3-dimensional planning data with intraoperative 2-dimensional fluoroscopic projections, thereby transforming the imaging workflow into a reproducible, protocol-driven procedure. This method markedly reduces the learning curve, minimizes the number of fluoroscopic exposures, and consequently lowers radiation exposure to both surgeon and patient. In patients with extremely small pedicles, the procedural standardization facilitates accurate screw insertion, prevents cortical breach, and ensures robust fixation.

Given the structural characteristics of extremely small pedicles, achieving a holding force comparable to that of conventional pinning is challenging regardless of the method used. This study’s results showed that after incisional reduction of thoracolumbar vertebral fracture patients with extracorporeal vertebrae, the height of the anterior margin of the injured vertebrae and the compression rate of the anterior margin of the vertebral body were significantly improved, and the Cobb angle of the injured vertebrae was improved, with statistically significant differences (P < 0.05). Additionally, the patients’ VAS, ODI, and SF-36 scores were significantly lower than preoperative levels (P < 0.05). All cases demonstrated excellent reconstruction and maintenance of spinal stability.