Influences of Increasing Pedicle Screw Diameter on Widening Vertebral Pedicle Size during Surgery in Spinal Deformities in Children and Adolescents without Higher Risk of Pedicle and Vertebral Breaches

Abstract

Background: A very common technique for treating spinal deformities in children and adolescents is the use of segmental screws. In order to obtain proper stability and the best possible correction, the screws must first be precisely inserted. Additional factors influencing the quality and success of the operation are the size and quality of the bone, the skills of the surgeon, and biomechanical factors, i.e., the width and length of the screws used during surgery. Our study was focused on evaluating the effect of increasing the diameter of the instrumented pedicles by pedicle screws and assessing the safety of expanding these pedicles with screws of various sizes in children with spinal deformities during the growth period, using preoperative magnetic resonance imaging and postoperative computed tomography (CT) to assess and compare preoperative size measurements from MRI to postoperative CT measurements. Methods: We obtained data for evaluation from the available medical records and treatment histories of patients aged 2 to 18 who underwent surgical treatment of spinal deformities in the years 2016–2023. In 234 patients (28 male and 206 female), 7954 vertebral bodies were scanned by preoperative MRI, and 5080 pedicle screws were inserted during surgery, which were then assessed by postoperative CT scan. For the most accurate assessment, patients were classified into three age groups: 2–5 years (Group 1), 6–10 years (Group 2), and 11–18 years (Group 3). In addition, we studied implant subgroups: vertebral bodies with inserted pedicles of screw sizes 5.0 mm and 5.5 mm (Group S), and pedicles of screw sizes 6.0 mm, 6.5 mm, and 7.0 mm (Group L). Results: The morphology of pedicles (Lenke classification) analyzed before surgery using MRI was 55.2% type A, 33.8% type B, 4.7% type C, and 6.3% type D. The postoperative lateral and medial breaches were noted, and these did not cause any complications requiring revision surgery. The mean pedicle diameter before surgery for T1–L5 vertebral pedicles was between 3.79 (1.44) mm and 5.68 (1.64) mm. The mean expanding diameter of pedicles after surgery for T1–L5 vertebral pedicles ranged from 1.90 (0.39) mm to 2.92 (0.28) mm, which corresponds to the extension of the pedicle diameter in the mean range of 47% (4.1)–71% (3.0). We noted that the mean vertebral pedicle expansion was 49% in Group 1, 52% in Group 2, and 62% in Group 3 (N.S.), and the mean expansion for 7.0 mm screw pedicles was 78%. Conclusions: Our study confirms that there is a wide range of expansion of the vertebral pedicle during screw insertion (up to 78%) with a low risk of lateral or medial breaches and without an increased risk of complications. The larger the diameter of the screw inserted into the pedicle, the more the pedicle expands. Pedicle measurements by preoperative MRI may be helpful for sufficient reliability in preoperative planning.

The Influence of Increased Pedicle Screw Diameter and Thicker Rods on Surgical Results in Adolescents Undergoing Posterior Spinal Fusion for Idiopathic Scoliosis

“…The available medical literature has often confirmed the greater stiffness of the structure, which was at least partially dependent on the diameter of the structure rod [58]. By using a thicker and stiffer rod, we are able to obtain greater corrective forces on the deformed spine, and in combination with larger sizes of pedicle screws and Ponte osteotomy of the posterior column of the spine, we will obtain the most desirable correction in three planes, as our study shows [22,23,30,57]. This trend persisted even after separating patients by curve flexibility.…”

“…Segmental screw placement in the upper-and mid-thoracic spine is technically challenging, with high misplacement rates [51,59,60]. In particular, increased screw diameters are often avoided for pediatric thoracic vertebrae, given their smaller pediatric pedicle size [22,59,61]. In the study by Cho et al, the authors concluded that while large screw diameters (up to 9.5 mm) caused an increase in the pedicle circumference, there was no spinal canal compression [52].…”

“…This was possible because the medial wall is 2-3 times thicker than the lateral wall at the thoracic level, which resists medial breaching [22,56]. However, in another study of screw placement, analyzing the increased diameter of the vertebral pedicle screw in the pediatric population, very interesting results were obtained that there is a wide range of vertebral pedicle expansion during screw insertion (up to 78%), with a low risk of lateral or medial fracture and no increased risk of complications [22], which is confirmed and justified by other previous biomechanical studies [52,66,67]. The larger the diameter of the screw inserted into the pedicle, the more the pedicle expands [22,52,66,67].…”

“…However, in another study of screw placement, analyzing the increased diameter of the vertebral pedicle screw in the pediatric population, very interesting results were obtained that there is a wide range of vertebral pedicle expansion during screw insertion (up to 78%), with a low risk of lateral or medial fracture and no increased risk of complications [22], which is confirmed and justified by other previous biomechanical studies [52,66,67]. The larger the diameter of the screw inserted into the pedicle, the more the pedicle expands [22,52,66,67]. Additionally, previous studies analyzing pedicle screw size have been on cadavers or adult spine deformities.…”

“…Since the introduction of Cotrel-Dubousset instrumentation, it has become the "gold standard" in the treatment of idiopathic scoliosis, with many modifications of implants and instruments allowing for the optimal correction of deformities [10,14]. However, these instruments have different implant designs, screws, and rod sizes and can be composed of different metal alloys with different hardnesses and rod thickness, which can have a significant impact on the effect of correcting spinal deformities [15][16][17][18][19][20][21][22][23].…”