Transverse Screw Angles Research Articles

Minimally Invasive Subaxial Cervical Pedicle Screw Placement with Routine Fluoroscopy: Cadaveric Feasibility Study and Report of 6 Clinical Cases

Objective: Conventional cervical pedicle screw insertion necessitates extensive paraspinal muscle dissection and retraction in order to achieve the lateral to medial angulation needed to achieve the optimal screw trajectory. Minimally invasive transmuscular approach can comfortably achieve this angulation without significant injury to the midline structures and its musculo-ligamentous attachments.Methods: Minimally invasive cervical pedicle screws were inserted in 4 fresh frozen cadaveric specimens. Pre-procedure and post-procedure CT scans were done to assess the pedicle dimensions, suitability for screw insertion and integrity of the screws. The same technique was applied in a clinical cohort of six cases – 3 cases of traumatic subluxation; one case of traumatic vertebral fracture and 2 cases of infective facet destruction (Koch’s); with successful outcomes.Results: Among the 38 screws in the cadaver specimens, a total of 11 screws (28.9%) had breached the pedicle wall (Lateral wall breach–9; Medial wall breach–2). Of the 9 screws (23.6%) that had a lateral breach into the vertebral canal, 4 (10.5%) each had Grade IIa breach and one (2.6%) had Grade III breach. The mean transverse screw angle in the subset of pedicle screws with no breach was 34.1 whereas it was 22.1 in screws that had lateral breach and 43.6 in those with medial breach. Among the 22 screws inserted in the clinical cohort of 6 cases, 4 screws (18.1%) had breached the pedicle wall. All the identified breaches were in the lateral wall (Grade IIa – 3; Grade IIb–1; Grade III–nil). Conclusion: Minimally invasive subaxial pedicle screw insertion can be utilized in cases where a robust posterior fixation is required, either in isolation or as an adjunct to anterior surgery, in cases where a direct posterior decompression is not warranted. It is a safe and effective approach which minimizes injury to the paraspinal structures and midline attachments.

The study of distance changes between lumbar bi-cortical pedicle screws and anterior large vessels in patients with lumbar spondylolisthesis

ObjectiveThis paper was a anatomical radiographic study of distance between lumbar bi-cortical pedicle screws (BPSs) and anterior large vessels (ALVs) in patients with lumbar spondylolisthesis, and to provide clinical basis for evaluating the safety of bi-cortical pedicle screw implantation during lumbar spondylolisthesis.MethodsComplete Computed tomography (CT) data of 104 patients with grade I lumbar spondylolisthesis (L4 52 and L5 52) and 107 non-spondylolisthesis patients (control group) were collected in this study. The distances between lumbar 4,5(L4,5) and sacrum 1(S1) BPSs and ALVs (abdominal aorta, inferior vena cava, left and right common iliac artery, internal and external iliac artery) were respectively measured at different transverse screw angles (TSAs) (L4:5°,10°; L5:10°,15°; S1:0°,5°,10°) and analyzed by SPSS (v25.0). There were three types of distances from the anterior vertebral cortex (AVC) to the ALVs (DAVC-ALV): DAVC-ALV N, DAVC-ALV ≥ 0.50 cm, and DAVC-ALV < 0.50 cm; these different distances represented non-contact, distant and close ALV respectively.ResultsWe calculated the incidences of screw tip contacting large vessels at different TSAs and provided the appropriate angle of screw implantation. In non-spondylolisthesis group, in L4, the appropriate left TSA was 5°, and the incidence of the close ALV was 4.62%. In S1, the appropriate left TSA was 0° and the incidence of the close ALV was 22.4%, while the appropriate right TSA was 10° and the incidence of the close ALV was 17.8%. In L4 spondylolisthesis group, in L4, the appropriate left TSA was 5°, and the incidence of the close ALV was 3.8%. In L5 spondylolisthesis group, in S1, the appropriate left TSA was 0° and the incidence of the close ALV was 19.2%, while the appropriate right TSA was 10° and the incidence of the close ALV was 21.2%. The use of BPS was not appropriate on the right side of L4 or on the either side of L5 both in spondylolisthesis and control group. In patients with lumbar 4 spondylolisthesis, the incidences of screw tip contacting large vessels were less than the control group in both L4 and 5. In patients with lumbar 5 spondylolisthesis, the incidences of screw tip contacting large vessels were less than the control group in L5, while there were no significant difference in S1.ConclusionIt is very important that considering the anatomical relationship between the AVC and the ALVs while planning BPSs. The use of BPS does not apply to every lumbar vertebra. In patients with lumbar spondylolisthesis and non-spondylolisthesis patients, the incidences of screw tip contacting large vessels are different.

The methods for inserting lumbar bicortical pedicle screws from the anatomical perspective of the prevertebral great vessels

BackgroundAt present, bicortical pedicle screws (BPSs) are not used clinically because they carry the potential risk of damaging the prevertebral great vessels (PGVs). The authors observed the anatomical relationship between the PGVs and simulated BPSs at different transverse screw angles (TSAs), exploring the insertion method of the BPS.MethodsComputed tomography angiography (CTA) images from 65 adults were collected. A total of 4–5 TSAs of the BPSs were simulated on the left and right sides of L1-L5 (L1-L3: 0°, 5°, 10°, 15°; L4-L5: 0°, 5°, 10°, 15°, 20°). There were three types of distances from the anterior vertebral cortex (AVC) to the PGVs (DAVC-PGV); DAVC-PGV < 0.50 cm, DAVC-PGV ≥ 0.50 cm, and DAVC-PGV↑; these distances represented close, distant, and noncontact PGV, respectively.ResultsThe ratio of every type of PGV was calculated, and the appropriate TSA of the BPS was recommended. In L1, the recommended left TSA of the BPS was 0°, and the ratio of the close PGV was 7.69%, while the recommended right TSA was 0°-10°, and the ratio of the close PGV was 1.54–4.62%. In L2, the recommended left TSA of the BPS was 0° and the ratio of the close PGV was 1.54%, while the recommended right TSA was 0°-15° and the ratio of the close PGV was 3.08–9.23%. In L3, the recommended left TSA was 0°-5°, and the ratio of the close PGV was 1.54–4.62%. In L4, the recommended left TSA was 0°, and the ratio of the close PGV was 4.62%. BPS use was not recommended on the right side of either L3 or L4 or on the either side of L5.ConclusionsFrom the anatomical perspective of the PGVs, BPSs were not suitable for insertion into every lumbar vertebra. Furthermore, the recommended methods for inserting BPSs were different in L1-L4.

Pedicle Screw With Increased Cortical Purchase Can Be Inserted With Same Accuracy as the Screw in Straightforward Trajectory Using 3D Modeling Landmarks

Study DesignComparison, in terms of insertion accuracy and biomechanical performance, between an increased cortical purchase and straightforward pedicle screw trajectory. ObjectiveThis study aims to compare a trajectory with increased cortical purchase to the more common straightforward trajectory in terms of strength and insertion accuracy using real-time navigation. Summary of Background DataIn previous studies, it was suggested that pedicle screw pullout strength is strongly correlated with bone mineral density, and using a more cortical tract allows a greater portion of the denser bone, the cortex, to be in contact with the screw. In light of this advantage, an insertion technique has been proposed more recently, to increase the cortical purchase to maximize screw thread contact with cortical bone. It is performed inserting the screw with reduced transverse inclination and results in cortical bone purchase in the lateral portion of the pedicle. MethodsEight T1 and eight T3 vertebra models were reconstructed in Mimics Suite (Materialise, Leuven, Belgium) using CT data obtained with a Medtronic O-arm. Using a previously developed computer algorithm, we calculated all achievable safe trajectories for pedicle screw placement ensuring a minimal distance of 0.5 mm between screw and pedicle edges. For both vertebrae, among these, the straightest and the most convergent trajectories with the calculated insertion region greater than 15% of the total were selected to safely instrument the vertebrae, respectively, as ICP and straightforward techniques. The straightforward technique was planned with a transverse angle of 22.50° in both vertebrae whereas the ICP was planned with a transverse angle of 12.50° for T1 and 2.5° for T3. The screws were implanted by a surgeon experienced in straightforward insertion, and other independent investigators measured placement accuracy and mechanical performance. ResultsThe transverse screw angles for T1 and T3 with straightforward technique had average values of 24.93° ± 2.96° and 23.53° ± 2.70°, respectively. For the ICP technique, the average values were 15.60° ± 2.95° for T1 and 2.29° ± 1.55° for T3. The resultant errors associated with screw placement for T1 and T3 were not significantly different (p > .05). The pullout failure loads with straightforward techniques ranged from 756 ± 164 N in T1 to 703 ± 74 N in T3 and were not significantly different (p > .05) from the values of 699 ± 84 N for T1 and of 732 ± 113 N measured for the ICP. ConclusionsFor the upper thoracic vertebrae tested, despite the use of shorter screws, the insertion technique with increased cortical purchase, in biomechanical terms, is comparable with the straightforward trajectory. Using guidance, the proposed ICP technique was performed with the same accuracy as the popular straightforward technique. Level of EvidenceLevel V.

A self-designed three-dimensional guiding instrument for percutaneous thoracolumbar pedicle screw implantation

Objective To evaluate the clinical eeficacy of the self-designed three-dimensional guiding instrument used in the implantation of percutaneous thoracolumbar pedicle screws. Methods This study enrolled 52 patients who had undergone internal fixation with percutaneous thoracolumbar pedicle screws from January 2014 to March 2015 at our department. They were divided two groups, the instrument group and the manual group. There were 18 males and 7 females in the instrument group, with an average age of 56.1 ± 12.7 years (range, from 27 to 74 years) . Of them, 12 suffered from lumbar disc herniation , 4 from lumbar instability, and 9 thoracolumbar fracture. There were 17 males and 10 females in the manual group, with an average age of 57.3 ± 13.5 years (range, from 32 to 78 years). Of them, 14 suffered from lumbar disc herniation,5 from lumbar instability, and 8 from thoracolumbar fracture. There were no significant differences in general clinical data between the 2 groups preoperation (P > 0.05) . The positioning time, intraoperative fluoroscopy frequency, transverse screw angle (TSA), and sagittal screw angle (SSA) were compared between the 2 groups. Results All the operations were performed uneventfully. The positioning time (7.4 ± 3.2 min) and intraoperative fluoroscopy frequency (3.4 ± 1.9 times) in the instrument group were significantly less than in the manual group (12.3 ±4.4 min and 6.4 ±2.2 times, respectively) (P < 0.05). The interior and exterior pedicle walls were each pierced in one case, and the excessive cephalad or caudal deviation occurred in 2 cases in the instrument group; the interior pedicle wall was pierced in 4 cases, the exterior wall was pierced in 3 cases and the excessive cephalad or caudal deviation occurred in 3 cases in the manual group. The deviation rates of TSA and SSA in the instrument group (6.5%±2.6% and 9.6% ±3.8%, respectively) were significantly lower than in the manual group(18.6% ±5.8% and 16.0% ±3.8%,respectively) (P <0.05) . Conclusion Since our self-designed three-dimensional guiding instrument can effectively reduce radiation exposure and operation time, and increase success rate of positioning without increasing operative compilations, it is a great aid in the internal fixation with percutaneous thoracolumbar pedicle screws. Key words: Spinal fractures; Fracture fixation, internal; Bone nails; Guiding instrument

Can intermuscular cleavage planes provide proper transverse screw angle? Comparison of two paraspinal approaches

The goal of this study was to determine which paraspinal approach provided a better transverse screw angle (TSA) for each vertebral level in lower lumbar surgery. Axial computed tomography (CT) images of 100 patients, from L3 to S1, were used to measure the angulation parameters, including transverse pedicle angle (TPA) and transverse cleavage plane angle (TCPA) of entry from the two approaches. The difference value between TCPA and TPA, defined as difference angle (DA), was calculated. Statistical differences of DA obtained by the two approaches and the angulation parameters between sexes, and the correlation between each angulation parameter and age or body mass index (BMI) were analyzed. TPA ranged from about 16° at L3 to 30° at S1. TCPA through the Wiltse's and Weaver's approach ranged from about -10° and 25° at L3 to 12° and 32° at S1, respectively. The absolute values of DA through the Weaver's approach were significantly lower than those through the Wiltse's approach at each level. The angulation parameters showed no significant difference with sex and no significant correlation with age or BMI. In the lower lumbar vertebrae (L3-L5) and S1, pedicle screw placement through the Weaver's approach may more easily yield the preferred TSA consistent with TPA than that through the Wiltse's approach. The reference values obtained in this paper may be applied regardless of sex, age or BMI and the descriptive statistical results may be used as references for applying the two paraspinal approaches.

In vivo accuracy of thoracic pedicle screws.

A retrospective observational study of 279 transpedicular thoracic screws using postoperative computed tomography (CT). To determine the accuracy of transpedicular thoracic screws. Previous studies have reported the importance of properly placed transpedicular thoracic screws. To our knowledge, the in vivo accuracy of pedicle screw placement throughout the entire thoracic spine by CT is unknown. The accuracy of thoracic screw placement within the pedicle and vertebral body and the resultant transverse screw angle (TSA) were assessed by postoperative CT. Cortical perforations of the pedicle were graded in 2-mm increments. Screws were regionally grouped for analysis. Forty consecutive patients underwent instrumented posterior spinal fusion using 279 titanium thoracic pedicle screws of various diameters (4.5-6.5 mm). The regional distribution of the screws was 39 screws at T1-T4, 77 screws at T5-T8, and 163 screws at T9-T12. Fifty-seven percent of screws were totally confined within the pedicle. Although medial perforation of the pedicle wall occurred in 14% of screws, in <1% there was >2 mm of canal intrusion. Lateral pedicular perforation occurred in 68% of perforating screws and was significantly more common than medial perforation (P < 0.0005). Seventeen screws penetrated the anterior vertebral cortex by an average of 1.7 mm. Screws inserted between T1 and T4 had a decreased incidence of full containment within the pedicle (P < 0.0005) and vertebral body (P = 0.039) compared with T9-T12. The mean TSA for screws localized within the pedicle was 14.6 degrees and was significantly different from screws with either medial (mean 18.0 degrees ) or lateral (mean 11.5 degrees ) pedicle perforation (P < 0.0005). Anterior vertebral penetration was associated with a smaller mean TSA of 10.1 degrees (P = 0.01) and with lateral pedicle perforation (P < 0.0005). There were no neurologic or vascular complications. Ninety-nine percent of screws were fully contained or were inserted with either < or =2 mm of medial cortical perforation or an acceptable lateral breech using the "in-out-in" technique. Anterior cortical penetration occurred significantly more often with lateral pedicle perforation and with a smaller mean TSA. The incidence of fully contained screws was directly correlated with the region of instrumented thoracic spine.