Three-dimensional spiral CT measurement of atlantal pedicle and its clinical application

The morphological classification and clinical significance of atlas vertebral artery sulcus based on computed tomography three-dimensional reconstruction

OBJECTIVE

The purpose of this study was to research the morphological classification and clinical significance of vertebral artery sulcus on atlas based on CT three-dimensional reconstruction.

METHODS

Three-dimensional reconstruction images of 300 adult atlases were collected. A total of 600 atlas vertebral artery sulci were selected in this study. The parameters required for placement of C1 pedicle screw, including depth of grinding drilling (ao), width (cd), length ab), height (H), lateral wall thickness (L1), inner wall thickness (L2), medial angle (∠α), and the cephalad angle to the transverse plane of atlas pedicle (∠β), were measured.

RESULTS

CT three-dimensional reconstruction images showed that there were five types of atlas vertebral artery sulci: no process type (n = 494 cases, 82.33%), upper process type (n = 29, 4.83%), lower process type (n = 25, 4.17%), double process type (n = 19, 3.17%), and posterior ring type (33, 5.50%). One-way ANOVA tests showed that the five groups differed significantly in the parameter of ao, L2, H, ∠α and ∠β. One-way ANOVA with the LSD post hoc tests showed that the parameter ao of the group of no process type was less than that of the group of upper or lower process type (P < 0.05), and ao of the group of lower process or posterior ring type was less than that of the group of the upper type (P < 0.05). The parameter of ao of the male group was larger than that of the female group.

CONCLUSION

No process type of the atlas vertebral artery sulcus was the most common, and the medial angle and cephalad angle of the atlas pedicle in this type were the smallest. When pedicle screws are inserted, the above two angles should not be too large. Male's ao was larger than that of female's. All these findings should be considered to avoid the deviation of the nail track.

Suggestion of a safe zone for C1 pedicle screws depending on anatomical peculiarities

OBJECTIVE

For surgical treatment of instable upper cervical injuries, the Harms technique using lateral mass screws provides rigid fixation and favourable clinical outcomes. The use of the posterior arch of C1 as a "pedicle" allows for screw anchorage, giving improved biomechanical stability. Therefore, the aim of this study was to introduce a bilateral safe zone for C1 pedicle screws, regarding screw angulation and pedicle height.

MATERIAL AND METHODS

We retrospectively reviewed the CT scans of 500 patients. Three-dimensional reformats were generated for detailed measurements. Centre screw entry point (EP), length of lateral mass as screw trajectory, lateral mass width (LMW), length of screw trajectory (ST), maximal divergence (DI) and maximal convergence (CON) from EP without perforation, and pedicle height (PH) of the posterior arch were measured.

RESULTS

The 500 cases consisted of 335 males and 165 females, with a mean age of 49.5 years. Measurements did not demonstrate significant side-related differences. The mean screw entry point was 22.8 mm from the midline-axis (left 22.6 mm; right 23.0 mm). From this point, a safe zone between 11.6° of divergence and 19.6° of convergence was detected. Measurements of female patients were generally smaller, with significant differences from male patients (p < 0.05). 158 subjects (31.6%) had a PH < 4 mm.

DISCUSSION

C1 pedicle screws were feasible in the majority of patients. Proposing a safe zone for screw angulation may provide safety and avoid screw perforation. However, detailed knowledge of the individual C1 anatomy and the preoperative measurement is essential in the operative planning.

Occipitocervical Fusion via Cervical Pedicle Fixation Assisted with O-arm Navigation

Objective

To describe the clinical outcomes of occipitocervical fusion (OCF) using cervical pedicle fixation with assistance of O‐arm navigation and present its clinical feasibility.

Methods

From January 2015 to December 2016, eight patients with a variety of diagnoses were surgically treated with occipitocervical fusion using cervical pedicle screws under O‐arm navigation. All patients received full workup consisting of clinical and radiological assessments. Perioperative parameters including operating time, intraoperative blood loss, postoperative complications, surgical outcomes were recorded. Postoperative data were acquired resorting to the scheduled follow‐up 3, 6 and 12 months after their discharge and annually afterwards. The Japanese Orthopaedic Association (JOA) Scores and American Spinal Injury Association (ASIA) Scale were used to evaluate neurological function. The accuracy of screw placement was classified according to a modified classification of Gertzbein and Robbins. The fusion status was evaluated in reference to the Bridwell's posterior fusion grades.

Results

The patient cohort comprised of five males and three females, with the average age of 51.9 years (range from 18 to 74 years). The patients all showed indications for OCF and were performed with polyaxial screws through cervical pedicles. The average operation time was 274 min (range from 226 to 380 min), with the intraoperative blood loss of 437.5 mL and the blood transfusion volume of 481.3 mL. The average follow‐up time was 23.5 months (range from 17 to 32 months). All patients exhibited radiographic evidence of osseous fusion by X‐ray and computed tomography (CT) at the final follow‐up. No neurovascular complications were found during the follow‐up time, and the clinical symptoms were observed to be significantly improved in all the patients. Thirty‐four cervical pedicle screws were implanted within the eight patients, with the accuracy of cervical pedicle screw placements as 94.1% (32/34), among which, two pedicle screws were found to broken through the cervical pedicles that were evaluated as Grade II.

Conclusions

Occipitocervical fusion via cervical pedicle fixation assisted with O‐arm navigation is a feasible and safe procedure with a vast range of indications.

Transposterior Arch Lateral Mass Screw for C1 Fixation: Application of a 3.5-mm-Diameter Screw in the Vertebral Artery Groove with a Height of ≤3.5 mm

OBJECTIVE

To explore the feasibility and effectiveness of C1 lateral mass fixation via the posterior arch using pedicle screws of 3.5-mm diameter in patients whose atlas in the vertebral artery groove (C1 pedicle) was ≤3.5 mm in height.

METHODS

A total of 14 patients who underwent transposterior arch lateral mass screw fixation between 2014 and 2017 due to atlantoaxial instability were retrospectively studied. The height of the atlas pedicle was ≤3.5 mm on one or both sides. The position of the screw and damage of the screw trajectory were assessed using the postoperative 3-dimensional computed tomography. The patients were regularly followed up to observe the fracture union and bone graft fusion.

RESULTS

In total, 27 atlas pedicle heights were ≤3.5 mm and 22 screws were successfully inserted without any neurovascular complications. However, the pedicle wall was found to have a certain degree of damage with damaged superior/inferior wall in 4 of 6 pedicles respectively. Clinical symptoms were relieved to varying degrees, and patients demonstrated bony fusion during the postoperative follow-up.

CONCLUSIONS

Pedicle screws of 3.5-mm diameter could be fixed with a high success rate using the viscoelasticity and expansivity of the bone tissue even if the atlas pedicles were ≤3.5 mm in height. Although the screws had a certain probability of breaking the superior/inferior wall, they provided sufficient stability and enabled fracture or bone graft healing. Extraverted atlas pedicle screws should be considered in some cases.

Application value of expansive pedicle screw in the lumbar short-segment fixation and fusion for osteoporosis patients

Clinical value of expansive pedicle screw in lumbar short-segment fixation and fusion for patients with osteoporosis was investigated. A total of 80 patients with lumbar compression fracture but without obvious nerve compression were selected and divided into the observation group (n=40) and the control group (n=40) using a random number table. The observation group used the expansive pedicle screw, and the control group received conventional pedicle screw fixation and bone graft fusion. In the observation group, the operation and hospitalization time after operation were shorter and the intraoperative bleeding amount was less than that in control group (p<0.05). At 1 week, 1, 3 and 6 months after operation, the observation group had better straight leg raising test (SLRT) scores, higher lower limb sensory scores but lower visual analogue scale (VAS) scores than control group (p<0.05). Besides, the proportions of postoperative infection, dural mater tear, nerve root injury and spinal cord injury during operation in the observation group were lower than those in the control group (p<0.05), and the bone graft fusion rates at 3 and 6 months after operation were obviously superior to those in control group (p<0.05). Moreover, after operation, the spinal stenosis rate in the observation group was lower than that in control group (p<0.05), the vertebral height ratio was larger than that in control group (p<0.05), and the Cobb's angle was smaller than that in the control group (p<0.05). In addition, there was a negative correlation between bone mineral density (BMD) and hospitalization time after operation in the observation group (p<0.05). In conclusion, the internal fixation with expansive pedicle screw for osteoporosis patients with lumbar compression fracture is characterized by short operation time, less intraoperative bleeding, few complications, quick recovery of postoperative neurological function and satisfactory surgical effect. However, reasonable intervention in osteoporosis is also necessary.