Morphology analysis of the C2 pediculoisthmic component and feasibility of safe C2 pedicle screw placement: comparison of multiplanar reconstruction versus traditional radiographic methods

BACKGROUND

Preoperatively evaluating the feasibility of safe C2 pedicle screw placement is the key to avoiding iatrogenic vertebral artery injury. However, it has not been verified whether the conventional CT measurements of C2 pediculoisthmic component (PIC) are reliable and accurate, and the results may lack validity. The purpose of this study is to analyze the evaluative performance of conventional CT measurements and to create an accurate predictor of morphometrics of C2 PIC.

METHODS

A total of 304 C2 PICs were measured in 152 consecutive patients who underwent CT examination of the cervical spine between April 2020 and December 2020. We obtained the morphometric parameters of C2 PIC by measuring minimum PIC diameter (MPD) in CT multiplanar reconstruction versus conventional measurements of transverse PIC width (TPW), oblique PIC width (OPW) and definition of high-riding vertebral artery (HRVA). The outer diameter measured less than 4 mm in MPD was regarded as the standard of precluding safe C2 pedicle screw insertion. The evaluative performance of the conventional CT measurements was assessed, and the correlation between conventional CT measurements and measurements in CT multiplanar reconstruction was calculated.

RESULTS

The parameters in OPW and MPD were measured significantly larger than those in TPW, and the preclusion of C2 pedicle screw placement evaluated from TPW and HRVA was significantly higher than that evaluated from OPW and MPD. The sensitivity of TPW was 93.09%, and the specificity was 79.31%. The sensitivity and specificity of OPW were 97.82% and 82.76%. The sensitivity of HRVA was 88.36%, and the specificity was 96.55%. Strong agreement with the highest correlation coefficient (0.879) and determination coefficient (0.7720) suggested that the outer diameter of OPW could be useful for the precise prediction of MPD.

CONCLUSIONS

CT MPR allows accurate measurement of the narrowest section of the C2 PIC. The outer diameter of OPW could be simply measured and be useful for precise prediction of MPD, which makes C2 pedicle screw placement more safely than the conventional measurement of TPW and HRVA.

C2 pedicle screw placement on 3D-printed models for the performance assessment of CTA-based screw preclusion

BACKGROUND

3-D printing technology has a large spectrum of applications in upper cervical spinal surgery, but none have evaluated the radiological analysis of the feasibility of C2 pedicle screw placement. Thus, this study aimed to perform 3.5-mm-diameter C2 pedicle screw placement on models for performance assessment of CTA-based preoperative screw preclusion.

METHODS

We enrolled 152 patients who underwent CTA of the cervical spine between April 2020 and December 2020. Transverse pediculoisthmic width (TPW), oblique pediculoisthmic width (OPW), minimum pediculoisthmic diameter (MPD), internal height, and isthmus height were measured preoperatively. Subsequently, 1:1 3D-printed bone models were created, and a 3.5-mm-diameter C2 pedicle screw was placed on the models. All 3D-printed models underwent postoperative CT multiplanar reconstruction to evaluate the screw trajectory for the performance assessment of CTA-based preoperative screw preclusion.

RESULTS

The ROC curves of the MPD, TPW, OPW, Internal height and Isthmus height showed that the optimal cutoff values for each of the five groups were measured values of 4.78, 4.44, 4.37, 4.22 and 5.59 mm, respectively. The AUC, sensitivity, and specificity of MPD were 0.992, 95.1% and 100%, respectively. The MPD had higher metrics than the TPW (AUC, 0.949; sensitivity, 87.9%), internal height (AUC, 0.885; sensitivity, 80.8%; specificity, 84.6%), and isthmus height (AUC, 0.941; sensitivity, 87.2%). We found no evidence of a difference between MPD and OPW in terms of the AUC and sensitivity (0.93 and 95.5%, respectively).

CONCLUSIONS

C2 pedicle screw placement on 3D-printed models is useful for performance assessment of CTA-based preoperative screw preclusion. MPD measurement with CTA multiplanar reconstruction showed the best performance for judging acceptable or unacceptable screws. However, the definition of HRVA could be modified by a 4.2 mm-internal height or by measuring only the isthmus height for judging the preclusion of C2 pedicle screw placement.

Cervical 1-2 Posterior Instrumented Fusion Utilizing Computer-Assisted Navigation With Harvest of Rib Strut Autograft: 2-Dimensional Operative Video

Nonunion of a type II odontoid fracture after the placement of an anterior odontoid screw can occur despite careful patient selection. Countervailing factors to successful fusion include the vascular watershed zone between the odontoid process and body of C2 as well as the relatively low surface area available for fusion. Patient-specific factors include osteoporosis, advanced age, and poor fracture fragment apposition. Cervical 1-2 posterior instrumented fusion is indicated for symptomatic nonunion. The technique leverages the larger posterolateral surface area for fusion and does not rely on bony growth in a watershed zone. Although loss of up to half of cervical rotation is expected after C1-2 arthrodesis, this may be better tolerated in the elderly, who may have lower physical demands than younger patients. In this video, we discuss the case of a 75-yr-old woman presenting with intractable mechanical cervicalgia 7 mo after sustaining a type II odontoid fracture and undergoing anterior odontoid screw placement at an outside institution. Cervical radiography and computed tomography exhibited haloing around the screw and nonunion across the fracture. We demonstrate C1-2 posterior instrumented fusion with Goel-Harms technique (C1 lateral mass and C2 pedicle screws), utilizing computer-assisted navigation, and modified Sonntag technique with rib strut autograft. Posterior C1-2-instrumented fusion with rib strut autograft is an essential technique in the spine surgeon's armamentarium for the management of C1-2 instability, which can be a sequela of type II dens fracture. Detailed video demonstration has not been published to date. Appropriate patient consent was obtained.

Correlation between osteoarthritis of the atlantoaxial facet joint and a high-riding vertebral artery

BACKGROUND

A high-riding vertebral artery (HRVA) is an intraosseous anomaly that narrows the trajectory for C2 pedicle screws. The prevalence of a HRVA is high in patients who need surgery at the craniovertebral junction, but reports about HRVAs in subaxial cervical spine disorders are limited. We sought to determine the prevalence of HRVAs among patients with subaxial cervical spine disorders to elucidate the potential risk for VA injury in subaxial cervical spine surgery.

METHODS

We included 215 patients, 94 were with a main lesion from C3 to C7 (subaxial group) and 121 were with a main lesion from T1 to L5 (thoracolumbar group). A HRVA was defined as a maximum C2 pedicle diameter of < 3.5 mm on axial CT. The sex, age of patients, body mass index (BMI), osteoarthritis of the atlantoaxial (C1-2) facet joints, and prevalence of a HRVA in the 2 groups were compared and logistic regression was used to identify the factors correlated with a HRVA.

RESULTS

The patients in the subaxial group were younger than those in the thoracolumbar group, but their sex and BMI did not differ significantly between the 2 groups. The mean osteoarthritis grade of the C1-2 facet joints of patients in the subaxial group was significantly higher than that in those in the thoracolumbar group. A HRVA was found in 26 patients of 94 (27.7 %) in the subaxial group and in 19 of 121 (15.7 %) in the thoracolumbar group. The prevalence of a HRVA in the subaxial group was significantly higher and osteoarthritis of C1-2 facet joints correlated significantly with a HRVA.

CONCLUSIONS

The prevalence of a HRVA in patients with subaxial cervical spine disorders is higher than in those without and osteoarthritis of the C1-2 facet joints is correlated with a HRVA.

C2 partial transpedicular screw technique for atlantoaxial dislocation with high-riding vertebral artery: A technique note with case series

OBJECTIVE

Although the C2 pedicle screw (C2PS) is currently the most biomechanically robust option for C2 fixation, the high-riding vertebral artery (HRVA) precludes safe C2PS placement. However, unintentional partial C2 pedicle perforation and vertebral foramen violation due to C2PS placement without neurovascular complications occurred frequently in clinic. Therefore, we have attempted to apply C2 partial transpedicular screw (C2PTS) in patients with HRVA with satisfactory preliminary outcomes. The aim of the present study is to introduce the C2PTS technique and report the preliminary radiological and clinical outcomes of application of C2PTS.

PATIENTS AND METHODS

The data of 15 patients with atlantoaxial dislocation underwent atlantoaxial arthrodesis with posterior screw-rod construct were retrospectively reviewed. All patients had unilateral or bilateral HRVA that precluded safe C2PS placement and C2PTS was used as an alternative. In this technique, a Penfield dissector was used to properly mobilize the HRVA inferiorly to preclude vertebral artery injury and pave the way for C2PTS placement. The C2PTS travelled under the superior border of the isthmus and toward the ipsilateral atlantoaxial articulation. The implant position and atlantoaxial reduction were evaluated using computed tomography (CT) scans and vertebral artery (VA) was assessed using CT angiography postoperatively.

RESULTS

Satisfactory C2PTS placement and atlantoaxial reduction were achieved in all patients. Postoperatively, no vertebral artery injury and implant failure were observed, and bone fusion was achieved in all the patients. Additionally, there were no VA occlusion or stenosis due to screws demonstrated on VA CT angiography.

CONCLUSION

C2PTS can achieve three-column fixation of axis and is an efficient alternative to C2PS which is prohibited due to HRVA; also, gently mobilizing the HRVA inferiorly is mandatory to prevent vertebral artery injury during C2PTS placement.

Freehand C2 Pedicle Screw Placement: Surgical Anatomy and Operative Technique

We present a surgical video demonstrating the anatomy and technique of freehand C2 pedicle screw placement using a cadaveric specimen and 3-dimensional simulation software. C2 pedicle screws have been shown to augment cervical constructs and provide increased biomechanical stability compared with pars screws due to the increased length and bony purchase of pedicle screws within the pedicle and vertebral body.¹ The presence of vertebral artery variations within the transverse foramen may preclude pedicle screw placement, and these should be identified on preoperative imaging. The C2 pedicle can be directly palpated at the time of screw placement, which aids screw placement in cases of deformity or trauma. A freehand technique without the use of computed tomography scan guidance or intraoperative fluoroscopy decreases radiation exposure for the operator and patient and has been shown to be safe for patient-related outcomes.^2-5 Complete exposure of the C2 posterior elements is key to identifying the pedicle. The trajectory is based on direct visualization of the medial and superior pedicle borders to avoid lateral or inferior breaches into the transverse foramen. A curved probe is used for access into the vertebral body, respecting the outer cortical walls of the pedicle. The intraosseous position is confirmed with a ball-tipped probe. Fluoroscopy should be performed after screw placement to confirm proper position. By accomplishing proper exposure and understanding the anatomy of the C2 pedicle, the placement of C2 pedicle screws using a freehand technique is a safe and efficient technique for high cervical fixation.

Reoperation for Proximal Adjacent Segment Pathology in Posterior Cervical Fusion Constructs that Fuse to C2 vs C3

BACKGROUND

Few studies have described rates of proximal clinical adjacent segment pathology (CASP) after posterior cervical decompression and fusion (PCDF).

OBJECTIVE

To investigate rates of proximal CASP at C2 vs C3 in PCDFs for degenerative spine disease.

METHODS

A retrospective review of 380 cases of PCDF for degenerative disease with proximal constructs ending at C2 vs C3 was performed. Minimum follow-up was 12 mo. The primary outcome was proximal CASP requiring reoperation. Variable analysis included demographic, operative, and complication data.

RESULTS

There were 119 patients in the C2 group and 261 in the C3 group with no significant differences in age, gender, comorbidities, presenting symptoms, or complications. Vertebral artery injury rates were 0.8% in the C2 group and 0.0% in the C3 group (P = .12). No patients in the C2 group had reoperation for proximal CASP, while 5.0% of patients in the C3 group did (P = .01). Patients with arthrodesis up to C3 had an increased risk of proximal failure when the fusion construct crossed the cervicothoracic junction (P = .03). Multivariate logistic regression analysis showed no factors that were independently associated with re-instrumentation for proximal CASP.

CONCLUSION

Instrumenting to the C2 level reduces the risk for proximal CASP compared to fusion only up to C3. The type of instrumentation used at these 2 levels, form of ASP disease at C1-C2, and natural motion of the relevant proximal adjacent joint may contribute to this difference. Furthermore, within the C3 cohort, fusion across the cervicothoracic junction increased the risk for proximal CASP.

Posterior C2 Fixation Using Trans-C2 Inferior Articular Process Screws: A Case Series and Technical Note

OBJECTIVE

Upper cervical fixation with C2 pedicle screw insertion may predispose patients to vertebral artery injury, in particular, patients with craniovertebral junction anomalies. The aim of this study was to describe an alternative technique with trans-C2 inferior articular process screw (C2IAPS) insertion for rigid C2 fixation, which can be used to anchor the C2 vertebra for upper cervical fixation.

METHODS

Records of 19 patients who underwent posterior atlantoaxial fixation using C2IAPS combined with C1 lateral mass screw were retrospectively reviewed. Efficacy was assessed by postoperative imaging and Japanese Orthopaedic Association scores.

RESULTS

There were 22 C2IAPSs successfully implanted (3 on both sides and 16 on 1 side). With the exception of 2 screws that had intruded into the outlet of the intervertebral foramen, all screws were safely implanted. Average Japanese Orthopaedic Association scores improved from 11.8 ± 1.9 preoperatively to 15.3 ± 1.3 postoperatively. Bony fusion rate was 100%.

CONCLUSIONS

For patients who are not eligible for C2 pedicle screw fixation, C2IAPS fixation can be considered as an alternative technique for upper cervical fixation of C2.

Can the position of the vertebral artery be predicted on a lateral view X-ray of the craniovertebral junction? A radiological anatomy study

Background

The most feared complication while inserting C2 screws is vertebral artery injury. This article proposes predicting the position of the vertebral artery on a true lateral X-ray of the axis vertebra from the background information acquired from the computed tomography (CT) scan utilizing fluoroscopy.

Methods

Spiral CT scans of 33 C2 vertebrae were performed utilizing a 16-slice CT scanner lateral X-rays of C2 were then obtained before and after painting the vertebral artery grooves with barium. The space available for transarticular and C2 pedicle screw insertion above the vertebral artery groove in the isthmus was then calculated as a ratio for both X-rays and CT scans.

Results

There was no statistically significant difference between the (mean) ratios calculated by CT scan and X-rays regarding the space available for transarticular and C2 pedicle screw insertion (left side: 0.3894 vs 0.3897; right side: 0.3892 vs 0.3925; P > 0.05). The Kappa test revealed that CT scan and X-ray findings were in agreement in majority of the bones (left side: n = 24, 72.7%, right side: n = 22, 73.3%; P < 0.05).

Conclusion

A thorough understanding of a true lateral view X-ray based on background information extracted from three dimensional CT scans helps predict the highest point of the vertebral artery groove. This proves useful for placement of C2 transarticular and pedicle screws during regular "open" and "minimally invasive" spine surgery.

Freehand technique for C2 pedicle and pars screw placement: is it safe?

BACKGROUND CONTEXT

During placement of C2 pedicle and pars screws, intraoperative fluoroscopy is used so that neurovascular complications can be avoided, and screws can be placed in the proper position. However, this method is time consuming and increases radiation exposure. Furthermore, it does not guarantee a completely safe and accurate screw placement.

PURPOSE

The objective of this study was to evaluate the safety of the C2 pedicle and pars screw placement without fluoroscopic or other guidance methods.

STUDY DESIGN

This is a retrospective comparative study.

PATIENT SAMPLE

One hundred ninety-eight patients who underwent placement of C2 pedicle or pars screws without any intraoperative radiographic guidance were included in the study.

OUTCOME MEASURES

Medical records and postoperative computed tomography (CT) scans were evaluated.

MATERIALS AND METHODS

Clinical data were reviewed for intraoperative and postoperative complications. The accuracy of screw placement was evaluated with postop CT scans using a previously published cortical-breach grading system (described by the location and the percentage of the screw diameter over the cortical edge [0=none, Grade I≤25% of the screw diameter, Grade II=26%-50%, Grade III=51%-75%, and Grade IV=76%-100%]).

RESULTS

A total of 148 pedicle screws and 219 pars screws were inserted by two experienced surgeons. There were no cases of cerebral spinal fluid leakage and no neurovascular complications during screw placement. Postoperative CT scans were available for 76 patients, which included 52 pedicle screws and 87 pars screws. For cases with C2 pedicle screws, there were 12 breaches (23%); these included 10 screws with a Grade I breach (19%), 1 screw with a Grade II breach (2%), and 1 screw with a Grade IV breach (2%). Lateral breaches occurred in seven screws (13%), inferior breaches occurred in three screws (6%), and superior breaches occurred in two screws (4%). For cases with C2 pars screws, there were 10 breaches (11%); these included 6 screws with a Grade I breach (7%), 2 screws with a Grade II breach (2%), and 2 screws with a Grade IV breach (2%). Medial breaches were found in four (5%), lateral breaches in two (2%), inferior breaches in two (2%), and superior breaches in two (2%). Two of the cases with superior breaches (one for pedicle and one for pars) experienced occipital neuralgia months after surgery. There was no statistically significant difference in the incidence of overall and high-grade breaches between the groups (p=.07 and 1.0, respectively).

CONCLUSIONS

Although even in experienced hands up to 23% of C2 pedicle screws and 11% of C2 pars screws placed using a freehand technique without guidance may be malpositioned, a clear majority of malpositioned screws demonstrated a low-grade breach, and only 2 of 198 patients (1%) experienced complications related to screw placement.

Contusional Cerebellar Hemorrhage Related to Placement in the Protrusion Position After Atlantoaxial Fusion

BACKGROUND

Various complications after C1 lateral mass and C2 pedicle screw fusion surgery (C1LM-C2PSFS) have been reported. However, to our knowledge, this is the first report of contusional cerebellar hemorrhage caused by placement in the protrusion (chin-out) position after C1LM-2PSFS.

CASE DESCRIPTION

An 81-year-old woman complaining of gait disturbance and clumsiness of both hands was diagnosed with cervical myelopathy with atlantoaxial subluxation. After we performed C1LM-C2PSFS, her neurologic deficits gradually improved, and there was no radiologic evidence of construct failure. One month after surgery, she had severe headache and vomiting immediately after taking some medications while in the protrusion position. Head computerized tomography scan showed left cerebellar hemorrhage, and titanium rods penetrated the occipital bone on both sides. Flexion/extension radiography showed no loosening of any screws or rods. However, protrusion radiography showed that the tip of the left titanium rod intruded into the intracranial region. We considered that the penetration of the occipital bone by the left titanium rod caused the contusional left cerebellar hemorrhage. We immediately performed revision surgery to replace the titanium rods on each side with shorter rods, and no cerebrospinal fluid leakage was observed. The headache disappeared after the revision surgery.

CONCLUSIONS

We report a case of contusional cerebellar hemorrhage caused by the intrusion of a rod into the occipital bone when the patient was placed in the protrusion position. The rod length on the cranial side must be as short as possible, with careful consideration of placing the head in the protrusion position after C1LM-2PSFS surgery.

Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws

BACKGROUND CONTEXT

To our knowledge, no large series comparing the risk of vertebral artery injury by C1-C2 transarticular screw versus C2 pedicle screw have been published. In addition, no comparative studies have been performed on those with a high-riding vertebral artery and/or a narrow pedicle who are thought to be at higher risk than those with normal anatomy.

PURPOSE

To compare the risk of vertebral artery injury by C1-C2 transarticular screw versus C2 pedicle screw in an overall patient population and subsets of patients with a high-riding vertebral artery and a narrow pedicle using computed tomography (CT) scan images and three-dimensional (3D) screw trajectory software.

STUDY DESIGN

Radiographic analysis using CT scans.

PATIENT SAMPLE

Computed tomography scans of 269 consecutive patients, for a total of 538 potential screw insertion sites for each type of screw.

OUTCOME MEASURES

Cortical perforation into the vertebral artery groove of C2 by a screw.

METHODS

We simulated the placement of 4.0 mm transarticular and pedicle screws using 1-mm-sliced CT scans and 3D screw trajectory software. We then compared the frequency of C2 vertebral artery groove violation by the two different fixation methods. This was done in the overall patient population, in the subset of those with a high-riding vertebral artery (defined as an isthmus height ≤ 5 mm or internal height ≤ 2 mm on sagittal images) and with a narrow pedicle (defined as a pedicle width ≤ 4 mm on axial images).

RESULTS

There were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%). Most (82%) of the narrow pedicles had a concurrent high-riding vertebral artery, whereas only 54% of the high-riding vertebral arteries had a concurrent narrow pedicle. Overall, 9.5% of transarticular and 8.0% of pedicle screws violated the C2 vertebral artery groove without a significant difference between the two types of screws (p=.17). Among those with a high-riding vertebral artery, vertebral artery groove violation was significantly lower (p=.02) with pedicle (49%) than with transarticular (63%) screws. Among those with a narrow pedicle, vertebral artery groove violation was high in both groups (71% with transarticular and 76% with pedicle screws) but without a significant difference between the two groups (p=.55).

CONCLUSIONS

Overall, neither technique has more inherent anatomic risk of vertebral artery injury. However, in the presence of a high-riding vertebral artery, placement of a pedicle screw is significantly safer than the placement of a transarticular screw. Narrow pedicles, which might be anticipated to lead to higher risk for a pedicle screw than a transarticular screw, did not result in a significant difference because most patients (82%) with narrow pedicles had a concurrent high-riding vertebral artery that also increased the risk with a transarticular screw. Except in case of a high-riding vertebral artery, our results suggest that the surgeon can opt for either technique and expect similar anatomic risks of vertebral artery injury.

Determining optimal c2 pedicle screw placement and length in patients with axis traumatic spondylolisthesis: a case series

We sought to determine the optimal placement and screw length for C2 pedicle screw fixation to compare with recommendations in literature. Nine patients were included in this study and underwent C2 pedicle instrumentation either for a hangman's fracture as part of C2 pedicle-C3 lateral mass fixation or for C2-C3 subluxation. All nine patients had good postoperative improvement with satisfactory fracture consolidation. Mediolateral and rostrocaudal angulations of the inserted screws were not consistent with the traditional angulations of 20 degrees in each plane due to the fracture lines and the anatomical variations. Because the frequent observation of the bony anatomical variations and the lines of fractures brought about by trauma, a shift from the classic 20 degrees of angulation in both trajectories has been concluded. But still fixed angles of angulations cannot be generalized. As a consequence, accurate preoperative planning can be obtained by computed tomography with three-dimensional images so that it gives the surgeon a good prediction of the best length of utilized screws in the procedure and the best angulations for safety of the neighboring neurovascular structures.

Inferolateral entry point for c2 pedicle screw fixation in high cervical lesions

OBJECTIVE

The purpose of this retrospective study was to evaluate the efficacy and safety of atlantoaxial stabilization using a new entry point for C2 pedicle screw fixation.

METHODS

Data were collected from 44 patients undergoing posterior C1 lateral mass screw and C2 screw fixation. The 20 cases were approached by the Harms entry point, 21 by the inferolateral point, and three by pars screw. The new inferolateral entry point of the C2 pedicle was located about 3-5 mm medial to the lateral border of the C2 lateral mass and 5-7 mm superior to the inferior border of the C2-3 facet joint. The screw was inserted at an angle 30° to 45° toward the midline in the transverse plane and 40° to 50° cephalad in the sagittal plane. Patients received followed-up with clinical examinations, radiographs and/or CT scans.

RESULTS

There were 28 males and 16 females. No neurological deterioration or vertebral artery injuries were observed. Five cases showed malpositioned screws (2.84%), with four of the screws showing cortical breaches of the transverse foramen. There were no clinical consequences for these five patients. One screw in the C1 lateral mass had a medial cortical breach. None of the screws were malpositioned in patients treated using the new entry point. There was a significant relationship between two group (p=0.036).

CONCLUSION

Posterior C1-2 screw fixation can be performed safely using the new inferolateral entry point for C2 pedicle screw fixation for the treatment of high cervical lesions.