The C2 Pedicle Width, Pars Length, and Laminar Thickness in Concurrent Ipsilateral Ponticulus Posticus and High-Riding Vertebral Artery: A Radiological Computed Tomography Scan-Based Study

STUDY DESIGN: Retrospective radiological study. PURPOSE: We aimed to determine the prevalence of ponticulus posticus (PP) and high-riding vertebral artery (HRVA) occurring simultaneously on the same side (PP+HRVA) and in cases of PP+HRVA, to assess C2 radio-anatomical measurements for C2 pars length, pedicle width, and laminar thickness. OVERVIEW OF LITERATURE: PP and HRVA predispose individuals to vertebral artery injuries during atlantoaxial fixation. In cases of PP+HRVA, the construct options thus become limited. METHODS: Consecutive computed tomography scans (n=210) were reviewed for PP and HRVA (defined as an internal height of <2 mm and an isthmus height of <5 mm). In scans with PP+HRVA, we measured the ipsilateral pedicle width, pars length, and laminar thickness and compared them with controls (those without PP or HRVA). RESULTS: PP was present in 14.76% and HRVA in 20% of scans. Of the 420 sides in 210 scans, PP+HRVA was present on 13 sides (seven right and six left). In scans with PP+HRVA, the C2 pars length was shorter compared with controls (13.69 mm in PP+HRVA vs. 20.65 mm in controls, p<0.001). The mean C2 pedicle width was 2.53 mm in scans with PP+HRVA vs. 5.83 mm in controls (p<0.001). The mean laminar thickness was 4.92 and 5.48 mm in scans with PP+HRVA and controls, respectively (p=0.209). CONCLUSIONS: The prevalence of PP+HRVA was approximately 3% in the present study. Our data suggest that, in such situations, C2 pedicle width and pars length create important safety limitations for a proposed screw, whereas the translaminar thickness appears safe for a proposed screw.

Surgical Morphometry of C1 and C2 Vertebrae: A Three-Dimensional Computed Tomography Analysis of 180 Chinese, Indian, and Malay Patients

STUDY DESIGN: Clinical imaging study. PURPOSE: To study the surgical morphometry of C1 and C2 vertebrae in Chinese, Indian, and Malay patients. OVERVIEW OF LITERATURE: C1 lateral mass and C2 pedicle screw fixation is gaining popularity. However, there is a lack of C1–C2 morphometric data for the Asian population. METHODS: Computed tomography analysis of 180 subjects (60 subjects each belonging to Chinese, Indian, and Malay populations) using simulation software was performed. Length and angulations of C1 lateral mass (C1LM) and C2 pedicle (C2P) screws were assessed. RESULTS: The predicted C1LM screw length was between 23.2 and 30.2 mm. The safe zone of trajectories was within 11.0°±7.7° laterally to 29.1°±6.2° medially in the axial plane and 37.0°±10.2° caudally to 20.9°±7.8° cephalically in the sagittal plane. The shortest and longest predicted C2P screw lengths were 22.1±2.8 mm and 28.5±3.2 mm, respectively. The safe trajectories were from 25.1° to 39.3° medially in the axial plane and 32.3° to 45.9° cephalically in the sagittal plane. CONCLUSIONS: C1LM screw length was 23–30 mm with the axial safe zone from 11° laterally to 29° medially and sagittal safe zone at 21° cephalically. C2P screw length was 22–28 mm with axial safe zone from 26° to 40° medially and sagittal safe zone from 32° to 46° cephalically. These data serve as an important reference for Chinese, Indian, and Malay populations during C1–C2 instrumentation.

Prevalence of High-Riding Vertebral Artery and Morphometry of C2 Pedicles Using a Novel Computed Tomography Reconstruction Technique

STUDY DESIGN: Cross-sectional, matched-pair comparative study. PURPOSE: To determine whether a thin-sliced pedicular-oriented computed tomography (TPCT) scan reconstructed from an existing conventional computed tomography (CCT) scan is more accurate for identifying vertebral artery groove (VAG) anomalies than CCT. OVERVIEW OF LITERATURE: Posterior atlantoaxial transarticular screw fixation and C2 pedicle screws can cause vertebral artery (VA) injury. Two anatomic variations of VAG anomalies are associated with VA injury: a high-riding VA (HRVA) and a narrow pedicle of the C2 vertebra. CCT scan is a reliable method used to evaluate VAG anomalies; however, its accuracy level remains debatable. Literature comparing the prevalence of C2 VAG anomalies between CCT and TPCT is limited. METHODS: A total of 200 computed tomography scans of the upper cervical spine obtained between January 2008 and December 2011 were evaluated for C2 VAG anomalies (HRVA and narrow pedicular width) using CCT and TPCT. The prevalence of C2 VAG anomalies was compared using these two different measurement methods via a McNemar's test. RESULTS: Of the 200 patients studied, 23 HRVA (6.01%; 95% confidence interval [CI], 3.61%–8.39%) were detected with CCT, whereas 66 HRVA (16.54%; 95% CI, 12.85%–20.23%) were detected with TPCT (p<0.001). Sixty-two narrow pedicles (15.58%; 95% CI, 11.99%–19.15%) were detected with CCT, whereas 90 narrow pedicles (22.83%; 95% CI, 18.58%–26.87%) were detected with TPCT (p<0.001). CONCLUSIONS: VAG anomalies are commonly observed. A preoperative evaluation using TPCT reconstructed from an existing CCT revealed a significantly higher prevalence of C2 VAG anomalies than did CCT and showed comparable prevalence to previously published studies using more sophisticated and higher risk techniques. Therefore, we propose TPCT as an alternative preoperative evaluation for C2 screw placement and trajectory planning.

Posterior Atlantoaxial Fixation with a Combination of Pedicle Screws and a Laminar Screw in the Axis for a Unilateral High-riding Vertebral Artery

A vertebral artery (VA) injury presents a difficult problem in atlantoaxial fixation. Recent technical reports described posterior C2 fixation using bilateral, crossing C2 laminar screws. The translaminar screw technique has the advantages of producing little risk of VA injury and the unconstrained screw placement. In addition, biomechanical studies have demonstrated the potential of the translaminar screw technique to provide a firmer construct that is equivalent to methods currently used. We report the successful treatment of C1-2 instability with a left-side high-riding VA. Because of the potential risk of VA injury, we performed a posterior C1-2 fixation with a combination of pedicle screws and a laminar screw in C2. We first placed bilateral C1 lateral mass screws and a right-side C2 pedicle screw. However, placement of the left- side C2 pedicle screw was technically difficult due to a narrow isthmus and pedicle. A laminar screw was inserted instead and authors believe that this posterior C1-C2 fixation with a combination of pedicle screws and a laminar screw in C2 can be a useful alternative technique for the treatment of C1-C2 instability in the presence of a unilateral high-riding VA.

Analysis of the Rate of High Riding Vertebral Artery Using Sagittal Reformatted Computed Tomography / 대한정형외과학회잡지

PURPOSE: The rate of high riding vertebral artery (VA) was investigated, and the rate in rheumatoid arthritis (RA) group was compared with that in non-RA group. MATERIALS AND METHODS: 67 consecutive patients were recruited. The male to female ratio was 44: 23. Sixteen patients were diagnosed as RA and 51 as cervical spondylosis. Sagittal reformatted view transecting mid-portion of the atlantoaxial facet joint was obtained and the height of the isthmus and the internal height of the axis were measured using a Picture Archiving and Communication System (PACS). High riding VA was defined as less than 5 mm of isthmus height or less than 2 mm of internal height. RESULTS: Thirty-six joints (26.9%) and twenty-seven patients (40.3%) showed high riding VA, and there was no significant difference between right and left side (8 right, 10 left, 9 both sides) (p=0.20). There was no difference among age distribution (p=0.06). In rheumatoid patients, the rate of high riding VA (10/16, 62.5%) was higher than in non-rheumatoid patients 17/51, 33.3%) (p=0.04). CONCLUSION: Preoperative evaluation of the VA using the reformatted CT should be performed in all patients who plan to undergo atlantoaxial transarticular screw fixation. In rheumatoid patients, possibility of high riding VA should always be considered.

Atlantoaxial Fixation using Rod and Screw for Bilateral High-riding Vertebral Artery

We report a case of atlantoaxial subluxation with bilateral high-riding vertebral artery with narrow isthmus. Because of the potential risk of bilateral vertebral artery injury, we performed atlantoaxial fixation using rod and screw instead of transarticular screw fixation. Although postoperative computed tomography reconstruction demonstrated slight breach of bilateral vertebral artery groove, postoperative angiography showed no evidence of vertebral artery injury. Though technically demanding, atlantoaxial fixation using rod and screw can be a one of the treatment options for atlantoaxial instability with bilateral high riding vertebral artery.