Evaluation of cervical posterior lateral mass screw placement by oblique radiographs

The Impact of Single-Level ACDF on Neural Foramen and Disc Height of Surgical and Adjacent Cervical Segments: A Case-Series Radiological Analysis

Background: ACDF has become one of the established procedures for the surgical treatment of symptomatic cervical spondylosis, showing excellent clinical results and effective improvements in neural functions and neck pain relief. The main purpose of ACDF is neural decompression, and it is considered by some authors as an indirect result of the intervertebral distraction and cage insertion and the consequent restoration of the disc space and foramen height. Methods: Radiological data from 28 patients who underwent single-level ACDF were retrospectively collected and evaluated. For neural foramen evaluation, antero-posterior (A-P) and cranio-caudal (C-C) diameters were manually calculated; for intervertebral disc height the anterior, centrum and posterior measurement were calculated. All measurements were performed at surgical and adjacent (above and below) segments. NRS, NDI and also the mJOA and Nurick scale were collected for clinical examination and complete evaluation of patients’ postoperative outcome. Results: The intervertebral disc height in all its measurements, in addition to the height (C-C diameter) of the foramen (both right and left) increase at the surgical segment when comparing pre and postop results (p < 0.001, and p = 0.033 and p = 0.001). NRS and NDI radiculopathy scores showed improved results from pre- to post-op evaluation (p < 0.001), and a negative statistical correlation with the improved disc height at the surgical level. Conclusions: The restoration of posterior disc height through cage insertion appears to be effective in increasing foraminal height in patients with symptomatic preoperative cervical foraminal stenosis.

Predictive Effect of Intervertebral Foramen Width on Pain Relief After ACDF for the Treatment of Cervical Radiculopathy

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To investigate the relationship between the preoperative width of the intervertebral foramen (WIVF) and the pain relief in patients who underwent anterior cervical discectomy and fusion (ACDF) for the treatment of cervical radiculopathy.

METHODS

Patients were divided into 2 groups based on pain relief status at the 6-month follow-up (pain relief group: 430 patients; persistent pain group: 108 patients). Possible factors such as age, sex, body mass index (BMI), the symptom duration, the preoperative Japanese Orthopedic Association (JOA) scores, the canal stenosis status, and the graft material were obtained. The C2-C7 Cobb angle, disc space, and width and height of the intervertebral foramen were measured on X-ray and CT 3-dimension reconstruction. Multivariate logistic regression was performed to identify the factors that affected pain relief. A receiver operating characteristic (ROC) curve was drawn for the predictive factors to determine the optimal threshold for foreseeing persistent pain.

RESULTS

There were significant differences in the preoperative WIVF, symptom duration and ratio of disc space distraction between the 2 groups (each P < 0.05). The regression model showed that pain relief was negatively affected by the symptom duration and ratio of disc space distraction. Besides, an increase in the preoperative width of the intervertebral foramen (WIVF) could significantly decrease the possibility of persistent pain. Based on the ROC curve, the optimal threshold of preoperative WIVF was 4.35 mm.

CONCLUSION

When the preoperative WIVF is equal to or less than 4.35 mm, the possibility of the occurrence of postoperative persistent pain significantly increased.

Is It "In" or "Out"? The Optimal Fluoroscopic Views for Intraoperative Determination of Proper Lateral Mass Screw Placement

STUDY DESIGN

Cadaveric.

OBJECTIVE

Determine optimal fluoroscopic views for detecting cervical lateral mass screw (LMS) violations.

SUMMARY OF BACKGROUND DATA

Single plane intraoperative x-rays are commonly used but frequently inadequate due to its complex trajectory. Fluoroscopy can be taken in multiple planes, but the ideal fluoroscopic view to assess malposition is not known: depending on the view, any given screw may look "in" or "out."

METHODS

C3-6 LMS were inserted in three cadavers. To evaluate neuroforaminal violation, LMS were inserted into the foramen with the tip penetrating the anterior cortex by 0, 2, and 4 mm. To assess facet joint violation, LMS were inserted toward the subjacent facet joint with the tip penetrating the anterior cortex by 0 and 2 mm. Fluoroscopic views were taken 0°, 10°, 20°, 30°, and 40° to the lateral plane. Views were independently evaluated by three blinded spine surgeons.

RESULTS

Twenty-degree oblique view correctly identified a 2 mm penetration into the neuroforamen in 79%, and a 4 mm penetration in 86%, for a sensitivity of 83% and specificity of 90%. Thirty-degree view had lower sensitivity (76%) but slightly higher specificity (93%). Twenty-degree and 30° views were significantly more sensitive than the other views. Zero-degree view correctly identified a 2 mm penetration into the facet joint in 93%, for a sensitivity of 93% and specificity of 92%. Ten-degree view had lower sensitivity (72%) but higher specificity (100%). The 0° view was significantly more sensitive than the other views.

CONCLUSION

Twenty-degree and 30° oblique views significantly provided the most sensitive assessment of LMS potentially violating the neuroforamen, whereas the 0° neutral lateral view significantly provided the most sensitive assessment of facet violations. The specificities were also high (in the 90% range) for these views. We recommend the use of these views intraoperatively when assessing proper placement of LMS fluoroscopically.

LEVEL OF EVIDENCE

N/A.

Lateral radiological evaluation of transarticular screw placement in the lower cervical spine

This study assessed the ideal district of lateral radiograph in evaluation of transarticular screw placement in the lower cervical spine. To assess the ideal zone of lateral radiographs in determining the safe or hazardous locations of the screw tips during transarticular screw implantation in the lower cervical spine. Transarticular screw in the lower cervical spine had been used as an alternative technique to achieve posterior cervical spine stability. Injury to the spinal nerves caused by transarticular screws which are too long must be identified quickly to minimize the neurologic complication. No previous radiological study regarding evaluation of the transarticular screw placement using lateral radiographs has been reported. Twelve cervical spines were removed from embalmed cadavers. Four transarticular screw placements with Dalcanto's technique under direct visualization, including placement of the screw tip staying the ventral cortex, 2, 4 and 6 mm over-penetration of the ventral cortex, were performed on each specimen. Following each placement, a lateral radiograph was taken. Each vertebral body was divided vertically into four equal zones, and another equal zone posterior to the posterior border of the vertebral body was defined as Zone pre-1. The numbers of screw tips seen in each zone were quantified for each placement. Partitions of chi (2) method was used to evaluate the ideal zone on lateral radiograph for transarticular screw insertion. At C34 and C45, no significant difference was found between Zone pre-1 and Zone 1 (chi(2) = 0.18, P > 0.50), while there was significant difference between Zones 1 and 2 (chi(2) = 73.6, P < 0.005), as well as Zones 2 and 3 (chi(2) = 13.2, P < 0.005). At C56 and C67, No significant difference was found between Zones 2 and 3 (chi(2) = 0.25, P > 0.50), while there was significant difference between Zone pre-1 and Zone 1 (chi(2) = 66.2, P < 0.005), as well as Zones 1 and 2 (chi(2) = 10.5, P < 0.005). Ideal screw tip positions on lateral radiograph for transarticular screw by Dalcanto's technique should be in Zone 1 at C34 and C45, in Zone pre-1 at C56 and C67. If the screw tip was in Zones 3 and 4, the safe rate will be decreased significantly and it might be too deep and be dangerous.

Anatomic study of the morphology of human cervical facet joint

STUDY DESIGN

Geometrical properties of the facet joint including cartilage thickness and gap were obtained using human cadaver cervical spinal columns and cryomicrotomy techniques.

OBJECTIVES

To determine the existence of level or gender dependency on facet joint morphology in the human cervical spine.

BACKGROUND DATA

Although measurements of the human cervical spine have been reported in literature, to the best of knowledge of the authors, geometrical data on the facet joint structures such as the cartilage are not available. These data are important to understand the anatomy of the cervical spine and the role of the cartilage in sharing the external load during physiologic and traumatic situations. Furthermore, the data will assist mathematical modelers to accurately simulate this component of the cervical facet joint in finite element analysis of the spine.

MATERIALS AND METHODS

Six unembalmed human cadaver cervical spinal columns were used. A heavy-duty cryomicrotome was used to obtain the geometrical characteristics. The specimens were sectioned in the sagittal plane at 20- to 40-microm intervals. Geometric properties of the facet joint width, cartilage thickness, and cartilage gap (defined as the distance from the ventral-most or dorsal-most region of the facet joint to the location where the cartilage began to appear) were extracted from the anatomic sections that were midsagittal with respect to the facet joints from occiput to T1 levels. Multiple factorial analysis of variance techniques were used to determine the statistical significance of various geometrical parameters obtained from the anatomic sections.

RESULTS

The cartilage gap in the upper cervical spine (UCS) (C1-C2, i.e., UCS, 5.4% +/- 0.8) was lower (P < 0.0001) than the gap in the lower cervical spine (LCS) (C3-C7, i.e., LCS, 16.4% +/- 0.8). The gap at the ventral and dorsal regions was lower in the UCS (ventral 3.8% +/- 0.6, dorsal 7.0% +/- 1.4) than in the LCS (ventral 18.5% +/- 0.9, dorsal 14.2% +/- 1.1) with p values of less than 0.0001 and equal to 0.0004, respectively. Further, the gap in the dorsal region for females (14.7% +/- 1.8) was greater (P = 0.0523) than the gap for males (10.8% +/- 1.1). The overall mean facet cartilage thickness was lower (P = 0.0111) in females (0.6 mm +/- 0.1) than males (0.9 mm +/- 0.2) in the UCS. It was also lower (P = 0.0077) in females (0.4 mm +/- 0.02) than males (0.5 mm +/- 0.03) in the LCS. The facet joint width demonstrated differences only between the UCS and LCS (P < 0.0001), with higher magnitudes in the upper (17.4 mm +/- 0.4) than in the lower (11.3 mm +/- 0.3) region.

CONCLUSIONS

Facet joint morphology varies with the regions of the cervical spine (upper vs. lower), gender (male vs. female), and location (dorsal vs. ventral). Because of the lack of intervertebral discs in the UCS region, variations in these geometrical characteristics affect the biomechanical behaviors of the human spine secondary to external loads. Furthermore, the lack of adequate cartilage in females may expose the underlying adjacent subchondral bone to direct stresses during normal physiologic and traumatic loads.

Characteristics of unicortical and bicortical lateral mass screws in the cervical spine

STUDY DESIGN

A biomechanical study evaluating the safety and efficacy of unicortical versus bicortical lateral mass screws in the cervical spine.

OBJECTIVES

To analyze the safety, pullout strength and radiographic characteristics of unicortical and bicortical screws placed in cadaveric spines and to evaluate the influence of level of training on the positioning of these screws.

SUMMARY OF BACKGROUND DATA

Lateral mass plating for posterior cervical spine fusion is an effective method for the treatment of traumatic and degenerative instability. The initial description of the technique included bicortical screw purchase. The added benefit of bicortical purchase must be weighed against the increased risk of injury to nerve roots and the vertebral artery.

METHODS

In 21 cadaveric spines (mean age 78.9 years), 3.5-mm anterior oblique lateral mass screws were placed bilaterally from C3 to C6 (n = 168) using a modification of the Magerl technique. In the right side (unicortical) only 14-mm screws (effective length of 11 mm) were used, whereas on the left side, bicortical purchase was obtained. All screws were evaluated clinically and radiographically for safety and zone placement. Pullout force was determined for all screws.

RESULTS

Most screws (92.8%) were rated satisfactory. There were no injuries to the spinal cord. On the right side (14 mm) 98.9% of the screws were satisfactory, and on the left side (bicortical) 68.1% were satisfactory. There was a 5.8% incidence of direct artery injury (compression of vessel wall) and a 17.4% incidence of direct nerve root injury by the bicortical screws. There were no direct injuries with the unicortical screws. Most of the direct-injury bicortical screws were placed by the surgeon with the least experience. The mean pullout force for all screws was 542.9 +/- 296.6 N. There was no statistically significant difference between the pullout force for unicortical (519.9 +/- 286.9 N) and bicortical (565.2 +/- 306 N) screws (P < 0.05). There were no significant differences in pullout strengths in association with zone placement.

CONCLUSIONS

Fourteen-millimeter lateral mass screws (effective length, 11 mm) placed in a superolateral trajectory in the adult cervical spine provide an equivalent strength with a much lower risk of injury than the longer bicortical screws placed in a similar orientation.

Lateral radiologic evaluation of lateral mass screw placement in the cervical spine

STUDY DESIGN

Assessment of the value of lateral radiographs in evaluation of lateral mass screw placement in the cervical spine.

OBJECTIVES

To assess the value of lateral radiographs in determining the safe or hazardous locations of the tips of screws used in lateral mass screw fixation.

SUMMARY OF BACKGROUND DATA

Posterior plating with lateral mass screw fixation is frequently used to stabilize the cervical spine and improve fusion. Injury to the spinal nerves caused by screws that are too long must be identified quickly to minimize neurologic complication. No previous radiologic study in which lateral mass screw placement was evaluated using lateral radiographs has been reported.

METHODS

Six cervical spines were removed from embalmed cadavers. Three screws using the Roy-Camille technique and another three using Magerl technique were placed into the lateral mass at C3-C5 in each specimen. Four screw placements under direct visualization, including placement of the screw tip staying the ventral cortex and 2-mm, 4-mm, and 6-mm overpenetration of the ventral cortex, were performed separately on each specimen for each of the two techniques. After each placement, a lateral radiograph was taken. Each vertebral body was divided vertically into four equal zones with Zone I the most posterior. Another equal zone, posterior to the posterior border of the vertebral body was defined as pre-Zone I. The number of screw tips seen in each zone were quantified for each placement.

RESULTS

In the screws placed using the Roy-Camille technique, 77.8% of screws placed without perforating the ventral cortex were found in Zone I; 72.2% placed with 2-mm overpenetration of the ventral cortex were noted in Zone II; and 61.1% of the screws with 4-mm overpenetration of ventral cortex and 77.8% with 6-mm overpenetration were located in Zone III. For the use of the Magerl technique, 44.4% of the screws placed without perforating the ventral cortex were found in pre-Zone I; 72.2% of the screws placed with 2-mm overpenetration were located in Zone I; and 66.6% with 4-mm overpenetration and 89.7% with 6-mm overpenetration were noted in Zones I and II, respectively.

CONCLUSIONS

Lateral radiographs may be valuable in evaluating lateral mass screw placement. Ideal screw tip positions on lateral radiograph for the Roy-Camille technique may be in Zone I, and for the Magerl technique may be in pre-Zone I.