Computed tomographic evaluation of the normal adult odontoid. Implications for internal fixation

Biomechanical comparison of two different compression screws for the treatment of odontoid fractures in human dens axis specimen

BACKGROUND

Lag screw osteosynthesis for odontoid fractures has a high rate of pseudoarthrosis, especially in elderly patients. Besides biomechanical properties of the different screw types, insufficient fragment compression or unnoticed screw stripping may be the main causing factors for this adverse event. The aim of the study was to compare two screws in clinical use with different design principles in terms of compression force and stability against screw stripping.

METHODS

Twelve human cadaveric C2 vertebral bodies were considered. Bone density was determined. The specimens were matched according to bone density and randomly assigned to two experimental groups. An odontoid fracture was induced, which were fixed either with a 3.5 mm standard compression screw or with a 5 mm sleeve nut screw. Both screws are certified for the treatment of odontoid fractures. The bone samples were fixed in a measuring device. The screwdriver was driven mechanically. The tests were analyzed for peak interfragmentary compression and screw-in torque with a frequency of 20 Hz.

FINDINGS

The maximum fragment compression was significantly higher with screw with sleeve nut at 346.13(SD ±72.35) N compared with classic compression screw at 162.68(SD ±114.13) N (p = 0.025). Screw stripping occurred significantly earlier in classic compression screw at 255.5(SD ±192.0)° rotation after reaching maximum compression than in screw with sleeve nut at 1005.2(SD ±341.1)° (p = 0.0039).

INTERPRETATION

Screw with sleeve nut achieves greater fragment compression and is more robust to screw stripping compared to classic compression screw. Whether the better biomechanical properties lead to a reduction of pseudoarthrosis has to be proven in clinical studies.

Feasibility of Two-Screw Anterior Fixation for Odontoid Fractures in a Chinese Population: A Morphometric Study Based on Computed Tomography

Background

To evaluate the feasibility of treating odontoid fractures in the Chinese population with two cortical screws based on computed tomography (CT) scans and describe a new measurement strategy to guide screw insertion in treating these fractures.

Methods

A retrospective review of cervical computed tomographic scans of 128 patients (aged 18-76 years; men, 55 [43.0%]) was performed. The minimum external transverse diameter (METD), minimum external anteroposterior diameter (MEAD), maximum screw length (MSL), and screw projection back angle (SPBA) of the odontoid process were measured on coronal and sagittal CT images.

Results

The mean values of METD and MEAD were 10.0 ± 1.1 mm and 12.0 ± 1.0 mm, respectively, in men and 9.2 ± 1.0 mm and 11.0 ± 1.0 mm, respectively, in women. Both measurements were significantly higher in men (p < 0.001). In total, 87 individuals (68%) had METD > 9.0 mm that could accommodate two 3.5-mm cortical screws. The mean MSL value and SPBA range were 34.4 ± 2.9 mm and 13.5°-24.2°, respectively, with no statistically significant difference between men and women.

Conclusions

The insertion of two 3.5-mm cortical screws was possible for anterior fixation of odontoid fractures in 87 patients (68%) in our study, and there was a statistically significant difference between men and women.

Morphometric analysis of odontoid process among Arab population: a retrospective cone beam CT study

Objective

This study aims to evaluate the feasibility of using cone beam computed tomography (CBCT) scans to assess the odontoid process diameter in the Arab population and to determine whether one or two cortical screws can be used for treating odontoid fractures.

Methods

The odontoid process of 142 individuals aged 12-75 years, including 72 males (mean age: 35.5) and 70 females (mean age: 36.2), were analyzed using CBCT scans. The sagittal and coronal CBCT views were used to evaluate the antero-posterior (AP) and transverse diameters of the odontoid process.

Results

Males had substantially bigger transverse and AP diameters of the odontoid process than females (p < 0.05 & P < 0.01 respectively). Among the sample, 97 individuals (67.4%) had external transverse diameter (METD) of less than 9 mm which is slightly bigger than that of Indians and 48 individuals (31.83%) had enough room for two 3.5 mm or two 2.7 mm screws as their METD was more than 9 mm like that of Greek and Turkish. Age had no significant impact on the morphometric measurements of the odontoid process.

Conclusion

More than sixty percent of the sample had METDs of less than 9 millimeters, indicating that a single 4.5-mm Herbert screw may be suggested for fixing fractured odontoid processes in the Arab population.

Morphometric parameters of the odontoid process of C2 vertebrae, in Indian population, a CT evaluation

Background:

Osteosynthesis of odontoid fractures, especially for type II odontoid fractures, is often achieved by the placement of screws. Here, utilizing CT, we evaluated the normal anatomy of the odontoid process in an Indian population to determine whether one or two screws could be anatomically accommodated to achieve fixation.

Methods:

CT-based morphometric parameters of the odontoid process were assessed in 200 normal Indian patients (2018–2020).

Results:

Of 200 patients, 127 were male, and 73 were female. The mean minimum external transverse diameter (METD) was 8.80 mm (range 6.1–11.9 mm). Six (3%) patients had a minimum internal transverse diameter (TD) of >8.0 mm that would allow for the insertion of two 3.5-mm cortical screws without tapping, while 10 (5%) patients had TDs of <7.4 mm; none had diameters of <5.5 mm. The mean length of the implant was 36.45 mm in females and 36.89 mm in males, and the mean angle of screw insertion was 60.34° in females and 60.53° in males.

Conclusion:

About two-thirds (59%) of the 200 subjects in our study had a METD of <9 mm, indicating the impracticality for introducing second screws for odontoid fixation.

Feasibility analysis of the use of anterior screw fixation in the treatment of pediatric odontoid fracture

BACKGROUND

This study aimed to determine the feasibility of using anterior percutaneous screw fixation to treat odontoid fractures in children of different ages based on computed tomography (CT) measurements.

METHODS

A total of 176 children were enrolled and divided into 3 groups: group A (<6 years of age; 18 males and 22 females), group B (6 to 12 years old; 40 males and 35 females), and group C (12 to 18 years old; 34 males and 27 females). Using 2-dimensional CT reconstruction technology, we measured the children's odontoid parameters, including the coronal external diameter of the base of the odontoid process, the sagittal external diameter of the base of the odontoid process, the length of the odontoid process, the height of the axis vertebral body, and the angle between the axial line of the odontoid process and the vertical line of the anterosuperior border of the C3 vertebral body.

RESULTS

The mean coronal external diameter of the odontoid process base in children under 6 years old was 4.21±1.62 mm, which was not sufficient to accommodate a single screw. Among children aged 6 to 12 years old, this parameter varied widely, and the mean diameter was 5.50±2.80 mm. In the 12- to 18-year-old group, the diameter was 8.64±1.68 mm, which is similar to that of adults. The values of the total height of the axis, and the angle between the axial line of the and the vertical line of the anterosuperior C3 vertebral body border were lower than those for adults.

CONCLUSIONS

The percutaneous odontoid screw fixation technique is not recommended for children under 6 years old. For children aged 6 to 18 years old, this technique is feasible, but individual differences must be considered preoperatively. Selecting the appropriate screw diameter, length, and angle according to the actual CT measurement result is critical.

Image measurements of os odontoideum in children

BACKGROUND

Conservative therapy is used for children with odontoid fracture; however, when the odontoid fracture is complicated by significant displacement and unstable, surgery is required. Anterior cervical hollow lag screw fixation has been successfully used in adult patients, but until now, there has not been any relevant image measurement research in children with os odontoideum. The aim of the present study was to identify the morphometric changes of normal os odontoideum in children of different ages and to discuss parameters for screw fixation.

METHODS

Computed tomography (CT) scanning data of normal os odontoideum in 120 children of different ages were measured. The parameters were as follows: transverse and vertical diameters of cancellous bone and cortical bone in os odontoideum basilar part, angle and distance from simulation screw insertion point (anterior mid-point of C2 vertebral body) to os odontoideum anterior angle as well as posterior angle, the optimal insertion angle, and the optimal screw length.

RESULTS

The basilar part of normal os odontoideum was roughly round, and vertical diameter was slightly larger than transverse diameter. All parameters measured in the present study increased with age. The safety screw insertion angle range was 16-36°, and the optimal insertion angle ranged from 19° to 22°. The safety screw path length ranges in the 3-5-, 6-9-, and 10-14-year groups were 8-14, 10-16, and 12-21 mm, respectively, and the optimal screw length ranges were 13-14, 15-16, and 19-20 mm, respectively. The height of the axis showed a growing dimension followed by the advancing age in all groups. In each group, the height of the axis of the male is greater than the female.

CONCLUSIONS

For children undergoing odontoid screw fixation for the treatment of type II odontoid fracture, it is important to select the appropriate screw diameter, length, and direction according to parameter changes of os odontoideum based on their age.

The role of single odontoid screw fixation in treatment of odontoid fracture type II

Background

Odontoid fractures are the most common cervical fractures specially type II. Anterior odontoid screw fixation has many advantages with low incidence of surgical complications.

Purpose

To evaluate the role of single odontoid screw fixation in surgical treatment of odontoid fracture type II.

Study design

A retrospective clinical case series.

Patients and methods

Twelve patients with acute traumatic odontoid fracture type II were surgically treated by anterior single odontoid screw fixation. The visual analogue scale (VAS) and neck disability index (NDI) were used to evaluate the functional outcome among our patients. Plain radiography and CT cervical spine were done in all cases preoperatively and during our period of follow-up (6 months). Preoperative MRI cervical spine was done in all cases.

Results

The study included 12 patients, four of them (33.3%) were females, and 8 (66.7%) were males with a mean age of 41.7 ± 11.4 years. All patients had acute traumatic odontoid fracture type II, oblique fractures in 10 (83.3%) cases, and transverse fractures in 2 (16.7%) cases. All cases operated for anterior single odontoid screw fixation. During our period of follow-up, VAS and neck disability index were improved in all cases. There were 5 cases (41.7%) with transient dysphagia. Solid fusion was achieved in all cases except in one patient (8.3%) (fibrous union).

Conclusion

Single odontoid screw fixation is useful and safe procedure in surgical treatment of odontoid fractures type II. Careful attention to the technical aspects of the procedure and selection of patients are essential for good outcome.

Biomechanical comparison of three different compression screws for treatment of odontoid fractures evaluation of a new screw design

BACKGROUND

Lag screw osteosynthesis in odontoid fractures shows a high rate of pseudarthrosis. Biomechanical properties may play a role with insufficient fragment compression or unnoticed screw stripping. A biomechanical comparison of different constructed lag-screws was carried out and the biomechanical properties determined.

METHODS

Two identical compression screws with different pilot holes (1.25 and 2.5 mm), a double-threaded screw and one sleeve-nut-screw were tested on artificial bone (Sawbone, densities 10-30pcf). Fragment compression and torque were continuously measured using thin-film force sensors (Flexiforce A201, Tekscan) and torque sensors (PCE-TM 80, PCE GmbH).

FINDINGS

The lowest compression reached the double-threaded screw. Compression and sleeve-nut-screw achieved 214-298% and 325-546%, respectively, of the compression force of double-threaded-screw, depending on the test material. The pilot hole optimization led to a significant improvement in compression only in the densest test material. Screw stripping took place significantly later with increasing density of the test material on all screws. In compression screws this was done at a screw rotation of 180-270°, in sleeve nut screw at 270-720° and in double-threaded screws at 300-600° after reaching the maximum compression.

INTERPRETATION

Double-threaded screw is robust against screw stripping, but achieves only low fragment compression. The classic compression screws achieve better compression, but are sensitive to screw stripping. Sleeve-nut screw is superior in compression and as robust as double-threaded screw against screw stripping. Whether the better biomechanical properties lead to a reduction in pseudarthrosis must be proven in clinical trials.

Computerized Tomography-Based Morphometric Analysis of Odontoid in 100 Egyptian Patients

Background

There is still no consensus in the literature regarding the use of 1 screw or 2 screws. A number of studies have proved ethnic variations in the morphometry of the odontoid. There is no literature on the morphometry of odontoid in Egyptian patients.

Methods

Computerized tomography (CT) scans of the head and cervical spine of 100 healthy (no evidence of cervical spine fracture) patients of Egyptian origin were studied. Measurements were performed using Horos software, which allowed exact morphometric measurements to be taken at a specific angle in the axial, coronal, and sagittal planes.

Results

The mean age was 48.57 ± 15.39 years (range, 18-79 years; 56 male and 44 female patients). The mean radiologically calculated screw length and the mean radiologically calculated screw insertion angle were 38.21 ± 2.2 mm and 55.7° ± 3.84°, respectively. The mean anteroposterior and transverse diameter of the odontoid at the waist in the axial cut were 11.02 ± 1.05 mm and 8.92 ± 0.93 mm, respectively. A total of 54% and 6% of the study sample had the transverse waist diameter of the odontoid in the axial cut below 9 mm and 7.4 mm, respectively. A total of 48% of the male and 61% of the female patients had their transverse diameter of the odontoid at the waist below 9 mm. There was a statistically significant difference in all the measurements of the odontoid between the male and female patients except in the anteroposterior diameter of the base of odontoid (P = .06) in the axial cut, and the radiologically calculated screw insertion angle (P = .57). The mean distance between the apex of the odontoid and the screw exit was 1.8 ± 0.75 mm (range, 0-3 mm).

Conclusions

CT-based morphometric analysis of the odontoid is necessary before using 2-screw fixation technique. Single 4.5-mm Herbert screws could be used in all Egyptian patients without the need for CT-based morphometric analysis of the odontoid. The posterior screw can violate the posterior wall of the odontoid, with a reduced fracture hold and a chance of injuring the thecal sac.

Internal Morphology of the Odontoid Process: Anatomic and Imaging Study with Application to C2 Fractures

OBJECTIVE

Fracture of the odontoid process is a critical injury to diagnose and often treat. The aim of this anatomic study was to present a comprehensive understanding of this part of the C2 vertebra.

METHODS

We used 20 C2 vertebrae. Samples underwent imaging (computed tomography [CT] with and without three-dimensional reconstruction, micro-CT, 1.5T magnetic resonance imaging) and sagittal and coronal sectioning using a bone saw. Sectioned specimens were imaged under a digital handheld microscope, and transillumination of the bone was used to highlight its internal trabecular pattern. Three samples underwent infusion of the odontoid process with a hardening substance and were then decalcified.

RESULTS

Internal trabecular patterns of the odontoid process of all specimens were discernible. In sagittal and coronal sections, trabecular patterns were highlighted with transillumination, but the patterns were much clearer using the digital microscope. Magnetic resonance imaging and CT provided the least detail of the imaging methods, but the trabecular patterns could be identified. Three-dimensional reconstruction of CT data was the preferred imaging method over magnetic resonance imaging and CT without three-dimensional reconstruction. The most distinct trabecular and cortical patterns were seen using micro-CT. Osteoporosis was seen in 2 specimens (10%). Five specimens (25%) were found to have a subdental synchondrosis. For most specimens, the trabeculae were found throughout the odontoid process.

CONCLUSIONS

Improved knowledge of the anatomy, structural composition, and variations within the C2 vertebra may allow for better treatment options and patient care.

Anatomy of the dens and its implications for fracture treatment: an anatomical and radiological study

PURPOSE

The most common injuries to the upper cervical spine are fractures of the dens axis. Therefore, the purpose of our study was to answer three questions, namely (1) whether the size of the dens is adequate at all levels to accommodate two screws, (2) what the angle of the posterior tilt of the dens is in a healthy individual and (3) compare the measured variables between the sexes.

METHODS

The cohort comprised 50 males and 50 females CT examination of the craniocervical junction. We measured the five diameters of the dens and posterior dens angulation angle (PDAA) and screw insertion angle (SIA). The same dimensions were measured in a control group, consisting of 40 non-pathological second cervical vertebrae specimens.

RESULTS

On CT scans, the mean PDAA was 162.7 degrees in males and 160.26 degrees in females; the mean SIA was 62.0 degrees in males and 60.2 degrees in females. On specimens, the mean PDAA was 169.47 degrees in males and 166.95 degrees in females; the mean SIA was 65.42 degrees in males and 64.47 degrees in females. All obtained values were higher in males; regardless of their measuring on either CT scans or specimens, differences between males and females were statistically significant (p < 0.05) in a, c, d and e values.

CONCLUSIONS

The values of our measurements correlate with the dimensions identified previously in other studies. Based on our clinical experience and measurements, we presume that two 3.5-mm screws can be inserted into the dens of all adult patients, except for those with pronounced anatomical anomalies. Posterior dens angulation angle is slightly larger than we expected. The dens is significantly larger in males almost in all measurement. These slides can be retrieved under Electronic Supplementary Material.

Feasibility of Modified Anterior Odontoid Screw Fixation: Analysis of a New Trajectory Using 3-Dimensional Simulation Software

BACKGROUND

Anterior odontoid screw fixation (AOSF) has been suggested as the optimal treatment for type II and some shallow type III odontoid fractures. However, only the classical surgical trajectory is available; no newer entry points or trajectories have been reported.

METHODS

We evaluated the anatomic feasibility of a new trajectory for AOSF using 3-dimensional (3D) screw insertion simulation software (Mimics). Computed tomography (CT) scans of patients (65 males and 59 females) with normal cervical structures were obtained consecutively, and the axes were reconstructed in 3 dimensions by Mimics software. Then simulated operations were performed using 2 new entry points below the superior articular process using bilateral screws of different diameters (group 1: 4 mm and 4 mm; group 2: 4 mm and 3.5 mm; group 3: 3.5 mm and 3.5 mm). The success rates and the required screw lengths were recorded and analyzed.

RESULTS

The success rates were 79.03% for group 1, 95.16% for group 2, and 98.39% for group 3. The success rates for groups 2 and 3 did not differ significantly, and both were significantly better than the rate for group 1. The success rate was much higher in males than in females in group 1, but the success rate was similar in males and females in the other 2 groups. Screw lengths did not differ significantly among the 3 groups, but an effect of sex was apparent.

CONCLUSIONS

Our modified trajectory is anatomically feasible for fixation of anterior odontoid fractures, but further anatomic experiments and clinical research are needed.

Feasibility of anterior screw fixation in children: a tomographic study

PURPOSE

Morphology measures of the odontoid process in children under 12 years old were carried out to demonstrate the viability of anterior internal fixation in this population once their active profile may not be compatible with successful conservative treatment.

METHODS

During a 6-month period, 36 tomographic examinations of the cervical spine region that provided visualization of the odontoid process were selected. Group 1 included children between 6 and 9 years of age, and group 2 contained children from 9 to 12 years of age. There were 23 (63.8%) male patients and 13 (36.2%) female patients. Patients diagnosed with a tumor, an infection, fracture non-union, or congenital malformation were excluded. Exams were ordered as part of a protocol applied to non-specific neck pain and pediatric trauma entries. The following parameters were analyzed: (1) screw attack angle, (2) height of the odontoid process, and (3) minimal transverse diameter of the odontoid process.

RESULTS

In Groups 1 and 2, the average values of the screw attack angle were 55.9° ± 2.3° and 54.8° ± 4.5°, respectively; the average heights of the odontoid process were 26.58 ± 3.28 and 29.48 ± 3 mm, respectively, and the average minimal transverse diameter of the odontoid process were 6.57 ± 1.08 and 6.23 ± 0.88 mm, respectively. The minimal transverse diameter of the odontoid process was statistically higher in males than that in females, regardless of age (p = 0.007).

CONCLUSION

In both groups, the minimal transverse diameter of the odontoid process allowed for the use of one 3.5-4.5 mm screw for anterior internal fixation. These slides can be retrieved under Electronic Supplementary Material.

Computational anatomy of the dens axis evaluated by quantitative computed tomography: Implications for anterior screw fixation

The surgical fracture fixation of the odontoid process (dens) of the second cervical vertebra (C2/axis) is a challenging procedure, particularly in elderly patients affected by bone loss, and includes screw positioning close to vital structures. The aim of this study was to provide an extended anatomical knowledge of C2, the bone mass distribution and bone loss, and to understand the implications for anterior screw fixation. One hundred and twenty standard clinical quantitative computed tomography (QCT) scans of the intact cervical spine from 60 female and 60 male European patients, aged 18-90 years, were used to compute a three-dimensional statistical model and an averaged bone mass model of C2. Shape and size variability was assessed via principal component analysis (PCA), bone mass distribution by thresholding and via virtual core drilling, and the screw placement via virtual positioning of screw templates. Principal component analysis (PCA) revealed a highly variable anatomy of the dens with size as the predominant variation according to the first principal component (PC) whereas shape changes were primarily described by the remaining PCs. The bone mass distribution demonstrated a characteristic 3D pattern, and remained unchanged in the presence of bone loss. Virtual screw positioning of two 3.5 mm dens screws with a 1 mm safety zone was possible in 81.7% in a standard, parallel position and in additional 15.8% in a twisted position. The approach permitted a more detailed anatomical assessment of the dens axis. Combined with a preoperative QCT it may further improve the diagnostic procedure of odontoid fractures. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2154-2163, 2017.

The Feasibility of Two Screws Anterior Fixation for Type II Odontoid Fracture Among Arabs

STUDY DESIGN

Retrospective, cross-sectional study.

OBJECTIVE

To evaluate the feasibility of two screws anterior fixation of the odontoid process among Arab adults.

SUMMARY OF BACKGROUND DATA

Anterior screw fixation is the treatment of choice for type II odontoid fractures. In order to perform the procedure safely, the diameter of the odontoid process should be wide enough to allow for the placement of one or two screws.

METHODS

A retrospective review of 156 computed tomography scans of the cervical spine was done. The included patients were Arabs, adults (at least 18 years old), and had no evidence of upper cervical spine trauma, deformity, infection, tumor, or surgery. The minimum external transverse diameter (METD), minimum internal transverse diameter (MITD), minimum external anteroposterior diameter (MEAD), and minimum internal anteroposterior diameter (MIAD) of the odontoid process were measured. A P value of ≤0.05 was considered as the cutoff level of statistical significance.

RESULTS

Our study included 94 (60.3%) males and 62 (39.7%) females. The mean age of the subjects was 37.8 ± 16.9 years (range 18-85). The mean values of the METD, MITD, MEAD, and MIAD were 8.7 ± 1.0 mm, 6.0 ± 1.1 mm, 10.3 ± 1.0 mm, and 7.4 ± 1.1 mm, respectively. Men had larger diameters compared to women. This was statistically significant for METD (P = 0.035) and MEAD (P < 0.001). The METD was <9.0 mm in 95 (60.9%) subjects, while the MITD was <8.0 mm in 153 (98.1%) subjects. These findings were not significantly different between males and females.

CONCLUSION

Two screws anterior fixation of type II odontoid fracture is not feasible among the majority of Arabs.

LEVEL OF EVIDENCE

3.

Morphometric analysis of the odontoid process: using computed tomography--in the Greek population

AIM

A morphometric analysis of the odontoid process of the A2 vertebra, in the Greek population, was conducted using CT scan. We aimed to determine the feasibility to use one or two screws when treating fractures of this anatomic element.

PATIENTS AND METHODS

One hundred and fifteen patients (57 men) of a mean age of 48 years (16-95 years) underwent a cervical spine CT scan examination. The anterior-posterior and transverse diameters of the odontoid process were measured from the base, at 1-mm interval upward on axial CT images. The length from the tip of the odontoid process to the anterior-inferior angle of the body of the axis was calculated. Data concerning the height and weight of the examined patients were collected.

RESULTS

The mean transverse and anterior-posterior distances were found to be 11.46 and 10.45 mm, respectively, for the upper end of the odontoid process. At the neck level of the odontoid process, the equivalent mean values were 11.12 and 8.73 mm, respectively, while at the base, these distances were found to be 13.84 and 12.3 mm, respectively. The mean distance from the tip of the odontoid to its base was 17.25 and 17.28 mm, respectively, while the mean distance from the tip of the dens to the anterior-inferior corner of the axis' body was 39.2 mm. Men showed greater values than women.

CONCLUSIONS

In this study, it was shown that in the Greek population there is enough room for one 4.5-mm or one 3.5-mm cannulated screw to be used. The application of two 3.5-mm screws is feasible in 58.6 % of the male and 26.3 % of the female population. This confirms that the knowledge of the true dimensions of the odontoid process is of paramount importance before the proper management of fractured dens using the anterior screw technique.

Quantification of pediatric cervical spine growth at the cranio-vertebral junction

Objective

The purpose of this study was to investigate morphological change at the craniovertebral junction (CVJ) region using computed tomography.

Methods

A total of 238 patients were included in this study, and mean age was 47.8±21.3 months. Spinal canal diameter, Power's ratio, McRae line, antero-posterior C1 ring height, atlantoaxial joint space, C2 growth, epidural space from the dens (M-PB-C2) and longitudinal distance (basion to C2 lower margin, B-C2) were measured. The mean value of each parameter was assessed for individual age groups. The cohorts were then divided into three larger age groups : infancy (I) (≤2 years), very early (VE) childhood (2-5 years) and early (E) childhood (5≥ years).

Results

Spinal canal diameter increased with age; however, this value did not increase with statistical significance after VE age. A significant age-related difference was found for all C2 body and odontoid parameters (p<0.05). Mean McRae line was 8.5, 8, and 7.5 mm in the I, VE, and E groups, respectively. The M-PB-C2 line showed up-and-down dynamic change during early pediatric periods.

Conclusion

Expansion of the spinal canal was restricted to the very early childhood period (less than 5 years) in the CVJ region; however, the C2 body and odontoid process increased continuously with age. The above results induced a dynamic change in the M-PB-C2 line. Although C2 longitudinal growth continued with age, the McRae line showed relatively little change.

Endoscopic endonasal atlantoaxial transarticular screw fixation technique: an anatomical feasibility and biomechanical study

OBJECT The primary disadvantage of the posterior cervical approach for atlantoaxial stabilization after odontoidectomy is that it is conducted as a second-stage procedure. The goal of the current study is to assess the surgical feasibility and biomechanical performance of an endoscopic endonasal surgical technique for C1-2 fixation that may eliminate the need for posterior fixation after odontoidectomy. METHODS The first step of the study was to perform endoscopic endonasal anatomical dissections of the craniovertebral junction in 10 silicone-injected fixed cadaveric heads to identify relevant anatomical landmarks. The second step was to perform a quantitative analysis using customized software in 10 reconstructed adult cervical spine CT scans to identify the optimal screw entry point and trajectory. The third step was biomechanical flexibility testing of the construct and comparison with the posterior C1-2 transarticular fixation in 14 human cadaveric specimens. RESULTS Adequate surgical exposure and identification of the key anatomical landmarks, such as C1-2 lateral masses, the C-1 anterior arch, and the odontoid process, were provided by the endonasal endoscopic approach in all specimens. Radiological analysis of anatomical detail suggested that the optimal screw entry point was on the anterior aspect of the C-1 lateral mass near the midpoint, and the screw trajectory was inferiorly and slightly laterally directed. The custommade angled instrumentation was crucial for screw placement. Biomechanical analysis suggested that anterior C1-2 fixation compared favorably to posterior fixation by limiting flexion-extension, axial rotation, and lateral bending (p > 0.3). CONCLUSIONS This is the first study that demonstrates the feasibility of an endoscopic endonasal technique for C1-2 fusion. This novel technique may have clinical utility by eliminating the need for a second-stage posterior fixation operation in certain patients undergoing odontoidectomy.

The three-dimensional morphometry of the odontoid peg and its impact on ventral screw osteosynthesis

Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis. Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability. The mean length of the odontoid peg was 39.76 mm (SD 2.68). The mean screw entry angle α was 59.45° (SD 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (SD 2.70), the maximum possible mean converging angle of two screws was 20.35° (SD 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (SD 0.84) for the inner diameter in the sagittal plane and 7.35 mm (SD 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (SD 0.91) in the sagittal plane and 11.77 mm (SD 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (SD 1.14) for the sagittal inner diameter and 5.50 mm (SD 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (SD 1.0) in the sagittal plane and 10.00 mm (SD 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible. The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws.

CT based evaluation of odontoid morphology in the Indian population

BACKGROUND

Anterior fixation using two 3.5 mm screws is typically recommended for type II odontoid fractures. However, it is unsuitable in patients with an odontoid diameter of <9.0 mm. There is no data regarding the morphology of odontoid process in the Indian population. The aim of our study was to: a) Measure the external diameters of odontoid process in the Indian population using CT scan and thus determine the feasibility of two 3.5 mm screw fixation in them. b) Determine if any correlation exists between body height (Ht) and weight (Wt) and external odontoid diameters.

MATERIALS AND METHODS

CT images of odontoid process of 100 consecutive patients were analyzed. Antero- posterior (AP) and transverse (TD), outer diameters of the odontoid process were measured from the base and at 1 mm interval upwards on axial CT images.

RESULTS

The mean AP and mean TD were 11.52 mm and 9.85 mm, respectively. Fifty-five (55%) of the patients had at least one TD <9.0 mm. Five (5%) patients had at least one TD <7.4 mm. None of the patients had any diameter <5.5 mm. Body Ht correlated significantly with mean AP and mean TD of the odontoid process (AP: r = 0.276, P = 0.013; TD: r = 0.359, P = 0.001), whereas body Wt correlated significantly only with mean TD (AP: r = 0.162, P = 0.15; TD: r = 0.297, P = 0.007).

CONCLUSION

More than half of the study population (55%) was unsuitable for two 3.5 mm screw fixation for type II odontoid fracture. Two 2.7 mm screws can be safely used in 95% of the population. A 4.5 mm Herbert screw can be safely used in the entire population. We recommend two 2.7 mm screws or a 4.5 mm Herbert screw for fixation of these fractures in the Indian population. Body height showed a significant correlation with external odontoid diameters, whereas weight showed significant correlation only with TD of the odontoid process.

One-screw fixation provides similar stability to that of two-screw fixation for type II dens fractures

BACKGROUND

Anterior screw fixation has been widely adopted for the treatment of type II dens fractures. However, there is still controversy regarding whether one- or two-screw fixation is more appropriate.

QUESTIONS/PURPOSES

We addressed three questions: (1) Do one- and two-screw fixation techniques differ regarding shear stiffness and rotational stiffness? (2) Can shear stiffness and rotational stiffness after screw fixation be restored to normal? (3) Does stiffness after screw fixation correlate with bone mineral density (BMD)?

METHODS

We randomly assigned 14 fresh axes into two groups (seven axes each): one receiving one-screw fixation and another receiving two-screw fixation. Shear and torsional stiffness were measured using a nondestructive low-load test in six directions. A transverse osteotomy then was created at the base of the dens and fixed using one or two screws. Shear and torsional stiffness were tested again under the same testing conditions.

RESULTS

Mean stiffness in all directions after screw fixation was similar in both groups. The stiffness after one- and two-screw fixation was not restored to normal: the mean shear stiffness restored ratio was less than 50% and the mean torsional stiffness restored ratio was less than 6% in both groups. BMD did not correlate with mean stiffness after screw fixation in both groups.

CONCLUSIONS

One- and two-screw fixation for type II dens fractures provide similar stability but neither restores normal shear or torsional stiffness.

CLINICAL RELEVANCE

One-screw fixation might be used as an alternative to two-screw fixation. Assumed BMD should not influence surgical decision making.

Avoiding pitfalls in anterior screw fixation for Type II odontoid fractures

Anterior screw fixation of Type II odontoid fractures provides immediate stabilization of the cervical spine while preserving C1–2 motion. This technique has a high fusion rate, but can be technically challenging. The authors identify key points that should be taken into account to maximize the chance for a favorable outcome. Keys to success include proper patient and fracture selection, identification of suitable screw entry point and correct screw trajectory, achieving bicortical purchase, and placing 2 screws when feasible and applicable. The authors review the operative technique and present guidance on appropriate patient selection and common pitfalls in anterior screw fixation, with strategies for avoiding complications.

The use of bioabsorbable screws to fix Type II odontoid fractures: a biomechanical study

OBJECT

Anterior screw fixation of the Type II odontoid fracture stabilizes the odontoid without restricting the motion of the cervical spine. The metal screw may limit bone remodeling because of stress shielding (if not placed properly) and limit imaging of the fracture. The use of bioabsorbable screws can overcome such shortcomings of the metal screws. The purpose of this study was to compare the strength of a 5-mm bioabsorbable screw with single 4-mm metal and double 3.5-mm lag screw fixation for Type II fractures of the odontoid process.

METHODS

Three different modalities of anterior screw fixation were used in 19 C-2 vertebrae. These fixation methods consisted of a single 5-mm cannulated bioabsorbable lag screw (Group A), a single 4-mm cannulated titanium lag screw (Group B), and two 3.5-mm cannulated titanium lag screws (Group C). Anteroposterior (AP) stiffness and rotational stiffness were evaluated in all constructs.

RESULTS

There was no statistical difference among the ages of the cadavers in each group (p = 0.52). The AP bending stiffness in Groups A, B, and C was 117 ± 86, 66 ± 43, and 305 ± 130 Nm/mm, respectively. The AP bending stiffness in Group C was significantly higher than that in Groups A and B (p = 0.01 and p = 0.001, respectively). The difference in AP bending stiffness values of bioabsorbable and 4-mm metal screws was not statistically significant (p = 0.23). The rotational stiffness of the double 3.5-mm metal screws was significantly greater than that of the 5-mm bioabsorbable and the 4-mm titanium screws.

CONCLUSIONS

Double screw fixation with 3.5-mm screws provides the stiffest construct in Type II odontoid fractures. Bioabsorbable lag screws (5 mm) have the same AP bending and rotational stiffness as the single titanium lag screw (4 mm) in odontoid fractures.

Computed tomographic evaluation of odontoid process: implications for anterior screw fixation of odontoid fractures in an adult population

INTRODUCTION

Odontoid diameter in some individuals may not be large enough to accommodate two 3.5-mm cortical screws for anterior odontoid fracture fixation. The study was performed to evaluate, in a Brazilian population, the diameter of the odontoid process and the feasibility of using two 3.5-mm cortical screws for anterior odontoid fracture fixation.

MATERIALS AND METHODS

Computed tomographic (CT) scans of 88 adult patients (aged 18-78 years) were analyzed; 40 patients (45%) were male (mean age: 43.08 years) and 48 (55%) were female (mean age: 43.39 years). The minimum external and internal anteroposterior and transverse diameters of the odontoid process on sagittal and coronal planes were measured on CT multiplanar reconstructions of the cervical spine.

RESULTS

The mean value of the minimum external anteroposterior diameter was 10.83 ± 1.08 and 7.53 ± 1.10 mm for the minimum internal anteroposterior diameter. The mean value of the minimum external transverse diameter was 9.19 ± 0.91 and 6.07 ± 1.08 mm for the minimum internal transverse diameter. The mean AP diameter was significantly larger than the mean transverse diameter; 57 (65%) individuals had the minimum external transverse diameter >9.0 mm that would allow the insertion of two 3.5-mm cortical screws with tapping, and five (6%) individuals had the minimum internal transverse diameter >8.0 mm that would allow the insertion of two 3.5-mm cortical screws without tapping.

CONCLUSIONS

The insertion of two 3.5-mm cortical screws was possible for anterior fixation of odontoid fracture in 57 (65%) individuals of our study, and there was no statistical difference between males and females.

Análise do diâmetro transverso do processo odontoide com uso da tomografia computadorizada

INTRODUÇÃO: o diâmetro reduzido do odontoide é um desafio para o cirurgião no planejamento pré-operatório e escolha na fixação da fratura com um ou dois parafusos. OBJETIVO: analisar a medida do diâmetro transverso (DT) do processo odontoide por meio da tomografia computadorizada para o planejamento pré-operatório da osteossíntese com um ou dois parafusos. MÉTODOS: foram analisadas 79 tomografias computadorizadas cervicais de pacientes adultos, sem deformidades congênitas ou queixas de dor em coluna cervical alta, atendidos em uma clínica privada de Blumenau - Santa Catarina. RESULTADOS: as médias de idade não revelaram diferença estatisticamente significante entre os sexos, mas observou-se diferença estatisticamente significante entre as médias do DT do odontoide de homens e mulheres. A média do diâmetro transverso nos homens foi de 10,29 mm, e nas mulheres de 9,39 mm. CONCLUSÃO: a tomografia computadorizada mostrou-se útil para a medição do diâmetro transverso do processo odontoide. A fixação com um parafuso cortical de 3,5 mm seria possível em todos os casos analisados e a fixação com dois parafusos seria possível em 83,9% dos homens e 62,5% das mulheres.

Avaliação tomográfica de parâmetros morfométricos do processo odontoide relacionados à fixação interna com parafusos

OBJETIVOS: avaliar, por meio da tomografia computadorizada, os parâmetros morfométricos do processo odontoide relacionados com a sua fixação interna. MÉTODOS: cinquenta e cinco exames de tomografia computadorizada (TC) da coluna cervical que permitissem o estudo do áxis foram utilizados para o estudo. Destes, 24 (47%) pertenciam a pacientes do sexo masculino e 31 do sexo feminino. A média de idade foi de 42,05 anos (± 15,82). Foram excluídos os casos com diagnóstico de tumores, infecções, sequelas de fratura, artrose muito avançada ou malformações congênitas. Nenhum dos exames tinha como indicação problemas relacionados à coluna cervical alta. Foram avaliados os seguintes parâmetros: 1 - comprimento estimado do implante (CEI), 2 - angulação do parafuso (aP), 3 - diâmetro transverso mínimo (DTmín) e 4 - diâmetro anteroposterior mínimo (DAPmín). Foi utilizado o teste t de Student para comparar os resultados entre o grupo de pacientes do sexo masculino e do feminino. RESULTADOS: o valor médio do CEI foi de 37,95 mm ± 3,44 para a população geral do estudo. O valor médio da angulação do parafuso (aP) foi de 60,91º ± 4,06. O diâmetro transverso mínimo (DTmín) foi de 9,05 mm ± 0,88 e o diâmetro antero-posterior mínimo DAPmín foi de 10,35 mm ±1,04. Os valores do CEI e do DAPmín na população masculina foram significativamente maiores do que aqueles encontrados na feminina, enquanto os outros parâmetros não apresentaram diferenças entre os dois sexos na população estudada. Dos 55 pacientes, 39% apresentaram DTmín < 9 mm, valor mínimo considerado para a colocação de dois parafusos de 3,5 mm. CONCLUSÕES: em nossa população, o sexo masculino apresentou valores significativamente maiores de CEI e DAPmín do que os encontrados no sexo feminino.

Treatment of remote type ii axis fractures in the elderly: feasibility of anterior odontoid screw fixation

OBJECTIVE

This preliminary study considers the feasibility and the results of anterior screw fixation in elderly patients with remote Type II axis fractures. Odontoid fractures are the most common fractures of the cervical spine in people 70 years of age or older. In developing countries, direct anterior fracture fixation is replacing posterior fusion in many cases. Recently, it has been demonstrated that patient age does not influence the outcome in terms of fusion after odontoid screw fixation. There is considerable disagreement about correct treatment in the case of remote fractures. In the literature, there have been no studies considering the feasibility and results of anterior screw fixation in elderly patients with remote Type II axis fractures.

METHODS

From 1989 to 2005, we observed 9 patients over the age of 65 years with isolated Type II remote fractures of the dens. All fractures were considered to be inveterate, as the traumatic events had occurred 6 to 12 months earlier. All fractures were treated with anterior infibulation of the dens with single 3.5-mm cannulated screws.

RESULTS

A bony fusion was radiologically documented in 7 patients (77%) 4 to 16 months after the intervention. In 1 patient, a fibrous union was observed. The neurological status remained unchanged in all patients, and no patients showed any neurological impairment at the time of follow-up.

CONCLUSION

According to our preliminary study, the technique appears to be feasible for remote axis fractures within 12 months of trauma, and it seems to be safe for elderly patients. Further data from additional studies are needed.

Anatomical study of axis for odontoid screw thickness, length, and angle

Anterior odontoid screw fixation is a safe and effective method for treatment of odontoid fractures. The screw treads should fit into the odontoid medulla, should pass the fracture line, and should pull fractured odontoid tip against body of axis in order to achieve optimum screw placement and treatment. This study has demonstrated optimal anterior odontoid screw thickness, length, and optimal angle for safe and strong anterior odontoid screw placement. Dry bone axis vertebrae were evaluated by direct measurements, X-ray measurements, and computerized tomography (CT) measurements. The screw thickness (inner diameter of the odontoid) was measured as well as screw length (distance between anterior-inferior point body of axis and tip of odontoid), and screw angle (the angle between basis of axis and tip of odontoid). The inner diameter of odontoid bone was measured as 6.5+/-1.9 mm, the screw length was 37.6+/-3.3 mm, and the screw angle was 62.4+/-4.7 on CT. There was no statistical difference between X-ray and CT in the measurements of screw thickness and angle. X-ray and CT measurements are both safe methods to determine the inner odontoid diameter and angle preoperatively. Screw length should be measured on CT only. To provide safe and strong anterior odontoid screw fixation, screw thickness, length, and angle should be known preoperatively, and these can be measured on X-ray and CT.

Odontoid fractures in the elderly: dorsal C1/C2 fusion is superior to halo-vest immobilization

BACKGROUND

Odontoid fractures in geriatric patients occur frequently and are associated with a high morbidity and mortality. The decision for operative or nonoperative therapy is still controversial. Recent studies confirmed that external stabilization with halo-vest immobilization is associated with high complication rates and mortality. An operation has a high perioperative risk because of comorbidities, but previous data suggest improved outcome in this group.

METHODS

To test this hypothesis, we retrospectively analyzed geriatric patients that underwent operation for isolated unstable type II odontoid fractures (Anderson and D'Alonzo classification) in our institution between March 2003 and March 2005. Twenty-seven patients (17 female, 10 male) with a median age of 85.5 (range, 63-98) years were stabilized by posterior C1/C2 fusion with transarticular screws and an additional modified Gallie fusion with a bone graft. Postoperatively, a rigid cervical collar was applied for 6 to 12 weeks.

RESULTS

Six patients died during the observation period (median, 40 days after trauma). Three patients (11%) died perioperatively (cardiac or pulmonary failure, pneumonia), and the other three died as a result of the same after discharge. All 21 surviving patients were reevaluated an average of 3 months after trauma. All but one showed a stable fusion, and all reported no or minor neck pain. No wound infections occurred; one reoperation was necessary for screw misplacement. An initial neurologic deficit improved in two of three cases. Patients were mobilized on day 1 after operation. About two-thirds of patients were discharged directly home.

CONCLUSIONS

Posterior stabilization of unstable odontoid fractures with transarticular screws and modified Gallie fusion in old patients can be performed safely, with good clinical results and few complications. However, mortality remains high, but is lower than reported after halo-vest immobilization alone. Dorsal C1/C2 Fusion is superior to halo-vest immobilization in terms of nonunion rate and mortality. Thus, it might be the treatment of choice in this high-risk patient population.

Computed tomographic evaluation of the odontoid process for two-screw fixation in type-II fracture: a Malaysian perspective

PURPOSES

To measure the diameter of the odontoid process in a Malaysian population using computed tomographic (CT) scan and determine the feasibility of treating type-II odontoid fractures using 2 cortical screws.

METHODS

CT images of the odontoid process of 85 patients aged 18 to 80 years were analysed; 69 (81%) were male (mean age, 44 years) and 16 (19%) were female (mean age, 48 years). Both anteroposterior (AP) and transverse diameters of the odontoid process were measured via axial CT images at 3 different levels: the base of the odontoid process and 1.2 mm and 2.4 mm above the base.

RESULTS

The mean AP and transverse diameters of the odontoid process in men were 11.3 (range, 10.0-12.6; standard deviation [SD], 0.7) mm and 10.2 (range, 8.5-12.3; SD, 0.8) mm respectively, whereas in women were 10.9 (range, 9.4-13.2; SD, 0.8) mm and 10.1 (range, 7.9-11.6; SD, 0.9) mm respectively. The difference in corresponding mean dimensions between men and women was not statistically significant. The mean AP diameter was significantly larger than the mean transverse diameter. At the base and 1.2 mm and 2.4 mm above the base, the respective transverse diameters of 4 (5%), 13 (15%), and 24 (28%) of the patients were <9.0 mm. None had an odontoid AP diameter of <9.0 mm at any level.

CONCLUSION

Two 3.5-mm cortical screws appear too big for fixation in one third of our sample presenting with type-II odontoid fracture. Fixation by two 2.7-mm screws is recommended for Malaysians and other Asian populations.

Surgical management of odontoid fractures

Odontoid fractures account for approximately 20% of all cervical fractures, with the majority being type II fractures according to the Anderson and D'Alonzo classification. The treatment of odontoid fractures is determined by multiple factors, including fracture type, presence of associated injuries, patient age, and patient comorbidities. It is generally well accepted that type I and type III injuries heal well with non-operative treatment. However, some type I injuries can be seen in association with occipito-atlantal dislocation; and some type III fractures can be closer to the neck of the odontoid (high and shallow based), and may act like a type II fracture, that is, with an increased probability of nonunion. The treatment of type II fractures remains controversial. Over the past decade, internal fixation has become an accepted treatment for unstable injuries of the cervical spine. Multiple surgical approaches have been proposed. This article reviews the various alternatives for treating odontoid fractures, attempting to give to the reader a broad perspective on the current techniques, including information taken from evidence-based medicine.

Screw placement in transoral atlantoaxial plate systems: an anatomical study

OBJECT

The placement of an anterior atlantoaxial plate after transoral odontoid resection has been described by Harms. Recently, the authors of biomechanical and clinical studies have shown that this procedure, especially in combination with posterior wiring, is a good alternative to established, isolated posterior atlantoaxial fixation techniques. Reports on the anatomy of the atlas and axis primarily focus on the posterior surgical approach. Scarce research regarding the quantitative anatomy of the anterior aspect of C-1 and C-2 has been reported. This study was undertaken to measure relevant dimensions of C-1 and C-2 and their relation to the anterior transoral approach. The aim of the study was to determine "safe zones" for screw placement in anterior atlantoaxial plate fixation.

METHOD

Fifty human dry C-1 and C-2 vertebrae were obtained for direct anatomical, radiographic, and computerized tomography (CT) measurements. Thirty-two linear and four angular parameters were evaluated. All measurements were made using a digital caliper, ruler, or goniometer. Anatomical measurements were correlated with radiographic (anteroposterior, lateral, and craniocaudal) and CT (0.5-mm-slice thickness) measurements of the corresponding vertebrae. Additionally, bone mineral density (BMD) measurements of C-1 and C-2 were obtained in 20 patients. A safe zone for anterior screw placement in an atlas of bilateral trapezoid shape could be characterized. The average medial and lateral height of the trapezoid was 4.1 +/- 1.01 mm (range 1.4-6.7 mm) and 12.9 +/- 1.73 mm (range 8.7-17.4 mm), respectively. The distance between the sagittal plane and the medial and lateral walls of the trapezoid was 10.2 +/- 1.42 mm (range 8.9-12.8 mm) and 23.5 +/- 2.98 mm (range 21.7-30.7 mm), respectively. The average depth of the lateral masses was 22.3 +/- 2.04 mm (range 17.0-26.7 mm) in the sagittal plane. The average BMD in the safe zone of C-1 was 0.89 +/- 0.11 g/cm3 (range 0.75-1.01 g/cm3). Bone mineral density measurements at C-2 revealed a spheroid zone of low density at the basis of the dens (0.68 +/- 0.09 g/cm3). In contrast, high zones of BMD were found near the articular surfaces (C1-2: 0.97 +/- 0.11 g/cm3; C2-3: 0.94 +/- 0.12 g/cm3). The safe zone for anterior axis screw placement was V-shaped, limited cranially by a zone of low bone density and laterally by the vertebral artery groove. Correlations between radiographic and anatomical measurements were generally good (r2 = 0.78-0.95), but they were higher between CT and anatomical measurements (r2 = 0.86-0.99).

CONCLUSIONS

A quantitative understanding of the anterior anatomy of C-1 and C-2 is necessary when considering anterior atlantoaxial plate fixation after transoral odontoid resection. In this study the authors defined safe zones for anterior atlas and axis screw placement. The anterior atlantoaxial plate, as originally described by Harms, only partially respects these safe zones.

Anderson type II fracture of the odontoid process: results of anterior screw fixation

Controversy exists in the literature regarding the adequacy of one or two screws for direct fixation of the odontoid process. Proponents of the two-screw technique believe that a single screw is not adequate to stabilize the fracture. Conversely, the insertion of two 3.5-mm screws in the medullary cavity of the odontoid process is technically difficult and can jeopardize the surface area left for fracture healing. The authors conducted a prospective study of 30 cases with Anderson type II fracture of the odontoid process treated by direct anterior fixation using the two-screw technique. The screws used were 2.7-mm cortical screws manufactured from titanium. Two C-arms were used to control reduction of the displaced fracture and for its direct anterior stabilization. The operation was performed with the patients under general anesthesia. The anterolateral incision was made at the level of C4 to facilitate exposure of the C2-C3 disk and for fracture fixation. No evidence of nonunion was encountered. Spontaneous fusion of the C2-C3 segment was found in one case. Limitation of rotation of the cervical spine was a subjective description in a single case. No major complications were attributed to the surgical technique. The two 2.7-mm self-tapping titanium cortical screws provided adequate stability for fixation of type II odontoid fractures.

Spine update: cervical spine internal fixation using screw and screw-plate constructs

Screw and screw-plate constructs have been used successfully in fixation of the cervical spine. This update focuses on the indications, complications, and nuances in the technique used for odontoid screws, transarticular C1-C2 screws, occipitocervical plating, posterior lateral mass screws, pedicle screws, and anterior plating.

A clinical comparison of one- and two-screw odontoid fixation

OBJECT

The optimal treatment of Type II odontoid fractures is controversial. Various therapies have been used, including nonrigid immobilization, halo orthosis, posterior atlantoaxial arthrodesis, and odontoid screw fixation. Of these, odontoid screw fixation is the only treatment modality that provides immediate stabilization and preserves normal motion at C1-2. It has been suggested in cadaveric biomechanical studies that there is no advantage to using more than one screw for anterior odontoid fixation. The authors compared the clinical safety and efficacy of one- and two-screw anterior odontoid fixation.

METHODS

The authors retrospectively reviewed the medical records and radiographs of 42 consecutive patients who had undergone fixation for treatment of odontoid fractures at a single institution between 1989 and 1995. The group treated with a single screw consisted of 20 patients (11 males and nine females) with an average age of 54 years. The union rate in this group, as determined by postoperative dynamic radiographs, was 81%. The group treated with two screws consisted of 22 patients (13 men and nine women) with an average age of 64 years, whose union rate was 85%.

CONCLUSIONS

Anterior odontoid screw fixation is a safe and efficacious treatment for odontoid fractures. In the authors' experience there was no significant difference in the successful union rates achieved with either the one- or two-screw fixation techniques (81% and 85%, respectively; chi(2) = 0.09, p = 0.76).

Management of odontoid fractures

During the past two decades, various reports on the management of odontoid and axis body fractures have been published and new methods of treatment have been developed. So far, there is no consensus, and management remains controversial. This article reviews the literature and formulates recommendations based on clinical experience.

Morphologic characteristics of human cervical pedicles

STUDY DESIGN

Cervical pedicle morphology was investigated using manual and computed tomography measurements.

OBJECTIVES

Normal anatomic variations of the cervical pedicles were measured to evaluate their safety as anchors for posterior cervical fixation systems.

SUMMARY OF BACKGROUND DATA

There have been no cervical pedicle measurements on a large number of specimens. No study has ever measured the inner pedicle diameter.

METHODS

Fifty-three spinal columns (C2-C7) of Euro-American origin identified by age, sex, and height (318 vertebrae or 636 pedicles) were measured using a digital caliper, a goniometer, and computed tomography scanning.

RESULTS

The pedicle axis lengths were similar from C3 to C7 (except for shorter C2 pedicles). In the horizontal plane, the medial inclination of the pedicles followed the cervical spinal cord enlargement. In the sagittal plane, the pedicles were directed superiorly in the upper spine and inferiorly in the lower cervical spine. Some pedicles had no medullary canal (i.e., were solid cortical bone: 0.9% C2, 2.8% C3 and C4, and 3.8% C5 pedicles). The outer pedicle width was smaller than the height in most of the pedicles. The inner pedicle width was equal to or smaller than 2 mm in 13.2% C2, 72.6% C3, 67.0% C4, 62.3% C5, 51.9% C6, and 16.0% C7. The outer pedicle width was equal to or smaller than 4 mm in 8.5% C2, 75.5% C3, 35.8% C4, 13.2% C5 and C6, and 6.6% C7 pedicles. The thinnest pedicle cortex was always the lateral cortex, which protects the vertebral artery. Measurements of the posterior pedicle projection also were taken.

CONCLUSIONS

These data provide anatomic limitations to pedicle screw use in the cervical spine.