Biomechanical investigation of a novel integrated device for intra-articular stabilization of the C1-C2 (atlantoaxial) joint

An In Vitro Biomechanical Study of the Ectopic Functional Reconstruction of the Transverse Ligament of Atlas

OBJECTIVE

To evaluate the stability and function of the C1-C2 joint after ectopic functional reconstruction (EFR) of the C1 transverse ligament.

METHODS

Eight human cadaveric cervical spines (C0-C4) were subjected to in vitro biomechanical test with moment control. Spine specimens were tested under the following conditions: 1) left intact; 2) destabilized by severing the transverse ligament of atlas; 3) after EFR of the transverse ligament. Range of motion was measured in flexion, extension, lateral bending, and axial rotation.

RESULTS

Destabilization significantly increased range of motion in all directions compared with the intact status (P < 0.001). However, after EFR of the transverse ligament, range of motion in all directions was restored to the intact state. Meanwhile, coupling motions were reproduced in the axial rotation.

CONCLUSIONS

EFR of the transverse ligament virtually recovers all the physiological functions of the native transverse ligament and might be a promising alternative for the treatment of anterior atlantoaxial dislocation. Further studies are warranted before clinical application of EFR of the transverse ligament.

Which traumatic spinal injury creates which degree of instability? A systematic quantitative review

BACKGROUND CONTEXT

Traumatic spinal injuries often require surgical fixation. Specific three-dimensional degrees of instability after spinal injury, which represent criteria for optimum treatment concepts, however, are still not well investigated.

PURPOSE

The aim of this review therefore was to summarize and quantify multiplanar instability increases due to spinal injury from experimental studies.

STUDY DESIGN/SETTING

Systematic review.

METHODS

A systematic review of the literature was performed using keyword-based search on PubMed and Web of Science databases in order to detect all in vitro studies investigating the destabilizing effect of simulated and provoked traumatic injury in human spine specimens. Together with the experimental designs, the instability parameters range of motion, neutral zone and translation were extracted from the studies and evaluated regarding type and level of injury.

RESULTS

A total of 59 studies was included in this review, of which 43 studies investigated the effect of cervical spine injury. Range of motion increase, which was reported in 58 studies, was generally lower compared to the neutral zone increase, given in 37 studies, despite of injury type and level. Instability increases were highest in flexion/extension for most injury types, while axial rotation was predominantly affected after cervical unilateral dislocation injury and lateral bending solely after odontoid fracture. Whiplash injuries and wedge fractures were found to increase instability equally in all motion planes.

CONCLUSIONS

Specific traumatic spinal injuries produce characteristic but complex three-dimensional degrees of instability, which depend on the type, level, and morphology of the injury. Future studies should expand research on the cervicothoracic, thoracic, and lumbosacral spine and should additionally investigate the destabilizing effects of the injury morphology as well as concomitant rib cage injuries in case of thoracic spinal injuries. Moreover, neutral zone and translation should be measured in addition to the range of motion, while mechanical injury simulation should be preferred to resection or transection of structures to ensure high comparability with the clinical situation.

A Novel Construct Incorporating C2 Unilateral Pedicle and Contralateral Translaminar Screws for Occipitocervical Internal Fixation: An In Vitro Biomechanical Study

BACKGROUND

Occipitocervical fixation using bilateral C2 pedicle screws (C0-C2BiPS) and occipitocervical fixation using bilateral C2 translaminar screws (C0-C2BiLS) provide satisfactory stability. Bilateral fixation is not feasible for cases of C2 unilateral pedicle morphology abnormality and ipsilateral laminectomy. This study proposed and evaluated novel occipitocervical fixation using C2 unilateral pedicle screw and contralateral translaminar screws (C0-C2PSLS).

METHODS

In 6 human cadaveric specimens, an in vitro experiment was performed with 2.0-Nm moment control in flexion-extension, lateral bending, and axial rotation to investigate biomechanical stability. Neutral zone and range of motion (ROM) between the occiput (C0) and C2 were measured in the intact state, after destabilization, and after sequential stabilization using C0-C2BiPS, C0-C2BiLS, and C0-C2PSLS constructs.

RESULTS

Flexion-extension ROM of the intact specimens at C0-C2 was 27.4° ± 2.4°. Instrumentation with C0-C2PSLS, C0-C2BiPS, and C0-C2BiLS reduced flexion-extension ROM to 3.7° ± 1.3°, 4.7° ± 1.4°, and 4.5° ± 1.4°, respectively. In lateral bending, ROM values were 7.0° ± 0.6°, 4.5° ± 1.4°, 4.2° ± 1.4°, 2.7° ± 1.0°, respectively. In axial rotation, ROM values were 65.3° ± 5.7°, 2.5° ± 0.5°, 1.4° ± 0.5°, and 0.9° ± 0.6°, respectively. Comparing destabilized and intact specimens, all 3 constructs significantly reduced ROM and neutral zone values in flexion-extension, lateral bending, and axial rotation (P < 0.05). Direct comparisons between the 3 constructs revealed no significant difference (P > 0.05).

CONCLUSIONS

Novel C0-C2PSLS provides similar stabilization effect as C0-C2BiPS and C0-C2BiLS constructs and has potential for clinical use, especially for cases of C2 unilateral pedicle morphology abnormality and ipsilateral laminectomy.

Biomechanical and Anatomical Validity of the Short Posterior Arch Screw

Objective

This study was conducted to clarify the validity of the short posterior arch screw (S-PAS). The S-PAS is inserted only in the pedicle-analogue portion of the posterior arch. The S-PAS screw length is almost half that conventional C1 lateral mass screws inserted via the posterior arch (via-PAS). S-PAS reduces the risk of vertebral artery injury (VAI) because it never reaches the transverse foramen. Although the biomechanical validity of various C1 lateral mass screws (C1LMS) analyzed in young specimens have been published, that of unicortically inserted C1LMS such as the unicortical Harms screw, S-PAS, and via-PAS for elderly patients is concerning because of the high prevalence of osteoporosis in the elderly.

Methods

Nine fresh frozen cadavers (average age at death, 72.1 years) were used for pullout testing. The bone mineral density of each specimen was evaluated using quantitative computed tomography.

Results

The pullout strength of via-PAS (1,048.5 N) was significantly greater than that of the unicortical Harms screw (257.9 N) (p<0.05). The pullout strength of S-PAS was 720.3 N, which was also significantly greater than that of the unicortical Harms screw (p<0.05).

Conclusion

The via-PAS and S-PAS are valid surgical options, even in elderly patients. Along with sufficient biomechanical strength, the S-PAS screw prevents VAI.

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.

Novel posterior artificial atlanto-odontoid joint for atlantoaxial instability: a biomechanical study

OBJECTIVE Atlantoaxial instability is usually corrected by anterior and/or posterior C1-2 fusion. However, fusion can lead to considerable loss of movement at the C1-2 level, which can adversely impact a patient's quality of life. In this study, the authors investigated the stability and function of a novel posterior artificial atlanto-odontoid joint (NPAAJ) by using cadaveric cervical spines. METHODS The Oc-C7 regions from 10 cadaveric spines were used for anteroposterior (AP) translation and range of motion (ROM) tests while intact and after destabilization, NPAAJ implantation, and double-rod fixation. RESULTS The mean AP C1-2 translational distances in the intact, destabilization, and double-rod groups were 6.53 ± 1.07 mm, 11.54 ± 1.59 mm, and 3.24 ± 0.99 mm, respectively, and the AP translational distance in the NPAAJ group was significantly different from that in the intact group (p < 0.05). The AP translational distance in the NPAAJ group was not significantly different from that in the double-rod group (p = 0.24). The mean flexion, extension, and axial rotation ROM values of the NPAAJ group were 9.87° ± 0.91°, 8.75° ± 0.99°, and 61.93° ± 2.93°, respectively, and these were lower than the corresponding values in the intact group (p < 0.05). The mean lateral bending ROM in the NPAAJ group (9.26° ± 0.86°) was not significantly different from that in the intact group (p = 0.23), and the flexion, extension, and rotation ranges in the NPAAJ group were 79.5%, 85.2%, and 82.3%, respectively, of those in the intact group. CONCLUSIONS Use of NPAAJ for correction of atlantoaxial instability disorders caused by congenital odontoid dysplasia, odontoid fracture nonunion, and C-1 transverse ligament disruption (IA, IB, and IIB) may restore the stability and preserve most of the ROM of C1-2. Additionally, the NPAAJ may prevent soft tissue from embedding within the joint. However, additional studies should be performed before the NPAAJ is used clinically.

Incorporating ligament laxity in a finite element model for the upper cervical spine

BACKGROUND CONTEXT

Predicting physiological range of motion (ROM) using a finite element (FE) model of the upper cervical spine requires the incorporation of ligament laxity. The effect of ligament laxity can be observed only on a macro level of joint motion and is lost once ligaments have been dissected and preconditioned for experimental testing. As a result, although ligament laxity values are recognized to exist, specific values are not directly available in the literature for use in FE models.

PURPOSE

The purpose of the current study is to propose an optimization process that can be used to determine a set of ligament laxity values for upper cervical spine FE models. Furthermore, an FE model that includes ligament laxity is applied, and the resulting ROM values are compared with experimental data for physiological ROM, as well as experimental data for the increase in ROM when a Type II odontoid fracture is introduced.

DESIGN/SETTING

The upper cervical spine FE model was adapted from a 50th percentile male full-body model developed with the Global Human Body Models Consortium (GHBMC). FE modeling was performed in LS-DYNA and LS-OPT (Livermore Software Technology Group) was used for ligament laxity optimization.

METHODS

Ordinate-based curve matching was used to minimize the mean squared error (MSE) between computed load-rotation curves and experimental load-rotation curves under flexion, extension, and axial rotation with pure moment loads from 0 to 3.5 Nm. Lateral bending was excluded from the optimization because the upper cervical spine was considered to be primarily responsible for flexion, extension, and axial rotation. Based on recommendations from the literature, four varying inputs representing laxity in select ligaments were optimized to minimize the MSE. Funding was provided by the Natural Sciences and Engineering Research Council of Canada as well as GHMBC. The present study was funded by the Natural Sciences and Engineering Research Council of Canada to support the work of one graduate student. There are no conflicts of interest to be reported.

RESULTS

The MSE was reduced to 0.28 in the FE model with optimized ligament laxity compared with an MSE 0f 4.16 in the FE model without laxity. In all load cases, incorporating ligament laxity improved the agreement between the ROM of the FE model and the ROM of the experimental data. The ROM for axial rotation and extension was within one standard deviation of the experimental data. The ROM for flexion and lateral bending was outside one standard deviation of the experimental data, but a compromise was required to use one set of ligament laxity values to achieve a best fit to all load cases. Atlanto-occipital motion was compared as a ratio to overall ROM, and only in extension did the inclusion of ligament laxity not improve the agreement. After a Type II odontoid fracture was incorporated into the model, the increase in ROM was consistent with experimental data from the literature.

CONCLUSIONS

The optimization approach used in this study provided values for ligament laxities that, when incorporated into the FE model, generally improved the ROM response when compared with experimental data. Successfully modeling a Type II odontoid fracture showcased the robustness of the FE model, which can now be used in future biomechanics studies.

Biomechanical Assessment of Stabilization of Simulated Type II Odontoid Fracture with Case Study

STUDY DESIGN

Researchers created a proper type II dens fracture (DF) and quantified a novel current posterior fixation technique with spacers at C1-C2. A clinical case study supplements this biomechanical analysis.

PURPOSE

Researchers explored their hypothesis that spacers combined with posterior instrumentation (PI) reduce range of motion significantly, possibly leading to better fusion outcomes.

OVERVIEW OF LITERATURE

Literature shows that the atlantoaxial joint is unique in allowing segmental rotary motion, enabling head turning. With no intervertebral discs at these joints, multiple ligaments bind the axis to the skull base and to the atlas; an intact odontoid (dens) enhances stability. The most common traumatic injury at these strong ligaments is a type II odontoid fracture.

METHODS

Each of seven specimens (C0-C3) was tested on a custom-built six-degrees-of-freedom spine simulator with constructs of intact state, type II DF, C1-C2 PI, PI with joint capsulotomy (PIJC), PI with spacers (PIS) at C1-C2, and spacers alone (SA). A bending moment of 2.0 Nm (1.5°/sec) was applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). One-way analysis of variance with repeated measures was performed.

RESULTS

DF increased motion to 320%, 429%, and 120% versus intact (FE, LB, and AR, respectively). PI significantly reduced motion to 41%, 21%, and 8%. PIJC showed negligible changes from PI. PIS reduced motion to 16%, 14%, and 3%. SA decreased motion to 64%, 24%, and 54%. Reduced motion facilitated solid fusion in an 89-year-old female patient within 1 year.

CONCLUSIONS

Type II odontoid fractures can lead to acute or chronic instability. Current fixation techniques use C1-C2 PI or an anterior dens screw. Addition of spacers alongside PI led to increased biomechanical rigidity over intact motion and may offer an alternative to established surgical fixation techniques.

"Soft that molds the hard:" Geometric morphometry of lateral atlantoaxial joints focusing on the role of cartilage in changing the contour of bony articular surfaces

Purpose:

The existing literature on lateral atlantoaxial joints is predominantly on bony facets and is unable to explain various C1-2 motions observed. Geometric morphometry of facets would help us in understanding the role of cartilages in C1-2 biomechanics/kinematics.

Objective:

Anthropometric measurements (bone and cartilage) of the atlantoaxial joint and to assess the role of cartilages in joint biomechanics.

Materials and Methods:

The authors studied 10 cadaveric atlantoaxial lateral joints with the articular cartilage in situ and after removing it, using three-dimensional laser scanner. The data were compared using geometric morphometry with emphasis on surface contours of articulating surfaces.

Results:

The bony inferior articular facet of atlas is concave in both sagittal and coronal plane. The bony superior articular facet of axis is convex in sagittal plane and is concave (laterally) and convex medially in the coronal plane. The bony articulating surfaces were nonconcordant. The articular cartilages of both C1 and C2 are biconvex in both planes and are thicker than the concavities of bony articulating surfaces.

Conclusion:

The biconvex structure of cartilage converts the surface morphology of C1-C2 bony facets from concave on concavo-convex to convex on convex. This reduces the contact point making the six degrees of freedom of motion possible and also makes the joint gyroscopic.

Incidence and age and gender profiles of hyperplasia in individual cervical vertebrae

Objective

To analyze the incidence and age and gender profiles of hyperplasia in individual cervical vertebrae.

Methods

In this retrospective study, computed tomography three-dimensional reconstruction images of cervical vertebrae from patients with neck discomfort were analyzed for the presence of hyperplasia and compared with age and gender data.

Results

Scans from a total of 580 patients (352 males, 228 females) were analyzed. The highest incidence of hyperplasia was seen in C2 (25%), followed by C1 (23%), C6 (16%), C5 (15%), C7 (9%), C4 (8%) and C3 (4%). Patients with C2 hyperplasia were the youngest and those with C1 hyperplasia were the second youngest, while patients with C7 hyperplasia were the oldest. Of those with C2, C1 and C7 hyperplasia, males were significantly younger than females, whereas of those with C3, C4, C5 and C6 hyperplasia, females were significantly younger than males.

Conclusions

Hyperplasia of the cervical spine shows different age and gender profiles among the seven vertebrae. These findings may be helpful for the early recognition of cervical hyperplasia and highlight the importance of protecting the atlanto-axial joint in daily life.

New Posterior Atlantoaxial Restricted Non-Fusion Fixation for Atlantoaxial Instability: A Biomechanical Study

BACKGROUND

Loss of axial rotation and lateral bending after atlantoaxial fusion reduces a patient's quality of life. Therefore, effective, nonfusion fixation alternatives are needed for atlantoaxial instability.

OBJECTIVE

To evaluate the initial stability and function of posterior atlantoaxial restricted nonfusion fixation (PAARNF), a new protocol, using cadaveric cervical spines compared with the intact state, destabilization, and posterior C1-C2 rod fixation.

METHODS

Cervical areas C0 through C3 were used from 6 cadaveric spines to test flexion-extension, lateral bending, and axial rotation range of motion (ROM). With the use of a machine, 1.5-Nm torque at a rate of 0.1 Nm/s was used and held for 10 seconds. The specimens were loaded 3 times, and data were collected in the third cycle and tested in the following sequence: (1) intact, (2) destabilization (using a type II odontoid fracture model), (3) destabilization with PAARNF (PAARNF group), and (4) rod implantation (rod group). The order of tests for the PAARNF and rod groups was randomly assigned.

RESULTS

The average flexion-extension ROM in the PAARNF group was 7.44 ± 2.05°, which was significantly less than in the intact (P = .00) and destabilization (P = .00) groups but not significantly different from that of the rod group (P = .07). The average lateral bending ROM (10.59 ± 2.33°; P = .00) and axial rotation ROM (38.79 ± 13.41°; P = .00) of the PAARNF group were significantly greater than in the rod group. However, the values of the PAARNF group showed no significant differences compared with those of the intact group.

CONCLUSION

PAARNF restricted atlantoaxial flexion-extension but preserved axial rotation and lateral bending at the atlantoaxial joint in a type II odontoid fracture model. However, it should not be used clinically until further studies have been performed to test the long-term effects of this procedure.

Postural Consequences of Cervical Sagittal Imbalance: A Novel Laboratory Model

STUDY DESIGN

A biomechanical study using human spine specimens.

OBJECTIVE

To study postural compensations in lordosis angles that are necessary to maintain horizontal gaze in the presence of forward head posture and increasing T1 sagittal tilt.

SUMMARY OF BACKGROUND DATA

Forward head posture relative to the shoulders, assessed radiographically using the horizontal offset distance between the C2 and C7 vertebral bodies (C2-C7 [sagittal vertical alignment] SVA), is a measure of global cervical imbalance. This may result from kyphotic alignment of cervical segments, muscle imbalance, as well as malalignment of thoracolumbar spine.

METHODS

Ten cadaveric cervical spines (occiput-T1) were tested. The T1 vertebra was anchored to a tilting and translating base. The occiput was free to move vertically but its angular orientation was constrained to ensure horizontal gaze regardless of sagittal imbalance. A 5-kg mass was attached to the occiput to mimic head weight. Forward head posture magnitude and T1 tilt were varied and motions of individual vertebrae were measured to calculate C2-C7 SVA and lordosis across C0-C2 and C2-C7.

RESULTS

Increasing C2-C7 SVA caused flexion of lower cervical (C2-C7) segments and hyperextension of suboccipital (C0-C1-C2) segments to maintain horizontal gaze. Increasing kyphotic T1 tilt primarily increased lordosis across the C2-C7 segments. Regression models were developed to predict the compensatory C0-C2 and C2-C7 angulation needed to maintain horizontal gaze given values of C2-C7 SVA and T1 tilt.

CONCLUSION

This study established predictive relationships between radiographical measures of forward head posture, T1 tilt, and postural compensations in the cervical lordosis angles needed to maintain horizontal gaze. The laboratory model predicted that normalization of C2-C7 SVA will reduce suboccipital (C0-C2) hyperextension, whereas T1 tilt reduction will reduce the hyperextension in the C2-C7 segments. The predictive relationships may help in planning corrective strategy in patients experiencing neck pain, which may be attributed to sagittal malalignment.

LEVEL OF EVIDENCE

N/A.

Biomechanical analysis of screw constructs for atlantoaxial fixation in cadavers: a systematic review and meta-analysis

OBJECT

The unique and complex biomechanics of the atlantoaxial junction make the treatment of C1–2 instability a challenge. Several screw-based constructs have been developed for atlantoaxial fixation. The biomechanical properties of these constructs have been assessed in numerous cadaver studies. The purpose of this study was to systematically review the literature on the biomechanical stability achieved using various C1–2 screw constructs and to perform a meta-analysis of the available data.

METHODS

A systematic search of PubMed through July 1, 2013, was conducted using the following key words and Boolean operators: “atlanto [all fields]” AND “axial [all fields]” OR “C1–C2” AND “biomechanic.” Cadaveric studies on atlantoaxial fixation using screw constructs were included. Data were collected on instability models, fixation techniques, and range of motion (ROM). Forest plots were constructed to summarize the data and compare the biomechanical stability achieved.

RESULTS

Fifteen articles met the inclusion criteria. An average (± SD) of 7.4 ± 1.8 cadaveric specimens were used in each study (range 5–12). The most common injury models were odontoidectomy (53.3%) and cervical ligament transection (26.7%). The most common spinal motion segments potted for motion analysis were occiput–C4 (46.7%) and occiput–C3 (33.3%). Four screw constructs (C1 lateral mass–C2 pedicle screw [C1LM–C2PS], C1–2 transarticular screw [C1–C2TA], C1 lateral mass–C2 translaminar screw [C1LM-C2TL], and C1 lateral mass–C2 pars screw [C1LM–C2 pars]) were assessed for biomechanical stability in axial rotation, flexion/extension, and lateral bending, for a total of 12 analyses. The C1LM–C2TL construct did not achieve significant lateral bending stabilization (p = 0.70). All the other analyses showed significant stabilization (p < 0.001 for each analysis). Significant heterogeneity was found among the reported stabilities achieved in the analyses (p < 0.001; I2 > 80% for all significant analyses). The C1LM–C2 pars construct achieved significantly less axial rotation stability (average ROM 36.27° [95% CI 34.22°–38.33°]) than the 3 other constructs (p < 0.001; C1LM–C2PS average ROM 49.26° [95% CI 47.66°–50.87°], C1–C2TA average ROM 47.63° [95% CI 45.22°–50.04°], and C1LM–C2TL average ROM 53.26° [95% CI 49.91°–56.61°]) and significantly more flexion/extension stability (average ROM 13.45° [95% CI 10.53°–16.37°]) than the 3 other constructs (p < 0.001; C1LM–C2PS average ROM 9.02° [95% CI 8.25°–9.80°], C1–C2TA average ROM 7.39° [95% CI 5.60°–9.17°], and C1LM–C2TL average ROM 7.81° [95% CI 6.93°–8.69°]). The C1–C2TA (average ROM 5.49° [95% CI 3.89°–7.09°]) and C1LM–C2 pars (average ROM 4.21° [95% CI 2.19°–6.24°]) constructs achieved significantly more lateral bending stability than the other constructs (p < 0.001; C1LM–C2PS average ROM 1.51° [95% CI 1.23°–1.78°]; C1LM–C2TL average ROM −0.07° [95% CI −0.44° to 0.29°]).

CONCLUSIONS

Meta-analysis of the existing literature showed that all constructs provided significant stabilization in all axes of rotation, except for the C1LM–C2TL construct in lateral bending. There were significant differences in stabilization achieved in each axis of motion by the various screw constructs. These results underline the various strengths and weaknesses in biomechanical stabilization of different screw constructs. There was significant heterogeneity in the data reported across the studies. Standardized spinal motion segment configuration and injury models may provide more consistent and reliable results.

Prevalence of degenerative changes of the atlanto-axial joints

BACKGROUND CONTEXT

Degeneration of the atlantodens and atlanto-axial joints is associated with cervical spine pain and may also be associated with an increased risk of dens fracture. However, there is paucity of literature describing the prevalence of specific degenerative changes in the atlantodens and atlanto-axial facet joints.

PURPOSE

To document age-related degenerative changes of the cervical spine in a large cohort of patients.

STUDY DESIGN/SETTING

This is a retrospective cohort study.

PATIENT SAMPLE

Adult trauma patients were admitted to our Level 1 trauma center.

OUTCOME MEASURES

Osteoarthritis of the atlantodens and atlanto-axial facet joints of the cervical spine and the presence of intraosseous cyst and calcific synovitis, as determined by computed tomography (CT) scans.

METHODS

We conducted a retrospective study of 1,543 adult trauma patients who received a cervical spine CT scan. The anterior atlantodens joint interval was measured. The presence or absence of intraosseous cysts and calcific synovitis was recorded. Degeneration of the atlantodens and atlanto-axial facet joints at age intervals was quantified.

RESULTS

The atlantodens interval narrowed linearly with age (R(2)=0.992, p<.001). The prevalence of intraosseous cysts increased exponentially with age from 4.2% to 37.4%, and calcific synovitis increased from 0% to 11.1%. Intraosseous cyst formation generally began in the second and third decades of life and synovitis in the fifth and sixth decades of life. Facet joints also demonstrated age-related changes; however, the rate of degenerative changes was lower than in the atlantodens joint.

CONCLUSIONS

To our knowledge, this is the first study that documents specific changes of both atlantodens and atlanto-axial facet joints as a function of age in a large cohort of 1,543 patients. These changes increased exponentially with age and may contribute to pain and limitation in motion. In light of our findings and recent studies demonstrating the association between degeneration and dens fracture in elderly, cervical spine radiographs of elderly patients should be carefully assessed for these changes.