Alar Ligaments Research Articles

Morphological Types of Foramen Magnum

Introduction: The foramen magnum (FM) is a unique and complex anatomical area located in the central basal region of the occipital bone. It is a three-dimensional opening through which vital structures pass, such as the medulla oblongata and its membranes, the spinal accessory nerve, the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membrane and the alar ligaments. Because of this vital relationship between the FM and its content, it is of great importance to study the morphological types of FM. Findings from such evaluations have essential applications in clinical practice and in surgery. Objective: To determine the incidence of different morphological types of FM. Materials and Methods: 110 FM from dry human crania of known sex and age were analyzed. The specimens belong to the anatomical collections of Tiradentes University (UNIT) and the Metropolitan University of Education and Culture (UNIME). Among these, 66 were male, 44 were female and their ages ranged from 11 to 91 years (mean: 58.01 Original Research Article Annual Research & Review in Biology, 4(9): 1372-1378, 2014 1373 years). FM morphology was studied using photographic images and with the aid of Corel Draw Photo-Paint X5. Results: Among the 110 FM analyzed, nine morphological types were found: pear-shaped 37.27%, rounded 15.45%, tetragonal 10.91%, biconvex 10.91%, hexagonal 9.09%, oval 5.45%, pentagonal 2.73% and heptagonal 1.82%. In the remaining 6.36% of the FM, it was not possible to define a regular and specific form. Conclusions: Pear-shaped FM predominated, followed by rounded FM. In relation to sex, the tetragonal and biconvex forms occurred five times more frequently in males than in females, while the hexagonal form occurred twice as frequently in females than in males.

English

Introduction We illustrated the anatomical aspect of the cartilage in a healthy and osteoarthritic knee joint. Osteoarthritis is a disease of high ethical and economical importance. In advanced stages, the patients suffer from severe pain, restriction of mobility and inability to work. In this mini review, we described the current knowledge about the macroscopic and microscopic anatomical features in healthy and osteoarthritic knee cartilage. Discussion Adult articular cartilage has a low capacity to repair itself, and thus even minor injuries may lead to progressive damage and osteoarthritic joint degeneration, resulting in significant pain and disability. Numerous studies on human osteoarthritic tissue and in animal models have addressed the microscopic and macroscopic anatomical aspects of OA progression to get a better understanding of the pathophysiology of this disease. Further, imaging studies show the macroscopic anatomical changes and are important for the diagnosis of this disease. Conclusion Further in vivo and in vitro studies must be carried out in order to improve the early diagnosis and the treatment of articular cartilage defects, leading to a better clinical outcome for the patients affected. Introduction The knee joint is a relatively complex anatomical structure. The stability of this synovial (or diarthrodial) joint is maintained by a variety of ligaments and the presence of large muscle groups1. Both the femur and tibia are enclosed in a joint capsule (Figure 1) lined with synovial tissue. Between the condyles of the femur and the condylar surface of the tibia, there are two C-shaped pieces of cartilage called menisci (Figure 2), which serve as shock absorbers for the knee joint, located medially and laterally inside the joint2–4. The joint capsule of the knee is strengthened by different ligaments: the patellar ligament or patellar tendon, the lateral and medial retinaculum of the patella, the medial and lateral alar ligaments, the medial and lateral collateral ligaments, the popliteal ligaments and the anterior and posterior cruciate ligaments (ACLs and PCLs) (Figure 3). Between each muscle group, there are fluid-filled sacs called bursa and fat bodies, which reduce friction and lend added protection to the joint capsule. The knee works during normal activity such as walking or running, and even for support while standing. It can tolerate moderate stress without significant injury. However, the knee lacks support to withstand many types of injury, especially rotational forces such as those seen in many athletic activities. The most important connective tissue for the correct functioning of the knee joint is the cartilage. Cartilage is classified into three types according to the amount of its components: elastic cartilage, hyaline cartilage and fibrocartilage5. Hyaline cartilage is a flexible connective tissue found in many areas of human and other animal bodies. It covers the opposing osseous ends of every synovial joint5–8, such as the knee joint, and it is found in the growth plate of the metaphysis9,10. Cartilage tissue has unique viscoelastic and compressive properties provided by the extracellular matrix, which is mainly composed of collagen type II and the large proteoglycan aggrecan5–8. Articular cartilage is not innervated and lacks blood vessels. For this reason, knee injuries, even though minor, if involving the cartilage, may have delayed healing time. Nutrients in the synovial fluid and cellular repair components are transported to the chondrocytes by diffusion from the synovial fluid5–8. Only small defects, associated with minimal loss of matrix components, can be regenerated by hyaline cartilage. * Corresponding author Email: g.musumeci@unict.it 1 Department of Bio-Medical Sciences, Human Anatomy and Histology Division, University of Catania, Italy 2 Department of Medical and Pediatric Sciences, Internal Medicine Division, University of Catania, Italy 3 Fondazione Mediterranea ‘‘G.B. Morgagni’’, Catania, Italy Figure 1: Surgery of the left knee with joint capsule on site.

Condylus tertius with atlanto-axial rotatory fixation: an unreported association

The "condylus tertius" or the "third occipital condyle" is an embryological remnant of the proatlas sclerotome. Anatomically, it is attached to the basion and often articulates with the anterior arch of the atlas and the odontoid apex; hence, it is also called the "median occipital condyle". It is a rare anomaly of the cranio-vertebral junction (CVJ) that can lead to instability and compression of important surrounding neurovascular structures. We report a case of a 16-year-old boy who presented with suboccipital neck pain, torticollis and right sided hemiparesis. Plain radiographs revealed an increased atlanto-dental interspace (ADI) with a retroflexed odontoid. Open mouth view showed asymmetry of the articular processes of the atlas with respect to the dens. Computed tomography (CT) of the CVJ delineated the third occipital condyle. Furthermore, on dynamic CT study, a type 3 atlanto-axial rotatory fixation (AARF) was clearly demonstrated. Magnetic resonance imaging (MRI) of the CVJ revealed severe right-sided spinal cord compression by the retroflexed and rightward deviated dens. It also revealed disruption of the left alar and transverse ligaments. The patient was treated with 8 weeks of cranial traction and reasonable alignment was obtained. This was followed by C1-C2 lateral mass screw fixation and C1-C2 interlaminar wiring to maintain the alignment. A review of the literature did not reveal any cases of condylus tertius associated with non-traumatic AARF. An accurate knowledge of the embryology and imaging features of this rare CVJ anomaly is useful in the prompt diagnosis and management of such patients.

Biomechanical evaluation of the stabilizing function of the atlantoaxial ligaments under shear loading: A canine cadaveric study

To evaluate the stabilizing function of atlanto-axial ligaments in dogs. Cadaveric biomechanical study. Beagle dog cadavers (n = 10). The craniocervical region was collected from 10 Beagle cadavers, and the occipito-atlanto-axial region was prepared and freed from the surrounding muscles. Care was taken to preserve integrity of the atlantoaxial ligaments and atlantoaxial joint capsule. The atlanto-occipital joints were blocked with 2 diverging transarticular 1.8 mm positive threaded K-wires. Specimen extremities were embedded in polymethylmethacrylate (PMMA) and mounted on a simulator testing shear load at the atlantoaxial joint. Range of motion (ROM) and neutral zone (NZ) were determined with all ligaments intact, after cutting the apical ligament, both alar ligaments, the transverse ligaments and finally after cutting the dorsal atlantoaxial ligament. ROM increased similarly and stepwise during testing. The most significant increase was observed after transection of the alar ligaments. The alar ligaments seem to be the most important ligamentous structures for stabilization of the atlantoaxial joint under shear load.

AB1067 Eighteen cases of crowned dens syndrome: Presentation and diagnosis

BackgroundEighteen cases of crowned dens syndrome: presentation and diagnosis.ObjectivesTo etablish the clinical, biological and radiological criteria of crowned dens syndrome, a little known etiology of acute neck pain.MethodsWe carried out...

Sequential imaging demonstrating os odontoideum formation after a fracture through the apical odontoid epiphysis: case report and review of the literature

The mechanism of formation of an os odontoideum is controversial and likely multifactorial. One theory states that the apex of the odontoid separates from the body because of a fracture. The intact alar and apical ligaments pull the fractured segment superiorly. The independent vascular supply of the apex allows the fractured bone to remain viable and remodel into the smooth, corticated bone characteristic of an os odontoideum. However, there are no publications with direct radiographic evidence supporting the theory. In this paper, the authors present a 7-year-old child with a fracture through the apical odontoid epiphysis, extending into the body of the dens. Serial imaging studies demonstrate progressive separation of the apex from the body of the odontoid. The fractured segment begins to remodel and assume the classic form of an os. The authors consider this case to be radiographic evidence supporting an acquired/traumatic origin of os odontoideum. Further, the mechanism of fracture through a cartilaginous epiphysis may explain the formation of an os after "normal" x-ray images or following seemingly minor trauma.

Morphology of the transverse ligament of the atlas and the alar ligaments in the silver fox (Vulpes vulpes var)

BackgroundRecent new anatomical and histological features of craniocervical junction in dogs and cats were described providing evidence of differences between the carnivore species. No information on these structures in foxes exists.ResultsTwo parts of the alar ligaments were found. A longer one aroused from dens of axis to the internal (medial) surface of the occipital condyles and was called apical part. A shorter part originated from the entire length of the lateral edge of the dens of axis and terminated on the internal wall of the vertebral foramen of atlas and thus was called the lateral part. The transverse ligament of the atlas was widened in the mid region, above the dens of axis, and thickened at enthesis. Periosteal fibrocartilage was detected in the transverse ligament of the atlas at the enthesis, and sesamoid fibrocartilage was present on periphery in the middle of the ligament.ConclusionsThe craniocervical junction in foxes differs in part from other carnivores such as dogs and cats but resembles that of mesaticephalic dogs. The sesamoid and periosteal fibrocartilage supports the transverse ligament of the atlas whereas the alar ligaments have no cartilage.

Toward Understanding Normal Craniocervical Rotation Occurring During the Rotation Stress Test for the Alar Ligaments

The rotation stress test is recommended for assessing alar ligament integrity. Although some authors, in the literature regarding the rotation stress test, accept that rotation will occur during testing, estimates of range occurring with a normal test response vary between 20 and 40 degrees. None of these estimates are based on formal examination of the test. The purposes of this study were: (1) to examine the range of craniocervical rotation occurring during rotation stress testing for the alar ligaments in individuals who are healthy and (2) to investigate a measurement protocol for quantifying rotation. A within-subject experimental study was conducted. Sixteen participants underwent magnetic resonance imaging in neutral and end-range rotation stress test positions. Measurements followed a standardized protocol relative to the position of the axis. A line connecting the transverse foramena of the axis created a reference plane. The position of the occiput in the head-neutral position was calculated as the angle formed between a line joining the foramena lacerum and the reference plane. Measurements were repeated at the end-range test position. Total rotation of the occiput was calculated as the difference in angles measured in neutral and test positions. Measurement was performed on 4 occasions, and reliability of measurements was assessed using the standard error of measurement (SEM) and the intraclass correlation coefficient (ICC). Measurement of rotation of the occiput relative to a stabilized axis ranged between 1.7 and 21.5 degrees (X=10.6, SD=5.1, SEM=1.14, ICC=.96, 95% confidence interval=.90-.98). Sustaining the test position for imaging increased the potential for loss of end-range position and image quality. Testing could be performed only in the neutral position, not in 3 planes as commonly described. The range of craniocervical rotation during rotation stress testing of intact alar ligaments should typically be 21 degrees or less. Rotation may be quantified using the method protocol outlined.

Are two readers more reliable than one? A study of upper neck ligament scoring on magnetic resonance images

BackgroundMagnetic resonance imaging (MRI) studies typically employ either a single expert or multiple readers in collaboration to evaluate (read) the image results. However, no study has examined whether evaluations from multiple readers provide more reliable results than a single reader. We examined whether consistency in image interpretation by a single expert might be equal to the consistency of combined readings, defined as independent interpretations by two readers, where cases of disagreement were reconciled by consensus.MethodsOne expert neuroradiologist and one trained radiology resident independently evaluated 102 MRIs of the upper neck. The signal intensities of the alar and transverse ligaments were scored 0, 1, 2, or 3. Disagreements were resolved by consensus. They repeated the grading process after 3–8 months (second evaluation). We used kappa statistics and intraclass correlation coefficients (ICCs) to assess agreement between the initial and second evaluations for each radiologist and for combined determinations. Disagreements on score prevalence were evaluated with McNemar’s test.ResultsHigher consistency between the initial and second evaluations was obtained with the combined readings than with individual readings for signal intensity scores of ligaments on both the right and left sides of the spine. The weighted kappa ranges were 0.65-0.71 vs. 0.48-0.62 for combined vs. individual scoring, respectively. The combined scores also showed better agreement between evaluations than individual scores for the presence of grade 2–3 signal intensities on any side in a given subject (unweighted kappa 0.69-0.74 vs. 0.52-0.63, respectively). Disagreement between the initial and second evaluations on the prevalence of grades 2–3 was less marked for combined scores than for individual scores (P ≥ 0.039 vs. P ≤ 0.004, respectively). ICCs indicated a more reliable sum score per patient for combined scores (0.74) and both readers’ average scores (0.78) than for individual scores (0.55-0.69).ConclusionsThis study was the first to provide empirical support for the principle that an additional reader can improve the reproducibility of MRI interpretations compared to one expert alone. Furthermore, even a moderately experienced second reader improved the reliability compared to a single expert reader. The implications of this for clinical work require further study.

Magnetic resonance imaging signal changes of alar and transverse ligaments not correlated with whiplash-associated disorders

Hypothesis that loss of integrity of the membranes in the craniocervical junction might be the cause of neck pain in patients with whiplash-associated disorders (WADs) has been proposed. In recent years, with development of more detailed magnetic resonance imaging (MRI) techniques, morphologic changes of the ligaments and membranes in the craniocervical junction, especially alar and transverse ligaments have been discussed. A meta-analysis was performed to evaluate the relationship of MRI signal changes of alar and transverse ligaments and WADs. A systematic search of EMBASE, PUBMED, and Cochrane Library and references from eligible articles were conducted. Comparative studies reporting on evaluating the relationship between MRI high-signal changes of alar and transverse ligaments and WADs were regarded eligible. A pooled estimate of effect size was produced. Alar ligaments: Six studies (total n = 622) were included. MRI signal changes of alar ligaments did not appear to be related with WADs (P = 0.20, OR = 1.54, 95 % CI = 0.80-2.94). Heterogeneity was present (I (2) = 46 %, P = 0.10), which was eliminated upon sensitivity analysis bringing the OR to 1.27 (95 % CI = 0.87-1.86, I (2) = 0 %). Transverse ligaments: Four studies (total n = 489) were included. MRI signal changes of transverse ligament did not appear to be related with WADs (P = 0.51, OR = 1.44, 95 % CI = 0.49-4.21). Heterogeneity was present (I (2) = 77 %, P = 0.005), which was eliminated upon sensitivity analysis bringing the OR to 0.79 (95 % CI = 0.49-1.28, I (2) = 0 %). MRI signal changes of alar and transverse ligaments are not supposed to be caused by whiplash injury, and MRI examination of alar and transverse ligaments should not be used as the routine workup of patients with WADs.

Delineation of Alar Ligament Morphology: Comparison of Magnetic Resonance Imaging at 1.5 and 3 Tesla

Rupture of the alar and transverse ligaments due to whiplash injury can lead to upper cervical spine instability and subsequent neurological deterioration. The purpose of this study was to evaluate the normal anatomical variability of the alar ligaments in asymptomatic individuals with 3-T magnetic resonance imaging (MRI) and to compare the findings with standard 1.5-T examinations. Thirty-six participants underwent 3-T and 1.5-T MRIs. Magnetic resonance imaging findings were analyzed by classifying the alar ligaments with regard to the features detectability, signal intensity compared with muscle tissue, homogeneity, shape, spatial orientation, and symmetry. Delineation of the alar ligaments was significantly better on 3-T images, which were subjectively preferred for evaluation. The alar ligaments showed great variability. In the majority of participants, the alar ligaments were hypointense to muscle tissue, inhomogeneous, and different in shape and orientation. A statistically significantly higher number of ligaments appeared symmetric on 3-T imaging, indicating that 1.5-T imaging may underestimate the proportion of patients with normal, symmetric ligaments. This study demonstrates that high-field 3-T MRI provides better visualization of the alar ligaments compared with 1.5-T MRI. The higher signal-to-noise ratio allows detection of small signal changes. A great interindividual variety of the MRI morphology of the alar ligaments was found in participants with no history of neck trauma. Further studies with more participants are necessary to evaluate alar ligament pathologies in patients with a history of whiplash injury.

Calcification of the alar ligament of the cervical spine in a patient with rheumatoid arthritis

Calcification of the alar ligament of the cervical spine in a patient with rheumatoid arthritis

Revisiting the clinical anatomy of the alar ligaments

The morphology of the alar ligaments has been inconsistently described, particularly with regard to the existence of an atlantal portion. Despite these inconsistencies, these descriptions have been used to develop physical tests for the integrity of these ligaments in patients with cervical spine problems. The purpose of this study was to describe the detailed macrostructure of the alar ligaments. The alar ligaments of 11 cervical spine specimens from embalmed adult cadavers were examined by fine dissection. A detailed description of the macrostructure of these ligaments and their attachment sites was recorded. Measurements were performed with respect to ligament dimensions and relations with selected bony landmarks. No atlantal portion of the alar ligament was viewed in any specimen. The attachment of the ligaments on the odontoid process occurred on its lateral and posterolateral aspects, frequently below the level of the apex. The occipital attachment was on the medial surface of the occipital condyles in close proximity to the atlanto-occipital joints. The orientation of the ligaments was primarily horizontal. The presence of transverse bands extending occiput to occiput with minimal or no attachment to the odontoid process was a common variant. The absence of findings with respect to the atlantal portion of the alar ligament suggests that it may be considered an anatomical variant, not an essential component for stability of the craniocervical complex. These findings may inform the use and interpretation of clinical tests for alar ligament integrity.

Effect of Magnetic Resonance Imaging Field Strength on Delineation and Signal Intensity of Alar Ligaments in Healthy Volunteers

A prospective study of healthy volunteers. To evaluate the influence of magnetic resonance imaging (MRI) field strength on the delineation and signal intensity of alar ligaments (AL) in healthy volunteers. The fact that AL physiologically show morphologic variabilities is well established. However, presence and etiology of high-signal intensities within the AL as well as the influence of the MRI field strength on the signal characteristics of AL are still not completely understood. METHODS.: Coronal and sagittal 2-mm proton-density weighted sequences were acquired in 50 healthy volunteers using different MRI field strengths (1 T, 1.5 T, 3 T). Delineation and signal characteristics of AL were evaluated by 2 neuroradiologists independently. Differences concerning delineation and signal intensity between the MRI scanners, inter rater reliability between the 2 readers, and intrarater reliability at different time points were calculated. Delineation of AL was significantly better both on 3 T and 1.5 T than on 1 T (P = 0.05) in sagittal as well as in coronal view. In coronal view delineation was significantly better on 3 T than on 1.5 T, whereas in sagittal view no significant difference was evident when comparing 1.5 T and 3 T. Concerning signal intensity of AL in sagittal view, there was no significant difference between the 3 different field strengths. Inter-rater and intrarater agreements were fair to moderate with respect to delineation as well as signal intensity of AL. 1.5 T and 3 T significantly improve the delineation of AL when compared with lower field strength (1 T), but signal intensity of the AL in healthy volunteers is not influenced by the field strength. Increased signal is present in asymptomatic subjects on both low- and high-field magnetic resonance systems. Accordingly, the pathologic relevance of increased signal intensity of the AL, regardless of field strength, may not be indicative of traumatic AL injury.

The transverse occipital ligament: an anatomic, histologic, and radiographic study

The craniocervical region is an osteoligamentous complex that provides structural stability and movement by means of numerous ligaments. Fundamental knowledge of these ligaments is important for physicians who treat patients with disorders of this region to reduce morbidity and mortality. There is a paucity of data in the literature regarding the morphology, function, and classification of the transverse occipital ligament (TOL). The purpose of this study was to investigate the prevalence, morphology, and variations of the TOL in a large number of adult human cadavers using dissection, histology, and digital radiography. Cadaveric laboratory study. Thirty-two formalin-fixed human adult cadavers were dissected in the study. Fourteen cadavers were found to have a TOL. Measurements using a digital caliper, high-resolution digital photography, histologic staining with bright-field microscopy, and digital radiography. The posterior musculature and related soft tissues were dissected and underlying bony elements removed. The TOL was identified, isolated, measured, and then removed for histologic preparation with hematoxylin and eosin staining. Anteroposterior open-mouth digital radiographs of the upper cervical spine with monofilament attached to the TOL were used to demonstrate its relations to the occiput, atlas, and axis. The TOL was present in 14 of 32 (44%) of the dissected cadavers (six male and eight female). Three types of TOLs were identified. Type 1 had bilateral connections to the alar ligaments and had fibers inserting onto the dens. Type 2 also had bilateral connections to the alar ligaments but did not have fibers inserting onto the dens. Type 3 neither had any connections to the alar ligaments nor had fibers that connected to the dens. Male cadavers always had a Type 1 TOL compared with 3 of 8 (38%) female cadavers and this difference was significant (p=.031). The TOL consisted of dense regular connective tissue with parallel arrangements of collagen fibers and interposed fibroblasts. Our data suggest that the TOL is not an anatomic variant and can be classified into three types. Future biomechanical studies can be designed to investigate the function of the TOL, although we hypothesize that it may act as a fulcrum during flexion and extension of the head because it is located between the apical ligament and superior crus of the cruciform ligament. Anteroposterior open-mouth digital radiographs revealed the location of the TOL with respect to the upper two cervical vertebrae. Future research should investigate the radiologic characteristics of the TOL using magnetic resonance imaging.

MAGNETIC RESONANCE IMAGING OF THE LIGAMENTOUS STRUCTURES OF THE OCCIPITOATLANTOAXIAL REGION IN THE DOG

Our objectives were to establish a magnetic resonance (MR) protocol for the examination of, and then describe, the normal ligaments and the supporting structures of the occipitoatlantoaxial region. This was done in 10 cadaver dogs. In addition, MR images of three patients with cervical pain localized to the occipitoatlantoaxial region are included to provide examples of ligamentous abnormalities. All ligaments were hypointense in all pulse sequences. The apical, dorsal atlantoaxial, and dorsal longitudinal vertebral ligaments were seen best in the sagittal T1W and PD-weighted images. The transverse ligament was best visualized in the transverse plane in all pulse sequences and appeared to be confluent with the dorsal longitudinal vertebral ligament dorsal to the dens in the sagittal plane. A 20° dorsal plane reconstructed image in 0.6-mm slice thickness was necessary to visualize the alar ligaments, which were visible in 9/10 dogs. The dorsal longitudinal vertebral ligament appeared continuous with the apical ligament and tectorial membrane. Abnormalities in clinically affected dogs included thickening of the alar ligaments, absence of transverse ligament and elongation, and irregularity of the apical ligament.

Atlantoaxial rotatory dislocation (AARD) in pediatric age: MRI study on conservative treatment with Philadelphia collar—experience of nine consecutive cases

Atlantoaxial rotatory fixation and atlantoaxial rotatory subluxation are the most frequent manifestations of atlantoaxial rotatory dislocation (AARD) in pediatric population and are often treated conservatively. The objective of this study is to correlate the changes highlighted on MRI T2-weighted and STIR sequences with the duration of conservative treatment. We analyzed nine consecutive patients treated surgically between 1 Jan 2006 and 1 Jan 2010 at the Policlinico Umberto I of Rome. All patients underwent cervical X-ray, computed tomography and magnetic resonance imaging (MRI) (T1 and T2-weighted, STIR, angio MRI). All patients were treated with bed rest, muscle relaxants and cervical collar, and radiological follow-up with MRI and cervical X-ray was performed. According to Fielding's classification, we observed seven patients with a type 1 subluxation and two patients with a type II subluxation. In type 1, STIR and T2 sequences showed a hyperintensity in the alar and capsular ligaments and in the posterior ligamentous system, with integrity of the transverse ligament (LTA). In type 2, the hyperintensity also involved the LTA. During the follow-up, MRI showed a progressive reduction until the disappearance of the hyperintensity described, which was followed by a break with orthotic immobilization. MRI with STIR sequences appears to be useful in addressing the duration of conservative treatment in AARD.

A geometrical model of vertical translation and alar ligament tension in atlanto-axial rotation

While allowing the greatest range of axial rotation of the entire spine with 40° to each side, gradual restraint at the extremes of motion by the alar ligaments is of vital importance. In order for the ligaments to facilitate a gradual transition from the neutral to the elastic zone, a complex interaction of axial rotation and vertical translation via the biconvex articular surfaces is essential. The aim of this investigation is to establish a geometrical model of the intricate interaction of the alar ligaments and vertical translatory motion of C1/C2 in axial rotation. Bilateral alar ligaments including the odontoid process and condylar bony entheses were removed from six adult cadavers aged 65-89 years within 48 h of death. All specimens were judged to be free of abnormalities with the exception of non-specific degenerative changes. Dimensions of the odontoid process and alar ligaments were measured. Graphical multiplanar reconstruction of atlanto-axial rotation was done in the transverse and frontal planes for the neutral position and for rotation to 40° with vertical translation of 3 mm. The necessary fibre elongation of the alar ligaments in the setting with and without vertical translation of the atlas was calculated. The mean diameter of the odontoid process in the sagittal plane was 10.6 mm (SD 1.1). The longest fibre length was measured from the posterior border of the odontoid enthesis to the posterior border of the condylar enthesis with an average of 13.2 mm (SD 2.5) and the shortest between the lateral (anterior) border odontoid enthesis and the anterior condylar enthesis with an average of 8.2 mm (SD 2.2). In graphical multiplanar reconstruction of atlanto-axial rotation to 40° without vertical translation of C1/C2, theoretical alar fibre elongation reaches 27.1% for the longest fibres, which is incompatible with the collagenous structure of the alar ligaments. Allowing 3 mm caudal translation of C1 on C2 at 40° rotation, as facilitated by the biconvex atlanto-axial joints, reduces alar fibre elongation to 23.3%. The biconvex configuration of the atlanto-axial joints is an integral feature of the functionality of upper cervical spine as it allows gradual vertical translation of the atlas against the axis during axial rotation, with gradual tensing of the alar ligaments. Vertical translation on its own, however, does not explain the tolerance of the alar ligaments towards the maximum of 40° of rotation and is most likely synergistic with the effects of the coupled motion of occipitocervical extension during rotation.

Investigation of whiplash injuries in the upper cervical spine using a detailed neck model

Whiplash injuries continue to have significant societal cost; however, the mechanism and location of whiplash injury is still under investigation. Recently, the upper cervical spine ligaments, particularly the alar ligament, have been identified as a potential whiplash injury location. In this study, a detailed and validated explicit finite element model of a 50th percentile male cervical spine in a seated posture was used to investigate upper cervical spine response and the potential for whiplash injury resulting from vehicle crash scenarios. This model was previously validated at the segment and whole spine levels for both kinematics and soft tissue strains in frontal and rear impact scenarios.The model predicted increasing upper cervical spine ligament strain with increasing impact severity. Considering all upper cervical spine ligaments, the distractions in the apical and alar ligaments were the largest relative to their failure strains, in agreement with the clinical findings. The model predicted the potential for injury to the apical ligament for 15.2g frontal or 11.7g rear impacts, and to the alar ligament for a 20.7g frontal or 14.4g rear impact based on the ligament distractions. Future studies should consider the effect of initial occupant position on ligament distraction.

Construct Validity of Clinical Tests for Alar Ligament Integrity: An Evaluation Using Magnetic Resonance Imaging

The alar ligaments are integral to limiting occipito-atlanto-axial rotation and lateral flexion and enhancing craniocervical stability. Clinical testing of these ligaments is advocated prior to the application of some cervical spine manual therapy procedures. Given the absence of validation of these tests and the potential consequences if manipulation is applied to an unstable upper cervical spine segment, exploration of these tests is necessary. The purpose of this study was to examine the direct effect of the side-bending and rotation stress tests on alar ligaments using magnetic resonance imaging (MRI). This was a within-participant experimental study. Sixteen participants underwent MRI in neutral and end-range stress test positions using proton density-weighted sequences in a 3-Tesla system. Measurements followed a standardized protocol relative to the position of the axis. Distances were measured from dens tip to the inferior margin of the foramen magnum and from midsubstance of the dental attachment of the ligament to its occipital insertion. Between-side differences were calculated for each measurement to account for inherent asymmetries in morphology. Differences were compared between the test and neutral positions using a Wilcoxon signed rank test. Side-bending stress tests produced a median between-side difference in ligament length of +1.15 mm. Rotation stress tests produced a median between-side difference in ligament length of +2.08 mm. Both results indicate increased measurement of the contralateral alar ligament. Limitations Assessment could be made only in the neutral position due to imaging limitations. Clinical texts state that tests should be performed in 3 positions: neutral, flexion, and extension. Both side-bending and rotation stress testing result in a measurable increase in length of the contralateral alar ligament. This finding is consistent with mechanisms that have been described to support their use in clinical practice.