Posterior Membrane Research Articles

Active Range of Motion as an Indicator for Ligament and Membrane Lesions in the Upper Cervical Spine after a Whiplash Trauma

In the present study, we examined whether active range of neck motion (AROM) differed between persons with and without a diagnosis of whiplash-associated disorder type 2 (WAD2) and explored whether magnetic resonance (MR)-verified lesions of specific ligaments or membranes at the craniovertebral junction was associated with increased or decreased motion in any particular direction among the WAD2 patients. A CROM goniometer was used for registration of flexion, extension, side bending (left and right) and rotation (left and right), respectively. The neck structures considered were the alar and the transverse ligaments, and the tectorial and the posterior atlanto-occipital membranes. Our study comprised 87 WAD2 patients and 29 control persons without any known neck injury. For comparing mean values of AROM between the groups, t-test and analysis of variance (ANOVA) were used. WAD patients had on average a shorter range of active motion for all movements compared with the control group. The difference was statistically significant for all measures considered, except side bending to the left. Among the WAD patients, increasing severity of lesions to the alar ligaments was associated with a decrease in maximal flexion and rotation. A similar pattern was seen for lesions to the transverse ligament, but the trend test was not significant. An abnormal posterior atlanto-occipital membrane was associated with shorter range of left rotation, with a significant trend test both in analyses with and without adjustment for lesions to other structures. No significant association was found in relation to lesions to the tectorial membrane, but very few persons had such lesions. These findings indicate that soft tissue lesions may affect neck motion as reflected by AROM. However, since lesions to different structures seem to affect the same movement, AROM alone is not a sufficient indicator for soft-tissue lesions to specific structure in the upper cervical spine.

Morphological variation in the electric organ of the little skate (Leucoraja erinacea) and its possible role in communication during courtship

Skates discharge an electrical current too weak to be used for predation or defense, and too infrequent and irregular to be used for electrolocation. Additionally, skates possess a specialized sensory system that can detect electrical stimuli at the same strength at which they discharge their organs. These two factors are suggestive of a communicative role for the electric organ in skates, a role that has been demonstrated in similarly weakly electric teleosts (e.g., mormyrids and gymnotiforms). There is evidence that the sexual and ontogenetic variations in the electric organ discharge (EOD) in these other weakly electric fishes are linked to morphological variations in electric organs and the electrogenerating cells of the organs, the electrocytes. Little work has been done to examine possible sexual and ontogenetic variations in skate EODs or variations in the electrocytes responsible for those discharges. Electric organs and electrocyte morphology of male and female, and mature and immature little skates, Leucoraja erinacea, are characterized here. Female electric organs were bigger than male electric organs. This is suggestive of a sexually dimorphic EOD waveform or amplitude, which might be used as a sex-specific identification signal during courtship. The shapes of electrocytes that make up the organ were found to be significantly different between mature and immature individuals and, in some cases, posterior membrane surface area of the electrocytes increased at the onset of maturity due to the formation of membrane surface invaginations and papillae. This is evidence that the EOD of skates may differ in its waveform or amplitude or frequency between mature and immature skates, and act as a signal for readiness to mate. This study supports a communicative role during courtship for the weak electric organs of little skates, but studies that characterize skate EOD dimorphisms are needed to corroborate this speculation before conclusions can be drawn about the role the electric organ plays in communication during courtship.

Osteotome Technique for Removal of Symptomatic Ear Canal Exostoses

This study was undertaken to assess a transcanal osteotome technique for removing symptomatic ear canal exostoses. Outcome measures included healing rates and the rate of complications. Prospective study in a private practice. A straight 1-mm osteotome and a curved 1-mm osteotome were used by way of a transcanal approach to incrementally remove obstructive ear canal exostoses. If anterior or superior bone growths were closely approximating the tympanic membrane, they were partially removed with a 1.5 mm cylindrical end- and side-cutting burr. Healing rates were monitored with weekly postoperative visits. Two hundred twenty-one ear canals (140 patients) were consecutively treated with this technique. Healing was achieved at 2 to 8 (average 3.50) weeks, with 90% healed by 4 weeks. There were 4 mobilizations of a full-thickness segment of anterior bony canal wall; 3 exposures of periosteum anterior to the anterior bony wall; 1 tear of the tympanic membrane requiring a tympanoplasty; 18 anterior and 11 posterior tympanic membrane tears that healed spontaneously; 3 instances of sensorineural hearing decrease; 3 cases of new-onset postoperative tinnitus; and 1 instance of postoperative positioning vertigo. There were no lacerations of the tympanic membrane by an osteotome, no facial nerve injuries, no soft tissue stenoses of an ear canal, and no skin grafting of an ear canal. The described technique of using osteotomes transcanal for removal of symptomatic obstructive ear canal exostoses promoted rapid healing and was effective and safe.

Surgical findings with the tinted AcrySof intraocular lens in children

The AcrySof foldable acrylic intraocular lens (IOL) has become an accepted and frequent means of treating pediatric aphakia. A new version of this lens with blue-light filtering properties purports to offer superior retinal protection. We describe our experience with this tinted lens and compare it to findings with the standard, nontinted IOL. A chart review identified 29 eyes of 21 children (tinted lens group; age 11 months to 13 years) who had the tinted IOL implanted. The standard lens group consisted of 38 eyes (31 patients; age 11 months to 15 years). Most eyes had an intact posterior capsule at the time of implantation. The incidence of postoperative inflammation was fairly high in both groups (71% in the tinted lens group, 60% in the standard lens group). The tinted lens group showed a higher incidence of transient inflammation than the standard lens group (p=0.03) but the rates of nontransient sequelae (posterior synechiae, iris synechiae, membranes formation, capsule, or IOL opacification) were similar (66% versus 47%; p=0.11). Posterior capsule opacification occurred in 15 eyes in the tinted lens group and 16 eyes in the standard lens group (p=0.15) but was visually significant in only 10 and 11 eyes, respectively (p=0.77). Transient inflammation is higher with implantation of tinted versus nontinted IOLs, but long-term inflammatory sequelae are roughly equal, as is the rate of posterior capsule opacification. The question as to whether the chromophore in the tinted lens caused the higher incidence of transient inflammation is unresolved.

Tracheal Replacement by Allogenic Aorta in the Pig

To assess whether fresh aortic allografts (AAs) can be used for tracheal replacement. Twenty-one male minipigs underwent tracheal replacement using AAs harvested from female pigs. The length of replaced segments exceeded 50% of the trachea. A stent was implanted into the lumen of the AA to prevent collapse. The animals were killed at 3-month intervals, and AAs were assessed for ingrowth of respiratory epithelium and cartilage formation and tested for type II collagen formation and the presence of the SRY gene. A high stent migration rate was observed. Only 10 pigs and 4 pigs made it to follow-up periods exceeding 3 months and 9 months, respectively. Neither rejection nor ischemia were observed. At 3 months, a metaplastic epithelium lined the graft. At 10 months, a posterior membrane could be seen with immature cartilage and disorganized elastic fibers. SRY gene assay showed that the cells engrafted in the AAs, particularly at the level of the newly formed cartilage, were of male origin and thus originated from the recipient. This study confirms that a fresh AA, replacing more than half of the trachea of the pig, transforms into a conduit containing the major tracheal components. These components are relatively immature and do not as of yet replicate the form and function of the native trachea. Questions remain concerning the exact mechanisms of this process. Further research on the role of tracheal replacement is recommended.

Diagnosis of Epithelial Ingrowth After Penetrating Keratoplasty With Confocal Microscopy

To report confocal microscopy use in the clinical diagnosis of epithelial ingrowth after penetrating keratoplasty (PKP). A 36-year-old female patient with keratoconus developed a well-delimited posterior hazy membrane covering the inferior two thirds of the cornea 3 months after an uneventful PKP. A posterior corneal line was present resembling an endothelial graft rejection line, but with no keratic precipitates or corneal edema. Ocular hypertension was not observed. Confocal microscopy was performed to elucidate the diagnosis. Confocal microscopy showed epithelium and stroma with normal findings. Two distinct cellular types were presented at the endothelium layer. Enlarged endothelial cells were observed in the superior part of the cornea up to the leading edge of the hazy membrane. In the middle and inferior part of the graft, the cells were larger, with polygonal shape and easily recognizable hyperreflective nuclei, suggestive of epithelial cells. With these confocal microscopy findings, the patient was promptly submitted to another PKP. Histologic analysis confirmed the diagnosis of epithelial ingrowth. Confocal microscopy imaging technique seems to be a useful tool in the early diagnosis of epithelial ingrowth after PKP.

Vitrectomie assistée par triamcinolone dans le traitement des récidives de décollement de rétine par trou maculaire du myope fort

To report the use of triamcinolone-assisted vitrectomy to assess the cause of vitrectomy failure in the treatment of retinal detachment due to myopic macular hole. We report the cases of three myopic patients presenting with recurrent retinal detachment due to macular hole after initial vitrectomy treatment with posterior vitreous detachment, a systematic attempt at membrane peeling, and gas injection (SF6). No retinal traction or tear other than the macular hole was observed. The recurrence of retinal detachment was treated with vitrectomy and intraoperative use of triamcinolone, which demonstrated persistent posterior hyaloid and thin and strongly adherent membrane remnants in each case. Anatomic success was obtained after peeling these structures. Intraoperative use of triamcinolone reduces the risk of overlooking hyaloid or membrane remnants during vitrectomy for the treatment of myopic retinal detachment. Transparent remnants of posterior hyaloid and membranes were visualized by triamcinolone-assisted vitrectomy. They could lead to traction on the retina and explain the failure of the initial vitrectomy. Anatomic success was obtained after peeling these structures.

The ultrastructure and reproduction of Amphiamblys capitellides (Microspora, Metchnikovellidae), a parasite of the gregarine Ancora sagittata (Apicomplexa, Lecudinidae), with redescription of the species and comments on the taxonomy

The ultrastructural cytology and reproduction of the hyperparasitic microsporidium Amphiamblys capitellides (Caullery and Mesnil, 1897) is described. Merogonial reproduction was not observed. The sporogony comprises two sequences: a sac-bound sporogony in close contact with the cytoplasm of the host and a free sporogony in parasitophorous vacuoles. The free sporogony, which probably precedes the sac-bound, yields a small number of rounded spores. The sac-bound sporogony is polysporoblastic, generating two rows of elongated spores. All stages have isolated nuclei. Both spore types have an extrusion apparatus of the metchnikovellidean type, with a polar sac devoid of anchoring disc, a polar filament with one manubroid and one bulbous part, and a posterior semicircular membrane fold enclosing rounded or tubular structures. Hosts are gregarines of the species Ancora sagittata living in the intestine of polychaetes of the genus Capitella, probably the species Capitella giardi. The cytology, life cycle and classification are discussed. The species is redescribed and the diagnosis of the genus Amphiamblys Caullery and Mesnil, 1914 is emended.

The marginal sinus

Descriptions of the marginal venous sinus are lacking in the extant medical literature. The aim of this study was to characterize the anatomy of this intracranial venous sinus. The authors examined the marginal sinuses in 15 adult cadavers following the injection of latex into the intracranial venous system. The maximal vertical height of the sinuses, which ranged from 7 to 15 mm (mean 10 mm), was located at the lateral aspect of the foramen magnum at or near the region at which the spinal accessory nerve crossed en route to the jugular foramen. In all specimens the sinus tapered as it traveled both anteriorly and posteriorly. Ninety-three percent of the specimens demonstrated significant drainage into the veins of the hypoglossal canal. The hypoglossal nerve rootlets pierced the sinus and its tributaries in 11 (73%) of 15 specimens. The marginal sinus communicated with the basilar venous plexus in 12 (80%) of 15 specimens and with the occipital sinus in all specimens (100%). There was venous communication with the sigmoid sinus in all specimens. The vertebral artery coursed through the marginal sinus as it pierced the posterior atlantooccipital membrane in all left sides and in 87% of the right sides. These quantitative data will be useful to the neurosurgeon who operates in the region of the marginal sinus.

Soft tissue connection between rectus capitus posterior minor and the posterior atlanto-occipital membrane: A cadaveric study

This investigation determined the variation, prevalence, tissue-type, and sex bias in the soft-tissue bridge between rectus capitis posterior minor (RCPMi) and the posterior atlanto-occipital membrane (PAO). Seventy-five cadavers (27 females and 48 males) were surveyed. When RCPMi was revealed, its superior attachment was detached and the muscle was reflected inferiorly to determine if it was attached to the underlying PAO. If a soft-tissue bridge was identified, the fibers found within the bridge were classified by visual inspection into three categories: tendon-like, muscle-like, and fascia-like. A fourth category of no attachment was also noted. These results show that RCPMi was present bilaterally in 93% of all cadavers surveyed (89% of the female cadavers and 96% of the male cadavers). On the right side, a soft-tissue bridge was present in 67% of males and 78% of females. On the left side, the soft-tissue bridge was present in 69% of males and 82% of females. The number of male cadavers possessing tendon fibers in a soft-tissue bridge was 56% on the right side and 55% on the left side. In females, the number of cadavers possessing tendon fibers in a soft-tissue bridge was 44% on the right side and 64% on the left side. In males, muscle fibers were present in the soft-tissue bridge, 34% on the right side and 36% on the left. In females, muscle fibers were found in the soft-tissue bridge, 43% on the right side and 36% on the left. There were no significant associations of sex and the presence of the soft-tissue bridge and a fiber-type within a soft-tissue bridge.

Increased Elasticity of Capsule After Immobilization in a Rat Knee Experimental Model Assessed by Scanning Acoustic Microscopy

Objectives: The mechanical property of immobilized joints is not well understood. The present study was designed to investigate the tissue elasticity of the anterior and posterior synovial membrane (SM) in a rat immobilized knee model using scanning acoustic microscopy (SAM). Moreover, the structural characteristics of the SM after immobilization were examined by transmission electron microscopy (TEM).Methods: Thirty rats had their knee joints immobilized with a plate and metal screws. The rats were fixed at 1, 2, 4, 8 and 16 weeks after surgery and the knee joints were sectioned sagittally for SAM. Selected specimens were processed for TEM. A new concept SAM using a single pulsed wave instead of continuous waves was applied to measure the sound speed of the anterior and posterior SM, comparing it with the corresponding light microscopic images.Results: The sound speed of the posterior SM increased significantly in the 8- and 16-week experimental group compared with that in the control group. The sound speed of the anterior SM showed no statistical difference between the experimental and the control groups at any period of immobilization. The posterior SM of the experimental group was different from that of the control group in the ultrastructural characteristics of extracellular matrices.Conclusions: Our data suggest that the increased elasticity and structural changes of the posterior SM are one of the main causes of limited extension after a long period of immobilization in flexion using SAM, which is a powerful tool for evaluating the elasticity of targeted tissues.

Treatment of Adult Tracheobronchomalacia and Excessive Dynamic Airway Collapse

Tracheobronchomalacia (TBM) and excessive dynamic airway collapse (EDAC) are both dynamic forms of central airway obstruction characterized by a decrease of >/=50% in the cross-sectional area of the tracheobronchial lumen. The differences between these two entities, however, are not uniformly accepted in the medical community. While TBM is characterized by a weakness of the tracheobronchial cartilaginous structures, EDAC is marked by excessive bulging of the posterior membrane into the airway lumen during exhalation. These disease entities are probably underdiagnosed because they present with a variety of nonspecific symptoms similar to patients with other obstructive ventilatory disorders such as asthma and COPD. Diagnosis is confirmed by dynamic radiologic imaging studies or bronchoscopy. Current therapeutic management depends on the extent, type, and severity of airway abnormalities noted and the clinical presentation. Proposed management alternatives include conservative medical therapy, and minimally invasive and open surgical interventions. Inhaled bronchodilators should be used only if symptoms and ventilatory function improve after use. Continuous positive airway pressure acts as a pneumatic stent and should be considered as an alternative or additional therapeutic modality. Endoluminal stent insertion can improve symptoms and pulmonary function in patients with central airway obstruction and should be considered for patients with symptoms refractory to conservative therapy. Several open surgical procedures have also been performed over the years, including tracheostomy, airway splinting, tracheal resection and, more recently, external tracheal stents. Endobronchial laser therapy, resorbable stents, application of grafting materials used to support the collapsed airway as well as the use of cartilage regeneration techniques are experimental, and their efficacy in humans remains to be determined. Future studies should compare therapeutic interventions and outcomes such as functional status, ventilatory function, and bronchoscopic and radiologic appearances in order to define the costs and benefits of individual and combined treatment modalities.

Fuchs Corneal Dystrophy: Aberrant Collagen Distribution in an L450W Mutant of theCOL8A2Gene

To characterize histologically Descemet's membrane in an early-onset Fuchs corneal dystrophy (FCD) COL8A2 mutant and compare these findings with corneas from late-onset FCD and normal corneas. A corneal explant from a patient with the L450W COL8A2 mutation and others with late-onset disease were studied with antibodies to collagens IV, VIIIA1, VIIIA2, fibronectin, and laminin. Transmission electron microscopy was performed on a portion of the explant. Control explants included eye bank corneas without known disease and surgical explants from unrelated conditions. In normal corneas, a regular array of colocalized COL8A1 and COL8A2 was observed in the anterior half of Descemet's membrane. In the L450W mutant, Descemet's membrane was several times thicker than normal and traversed by refractile strands and blebs that stained intensely for COL8A2, a feature also observed in late-onset FCD. Both the alpha1 and alpha2 subtypes of collagen VIII were observed at high levels along the anterior edge of Descemet's, another abnormal feature also found in late-onset FCD. Ultrastructure of the L450W cornea revealed a well-formed anterior banded layer more than three times thicker than normal. An unusual, thin internal layer was rich in patches of wide-spaced collagen. The layer is a distinctive pathologic structure that is associated with FCD and is characterized by approximately 120 nm periodicity and the presence of collagen VIII. Depositions of collagen IV, fibronectin, and laminin were also greatly increased in the of posterior Descemet's membrane, yet another general feature shared between early- and late-onset disease. Early-onset COL8A2 L450W disease involves massive accumulation and abnormal assembly of collagen VIII within Descemet's membrane, a process that is presumed to begin during fetal development. Both early- and late-onset subtypes of FCD appear to be the result of abnormal basement membrane assembly rather than a primary defect in endothelial metabolism.

Head Position and Impact Direction in Whiplash Injuries: Associations with MRI-Verified Lesions of Ligaments and Membranes in the Upper Cervical Spine

In the present study, we compared magnetic resonance imaging (MRI) findings of soft tissue structures in the upper cervical spine between whiplash-associated disorder (WAD) patients and population-based control persons, and examined whether MRI-verified abnormalities in WAD patients were related to accident-related factors hypothesized to be of importance for severity of injury. A total of 92 whiplash patients and 30 control persons, randomly drawn, were included. Information on the accident-related factors (i.e., head position and impact direction) was obtained by a questionnaire that was answered within 1 week after the accident. The MRI examination was performed 2-9 (mean 6) years after the accident. Focus was on MRI abnormalities of the alar and the transverse ligaments, and the tectorial and posterior atlanto-occipital membranes, graded 0-3. For all neck structures, the whiplash patients had more high-grade lesions (grade 2 or 3) than the control persons (Chi-square test, p < 0.055). An abnormal alar ligament was most common (66.3% graded 2 or 3). Whiplash patients who had been sitting with their head/neck turned to one side at the moment of collision more often had high-grade lesions of the alar and transverse ligaments (p < 0.001, p = 0.040, respectively). Severe injuries to the transverse ligament and the posterior atlanto-occipital membrane were more common in front than in rear end collisions (p < 0.001, p = 0.001, respectively). In conclusion, the difference in MRI-verified lesions between WAD patients and control persons, and in particular the association with head position and impact direction at time of accident, indicate that these lesions are caused by the whiplash trauma.

Pain Management Guidelines for Blunt Thoracic Trauma

Pain Management Guidelines for Blunt Thoracic Trauma Bruce Simon;James Cushman;Robert Barraco;Vivian Lane;Fred Luchette;Maurizio Miglietta;David Roccaforte;Ruth Spector; The Journal of Trauma: Injury, Infection, and Critical Care

Microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes

The goal of this study was to investigate the microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes. The interpeduncular cistern and related arachnoid membranes were studied in eight Han Chinese adult human cadaveric brains with the aid of an operating microscope. The interpeduncular cistern is one area in the cranial cavity in which the arachnoid membranes and trabeculae are extremely luxuriant and complicated. The Liliequist membrane, the medial pontomesencephalic membrane, and the lateral pontomesencephalic membranes form the walls of the interpeduncular cisterns. The basilar artery (BA) bifurcation membrane, posterior perforated membrane, and arachnoid trabeculae fill the cistern. These arachnoid membranes and trabeculae adhere to the hypothalamus, brainstem, and oculomotor nerves, and bind the bifurcation of the BA, posterior cerebral arteries, superior cerebellar arteries, posterior communicating arteries, and their perforating branches. Arachnoid membranes and trabeculae complicate the exposure and dissection of lesions within the interpeduncular cistern. All arachnoid membranes and trabeculae should be dissected and incised sharply during surgical procedures. The BA bifurcation membrane and the posterior perforated membrane must be incised after opening the Liliequist membrane for sufficient exposure of deep structures within the interpeduncular cistern.

Opposing Gradients of Ephrin-As and EphA7 in the Superior Colliculus Are Essential for Topographic Mapping in the Mammalian Visual System

During development of the retinocollicular projection in mouse, retinal axons initially overshoot their future termination zones (TZs) in the superior colliculus (SC). The formation of TZs is initiated by interstitial branching at topographically appropriate positions. Ephrin-As are expressed in a decreasing posterior-to-anterior gradient in the SC, and they suppress branching posterior to future TZs. Here we investigate the role of an EphA7 gradient in the SC, which has the reverse orientation to the ephrin-A gradient. We find that in EphA7 mutant mice the retinocollicular map is disrupted, with nasal and temporal axons forming additional or extended TZs, respectively. In vitro, retinal axons are repelled from growing on EphA7-containing stripes. Our data support the idea that EphA7 is involved in suppressing branching anterior to future TZs. These findings suggest that opposing ephrin-A and EphA gradients are required for the proper development of the retinocollicular projection.

Ossification of the Posterior Atlantoaxial Membrane and the Transverse Atlantal Ligament

Case report. To report a case of ossification of the posterior atlantoaxial membrane (PAAM) and ossification of the transverse ligament of the atlas (TAL). Ossification of the PAAM and TAL are both very rare clinical entities. This is the first case involving ossification of both the PAAM and TAL with the development of cervical myelopathy. Patient's history, physical examination, radiographic evaluation, surgical treatment, and outcome are examined. Relevant literature is also reviewed. The patient's neurological symptoms significantly improved after posterior decompressive surgery. Ossification of various parts of the spinal ligament have been reported previously. Among them, ossification of both the PAAM and TAL has never been reported previously and is thus extremely rare. Surgical intervention improved the neurological impairment.

Whiplash-Associated Disorders Impairment Rating: Neck Disability Index Score According to Severity of MRI Findings of Ligaments and Membranes in the Upper Cervical Spine

The aim of this study was to explore whether reported pain and functional disability in whiplash-associated disorders (WAD) patients is associated with lesions to specific soft tissue structures in the upper cervical spine, as assessed by MRI. Pre-selected structures for MRI assessment included the alar ligaments, the transverse ligament, the tectorial and the posterior atlanto-occipital membranes. The questionnaire employed was a modification of the Oswestry Low Back Pain Index. It was comprised of ten single items related to pain and activity of daily living. Ninety-two whiplash patients and 30 control persons, randomly drawn, were included. WAD patients reported significantly more pain and functional disability than the controls, both for total score and each of the ten single items. In the WAD patients, MRI lesions to the alar ligaments showed the most consistent association to the reported pain and disability. Lesions to other structures often occurred in combination with lesions to the alar ligaments. Lesions to the transverse ligament and to the posterior atlanto-occipital membrane also appeared to be related to the NDI score, although the association was weaker than for the alar ligament. The disability score increased with increasing number of abnormal (grade 2-3) structures. These results indicate that symptoms and complaints among WAD patients can be linked with structural abnormalities in ligaments and membranes in the upper cervical spine, in particular the alar ligaments.

Cervical Spine Considerations When Anesthetizing Patients with Down Syndrome

It is characterized by mental retardation, as well as craniofacial, upper airway, cardiovascular, and gastrointestinal anomalies. One manifestation of DS relevant to anesthesiologists is upper cervical spine instability produced by ligamentous laxity, skeletal anomalies, or both. This instability can result in neurologic impairment, including quadriplegia. However, there are no evidencebased practical guidelines to aid anesthesiologists in caring for these patients. The risk of spinal cord injury during anesthesia is unknown, as are the preoperative factors that might aid in accurately defining the risk in specific patients. Review of Normal Upper Cervical Spine Anatomy The structures relevant to this discussion include the base of the skull, the atlas (C1), and the axis (C2). The articulations between these structures are complex but are designed to facilitate maximal movement without compressing the spinal cord. The motions are flexion extension and rotation; little lateral bending occurs in this area.